Question

Draw typical output characteristics of an n-p-n transistor in CE configuration. Show how these characteristics can be used to determine output resistance.

Answer 1

Output characteristics is the plot between collector-emitter voltage (V_CE) and the collector current (I_C) at different constant values of base current (I_B).

Output resistance is defined as the ratio of the change in collector-emitter voltage (ΔV_CE) to the change in collector current (ΔI_C) at a constant base current (I_B).

Initially with the increase in VCE the collector current increases 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, IC increases very little with VCE.

The reciprocal of slope of the linear part of the curve gives the value of output resistance i.e. `r_0 = ((ΔV_(CE))/(ΔI_C))I_B` .