Question

In the figure, an $n-p-n$ transistor is shown in common emitter configuration. If $V_{BB}=10V,V_{CC}=20V,R_E=2k\Omega ,V_i=2\sin \omega t$ in milli-volts, then find the maximum voltage gain of the transistor. Assume that $\beta$ is very large.

Answer 1

Answer: 5000

$A_V=\text{ Voltage gain }=\frac{\beta R_C}{R_{\text{in }}+(\beta +1)R_E}\cong \frac{R_C}{R_E}=\frac{R_C}{2}$
For proper biasing, $V_C>V_B$
$\Rightarrow 20-\frac{2A_V}{1000}>10+\frac{2}{1000}$
$\Rightarrow \frac{2A_V}{1000}<10-\frac{2}{1000}$
$\Rightarrow 2A_V<1000$
$\Rightarrow A_V<5000$
$\Rightarrow A_{V\max }=5000$