Question

Consider a square wave stable multivibrator circuit shown in the figure below:



Then, the value of output frequency of the amplifier circut is equal to

• A. 12.25 Hz
• B. 8.32 Hz
• C. 2.57 Hz
• D. 389.18 Hz

Answer 1

The correct option is C 2.57 Hz

For an astable multivibrator, the output will be a square wave with amplitude $V_{\text{sat}}$ andd time period T.

$T=2RCln\left[\frac{1+\beta }{1-\beta }\right]$
$(\text{Given}:R_1=5k\Omega ,R_2=15k\Omega ,C=10\mu F,R=10k\Omega )$
$\text{where,}\beta =\frac{R_2}{R_1+R_2}=\frac{15k\Omega }{R_1+R_2}=\frac{15k\Omega }{15k\Omega +5k\Omega }=\frac{15}{20}=0.75$
$\therefore T=2\times 10\times {10}^{-6}\times 10\times {10}^{3}ln\left[\frac{1+0.75}{1-0.75}\right]$
$T=389.18\text{msec}$
$f=2.57Hz$