Important Short Questions and Answers: Semiconductor Devices And Applications

SEMICONDUCTOR DEVICES AND APPLICATIONS

1) Define Transistor

Transistor consists of two junctions formed by sand witching either P-type or N-type semiconductor between a pair of opposite types.

2). Write the current amplification factor for a CB transistor.

α = Change in Collector Current / at constant VCB Change in emitter current

3) Write the formula for input resistance in a CB transistor Input resistance = Change in base - emitter voltage /

Change in emitter current/at constant VCB

4). Write the current amplification factor for a CE transistor. b = Change in Collector Current /

Change in base current at constant VCE

5). Define transistor action.

A transistor consists of 2 coupled PN junctions. The base is a common region to both junctions and makes a coupling between them. Since the base regions are smaller, a significant interaction between junctions will be available. This is called transistor actions.

6).Define delay time

It is defined as the time required for the current to rise from 0 to 10% of its maximum value.

7). Define rise time

It is the time required for the current to rise from 0 to 90 percentage of the maximum

value.

8). Define turn-on time

It is the time required for the current to rise from 0 to 90 percentage of the maximum value ton = td + tr

9).Define fall time

It is the time required for the Collector current to fall from 90 to 10 percentage of Ics.

10).Define Storage time

It is the time required to fall from 100 to 90 percent of Ics.

11).Define turn-off time

It is the time required to fall from 100 to 90 percent of Ics. Toff=ts+tr

12).Define hybrid parameters.

Any linear circuit having input and output terminals can be analysed by four parameters(one measured on ohm, one in mho and two dimensionless) called hybrid or hparameters.

13). What are the use of h - Parameters?

It perfectly isolates the input and output circuits. Its source and load currents are taken into account.

14).Define power transistors

Power transistors are those which handles a large amount of current and also dissipates large amount of power across collector base junction.

15).Define current amplification factor in CC transistor. g =Change in emitter current

Change in base current / at constant VCE

16 )Which is the most commonly used transistor configuration? Why? The CE Configuration is most commonly used. The reasons are

^Ø   High Current gain

^Ø   High voltage gain

^Ø    High power gain

^Ø   Moderate input to output ratio.

17)           What are the values of input resistance in CB, CE & CC Configuration

CB - Low about 75

CE - Medium About 750

CC- Very high about 750

18)           Write the voltage and current equation for hybrid parameters.

V₁ = h₁₁i₁ + h₁₂V₂

I2 = h21i1 + h22V2

19) What are the values of h-parameters?

h₁₁ = V₁/ i₁

h₁₂ = V₁ / V₂ h₂₁ = i₂ / i₁ h₂₂ = i₂ / V₂

20)           h – parameter is applied to linear circuit True or False. True

21)           What are the advantages of transistors?

1.Low operating voltage. 2.Higher efficiency. 3.Small size and ruggedness

22)           What are the types of transistors?

^Ø   Unipolar junction transistor

^Ø   Bipolar junction transistor.

23)           What are the basic techniques used to construct a transistor?

^Ø   Grown type.

^Ø   Alloy type.

^Ø   Electro chemically etched type

^Ø   Diffusion type.

^Ø   Epitaxial type.

Ø

24)What is mean by characteristics of transistor?

The interrelation of the various currents and voltages can be plotted graphically which are commonly known as the characteristics of transistor.

25)What are the types of BJT?

^Ø   n-p-n type.

^Ø   p-n-p type.