Question

Draw the circuit diagram to study the characteristics of npn transistor in common emitter configuration. Sketch typical (i) Input characteristics (ii) output characteristic for such a configuration. Explain how the current gain of transistor is calculated from output characteristics.

Answer 1

Output characteristics is the plot between collector-emitter voltage $\left(V_{CE}\right)$ and the collector current $\left(I_C\right)$ at different constant values of base current $\left(I_B\right)$

Output resistance is defined as the ratio of the change in collector- emitter voltage $\left(\Delta V_{CE}\right)$ to the change in collector current $\left(\Delta I_C\right)$ at a constant base current $I_B$.

Initially with the increase in $V_{CE}$, the collector current increase almost linearly this is because the junction is not reverse biased. When the supply is more than required to reverse bias the base -collector junction $I_C$ increase very little with $V_{CE}$.

The reciprocal of slope of the linear part of the curve gives the value of output resistance.