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SUBMMITTED BY-SUDHIR KUMAR SUDHAKAR

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CONTENT:-1.Introduction

2.Definition & Types3.Construction of npn & pnp Transistor

4.Working of pnp & npn Transistor

5.Configuration of circuit connection->Common base->Common emitter->Common collector

6.Advantages of Transistor->Transistor as a switch

->Transistor as an amplifier->Transistor as an oscillator

7.Disadvantages of Transistor8.Testing of Transistor

9.Summary

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Invented in 1948 by J. Barden and W.H.Brattain, USA

“Trans” means the signal transfer property of

the device while “istor” classifies it as a solidelement in the family of the resistors.

It is capable of achieving of amplification ofweak signals in a fashion comparable and oftensuperior to that realized by vacuum tubes.

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1.PNP TRANSISTOR:-IT CONSISTS OF A VERYTHIN SLICE OF N-TYPESEMICONDUCTORSANDWICHED B/W TWOSMALL BLOCK OF P-TYPE

SEMICONDUCTOR.

2.NPN TRANSISTOR:-IT CONSISTS OF A VERY THIN

SLICE OF P-TYPESEMICONDUCTOR SANDWICHEDB/W TWO SMALL BLOCK OF N-TYPE SEMICONDUCTOR.

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WORKING OF

pnpTRANSISTOR :-

The small current whichleaves the base terminalB is called the base

current (Ib).While the

large current whichleaves the collector

current (Ic).Both thesecurrents combines toenter the emitter

terminal (E) & constitutethe emitter current (Ie).

i.e Ie=Ib+Ic

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 WORKING OF

npnTRANSISTOR

:-

The small currententering the baseterminal be in the base

current Ib,while the

large current enteringthe collector terminal C

is the collector current Ic.Both these currentcombines to leave the

emitter terminal E andconstitute the emittercurrent.

i.e- Ie=Ib+Ic 

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 Transistor as a switch:-BJT used as an electronic switch, in grounded-emitter configuration.Transistors are commonly used as electronic switches, both for high-power applications such as switched-mode power supplies and for low-

power applications such as logic gates.In a grounded-emitter transistor circuit, such as thelight-switch circuitshown, as the base voltage rises the base and collectorcurrent rise

exponentially, and the collector voltage drops becauseof the collectorload resistor. The relevant equations:

VRC = ICE × RC, the voltage across the load (thelampwithresistanceRC)VRC + VCE = VCC, the supply voltage shown as 6V

If VCE could fall to 0 (perfect closed switch) then Ic could go no higherthan VCC / RC, even with higher base voltage and current. The transistoris then said to be saturated. Hence, values of input voltage can bechosen such that the output is either completelyoff,[20] or completely on. The transistor is acting as a switch, and thistype of operation is common in digital circuits where only "on" and "off"values are relevant.

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Transistor as an oscillator:-The oscillatory circuit or element, also called the tankcircuit, consists of an inductive coil of inductance Lconnected inparallel with a capacitor of capacitance C. The frequencyof oscillation in the circuit depends upon the values of Land C. The actual frequency of oscillation is the resonantor natural frequency and is given by the expressionf = 1 / 2∏√LC Hz , where L is inductance of coil inhenrys, and C is the capacitance of capacitor in farads.The electronic amplifier receives dc power from thebattery or dc power supply and converts it into ac powerfor supply to the tank circuit. The oscillations occurringin the tank circuit are applied to the input of theelectronic amplifier. Because of the amplifying propertiesof the amplifier, we get increased output of these

oscillations. This amplified output of oscillations isbecause of dc power supplied from the external source (abattery or power supply). The output of the amplifier canbe supplied to the tank circuit to meet the losses.The feedback network supplies a part of output power tothe tank or oscillatory circuit in correct phase to aid the

oscillations. In other words the feedback circuit providespositive feedback.

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Transistor as an amplifier:-

 Amplifier circuit, common-emitter configuration.

The common-emitter amplifier is designed so that a small change

in voltage in (V in) changes the small current through the base of 

the transistor; the transistor's current amplification combinedwith the properties of the circuit mean that small swings in V in 

produce large changes in V out.

Various configurations of single transistor amplifier 

are possible, with some providing current gain,

some voltage gain, and some both.From mobile phones to televisions, vast numbers

of products include amplifiers for sound reproduction,

radio transmission, and signal processing. The first

discrete transistor audio amplifiers

barely supplied a few hundred milliwatts, but power and audio fidelity gradually increased as better 

transistors became available and amplifier 

architecture evolved.

Modern transistor audio amplifiers of up to a

few hundred watts are common and relatively

inexpensive

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Disadvantages:-

1. Silicon transistors typically do not operate at voltages higher than about 1000 volts (SiC devices can be operated as high as 3000 volts). In contrast, vacuum tubes have

been developed that can be operated at tens of thousands of volts.

2.High-power, high-frequency operation, such as that used in over-the-air televisionbroadcasting, is better achieved in vacuum tubes due to improved electron mobility ina vacuum.

3.Silicon transistors are much more vulnerable than vacuum tubes to anelectromagnetic pulse generated by a high-altitude nuclear explosion.

4.Silicon transistors when amplifying near the saturation point typically fail and createdistortion. Vacuum tubes under the same stress conditions fail more gradually and

create a distortion that is more pleasant to the ear.

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