Basic Electrical & Electronics Lab

LAB MANNUALBASIC ELECTRICAL AND ELECTRONICS ENGINEERING(BE-104)

Submit ByName-..Roll no-Session -.Submit to Prof. Prof. Prateek MishraAsst. professor HOD EC Dept. GNCSGI EC Dept. GNCSI

DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING, GNCSGI GLOBAL NATURE CARE SANGATHANS GROUP OF INSTITUTION, JABALAPURBASIC ELECTRICAL AND ELECTRONICS ENGINEERING(BE-104)List of Experiments

1. Verifications of Thevenins Superposition theorem.

2. Study of Transformer, name plate rating, determination of rayio and polarity.

3. Determination of equivalent circuit parameters of a single phase transformer by O.C. and S.C. tests and estimation of voltage regulation and efficiency at various loading conditions and verification by load test.4. Separation of resistance and inductance of choke coil.

5. Measurement of various line & phase quantities for a 3-phase circuit.6. Identification of different Electronics components.7. Observing input and output waveforms of rectifiers. 8. Transistor application as amplifier and switch.9. Verification of truth table for various gates.

Unit I

Electrical circuit analysis- Voltage and current sources, dependent and independent sources, source conversion, DC circuits analysis using mesh & nodal method, Thevenins & superposition theorem, star-delta transformation.1-phase AC circuits under sinusoidal steady state, active, reactive and apparent power, physical meaning of reactive power, power factor, 3-phase balanced and unbalanced supply, star and delta connections.

Unit II

Transformers-Review of laws of electromagnetism, mmf, flux, and their relation, analysis of magnetic circuits. Single-phase transformer, basic concepts and construction features, voltage, current and impedance transformation, equivalent circuits, phasor diagram, voltage regulation, losses and efficiency, OC and SC test.

Unit III

Rotating Electric machines- Constructional details of DC machine, induction machine and synchronous machine, Working principle of 3-Phase induction motor, Emf equation of 3-Phase induction motor, Concept of slip in 3-Phase induction motor, Explanation of Torque-slip characteristics of 3-Phase induction motor, Classification of self excited DC motor and generator.

Unit IV

Digital Electronics-Number systems used in digital electronics, decimal, binary, octal, hexadecimal, their complements, operation and conversion, floating point and signed numbers, Demorgans theorem, AND, OR, NOT, NOR, NAND, EX-NOR, EX-OR gates and their representation, truth table, half and full adder circuits, R-S flip flop, J-K flip flop.

Unit V

ELECTRONICCOMPONENTSANDCIRCUITS-Introductionto Semiconductors, Diodes, V-I characteristics, Bipolar junction transistors (BJT) and their working, introduction to CC, CB & CE transistor configurations, different configurations and modes of operation of BJT, DC biasing of BJT.

Experiment detailS no. Object Pg no 1Verificatiions of Thevenins Superposition theorem.2Studyof Transformer, name plate rating, determination of rayio and polarity.3 Determination of equivalent circuit parameters of a single phase transformer by O.C. and S.C. tests and estimation of voltage regulation and efficiency at various loading conditions and verification by load test.4Seperation of resistance and inductance of choke coil.5Measurement of various line & phase quantities for a 3-phase circuit.6Identification of different Electronics components.7Observing input and output waveforms of rectifiers. 8Transistor application as amplifier and switch.9Verification of truthtable for various gates.10To study KVL & KCL11Constructional Features of D.C machine

Experiment : 1

A.VERIFICATION OF THEVENINS THEOREM

AIM:

To verify Thevenins theorem and to find the current flowing through the load resistance.

APPARATUS REQUIRED:

Model no. TVS NET -01

THEORY:

Thevenin`s theorem:

Any linear active network with output terminals can be replaced by a single voltage source Vth in series with a single impedance Zth. Vth is the Thevenin`s voltage. It is the voltage between the terminals on open circuit condition, Hence it is called open circuit voltage denoted by Voc. Zth is called Thevennin`s impedance. It is the driving point impedance at the terminals when all internal sources are set to zero too.

If a load impedance ZL is connected across output terminals, we can find the current through it IL = Vth/ (Zth + ZL).

PROCEDURE:

1. Connections are made as per the circuit diagram.

2. Check your connections before switch on the supply.

3. Find the Thevenins voltage (or) open circuit voltage.

4. Replace voltage source by internal resistor.

5. Determine the Thevenins resistance.

6. Find IL by using Thevenins formula. 7. Compare the observation reading to theoretical value.

8. switch off the supply

9. Disconnect the circuit.

Basic Electrical & Electronics Lab2014

Basic Electrical & Electronics Lab2014

Circuit diagram1.0k3.3k1.0k3.3k

XMM1

5V2.2k2.7kRth2.7k

To find Rth

To find VthTo find IL

1.0k3.3k1.0k3.3k

v5V2.2k

5V2.7k+2.7k

A (0-5)mA-

Equivalent ciruitI1

RthRL

2.2kVth+

A (0-5)mA-

Tabulation

VthRthIL(mA)

theoreticalpracticaltheoreticalpracticaltheoreticalpractical

Calculation:

RESULT:

Thus the Thevenins theorem was verified.

Theoretical:Vth =Rth =IL =Practical:Vth =Rth =IL =

B.SUPER POSITION THEOREM

AIM:

To verify the superposition theorem and determine the current following through the load resistance.

APPARATUS REQUIRED:

MODEL NO. NET- 02

Superposition theorem

In a linear circuit containing more than one source, the current that flows at any point or the voltage that exists between any two points is the algebraic sum of the currents or the voltages that would have been produced by each source taken separately with all other sources removed.

PROCEDURE:

1. Connections are made as per the circuit diagram.

2. Check your connections before switch on the supply.

3. Determine the current through the load resistance. 4. Now one of the sources is shorted and the current flowing through the resistance IL measured by ammeter.

5. Similarly, the other source is shorted and the current flowing through the resistance IL measured by ammeter.

6. Compare the value obtained with the sum of I1&I2 should equal to I 7. Compare the observation reading to theoretical value.

8. switch off the supply

9. Disconnect the circuit.

Circuit diagram

Superposition

220 ohm470 ohm

12V1 K10 V

TO find I2 When 10V source is acting alone

220 ohm470 ohm

10 V

1 K

+

A (0-20)mA

-

Tabulation:

To find I1 when 12V source is acting alone

220 ohm470 ohm

12V1 K

+

A (0-20)mA

-

To find I when two sources are acting

220 ohm470 ohm

12V10 V

1 K

+

A (0-20)mA

-

V(volt)I1(mA)I2(mA)I(mA)

V1V2theoreticalpracticaltheoreticalpracticaltheoreticalpractical

Calculation:

RESULT:Thus the superposition theorem was verified

Experiment ; 2

OBECT:

1. Name plate rating of single phase transformer

2.Determination of transformation ration.

APPARATUS REQUIRED:

S.NO.Name of equipmentQuantityRangeType

1.1- Transformer1230/115V,1KVAShell type

2.Auto Transformer10-270,10AVariac type

3.Voltmeter10-300 VMoving iron

4.Voltmeter10-150 VMoving iron

THEORY:

Study & construction of single phase transformer: The main elements of a transformer are two copper coils & laminated silicon steel core.A transformer is a static device or a machine that transforms electrical energy from one circuit to another electrical circuit through the medium magnetic flux. And without a change in frequency. The electrical circuit which receive energy from the supply mains is called primary winding and the other circuit which ,which delivers electrical energy to the load ,is called secondary winding .Theoretically it may seem that transformers may be built to handle any voltage or current. But in reality there are limits to both the voltage & current.

The name plate rating of a power transformer : The name plate rating of a power transformer usually contains

Volt ampere rating of transformer in KVA.

Voltage ratio or turn ratio in V1/V2....

Frequency of 1- or 3-.

Equivalent impedance of a transformers in %.

A typical name plate of a 1- transformer is as follows:

230 Volts/115Volts, 50 Hz, 1KVA, Shell type,10 Amp.

Here 1 KVA is the rated output at output terminals.230/115means when 230V. is the applied to the primary ,the secondary voltage on full load at specified power factor is 115volts.The ratio of V1& V2 is not exactly equal to N1/N2,because of voltage drop in primary & secondary. Rated primary & secondary current can be calculated from the rated KVA and corresponding rated voltage thus

Rated (Full load ) primary current = KVA /V1 = 1000/230 = 4.35Amps

Rated (Full load ) secondary current = KVA /V2 = 1000/115 = 4.35 Amps

Rated frequency is the frequency for which the transformer is designed to operate.

E1 =4.44f N1 Volts E2 =4.44f N2 Volts E1 = V1 and E2 = V2K = V2/ V1 = N2/ N1 = I1/ I2

TRANSFORMATION RATIO:

The turn ratio of the single phase transformer can be found by measuring the primary & secondary voltage. Let V1 &V2 is the primary and secondary voltage at on load.1/K = V1/ V2 = N1/N2 = I2/I1 = Turn Ratio

Induced E.M.F. in primary winding, Induced E.M.F. in secondary winding, For ideal transformer

Hence, Transformation Ratio

PROCEDURE:

1. Connect the circuit as per figure & set up auto transformer to zero position.

2. Switch on A .C. supply and adjust the Auto transformer till a suitable voltage.

3. Record voltage, V1 across the primary and V2 across the secondary winding.

4. Vary the Auto transformer and repeat above step,take at least 3 readings.

5. switch off the supply.

OBSERVATION:

S.NO.Primary Voltage V1Secondary Voltage V2K = V2/ V1

1.

2.

3.

CIRCUIT DIAGRAM:

RESULT:

The transformation ratio of given transformer is ..

PRECAUTION:

1. Connection should be tight. 2. Do not touch on live wire.

3. Load on the transfer should not increase beyond its capacity.

Experiment :3

OBECT:

1. To calculate the complete parameter of the equipment of 1- transformer.

2. To determine iron & copper losses.

3. To calculate efficiency & voltage regulation at 1/4, 1/3, 1/2, 3/4 full load and 1.25times full load at 0.8 P.F. lagging. 4. To plot the efficiency curve vs load.

APPARATUS REQUIRED:

S.NO.Name of equipmentQuantityRangeType

1.1- Transformer1230/115V,1KVAShell type

2.Auto Transformer10-270,10AVariac type

3.Voltmeter10-150 VMoving iron

4.Ammeter10-0.5AMoving iron

5.Ammeter10-0.10AMoving iron

6.Wattmeter12.5/0.5A,125/250/500VDynamometer

7.Connecting leads10-12..

THEORY:

These two test on transformer help to determine-

1. The parameters of equipments circuit of 1- transformer.

2. The voltage regulation of 1- transformer.

3. The efficiency of 1- transformer.

OPEN CIRCUIT TEST OR NO LOAD TEST:

In this test voltmeter, Ammeter & Wattmeter are connected on low voltage side of transformer.The high voltage is left open circuited.The rated voltage applied to the primary.The ammeter reads no load current, or the exciting I0.Since I0 is quite small (2 to 6% of rated current) the primary leakage impedance drop is almost negligible and for all practical purpose the applied voltage V1,is equal to induced E.M.F V1.The input power (iron loss) is given by wattmeter reading,consist of core loss and ohmic loss.Since the exciting current is very small, the ohmic losses during open circuit test is negligible as compared to normal core loss.CIRCUIT DIAGRAM: -

CALCULATION:

Applied rated voltage on low voltage side= V1

Exciting Current or no load current= I0

Wattmeter reading, Wo/ Iron loss, PC= VOIOCos o

No load power factor, Cos o= PC/ VOIO

Working component , IW= IO Cos o

Magnetizing component, I= IO Sin o

Core loss Resistance, RC= PcI2W=V1 /IW =V1/I0 Cos 0

Magnetising reactance, X= V1 /I=V1 /Io Sin o

Thus open circuit test gives the following information:

1. Core loss at rated voltage & frequency.

2. The shunt branch parameter of equivalent circuit i.e., X & RC.

SHORT CIRCUIT TEST:

The low voltage side of the transformer of the transformer is short circuited & instrument are placed on H.V. side. Apply the low voltage on H.V. side & with the help of autotransformer go on increasing the applied voltage till the rated current starts flowing in the short circuited winding(L.V. side).The primary voltage 10% to 12% of its rated value is sufficient to circulate the rated current in short circuited winding. Since the core flux induces the voltage, which is 1% to 6% of its rated value hence core loss can be neglected. The wattmeter records only the ohmic loss is both, the primary & secondary winding.

CALCULATION:

Vsc, Isc & Psc are the voltmeter ammeter & wattmeter reading

ZSC = VSC /ISC

RSC = PSC/I2SC

XSC = Z2SC R2SC

Thus the short circuit test gives the following information

1. Ohmic loss at rated current and frequency.

2. Equivalent resistance and leakage reactance and leakage impedance.

Load x P.F.

The efficiency at any load, =X 100 %

Load x P.F.+ Wo+ Io2Ro

PROCEDURE FOE OPEN CIRCUIT TEST:

1. Connect the circuit diagram as shown in figure and set up the autotransformer at zero position . 2. Adjust the supply voltage with the help of autotransformer to 230 volts with secondary winding terminal open.

3. Record the ammeter, voltmeter ,wattmeter reading.

4. Vary the supply voltage with the help of the auto transformer and enter the reading in observation table.

OBSERVATION TABLE FOR OPEN CIRCUIT TEST

S.NO.Primary VoltageInput CurrentInput power in watts

Voltmeter ReadingAmmeter ReadingWattmeter reading

1.

2.

3.

PROCEDURE FOE SHORT CIRCUIT TEST:

1. Connect the circuit diagram as shown in figure and set up the autotransformer at zero position .

2. Adjust the supply voltage with the help of autotransformer (keep in mind that 10-12% of rated voltage is sufficiency) with secondary winding terminal short circuited and circulate full rated current in short circuited winding.

3. Record the ammeter, voltmeter ,wattmeter reading.

4. Vary the supply voltage with the help of the auto transformer and enter the reading in observation table. 5. Three readings adjust at 50% ,86.6% & 100% rated full load current.

OBSERVATION TABLE FOR SHORT CIRCUIT TEST

S.NO.Primary VoltageInput CurrentInput power in watts

Voltmeter ReadingAmmeter ReadingWattmeter reading

1.

2.

3.

RESULT:

PRECAUTION:

1. In open circuit test, the H.V. side should be open circuited(left side).

2. In open circuit test, low voltage should be apply to the H.V. side & it should be increased gradually to circulate the rated current in H.V. side.

3. Connection should be tight.

4. Do not touch on livewire.

Experiment :4

Aim: - To determine resistance and inductance of Choke.

APPARATUS:-

1)1 phase, 230 V dimmerstat-1 no.

2)0-1 Amp, AC Ammeter- 1 No.

3)0-300 V , AC Voltmeter- 1 No

4)0-300 V ,1 A, Wattmeter-1No

5)Choke 230 V 50 Hz, 0.675 A -1No.

CONNECTIONDIAGRAM:

WATTMETER300 V,1A

THEORY:-

The theory should cover details about following points. 1)Ideal Choke coil

2)Quality factor of inductor

PROCEDURE:-

1) Connect the circuit as shown in figure. 2) Ensure that the dimmerstat is at zero position. 3) Switch on 1-phase ac supply.

4) Increase the output voltage of the dimmerstat slowly.

11

5) Note down the readings of ammeter, voltmeter and wattmeter for various values of output voltages of dimmerstat.

PRECAUTIONS :-1) All connections should be perfectly tight.

2) Do not switch on the supply until and unless the connections are checked by the teacher.

3) Ensure the dimmer stat at zero position and all rheostats to maximum resistance position before switching the supply ON. 4) Avoid error due to parallel while reading the meters. 5) The current flowing through the rheostat should not exceed their ratings.

OBSERVATION & CALCULATION:

Sr.VoltmeterAmmeterWattmeterResistanceZ=V/IXL =

No.ReadingReadingReadingR = W/I2 Z2 R2L(H)

VIW

CONCLUSION:

The calculated values of resistance and inductance of choke coil are found _______

DISCUSSION :- ( Answer any 02 as told by your teacher)

1. What are various losses of choke. 2. What are application of choke.

3. Draw the phasor diagram of choke.

4. If you apply d.c supply instead of a.c supply to the choke, the resistance offered by choke will be same or not. Explain.

REFERENCES:1. Electrical Technology Vol. I by B.L. Thereja.

2. A text book on laboratory experiments in Electrical Engg . by Kharbanda & Tarnekar .

Experiment :5

AIM: - Verification of relationship between line voltage and phase voltage in a 3-Phase star connected balanced load.

APPARATUS:-6) 3 phase, 440 volt dimmerstat -01 no. 7) 0-5 Amp, AC Ammeter -03 no. 8) 0-600 V , AC Voltmeter- 01 No 9) 0-300 V , AC Voltmeter-01 No 10) 0-100 ohm, 5 Amp rheostat 03 no.

CIRCUITDIAGRAM:-

The theory should cover details about following points.

Explanation about star connection with neat labeled diagram. Relationship between and line quantities for star connection.

Expressions for 3 phase active, reactive, and apparent power in terms of line and phase quantities.

Phasor diagram of balanced star connected resistive load.

PROCEDURE:-1.Connect the circuit as shown below.

2.Ensure that the dimmerstat is at zero output position and all rheostats are at maximum resistance position

3.Switch ON the 3-phase AC supply.

4.Increase the output voltage of the dimmerstat slowly up to 150 V ( L-L) 5.Adjust the rheostat position such that all ammeters show same readings that is

creating a balanced load condition. 6.Note the meter readings.

7.Repeat the above procedure for different values of line voltages.

PRECAUTIONS :-

1.All connections should be perfectly tight.

2.Do not switch on the supply until and unless the connections are checked by the teacher.

3.Ensure the dimmer stat at zero position and all rheostats to maximum resistance position before switching the supply ON.

4.Avoid error due to parallel while reading the meters.5.The current flowing through the rheostat should not exceed their ratings.

OBSERVATION & CALCULATION:

Sr.NoLine currentMeasuredPhaseCalculatedThree phase

= Phaseline voltageVoltageline VoltagePower

currentVLVph3 VphP= 3 Vph Iph

IL= Iph

1)

2)

3)

CONCLUSION:

The calculated values of line voltage are closely equal to their measured values . Hence the relation VL= 3 Vph for a star connected balanced load is verified .

DISCUSSION :- ( Answer any 03 as told by your teacher)

Q.1Draw phasor diagram for a 3 phase balanced star connected inductive load.

Q.2 Draw phasor diagram for a 3- phase star connected capacitive load. Q.3 A 3- phase balanced delta connected source having Line voltage

of 440 V is supplying power to a 3-phase star connected load if the per phase impedance of load is 200 ohm . What will be the total power consumed by the load ?

Experiment : 6

LAB #1: IDENTIFICATION OF CIRCUIT COMPONENTS

Breadboards:

In order to temporarily construct a circuit without damaging the components used to build it, we must have some sort of a platform that will both hold the components in place and provide the needed electrical connections. In the early days of electronics, most experimenters were amateur radio operators. They constructed their radio circuits on wooden breadboards. Although more sophisticated techniques and devices have been developed to make the assembly and testing of electronic circuits easier, the concept of the breadboard still remains in assembling components on a temporary platform.

(a)

(b)

Fig. 1: (a) A typical Breadboard and (b) its connection details

A real breadboard is shown in Fig. 1(a) and the connection details on its rear side are shown in Fig. 1(b). The five holes in each individual column on either side of the central groove are electrically connected to each other, but remain insulated from all other sets of holes. In addition to the main columns of holes, however, you'll note four sets or groups of holes along the top and bottom. Each of these consists of five separate sets of five holes each, for a total of 25 holes. These groups of 25 holes are all connected together on either side of the dotted line indicated on Fig.1(a) and needs an external connection if one wishes the entire row to be connected. These breadboard sockets are sturdy and rugged, and can take quite a bit of handling. However, there are a few rules you need to observe, in order to extend the useful life of the electrical contacts and to avoid damage to components. These rules are:

Always make sure power is disconnected when constructing or modifying your experimental circuit. It is possible to damage components or incur an electrical shock if you leave power connected when making changes. Never use larger wire as jumpers. #24 wire (used for normal telephone wiring) is an excellent choice for this application. Observe the same limitation with respect to the size of component leads. Whenever possible, use watt resistors in your circuits. watt resistors may be used when necessary; resistors of higher power ratings should never be inserted directly into a breadboard socket. Never force component leads into contact holes on the breadboard socket. Doing so can damage the contact and make it useless. Do not insert stranded wire or soldered wire into the breadboard socket. If you must have stranded wire (as with an inductor or transformer lead), solder (or use a wire nut to connect) the stranded wire to a short length of solid hookup wire, and insert only the solid wire into the breadboard.

If you follow these basic rules, your breadboard will last indefinitely, and your experimental components will last a long time.

Resistors

Most axial resistors use a pattern of colored stripes to indicate resistance. A 4 band identification is the most commonly used color coding scheme on all resistors. It consists of four colored bands that are painted around the body of the resistor. Resistor values are always coded in ohms (). The color codes are given in the following table in Fig. 1.

Basic Electrical & Electronics Lab2014

Fig. 1: Color codes of Resistor

Capacitors:

You will mostly use electrolytic and ceramic capacitors for your experiments.

Electrolytic capacitors

An electrolytic capacitor is a type of capacitor that uses an electrolyte, an ionic conducting liquid, as one of its plates, to achieve a larger capacitance per unit volume than other types. They are used in relatively high-

current and low-frequency electrical circuits. However, the voltage applied to these capacitors must be polarized; one specified terminal must always have positive potential with respect to the other. These are of two types, axial and radial capacitors as shown in adjacent figure. The arrowed stripe indicates the polarity, with the arrows pointing towards the negative pin.

Fig. 2:Axial and Radial Electrolytic capacitors

Warning: connecting electrolytic capacitors in reverse polarity can easily damage or destroy the capacitor. Most large electrolytic capacitors have the voltage, capacitance, temperature ratings, and company name written on them without having any special color coding schemes.

Axial electrolytic capacitors have connections on both ends. These are most frequently used in devices where there is no space for vertically mounted capacitors.

Radial electrolytic capacitors are like axial electrolytic ones, except both pins come out the same end. Usually that end (the "bottom end") is mounted flat against the PCB and

the capacitor rises perpendicular to the PCB it is mounted on. This type of capacitor probably accounts for at least 70% of capacitors in consumer electronics.

Ceramic capacitors are generally non-polarized and almost as common as radial electrolytic capacitors. Generally, they use an alphanumeric marking system. The number part is the same as for SMT resistors, except that the value represented is in pF. They may also be written out directly, for instance, 2n2 = 2.2 nF.

Fig. 3: Ceramic capacitors

Diodes:

A standard specification sheet usually has a brief description of the diode. Included in this description is the type of diode, the major area of application, and any special features. Of particular interest is the specific application for which the diode is suited. The manufacturer also provides a drawing of the diode which gives dimension, weight, and, if appropriate, any identification marks. In addition to the above data, the following information is also provided: a static operating table (giving spot values of parameters under fixed conditions), sometimes a characteristic curve (showing how parameters vary over the full operating range), and diode ratings (which are the limiting values of operating conditions outside which could cause diode damage). Manufacturers specify these various diode operating parameters and characteristics with "letter symbols" in accordance with fixed definitions. The following is a list, by letter symbol, of the major electrical characteristics for the rectifier and signal diodes.

RECTIFIER DIODES

DC BLOCKING VOLTAGE [VR]the maximum reverse dc voltage that will not cause breakdown.AVERAGE FORWARD VOLTAGE DROP [VF(AV)]the average forward voltage drop across the rectifier given at a specified forward current and temperature.AVERAGE RECTIFIER FORWARD CURRENT [IF(AV)]the average rectified forward current at a specified temperature, usually at 60 Hz with a resistive load.AVERAGE REVERSE CURRENT [IR(AV)]the average reverse current at a specified temperature, usually at 60 Hz.PEAK SURGE CURRENT [ISURGE]the peak current specified for a given number of cycles or portion of a cycle.SIGNAL DIODESPEAK REVERSE VOLTAGE [PRV]the maximum reverse voltage that can be applied before reaching the breakdown point. (PRV also applies to the rectifier diode.) REVERSE CURRENT [IR]the small value of direct current that flows when a semiconductor diode has reverse bias.MAXIMUM FORWARD VOLTAGE DROP AT INDICATED FORWARD CURRENT [V F@IF] the maximum forward voltage drop across the diode at the indicated forward current.

REVERSE RECOVERY TIME [trr]the maximum time taken for the forward-bias diode to recover its reverse biaThe ratings of a diode (as stated earlier) are the limiting values of operating conditions, which if exceeded could cause damage to a diode by either voltage breakdown or overheating.The PN junction diodes are generally rated for: MAXIMUM AVERAGE FORWARD CURRENT, PEAK RECURRENT FORWARD CURRENT, MAXIMUM SURGE CURRENT, and PEAK REVERSE VOLTAGE

Maximum average forward current is usually given at a special temperature, usually 25 C, (77 F) and refers to the maximum amount of average current that can be permitted to flow in the forward direction. If this rating is exceeded, structure breakdown can occur.

Peak recurrent forward current is the maximum peak current that can be permitted to flow in the forward direction in the form of recurring pulses.

Maximum surge current is the maximum current permitted to flow in the forward direction in the form of nonrecurring pulses. Current should not equal this value for more than a few milliseconds.

Peak reverse voltage (PRV) is one of the most important ratings. PRV indicates the maximum reverse-bias voltage that may be applied to a diode without causing junction breakdown. All of the above ratings are subject to change with temperature variations. If, for example, the operating temperature is above that stated for the ratings, the ratings must be decreased.

There are many types of diodes varying in size from the size of a pinhead (used in subminiature circuitry) to large 250-ampere diodes (used in high- power circuits). Because there are so many different types of diodes, some system of identification is needed to distinguish one diode from another. This is accomplished with the semiconductor identification system shown in Fig. 4. This system is not only used for diodes but transistors and many other special semiconductor devices as well. As illustrated in this figure, the system uses numbers and letters to identify different types of semiconductor devices. The first number in the system indicates the number of junctions in the semiconductor device and is a number, one less than the number of active elements. Thus 1 designates a diode; 2 designates a transistor (which may be considered as made up of two diodes); and 3 designates a tetrode (a four -element transistor). The letter "N" following the first number indicates a semiconductor. The 2- or 3-digit number following the letter "N" is a serialized identification number. If needed, this number may contain a suffix letter after the last digit. For example, the suffix letter "M" may be used to describe matching pairs of separate semiconductor devices or the letter "R" may be used to indicate reverse polarity. Other letters are used to indicate modified versions of the device which can be substituted for the basic numbered unit. For example, a semiconductor diode designated as type 1N345A signifies a two -element diode (1) of semiconductor material (N) that is an improved version (A) of type 345.

When working with different types of diodes, it is also necessary to distinguish one end of the diode from the other (anode from cathode). For this reason, manufacturers generally code the cathode end of the diode with a "k," "+," "cath," a color dot or band, or by an unusual shape (raised edge or taper) as shown in Fig. 5. In some cases, standard color code bands are placed on the cathode end of the diode. This serves two purposes:(1) it identifies the cathode end of the diode, and (2) it also serves to identify the diode by number.

Transistors:

Transistors are identified by a Joint Army-Navy (JAN) designation printed directly on the case of the transistor. If in doubt about a transistor's markings, always replace a transistor with one having identical markings, or consult an equipment or transistor manual to ensure that an identical replacement or substitute is used.

There are three main series of transistor codes used:

Codes beginning with B (or A), for example BC108, BC478

The first letter B is for silicon, A is for germanium (rarely used now). The second letter indicates the type; for example C means low power audio frequency; D means high power audio frequency; F means low power high frequency. The rest of the code identifies the particular transistor. There is no obvious logic to the numbering system. Sometimes a letter is added to the end (eg BC108C) to identify a special version of the main type, for example a higher current gain or a different case style. If a project specifies a higher gain version (BC108C) it must be used, but if the general code is given (BC108) any transistor with that code is suitable.

or transistor tester. PRECAUTIONS should be

taken when working with transistors since they

are susceptible to damage by electrical

overloads, heat, humidity, and radiation.

TRANSISTORLEAD IDENTIFICATION

plays an important part in transistor

maintenance because before a transistor can be

tested or replaced, its leads must be identified.

Since there is NO standard method of

identifying transistor leads, check some typical

lead identification schemes or a transistor

manual before attempting to replace a

transistor. Identification of leads for someFig. 6

common case styles is shown in Fig. 6.

Testing a transistor

Transistors are basically made up of two Diodes connected together back-to-back (Fig. 7). We can use this analogy to determine whether a transistor is of the type PNP or NPN by testing its Resistance between the threedifferent leads, Emitter, Base and Collector.

Testing with a multimeter

Use a multimeter or a simple tester (battery, resistor and LED) to check each pair of leads for conduction. Set a digital multimeter to diode test and an analogue multimeter to a low resistance range.

Test each pair of leads both ways (six tests in total):Fig. 7: Testing an NPN transistorThe base-emitter (BE) junction should behave like a diode and conduct one way only. The base-collector (BC) junction should behave like a diode and conduct one way only.

The collector-emitter (CE) should not conduct either way.

The diagram shows how the junctions behave in an NPN transistor. The diodes are reversed in a PNP transistor but the same test procedure can be used.

Transistor Resistance Values for the PNP and NPN transistor types

Between Transistor TerminalsPNPNPN

CollectorEmitterRHIGHRHIGH

CollectorBaseRLOWRHIGH

EmitterCollectorRHIGHRHIGH

EmitterBaseRLOWRHIGH

BaseCollectorRHIGHRLOW

BaseEmitterRHIGHRLOW

6

Experiment : 7

AIM: To study the input & output waveforms of rectifier.

(a): HALF-WAVE RECTIFIER CIRCUIT WITHOUT AND WITH

FILTER

Objectives:

1. To construct a half-wave rectifier circuit and analyze its output.

2. To analyze the rectifier output using a capacitor in shunt as a filter.

Overview:

The process of converting an alternating current into direct current is known as rectification. The unidirectional conduction property of semiconductor diodes (junction diodes) is used for rectification. Rectifiers are of two types: (a) Half wave rectifier and (b) Full wave rectifier. In a half-wave rectifier circuit (Fig. 1), during the positive half-cycle of the input, the diode is forward biased and conducts. Current flows through the load and a voltage is developed across it. During the negative half-cycle, it is reverse bias and does not conduct. Therefore, in the negative half cycle of the supply, no current flows in the load resistor as no voltage appears across it. Thus the dc voltage across the load is sinusoidal for the first half cycle only and a pure a.c. input signal is converted into a unidirectional pulsating output signal.

Fig.1: Half-wave rectifier circuit

Since the diode conducts only in one half-cycle (0-), it can be verified that the d.c. component in the

output is Vmax/, where Vmax is the peak value of the voltage. Thus,Vdc Vmax 0.318Vmax

The current flowing through the resistor,IdcVdcand power consumed by the load, P Idc2 R .

R

Ripple factor:

As the voltage across the load resistor is only present during the positive half of the cycle, the resultant voltage is "ON" and "OFF" during every cycle resulting in a low average dc value. This variation on the rectified waveform is called "Ripple" and is an undesirable feature. The ripple factor is a measure of purity of the d.c. output of a rectifier and is defined asrVacVrms2 Vdc2Vrms20.52

11 1.21

VdcVdc2Vdc20.318

output

In case of a half-wave rectifier Vrms = Vmax/2 = 0.5Vmax. (How?)

Rectification Efficiency:

Rectification efficiency, , is a measure of the percentage of total a.c. power input converted to useful d.c. power output.

d .c. power delivered to load a.c. power at inputVdc Idc Vac Iac

Idc2 R0.318Vmax20.405

I2(r R)0.5Vmax2rdrd

acd11

R

R

Here rd is the forward resistance of diode. Under the assumption of no diode loss (rd