1 March 2020

Transistor Interview Short Question Answer - 1

1
What is meaning of the transistor?


Transistor
  • The transistor is a three terminal semiconductor device in which one type of semiconductor material (either P or N) is sandwich between other types of semiconductor material (either N or P) of opposite polarity.


2
Why the transistor is called as Bipolar junction transistor?


Bipolar junction transistor
  • The current conduction is the transistor is done by holes as well as electrons therefore it is called as Bipolar junction transistor.


3
Describe the main function of the transistor.


To amplify weak signal

4
How many PN junction the transistor consists of?


Two

5
How many terminals the transistor consists of?


Three terminals – Emitter, Base and Collector

6
Why the collector terminal is made larger than the emitter and base?


Because most of the heat produced across collector junction

7
Whether the holes or electrons are responsible for collector cut off current in the transistor?


  • The collector cut off current flows due to minority charge carriers. The collector cut off current flows due to holes in the NPN transistor and electrons in the PNP transistor.


8
What are the doping levels in the transistor?


The transistor consists of three terminals.
Emitter
  • The emitter is heavily doped therefore it supplies large numbers of charge carriers to the base and collector of the transistor.

Base
  • The base is lightly doped and very thin, therefore only small current passes through the base.

Collector
  • The collector is moderately doped therefore the most of the current passes through it which is supplied by the emitter. The emitter current ( IE ) is sum of the base current ( IB ) and collector current ( IC ).

IE = IB + IC

9
Explain : Current amplification factor α


Current amplification factor α
  • The ratio of change in collector current to the change in emitter current at constant collector base voltage in the Common Base transistor is known as current amplification factor.

                 α  = dIC / dIE at constant VCB

10
Explain : Current amplification factor β


Current amplification factor β
  • The ratio of change in collector current to the change in base current at constant collector emitter voltage in the Common Emitter transistor is known as current amplification factor.

             β = dIC / dIB at constant VCE

11
Explain : Current amplification factor  γ                                               


Current amplification factor γ
  • The ratio of change in emitter current to the change in base current at constant collector emitter voltage in the common collector transistor is known as current amplification factor.

              γ = dIE / dIB at constant VCE

12
Describe the different configurations are used in the transistor.


Different configuration of the transistor
  • As the transistor consists of three terminals. The transistor must be one common terminal in order to supply input and get output of the transistor. The following  three types of configurations are used in the transistor

       Common emitter (CE) configuration
       Common base (CB) configuration
       Common collector (CC) configuration

13
What is practical value of α and β?


  • The practical value of α is in the range of 0.9 to 0.99 and β is in the range of 20 to 500. The value of α is increased by making base thin and lightly doped.


14
Explain : Bias voltage. Describe the function of bias voltage in the transistor.


Bias voltage
  • The DC voltage at the input side of the transistor is called as bias voltage.
  • The emitter base circuit is always forward biased for faithful amplification. 
  • The emitter base becomes reverse biased during negative half cycle of the signal without bias voltage. 
  • Therefore magnitude of the bias voltage should be such that it always keep the emitter base circuit forward biased.


15
What is ICBO?
    OR
What is meant by collector leakage current in the transistor?


Collector leakage current
  • The flow of the collector current while input or emitter circuit kept open circuited in the common base transistor is called as collector leakage current. It is donated by ICBO.

OR
  • The flow of the collector current while input or base circuit is kept open circuited in the common emitter transistor is called as collector leakage current. It is donated by ICEO.


16
Write the relation between current amplification factor α and β


Relation between current amplification factor α and β

β = α / (1 – α )

OR

α = β / ( 1 + β )

17
What is zero signal collector current in the transistor?


Zero signal collector current
  • It is defined as the collector current flows when the input circuit of the transistor is forward biased by only battery or direct voltage.

OR
  • It is defined as the flow of collector current when no signal is applied, the input circuit is forward biased by battery or direct voltage.     


18
Describe the main factor affecting value of collector leakage current.


Factor affecting collector leakage current
  • The value of collector leakage current is neglected in the low power transistor whereas it is in the range of micro – ampere for high powered transistor. 
  • The collector leakage current depends upon the temperature and its value increases rapidly with increase in the temperature.


19
Explain the term :  Cut off region, Saturation region,  Active region


Cut off region
  • The transistor is operated in the cut off region when base current is equal to zero.

Saturation region
  • The collector and emitter terminal of the transistor are shorted together. The transistor behaves like closed switch between collector and emitter.

Active region
  • The region between cut off and saturation is called as active region of the transistor.  
  • The base – emitter of the transistor always forward biased whereas the collector – base junction remains reverse biased in this region under all conditions.


20
Describe the working of two back to back diodes in the cut off, active and saturation region of the CE transistor?


Status of back to back diode in the transistor
  • Cut off : Emitter diode OFF, Collector diode OFF
  • Active : Emitter diode ON, Collector diode OFF
  • Saturation : Emitter diode ON, Collector diode ON




You may also like :

No comments:

Post a Comment