Page 48 - Bebop to The Boolean Boogie An Unconventional Guide to Electronics Fundamentals, Components, and Processes

Semiconductors: Diodes and Transistors 29

If the triangular body of the symbol is pointing in the classical direction of
current flow (more positive to more negative), the diode will conduct. An
individually packaged diode consists of a piece of silicon with connections to
external leads, all encapsulated in a protective package (the silicon is typically
smaller than a grain of sand). The package protects the silicon from moisture
and other impurities and, when the diode is operating, helps to conduct heat
away from the silicon.
Due to the fact that diodes (and transistors as discussed below) are formed
from solids-as opposed to vacuum tubes, which are largely formed from empty
space-people started to refer to them as solid-state electronics.

Bipolar Junction Transistors
More complex components called transistors can be created by forming a
sandwich out of three regions of doped silicon. One family of transistors is
of
known as bipolar junction transistors (BJTs)~ which there are two basic types
called NPN and PNP; these names relate to the way in which the silicon is
doped (Figure 4-7).

collector I collector I collector I collector I

5ilicon

base

I emitter I emitter I emitter
(a) NPN Bipolar Junction Transistor (b) PNP Bipolar Junction Transistor

Figure 4-7. Bipolar junction transistors (BJTs)

4 In conversation, the term BJT is spelled out as “B-J-T”.