Question

Which of the following graphs represent the input characteristics of a common emitter transistor correctly?

• A.
• B.
• C.
• D.

Answer 1

Answer: (A)

The correct plotting of the base current vs base voltage (i.e., input characteristics of a common emitter transistor) is shown below.

The curve plotted between the base current $I_B$ and the base-emitter voltage $V_{EB}$ is called the input characteristics curve. For drawing the input characteristics, the reading of base currents is taken through the ammeter on emitter voltage $V_{BE}$ at constant collector-emitter current. The curve for different values of collector-base current is shown in the figure below.
The curve for common base configuration is similar to a forward diode characteristic. The base current $I_B$ increases with increase in the emitter-base voltage $V_{BE}$ . Thus, the input resistance of the $CE$ configuration is comparatively higher than that of $CB$ configuration.
The effect does not cause a large deviation on the curves and, hence, the effect of change in $V_{CE}$ on the input characteristics is ignored.