Semiconductors
You know
semiconductors as transistors, diodes, and chips. Silicon material is used to
make devices that will conduct a certain amount of current when needed.
These
devices are made for easy use and with low voltages. You will encounter semiconductor
chips in memory devices and computers; transistors are used in many types of
circuits, and diodes are used as rectifiers and control devices.
Diodes
Diodes have
an anode and a cathode. The cathode end is marked (+) to indicate which
polarity it must be connected to in order to work properly.
Diodes have many
uses. They are found in circuits that are used to change ac to dc for certain control
devices. They may also be used as protective devices in circuits.
Transistors
The
transistor is used for switching and amplification. It consists of three active
elements. There are two basic types of transistors, PNP and NPN.
These terms
will be discussed later. E stands for emitter, C stands for collector, and B is
used to indicate the base connection.
Switches
Switches are
used to turn on or off a circuit. They can be made as a simple on off device or
used to control many functions in a number of circuits. Switches have names
that designate what they can do in terms of turning on or off a circuit or
circuits.
For
instance, there are SPST (single pole, single throw) switches, DPDT (double
pole, double throw), DPST (double pole, single throw), single-pole,
six-position, and so forth.
Relays
Relays are
switches that are moved electrically instead of by hand. They can be made in
almost any configuration of poles, throws, and construction.
The force
that operates a relay is magnetic. The magnetic pull is produced by current passing
through a coil of wire. The attraction of an armature causes the switch
sections to operate
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