Figure 1-27.
Cathode-Ray Tube (CRT)
7. Solid-State Devices. Solid-state devices (sometimes referred to
as semiconductors) have, to a large extent, replaced vacuum tubes in
the design of most modern electronic equipment. Solid-state devices
are generally made of silicon or germanium that is "doped" with
impurities to provide the desired conductivity. They may be doped to
produce either p-type material (positive) or n-type material
(negative).
These semiconductors are used in the place of vacuum
tubes due to these advantages: they are smaller, take less power to
operate, usually cost less, and are more rugged.
a. Transistors.
Probably the most common of these solid-state
devices is the transistor. While there are numerous variations, most
transistors are either pnp transistors or npn transistors. Figure 1-
28 shows the symbol for a npn and a pnp transistor.
The key to
recognizing a npn or pnp is the direction of the arrow on the
emitter.
On the pnp transistor symbol, the arrow points inward; on
the npn, the arrow points outward.
The elements of the transistor
operate much like the elements of the vacuum tube.
The emitter
functions much as the cathode; the collector as the plate; and the
base much like the grids.
Transistors are labeled with the letter
"Q."
Figure 1-28.
NPN, PNP Transistors.
b. Diodes. Another common solid-state component is the diode. A
diode consists of one piece of p-type material and one piece of
n-type material formed together to create a p-n junction.
This p-n
junction has the property to pass current in only one direction.
Diodes are also designed in a number of
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