electronic devices and circuits lab viva questions part3 Bipolar Junction Transistor

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BJT:

1.What is a transistor?

A junction transistor is simply a sandwich of one type of semiconductor material between two layers of the other type. A transistor is a three terminal current sensing device. It can be looked upon as two pn junction placed back to back. The three terminals are named as emitter base & collector.

2.What is BJT, explain about its terminals, what are types, and which type is better, why?

Bipolar junction Transistor in this corrent flows due to two polarities(electrons, holes), NPN or PNP type ,NPN is best because mobility of electrons is more than mobility of holes so electron current is more.

3.What are the different configurations of transistor?

a) Common Emitter (CE) b) Common Base (CB) c) Common collector (CC)

4.What is Common Base configuration?

base is common between input and output circuits. emitter-base terminal input signal is applied and in collector-base terminal output is taken from it.

5.What are the characteristics of CB?

since it has a low input resistance and a high output resistance, current gain of less than 1. The input and output signals in the common-base circuit are in phase

6.What is transistor and why it is called like that?

Because it transfers the input signal from low resistance to high resistance

7.Define α, β, γ, what is the relation between them?

These are current gains in CB,CE,CC configurations respectively, ; αγ=

8.Compare CE,CC,CB configurations?

9.Define cut-off, active and saturation regions?

Cut off- both emitter Je, collector Jc junctions in Reverse bias

Active – Je forward, Jc Reverse bias

Saturation – Je,Jc in forward bias

10.What do you understand by input and output characteristics?

characteristics gives the information about input resistance and output resistances.

11.Explain the physical structure of a BJT?

One N type material is sandwiched between two P type materials or One P type material is sandwiched between two N type materials , widths (C>E>B), doping concentration(E>C>B)

12.Explain Early Effect?

The variation in base width of BJT due to variation in the applied base- collector voltage

13.Why does the emitter current increase with increase in reverse bias at the collector junction?

Due to breakdown in collector junction

14.What is meant by collector reverse saturation current?

Minority carriers flow throw collector junction when it is connected in reverse bias

15.Write the collector current expression for BJT in CB configuration?

Cutoff region Ic=0

Active regionIc= βIb

Saturation   Ic<βIb

16.Give the values of V_{CE Sat} for the transistor BC107.

Vce sat=0.2v

17.Explain the performance of the transistor as    an   electronic switch?

When transistor is in cut off it works as off switch, when transistor is in saturation it works as on switch

18.Is the BJT Transistor a current controlled device or a voltage-controlled device?

Current controlled current device

19.Draw the symbolic representations of NPN and PNP transistors.

20.Sketch the characteristics of a BJT in Common-Emitter Configuration.

21.Why is it called Common-Emitter configuration?

Emitter terminal is common to input and out put

22.What is a “load-line”?  What is its significance?  Differentiate between a.c. load line and d.c. load line.

Load line specifies the operating point, Dc load line is the line based on the relation between output voltage and currents when input is zero, Ac load line is the line which pocess through the Q point with slope of (-1/Rac, Rac= Rc//Rl)

23.What is meant by Q- point?

It specifies the correct biasing at which gives required amplification

24.What is Biasing and why it is needed for transistor?

The process of giving proper supply voltage and resistances for obtaining desired operating point

25.What are the methods of transistor biasing, which type is best and why?

Fixed bias, Emitter feedback bias, Collector to base bias, Collector- emitter feedback bias, self bias(voltage divider bias), in these all self bias is best because it is more stable for a greater range of input signal

26.What is thermal Runaway?

It is a situation where an increase in temperature changes the conditions in a way that causes a further increase in temperature.

27.Thermistor temperature co efficient is?

It may be + or – based on the material used.

28.Define two port networks, types, which one is best for bjt and why?

Z, Y, h, g, ABCD parameters, best one is hybrid parameters bczthethese gives all parameters about amplifier like input, output impedance, voltage and current gains.

29.What are the typical h-parameter values for a transistor?

30.Draw the H parameter equivalent circuit?

31.Compare CB,CE,CC amplifiers, and what are the applications?