Question

Define common emitter output characteristic for a transistor. Draw a circuit diagram for studying the characteristics of n-p-n transistor in common emitter configuration.
Among emitter, base and collector regions of a transistor which one is:
(a) largest in size and (b) most heavily doped?

Answer 1

The attached diagram in figure (a) shows the circuit diagram for a n-p-n transistor in common-emitter configuration. In this configuration, output is current $I_c$. Output characteristics is plotted between $I_c$ and $V_{CE}$. The different lines show the variation in the output characteristics with the variation in input voltage $V_{BE}$.

(a)

Collector has the largest region in a transistor. The large surface area allows high efficiency and larger area to allow dissipation of heat generated. The large area limits the temperature rise in the transistor.

(b)

Emitter region has highest doping. This allows the creation of high number of charge current and increase the output current in the circuit.