Question

Consider the circuit shown in the figure below.

The above silicon transistor is biased at operating point Q(7V, 1 mA) and with $V_{cc}=12V.$ If the value of $\beta =100$, then the value of stability factor $S\left(I_{co}\right)$ is _________

• A. 56.75

Answer 1

The correct option is A 56.75


Given, $V_{CE}=7V$ and $I_C=1mA$
$\therefore R_C=\frac{V_{cc}-V_{CE}}{I_C}=\frac{12-7}{1\times {10}^{-3}}=5k\Omega$
now, $I_B=\frac{I_c}{\beta }=\frac{1\times {10}^{-3}}{100}=10\mu A$
$R_B=\frac{V_{cc}-V_{BE}-I_C{R}_C}{I_B}=\frac{12-0.7-1\times {10}^{-3}\times 5\times {10}^3}{10\times {10}^{-6}}=630k\Omega$
$S=\frac{1+\beta }{1+\beta \left[\frac{R_C}{R_C+R_B}\right]}=\frac{1+100}{1+100\left[\frac{5\times {10}^3}{(5+630)\times {10}^3}\right]}=56.50$