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Transistor Feedback Circuit Interview Question Answer

Explain the terms : Feedback                   

  • The process of injecting output energy back to input side with some external device is called as feedback.

Explain the term : Positive feedback

Positive feedback
  • When the feedback energy is in phase with input signal it is called as positive feedback.

Explain the term : Negative feedback

Negative feedback
  • When the feedback energy is out of phase with input signal, it is called as Negative feedback.

Explain the term : Negative current feedback

Negative current feedback
  • When fraction of output current is feedback to the input side, it is called as Negative current or current – shunt feedback.

How the feedback circuit is connected with amplifier?

The input of the amplifier and feedback circuits is connected in series whereas output of the both devices is connected in parallel.

Describe the advantages and disadvantages of Negative voltage feedback.

  • Distortion is reduced.
  • Non – linear distortion is reduced.
  • Frequency response of the amplifier is improved.
  • Gain stability is increased because the feedback circuit is unaffected by the variation of the supply voltage, transistor parameter and changes in temperature.
  • Increase input impedance and decrease output impedance of the amplifier. 

  • Voltage gain of the amplifier is decreased.

Describe the advantages and disadvantages of positive voltage feedback.

The positive feedback increases the gain of the amplifier but at the same time it also increased distortion and instability.

Describe the effect of Negative feedback on power gain of the amplifier?

  • The Negative feedback decreases the voltage gain but current gain remains constant therefore the power gain ( AP = AV × Ai  ) of the amplifier is reduced.

Describe the effect of the temperature and frequency on the feedback circuit.

  • The feedback circuit is resistive therefore it is unaffected by the temperature and frequency.

Describe the effect of Negative current feedback on the transistor amplifier gain.

Effect of Negative current feedback
  • When Negative current feedback circuit is introduced, the current gain of the amplifier is reduced but it does not affect the value of voltage gain of the amplifier. 
  • The Negative current feedback also increases the bandwidth of the amplifier.

Explain : Current Shunt feedback

Current shunt feedback
  • The Negative current feedback is called as current shunt feedback because the fraction of output current is feedback to the input of the amplifier.

What is emitter follower circuit?

Emitter follower
  • The emitter follower is basically common emitter (CE) transistor amplifier circuit in which collector load and emitter bypass capacitor does not included.
  • The emitter resistance itself acts as a load and output is taken from it.

Explain : Darlington amplifier

Darlington amplifier
  • When the emitter of the first transistor is connected to the base of the second transistor and collector of the both transistor are connected together, the resulting current gain of the both transistor is increased

β = β1 × β2
β = Current gain of the both transistor
β1 = Current gain of the transistor 1
β2 = Current gain of the transistor 2
  • Therefore the Darlington amplifier is a transistor in which high current gain and high input impedance is achieved.

State the applications of emitter follower circuit.

Applications of emitter follower
  • The emitter follower circuit provides current gain but no voltage gain. 
  • The main application of the emitter follower is impedance matching in the transistor amplifier circuit.

Give reason : The emitter follower is better than transformer coupling amplifier for impedance  matching.

  • The emitter follower and transformer coupling amplifier both are used for impedance matching but emitter follower has much better frequency response ( working over wide range of frequency range ) than transformer coupling amplifier.

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