Page 978 - Basic Electrical Engineering

The circuit diagram for determining the common-emitter transistor
characteristics has been shown in Fig. 14.19. In this p–n–p transistor, input
voltage is applied between the base and the emitter terminals. The output is

taken from the collector and the emitter terminals as has been shown. The
emitter terminal is common to both input and output. That is why this

connection is called the common-emitter configuration.
The input characteristic is drawn between V and I . To draw the input
BE
B
characteristic, the voltage between the collector and the emitter, i.e., V is
CE
kept constant at a value. By changing V through V , current I is
B
BE
BB
recorded for atleast, say five readings. A plot of I against V when made
B
BE
shows that the characteristic is similar to the characteristic of a forward-
biased p–n junction. The value of I is very small, is of the order of several
B
microamperes only.

The output characteristics are drawn between I and V keeping I B
C
CE
constant at different values. For each value of I , V is adjusted in steps and
CE
B
the values of I are recorded. The values of I are plotted against V for
CE
C
C
each value of I as shown in Fig. 14.20. Fig. 14.20 (a) shows the input
B
characteristic and Fig. 14.20 (b) shows the output characteristics.