beee notes.doc

T104 Basic Electrical & Electronics Engineering

T104 BASIC ELECTRICAL AND ELECTRONICS ENGINEERINGOBJECTIVES_ To understand and gain basic knowledge about magnetic and electrical circuits, single phase and three phase power measurement and the operating principles of stationary and rotating machines_ To understand the basic operation, functions and applications of PN junction diode, transistor, logic gates and flip flops._ To gain knowledge on various communication systems and network models and the use of ISDN

PART A - ELECTRICALUNIT – I - DC CIRCUITSDefinition of Voltage, Current, Power & Energy, circuit parameters, Ohm’s law, Kirchoff’s law & its applications – Simple Problems - Division of current in Series & parallel circuits - star/delta conversion - Node and mesh methods of analysis of DC circuits.UNIT – II - AC CIRCUITSConcepts of AC circuits – rms value, average value, form and peak factors – Simple RLC series circuits – Concept of real and reactive power – Power factor - Introduction to three phase system - Power measurement by two wattmeter method.UNIT – III – ELECTRICAL MACHINES AND POWER PLANTSLaw of Electromagnetic induction, Fleming’s Right & Left hand rule - Principle of DC rotating machine, Single phase transformer and single phase induction motor (Qualitative approach only) - Simple layout of thermal and hydro generation (block diagram approach only).Fundamentals of fuses and circuit breakers

PART B – ELECTRONICSUNIT – IV ELECTRONIC CIRCUITSV-I Characteristics of diode - Half-wave rectifier and Full-wave rectifier – with and without capacitor filter - Transistor - Construction & working - Input and output characteristics of CB and CE configuration - Transistor as an Amplifier - Principle and working of Hartley oscillator and RC phase shift oscillator - Construction and working of JFET & MOSFET.UNIT – V DIGITAL ELECTRONICSBoolean algebra – Reduction of Boolean expressions - De-Morgan’s theorem – Logic gates -Implementation of Boolean expressions - Flip flops - RS, JK, T and D. Combinational logic - Half adder, Full adder and Subtractors. Sequential logic - Ripple counters and shift registers.UNIT – VI COMMUNICATION AND COMPUTER SYSTEMSModel of communication system - Analog and digital - Wired and wireless channel. Block diagram of various communication systems - Microwave, satellite, optical fiber and cellular mobile system. Network model - PAN, LAN, MAN and WAN - Circuit and packet switching - Overview of ISDN.

Text Books1. Kothari D P and Nagrath I J , Basic Electrical Engineering , Tata McGraw Hill,2009. (For Units I to III)J.C.Vijayshree 1


2. Rajendra Prasad , “ Fundamentals of Electronic Engineering”, Cengage learning, New Delhi, First Edition, 2011 (For Unit IV)3. Morris Mano, “Digital design”, PHI Learning, Fourth Edition, 2008 (For Unit V)4. Wayne Tomasi, “Electronic Communication Systems- Fundamentals Theory Advanced”, Sixth Edition, Pearson Education, 2004. (For Unit VI)Reference Books1. R.Muthusubramaniam, S.Salivahanan and K.A. Mureleedharan, Basic Electrical Electronics and Computer Engineering, Tata McGraw Hill, 2004..2. J.B.Gupta, A Course in Electrical Power, Katson Publishing House, New Delhi, 1993.3. David. A. Bell, “Electronic Devices and Circuits”, PHI Learning Private Ltd, India, Fourth Edition, 20084. Donald P Leach, Albert Paul Malvino and Goutam Saha, “Digital Principles and Applications,” 6th edition, Tata McGraw Hill Publishing Company Ltd., New Delhi,2008.5. S.K. Sahdev, Fundamentals of Electrical Engineering and Electronics, Dhanpat Rai & Co, 2013.6. Jacob Millman and Christos C. Halkias, “Electronic Devices and Circuits” Tata McGraw Hill,20087. R.L. Boylestad and L. Nashelsky, “Electronic Devices and Circuit Theory”, PHI Learning Private Limited, Ninth Edition, 2008.8. M.S.Sukhija and T.K.Nagsarkar, “Basic Electrical and Electronics Engineering”, Oxford University Press, 2012.

PART A - ELECTRICALUNIT – I

DC CIRCUITS1.1.Definition of Voltage, Current, Power & Energy1.1.1. Voltage

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Voltage is a representation of the electric potential energy per unit charge. If a unit of electrical charge were placed in a location, the voltage indicates the potential energy of it at that point. In other words, it is a measurement of the energy contained within an electric field, or an electric circuit, at a given point.Voltage is a scalar quantity. The SI unit of voltage is the volt, such that 1 volt = 1 joule/coulomb.1.1.2. CurrentElectrical current is a measure of the amount of electrical charge transferred per unit time. It represents the flow of electrons through a conductive material.Current is a scalar quantity (though in circuit analysis, the direction of current is relevant). The SI unit of electrical current is the ampere, defined as 1 coulomb/second.1.1.3. PowerPower is the time rate at which work is done or energy is transferred. In calculus terms, power is the derivative of work with respect to time.The SI unit of power is the watt (W) or joule per second (J/s). Horsepower is a unit of power in the British system of measurement.1.1.4. EnergyEnergy is the capacity of a physical system to perform work. Energy exists in several forms such as heat, kinetic or mechanical energy, light, potential energy, electrical, or other forms.According to the law of conservation of energy, the total energy of a system remains constant, though energy may transform into another form. Two billiard balls colliding, for example, may come to rest, with the resulting energy becoming sound and perhaps a bit of heat at the point of collision.The SI unit of energy is the joule (J) or newton-meter (N * m). The joule is also the SI unit of work.1.1.5. Current Vs Voltage - Comparison

Current Voltage

Definition

Current is the rate at which electric charge flows past a point in a circuit. In other words, current is the rate of flow of electric charge.

Voltage, also called electromotive force, is the potential difference in charge between two points in an electrical field. In other words, voltage is the "energy per unit charge”.

Symbol I VUnit A or amps or amperage V or volts or voltageSI Unit 1 ampere =1

coulomb/second.1 volt = 1 joule/coulomb. (V=W/C)

Measuring Instrument Ammeter VoltmeterRelationship

Current is the effect (voltage being the cause). Current

Voltage is the cause and current is its effect. Voltage can exist

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http://chemistry.about.com/od/engineeringglossary/g/current-definition.htm

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http://chemistry.about.com/od/chemistryglossary/g/Circuit-Or-Electric-Circuit-Definition.htm

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Current Voltagecannot flow without Voltage. without current.

Field created A magnetic field An electrostatic field

In series connection

Current is the same through all components connected in series.

Voltage gets distributed over components connected in series.

In a parallel connection

Current gets distributed over components connected in parallel.

Voltages are the same across all components connected in parallel.

1.1.6. Energy Vs Power - Comparison Energy Power

DefinitionEnergy is the capacity to do work. Energy is power integrated over time.

Power is the rate at which work is done, or energy is transmitted.

Unit joules = watt-seconds watt = joules/secondCommon symbol(s) W P

ExampleI left a 60W light bulb on for 30 days, which raised my electric bill by 43.2 kWh (kilowatt-hours).

My car's battery can provide 500 amps at 12 volts, which equals 6kW of power.

1.2. Circuit parameters Circuit parameters can be classified as: 1-- Active or Passive 2-- Linear or Non-linear 3-- Unilateral or Bilateral 4-- Lumped or Distributive 1.2.1 Active elementsThose circuit elements that supply energy to an energised circuit are called active circuit elements. Eg.: Voltage source, current source, etc. Note: It is important to note that dependent sources cannot be placed under this category as they depend on the value of current or voltage in any other branch of the network. 1.2.2 Passive elementsPassive circuit elements, on the other hand, are those elements that use up the energy supplied by the active sources and\or do not supply their own energy to the circuit. Eg.: Resistor, capacitor, inductor, etc.Note: It is important to note that a capacitor does store energy and also supplies it back to the circuit but this energy is not of its own, instead it's the energy supplied by some active component. Hence, it cannot be placed under the category of active circuit parameters.Thus an energised network(or a circuit) consists of both active and passive elements.

1.2.3 Linear circuits

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In simple words, a linear circuit is an electric circuit in which circuit parameters (Resistance, inductance, capacitance, waveform, frequency etc) are constant. In other words, a circuit whose parameters are not changed with respect to Current and Voltage is called Linear Circuit.If we draw the circuit output characteristic curve in between Current and Voltage, it will look like a straight line (Diagonal) as shown in fig (1).In a linear circuit, the output response of the circuit is directly proportional to the input. Linear Circuit and its characteristic curve are shown in below fig (1).

Examples of Liner Circuits and Linear ElementsResistance and Resistive CircuitInductor and Inductive CircuitsCapacitor and Capacitive Circuits1.2.4 Non-linear circuitsA nonlinear circuit is an electric circuit whose parameters are varied with respect to Current and Voltage. In other words, an electric circuit in which circuit parameters (Resistance, inductance, capacitance, waveform, frequency etc) is not constant, is called Non Linear Circuit.If we draw the circuit output characteristic curve in between Current and Voltage, it will look like a curved or bending line as shown in fig (2).Non Linear Circuit and its characteristic curve are shown in below fig (2).

Examples of NonLinear Circuits and ElementsDiode, Transistor, Transformer, Iron Core inductor when the core is saturated and any circuit composed exclusively of ideal Diode, Transistor, Transformer, and Iron Core inductor is called Non linear circuit.1.2.5 Unilateral circuitsIn unilateral circuits, the property of circuit changes with the change of direction of supply voltage or current. In other words, unilateral circuit allows the current to flow only in one direction. Diode rectifier is the best example of unilateral circuit because it does not perform the rectification in both direction of supply. 1.2.6 Bi-lateral circuitsIn bilateral circuits, the property of circuit does not change with the change of direction of supply voltage or current. In other words, bilateral circuit allows the current to flow in both directions.J.C.Vijayshree 5


Transmission line is the best example of bilateral circuit because, if you give supply from any direction, the circuit properties remain constant1.2.7 Lumped elements• Physical dimensions of circuit are such that voltage across and current through conductors connecting elements does not vary. • Current in two-terminal lumped circuit element does not vary

1.2.8 Distributive elements• Current varies along conductors and elements• Voltage across points along conductor or within element varies

1.3. Ohm’s law1.3.1. DefinitionThe potential difference (voltage) across an ideal conductor is proportional to the current through it. The relationship between Voltage, Current and Resistance in any DC electrical circuit was firstly discovered by the German physicist Georg Ohm. Ohm found that, at a constant temperature, the electrical current flowing through a fixed linear resistance is directly proportional to the voltage applied across it, and also inversely proportional to the resistance. This relationship between the Voltage, Current and Resistance forms the bases of Ohms Law and is shown below.1.3.2 Ohms Law Relationship

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http://electricaltechnology.org/?p=137


By knowing any two values of the Voltage, Current or Resistance quantities we can use Ohms Law to find the third missing value. Ohms Law is used extensively in electronics formulas and calculations so it is “very important to understand and accurately remember these formulas”.1.3.3 To find the Voltage, ( V )[ V = I x R ] V (volts) = I (amps) x R (Ω)1.3.4 To find the Current, ( I )[ I = V ÷ R ] I (amps) = V (volts) ÷ R (Ω)1.3.5 To find the Resistance, ( R )[ R = V ÷ I ] R (Ω) = V (volts) ÷ I (amps)

Ohms Law Example For the circuit shown below find the Voltage (V), the Current (I), the Resistance (R) and the Power (P).

Voltage [ V = I x R ] = 2 x 12Ω = 24VCurrent [ I = V ÷ R ] = 24 ÷ 12Ω = 2AResistance [ R = V ÷ I ] = 24 ÷ 2 = 12 ΩPower [ P = V x I ] = 24 x 2 = 48W1.4. Kirchoff’s law & its applications – 1.4.1 Kirchoffs Circuit LawIn 1845, a German physicist, Gustav Kirchoff developed a pair or set of rules or laws which deal with the conservation of current and energy within Electrical Circuits. These two rules are commonly known as: Kirchoffs Circuit Laws with one of Kirchoffs laws dealing with the current flowing around a closed circuit, Kirchoffs Current Law, (KCL) while the other law deals with the voltage sources present in a closed circuit, Kirchoffs Voltage Law, (KVL).

1.4.2 Kirchoffs First Law – The Current Law, (KCL)Kirchoffs Current Law or KCL, states that the “total current or charge entering a junction or node is exactly equal to the charge leaving the node as it has no other place to go except to leave, as no charge is lost within the node“. In other words the algebraic sum of ALL the currents entering and leaving a node must be equal to zero, I(exiting) + I(entering) = 0. This idea by Kirchoff is commonly known as the Conservation of Charge.1.4.3 Kirchoffs Current Law - Illustration

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Here, the 3 currents entering the node, I1, I2, I3 are all positive in value and the 2 currents leaving the node, I4 and I5 are negative in value. Then this means we can also rewrite the equation as;I1 + I2 + I3 – I4 – I5 = 0The term Node in an electrical circuit generally refers to a connection or junction of two or more current carrying paths or elements such as cables and components. Also for current to flow either in or out of a node a closed circuit path must exist. We can use Kirchoff’s current law when analysing parallel circuits.1.4.4 Kirchoffs Second Law – The Voltage Law, (KVL)Kirchoffs Voltage Law or KVL, states that “in any closed loop network, the total voltage around the loop is equal to the sum of all the voltage drops within the same loop” which is also equal to zero. In other words the algebraic sum of all voltages within the loop must be equal to zero. This idea by Kirchoff is known as the Conservation of Energy.1.4.5 Kirchoffs Voltage Law- Illustration

Starting at any point in the loop continue in the same direction noting the direction of all the voltage drops, either positive or negative, and returning back to the same starting point. It is important to maintain the same direction either clockwise or anti-clockwise or the final voltage sum will not be equal to zero. We can use Kirchoff’s voltage law when analysing series circuits.When analysing either DC circuits or AC circuits using Kirchoffs Circuit Laws a number of definitions and terminologies are used to describe the parts of the circuit being analysed such as: node, paths, branches, loops and meshes. These terms are used frequently in circuit analysis so it is important to understand them.

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1.4.6 Common DC Circuit Theory Terms: Circuit – a circuit is a closed loop conducting path in which an

electrical current flows. Path – a single line of connecting elements or sources. Node – a node is a junction, connection or terminal within a circuit

were two or more circuit elements are connected or joined together giving a connection point between two or more branches. A node is indicated by a dot.

Branch – a branch is a single or group of components such as resistors or a source which are connected between two nodes.

Loop – a loop is a simple closed path in a circuit in which no circuit element or node is encountered more than once.

Mesh – a mesh is a single open loop that does not have a closed path. There are no components inside a mesh.

Note that: Components are said to be connected in Series if the same current flows through component. Components are said to be connected in Parallel if the same voltage is applied across them.1.4.7 A Typical DC Circuit

1.4.8 Application of Kirchoffs Circuit LawsThese two laws enable the Currents and Voltages in a circuit to be found, ie, the circuit is said to be “Analysed”, and the basic procedure for using Kirchoff’s Circuit Laws is as follows:

1. Assume all voltages and resistances are given. ( If not label them V1, V2,… R1, R2, etc. )2. Label each branch with a branch current. ( I1, I2, I3 etc. )3. Find Kirchoff’s first law equations for each node.4. Find Kirchoff’s second law equations for each of the independent loops of the circuit.5. Use Linear simultaneous equations as required to find the unknown currents.As well as using Kirchoffs Circuit Law to calculate the various voltages and currents circulating around a linear circuit, we can also

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use loop analysis to calculate the currents in each independent loop which helps to reduce the amount of mathematics required by using just Kirchoff's laws.Kirchoffs Circuit Law Example Find the current flowing in the 40Ω Resistor, R3

The circuit has 3 branches, 2 nodes (A and B) and 2 independent loops.Using Kirchoffs Current Law, KCL the equations are given as;At node A : I1 + I2 = I3At node B : I3 = I1 + I2Using Kirchoffs Voltage Law, KVL the equations are given as;Loop 1 is given as : 10 = R1 x I1 + R3 x I3 = 10I1 + 40I3Loop 2 is given as : 20 = R2 x I2 + R3 x I3 = 20I2 + 40I3Loop 3 is given as : 10 – 20 = 10I1 – 20I2As I3 is the sum of I1 + I2 we can rewrite the equations as;Eq. No 1 : 10 = 10I1 + 40(I1 + I2) = 50I1 + 40I2Eq. No 2 : 20 = 20I2 + 40(I1 + I2) = 40I1 + 60I2We now have two “Simultaneous Equations” that can be reduced to give us the values of I1 and I2 Substitution of I1 in terms of I2 gives us the value of I1 as -0.143 AmpsSubstitution of I2 in terms of I1 gives us the value of I2 as +0.429 AmpsAs : I3 = I1 + I2The current flowing in resistor R3 is given as : -0.143 + 0.429 = 0.286 Amps and the voltage across the resistor R3 is given as : 0.286 x 40 = 11.44 volts. The negative sign for I1 means that the direction of current flow initially chosen was wrong, but never the less still valid. In fact, the 20v battery is charging the 10v battery.1.5. Simple Problems – Solving Circuits with Kirchoff Laws Example 1: Find the three unknown currents ( ) and three unknown voltages ( ) in the circuit below:

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Note: The direction of a current and the polarity of a voltage source can be assumed arbitrarily. To determine the actual direction and polarity, the sign of the values also should be considered. For example, a current labeled in left-to-right direction with a negative value is actually flowing right-to-left. All voltages and currents in the circuit can be found by either of the following two methods, based on either the KVL or KCL. The loop-current method based on KVL: 1. For each of the independent loops in the circuit, define a loop current around the loop in clockwise (or counter clockwise) direction. These loop currents are the unknown variables to be obtained. 2. Apply KVL around each of the loops in the same clockwise direction to obtain equations. While calculating the voltage drop across each resistor shared by two loops, both loop currents (in opposite positions) should be considered. 3. Solve the equation system with equations for the unknown loop currents.

Find currents from a to b, from c to b, and from b to d. o Assume two loop currents and around loops abda and bcdb and apply the KVL to them:

We rewrite these as:

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and then get , , and . Having

found and , we can easily find all voltages in the circuit. o We could also apply KVL around the third loop of abcda to get an additional equation:

However, this equation is simply the sum of the previous two equations,

i.e., it is not independent. Substituting and from the first two

equations into this equation we get . In general, if all branches in the circuit have been covered, no additional loop currents will be needed.

o Alternatively, consider the two loop currents and around loops abda and bcdb:

i.e.,

and we get and , in consistent with the previous results.

The node-voltage method based on KCL: 1. Assume there are nodes in the circuit. Select one of them as the ground, the reference point for all voltages of the circuit. The voltage at

each of the remaining nodes is an unknown to be obtained.

2. Apply KCL to each of the nodes to obtain equations.

3. Solve the equation system with equations for the unknown node voltages.

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In the same circuit considered previously, there are only 2 nodes and (note and are not nodes). We assume node is the ground, and

consider just voltage at node as the only unknown in the problem. Apply KCL to node , we have

where

Substituting , , and into the equation, we get

Solving this we get , and all other currents and voltages can be found subsequently. We could also apply KCL to node d, but the resulting equation is exactly

the same as simply because this node d is not independent. As special case of the node-voltage method with only two nodes, we have the following theorem: Millman's theorem If there are multiple parallel branches between two nodes and , then the voltage at node can be found as shown below if the other node is treated as the reference point. Assume there are three types of branches:

o current branches with (independent of resistors in series). The

direction of each is toward node a.

o resistor branches with . Applying KCL to node , we have:

Solving for , we get

where the reciprocal of the resistance is called the conductance.

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In summary, Loop current method: each equation is for one of the independent loops. Node voltage method: each equation is for one of the independent nodes. Example 2: Solve the following circuit:

Loop current method: Let the three loop currents in the example

above be , and for loops 1 (top-left bacb), 2 (top-right adca), and 3 (bottom bcdb), respectively, and applying KVL to the three loops, we get

We can then solve these 3 loop equations to find the 3 loop currents. Node voltage method: If we choose node d as ground, we can apply KCL to the remaining 3 nodes at a, b, and c, and get (assuming all currents leave each node):

We can then solve these 3 node equations to find the 3 node voltages. We see that either of the loop-current and node-voltage methods requires to solve a linear system of 3 equations with 3 unknowns. J.C.Vijayshree 14


Example 3: Solve the following circuit with , , ,

, , . This circuit has 3 independent loops and 3 independent nodes.

Loop current method:

Assume three loop currents (left), (right), (top) all in clock-wise direction. We have

We can also get the three node voltages with respect to the bottom node

as ground: (right), (middle),

and (left). Node voltage method: Assume the three node voltages with respect to the bottom node as

ground to be (left), (middle), (right). Applying KCL to the first two nodes, we get

The voltages are the same as before. In the problem, we have taken advantage of either the given current source treated as a loop current, or the given voltage source when one end of it is assumed to be ground, so that in either method, one of the three unknowns readily available, we only need to solve a 2-equation system for the remaining two unknowns. EXAMPLE PROBLEM ON OHM'S LAW: The Basic Circuit Example 4: An emf source of 6.0V is connected to a purely resistive lamp and a current of 2.0 amperes flows. All the wires are resistance-free. What is the resistance of the lamp? Hints

1. Where in the circuit does the gain in potential energy occur?J.C.Vijayshree 15


2. Where in the circuit does the loss of potential energy occur?3. What is Ohm's Law?

Solution The gain of potential energy occurs as a charge passes through the battery, that is, it gains a potential of =6.0V. No energy is lost to the wires, since they are assumed to be resistance-free. By conservation of energy, the potential that was gained (i.e. =V=6.0V) must be lost in the resistor. So, by Ohm's Law:

V = I R R=V/I R = 3.0

Figure 1 Diagram of the circuit in this problem.

Example 5: If 0.6A current flows through a resistor shown in figure. Voltage of two points of resistor is 12V. What is the resistance of the resistor?

Solution:

Here, Current, I = 0.6APotential difference or Voltage, V = 12VResistance, R =?According to ohms law questions we know,V = IROr, R =V / I=12V / 0.6A=20 ΩAns: 20 Ω.Example 6: Resistance of an electric iron 50 Ω.4.2A Current flows through the resistance. Find the voltage between two points.Solution:Here, Resistance, R = 50 Ω.Current, I =4.2 AVoltage, V =?From Ohm’s law,V=IR=4.2×50= 210VJ.C.Vijayshree 16

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Ans: 210V.1.6. Division of current in Series & parallel circuits –Electric circuits often consist of several elements, some combined in series and others in parallel. The methods used to analyze series and parallel circuits can be combined to analyze these series-parallel circuits.1.6.1 Series-parallel circuit. The Figure at right shows three impedances; two are connected in parallel and then connected in series with a third impedance. Each impedance can be a pure resistance, a pure inductance, a pure capacitance, or any combination of the three.

Here current (I) flows from the voltage source (V). The total current flowing from the source flows through impedance Z1 (I = I1). Using node C as a voltage reference, the voltage at node A is the voltage of the source (V). To obtain the voltage at node B, the voltage at node A must be decreased by the voltage drop across the impedance Z1, or VB=VA-(I1×1).1.6.2 Current division. The elements between nodes B and C are connected in parallel, so it's now necessary to use parallel circuit analysis methods. 1.6.3 Using Ohm’s law: Both impedance elements (Z 2 and Z 3) have the same voltage across them (V B - V C), but the currents through them (I 2 and I 3) can be different. These currents can be found by applying Ohm's Law:

Using these results, you can derive an expression for current division. The voltage difference VB - VC can be expressed using Ohm's Law: VB - VC = I2 ×2 = I3 ×3. Rearranging this equation gives you

1.6.4 Using Kirchhoff's law: Applying Kirchhoff's Current Law at node B yields I1 = I2 + I3, or I2 = I1 - I3. Substituting for I3 gives you

Solving for I1 gives you

Now, resolving for I2 gives you

Similarly, it can be shown that

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These equations show how current divides through parallel impedances.1.6.5 Voltage division. Determining the voltage at node B relative to node C illustrates the concept of voltage division. The paralleled impedances Z 2 and Z 3 can be equivalence as Z T, where

Solving this equation for ZT gives you

Using node C as the voltage reference, the voltage at node B is the total current (I) times the equivalent impedance ZT. It's been shown that VB = VA - (I1 × Z1). Setting the two expressions for VB equal,

Solving for VA gives you

or VA-C = I1 (Z1 + ZT). You can also express it as VB-C = I1 ZT. You can use these equations to determine the voltage division across two series impedances. Applied to our sample circuit,

Example 1First, we'll solve for the currents using Ohm's Law.

The total resistance:

The voltage:V = RT*IS = 1.2*5 = 6 V; and so the currents:

Now let's see how to use the current divider formula. Although at first glance it looks as though we're using a different formula from the one given at the beginning of this tutorial, in fact the formula is equivalent for the case of two resistors in parallel. Starting from the formula given earlier, substitute (R1*R2)/(R1+R2) for Rt and simplify to arrive at the formula used below.J.C.Vijayshree 18

https://tinacloud.com/tinademo/tina.php?url=http://www.tina.com/English/tina/course/7current/cd0.sch


The results are the same as those calculated by TINA.

Example 2Find the current in resistor R1.

Here we have two branches in parallel connected to the current source. One of the branches is a series-parallel circuit. Current division must be

used twice:

1.7. Star/Delta conversion – Star Delta Transformations allow us to convert impedances connected together from one type of connection to another. We can now solve simple series, parallel or bridge type resistive networks using Kirchoff´s Circuit Laws, mesh current analysis or nodal voltage analysis techniques but in a balanced 3-phase circuit we can use different mathematical techniques to simplify the analysis of the circuit and thereby reduce the amount of math’s involved which in itself is a good thing.Standard 3-phase circuits or networks take on two major forms with names that represent the way in which the resistances are connected, a Star connected network which has the symbol of the letter, Υ (wye) and a Delta connected network which has the symbol of a triangle, Δ (delta).If a 3-phase, 3-wire supply or even a 3-phase load is connected in one type of configuration, it can be easily transformed or changed it into an equivalent configuration of the other type by using either the Star Delta Transformation or Delta Star Transformation process.A resistive network consisting of three impedances can be connected together to form a T or “Tee” configuration but the network can also be redrawn to form a Star or Υ type network as shown below.1.7.1 T-connected and Equivalent Star Network

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http://www.electronics-tutorials.ws/dccircuits/dcp_4.html



As we have already seen, we can redraw the T resistor network to produce an equivalent Star or Υ type network. But we can also convert a Pi or π type resistor network into an equivalent Delta or Δ type network as shown below.1.7.2 Pi-connected and Equivalent Delta Network.

Having now defined exactly what is a Star and Delta connected network it is possible to transform the Υ into an equivalent Δ circuit and also to convert a Δ into an equivalent Υ circuit using a the transformation process. This process allows us to produce a mathematical relationship between the various resistors giving us a Star Delta Transformation as well as a Delta Star Transformation.These Circuit Transformations allow us to change the three connected resistances (or impedances) by their equivalents measured between the terminals 1-2, 1-3 or 2-3 for either a star or delta connected circuit. However, the resulting networks are only equivalent for voltages and currents external to the star or delta networks, as internally the voltages and currents are different but each network will consume the same amount of power and have the same power factor to each other.1.7.3 Delta Star TransformationTo convert a delta network to an equivalent star network we need to derive a transformation formula for equating the various resistors to each other between the various terminals. Consider the circuit below.1.7.4 Delta to Star Network.

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Compare the resistances between terminals 1 and 2.

Resistance between the terminals 2 and 3.

Resistance between the terminals 1 and 3.

This now gives us three equations and taking equation 3 from equation 2 gives:

Then, re-writing Equation 1 will give us:

Adding together equation 1 and the result above of equation 3 minus equation 2 gives:

From which gives us the final equation for resistor P as:

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Then to summarize a little about the above maths, we can now say that resistor P in a Star network can be found as Equation 1 plus (Equation 3 minus Equation 2) or Eq1 + (Eq3 – Eq2).Similarly, to find resistor Q in a star network, is equation 2 plus the result of equation 1 minus equation 3 or Eq2 + (Eq1 – Eq3) and this gives us the transformation of Q as:

and again, to find resistor R in a Star network, is equation 3 plus the result of equation 2 minus equation 1 or Eq3 + (Eq2 – Eq1) and this gives us the transformation of R as:

When converting a delta network into a star network the denominators of all of the transformation formulas are the same: A + B + C, and which is the sum of ALL the delta resistances. Then to convert any delta connected network to an equivalent star network we can summarized the above transformation equations as:1.7.5 Delta to Star Transformations Equations

If the three resistors in the delta network are all equal in value then the resultant resistors in the equivalent star network will be equal to one third the value of the delta resistors, giving each branch in the star network as: RSTAR = 1/3RDELTADelta – Star Example No1Convert the following Delta Resistive Network into an equivalent Star Network.

1.7.6 Star Delta TransformationStar Delta transformation is simply the reverse of above. We have seen that when converting from a delta network to an equivalent star network that the resistor connected to one terminal is the product of the two delta resistances connected to the same terminal, for example resistor P is the product of resistors A and B connected to terminal 1.By rewriting the previous formulas a little we can also find the transformation formulas for converting a resistive star network to an equivalent delta network giving us a way of producing a star delta transformation as shown below.1.7.7 Star to Delta Transformation

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The value of the resistor on any one side of the delta, Δ network is the sum of all the two-product combinations of resistors in the star network divide by the star resistor located “directly opposite” the delta resistor being found. For example, resistor A is given as:

with respect to terminal 3 and resistor B is given as:

with respect to terminal 2 with resistor C given as:

with respect to terminal 1.By dividing out each equation by the value of the denominator we end up with three separate transformation formulas that can be used to convert any Delta resistive network into an equivalent star network as given below.1.7.8 Star Delta Transformation Equations

Star Delta Transformation allows us to convert one type of circuit connection into another type in order for us to easily analyse the circuit and star delta transformation techniques can be used for either resistances or impedances.Q1). Determine the resistance between the terminals A&B and hence find the current through the voltage source. Refer figure

The resistors in between point 1, 2&3 are about to replace by a star connected system. Otherwise is difficult to find the total resistance.So we have to use the delta to star transformation equations.

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R1 = R12R31 / (R12+R23+R31)R1 = (60*40)/ (60+40+100)R1 = 12ΩR2 = R23R12 / (R12+R23+R31)R1 = (100*60)/ 200R1 = 30ΩR3 = R31R23 / (R12+R23+R31)R3 = (100*40)/ 200R3 = 20ΩSo we can redraw the network as shown in figure

Now we can easily find the total resistance between A&B terminals Rtotal = [(80+20)//(88+12)] + 30Rtotal = 50 + 30 Rtotal = 80ΩApplying ohm’s law to the total resistance,I = V/RI = 160v/80ΩI = 2AQ2) Find the total resistance between A&B terminals for the network shown in figure

We are about to replace the delta system by star system in between point 1, 2 &3 So we have to use the delta to star transformation equations. R1 = R12R31 / (R12+R23+R31)R1 = (3*6)/ (3+6+9)R1 = 1ΩR2 = R23R12 / (R12+R23+R31)J.C.Vijayshree 24


R2 = (9*3)/18R2 = 1.5ΩR3 = R31R23 / (R12+R23+R31)R3 = (6*9)/18R3 = 3ΩSo now we can replace the system as shown in figure

Now we can easily find the total resistance between A&B terminalsRAB = (7Ω+3Ω) + (8.5Ω+1.5Ω) + 1ΩRAB = 6ΩQ3). Find the total resistance between A&B terminals (RAB) shown in figure

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R12 = R1 + R2 + (R1R2/R3)R12 = 3 + 2 + (3*2)/2R12 = 8ΩR23 = R2 + R3 + (R2R3/R1)R23 = 2 + 2 + (2*2)/3R23 = 16/3ΩR31 = R3 + R1 + (R3R1/R2)R13 = 3 + 2 + (3*2)/2R13 = 8ΩSo we can redraw the network as shown in figure

RAB = { [ (7+5)//8//8 ] + 5 } //8//4RAB = (3 + 5) // 8 // 4RAB = 4//4RAB = 2Ω1.8. Node and mesh methods of analysis of DC circuits.1.8.1 Mesh Current Analysis Circuit

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One simple method of reducing the amount of math’s involved is to analyse the circuit using Kirchoff’s Current Law equations to determine the currents, I1 and I2 flowing in the two resistors. Then there is no need to calculate the current I3 as its just the sum of I1 and I2. So Kirchoff’s second voltage law simply becomes:

Equation No 1 : 10 = 50I1 + 40I2 Equation No 2 : 20 = 40I1 + 60I2

therefore, one line of math’s calculation have been saved.1.8.2 Mesh Current AnalysisAn easier method of solving the above circuit is by using Mesh Current Analysis or Loop Analysis which is also sometimes called Maxwell´s Circulating Currents method. Instead of labelling the branch currents we need to label each “closed loop” with a circulating current.As a general rule of thumb, only label inside loops in a clockwise direction with circulating currents as the aim is to cover all the elements of the circuit at least once. Any required branch current may be found from the appropriate loop or mesh currents as before using Kirchoff´s method.For example: : i1 = I1 , i2 = -I2 and I3 = I1 – I2We now write Kirchoff’s voltage law equation in the same way as before to solve them but the advantage of this method is that it ensures that the information obtained from the circuit equations is the minimum required to solve the circuit as the information is more general and can easily be put into a matrix form.For example, consider the circuit from the previous section.

These equations can be solved quite quickly by using a single mesh impedance matrix Z. Each element ON the principal diagonal will be “positive” and is the total impedance of each mesh. Where as, each element OFF the principal diagonal will either be “zero” or “negative” and represents the circuit element connecting all the appropriate meshes. This then gives us a matrix of:

Where:

[ V ] gives the total battery voltage for loop 1 and then loop 2. [ I ] states the names of the loop currents which we are trying to

find. [ R ] is called the resistance matrix.

and this gives I1 as -0.143 Amps and I2 as -0.429 AmpsAs : I3 = I1 – I2

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The combined current of I3 is therefore given as : -0.143 – (-0.429) = 0.286 Amps which is the same value of 0.286 amps, we found using Kirchoff´s circuit law in the previous tutorial.1.8.3 Mesh Current Analysis Summary.This “look-see” method of circuit analysis is probably the best of all the circuit analysis methodswith the basic procedure for solving Mesh Current Analysis equations is as follows:

1. Label all the internal loops with circulating currents. (I1, I2, …IL etc)2. Write the [ L x 1 ] column matrix [ V ] giving the sum of all voltage

sources in each loop.3. Write the [ L x L ] matrix, [ R ] for all the resistances in the circuit as

follows;i. R11 = the total resistance in the first loop.ii. Rnn = the total resistance in the Nth loop.iii. RJK = the resistance which directly joins loop J to Loop K.

4. Write the matrix or vector equation [V] = [R] x [I] where [I] is the list of currents to be found.

1.8.4 Nodal Voltage Analysis Circuit

1.8.5 Nodal Voltage AnalysisIn the above circuit, node D is chosen as the reference node and the other three nodes are assumed to have voltages, Va, Vb and Vc with respect to node D. For example;

As Va = 10v and Vc = 20v , Vb can be easily found by:

again is the same value of 0.286 amps, we found using Kirchoff’s Circuit Law in the previous tutorial.From both Mesh and Nodal Analysis methods we have looked at so far, this is the simplest method of solving this particular circuit. Generally, nodal voltage analysis is more appropriate when there are a larger number of current sources around. The network is then defined as: [ I ] = [ Y ] [ V ] where [ I ] are the driving current sources, [ V ] are the nodal J.C.Vijayshree 28





voltages to be found and [ Y ] is the admittance matrix of the network which operates on [ V ] to give [ I ].1.8.6 Nodal Voltage Analysis Summary.The basic procedure for solving Nodal Analysis equations is as follows:1. Write down the current vectors, assuming currents into a node are positive. ie, a (N x 1) matrices for “N” independent nodes.2. Write the admittance matrix [Y] of the network where:

o Y11 = the total admittance of the first node.o Y22 = the total admittance of the second node.o RJK = the total admittance joining node J to node K.

3. For a network with “N” independent nodes, [Y] will be an (N x N) matrix and that Ynn will be positive and Yjk will be negative or zero value. 4. The voltage vector will be (N x L) and will list the “N” voltages to be found.What is the voltage across the current source? Via nodal analysis:Defining the nodal voltages in the conventional way (with the reference node at the bottom grounded to 0 V) leads to:

KCL at node 1:(V1-2)/2 + V1/3 + (V1-V2) = 0KCL at node 2:(V2-V1) + V2/5 -2 = 0Multiplying eqn. 1 through by 6, eqn. 2 through by 5, and consolidating terms leads to the following two equations to solve:11 V1 – 6 V2 = 6-5 V1 + 6 V2 = 10Adding the two equations produces:V1 = 2.67 VBacksubstitution yields the desired answer:V2 = 3.89 V

UNIT – IIAC CIRCUITS

2.1. Concepts of AC circuits – 2.1.1. AC Waveform: An alternating function or AC Waveform on the other hand is defined as one that varies in both magnitude and direction in more or less an even manner with respect to time making it a “Bi-directional” waveform. An AC function can represent either a power source or a signal source with the shape of an AC waveform generally following that of a mathematical sinusoid as defined by:- A(t) = Amax x sin(2πƒt).2.1.2 AC Waveform CharacteristicsJ.C.Vijayshree 29


The Period, (T) is the length of time in seconds that the waveform takes to repeat itself from start to finish. This can also be called the Periodic Time of the waveform for sine waves, or the Pulse Width for square waves.

The Frequency, (ƒ) is the number of times the waveform repeats itself within a one second time period. Frequency is the reciprocal of the time period, ( ƒ = 1/T ) with the unit of frequency being the Hertz, (Hz).

The Amplitude (A) is the magnitude or intensity of the signal waveform measured in volts or amps.

2.1.3 Types of Periodic Waveform

2.1.4 Relationship Between Frequency and Periodic Time

2.1.5 AC Waveform Example 1. What will be the periodic time of a 50Hz waveform and 2. what is the frequency of an AC waveform that has a periodic time of 10mS.

1).

2).

2.2. RMS value, Average value, Form and Peak factors – 2.2.1 The Average Value of an AC WaveformThe average or mean value of a continuous DC voltage will always be equal to its maximum peak value as a DC voltage is constant. This average value will only change if the duty cycle of the DC voltage changes. J.C.Vijayshree 30


2.2.2 Average Value of a Non-sinusoidal Waveform

The zero axis base line is divided up into any number of equal parts and in our simple example above this value was nine, ( V1 to V9 ).

Where: n equals the actual number of mid-ordinates used.2.2.3 Average Value of a sinusoidal WaveformFor a pure sinusoidal waveform this average or mean value will always be equal to 0.637 x Vmax and this relationship also holds true for average values of current.2.2.4 The RMS Value of an AC WaveformThe average value of an AC waveform is NOT the same value as that for a DC waveforms average value. This is because the AC waveform is constantly changing with time and the heating effect given by the formula ( P = I 2.R ), will also be changing producing a positive power consumption. The equivalent average value for an alternating current system that provides the same power to the load as a DC equivalent circuit is called the “effective value”.RMS Value of an AC Waveform

Where: n equals the number of mid-ordinates.2.2.5 Form Factor and Crest FactorForm Factor is the ratio between the average value and the RMS value and is given as.

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For a pure sinusoidal waveform the Form Factor will always be equal to 1.11. Crest Factor is the ratio between the R.M.S. value and the Peak value of the waveform and is given as.

For a pure sinusoidal waveform the Crest Factor will always be equal to 1.414. Example A sinusoidal alternating current of 6 amps is flowing through a resistance of 40Ω. Calculate the average voltage and the peak voltage of the supply.The R.M.S. Voltage value is calculated as:

The Average Voltage value is calculated as:

The Peak Voltage value is calculated as:

2.3. Simple RLC series circuits – 2.3.1 Element ImpedanceThe three basic passive components, R, L and C have very different phase relationships to each other when connected to a sinusoidal AC supply. In a pure ohmic resistor the voltage waveforms are “in-phase” with the current. In a pure inductance the voltage waveform “leads” the current by 90o. In a pure capacitance the voltage waveform “lags” the current by 90o.Circuit Element

Resistance, (R) Reactance, (X) Impedance, (Z)

Resistor R 0

Inductor 0 ωL

Capacitor 0

2.3.2 Series RLC Circuit

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The series RLC circuit above has a single loop with the instantaneous current flowing through the loop being the same for each circuit element. Since the inductive and capacitive reactance’s are a function of frequency, the sinusoidal response of a series RLC circuit will vary with the applied frequency, ( ƒ ). Therefore the individual voltage drops across each circuit element of R, L and C element will be “out-of-phase” with each other as defined by:

i(t) = Imax sin(ωt) The instantaneous voltage across a pure resistor, VR is “in-

phase” with the current. The instantaneous voltage across a pure inductor, VL “leads” the

current by 90o

The instantaneous voltage across a pure capacitor, VC “lags” the current by 90o

Therefore, VL and VC are 180o “out-of-phase” and in opposition to each other.

2.3.3 Individual Voltage Vectors

This means then that we can not simply add together VR, VL and VC to find the supply voltage, VS across all three components as all three voltage vectors point in different directions with regards to the current vector. Therefore we will have to find the supply voltage, VS as the Phasor Sum of the three component voltages combined together vectorially.2.3.4 Instantaneous Voltages for a Series RLC Circuit

2.3.5 Phasor Diagram for a Series RLC Circuit

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2.3.6 Voltage Triangle for a Series RLC Circuit

Then the voltage across each component can also be described mathematically according to the current flowing through, and the voltage across each element as.

By substituting these values into Pythagoras’s equation above for the voltage triangle will give us:

2.3.7 The Impedance of a Series RLC CircuitAs the three vector voltages are out-of-phase with each other, XL, XC and R must also be “out-of-phase” with each other with the relationship between R, XL and XC being the vector sum of these three components thereby giving us the circuits overall impedance, Z.

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The phase angle, θ between the source voltage, VS and the current, i is the same as for the angle between Z and R in the impedance triangle.

Series RLC Circuit Example A series RLC circuit containing a resistance of 12Ω, an inductance of 0.15H and a capacitor of 100uF are connected in series across a 100V, 50Hz supply. Calculate the total circuit impedance, the circuits current, power factor and draw the voltage phasor diagram.

Inductive Reactance, XL.

Capacitive Reactance, XC.

Circuit Impedance, Z.

Circuits Current, I.

Voltages across the Series RLC Circuit, VR, VL, VC.

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Circuits Power factor and Phase Angle, θ.

Phasor Diagram.

Since the phase angle θ is calculated as a positive value of 51.8o the overall reactance of the circuit must be inductive. As we have taken the current vector as our reference vector in a series RLC circuit, then the current “lags” the source voltage by 51.8o so we can say that the phase angle is lagging as confirmed by our mnemonic expression “ELI”.2.4. Concept of real and reactive power – 2.4.1 Reactive power: We know that reactive loads such as inductors and capacitors dissipate zero power, yet the fact that they drop voltage and draw current gives the deceptive impression that they actually do dissipate power. This “phantom power” is called reactive power, and it is measured in a unit called Volt-Amps-Reactive (VAR), rather than watts. The mathematical symbol for reactive power is (unfortunately) the capital letter Q. 2.4.2 Real power: The actual amount of power being used, or dissipated, in a circuit is called true power, and it is measured in watts (symbolized by the capital letter P, as always). The combination of reactive power and true power is called apparent power, and it is the product of a circuit's voltage and current, without reference to phase angle. Apparent power is measured in the unit of Volt-Amps (VA) and is symbolized by the capital letter S. As a rule, true power is a function of a circuit's dissipative elements, usually resistances (R). Reactive power is a function of a circuit's reactance (X). Apparent power is a function of a circuit's total impedance (Z). 2.4.3 Power equations: There are several power equations relating the three types of power to resistance, reactance, and impedance (all using scalar quantities):

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2.4.4 Resistive load only:

True power, reactive power, and apparent power for a purely resistive load.

2.4.5 Reactive load only:

True power, reactive power, and apparent power for a purely reactive load.2.4.6 Resistive/reactive load:

True power, reactive power, and apparent power for a resistive/reactive load.

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2.4.7 Power triangle: These three types of power -- true, reactive, and apparent -- relate to one another in trigonometric form. We call this the power triangle: (Figure below).

Power triangle relating appearant power to true power and reactive power.

Using the laws of trigonometry, we can solve for the length of any side (amount of any type of power), given the lengths of the other two sides, or the length of one side and an angle. 2.5. Power factor – 2.5.1 Power factor definitionThe power factor is equal to the real or true power P in watts (W) divided by the apparent power |S| in volt-ampere (VA):PF = P(W) / |S(VA)|PF - power factor.P - real power in watts (W).|S| - apparent power - the magnitude of the complex power in volt·amps (VA).2.5.2 Power factor calculationsFor sinusuidal current, the power factor PF is equal to the absolute value of the cosine of the apparent power phase angle φ (which is also is impedance phase angle):PF = |cos φ|PF is the power factor.φ is the apprent power phase angle. 2.5.3 In terms of real & apparent powerThe real power P in watts (W) is equal to the apparent power |S| in volt-ampere (VA) times the power factor PF:P(W) = |S(VA)| × PF = |S(VA)| × |cos φ| 2.5.4 For resistive loadWhen the circuit has a resistive impedance load, the real power P is equal to the apparent power |S| and the power factor PF is equal to 1:PF(resistive load) = P / |S| = 12.5.5 In terms of phase angleThe reactive power Q in volt-amps reactive (VAR) is equal to the apparent power |S| in volt-ampere (VA) times the sine of the phase angle φ:Q(VAR) = |S(VA)| × |sin φ|

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Single phase circuit calculation from real power meter reading P in kilowatts (kW), voltage V in volts (V) and current I in amps (A):PF = |cos φ| = 1000 × P(kW) / (V(V) × I(A)) Three phase circuit calculation from real power meter reading P in kilowatts (kW), line to line voltage VL-L in volts (V) and current I in amps (A):PF = |cos φ| = 1000 × P(kW) / (√3 × VL-L(V) × I(A)) Three phase circuit calculation from real power meter reading P in kilowatts (kW), line to line neutral VL-N in volts (V) and current I in amps (A):PF = |cos φ| = 1000 × P(kW) / (3 × VL-N(V) × I(A))2.6. Introduction to three phase system – 2.6.1 Three phase circuit Three phase circuit is the polyphase system where three phases are send together from the generator to the load. Each phase are having a phase difference of 120°, i.e 120° angle electrically. So from the total of 360°, three phases are equally divided into 120° each. The power in three phase system is continuous as all the three phases are involved in generating the total power. The sinusoidal waves for 3 phase system is shown belowThe three phases can be used as single phase each. So if the load is single phase, then one phase can be taken from the three phase circuit and the neutral can be used as ground to complete the circuit.

2.6.2 Why Three Phase is preferred Over Single Phase? The three phase system can be used as three single phase line so it can act as three single phase system. The three phase generation and single phase generation is same in the generator except the arrangement of coil in the generator to get 120° phase difference. The instantaneous power in single phase system falls down to zero as in single phase we can see from the sinusoidal curve but in three phase system the net power from all the phases gives a continuous power to the load.The size or metal quantity of three phase devices is not having much difference. The three phase system will have higher efficiency compared to single phase 2.6.3. Connection TypesIn three phase circuit, connections can be given in two types:

1. Star connection2. Delta connection

2.6.4 Star Connection

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In star connection, there is four wire, three wires are phase wire and fourth is neutral which is taken from the star point. Star connection is preferred for long distance power transmission because it is having the neutral point. In this we need to come to the concept of balanced and unbalanced current in power system.The star connection is shown below-

In star connection, the line voltage is √3 times of phase voltage. Line voltage is the voltage between two phases in three phase circuit and phase voltage is the voltage between one phase to the neutral line. And the current is same for both line and phase. It is shown as expression below

2.6.5 Delta ConnectionIn delta connection, there is three wires alone and no neutral terminal is taken. Normally delta connection is preferred for short distance due to the problem of unbalanced current in the circuit. The figure is shown below for delta connection. In the load station, ground can be used as neutral path if required.

In delta connection, the line voltage is same with that of phase voltaage. And the line current is √3 times of phase current. It is shown as expression below,

In three phase circuit, star and delta connection can be arranged in four different ways-

1. Star-Star connection2. Star-Delta connection3. Delta-Star connection4. Delta-Delta connection

2.7. Power measurement by two wattmeter method.2.7.1 Types of connectionIn this method we have two types of connections (a)Star connection of loads (b)Delta connection of loads. 2.7.2 Star Connection J.C.Vijayshree 40

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When the star connected load, the diagram is shown in below-

2.7.2 Power measurement in star connectionFor star connected load clearly the reading of wattmeter one is product phase current and voltage difference (V2-V3). Similarly the reading of wattmeter two is the product of phase current and the voltage difference (V2-V3). Thus the total power of the circuit is sum of the reading of both the wattmeters. Mathematically we can write

but we have I1+I2+I3=0,hence putting the value of I1+I2=-I3.We get total power as V1I1+V2I2+V3I3.2.7.3 Delta connection

When delta connected load, the diagram is shown in below

2.7.4 Power measurement in delta connectionThe reading of wattmeter one can be written as

and reading of wattmeter two is

but V1+V2+V3=0, hence expression for total power will reduce to V1I1+V2I2+V3I3.

UNIT – IIIELECTRICAL MACHINES AND POWER PLANTS

3.1. Law of Electromagnetic induction3.1.1.Faraday's laws of of electromagnetic induction Faraday's laws of of electromagnetic induction explains the relationship between electric circuit and magnetic field. This law is the basic working principle of the most of the electrical motors, generators, transformers, inductors etc.J.C.Vijayshree 41

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3.1.2 Faraday's first law:Whenever a conductor is placed in a varying magnetic field an EMF gets induced across the conductor (called as induced emf), and if the conductor is a closed circuit then induced current flows through it.Magnetic field can be varied by various methods –

1. By moving magnet2. By moving the coil3. By rotating the coil relative to magnetic field

3.1.3 Faraday's second law:Faraday's second law of electromagnetic induction states that, the magnitude of induced emf is equal to the rate of change of flux linkages with the coil. The flux linkages is the product of number of turns and the flux associated with the coil.3.1.4 Formula of Faraday's law:Consider the conductor is moving in magnetic field, thenflux linkage with the coil at initial position of the conductor = NΦ1 (Wb) (N is speed of the motor and Φ is flux)flux linkage with the coil at final position of the conductor = NΦ2 (Wb)change in the flux linkage from initial to final = N(Φ1 - Φ2) let Φ1 - Φ2 = Φ therefore, change in the flux linkage = NΦ and, rate of change in the flux linkage = NΦ/t taking the derivative of RHS rate of change of flux linkages = N (dΦ/dt)According to Faraday's law of electromagnetic induction, rate of change of flux linkages is equal to the induced emfSo, E = N (dΦ/dt) (volts)3.1.5 Phenomenon of Mutual InductionAlternating current flowing in a coil produces alternating magnetic field around it. When two or more coils are magnetically linked to each other, then an alternating current flowing through one coil causes an induced emf across the other linked coils. This phenomenon is called as mutual induction.3.1.6 Lenz's lawLenz's law of electromagnetic induction states that, when an emf is induced according to Faraday's law, the polarity (direction) of that induced emf is such that it opposes the cause of its production.Thus, considering Lenz's lawE = -N (dΦ/dt) (volts)The negative sign shows that, the direction of the induced emf and the direction of change in magnetic fields have opposite signs. 3.2. Fleming’s Right & Left hand rule – 3.2.1Fleming’s rule

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Whenever a current carrying conductor comes under a magnetic field, there will be force acting on the conductor and on the other hand, if a conductor is forcefully brought under a magnetic field, there will be an induced current in that conductor. In both of the phenomenons, there is a relation between magnetic field, current and force. This relation is directionally determined by Fleming Left Hand rule and Fleming Right Hand rule respectively. 3.2.2 Directionality'Directionally' means these rules do not show the magnitude but show the direction of any of the three parameters (magnetic field, current, force) if the direction of other two are known. 3.2.3 ApplicationFleming Left Hand rule is mainly applicable for electric motor and Fleming Right Hand rule is mainly applicable for electric generator. In late 19th century, John Ambrose Fleming introduced both these rules and as per his name, the rules are well known as Fleming left and right hand rule.3.2.4 Fleming Left Hand Rule

It is found that whenever an current carrying conductor is placed inside a magnetic field, a force acts on the conductor, in a direction perpendicular to both the directions of the current and the magnetic field. In the figure it is shown that, a portion of a conductor of length L placed vertically in a uniform horizontal magnetic field strength H, produced by two magnetic poles N and S. If i is the current flowing through this conductor, the magnitude of the force acts on the conductor is, F = BiL

Hold out your left hand with forefinger, second finger and thumb at right angle to one another. If the fore finger represents the direction of the field and the second finger that of the current, then thumb gives the direction of the force. 3.2.5 Fleming Right Hand Rule

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As per Faraday's law of electromagnetic induction, whenever a conductor moves inside a magnetic field, there will be an induced current in it. If this conductor gets forcefully moved inside the magnetic field, there will be a relation between the direction of applied force, magnetic field and the current. This relation among these three directions is determined by Fleming Right Hand ruleThis rule states "Hold out the right hand with the first finger, second finger and thumb at right angle to each other. If forefinger represents the direction of the line of force, the thumb points in the direction of motion or applied force, then second finger points in the direction of the induced current. 3.3. Principle of DC rotating machine 3.3.1 DC Rotating MachineA DC motor in simple words is a device that converts direct current(electrical energy) into mechanical energy. It’s of vital importance for the industry today, and is equally important for engineers to look into the working principle of DC motor in details that has been discussed in this article. In order to understand the operating principle of dc motor we need to first look into its constructional feature.

3.3.2 Construction

The very basic construction of a dc motor contains a current carrying armature which is connected to the supply end through commutator segments and brushes and placed within the north south poles of a permanent or an electro-magnet as shown in the Now to go into the details of the operating principle of DC motor its important that we J.C.Vijayshree 44


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have a clear understanding of Fleming’s left hand rule to determine the direction of force acting on the armature conductors of dc motor.3.3.3 Fleming’s left hand ruleFleming’s left hand rule says that if we extend the index finger, middle finger and thumb of our left hand in such a way that the current carrying conductor is placed in a magnetic field (represented by the index finger) is perpendicular to the direction of current (represented by the middle finger), then the conductor experiences a force in the direction (represented by the thumb) mutually perpendicular to both the direction of field and the current in the conductor.3.3.4 PrincipleFor clear understanding the principle of DC motor we have to determine the magnitude of the force, by considering the diagram below.We know that when an infinitely small charge dq is made to flow at a velocity ‘v’ under the influence of an electric field E, and a magnetic field B, then the Lorentz Force dF experienced by the charge is given by:-

3.3.5 OperationFor the operation of dc motor, considering E = 0

i.e. it’s the cross product of dq v and magnetic field B.

Where dL is the length of the conductor carrying charge q.

From the 1st diagram we can see that the construction of a DC motor is such that the direction of current through the armature conductor at all instance is perpendicular to the field. Hence the force acts on the armature conductor in the direction perpendicular to the both uniform field and current is constant.

So if we take the current in the left hand side of the armature conductor to be I, and current at right hand side of the armature conductor to be − I, because they are flowing in the opposite direction with respect to each other. Then the force on the left hand side armature conductor, J.C.Vijayshree 45





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Similarly force on the right hand side conductor

∴ we can see that at that position the force on either side is equal in magnitude but opposite in direction. And since the two conductors are separated by some distance w = width of the armature turn, the two opposite forces produces a rotational force or a torque that results in the rotation of the armature conductor.3.4. Single phase transformer 3.4.1 Voltage Transformer BasicsA transformer basically is very simple static (or stationary) electro-magnetic passive electrical device that works on the principle of Faraday’s law of induction by converting electrical energy from one value to another.The transformer does this by linking together two or more electrical circuits using a common oscillating magnetic circuit which is produced by the transformer itself. A transformer operates on the principals of “electromagnetic induction”, in the form of Mutual Induction.Mutual induction is the process by which a coil of wire magnetically induces a voltage into another coil located in close proximity to it. Transformers are capable of either increasing or decreasing the voltage and current levels of their supply, without modifying its frequency, or the amount of Electrical Power being transferred from one winding to another via the magnetic circuit.3.4.2 Single Phase Voltage Transformer

In other words, for a transformer there is no direct electrical connection between the two coil windings, thereby giving it the name also of an Isolation Transformer. Generally, the primary winding of a transformer is connected to the input voltage supply and converts or transforms the electrical power into a magnetic field. While the job of the secondary winding is to convert this alternating magnetic field into electrical power producing the required output voltage as shown.3.4.3 Transformer Construction (single-phase)

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VP - is the Primary Voltage VS - is the Secondary Voltage NP - is the Number of Primary Windings NS - is the Number of Secondary Windings Φ (phi) - is the Flux Linkage

Notice that the two coil windings are not electrically connected but are only linked magnetically. A single-phase transformer can operate to either increase or decrease the voltage applied to the primary winding. When a transformer is used to “increase” the voltage on its secondary winding with respect to the primary, it is called a Step-up transformer. When it is used to “decrease” the voltage on the secondary winding with respect to the primary it is called a Step-down transformer.However, a third condition exists in which a transformer produces the same voltage on its secondary as is applied to its primary winding. In other words, its output is identical with respect to voltage, current and power transferred. This type of transformer is called an “Impedance Transformer” and is mainly used for impedance matching or the isolation of adjoining electrical circuits.The difference in voltage between the primary and the secondary windings is achieved by changing the number of coil turns in the primary winding ( NP ) compared to the number of coil turns on the secondary winding ( NS ).As the transformer is basically a linear device, a ratio now exists between the number of turns of the primary coil divided by the number of turns of the secondary coil. This ratio, called the ratio of transformation, more commonly known as a transformers “turns ratio”, ( TR ). This turns ratio value dictates the operation of the transformer and the corresponding voltage available on the secondary winding.3.4.4 A Transformers Turns Ratio

Assuming an ideal transformer and the phase angles: ΦP ≡ ΦSNote that the order of the numbers when expressing a transformers turns ratio value is very important as the turns ratio 3:1 expresses a very different transformer relationship and output voltage than one in which the turns ratio is given as: 1:3.3.4.5 Transformer ActionWhen an alternating voltage ( VP ) is applied to the primary coil, current flows through the coil which in turn sets up a magnetic field around itself, called mutual inductance, by this current flow according to Faraday’s Law of electromagnetic induction. The strength of the magnetic field builds up as the current flow rises from zero to its maximum value which is given as dΦ/dt.

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As the magnetic flux varies sinusoidally, Φ = Φmax sinωt, then the basic relationship between induced emf, ( E ) in a coil winding of N turns is given by:emf = turns x rate of change

Where: ƒ - is the flux frequency in Hertz, = ω/2π Ν - is the number of coil windings. Φ - is the flux density in webers

This is known as the Transformer EMF Equation. 3.4.6 Electrical Power in a TransformerIn an ideal transformer (ignoring any losses), the power available in the secondary winding will be the same as the power in the primary winding, they are constant wattage devices and do not change the power only the voltage to current ratio. Thus, in an ideal transformer the Power Ratio is equal to one (unity) as the voltage, V multiplied by the current, I will remain constant.

Where: ΦP is the primary phase angle and ΦS is the secondary phase angle.

3.4.7 Transformer Efficiency

where: Input, Output and Losses are all expressed in units of power.Generally when dealing with transformers, the primary watts are called “volt-amps”, VA to differentiate them from the secondary watts. Then the efficiency equation above can be modified to:

3.5 Single phase induction motor– 3.5.1 Single phase ac motorsFor lightning and general purposes in homes, offices, shops, small factories single phase system is widely used as compared to three phase J.C.Vijayshree 48



system as the single phase system is more economical and the power requirement in most of the houses, shops, offices are small, which can be easily met by single phase system. The single phase motors are simple in construction, cheap in cost, reliable and easy to repair and maintain. Due to all these advantages the single phase motor finds its application in vacuum cleaner, fans, washing machine, centrifugal pump, blowers, washing machine, small toys etc.3.5.2 ClassificationThe single phase ac motors are further classified as:

1. Single phase induction motors or asynchronous motors.2. Single phase synchronous motors.3. Commutator motors.

3.5.3 Construction of Single Phase Induction MotorLike any other electrical motor asynchronous motor also have two main parts namely rotor and stator.Stator: As its name indicates stator is a stationary part of induction motor. A single phase ac supply is given to the stator of single phase induction motor.Rotor: The rotor is a rotating part of induction motor. The rotor is connected to the mechanical load through the shaft. The rotor in single phase induction motor is of squirrel cage rotor type.The construction of single phase induction motor is almost similar to the squirrel cage three phase motor except that in case of asynchronous motor the stator have two windings instead of one as compare to the single stator winding in three phase induction motor. 3.5.4 Working Principle of Single Phase Induction MotorWhen single phase ac supply is given to the stator winding of single phase induction motor, the alternating current starts flowing through the stator or main winding. This alternating current produces an alternating flux called main flux. This main flux also links with the rotor conductors and hence cut the rotor conductors. According to the Faraday’s law of electromagnetic induction, emf gets induced in the rotor. As the rotor circuit is closed one so, the current starts flowing in the rotor. This current is called the rotor current. This rotor current produces its own flux called rotor flux. Since this flux is produced due to induction principle so, the motor working on this principle got its name as induction motor. Now there are two fluxes one is main flux and another is called rotor flux. These two fluxes produce the desired torque which is required by the motor to rotate.3.5.5 Types of single phase induction motorDepending upon the methods for making asynchronous motor as Self Starting Motor, there are mainly four types of single phase induction motor namely,

1. Split phase induction motor,2. Capacitor start inductor motor,3. Capacitor start capacitor run induction motor,4. Shaded pole induction motor.

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3.5.6 Comparison between Single Phase and Three Phase Induction Motors

o Single phase induction motors are simple in construction, reliable and economical for small power rating as compared to three phase induction motors.

o The electrical power factor of single phase induction motors is low as compared to three phase induction motors.

o For same size, the single phase induction motors develop about 50% of the output as that of three phase induction motors.

o The starting torque is also low for asynchronous motors.o The efficiency of single phase induction motors is less as

compare it to the three phase induction motors.3.6. Simple layout of thermal generation 3.6.1 Thermal power generation plant Thermal power generation plant or thermal power station is the most conventional source of electric power. Thermal power plant is also referred as coal thermal power plant and steam turbine power plant. Before going into detail of this topic, we will try to understand the line diagram of electric power generation plant. 3.6.2 Theory of Thermal Power StationThe theory of thermal power station or working of thermal power station is very simple. A power generation plant mainly consists of alternator runs with help of steam turbine. The steam is obtained from high pressure boilers. Generally in India, bituminous coal, brown coal and peat are used as fuel of boiler. The bituminous coal is used as boiler fuel has volatile matter from 8 to 33 % and ash content 5 to 16 %. To increase the thermal efficiency, the coal is used in the boiler in powder form.In coal thermal power plant, the steam is produced in high pressure in the steam boiler due to burning of fuel (pulverized coal) in boiler furnaces. This steam is further supper heated in a super heater. This supper heated steam then enters into the turbine and rotates the turbine blades. The turbine is mechanically so coupled with alternator that its rotor will rotate with the rotation of turbine blades. After entering in turbine the steam pressure suddenly falls and corresponding volume of the steam increases. After imparting energy to the turbine rotor the steam passes out of the turbine blades into the condenser. In the condenser the cold water is circulated with the help of pump which condenses the low pressure wet steam. This condensed water is further supplied to low pressure water heater where the low pressure steam increases the temperature of this feed water, it is again heated in high pressure. 3.6.3 Functional StepsFor better understanding we furnish every step of function of a thermal power station as follows,1) First the pulverized coal is burnt into the furnace of steam boiler.2) High pressure steam is produced in the boiler.3) This steam is then passed through the super heater, where it further heated up.J.C.Vijayshree 50

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4) This supper heated steam is then entered into a turbine at high speed.5) In turbine this steam force rotates the turbine blades that means here in the turbine the stored potential energy of the high pressured steam is converted into mechanical energy.

Line Diagram of Power Plant6) After rotating the turbine blades, the steam has lost its high pressure, passes out of turbine blades and enters into a condenser.7) In the condenser the cold water is circulated with help of pump which condenses the low pressure wet steam.8) This condensed water is then further supplied to low pressure water heater where the low pressure steam increases the temperature of this feed water, it is then again heated in a high pressure heater where the high pressure of steam is used for heating.9) The turbine in thermal power station acts as a prime mover of the alternator. 3.6.4 Overview of Thermal Power Plant

A typical Thermal Power Station Operates on a Cycle which is shown

below. The working fluid is water and steam. This is called feed water and steam cycle. The ideal Thermodynamic Cycle to which the operation of a Thermal Power Station closely resembles is the RANKINE CYCLE.In steam boiler the water is heated up by burning the fuel in air in the furnace & the function of the boiler is to give dry super heated steam at required temperature.J.C.Vijayshree 51




The steam so produced is used in driving the steam Turbines. This turbine is coupled to synchronous generator (usually three phase synchronous alternator), which generates electrical energy.The exhaust steam from the turbine is allowed to condense into water in steam condenser of turbine, which creates suction at very low pressure and allows the expansion of the steam in the turbine to a very low pressure. The principle advantages of condensing operation are the increased amount of energy extracted per kg of steam and thereby increasing efficiency and the condensate which is fed into the boiler again reduces the amount of fresh feed water.The condensate along with some fresh make up feed water is again fed into the boiler by pump (called the boiler feed pump).In condenser the steam is condensed by cooling water. Cooling water recycles through cooling tower. This constitutes cooling water circuit.The ambient air is allowed to enter in the boiler after dust filtration. Also the flue gas comes out of the boiler and exhausted into atmosphere through stacks. These constitute air and flue gas circuit. The flow of air and also the static pressure inside the steam boiler (called draught) is maintained by two fans called Forced Draught (FD) fan and Induced Draught(ID) fan.3.6.5 Scheme of operationThe total scheme of a typical thermal power station along with different circuits is illustrated below.

Inside the boiler there are various heat exchangers, viz.’ Economiser’, ‘Evaporator’ (not shown in the fig above, it is basically the water tubes, i.e. downcomer riser circuit), ‘Super Heater’ (sometimes ‘Reheater’, ‘air preheater’ are also present).In Economiser the feed water is heated to considerable amount by the remaining heat of flue gas.The Boiler Drum actually maintains a head for natural circulation of two phase mixture (steam + water) through the water tubes.There is also Super Heater which also takes heat from flue gas and raises the temperature of steam as per requirement. 3.6.6 Efficiency of Thermal Power Station or PlantThe overall efficiency of a thermal power station or plant varies from 20% to 26% and it depends upon plant capacity. Installed plant Average overall thermal J.C.Vijayshree 52


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capacity efficiencypto 1MW 4%1MW to 10MW 12%10MW to 50MW 16%50MW to 100MW 24%above 100MW 27%3.6.7 Thermal Power Plant Location deciding factors1) The electric power generation plant must be constructed at such a place where the cost of land is quite reasonable.2) The land should be such that the acquisition of private property must be minimum.3) A large quantity of cooling water is required for the condensers etc of thermal power generation plant, hence the plant should preferably situated beside big source of natural water source such as big river.4) Availability of huge amount of fuel at reasonable cost is one of the major criterion for choosing plant location.5) The plant should be established on plane land.6)The soil should be such that it should provide good and firm foundation of plant and buildings.7) The thermal power plant location should not be very nearer to dense locality as there are smoke, noise steam, water vapors etc.8) There must be ample scope of development of future demand.9) Place for ash handling plant for thermal power station should also be available very near by.10) Very tall chimney of power station should not obstruct the traffics of air ships. 3.6.8 Advantages of Thermal Power Station1) Economical for low initial cost other than any generating plant.2) Land required less than hydro power plant.3) Since coal is main fuel & its cost is quite cheap than petrol/diesel so generation cost is economical.4) There are easier maintenance.5) Thermal power plant can be installed in any location where transportation & bulk of water are available.3.6.9 Disadvantages of Thermal Power Station1) The running cost for a thermal power station is comparatively high due to fuel, maintenance etc.2) Large amount of smoke causes air pollution. The thermal power station is responsible for Global warming.3) The heated water that comes from thermal power plant has an adverse effect on the lives in the water and disturbs the ecology.4) Overall efficiency of thermal power plant is low like less 30%. 3.7. Simple layout of hydro generation 3.7.1 Hydroelectric Power PlantsHydroelectric power plants convert the hydraulic potential energy from water into electrical energy. Such plants are suitable were water with

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suitable head are available. The layout covered in this article is just a simple one and only cover the important parts of hydroelectric plant.3.7.2 Different parts of a hydroelectric power plant (1) DamDams are structures built over rivers to stop the water flow and form a reservoir.The reservoir stores the water flowing down the river. This water is diverted to turbines in power stations. The dams collect water during the rainy season and stores it, thus allowing for a steady flow through the turbines throughout the year. Dams are also used for controlling floods and irrigation. The dams should be water-tight and should be able to withstand the pressure exerted by the water on it. There are different types of dams such as arch dams, gravity dams and buttress dams. The height of water in the dam is called head race.(2) SpillwayA spillway as the name suggests could be called as a way for spilling of water from dams. It is used to provide for the release of flood water from a dam. It is used to prevent over toping of the dams which could result in damage or failure of dams. Spillways could be controlled type or uncontrolled type. The uncontrolled types start releasing water upon water rising above a particular level. But in case of the controlled type, regulation of flow is possible.(3) Penstock and TunnelPenstocks are pipes which carry water from the reservoir to the turbines inside power station. They are usually made of steel and are equipped with gate systems.Water under high pressure flows through the penstock. A tunnel serves the same purpose as a penstock. It is used when an obstruction is present between the dam and power station such as a mountain. (4) Surge TankSurge tanks are tanks connected to the water conductor system. It serves the purpose of reducing water hammering in pipes which can cause damage to pipes. The sudden surges of water in penstock is taken by the surge tank, and when the water requirements increase, it supplies the collected water thereby regulating water flow and pressure inside the penstock.

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(5) Power StationPower station contains a turbine coupled to a generator (see the cross section of a power house on the left). The water brought to the power station rotates the vanes of the turbine producing torque and rotation of turbine shaft. This rotational torque is transferred to the generator and is converted into electricity. The used water is released through the tail race. The difference between head race and tail race is called gross head and by subtracting the frictional losses we get the net head available to the turbine for generation of electricity.3.7.3 Working principle:Hydro-electric power plant utilizes the potential energy of water stored in a dam built across the river. The potential energy of the water is used to run water turbine to which the electric generator is coupled. The mechanical energy available at the shaft of the turbine is converted into electrical energy by means of the generator.3.7.4 General arrangement of a hydro-electric power plant:Image below shows the schematic representation of the hydro-electric power plant.

Water reservoir:Continuous availability of water is the basic necessity for a hydro-electric plant. Water collected from catchment area during rainy season is stored in the reservoir. Water surface in the storage reservoir is known as head race.Dam:The function of a dam is to increase the height of water level behind it, which ultimately increases the reservoir capacity. The dam also helps to increase the working head of the power plant.Spillway:Water in the dam after a certain level in the reservoir overflows through spillway without allowing the increase in water level in the reservoir during rainy season.Pressure tunnel:It carries water from the reservoir to surge tank.

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Penstock:Water from surge tank is taken to the turbine by means of pen stocks, made up of reinforced concrete pipe or steel.Surge tank: There is sudden increase of pressure in the penstock due to sudden backflow of water, as load on the turbine is reduced. The sudden rise of pressure in the penstock is known as water hammer. The surge tank is introduced between the dam and the power house to keep in reducing the sudden rise of pressure in the penstock. Otherwise penstock will be damaged by the water hammer.Water turbine:Water through the penstock enters into the turbine through an inlet valve. Prime motors which are in common use are pelton turbine, francis turbine and kalpan turbine. The potential energy of water entering the turbine is converted into mechanical energy. The mechanical energy available at the turbine shaft is used to run the electric generator. The water is then discharged through the draft tube.Draft tube:It is connected to the outlet of the turbine. It allows the turbine to be placed over tail race level.Tail race:Tail race is a water way to lead the water discharged from the turbine to the river. The water held in the tail race is called tail race water level.Step-up transformer:Its function is to rasie the voltage generated at the generator terminal before transmitting the power consumers.Power house:The power house accommodates the turbine, generator, transformer and control room.3.7.5 Classification of hydro-power plantsHydro-plants are classified according to the head of water under which they work.When the operating head of water exceeds 70 meters, the plant is known as “high head power plant”. Peloton turbine is used as prime mover in such power plants.When the head of water range is from 15 to 70 meters then the power plant is known as “medium head plant”. It uses francis turbine.When the head is less than 15 meters the plant is named as “low head plant”. It uses francis or Kaplan turbine as prime mover.3.7.6 Advantages of hydro-electric power plants

1. Water is a renewable source of energy. Water which is the operating fluid, is neither consumed or converted into something else..

2. Water is the cheapest source of energy because it exists as a free gift of nature. The fuels needed for thermal, diesel and nuclear plants are exhaustible and expensive.

3. There are no ash disposable problems as in case of thermal power plant.

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4. Hydro-plant does not pose the problem of air pollution as in the case of thermal plant or radiation hazards as in the case of nuclear plant.

5. Variable loads do not affect the efficiency in the case of a hydro-plant.

6. Life of hydro-plant is very long (1 or 2 centuries) compared with thermal plant ( 3 to 4 decades). This is because the hydro-plants operate at atmospheric temperature, whereas thermal plants operate at very high temperature (about 500 to 800’c).

7. Hydro plants provide additional benefits like irrigation, flood control, fishery and recreation.

3.7.7 Disadvantages of hydro-electric power plant:1. Hydro-plants are generally situated away from the load centres.

Hence long transmission lines are required for delivery of power. This increases the cost of transmission lines and also transmission losses. But a thermal plant can be located near the load centre, thereby the transmission cost and transmission losses are considerably reduced.

2. The power produced by hydro-plant depends upon the quantity of water which in turn is dependent upon the rainfall. The dry year affects the hydro power generation considerably.

3. Initial cost of the plant is high.4. Erection of hydro-plant (construction of dam) usually takes a long

period of time.3.8. Fundamentals of fuses and circuit breakers3.8.1. IntroductionLarge power overloads may potentially destroy electrical equipment, or in more serious cases, cause a fire. A fuse and circuit breaker both serve to protect an overloaded electrical circuit by interrupting the continuity, or the flow of electricity. How they interrupt the flow of electricity is very different, however. 3.8.2 FusesA fuse is made up of a piece of metal that melts when overheated; a circuit breaker has an internal switch mechanism that is tripped by an unsafe surge of electricity. Fuses tend to be quicker to interrupt the flow of power, but must be replaced after they melt, while circuit breakers can usually simply be reset.3.8.3 How Fuses WorkThere are many different types of fuses for residential and commercial use, but the most common type is made up of a metal wire or filament that is enclosed in a glass or ceramic and metal casing. In a home, the fuse is typically plugged into a central fuse box where all the building’s wiring passes through. When the electricity is flowing normally, the fuse permits the power to pass unobstructed across its filament, between circuits. If an overload occurs, the filament melts, stopping the flow of electricity.It generally takes very little time for the filament in the type of fuse used in a home to melt, so any power surge is quickly stopped. Once a fuse is blown, however, it must be discarded and replaced with a new one. There J.C.Vijayshree 57

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are many different voltage and ratings available that handle different capacities of electricity, and the best fuse for a circuit is typically one that is rated for slightly higher than the normal operating current.3.8.4 How Circuit Breakers WorkA circuit breaker works in one of two ways, with an electromagnet (or solenoid) or a bi-metal strip. In either case, the basic design is the same: when turned on, the breaker allows electrical current to pass from a bottom to an upper terminal across the solenoid or strip. When the current reaches unsafe levels, the magnetic force of the solenoid becomes so strong that a metal lever within the switch mechanism is thrown, and the current is broken. Alternately, the metal strip bends, throwing the switch and breaking the connection.To reset the flow of electricity after the problem is resolved, the switch can simply be turned back on, reconnecting the circuit. Circuit breakers are often found in a cabinet of individual switches, called a breaker box. The simple switch action of a circuit breaker also makes it easy to turn off an individual circuit in a house if it's necessary to work on the wiring in that location.Another use of the circuit breaker is a ground fault circuit interrupter (GFCI) outlet, which functions to prevent electric shock instead of overheating. It works by breaking the circuit in an outlet if the current becomes unbalanced, and can be reset by the push of a button. This technology is particularly useful in bathrooms or kitchens where electrocution is a risk due to the frequent use of electric appliances near a source of water.3.8.5 Advantages of fusesThe fuse and circuit breaker both have advantages and disadvantages, each of which can depend on the situation in which they are used. Fuses are inexpensive and can be purchased from any hardware store. They also tend to react very quickly to overloading, which means that they can offer more protection to sensitive electronic devices. This quick reaction can be a disadvantage, however, if the circuit is prone to surges that regularly cause fuses to blow.3.8.6 Disadvantages of fusesFuses must always be replaced once they are blown, which can be challenging in a darkened room or if the appropriate replacement is not immediately available. Another issue is that a do-it-yourselfer can mistakenly select a fuse that has a voltage or current rating that is too high for his needs, which can result in an overheated circuit. In addition, there may be exposed electrical connections in a fuse box, which can pose a danger to someone who does not follow the proper safety precautions.3.8.7 Advantages of Circuit breakersCircuit breakers have many advantages, not the least of which is how quickly they can be reset. It is usually clear which switch has tripped, and it can be easily reset in most cases. For the average homeowner, it is also safer because there is no question about choosing the right fuse rating and all of the electrical connections are hidden in a breaker box.J.C.Vijayshree 58

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3.8.8 Disadvantages of Circuit breakers A drawback to using a circuit breaker is that it is usually more expensive to install and repair. A circuit breaker also typically does not react as quickly as a fuse to surges in power, meaning that it is possible that electronics connected to the circuit could be damaged by "let-through" energy. It also is more sensitive to vibration and movement, which can cause a switch to trip for reasons unrelated to an electricity overload.3.8.9 ApplicationA fuse and circuit breaker are not interchangeable for all power applications. For example, a fuse cannot be used in situations that require a GFCI. Electricians are best qualified to determine whether a fuse or circuit breaker system is better for a particular electrical installation or upgrade.

PART B – ELECTRONICSUNIT – IV

ELECTRONIC CIRCUITS4.1.V-I Characteristics of diode – 4.1.1 The PN Junction DiodeA PN Junction Diode is one of the simplest Semiconductor Devices around, and which has the characteristic of passing current in only one direction only. However, unlike a resistor, a diode does not behave linearly with respect to the applied voltage as the diode has an exponential current-voltage ( I-V ) relationship and therefore we can not described its operation by simply using an equation such as Ohm’s law.4.1.2 Forward biasingIf a suitable positive voltage (forward bias) is applied between the two ends of the PN junction, it can supply free electrons and holes with the extra energy they require to cross the junction as the width of the depletion layer around the PN junction is decreased.4.1.3 Reverse biasingBy applying a negative voltage (reverse bias) results in the free charges being pulled away from the junction resulting in the depletion layer width being increased. This has the effect of increasing or decreasing the effective resistance of the junction itself allowing or blocking current flow through the diode.Then the depletion layer widens with an increase in the application of a reverse voltage and narrows with an increase in the application of a forward voltage. This is due to the differences in the electrical properties on the two sides of the PN junction resulting in physical changes taking place.

4.4.4 Junction Diode Symbol and Static I-V Characteristics.

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But before we can use the PN junction as a practical device or as a rectifying device we need to firstly bias the junction, ie connect a voltage potential across it. On the voltage axis above, “Reverse Bias” refers to an external voltage potential which increases the potential barrier. An external voltage which decreases the potential barrier is said to act in the “Forward Bias” direction.4.1.5 Operating regionsThere are two operating regions and three possible “biasing” conditions for the standard Junction Diode and these are:

1. Zero Bias – No external voltage potential is applied to the PN junction diode.

2. Reverse Bias – The voltage potential is connected negative, (-ve) to the P-type material and positive, (+ve) to the N-type material across the diode which has the effect of Increasing the PN junction diode’s width.

3. Forward Bias – The voltage potential is connected positive, (+ve) to the P-type material and negative, (-ve) to the N-type material across the diode which has the effect of Decreasing the PN junction diodes width.

4.2. Half-wave rectifier without capacitor filter – 4.2.1. Half-wave rectifier without capacitor filter

A simple Half Wave Rectifier is nothing more than a single pn junction diode connected in series to the load resistor. If you look at the above diagram, we are giving an alternating current as input. Input voltage is given to a step down transformer and the resulting reduced output of

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transformer is given to the diode ‘D’ and load resistor RL. The output voltage is measured across load resistor RL.As part of our “Basic Electronics Tutorial” series, we have seen that rectification is the most important application of a PN junction diode. The process of rectification is converting alternating current (AC) to direct current (DC).4.2.2 Half Wave Rectifier OperationThe operation of a half wave rectifier is pretty simple. From the theory part, you should know that a pn junction diode conducts current only in 1 direction. In other words, a pn junction diode conducts current only when it is forward biased. The same principle is made use of in a half wave rectifier to convert AC to DC. The input we give here is an alternating current. This input voltage is stepped down using a transformer. The reduced voltage is fed to the diode ‘D’ and load resistance RL. During the positive half cycles of the input wave, the diode ‘D’ will be forward biased and during the negative half cycles of input wave, the diode ‘D’ will be reverse biased. We take the output across load resistor RL. Since the diode passes current only during one half cycle of the input wave, we get an output as shown in diagram. The output is positive and significant during the positive half cycles of input wave. At the same time output is zero or insignificant during negative half cycles of input wave. This is called half wave rectification.4.2.3 Working of a Half wave rectifier The half-wave rectifier circuit using a semiconductor diode (D) with a load resistance RL but no smoothing filter is given in figure. The diode is connected in series with the secondary of the transformer and the load resistance RL. The primary of the transformer is being connected to the ac supply mains.The ac voltage across the secondary winding changes polarities after every half cycle of input wave. During the positive half-cycles of the input ac voltage i.e. when upper end of the secondary winding is positive w.r.t. its lower end, the diode is forward biased and therefore conducts current. If the forward resistance of the diode is assumed to be zero (in practice, however, a small resistance exists) the input voltage during the positive half-cycles is directly applied to the load resistance RL, making its upper end positive w.r.t. its lower end. The waveforms of the output current and output voltage are of the same shape as that of the input ac voltage.During the negative half cycles of the input ac voltage i.e. when the lower end of the secondary winding is positive w.r.t. its upper end, the diode is reverse biased and so does not conduct. Thus during the negative half cycles of the input ac voltage, the current through and voltage across the load remains zero. The reverse current, being very small in magnitude, is neglected. Thus for the negative half cycles no power is delivered to the load.Thus the output voltage (VL) developed across load resistance RL is a series of positive half cycles of alternating voltage, with intervening very small constant negative voltage levels, It is obvious from the figure that the output is not a steady dc, but only a pulsating dc wave. To make the J.C.Vijayshree 61


output wave smooth and useful in a DC power supply, we have to use a filter across the load. Since only half-cycles of the input wave are used, it is called a half wave rectifier.

4.2.4 Advantages of Half wave rectifierA half wave rectifier is rarely used in practice. It is never preferred as the power supply of an audio circuit because of the very high ripple factor. High ripple factor will result in noises in input audio signal, which in turn will affect audio quality.Advantage of a half wave rectifier is only that its cheap, simple and easy to construct. It is cheap because of the low number of components involved. Simple because of the straight forwardness in circuit design. Apart from this, a half wave rectifier has more number of disadvantages than advantages!4.2.5 Disadvantages of Half wave rectifier1. The output current in the load contains, in addition to dc component, ac components of basic frequency equal to that of the input voltage frequency. Ripple factor is high and an elaborate filtering is, therefore, required to give steady dc output.2. The power output and, therefore, rectification efficiency is quite low. This is due to the fact that power is delivered only during one half cycle of the input alternating voltage.3. Transformer utilization factor is low.4. DC saturation of transformer core resulting in magnetizing current and hysteresis losses and generation of harmonics.The DC output available from a half-wave rectifier is not satisfactory to make a general power supply. However it can be used for some applications like battery charging. 4.3.Half Wave Rectifier with Capacitor Filter 4.3.1 Half Wave Rectifier with Capacitor Filter Output of half wave rectifier is not a constant DC voltage. You can observe from the output diagram that its a pulsating dc voltage with ac ripples. In real life applications, we need a power supply with smooth wave forms. In other words, we desire a DC power supply with constant output voltage. A constant output voltage from the DC power supply is very important as it directly impacts the reliability of the electronic device we connect to the power supply.We can make the output of half wave rectifier smooth by using a filter (a capacitor filter or an inductor filter) across the diode. In some cases an resistor-capacitor coupled filter (RC) is also used. The circuit diagram below shows a half wave rectifier with capacitor filter.

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Half Wave Rectifier with Capacitor Filter – Circuit Diagram & Output Waveform

4.3.2 Half Wave Rectifier AnalysisThe following parameters will be explained for the analysis of Half Wave Rectifier:-4.3.3 Peak Inverse Voltage (PIV)Peak Inverse Voltage (PIV) rating of a diode is important in its design stages. It is the maximum voltage that the rectifying diode has to withstand, during the reverse biased period. When the diode is reverse biased, during the negative half cycle, there will be no current flow through the load resistor RL. Hence, there will be no voltage drop through the load resistance RL which causes the entire input voltage to appear across the diode. Thus VSMAX, the peak secondary voltage, appears across the diode. Therefore,Peak Inverse Voltage (PIV) of half wave rectifier = VSMAX4.3.4 Average and Peak Currents in the diodeBy assuming that the voltage across the transformer secondary be sinusoidal of peak values VSMAX, instantaneous value of the voltage given to the rectifier can be written as

Instantaneous value of voltage applied to Half Wave RectifierAssuming that the diode has a forward resistance of RF ohms and infinite reverse resistance value, the current flowing through the output load resistance RL is

Current flowing through the diodeIMAX = VSMAX/(RF + RL)4.3.5 DC Output CurrentThe dc output current is given as

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Substituting the value of IMAX for the equation IMAX = VSMAX/(RF + RL), we haveIdc = VSMAX/ = VSMAX/ RL if RL >> RF4.3.6 DC Output VoltageDc value of voltage across the load is given byVdc = Idc RL = VSMAX/pi(RF + RL)X RL = VSMAX/{1+RF/RL }If RL >> RF, Vdc = VSMAX/pi4.3.7 Root Mean Square (RMS) Value of CurrentRMS value of current flowing through the diode is given as

4.3.8 Root Mean Square (RMS) Value of Output VoltageRMS value of voltage across the load is given asVLrms = Irms RL = VSMAX RL /2(RF + RL) = VSMAX/2{1+RF/RL }If RL >> RF, VLrms = VSMAX/24.3.9 Rectification EfficiencyRectification efficiency is defined as the ratio between the output power to the ac input power.Efficiency, Ƞ = DC power delivered to the load/AC input power from the transformer = Pdc/PacDC power delivered to the load, Pdc = I2dc RL = (Imax/pi)2 RLAC power input to the transformer, Pac = Power dissipated in diode junction + Power dissipated in load resistance RL= I2rms RF + I2rms RL = {I2MAX/4}[ RF + RL]So, Rectification Efficiency, Ƞ = Pdc/Pac = {4/2}[ RL/ (RF + RL)] = 0.406/{1+ RF/RL }The maximum efficiency that can be obtained by the half wave rectifier is 40.6%. This is obtained if RF is neglected.4.3.10 Ripple Factor Ripple factor is in fact a measure of the remaining alternating components in a filtered rectifier output. It is the ratio of the effective value of the ac components of voltage (or current) present in the output from the rectifier to the dc component in output voltage (or current).The effective value of the load current is given asI2 =I2dc+I21+I22+I24 = I2dc +I2acWhere, I1,I2, I4 and so onare the rms values of fundamental, second, fourth and so on harmonics and I2acis the sum of the squares if the rms values of the ac components.So, ripple factor, γ = Iac/ Idc = I2 – I2dc)/ Idc = {( Irms/ Idc

2)-1} = Kf2 – 1)

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Where Kf is the form factor of the input voltage. For half wave rectifier, form factor is given as Kf = Irms /Iavg = (Imax/2)/ (Imax/pi) = pi/2 = 1.57So, ripple factor, γ = (1.572 – 1) = 1.214.3.11 RegulationThe variation of the output voltage as a function of dc load current is called regulation. Percentage regulation is given as% Regulation = {(Vno-load – Vfull-load)/ Vfull-load}* 100Fror an ideal power supply, the output voltage should be independent of load current and the percentage regulation should be equal to zero.4.3.12 Uses of Half wave rectifierAny rectifier is used to construct DC power supplies. The practical application of any rectifier (be it half wave or full wave) is to be used as a component in building DC power supplies. A half wave rectifier is not special than a full wave rectifier in any terms. In order to build an efficient & smooth DC power supply, a full wave rectifier is always preferred. However for applications in which a constant DC voltage is not very essential, you can use power supplies with half wave rectifier.4.4. Full-wave rectifier without capacitor filter – 4.4.1 Full Wave Rectifier In a Full Wave Rectifier circuit two diodes are now used, one for each half of the cycle. A multiple winding transformer is used whose secondary winding is split equally into two halves with a common centre tapped connection, (C). This configuration results in each diode conducting in turn when its anode terminal is positive with respect to the transformer centre point C producing an output during both half-cycles, twice that for the half wave rectifier so it is 100% efficient as shown below.4.4.2 Full Wave Rectifier Circuit

The full wave rectifier circuit consists of two power diodes connected to a single load resistance (RL) with each diode taking it in turn to supply current to the load. When point A of the transformer is positive with respect to point C, diode D1 conducts in the forward direction as indicated by the arrows.J.C.Vijayshree 65

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When point B is positive (in the negative half of the cycle) with respect to point C, diode D2 conducts in the forward direction and the current flowing through resistor R is in the same direction for both half-cycles. As the output voltage across the resistor R is the phasor sum of the two waveforms combined, this type of full wave rectifier circuit is also known as a “bi-phase” circuit.As the spaces between each half-wave developed by each diode is now being filled in by the other diode the average DC output voltage across the load resistor is now double that of the single half-wave rectifier circuit and is about 0.637Vmax of the peak voltage, assuming no losses.

Where: VMAX is the maximum peak value in one half of the secondary winding and VRMS is the rms value.The peak voltage of the output waveform is the same as before for the half-wave rectifier provided each half of the transformer windings have the same rms voltage value. To obtain a different DC voltage output different transformer ratios can be used. The main disadvantage of this type of full wave rectifier circuit is that a larger transformer for a given power output is required with two separate but identical secondary windings making this type of full wave rectifying circuit costly compared to the “Full Wave Bridge Rectifier” circuit equivalent.4.4.3 The Full Wave Bridge RectifierAnother type of circuit that produces the same output waveform as the full wave rectifier circuit above, is that of the Full Wave Bridge Rectifier. This type of single phase rectifier uses four individual rectifying diodes connected in a closed loop “bridge” configuration to produce the desired output. The main advantage of this bridge circuit is that it does not require a special centre tapped transformer, thereby reducing its size and cost. The single secondary winding is connected to one side of the diode bridge network and the load to the other side as shown below.4.4.4 The Diode Bridge Rectifier

The four diodes labelled D1 to D4 are arranged in “series pairs” with only two diodes conducting current during each half cycle. During the positive half cycle of the supply, diodes D1 and D2 conduct in series while diodes D3 and D4 are reverse biased and the current flows through the load as shown below.4.4.5 The Positive Half-cycle

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During the negative half cycle of the supply, diodes D3 and D4 conduct in series, but diodes D1 and D2 switch “OFF” as they are now reverse biased. The current flowing through the load is the same direction as before.4.4.6The Negative Half-cycle

As the current flowing through the load is unidirectional, so the voltage developed across the load is also unidirectional the same as for the previous two diode full-wave rectifier, therefore the average DC voltage across the load is 0.637Vmax.4.4.7 Bridge Rectifier

Typical Bridge RectifierHowever in reality, during each half cycle the current flows through two diodes instead of just one so the amplitude of the output voltage is two voltage drops ( 2 x 0.7 = 1.4V ) less than the input VMAX amplitude. The ripple frequency is now twice the supply frequency (e.g. 100Hz for a 50Hz supply or 120Hz for a 60Hz supply.)Although we can use four individual power diodes to make a full wave bridge rectifier, pre-made bridge rectifier components are available “off-the-shelf” in a range of different voltage and current sizes that can be soldered directly into a PCB circuit board or be connected by spade connectors.The image to the right shows a typical single phase bridge rectifier with one corner cut off. This cut-off corner indicates that the terminal nearest to the corner is the positive or +ve output terminal or lead with the opposite (diagonal) lead being the negative or -ve output lead. The other

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two connecting leads are for the input alternating voltage from a transformer secondary winding.4.5. Full-wave Rectifier with Smoothing Capacitor4.5.1 Full-wave Rectifier with Smoothing Capacitor

The smoothing capacitor converts the full-wave rippled output of the rectifier into a smooth DC output voltage. Generally for DC power supply circuits the smoothing capacitor is an Aluminium Electrolytic type that has a capacitance value of 100uF or more with repeated DC voltage pulses from the rectifier charging up the capacitor to peak voltage.4.5.2 ParametersHowever, their are two important parameters to consider when choosing a suitable smoothing capacitor and these are its Working Voltage, which must be higher than the no-load output value of the rectifier and its Capacitance Value, which determines the amount of ripple that will appear superimposed on top of the DC voltage.Too low a capacitance value and the capacitor has little effect on the output waveform. But if the smoothing capacitor is sufficiently large enough (parallel capacitors can be used) and the load current is not too large, the output voltage will be almost as smooth as pure DC. As a general rule of thumb, we are looking to have a ripple voltage of less than 100mV peak to peak.4.5.3 Ripple VoltageThe maximum ripple voltage present for a Full Wave Rectifier circuit is not only determined by the value of the smoothing capacitor but by the frequency and load current, and is calculated as:Bridge Rectifier Ripple Voltage

Where: I is the DC load current in amps, ƒ is the frequency of the ripple or twice the input frequency in Hertz, and C is the capacitance in Farads.4.5.4 AdvantagesThe main advantages of a full-wave bridge rectifier is that it has a smaller AC ripple value for a given load and a smaller reservoir or smoothing capacitor than an equivalent half-wave rectifier. Therefore, the fundamental frequency of the ripple voltage is twice that of the AC supply

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frequency (100Hz) where for the half-wave rectifier it is exactly equal to the supply frequency (50Hz).4.5.5 Ripple reductionThe amount of ripple voltage that is superimposed on top of the DC supply voltage by the diodes can be virtually eliminated by adding a much improved π-filter (pi-filter) to the output terminals of the bridge rectifier. This type of low-pass filter consists of two smoothing capacitors, usually of the same value and a choke or inductance across them to introduce a high impedance path to the alternating ripple component Another more practical and cheaper alternative is to use an off the shelf 3-terminal voltage regulator IC, such as a LM78xx (where “xx” stands for the output voltage rating) for a positive output voltage or its inverse equivalent the LM79xx for a negative output voltage which can reduce the ripple by more than 70dB (Datasheet) while delivering a constant output current of over 1 amp.4.6. Transistor - Construction & working –4.6.1 Junction TransistorsWe already know what is p - type and n - type semiconductors. Now, in this type of transistor any one type of semiconductors is sandwiched between the other type of semiconductor. For example, an n - type can be sandwiched between two p - type semiconductors or similarly one p - type can be sandwiched between two n - type semiconductors. These are called p - n - p and n - p - n transistors respectively. We will discuss about them later. Now as there are two junctions of different types of semiconductors, this is called junction transistor. It’s called “bipolar” because the conduction takes place due to both electrons as well as holes. 4.6.2 Definition of BJTA bipolar junction transistor is a three terminal semiconductor device consisting of two p-n junctions which is able to amplify or “magnify” a signal. It is a current controlled device. The three terminals of the BJT are the base, the collector and the emitter. A signal of small amplitude if applied to the base is available in the amplified form at the collector of the transistor. This is the amplification provided by the BJT. Note that it does require an external source of DC power supply to carry out the amplification process.The basic diagrams of the two types of bipolar junction transistors mentioned above are given below.

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From the above figure, we can see that every BJT has three parts named emitter, base and collector. JE and JC represent junction of emitter and junction of collector respectively. Now initially it is sufficient for us to know that emitter based junction is forward biased and collector base junctions is reverse biased. The next topic will describe the two types of this transistors.4.6.3 N-P-N Bipolar Junction TransistorAs started before in n - p - n bipolar transistor one p - type semiconductor resides between two n - type semiconductors the diagram below a n - p - n transistor is shown

Now IE, IC is emitter current and collect current respectively and VEB and VCB are emitter base voltage and collector base voltage respectively. According to convention if for the emitter, base and collector current IE, IB and IC current goes into the transistor the sign of the current is taken as positive and if current goes out from the transistor then the sign is taken as negative. We can tabulate the different currents and voltages inside the n - p - n transistor. Transistor type IE IB IC VEB VCB VCE

n - p - n - ++- + +4.6.4 P-N-P Bipolar Junction TransistorSimilarly for p - n - p bipolar junction transistor a n-type semiconductors is sandwiched between two p-type semiconductors. The diagram of a p - n - p transistor is shown below

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junction is forward biased and the collector – base junction is reverse biased. We can tabulate the emitter, base and collector current, as well as the emitter base, collector base and collector emitter voltage for p - n - p transistors also. Transistor type IE IB IC VEB VCB VCE

p - n - p +- - + - -4.6.5 Working Principle of BJTFigure shows an n-p-n transistor biased in the active region (See transistor biasing), the BE junction is forward biased whereas the CB junction is reversed biased. The width of the depletion region of the BE junction is small as compared to that of the CB junction. The forward bias at the BE junction reduces the barrier potential and causes the electrons to flow from the emitter to base. As the base is thin and lightly doped it consists of very few holes so some of the electrons from the emitter (about 2%) recombine with the holes present in the base region and flow out of the base terminal. This constitutes the base current, it flows due to recombination of electrons and holes (Note that the direction of conventional current flow is opposite to that of flow of electrons). The remaining large number of electrons will cross the reverse biased collector junction to constitute the collector current. Thus by KCL,

The base current is very small as compared to emitter and collector current.

Here, the majority charge carriers are electrons. The operation of a p-n-p transistor is same as of the n-p-n, the only difference is that the majority charge carriers are holes instead of electrons. Only a small part current flows due to majority carriers and most of the current flows due to minority charge carriers in a BJT. Hence, they are called as minority carrier devices.4.6.6 Equivalent Circuit of BJTA p-n junction is represented by a diode. As a transistor has two p-n junctions, it is equivalent to two diodes connected back to back. This is called as the two diode analogy of the BJT.4.7. Input and output characteristics of CB and CE configuration – 4.7.1 Bipolar Junction Transistors CharacteristicsThe three parts of a BJT are collector, emitter and base. Before knowing about the bipolar junction transistor characteristics, we have to know about the modes of operation for this type of transistors. The modes are i) Common Base (CB) modeii) Common Emitter (CE) modeiii) Common Collector (CC) modeAll three types of modes are shown below

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Now coming to the characteristics of BJT there are different characteristics for different modes of operation. Characteristics is nothing but the graphical forms of relationships among different current and voltage variables of the transistor. The characteristics for p - n - p transistors are given for different modes and different parameters.4.7.2. Common Base Input CharacteristicsFor p - n - p transistor, the input current is the emitter current (IE) and the input voltage is the collector base voltage (VCB).

As the emitter - base junction is forward biased, therefore the graph of IE Vs VEB is similar to the forward characteristics of a p - n diode. IE increases for fixed VEB when VCB increases. 4.7.3 Common Base Output CharacteristicsThe output characteristics shows the relation between output voltage and output current IC is the output current and collector – base voltage and the emitter current IE is the input current and works as the parameters. The figure below shows the output characteristics for a p - n - p transistor in CB mode.

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As we know for p - n - p transistors IE and VEB are positive and IC, IB, VCB are negative. These are three regions in the curve, active region saturation region and the cut off region. The active region is the region where the transistor operates normally. Here the emitter junction is reverse biased. Now the saturation region is the region where both the emitter collector junctions are forward biased. And finally the cut off region is the region where both emitter and the collector junctions are reverse biased.4.7.4 Common Emitter Input CharacteristicsIB (Base Current) is the input current, VBE (Base - Emitter Voltage) is the input voltage for CE (Common Emitter) mode. So, the input characteristics for CE mode will be the relation between IB and VBE with VCE as parameter. The characteristics are shown below

The typical CE input characteristics are similar to that of a forward biased of p - n diode. But as VCB increases the base width decreases.4.7.5 Common Emitter Output characteristicsOutput characteristics for CE mode is the curve or graph between collector current (IC) and collector - emitter voltage (VCE) when the base current IB is the parameter. The characteristics is shown below in the figure.

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Like the output characteristics of common - base transistor CE mode has also three regions named (i) Active region, (ii) cut-off regions, (iii) saturation region. The active region has collector region reverse biased and the emitter junction forward biased. For cut-off region the emitter junction is slightly reverse biased and the collector current is not totally cut-off. And finally for saturation region both the collector and the emitter junction are forward biased.4.7.6 Application of BJTBJT's are used in discrete circuit designed due to availability of many types, and obviously because of its high transconductane and output resistance which is better than MOSFET. BJT's are suitable for high frequency application also. That’s why they are used in radio frequency for wireless systems. Another application of BJT can be stated as small signal amplifier, metal proximity photocell, etc.4.8. Transistor as an Amplifier – 4.8.1 Bipolar Junction Transistor AmplifierTo understand the concept of Bipolar Junction Transistor Amplifier, we should look through the diagram of a p-n-p transistor first.4.8.2. Diagram of PNP transistor

4.8.3 Voltage dropNow as the input voltage is changed a little, say ΔVi of the emitter - base voltage changes the barrier height and the emitter current by ΔIE. This change in emitter current develops a voltage drop ΔVO across the load resistance RL, where,J.C.Vijayshree 74

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ΔVO = - RLΔICΔVO gives the output voltage of the amplifier. There is a negative sign because of the collector current gives a voltage drop across RL with polarity opposite to the reference polarity. 4.8.4 Voltage gainThe voltage gain AV for the amplifier is given the ratio between the output voltages ΔVO to the input voltage ΔVi, so,

ΔIC / ΔIE = AI is called the current gain ratio of the transistor. From the figure diagram shown above we can see that an increase in the emitter voltage reduces the forward bias at the emitter junction thus decreases the collector current. It indicates that the output voltage and the input voltage are in phase. 4.8.5 Power gainNow, finally the power gain Ap of the transistor is the ratio between the output power and the input power

4.9. Principle and working of Hartley oscillator–4.9.1 Voltage Controlled Oscillator If the amplitude of the oscillations decreases the bias decreases and the gain of the amplifier increases, thus increasing the feedback. In this way the amplitude of the oscillations are kept constant using a process known as Automatic Base Bias.One big advantage of automatic base bias in a Voltage Controlled Oscillator, is that the oscillator can be made more efficient by providing a Class-B bias or even a Class-C bias condition of the transistor. This has the advantage that the collector current only flows during part of the oscillation cycle so the quiescent collector current is very small. Then this “self-tuning” base oscillator circuit forms one of the most common types of LC parallel resonant feedback oscillator configurations called the Hartley Oscillator circuit.

Hartley Oscillator Tank Circuit4.9.2. The Hartley Oscillator In the Hartley Oscillator the tuned LC circuit is connected between the collector and the base of a transistor amplifier. As far as the oscillatory

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voltage is concerned, the emitter is connected to a tapping point on the tuned circuit coil.The feedback part of the tuned LC tank circuit is taken from the centre tap of the inductor coil or even two separate coils in series which are in parallel with a variable capacitor, C as shown.The Hartley circuit is often referred to as a split-inductance oscillator because coil L is centre-tapped. In effect, inductance L acts like two separate coils in very close proximity with the current flowing through coil section XY induces a signal into coil section YZ below.An Hartley Oscillator circuit can be made from any configuration that uses either a single tapped coil (similar to an autotransformer) or a pair of series connected coils in parallel with a single capacitor as shown below.4.9.3 Basic Hartley Oscillator Design

When the circuit is oscillating, the voltage at point X (collector), relative to point Y (emitter), is 180o out-of-phase with the voltage at point Z (base) relative to point Y. At the frequency of oscillation, the impedance of the Collector load is resistive and an increase in Base voltage causes a decrease in the Collector voltage. Then there is a 180o phase change in the voltage between the Base and Collector and this along with the original 180o phase shift in the feedback loop provides the correct phase relationship of positive feedback for oscillations to be maintained.The amount of feedback depends upon the position of the “tapping point” of the inductor. If this is moved nearer to the collector the amount of feedback is increased, but the output taken between the Collector and earth is reduced and vice versa. Resistors, R1 and R2 provide the usual stabilizing DC bias for the transistor in the normal manner while the capacitors act as DC-blocking capacitors.4.9.4 Frequency of Oscillation In this Hartley Oscillator circuit, the DC Collector current flows through part of the coil and for this reason the circuit is said to be “Series-fed” with the frequency of oscillation of the Hartley Oscillator being given as.

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Note: LT is the total cumulatively coupled inductance if two separate coils are used including their mutual inductance, M.4.9.5 Shunt-fed Hartley Oscillator Circuit

In the shunt-fed Hartley oscillator circuit, both the AC and DC components of the Collector current have separate paths around the circuit. Since the DC component is blocked by the capacitor, C2 no DC flows through the inductive coil, L and less power is wasted in the tuned circuit.The Radio Frequency Coil (RFC), L2 is an RF choke which has a high reactance at the frequency of oscillations so that most of the RF current is applied to the LC tuning tank circuit via capacitor, C2 as the DC component passes through L2 to the power supply. A resistor could be used in place of the RFC coil, L2 but the efficiency would be less.

Hartley Oscillator Example A Hartley Oscillator circuit having two individual inductors of 0.5mH each, are designed to resonate in parallel with a variable capacitor that can be adjusted between 100pF and 500pF. Determine the upper and lower frequencies of oscillation and also the Hartley oscillators bandwidth.From above we can calculate the frequency of oscillations for a Hartley Oscillator as:

The circuit consists of two inductive coils in series, so the total inductance is given as:

Hartley Oscillator Upper Frequency

Hartley Oscillator Lower Frequency

Hartley Oscillator Bandwidth

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4.10. Principle and working of RC phase shift oscillator –4.10.1 The RC OscillatorIn an RC Oscillator circuit the input is shifted 180o through the amplifier stage and 180o again through a second inverting stage giving us “180o + 180o = 360o” of phase shift which is effectively the same as 0o

thereby giving us the required positive feedback. In other words, the phase shift of the feedback loop should be “0”.In a Resistance-Capacitance Oscillator or simply an RC Oscillator, we make use of the fact that a phase shift occurs between the input to a RC network and the output from the same network by using RC elements in the feedback branch, for example.4.10.2 RC Phase-Shift Network

The circuit on the left shows a single Resistor-Capacitor Network whose output voltage “leads” the input voltage by some angle less than 90o. An ideal single-pole RC circuit would produce a phase shift of exactly 90o, and because 180o of phase shift is required for oscillation, at least two single-poles must be used in an RC oscillator design.However in reality it is difficult to obtain exactly 90o of phase shift so more stages are used. The amount of actual phase shift in the circuit depends upon the values of the resistor and the capacitor, and the chosen frequency of oscillations with the phase angle ( Φ ) being given as:4.10.3 RC Phase Angle

In our simple example above, the values of R and C have been chosen so that at the required frequency the output voltage leads the input voltage by an angle of about 60o. Then the phase angle between each successive RC section increases J.C.Vijayshree 78

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by another 60o giving a phase difference between the input and output of 180o (3 x 60o) as shown by the following vector diagram.4.10.4 Vector Diagram

Then by connecting together three such RC networks in series we can produce a total phase shift in the circuit of 180o at the chosen frequency and this forms the bases of a “phase shift oscillator” otherwise known as a RC Oscillator circuit.We know that in an amplifier circuit either using a Bipolar Transistor or an Operational Amplifier, it will produce a phase-shift of 180o between its input and output. If a three-stage RC phase-shift network is connected between this input and output of the amplifier, the total phase shift necessary for regenerative feedback will become 3 x 60o + 180o = 360o as shown.

The three RC stages are cascaded together to get the required slope for a stable oscillation frequency. The feedback loop phase shift is -180o when the phase shift of each stage is -60o. This occurs when ω = 2πƒ = 1.732/RC as (tan 60o = 1.732). Then to achieve the required phase shift in an RC oscillator circuit is to use multiple RC phase-shifting networks such as the circuit below.4.10.5 Basic RC Oscillator Circuit

The basic RC Oscillator which is also known as a Phase-shift Oscillator, produces a sine wave output signal using regenerative feedback obtained from J.C.Vijayshree 79


the resistor-capacitor combination. This regenerative feedback from the RC network is due to the ability of the capacitor to store an electric charge, (similar to the LC tank circuit).This resistor-capacitor feedback network can be connected as shown above to produce a leading phase shift (phase advance network) or interchanged to produce a lagging phase shift (phase retard network) the outcome is still the same as the sine wave oscillations only occur at the frequency at which the overall phase-shift is 360o.By varying one or more of the resistors or capacitors in the phase-shift network, the frequency can be varied and generally this is done by keeping the resistors the same and using a 3-ganged variable capacitor.If all the resistors, R and the capacitors, C in the phase shift network are equal in value, then the frequency of oscillations produced by the RC oscillator is given as:

Where: ƒr is the Output Frequency in Hertz R is the Resistance in Ohms C is the Capacitance in Farads N is the number of RC stages. (N = 3)

Since the resistor-capacitor combination in the RC Oscillator circuit also acts as an attenuator producing an attenuation of -1/29th ( Vo/Vi = β ) per stage, the gain of the amplifier must be sufficient to overcome the circuit losses. Therefore, in our three stage RC network above the amplifier gain must be greater than 29.The loading effect of the amplifier on the feedback network has an effect on the frequency of oscillations and can cause the oscillator frequency to be up to 25% higher than calculated. Then the feedback network should be driven from a high impedance output source and fed into a low impedance load such as a common emitter transistor amplifier but better still is to use an Operational Amplifier as it satisfies these conditions perfectly.RC Oscillators are stable and provide a well-shaped sine wave output with the frequency being proportional to 1/RC and therefore, a wider frequency range is possible when using a variable capacitor. However, RC Oscillators are restricted to frequency applications because of their bandwidth limitations to produce the desired phase shift at high frequencies.

RC Oscillator Example A 3-stage RC Phase Shift Oscillator is required to produce an oscillation frequency of 6.5kHz. If 1nF capacitors are used in the feedback circuit, calculate the value of the frequency determining resistors and the value of the feedback resistor required to sustain oscillations. Also draw the circuit.The standard equation given for the phase shift RC Oscillator is:

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The circuit is to be a 3-stage RC oscillator which will therefore consist of three resistors and three 1nF capacitors. As the frequency of oscillation is given as 6.5kHz, the value of the resistors are calculated as:

The operational amplifiers gain must be equal to 29 in order to sustain oscillations. The resistive value of the three oscillation resistors are 10kΩ, therefore the value of the op-amps feedback resistor Rf is calculated as:

RC Oscillator Op-amp Circuit

4.11. Construction and working of JFET.4.11.1. JFETJFET’s are of two types, namely N-channel JFETs and P-channel JFETs. Generally N-channel JFETs are more preferred than P-channel. N-channel and P-channel JFETs are shown in the figures below.

JFET - Junction Field Effect Transistors4.11.2 Basic Construction.

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The structure is quite simple. In an N-channel JFET an N-type silicon bar, referred to as the channel, has two smaller pieces of P-type silicon material diffused on the opposite sides of its middle part, forming P-N junctions, as illustrated in figure. The two P-N junctions forming diodes or gates are connected internally and a common terminal, called the gate terminal, is brought out. Ohmic contacts (direct electrical connections) are made at the two ends of the channel—one lead is called the Source terminal S and the other Drain terminal D.The silicon bar behaves like a resistor between its two terminals D and S. The gate terminal is analogous to the base of an ordinary transistor(BJT). It is used to control the flow of current from source to drain. Thus, source and drain terminals are analogous to emitter and collector terminals respectively of a BJT.4.11.3 Standard Notations in FET:Source – The terminal through which the majority carriers enter the channel, is called the source terminal S and the conventional current entering the channel at S is designated as Ig.Drain – The terminal, througih which the majority carriers leave the channel, is called the drain terminal D and the conventional current leaving the channel at D is designated as ID. The drain-to-source voltage is called VDS, and is positive if D is more positive than source SGate – There are two internally connected heavily doped impurity regions formed by alloying, by diffusion, or by any other method available to create two P-N junctions. These impurity regions are called the gate G. A voltage VGS is applied between the gate and source in the direction to reverse-bias the P-N junction. Conventional current entering the channel at G is designated as IG.Channel – The region between the source and drain, sandwiched between the two gates is called the channel and the majority carriers move from source to drain through this channel.

4.11.4 Schematic Symbols of JFET

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The schematic symbols for N-type and P-type JFETs are shown in the figure below. The vertical line in the symbol may be thought as channel and source S and drain D connected to the line.Note that the direction of the arrow at the gate indicates the direction in which the gate current flows when the gate junction is forward biased. Thus for the N-channel JFET, the arrow at the gate junction points into the device and in P-channel JFET, it is away from the device.

Polarity Conventions of JFET4.11.5 Polarity Conventions-JFETThe polarities for N-channel and P-channel JFET’s are shown in figures. In both of the cases the voltage between the gate and source is such that the gate is reverse biased. This is the normal method of connection of JFET’s. The drain and source terminals are interchangeable, that is either end can be used as a source and the other end as a drain. The source terminal is always connected to that end of the drain voltage supply which provides the necessary charge carriers, that is, in an N-channel JFET source terminal, S is connected to the negative end of the drain voltage supply for obtaining.

Bias-Circuit-for-JFET4.11.6 Operation of JFETJ.C.Vijayshree 83

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Let us consider an N-channel JFET for discussing its operation.1. When neither any bias is applied to the gate (i.e. when VGS = 0) nor any voltage to the drain w.r.t. source (i.e. when VDS = 0), the depletion regions around the P-N junctions , are of equal thickness and symmetrical.2. When positive voltage is applied to the drain terminal D w.r.t. source terminal S without connecting gate terminal G to supply, as illustrated in fig. 9.4, the electrons (which are the majority carriers) flow from terminal S to terminal D whereas conventional drain current ID flows through the channel from D to S. Due to flow of this current, there is uniform voltage drop across the channel resistance as we move from terminal D to terminal S. This voltage drop reverse biases the diode. The gate is more “negative” with respect to those points in the channel which are nearer to D than to S. Hence, depletion layers penetrate more deeply into the channel at points lying closer to D than to S. Thus wedge-shaped depletion regions are formed, as shown in figure. when Vds is applied. The size of the depletion layer formed determines–the width of the channel and hence the magnitude of current ID flowing through the channel. To see how the width of the channel varies with the variation in gate voltage, let us assume that the gate is negative biased with respect to the source while the drain is applied with positive bias with respect to the source. This is shown in the figure above. The P-N junctions are then reverse biased and depletion regions are formed. P regions are heavily doped compared to the N-channel, so the depletion regions penetrate deeply into the channel. Since a depletion region is a regions depleted of the charge carriers, it behaves as an insulator. The result is that the channel is narrowed, the resistance is increased and drain current ID is reduced. If the negative voltage at the gate is again increased, depletion layers meet at the centre and the drain current s cut-off completely. If the negative bias to the gate is reduced, the width of the depletion layers gets reduced causing decrease in resistance and , therefore, increase in drain current ID.(The gate-source voltage VGS at which drain current ID is cut-off completely (pinched off) is called the pinch-off voltage Vp. It is also to be noted that the amount of reverse bias is not the same throughout the length of the P-N junction. When the drain current flows through the channel, there is a voltage drop along its length. The result is that the reverse bias at the drain end is more than that at the source end making the width of depletion layer more at the drain. To see how the width of the channel varies with the variation in gate, go through the figure above. 4.12. Construction and working of MOSFET.4.12.1 The MOSFET – Metal Oxide FETMOSFETs are three terminal devices with a Gate, Drain and Source and both P-channel (PMOS) and N-channel (NMOS) MOSFETs are available. The main difference this time is that MOSFETs are available in two basic forms:

1. Depletion Type – the transistor requires the Gate-Source voltage, ( VGS ) to switch the device “OFF”. The depletion mode MOSFET is equivalent to a “Normally Closed” switch.

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2. Enhancement Type – the transistor requires a Gate-Source voltage, ( VGS ) to switch the device “ON”. The enhancement mode MOSFET is equivalent to a “Normally Open” switch.

The symbols and basic construction for both configurations of MOSFETs are shown below.

The four MOSFET symbols above show an additional terminal called the Substrate and is not normally used as either an input or an output connection but instead it is used for grounding the substrate. It connects to the main semiconductive channel through a diode junction to the body or metal tab of the MOSFET. Usually in discrete type MOSFETs, this substrate lead is connected internally to the source terminal. When this is the case, as in enhancement types it is omitted from the symbol for clarification.The line between the drain and source connections represents the semiconductive channel. If this is a solid unbroken line then this represents a “Depletion” (normally closed) type MOSFET and if the channel line is shown dotted or broken it is an “Enhancement” (normally open) type MOSFET. The direction of the arrow indicates either a P-channel or an N-channel device.4.12.2 Basic MOSFET Structure and Symbol

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The construction of the Metal Oxide Semiconductor FET is very different to that of the Junction FET. Both the Depletion and Enhancement type MOSFETs use an electrical field produced by a gate voltage to alter the flow of charge carriers, electrons for N-channel or holes for P-channel, through the semiconductive drain-source channel. The gate electrode is placed on top of a very thin insulating layer and there are a pair of small N-type regions just under the drain and source electrodes.With a insulated gate MOSFET device no such limitations apply so it is possible to bias the gate of a MOSFET in either polarity, positive (+ve) or negative (-ve). This makes the MOSFET device especially valuable as electronic switches or to make logic gates because with no bias they are normally non-conducting and this high gate input resistance means that very little or no control current is needed as MOSFETs are voltage controlled devices. Both the P-channel and the N-channel MOSFETs are available in two basic forms, the Enhancement type and the Depletion type.4.12.3 Depletion-mode MOSFETThe Depletion-mode MOSFET, which is less common than the enhancement types is normally switched “ON” without the application of a gate bias voltage making it a “normally-closed” device. However, a gate to source voltage ( VGS ) will switch the device “OFF”. Similar to the JFET types. For an N-channel MOSFET, a “positive” gate voltage widens the channel, increasing the flow of the drain current and decreasing the drain current as the gate voltage goes more negative.In other words, for an N-channel depletion mode MOSFET: +VGS means more electrons and more current. While a -VGS means less electrons and less current. The opposite is also true for the P-channel types. Then the depletion mode MOSFET is equivalent to a “normally-closed” switch.4.12.4 Depletion-mode N-Channel MOSFET and circuit Symbols

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The depletion-mode MOSFET is constructed in a similar way to their JFET transistor counterparts were the drain-source channel is inherently conductive with the electrons and holes already present within the N-type or P-type channel. This doping of the channel produces a conducting path of low resistance between the Drain and Source with zero Gate bias.4.12.5 Enhancement-mode MOSFETThe more common Enhancement-mode MOSFET is the reverse of the depletion-mode type. Here the conducting channel is lightly doped or even undoped making it non-conductive. This results in the device being normally “OFF” when the gate bias voltage is equal to zero.A drain current will only flow when a gate voltage ( VGS ) is applied to the gate terminal greater than the threshold voltage ( VTH ) level in which conductance takes place making it a transconductance device. This positive +ve gate voltage pushes away the holes within the channel attracting electrons towards the oxide layer and thereby increasing the thickness of the channel allowing current to flow. This is why this kind of transistor is called an enhancement mode device as the gate voltage enhances the channel.Increasing this positive gate voltage will cause the channel resistance to decrease further causing an increase in the drain current, ID through the channel. In other words, for an N-channel enhancement mode MOSFET: +VGS turns the transistor “ON”, while a zero or -VGS turns the transistor “OFF”. Then, the enhancement-mode MOSFET is equivalent to a “normally-open” switch.4.12.6 Enhancement-mode N-Channel MOSFET and circuit Symbols

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Enhancement-mode MOSFETs make excellent electronics switches due to their low “ON” resistance and extremely high “OFF” resistance as well as their infinitely high gate resistance. Enhancement-mode MOSFETs are used in integrated circuits to produce CMOS type Logic Gates and power switching circuits in the form of as PMOS (P-channel) and NMOS (N-channel) gates. CMOS actually stands for Complementary MOS meaning that the logic device has both PMOS and NMOS within its design.

UNIT – V DIGITAL ELECTRONICS

5.1.Boolean algebra – 5.1.1 Description Boolean Algebra is a system of mathematics based on logic that has its own set of rules or laws which are used to define and reduce Boolean expressions.5.1.2 Variables UsedThe variables used in Boolean Algebra only have one of two possible values, a logic “0” and a logic “1” but an expression can have an infinite number of variables all labelled individually to represent inputs to the expression, For example, variables A, B, C etc, giving us a logical expression of A + B = C, but each variable can ONLY be a 0 or a 1.Examples of these individual laws of Boolean, rules and theorems for Boolean Algebra are given in the following table.5.1.3 Truth Tables for the Laws of BooleanBooleanExpression

Description EquivalentSwitching Circuit

Boolean AlgebraLaw or Rule

A + 1 = 1 A in parallel with closed= "CLOSED" Annulment

A + 0 = A A in parallel with open= "A" Identity

A . 1 = A A in series with closed= "A" Identity

A . 0 = 0 A in series with open= "OPEN" Annulment

A + A = AA in parallel with A = "A" Indempotent

A . A = A A in series with A = "A" Indempotent

NOT A = A

NOT NOT A(double negative) = "A" Double Negation

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A + A = 1 A in parallel with not A= "CLOSED" Complement

A . A = 0 A in series with not A= "OPEN" Complement

A+B = B+A

A in parallel with B =B in parallel with A Commutative

A.B = B.A A in series with B =B in series with A Commutative

A+B = A.B

invert and replace OR with AND de Morgan’s

TheoremA.B = A+B

invert and replace AND with OR de Morgan’s

Theorem5.1.4 Description of the Laws of Boolean Algebra

Annulment Law – A term ANDéd with a “0” equals 0 or ORéd with a “1” will equal 1.

o A . 0 = 0, A variable AND’ed with 0 is always equal to 0.o A + 1 = 1, A variable OR’ed with 1 is always equal to 1.

Identity Law – A term ORéd with a “0” or ANDéd with a “1” will always equal that term.

o A + 0 = A, A variable OR’ed with 0 is always equal to the variable.

o A . 1 = A, A variable AND’ed with 1 is always equal to the variable.

Indempotent Law – An input ANDéd with itself or ORéd with itself is equal to that input.

o A + A = A, A variable OR’ed with itself is always equal to the variable.

o A . A = A, A variable AND’ed with itself is always equal to the variable.

Complement Law – A term ANDéd with its complement equals “0” and a term ORéd with its complement equals “1”.

o A . A = 0, A variable AND’ed with its complement is always equal to 0.

o A + A = 1, A variable OR’ed with its complement is always equal to 1.

Commutative Law – The order of application of two separate terms is not important.

o A . B = B . A, The order in which two variables are AND’ed makes no difference.

o A + B = B + A, The order in which two variables are OR’ed makes no difference.

Double Negation Law – A term that is inverted twice is equal to the original term.

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o A = A, A double complement of a variable is always equal to the variable.

de Morgan´s Theorem – There are two “de Morgan´s” rules or theorems,

o Two separate terms NORéd together is the same as the two terms inverted (Complement) and ANDéd for example, A+B = A. B.

o Two separate terms NANDéd together is the same as the two terms inverted (Complement) and ORéd for example, A.B = A +B.

5.1.5 Other algebraic Laws of Boolean Distributive Law – This law permits the multiplying or factoring out of an expression.

o A(B + C) = A.B + A.C (OR Distributive Law)o A + (B.C) = (A + B).(A + B) (AND Distributive Law)

Absorptive Law – This law enables a reduction in a complicated expression to a simpler one by absorbing like terms.

o A + (A.B) = A (OR Absorption Law)o A(A + B) = A (AND Absorption Law)

Associative Law – This law allows the removal of brackets from an expression and regrouping of the variables.

o A + (B + C) = (A + B) + C = A + B + C (OR Associate Law)o A(B.C) = (A.B)C = A . B . C (AND Associate Law)

Laws of Boolean Algebra Example Using the above laws, simplify the following expression: (A + B)(A + C)Q = (A + B)(A + C)

AA + AC + AB + BC – Distributive law

A + AC + AB + BC – Identity AND law (A.A = A)

A(1 + C) + AB + BC – Distributive law

A.1 + AB + BC – Identity OR law (1 + C = 1)

A(1 + B) + BC – Distributive law A.1 + BC – Identity OR law (1 + B

= 1)Q = A + BC – Identity AND law (A.1 =

A) Then the expression: (A + B)(A + C) can be simplified to A + BC5.2.Reduction of Boolean expressions – Here are some examples of Boolean algebra simplifications. Each line gives a form of the expression, and the rule or rules used to derive it from the previous one. Generally, there are several ways to reach the result. Here is the list of simplification rules. 5.2.1 Simplify: C + BC:

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Expression Rule(s) UsedC + BC Original Expression

C + (B + C) DeMorgan's Law. (C + C) + B

Commutative, Associative Laws.

T + B Complement Law. T Identity Law. 5.2.2 Simplify: AB(A + B)(B + B):Expression Rule(s) UsedAB(A + B)(B + B) Original Expression

AB(A + B) Complement law, Identity law. (A + B)(A + B) DeMorgan's Law

A + BB Distributive law. This step uses the fact that or distributes over and. It can look a bit strange since addition does not distribute over multiplication.

A Complement, Identity. 5.2.3 Simplify: (A + C)(AD + AD) + AC + C:Expression Rule(s) Used(A + C)(AD + AD) + AC + C Original Expression

(A + C)A(D + D) + AC + C Distributive. (A + C)A + AC + C Complement, Identity. A((A + C) + C) + C Commutative, Distributive. A(A + C) + C Associative, Idempotent. AA + AC + C Distributive. A + (A + T)C Idempotent, Identity,

Distributive. A + C Identity, twice.

You can also use distribution of or over and starting from A(A+C)+C to reach the same result by another route.

5.2.4 Simplify: A(A + B) + (B + AA)(A + B):Expression Rule(s) UsedA(A + B) + (B + AA)(A + B) Original Expression

AA + AB + (B + A)A + (B + A)B Idempotent (AA to A), then Distributive, used twice. AB + (B + A)A + (B + A)B Complement, then Identity. (Strictly speaking, we

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applications.) AB + BA + AA + BB + AB Distributive, two places. AB + BA + A + AB Idempotent (for the A's), then Complement and

Identity to remove BB. AB + AB + AT + AB Commutative, Identity; setting up for the next step. AB + A(B + T + B) Distributive. AB + A Identity, twice (depending how you count it). A + AB Commutative. (A + A)(A + B) Distributive. A + B Complement, Identity.

5.3. De-Morgan’s theorem –The two theorems suggested by De-Morgan which are extremely useful in Boolean Algebra are as following.

5.3.1 Theorem 1

The left hand side (LHS) of this theorem represents a NAND gate with input A and B where the right hand side (RHS) of the theorem represents an OR gate with inverted inputs.

This OR gate is called as Bubbled OR.5.3.2 Theorem 1 – Diagramatic representation

5.3.3 Theorem 1 – Verification tableTable showing verification of the De-Morgans's first theorem

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5.3.4 Theorem 2

The LHS of this theorem represented a NOR gate with input A and B whereas the RHS represented an AND gate with inverted inputs.

This AND gate is called as Bubbled AND.

5.3.4 Theorem 2 – Diagramatic representation

5.3.6 Theorem 2 – Verification tableTable showing verification of the De-Morgans's second theorem

5.4. Logic gates –5.4.1 Logic Gate Truth TablesThe table used to represent the boolean expression of a logic gate function is commonly called a Truth Table. A logic gate truth table shows each possible input combination to the gate or circuit with the resultant output depending upon the combination of these input(s).5.4.2 2-input AND GateFor a 2-input AND gate, the output Q is true if BOTH input A “AND” input B are both true, giving the Boolean Expression of: ( Q = A and B ).Symbol Truth Table

A B Q

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0 0 00 1 01 0 01 1 1

Boolean Expression Q = A.B Read as A AND B gives QNote that the Boolean Expression for a two input AND gate can be written as: A.B or just simply AB without the decimal point.5.4.3 2-input OR (Inclusive OR) GateFor a 2-input OR gate, the output Q is true if EITHER input A “OR” input B is true, giving the Boolean Expression of: ( Q = A or B ).Symbol Truth Table

A B Q0 0 00 1 11 0 11 1 1

Boolean Expression Q = A+B Read as A OR B gives Q5.4.4 NOT GateFor a single input NOT gate, the output Q is ONLY true when the input is “NOT” true, the output is the inverse or complement of the input giving the Boolean Expression of: ( Q = NOT A ).Symbol Truth Table

A Q0 1

1 0

Boolean Expression Q = NOT A or A

Read as inversion of A gives Q

The NAND and the NOR Gates are a combination of the AND and OR Gates with that of a NOT Gate or inverter.5.4.5 2-input NAND (Not AND) GateFor a 2-input NAND gate, the output Q is true if BOTH input A and input B are NOT true, giving the Boolean Expression of: ( Q = not(A and B) ).Symbol Truth Table

A B Q0 0 10 1 11 0 11 1 0

Boolean Expression Q = A .B Read as A AND B gives NOT-Q

5.4.6 2-input NOR (Not OR) GateFor a 2-input NOR gate, the output Q is true if BOTH input A and input B are NOT true, giving the Boolean Expression of: ( Q = not(A or B) ).J.C.Vijayshree 94


Symbol Truth TableA B Q0 0 10 1 01 0 01 1 0

Boolean Expression Q = A+B Read as A OR B gives NOT-Q

As well as the standard logic gates there are also two special types of logic gate function called an Exclusive-OR Gate and an Exclusive-NOR Gate. The actions of both of these types of gates can be made using the above standard gates however, as they are widely used functions, they are now available in standard IC form and have been included here as reference.5.4.7 2-input EX-OR (Exclusive OR) GateFor a 2-input Ex-OR gate, the output Q is true if EITHER input A or if input B is true, but NOT both giving the Boolean Expression of: ( Q = (A and NOT B) or (NOT A and B) ).Symbol Truth Table

A B Q0 0 00 1 11 0 11 1 0

Boolean Expression Q = A B 5.4.8 2-input EX-NOR (Exclusive NOR) GateFor a 2-input Ex-NOR gate, the output Q is true if BOTH input A and input B are the same, either true or false, giving the Boolean Expression of: ( Q = (A and B) or (NOT A and NOT B) ).Symbol Truth Table

A B Q0 0 10 1 01 0 01 1 1

Boolean Expression Q = A B The following table gives a list of the common logic functions and their equivalent Boolean notation.Logic Function Boolean NotationAND A.BOR A+BNOT ANAND A .B

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NOR A+BEX-OR (A.B) + (A.B) or A BEX-NOR (A.B) + or A B5.5. Implementation of Boolean expressions – If the operation of a circuit is defined by a Boolean expression, a logic-circuit diagram can he implemented directly from that expression.Suppose that we wanted to construct a circuit whose output is y = AC+ BC' + A'BC. This Boolean expression contains three terms (AC, BC', A'BC), which are OR ed together. This tells us that a three-input OR gate is required with inputs that are equal to AC, BC', and A'BC, respectively. Each OR-gate input is an AND product term, which means that an AND gate with appropriate inputs can be used to generate each of these terms. Note the use of Inverters to produce the A' and C' terms required in the expression.

5.6. Flip flops - RS, JK, T and D.5.6.1 Flip flopA flip flop is a binary storage device. It can store binary bit either 0 or 1. It has two stable states HIGH and LOW i.e. 1 and 0. It has the property to remain in one state indefinitely until it is directed by an input signal to switch over to the other state. It is also called bistable multivibrator.The basic formation of flip flop is to store data. They can be used to keep a record or what value of variable (input, output or intermediate). Flip flop are also used to exercise control over the functionality of a digital circuit i.e. change the operation of a circuit depending on the state of one or more flip flops. These devices are mainly used in situations which require one or more of these three.Operations, storage and sequencing.

5.6.2 Latch Flip FlopOperationThe R-S (Reset Set) flip flop is the simplest flip flop of all and easiest to understand. It is basically a device which has two outputs one output

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being the inverse or complement of the other, and two inputs. A pulse on one of the inputs to take on a particular logical state. The outputs will then remain in this state until a similar pulse is applied to the other input. The two inputs are called the Set and Reset input (sometimes called the preset and clear inputs).Such flip flop can be made simply by cross coupling two inverting gates either NAND or NOR gate could be used Figure 1(a) shows on RS flip flop using NAND gate and Figure (b) shows the same circuit using NOR gate.Circuit Diagram

Figure : Latch R-S Flip Flop Using NAND and NOR GatesTruth Table

Table : Simple NAND R-S Flip Flop Truth TableS R Q0 0 indeterminate0 1 Set (1)1 0 Reset(0)1 1 No Change

When NOR gate are used the R and S inputs are transposed compared with the NAND version. Also the stable state when R and S are both 0. A change of state is effected by pulsing the appropriate input to the 1 state. The indeterminate state is now when both R and S are simultaneously at logic 1. Table 3 shows this operation.

Table : NOR Gate R-S Flip Flop Truth TableS R Q0 0 No Change0 1 Reset (0)1 0 Set (1)1 1 Indeterminate

5.6.3 Clocked RS Flip FlopOperationIn the clocked R-S flip flop the appropriate levels applied to their inputs are blocked till the receipt of a pulse from an other source called clock.

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The flip flop changes state only when clock pulse is applied depending upon the inputs.Circuit Diagram

Figure : Clocked RS Flip FlopTruth Table

Table : The truth table for the Clocked R-S flip flop

Initial Conditions Inputs (Pulsed) Final Output

Q S R Q (t + 1)0 0 0 00 0 1 00 1 0 10 1 1 indeterminate1 0 0 11 0 1 01 1 0 11 1 1 indeterminate

Excitation table The excitation table for R-S flip flop is very simply derived as given below

Table : Excitation table for R-S Flip FlopS R Q0 0 No Change0 1 Reset (0)1 0 Set (1)1 1 Indeterminate

5.6.4 D Flip FlopA D type (Data or delay flip flop) has a single data input in addition to the clock input as shown in Figure .Circuit Diagram

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Figure : D Flip FlopTruth Table

Table : Truth table for D Flip FlopS R Q(t + 1)0 0 00 1 11 0 01 1 1

The excitation table for D flip flop is very simply derived given as under.Excitation table

Table : Excitation table for D Flip FlopS Q0 01 1

5.6.5 JK Flip FlopOne of the most useful and versatile flip flop is the JK flip flop the unique features of a JK flip flop are:

1. If the J and K input are both at 1 and the clock pulse is applied, then the output will change state, regardless of its previous condition.

2. If both J and K inputs are at 0 and the clock pulse is applied there will be no change in the output. There is no indeterminate condition, in the operation of JK flip flop i.e. it has no ambiguous state. The circuit diagram for a JK flip flop is shown in Figure 4.

Circuit Diagram

Figure : JK Flip FlopTruth Table

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Table : The truth table for the JK flip flop

Initial Conditions Inputs (Pulsed) Final Output

Q S R Q (t + 1)0 0 0 00 0 1 00 1 0 10 1 1 11 0 0 11 0 1 01 1 0 11 1 1 0

The excitation table for JK flip flop is very simply derived as given in table.Excitation table

Table : Excitation table for JK Flip FlopS R Q0 0 No Change0 1 01 0 01 1 Toggle

5.6.6 T Flip FlopA method of avoiding the indeterminate state found in the working of RS flip flop is to provide only one input ( the T input ) such, flip flop acts as a toggle switch. Toggle means to change in the previous stage i.e. switch to opposite state. It can be constructed from clocked RS flip flop be incorporating feedback from output to input as shown in Figure.Circuit Diagram

Figure: T Flip FlopTruth Table

Table: Truth table for T Flip FlopQn T Qn + 10 0 00 1 11 0 1

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Table: Truth table for T Flip FlopQn T Qn + 11 1 0

The excitation table for T flip flop is very simply derived as shown in Table .Excitation table

Table : Excitation table for T Flip FlopT Q0 Qn

1 n

5.6.7 Master Slave Flip FlopFigure shows the schematic diagram of master sloave J-K flip flopSchematic Diagram

Figure : Master Slave JK Flip FlopA master slave flip flop contains two clocked flip flops. The first is called master and the second slave. When the clock is high the master is active. The output of the master is set or reset according to the state of the input. As the slave is incative during this period its output remains in the previous state. When clock becomes low the output of the slave flip flop changes because it become active during low clock period. The final output of master slave flip flop is the output of the slave flip flop. So the output of master slave flip flop is available at the end of a clock pulse.5.7. Combinational logic -5.7.1 Combinational circuit Combinational circuit is circuit in which we combine the different gates in the circuit for example encoder, decoder, multiplexer and demultiplexer. 5.7.2 CharacteristicsSome of the characteristics of combinational circuits are following.

The output of combinational circuit at any instant of time, depends only on the levels present at input terminals.

The combinational circuit do not use any memory. The previous state of input does not have any effect on the present state of the circuit.

A combinational circuit can have a n number of inputs and m number of outputs.

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We're going to elaborate few important combinational circuits as follows.5.8. Half Adder5.8.1 DescriptionHalf adder is a combinational logic circuit with two input and two output. The half adder circuit is designed to add two single bit binary number A and B. It is the basic building block for addition of two single bit numbers. This circuit has two outputs carry and sum.5.8.2 Block diagram

5.8.3 Truth Table

5.8.4 Circuit Diagram

5.9. Full Adder5.9.1 DescriptionFull adder is developed to overcome the drawback of Half Adder circuit. It can add two one-bit numbers A and B, and carry c. The full adder is a three input and two output combinational circuit.5.9.2 Block diagram

Truth Table

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Circuit Diagram

5.10. Half Subtractors5.10.1 DescriptionHalf subtractor is a combination circuit with two inputs and two outputs (difference and borrow). It produces the difference between the two binary bits at the input and also produces a output (Borrow) to indicate if a 1 has been borrowed. In the subtraction (A-B), A is called as Minuend bit and B is called as Subtrahend bit.5.10.2 Truth Table

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5.11. Full Subtractors5.11.1 DescriptionThe disadvantage of a half subtractor is overcome by full subtractor. The full subtractor is a combinational circuit with three inputs A,B,C and two output D and C'. A is the minuend, B is subtrahend, C is the borrow produced by the previous stage, D is the difference output and C' is the borrow output.5.11.2 Truth Table

5.11.3 Circuit Diagram

5.12. Sequential logic - 5.12.1 Sequential Logic circuits J.C.Vijayshree 104


The output state of a “sequential logic circuit” is a function of the following three states, the “present input”, the “past input” and/or the “past output”. Sequential Logic circuits remember these conditions and stay fixed in their current state until the next clock signal changes one of the states, giving sequential logic circuits “Memory”.Sequential logic circuits are generally termed as two state or Bistable devices which can have their output or outputs set in one of two basic states, a logic level “1” or a logic level “0” and will remain “latched” (hence the name latch) indefinitely in this current state or condition until some other input trigger pulse or signal is applied which will cause the bistable to change its state once again.5.12.2 Sequential Logic Representation

The word “Sequential” means that things happen in a “sequence”, one after another and in Sequential Logic circuits, the actual clock signal determines when things will happen next. Simple sequential logic circuits can be constructed from standard Bistable circuits such as: Flip-flops, Latches and Counters and which themselves can be made by simply connecting together universal NAND Gates and/or NOR Gates in a particular combinational way to produce the required sequential circuit.5.13. Ripple Counter5.13.1 DescriptionA ripple counter is an asynchronous counter where only the first flip-flop is clocked by an external clock. All subsequent flip-flops are clocked by the output of the preceding flip-flop. Asynchronous counters are also called ripple-counters because of the way the clock pulse ripples it way through the flip-flops.5.13.2 ModThe MOD of the ripple counter or asynchronous counter is 2n if n flip-flops are used. For a 4-bit counter, the range of the count is 0000 to 1111 (24-1). 5.13.3 Count up / Count downA counter may count up or count down or count up and down depending on the input control. The count sequence usually repeats itself. When counting up, the count sequence goes from 0000, 0001, 0010, ... 1110 , 1111 , 0000, 0001, ... etc. When counting down the count sequence goes in the opposite manner: 1111, 1110, ... 0010, 0001, 0000, 1111, 1110, ... etc.The complement of the count sequence counts in reverse direction. If the uncomplemented output counts up, the complemented output counts

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down. If the uncomplemented output counts down, the complemented output counts up.5.13.4 Ways of implementationThere are many ways to implement the ripple counter depending on the characteristics of the flip flops used and the requirements of the count sequence.

Clock Trigger: Positive edged or Negative edged JK or D flip-flops Count Direction: Up, Down, or Up/Down

5.13.5 Asynchronous / SynchronousAsynchronous counters are slower than synchronous counters because of the delay in the transmission of the pulses from flip-flop to flip-flop. With a synchronous circuit, all the bits in the count change synchronously with the assertion of the clock. Examples of synchronous counters are the Ring and Johnson counter.It can be implemented using D-type flip-flops or JK-type flip-flops.The circuit below uses 2 D flip-flops to implement a divide-by-4 ripple counter (2n = 22 = 4). It counts down.

5.14. The Shift Register5.14.1 DescriptionThe Shift Register is another type of sequential logic circuit that can be used for the storage or the transfer of data in the form of binary numbers. This sequential device loads the data present on its inputs and then moves or “shifts” it to its output once every clock cycle, hence the name “shift register”.5.14.2 ConstructionA shift register basically consists of several single bit “D-Type Data Latches”, one for each data bit, either a logic “0” or a “1”, connected J.C.Vijayshree 106

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together in a serial type daisy-chain arrangement so that the output from one data latch becomes the input of the next latch and so on.5.14.3 Ways of shiftingData bits may be fed in or out of a shift register serially, that is one after the other from either the left or the right direction, or all together at the same time in a parallel configuration.5.14.4 LatchesThe number of individual data latches required to make up a single Shift Register device is usually determined by the number of bits to be stored with the most common being 8-bits (one byte) wide constructed from eight individual data latches.5.14.5 UsageShift Registers are used for data storage or for the movement of data and are therefore commonly used inside calculators or computers to store data such as two binary numbers before they are added together, or to convert the data from either a serial to parallel or parallel to serial format. The individual data latches that make up a single shift register are all driven by a common clock ( Clk ) signal making them synchronous devices.5.14.6 Modes of operationShift register IC’s are generally provided with a clear or reset connection so that they can be “SET” or “RESET” as required. Generally, shift registers operate in one of four different modes with the basic movement of data through a shift register being:

• Serial-in to Parallel-out (SIPO) - the register is loaded with serial data, one bit at a time, with the stored data being available at the output in parallel form.

• Serial-in to Serial-out (SISO) - the data is shifted serially “IN” and “OUT” of the register, one bit at a time in either a left or right direction under clock control.

• Parallel-in to Serial-out (PISO) - the parallel data is loaded into the register simultaneously and is shifted out of the register serially one bit at a time under clock control.

• Parallel-in to Parallel-out (PIPO) - the parallel data is loaded simultaneously into the register, and transferred together to their respective outputs by the same clock pulse.

UNIT – VICOMMUNICATION AND COMPUTER SYSTEMS

6.1.Model of communication system – Shannon's Model of the Communication Process

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Shannon's model, as shown in Figure, breaks the process of communication down into eight discrete components: 6.1.1Source

An information source. Presumably a person who creates a message.

6.1.2Message The message, which is both sent by the information source and received by the destination.

6.1.3Transmitter A transmitter. For Shannon's immediate purpose a telephone instrument that captures an audio signal, converts it into an electronic signal, and amplifies it for transmission through the telephone network. Transmission is readily generalized within Shannon's information theory to encompass a wide range of transmitters. The simplest transmission system, that associated with face-to-face communication, has at least two layers of transmission. The first, the mouth (sound) and body (gesture), create and modulate a signal. The second layer, which might also be described as a channel, is built of the air (sound) and light (gesture) that enable the transmission of those signals from one person to another. A television broadcast would obviously include many more layers, with the addition of cameras and microphones, editing and filtering systems, a national signal distribution network (often satellite), and a local radio wave broadcast antenna.

6.1.4Signal The signal, which flows through a channel. There may be multiple parallel signals, as is the case in face-to-face interaction where sound and gesture involve different signal systems that depend on different channels and modes of transmission. There may be multiple serial signals, with sound and/or gesture turned into electronic signals, radio waves, or words and pictures in a book.

6.1.5Channel A carrier or channel, which is represented by the small unlabeled box in the middle of the model. The most commonly used channels include air, light, electricity, radio waves, paper, and postal systems. Note that there may be multiple channels associated with the multiple layers of transmission, as described above.

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6.1.6Noise Noise, in the form of secondary signals that obscure or confuse the signal carried. Given Shannon's focus on telephone transmission, carriers, and reception, it should not be surprising that noise is restricted to noise that obscures or obliterates some portion of the signal within the channel. This is a fairly restrictive notion of noise, by current standards, and a somewhat misleading one. Today we have at least some media which are so noise free that compressed signals are constructed with an absolutely minimal amount information and little likelihood of signal loss. In the process, Shannon's solution to noise, redundancy, has been largely replaced by a minimally redundant solution: error detection and correction. Today we use noise more as a metaphor for problems associated with effective listening.

6.1.7Receiver A receiver. In Shannon's conception, the receiving telephone instrument. In face to face communication a set of ears (sound) and eyes (gesture). In television, several layers of receiver, including an antenna and a television set.

6.1.8Destination A destination. Presumably a person who consumes and processes the message.

6.2. Analog and digital Communication – 6.2.1 COMMUNICATION SYSTEMCommunications is the field of study concerned with the transmission of information through various means. It can also be defined as technology employed in transmitting messages. It can also be defined as the inter-transmitting the content of data (speech, signals, pulses etc.) from one node to another.A communication system is a combination of processes and the hardware used to accomplish the transfer of the Information (communication).Communication system consists of Analog and Digital communication.6.2.2 ANALOG COMMUNICATIONAnalog communication is a communication method of conveying voice, data, image, signal or video information using a continuous signal which varies in amplitude, phase, or some other property in proportion to that of a variable. Analog systems are very tolerant to noise, make good use of bandwidth, and are easy to manipulate mathematically. However, analog signals require hardware receivers and transmitters that are designed to perfectly fit the particular transmission. Analog signals are signals with continuous values. Analog signals are used in many systems, although the use of analog signals has declined with the advent of cheap digital signals.6.2.3 DIGITAL COMMUNICATIONDigital communications is the physical transfer of data (a digital bit stream) over a point-to-point or point-to-multi point transmission medium.

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Examples of such media are copper wires, optical fibers, wireless communication media, and storage media. Digital communication enables the data to be transmitted in an efficient manner through the use of digitally encoded information sent through data signals. These data signals are easily compressed and, as such, can be transmitted with accuracy and speed.6.2.4 ADVANTAGES OF DIGITAL COMMUNICATION: a). It is fast and easier. b). No paper is wasted.c). The messages can be stored in the device for longer times, without being damaged, unlike paper files that easily get damages or attacked by insects. d). Digital communication can be done over large distances through internet and other things.e). It is comparatively cheaper and the work which requires a lot of people can be done simply by one person as folders and other such facilities can be maintained.

6.2.5 DISADVANTAGES OF DIGITAL COMMUNICATION: a). It is unreliable as the messages cannot be recognised by signatures. Though software can be developed for this, yet the softwares can be easily hacked. b). Sometimes, the quickness of digital communication is harmful as messages can be sent with the click of a mouse. The person oes not think and sends the message at an impulse. c). Digital Communication has completely ignored the human touch. A personal touch cannot be established because all the computers will have the same font! 6.3. Wired and wireless channel.6.3.1 TelecommunicationData or telecommunications is the process of the electronically sending and receiving messages between two points. In communications, both analog and digital signals move data over communication channels. 6.3.2 Types of communicationThe two main types of communication through the internet connection is Wired and Wireless. 6.3.3 Wired communicationWired transmission media for data travel is still widely used. A twisted pair wire is a copper cable used for telephone and data communications. The twisted pair wire or a basic telephone connection is cheap, but the speed does not work well enough to carry vidoes, voice notes, and data at the same time. Other wired communication methods are a coaxial cable, a copper wire surrounded by a layer of braided wire. This wire transfers data at rates of 10 Mbps.6.3.4 Wireless CommunicationWireless Communication is often more popular these days. Wireless communication is used in our everyday lives not only by internet

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connection but through the use of radio, microwaves, satellites, and even devices such as bluetooth. 6.3.5 ExamplesInfrared is a wireless transmission used through beams of light that travel through the air. Bluetooth technology is another wireless communication method that has become very popular in the past couple of years. 6.4. Block diagram of Microwave communication systems 6.4.1 MicrowaveMicrowave refer to high frequencies (above 300MHz) and short wave lengths, at the microwave components depends on the changing electro magnetic fields instead of current in the conductor or voltage across the 2 points a microwave propagated through the line of sight , there fore it is necessary to install repeater station at about 50km interval.6.4.2 UsesMicrowave signal are used for communication over long distance continental or intercontinental. Microwave is the communication link which make the communication possible. The basic block diagram of microwave communication system is shown in figure.

6.4.3 Block Diagram

6.4.4 Construction:Antenna:- Mostly a parabolic refractor types of antenna are used which is used to transmit and receive the signal.Circulator: A circulator is used to isolate transmitter with the receiver input and to couple transmitter to antenna and antenna to receiver input.Protection Circuitry: It provides safety to the mixer from overloads.Mixer (Receiver): It has two outputs. One is the incoming signal and other is the signal from lower band pass filter (BPF).The mixer gives an IF signal of 70Mhz.Band pass filter (BPF): It provides the necessary selectivity to the receiver and it prevents the interference.

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IF amplifier and AGC:- It amplifies the signal up to a intermediate frequency of 70Mhz. and its gain is controlled through AGC (automatic gain control)Amplitude limiter: As the signal is frequency modulated one so as amplitude limiter is used to avoid unwanted amplitude variations.Mixer (Transmitter): It is used to convert IF frequency to transmitting microwave frequency band to pass through it and hence prevent interference.POWER AMPLIFIER:-This amplifier amplifies the transmitted power from a repeater section in the range of 0.2W to 10W.MICROWAVE SOURCE:- Klystron & Gunn Oscillators were used as microwave source. Now, V H F transistor crystal oscillators are used for microwave source.POWER SPLITTER:- It divides the output power from a microwave source and feeds a large portion to the transmitter mixer, which converts it into transmitting microwave frequency.SHIFT OSCILATOR:- It provides one of the inputs to the balanced mixer so that it produces 70MHz IF at the output of receiver mixer. This microwave link communicates with 600 to 2700 channels per carrier. Thus the number of carriers in each direction can be four to twelve.6.5. Block diagram of satellite communication systems 6.5.1 Natural satelliteMoon is a natural satellite of earth. However we are not interested in the natural satellites. We want to learn something different about the artificial (man made) satellites. 6.5.2 Artificial satelliteAn artificial satellite orbits or revolves around the earth in exactly the same manner as electrons revolve around the nucleus of an atom. The path in which satellites move are call as orbits. The orbits are of different types such as synchronous orbits, polar orbits and inclined orbits, out of which the synchronous or geostationary orbit is used by the geostationary satellites. The geostationary satellites take exactly 24 hours to complete one revolution around the earth, therefore they appear to be stationary. 6.5.3 Types of satellitesThe satellites can be used for variety of purposes. Depending on the type of application, the satellites are classified into the following categories:1.Communication Satellites2.Remote sensing Satellites3.Weather Satellites4.Scientific SatellitesA geostationary communication satellite is basically a relay station in space. It receives signal from one earth station, amplifies it, improves the signal quality and radiate the signal back to other earth stations. Such a relay system allows us to communicate with any corner of the world.6.5.4 Block Diagram of a Satellite Communication System

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6.5.5 Basic operation of satellite communication system The block diagram of a satellite communication system is shown in

above fig. An earth station transmits information signal to the satellite using a

highly directional dish antenna. The satellite receives this signal, processes it and transmits it back

at a reduced frequency. The receiving earth stations will receive this signal using parabolic

dish antennas pointed towards the satellite. The signal which being transmitted upwards to the satellite is called

as the "up-link" and it is normally at a frequency of 6 GHz. The signal which is transmitted back to the receiving earth station is

called as the "down-link" and it is normally at a frequency of 4 GHz. Thus a satellite has to receive, process and transmit the signal. All

these functions are performed by a unit called satellite transponder. A communication satellite generally has two sets of transponders, each set having 12 transponders making it a total of 24 transponders. Each transponder has a bandwidth of 36 MHz which is sufficient to handle at least one TV channel.

The up-link signal received by a transponder is a weak and down-link signal transmitted by the transponder is strong. Therefore to avoid interference between them, the up-link and down-link frequencies are selected to be of different value

The operation of satellite takes place at a very high signal frequencies in the microwave range. The typical band of signal frequencies used for the communication satellites are as follows:

1.C band : 4/6 GHz2.Ku band : 11/14 GHz3.Ka band : 20/30 GHzThe C band frequencies of 4/6 GHz indicate that the down-link frequency is 4 GHz whilethe up-link frequency is 6 GHz. One of the advantages of operating at such a highfrequency is reduction in the size of antennas and other components of the system.J.C.Vijayshree 113

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It is extremely important to maintain the position of the satellite with respect to earth. Therefore control routines such as station keeping and altitude control are executed from the control room in the earth stations.

Multiple access methods such as FDMA (frequency division multiple access), TDMA (time division multiple access) and CDMA (code division multiple access) are used to allow the access of a satellite to the maximum number of earth stations.

The power requirement of a satellite is satisfied by solar panels and a set of nickel cadmium batteries, carried by the satellite itself.

6.6. Block diagram of optical fiber communication systems 6.6.1 optical fiber communication systems The transmission media used for the communication of signals from one point to another are copper wires, coaxial cables, wave-guides and radio links. All these media have their own advantages and disadvantages. Recently, the most modern medium of transmission for communication has been developed. This modern medium of transmission, called optical fiber, has presented the new frontier in the field of telecommunication transmission.Light is an old friend to the human beings. Light was used as a medium for communication in the earliest days. About two hundreds years ago light was used for transmission of information over long distances. But after many years of research and experience gained so far with the new technology, communication has developed into the present state. The idea of harnessing light as a communications medium was transformed into a practical communication system. The practical use of optical fibers was made possible by the perfection of the Laser and manufacturing of hair-thin glass lines called "optical fiber". In the optical fiber a modulated beam of light are used to carry the information on the principle of total internal reflection.6.6.2 Optical Fiber Transmitter

ExplanationOptical transmitter is a device that generates the signal sent through optical fibers. The basic elements of optical fiber transmitter are shown in above Fig:Electronic InterfaceThere is wires standard electronic connection or pins energizing the transmitter. They provide power Electronic I/P and Optical O/P signals.

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Optical InterfaceThere are actually the connectors between the light source and fiber may have different forms.Drive CKTThis depends on application, requirements, data format and the light source.Electronic ProcessingIn some transmitters the I/P Electrical signals are electronically processed to put them into of suitable from to drive the light source.Optical MonitorIt Monitors the O/P of the LASER and provides feedback to the drive CKT so that the O/P power remains stable.Temperature MonitorThe characteristic of semi-conductor LASER changes in temperature. The life time of LASER decreases with increase in operating temp and the O/P power also decrease which produce some change in 0/p wave length of the light, to keep the operating temp stable theThermo-electric coolers are used in optical fiber transmitters these coolers control the temp of LASER.AttenuationThe optical fiber transmitters should produce some standard level of power and this level should not desired for the receivers, to handle the receiver I/P power, the attenuator is used in the transmitter to reduce the O/P level of the transmitter to a safe value for the receivers.

External modulatorThe external modulation means modulation of light source by on external device in order to prevent spreading of wave-length range of light emitted by LASER.6.6.3 Optical Fiber Receiver

This is a device that converts the optical signal received through the fiber into Electrical from for the use of other devices as an I/P signals; the basic elements of optical receiver either analog or digital are shown below.DetectorThe 1st stage of optical fiber receiver is a detector, which converts the received signal into an Electrical from.Amplification StagesIn the amplification stages there are 2, stage of amplifier are used which amplifies the converted signal, for further processing.De modulator or Decision CKTIt reproduces the original Electrical signal from modulated incoming signals.6.6.4 Merits of Optical Fiber SystemJ.C.Vijayshree 115


1. Using optical fiber the transmission loss is very low.2. Also the long distance transmission is possivle with fibers with out

the need to ampligy and retransmits the signal along the way.3. Fiber is lighter and less bulky than equivalent copper cable4. In fiber optic communication, there is no need of electrical

connection between the sender and receiver.5. Optical fiber is more reliable than copper cables.6. Optical fiber can be bending at any signal angle or even in circle.

6.6.5 Demerits of Optical Fiber System1. The joining of fiber optics cables need greater care because if the

Joining is not correct; a lot of attenuation will produce in high Wave length.

2. As the fiber optics have no electrical conductivity, there fore additional Copper cable is not used with optical fiber to provide power supply to the repeaters.

3. The installation cost is very high as compare to the other types of T/N lines.

4. The big and base disadvantage of optical fiber is its cost, means its cost is slightly more expansive than copper cable. However its cast is falling day by day. When it comes down in price, then the fiber will be the choice of everyone for network/communication cabling.

6.7.Block diagram of cellular mobile communication systems 6.7.1 Mobile Network

6.7.2 The GSM SystemGlobal System for Mobile Communications is the standard for mobile telephone systems in the world. In GSM, the signaling and speech channels are digital, therefore GSM is considered a 2G (Second Generation) system. This helps wide-spread implementation of data

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communication applications. There are five different cell sizes in a GSM network These are macro, micro, pico, femto and umbrella cells. 6.7.3 Macro cellsMacro cells are cells where the base station antenna is installed on a mast above average roof top level. Micro cells are cells whose antenna height is under average roof top level. 6.7.4 Pico cellsPico cells are small cells whose coverage diameter is a few dozen metres. These are mainly used in indoors applications. 6.7.5 Femto cellsFemto cells are cells designed for use in residential or small business environments and connect to the service provider’s network via a broadband internet connection. 6.7.6 Umbrella cellsUmbrella cells are used to cover shadowed regions of smaller cells and fill in gaps in coverage between those cells.Horizontal radius of the cell varies depending on the antenna height, antenna gain and propagation conditions. Maximum distance the GSM supports is 35 kilometers. Most 2G GSM networks operate in the 900 MHz or 1800 MHz bands while 3G GSM in the 2100 MHz frequency band.6.7.7 What happens when we make a call?

1. When we switch on the mobile phone, it tries for an SID on the Control channel. The Control channel is a special frequency that the phone and base station use to talk to one another. If the Mobile phone finds difficulty to get link with the control channel, it displays a “no service” message.

2. If the Mobile phone gets the SID, it compares the SID with the SID programmed in the phone. If both SID match, the phone identifies that the cell it is communicating is the part of its home system.

3. The phone also transmits a registration request along with the SID and the MTSO keeps track of your phone’s location in a database. MTSO knows in which cell you are when it wants to ring the phone.

4. The MTSO then gets the signal, it tries to find the phone. The MTSO looks in its database to find the cell in which the phone is present. The MTSO then picks a frequency pair to take the call.

5. The MTSO communicates with the Mobile phone over the control channel to tell it what frequencies to use. Once the Mobile phone and the tower switch on those frequencies, the call is connected.

6. When the Mobile phone move toward the edge of the cell, the cell’s base station will note that the signal strength is diminishing. At the same time, the base station in the cell in which the phone is moving will be able to see the phone’s signal strength increasing.

7. The two base stations coordinate themselves through the MTSO. At some point, the Mobile phone gets a signal on a control channel and directs it to change frequencies. This will switch the phone to the new cell.

6.8. Network model – 6.8.1 Computer Networks

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Computer networks are bunch of interconnected PC or computers that facilitate the exchange of data or some other purposeful work. The first computer network to be designed was the "Advanced Research Projects Agency Network" (ARPANET) for the United States Department of Defense in the late 1960s and early 1970s. From then on, numerous new network technologies have been developed.Computer networks can be classified into different types based on their scale of operation. 6.8.2 Personal Area NetworkA personal area network, or PAN, is a computer network organized around an individual person within a single building. This could be inside a small office or residence. A typical PAN would include one or more computers, telephones, peripheral devices, video game consoles and other personal entertainment devices. If multiple individuals use the same network within a residence, the network is sometimes referred to as a home area network, or HAN. In a very typical setup, a residence will have a single wired Internet connection connected to a modem. This modem then provides both wired and wireless connections for multiple devices. The network is typically managed from a single computer but can be accessed from any device. This type of network provides great flexibility. For example, it allows you to:

Send a document to the printer in the office upstairs while you are sitting on the couch with your laptop.

Upload the photo from your cell phone to your desktop computer. Watch movies from an online streaming service to your TV.

If this sounds familiar to you, you likely have a PAN in your house without having called it by its name. 6.8.3 Local Area NetworkA local area network, or LAN, consists of a computer network at a single site, typically an individual office building. A LAN is very useful for sharing resources, such as data storage and printers. LANs can be built with relatively inexpensive hardware, such as hubs, network adapters and Ethernet cables. The smallest LAN may only use two computers, while larger LANs can accommodate thousands of computers. A LAN typically relies mostly on wired connections for increased speed and security, but wireless connections can also be part of a LAN. High speed and relatively low cost are the defining characteristics of LANs. LANs are typically used for single sites where people need to share resources among themselves but not with the rest of the outside world. Think of an office building where everybody should be able to access files on a central server or be able to print a document to one or more central printers. Those tasks should be easy for everybody working in the same office, but you would not want somebody just walking outside to be able to send a document to the printer from their cell phone! If a local area network, or LAN, is entirely wireless, it is referred to as a wireless local area network, or WLAN. J.C.Vijayshree 118


6.8.4 Metropolitan Area NetworkA metropolitan area network, or MAN, consists of a computer network across an entire city, college campus or small region. A MAN is larger than a LAN, which is typically limited to a single building or site. Depending on the configuration, this type of network can cover an area from several miles to tens of miles. A MAN is often used to connect several LANs together to form a bigger network. When this type of network is specifically designed for a college campus, it is sometimes referred to as a campus area network, or CAN. 6.8.5 Wide Area NetworkA wide area network, or WAN, occupies a very large area, such as an entire country or the entire world. A WAN can contain multiple smaller networks, such as LANs or MANs. The Internet is the best-known example of a public WAN. WAN, in contrast to a LAN, refers to a wide area network. The name is exactly what it sounds like: a network that covers an area wider than a LAN. Beyond that, the definition is less clear. Distances can range from a network connecting multiple buildings on a corporate or college campus to satellite links connecting offices in different countries. The most popular WAN is the one you're using to read this article: the Internet. It's actually a collection of other networks, including other LANs and WANs - hence, the name.WANs can be wired, using fiber-optic cable, for example, or wireless. A wireless WAN might use microwave or infrared (IR) transmission technology, or even satellite. Laying fiber may make sense when connecting a campus but becomes more expensive when connecting greater distances. To save money, an organization may opt for wireless technology or lease lines from a third party.

6.9.Circuit and packet switching – 6.9.1 Circuit SwitchingIn circuit switching network dedicated channel has to be established before the call is made between users. The channel is reserved between the users till the connection is active. For half duplex communication, one channel is allocated and for full duplex communication, two channels are allocated. It is mainly used for voice communication requiring real time services without any much delay.

As shown in the figure, if user-A wants to use the network; it need to first ask for the request to obtain the one and then user-A can communicate with user-C. During the connection phase if user-B tries to J.C.Vijayshree 119

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call/communicate with user-D or any other user it will get busy signal from the network.6.9.2 Packet SwitchingIn packet switching network unlike CS network, it is not required to establish the connection initially. The connection/channel is available to use by many users. But when capacity or number of users increases then it will lead to congestion in the network. Packet switched networks are mainly used for data and voice applications requiring non-real time scenarios.

As shown in the figure, if user-A wants to send data/information to user-C and if user-B wants to send data to user-D, it is simultaneously possible. Here information is padded with header which contains addresses of source and destination. This header is sniffed by intermediate switching nodes to determine their route and destination.In packet switching, station breaks long message into packets. Packets are sent one at a time to the network. Packets are handled in two ways, viz. datagram and virtual circuit. In datagram, each packet is treated independently. Packets can take up any practical route. Packets may arrive out of order and may go missing.In virtual circuit, preplanned route is established before any packets are transmitted. The handshake is established using call request and call accept messages. Here each packet contains virtual circuit identifier (VCI) instead of the destination address. In this type, routing decisions for each packet are not needed. 6.9.3 Comparison between CS vs. PS networks

Circuit SwitchingPacket Switching(Datagram type)

Packet Switching(Virtual Circuit type)

Dedicated path No Dedicated path No Dedicated path Path is established for entire conversation

Route is established for each packet

Route is established for entire conversation

Call setup delay packet transmission delay

call setup delay as well as packet transmission delay

Overload may block call setup

Overload increases packet delay

Overload may block call setup and increases packet delay

Fixed bandwidth Dynamic bandwidth Dynamic bandwidth

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No overhead bits after call setup

overhead bits in each packet overhead bits in each packet

6.10.Overview of ISDN.6.10.1 ISDNISDN [I*SD'N] n. 1. Integrated Services Digital Network. 2. A digital telephone service that provides fast, accurate data transmission over existing copper telephone wiring. 3. The way fast way to go online. 6.10.2 The BasicsISDN is based on a number of fundamental building blocks. First, there are two types of ISDN "channels" or communication paths:

B-channelThe Bearer ("B") channel is a 64 kbps channel which can be used for voice, video, data, or multimedia calls. B-channels can be aggregated together for even higher bandwidth applications.

D-channelThe Delta ("D") channel can be either a 16 kbps or 64 kbps channel used primarily for communications (or "signaling") between switching equipment in the ISDN network and the ISDN equipment at your site.

6.10.3 ConfigurationsThese ISDN channels are delivered to the user in one of two pre-defined configurations:

Basic Rate Interface (BRI)BRI is the ISDN service most people use to connect to the Internet.

An ISDN BRI connection supports two 64 kbps B-channels and one 16 kbps D-channel over a standard phone line. BRI is often called "2B+D" referring to its two B-channels and one D-channel. The D-channel on a BRI line can even support low-speed (9.6 kbps) X.25 data, however, this is not a very popular application in the United States.

Primary Rate Interface (PRI)ISDN PRI service is used primarily by large organizations with

intensive communications needs. An ISDN PRI connection supports 23 64 kbps B-channels and one 64 kbps D-channel (or 23B+D) over a high speed DS1 (or T-1) circuit. The European PRI configuration is slightly different, supporting 30B+D. BRI is the most common ISDN service for Internet access. A single BRI line can support up to three calls at the same time because it is comprised of three channels (2B+D). Two voice, fax or data "conversations," and one packet switched data "conversation" can take place at the same time. Multiple channels or even multiple BRI lines can be combined into a single faster connection depending on the ISDN equipment you have. Channels can be combined as needed for a specific application (a large multimedia file transfer, for example), then broken down and reassembled into individual channels for different applications (normal voice or data transmissions). 6.10.4 UsesJ.C.Vijayshree 121


ISDN offers the speed and quality that previously was only available to people who bought expensive, point-to-point digital leased lines. Combined with its flexibility as a dial-up service, ISDN has become the service of choice for many communications applications. Popular ISDN applications include:

Internet access Telecommuting/remote access to corporate computing Video conferencing Small and home office data networking

6.10.5 ISDN Benefits Even faster

By combining your two B-channels you have access to up to 128 kbps -- more than four times as fast as a 28.8 kbps modem on a standard phone line. And ISDN's digital technology assures you the cleanest connection to the Internet so you won't be slowed down by re-transmissions because of old analog technology.

More efficient and economicalISDN brings increased capabilities, reduced costs and improved productivity to organizations both large and small. When you're looking for something on the Internet, you can get there faster. You can be more productive because you aren't waiting as long to get to that next website or download that large file.

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