Important Questions of Transistor Feedback Circuit
In this post, some of the important questions of transistor feedback are given. It included definition of feedback, meaning of positive feedback, meaning of negative feedback, negative current feedback, advantages and disadvantages of negative voltage feedback, advantages and disadvantages of positive voltage feedback, negative current feedback, current shunt feedback, emitter follower, Darlington amplifier, application of emitter follower and impedance matching.
Explain the terms : Feedback
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.
Advantages
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.
Disadvantages
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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