Question

10 mV input to an amplifier gives 5 V output without feedback, with negative feedback, 160 mV input is required to give the same output. The feedback factor $\beta$ used is _________%.

• A. 3

Answer 1

The correct option is A 3
$A_{OL}=\frac{5}{10\times {10}^{-3}}=500$
$A_{CL}=\frac{5}{160\times {10}^{-3}}=31.25$
$A_{CL}=\frac{A_{OL}}{1+\beta A_{OL}}=\frac{500}{1+\beta 500}=31.25$
$1+\beta 500=\frac{500}{31.25}$
Feedback factor, $\beta =\frac{15}{500}=3\%$