Page 974 - Basic Electrical Engineering

the base material.
v. Variation of base–emitter voltage changes base, emitter, and collector currents.

14.7.2 Working of a p–n–p Transistor

The p–n–p transistors work the same way as n–p–n transistors except that in

p–n–p transistors the majority charge carriers are holes. The biasing is same
as that of a n–p–n transistor. The emitter-base junction is forward biased and

the collector–base junction is reverse biased as shown in Fig. 14.16.
The majority charge carriers from the emitter are the holes. As the base is

thin and lightly doped only a small percentage of holes emanating from the
emitter recombine with electrons in the base region. The rest of the holes,
which are nearly 98 per cent, cross the base–collector barrier potential,

because they are attracted by the negative terminal of the base–collector bias
voltage.

Thus, holes are emitted from the p-type emitter across the forward-biased
emitter–base junction and only a few of them find electrons in the base region

to recombine with. Most of the holes get attracted to the collector side by the
reverse-biased collector–base junction.

By varying the forward bias voltage at the base–emitter junction, we can
control the large emitter and collector current through small variations of
base current.

Both n–p–n and p–n–p type of transistors are called bipolar junction
transistors, or simply BJTs because the charge carriers for both types of

transistors are electrons, and holes, although for n–p–n transistors the
majority charge carriers are electrons and for p–n–p transistors the majority
charge carriers are the holes.