2 March 2020

Transistor Power Amplifier Interview Question Answer


1
Describe the function of the voltage amplifier.


Voltage amplifier                                                 
  • The function of the voltage amplifier is to raise the voltage level of the input signal to desired value. 
  • The first stage of the multistage amplifier should be voltage amplifier.


2
Describe the function of the Power amplifier.


Power amplifier
  • The function of the Power amplifier is to raise the power level of the input signal to desired value. 
  • The last stage of the multistage amplifier should be power amplifier.


3
What is range of frequencies that human ear can hear?


The human ear can hear the range of audio frequency from 20 Hz to 20 kHz.

4
Describe the main difference between small signal amplifier and large signal amplifier.


Small signal amplifier
  • Small alternating input signal
  • It operates in the linear portion of the output characteristics.
  • No distortion in the output. 

Large signal amplifier
  • Large alternating input signal.
  • It produces large alternating power output.
  • The main function of the large signal amplifier impedance matching.


5
Explain the term : Collector efficiency. Describe the importance of it.


Collector efficiency
  • The ratio of the AC power output to the DC input power is known as collector efficiency. 
  • If the input DC power is 20 W and output AC power is 10 W, the collector efficiency is 50%. 
  • The collector efficiency must be higher in order to achieve large output power. 
  • The power amplifier converts DC input power in to AC output power. 
  • Therefore the collector efficiency measures the effectiveness of the power conversion from DC to AC.


6
Explain the term : Distortion


Distortion
  • When the shape of the output signal is not exactly same at that of input signal, it is called as distortion.


7
Give reason : The distortion in the power amplifier is critical than that of voltage  amplifier.


The power amplifier handles large current whereas the voltage amplifier handles only small signals therefore the distortion is very large in the power amplifier as compared to voltage amplifier.

8
How the power amplifiers are classified?


Classification of power amplifier
Class A amplifier
  • If the biasing of the power amplifier must be such that the collector current flows for full cycle, it is known as class A amplifier.

Class B amplifier
  • If the biasing of the power amplifier must be such that the collector current flows only during positive half cycle, it is known as class B amplifier.

Class C amplifier
  • If the biasing of the power amplifier must be such that the collector current flows only less than half cycle, it is known as class C amplifier.


9
Describe the disadvantages of the class A power amplifier.


Disadvantages of class A power amplifier
  • Low collector efficiency
  • Low power output


10
Which type of power amplifier has very less distortion?


The output signal of the class A power amplifier is exactly same as that of input signal therefore class A amplifier produces very low distortion.

11
Describe the advantages of the class B power amplifier.


Advantages of the class B power amplifier
  • High collector efficiency
  • High power output


12
Which type of power amplifier works as half wave rectifier?


Power amplifier as half wave rectifier
  • The operating point in the Class B power amplifier is selected such that during positive half cycle, the input circuit becomes forward biased and output circuit becomes reverse biased.
  • Therefore the collector current flow only for positive half cycle. 
  • The input circuit becomes reversed biased during negative half cycle resulting collector current does not flow. Therefore the class B amplifier works as half wave rectifier.              .


13
Which type of amplifier never used in the power amplification?


Class C power amplifier

14
Describe the application of the class B and class C power amplifier.


The class B power amplifier is used for power amplification in the push pull arrangement whereas the Class C power amplifier is used as tuned amplifier.

15
Explain the term : Driver stage


Driver stage
  • The stage between voltage amplifier and power amplifier is known as the driver stage. 
  • The output of last stage voltage amplifier is given to the input of the driver stage and output of the driver stage is connected to the input of the power stage.


16
Describe the function of the driver stage.


Function of driver stage
  • The function of the driver stage is to impedance matching and transfer maximum power.


17
Which type of transformer is used in the driver stage of the power amplifier? Step up transformer or step down transformer


Step down transformer

18
Why the centre tapping transformer is used in the driver stage of the power amplifier?


The output of the centre tapping transformer is connected to the input of the push pull amplifier.

19
What is push – pull amplifier?
                OR
How class B amplifiers are employed to produce high efficiency?


Push – Pull amplifier
  • The two class B power amplifier in the Push – Pull arrangement is connected such that one amplifier amplify only positive half cycle of the input signal whereas the other amplifier amplify negative half cycle of the input signal.
  • Therefore such an arrangement produces complete sinusoidal waveform or it is called as Push – Pull amplifier.


20
Describe the function of transformer in the transformer coupled power amplifier.


Function of transformer in the power amplifier
  • Impedance matching
  • To keep small DC power loss due to small resistance of the primary winding


21
At which condition, the power dissipation in the class A power amplifier?


Zero signal condition

22
Describe the advantages and disadvantages of complementary symmetry amplifier


Advantages
  • No center tap transformer requires
  • Low weight and cost

Disadvantages
  • Two supply source requires
  • It is quite difficult to get pair of NPN and PNP transistor having same characteristics.


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