Electronic Assignment

7/31/2019 Electronic Assignment

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SUMMER TRAINING

REPORT ON

FROM 07/06/2010 TO 09/07/2010

SUBMITTED TO : SUBMITTED BY:RAJAN VERMAM.E. (3rd SEM)ROLL NO.90191125089

Practical 1: Introduction to Electronics:


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What is Electronics?

The word electronics is derived from electron mechanics which means the study of the behavior of an

electron under different conditions of externally applied fields.

The Institution of Radio Engineers (IRE) has given a standard definition of electronics in

proceedings of IRE as that field of science and engineering, which deals with electron devices and their

utilization. Here, an electron device is a device in which conduction takes place by the movement ofelectrons through a vacuum, a gas, or a semiconductor.

ELECTRONIC COMPONENTS:

All electronics circuits, however complicated, contain a few basics components. There are only five

components that are mostly used in all circuits:-

(i) Three passive components

(ii) Two active components.

Resistors, capacitors and indicators are called Passive components. These components by

themselves are not capable of amplifying or processing an electrical signal. These components are as

important, in an electronic circuit, as active components are without the aid of these components atransistors cannot be made to amplify signals.

The components which by themselves are capable of amplifying or processing an electrical signal

are called Active components. There are many active components used in electronic circuits. But all the

active devices or components can be broadly classified into two types: vacuum tube and gas tubes. These

devices came prior to the semiconductors devices because of their advantages; the semiconductors devices

are replacing the tube devices in almost all electronic applications.

Applications of Electronics:

Life today offers many convince which involve the use electronic devices. It is used in communication andentertainment. Arithmetic calculations, desk calculators are commonly used in banks, solving math

problems etc. electronically controlled systems, using suitable timers, are used for heating and welding in

the industry. Oscillographs are used for studying muscle action.

Types of Electronic components:

1. Passive components

2. Active components

1. Passive Components: The passive components are of three types, which are discussed below:

a) Resistors:Resistors are the passive components. The flow of charge or material, encounters an opposing force.

This opposing force is known as resistance of the material. It is measured in ohms. The circuit symbol

for resistance is R. Resistance is deliberately introduced in some parts of an electronic circuit. The

device to do this is called resistors. The resistances of the resistors depend upon their color coding.

Resistors are of three types:

Fig. Resistor


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Color 1st band 2nd band 3rd band (multiplier) 4th band (tolerance) Temp. Coefficient

Black 0 0 100

Brown 1 1 101 1% (F) 100 ppm

Red 2 2 102 2% (G) 50 ppm

Orange 3 3 103 15 ppm

Yellow 4 4 104 25 ppm

Green 5 5 105 0.5% (D)

Blue 6 6 106 0.25% (C)

Violet 7 7 107 0.1% (B)

Gray 8 8 108 0.05% (A)

White 9 9 109

Gold 101 5% (J)

Silver 102 10% (K)

None 20% (M)

Table: Color code of Resistors

Fig. Resistance measuring using color coding

b) Capacitors:


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Capacitor consists of two conducting plates, separated by an insulating

material known as dielectric. Since the two plates of capacitor can be of

different conducting material and dielectric may be of different insulating

material, there are many types of capacitors. Capacitors may be fixed or

variable. Some types of capacitors are given below:

Fig. Capacitors

(i) Mica Capacitors:Mica capacitor are constructed from plates of aluminum (Al) foil separated by sheets of mica plates

are connected to two electrodes. These have excellent characteristics under stress of temperaturevariations and high voltage. These rated at 500V capacitors ranges from 5-10000 p.f. Its leakage

current is very small (Rleakage is about 1000 M ). FIG

(ii) Ceramic Capacitors:Ceramic capacitors are made in many shapes sizes. A ceramic

disc is coated on two sides with a metal, such as copper or

silver. These coatings act as the two plates. Ceramic capacitors

are very versatile. Their working voltage ranges from 3V to

6000V. The capacitance ranges from 3p.F to about 2F.

Ceramic capacitors have a very low leakage currents (Rleakage is

about 1000M) and can be used in both DC and AC circuits.

Fig. Ceramic Capacitors

(iii) Paper Capacitors:The capacitor consists of two metal foils separated by strips of paper. This paper is impregnated with a

dielectric material such as wax, plastic or oil. These have capacitance ranging from 0.0005F to

several f and are rated from 100V to several thousand volts. They can be used for both dc and ac

circuits. Its leakage resistance is of the order of 100M.

(iv) Electrolytic Capacitors:

Electrolytic capacitors are commonly used in situations where alarge capacitance is required. These are extremely varied in their

characteristics. The capacitance value may range from 1F to

several thousand microfarads. The voltage rating may range from

1V to 500V. The electrolytic capacitor consists of an aluminum-

oxide film covering on one side. The aluminum plate serves as

the positive plate and the oxide as the dielectric. The capacitor

should be properly connected so that the applied voltage

encounters the high resistance. A new type of electrolytic

capacitor is the tantalum capacitor. It has an excellent

capacitance-to-size ratio.

Fig. Electrolytic Capacitors

(v) Variable Capacitors:In some circuits such as tuning circuit, it is desirable to be

able to change the value of capacitance readily. This is

done by means of a variable capacitor. The most common

variable capacitor is the air-gang capacitor. The dielectric

for this capacitor is air. By rotating the shaft at one end, the

common area between the movable and fixed set of platescan be changed. The greater the common area, the larger

the capacitance.

Fig. Air-gang capacitor (variable)


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c) Inductors:When current flows through a wire that has been coiled, it generates a magnetic field. This magnetic

field reacts so as to oppose any change in the current. This reaction of the magnetic field, trying to

keep the current flowing at a steady rate, is known as inductance; and the force it develops is called

induced emf. The electronic component producing inductance is called an inductor. The inductance ismeasured in henrys (H). All inductors, like resistors and capacitors, can be listed under two general

categories: fixed and variable. Different types of inductors are available for different applications.

(i) Filter Chokes:These are the inductors used in smoothing the pulsating current produced by rectifying AC into DC.

A typical filter choke has many turns of wire wound on an iron core. To avoid power losses, the core

is made of laminated sheets of E-shapes and I-shapes. Many power supplies use filter chokes of 5 to

20 H, capable of carrying current up to 0.3 A.

FIG

(ii) Audio-frequency Chokes:Audio frequency chokes (AFC) are used to provide high impedance to audio frequencies (such as 60

Hz to 5 Hz). Compared to filter chokes, they are smaller in size, and have lower inductance. Chokes

having still smaller inductance are used to block the radio frequencies.

FIG

(iii) Variable Inductors:Variable inductors are used in tuning circuits for radio frequencies. The permeability-tuned variable

coil has a ferromagnetic shaft. This shaft can be moved within the coil to vary the inductance. Theyare also known as Radio frequency chokes.

FIG

2. Active Components: The active components are discussed below:

a) Transistors:A semiconductor device consisting of two pn junctions formed by sandwiching

either p-type or n-type semiconductor between a pair of opposite types is

known as transistor.A transistor is basically a silicon or germanium crystal containing three

separate regions. It can be either NPN-type or PNP-type. It has three regions.

The middle region is called the base and the two outer regions are called the

emitter, and collector.

Fig. Transistor

Emitter:The section on one side of the transistor that supplies a large number of majority carriers is called

emitter. The emitter is always forward biased with respect to base so that is can supply a large number

of majority carriers to its junction with the base. Since emitter is to supply or inject a large amount of

majority carriers into the base, it is heavily doped but moderate in size.

Collector:The section on the other side of the transistor that collects the major portion of the majority carriers

supplied by the emitter is called collector. The collector base junction is always reverse biased. Its


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main function is to remove majority carriers from its junction with the base. It is moderately doped

and some what bigger in sizes than emitter so as to dissipate heat generated.

Base:The middle section, which forms two pn junctions between emitter and collector, is called base. The

base forms two circuits, one input circuit with emitter and the other output circuit with collector. The

base-emitter junction is forward biased, providing low resistance for the emitter circuits. The base-collector junction is reverse biased, offering high resistance path to the collector circuit. The base is

lightly doped and very thin so that it can pass on most of the majority carriers supplied by the emitter

to the collector.

The transistors can be of two types as:

(i) NPN Transistors

(ii) PNP Transistors

(i) NPN Transistors:A transistor in which two blocks of n-type semiconductor are separated by a thin layer of p-type

semiconductor is known as NPN transistor. In npn transistors, the emitter base junction is forward

biased while collector base junction is reversed biased. The forward biased voltage is quite small,

whereas, reverse biased voltage is considerably high. In npn transistor, the electrons control the flow

of current inside as well as outside the transistor.

(a) (b)

Fig. (a) NPN Transistor; (b) schematic symbol of NPN Transistor

(ii) PNP Transistors:A transistor in which two blocks of p-type semiconductor are separated by a thin layer of n-type

semiconductor is known as PNP transistor. In pnp transistors, the emitter base junction is forward

biased while collector base junction is reversed biased. The forward biased voltage is quite small,

whereas, reverse biased voltage is considerably high. In pnp transistor current flows in the external

circuit due to electrons and inside the transistor due to holes.

(a) (b)

Fig. (a) PNP Transistor; (b) schematic symbol of PNP Transistor

Construction of Transistors:


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The construction of transistors has undergone a great many changes and improvements. A number of

different methods of manufacturing transistors have been developed. The descriptions of few of them are

given below:

(i) Silicon Planer Transistors:In this transistor is that the PN junction is buried under a layer of silicon dioxide. The layer protects

the pn junction from impurities. These used more widely because of their higher voltage rating, greater

current and less temperature sensitivity.

(ii) F.E.T:FET stands for Field Effect Transistor. It is a three

terminal device. The current flow because only one

type of carriers (electrons in n-channels or holes in p-

channels) and is controlled by the effect of electric

field. Its operation depends upon the flow of majority

carriers only i.e. the current conduction in this case is

either by electrons or holes. The current flows from

source to drain terminal.

Fig. A p-channel Field Effect Transistor

(iii) MOSFET:MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor. In this, oxide layer acts as

dielectric between a conductor. It is a three terminal device. The three terminals are source, gate and

drain. In this device, the gate is insulating from the channel and, therefore, sometimes it is also known

as Insulated Gate FET (IGFET). Its input impedance is higher than JFET because of this oxide layer,

which is an insulator.

Fig. MOSFET: (a) Cross section (b) schematic symbol

(iv) JFET:JFET stands for Junction Field Effect Transistor. It can be of N-channel or of P-channel type. They

have three terminals gate, drain and source. The gate terminal is analogous to the base of a BJT. This

is used to control the current flow from source to drain. Thus, source and drain terminals are

analogous to emitter and collector terminal respectively, of a BJT (Bipolar Junction Transistor).They

are used in various circuits and applications. They are based upon field and the operation of JFET

involves a flow of majority carriers.

(a) Schematic Symbol (b) Physical Diagram (a) Schematic Symbol (b) Physical Diagram


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Fig. N-channel JFET Fig. P-channel JFET

b) Diodes:When p-type and n-type semiconductors are joined together, they form a junction called pn-junction.

Such a p-n junction makes a useful device called semiconductor diode. It is also known as crystal

diode since it is grown out of crystal (like germanium or silicon). The semiconductor diode has two

terminals. Diode is a device, which conducts current only in one direction (forward biased) i.e. when

terminals connected to the bar. However, when it is reversed biased, practically it does not conduct

any current through itself.

(a)

Fig. (a) Diodes; (b) Symbol of diode

The main types of diodes used in electronic circuits are given below:

(i) Signal Diodes

(ii) Power Diodes

(iii)Zener Diodes

(iv)Photo Diodes

(v) Light-Emitting Diodes (LEDs)

(i) Signal Diodes:These diodes are not requires to handle large currents and voltages. The usual requirements are a large

reverse resistor forward resistance ratio and a minimum of junction capacitance. Some are the best

suited to a particular type of circuit application, such as a radio wave detector, or as an electronic

switch in logic circuitry.

(ii) Power Diodes:

Power diodes are usually silicon diodes. A power diode must have a forward resistance as low aspossible. This helps in reducing the voltage drop across the diode when a large forward current flows.

Power diodes are used in rectifiers. The important parameters are the peak inverse voltage, the

maximum voltage or forward current.

(iii) Zener Diodes:A specially designed silicon diode, which is optimized to operate in

the breakdown region, is known as Zener diode. In this diode, the

doping concentration is quite large and they are made to work in the

reversed breakdown region. The maximum current, which can be

flow through it, depends on the break down voltage and power rating.

It is always connected in reversed biased.

Fig. Symbol of Zener diode


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(iv) Photo Diodes:The diode through which current flows when light is incident on it, is called photo diode. It is a

semiconductor PN junction kept in a scaled plastic or glass casing. It is connected in reverse biasing.

They are used in optical communication signals, light based switches etc. In this diode, some current is

also obtained even when no light is incident. It is called Dark current. It is due to the thermal motion

of minority charge.

(a) (b)

Fig. Photo Diode: (a) Schematic Symbol; (b) Cross Section

(v) LED (Light Emitting Diodes):It is heavily dope p-n junction diode whose band gap is very large and lies in the visible region of E-M

spectrum. Their reverse breakdown voltage is very small so these are never used in reversed mode.

They are always connected in forward biased mode and when a large amount of current flows through

it, the electron-hole semi combination takes place and energy is emitted the form of visible radiation.

They consume low power. These are small in size and have very long life.

Fig. Light Emitting Diode (LED): (a) Schematic Symbol; (b) Flat side and short lead of device correspond

to cathode; (c) Cross section of Led die


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Practical 2: Introduction to CRO:

Cathode-Ray Oscilloscope (CRO) is a common laboratory instrument, which is basically a very fast X-Y

plotter that provides accurate time and amplitude measurements of voltage signals over a wide range of

frequencies. The stylus of this plotter is a luminous spot, which moves over the display area in

response to input voltages. It is use for the display of waveforms and helps to see what is happening in each

part of electronic circuit. The heart of the oscilloscope is the Cathode-ray Tube (CRT). The rest of the

instrument consists of circuitry necessary to operate the CRT.

Block diagram of a CRO:A block diagram of CRO shows the various subsystems. These subsystems are:

(i) The vertical deflection system.(ii) The horizontal-deflection system, including the time base generator and synchronization

circuitry.

(iii) The CRT; and

(iv) The high voltage and low voltage power supplies

The vertical deflection system consists of an input attenuator and a number of amplifier stages. The

attenuator can control the gain of the vertical amplifier. The waveform to be displayed is fed to this y-input.

The horizontal deflection system provides the voltage for moving the beam horizontally. It includes the

number of amplifier stages, the gain of which can be controlled. It has a sawsmooth oscillator, or a time

base generator. Also include in this subsystem is a synchronization circuit. The purpose of this circuit is to

start the horizontal sweep at a specific instant, with respect to the waveform under observation. In additionto the internal sweep, there is a provision for the external horizontal inputs (or x-inputs). Either one may

select the internal sweep voltage or any other voltage fed externally for deflecting the beam horizontally.

Basically, the operation of the vertical section does not affect the horizontal section, and vice versa. When

operated together, they will display the incoming signal on the screen of the CRO.

Front Panel Controls of a General-Purpose CRO:The front panel of Aplab Solid-State Oscilloscope, Type DC-15. it is the general-purpose oscilloscope

manufactured by Applied Electronic Limited, Thana, India. The bandwidth of its vertical amplifier ranges

from DC to 15 MHz. The time base and trigger facilities provide a sweep speed ranging from 0.2 s/cm to

50 ms/cm. Waveform can be trigged from 1Hz to 20 MHz and presented with complete stability. The scope

consumers only 55W of power at 220 V and 50 Hz.

General:

(i) ON POWER: It is toggle switch meant for switching on power. In on position, power issupplied to the instrument and neon lamp glows.


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