1445326735900-0

Transistors
Figure 8.10
transistors
The internal construction and circuit symbols for NPN and PNP
sistor flows from base-to-emitter, while in the PNP transistor
it flows from emitter-to-base. Likewise collector current flow
in the NPN transistor is from collector-to-emitter and from
emitter-to-collector in the PNP transistor.
Knowing this and comparing the PNP construction to that of
the NPN transistor we can further work out that a tiny emitterto-base
current (still called the base current, incidentally) will
cause a much larger emitter-to-collector current (still called
the collector current). This is illustrated in Figure 8.11. The
ratio of collector current to base current of a PNP transistor
is still the current gain. In fact, apart from the different
directions of currents, a PNP transistor functions identically
to an NPN transistor. As we’ve started our look at transistors
with the use of an NPN transistor, however, we’ll finish it the
same way.
179