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An amplifier with a positive feedback circuit causes ____

This question was previously asked in
RRB ALP CBT 2 Electronic Mechanic Previous Paper: Held on 23 Jan 2019 Shift 1
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  1. bandwidth to stabilize
  2. gain of an amplifier to stabilize
  3. bandwidth to decrease 
  4. bandwidth to increase 

Answer (Detailed Solution Below)

Option 3 : bandwidth to decrease 
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Detailed Solution

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Positive feedback

The structure of the feedback is shown below

5f958fd06802efcb2887b9c5 16471771399831

\(Gain = \frac{{{X_o}}}{{{X_i}}} = \frac{A}{{1 - A\beta }}\)

  • In the positive feedback, the gain is increased and the bandwidth is reduced. 
  • In the positive feedback, the error also diverges.
  • It is also called the “Regenerative circuit". 
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Q1.A unity-gain negative-feedback control system has a loop-gain 𝐿(𝑠) given by \(\rm L(s)=\frac{6}{s(s-5)}\) The closed-loop system is ________
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Q7.Consider the negative feedback control system using amplifiers. If the system has two open loop poles in the left half of S plane, then the system is:
Q8.Consider the negative feedback control system, which has open loop gain G and feedback factor H. The bandwidth of the closed loop control system is given by (Note: Consider BWf as bandwidth with feedback and BW as open loop bandwidth):
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Q1.A unity feedback system is characterized by the open-loop transfer function \(G(s)=\frac{100}{s(5 s+10)(2 s+10)}\) The steady-state errors for unit-step and unit-ramp inputs are :
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