A transistor
is a semiconductor device used to amplify or switch electronic signals and
electrical power. It is composed of semiconductor material usually with at
least three terminals for connection to an external circuit. A voltage or
current applied to one pair of the transistor’s terminals controls the current
through another pair of terminals. Because the controlled (output) power can be
higher than the controlling (input) power, a transistor can amplify a signal.
How it works
A transistor is really simple and really
complex. Let’s start with the simple part. A transistor is a miniature
electronic component that can do two different jobs. It can work either as an
amplifier or a switch:
- When it works as an amplifier,
it takes in a tiny electric current at one end (an input
current) and produces a much bigger electric current (an output current)
at the other. In other words, it's a kind of current booster. That comes
in really useful in things like hearing aids, one of the first things
people used transistors for. A hearing aid has a tiny microphone in
it that picks up sounds from the world around you and turns them
into fluctuating electric currents. These are fed into a transistor that
boosts them and powers a tiny loudspeaker, so you hear a much louder
version of the sounds around you. William Shockley, one of the inventors
of the transistor, once explained transistor-amplifiers to a student in a
more humorous way: "If
you take a bale of hay and tie it to the tail of a mule and then strike a
match and set the bale of hay on fire, and if you then compare the energy
expended shortly thereafter by the mule with the energy expended by
yourself in the striking of the match, you will understand the concept of
amplification."
- Transistors can also work as switches.
A tiny electric current flowing through one part of a transistor can make
a much bigger current flow through another part of it. In other words, the
small current switches on the larger one. This is essentially how all
computer chips work. For example, a memory chip contains
hundreds of millions or even billions of transistors, each of which can be
switched on or off individually. Since each transistor can be in two
distinct states, it can store two different numbers, zero and one. With
billions of transistors, a chip can store billions of zeros and ones, and
almost as many ordinary numbers and letters (or characters, as we call
them). More about this in a moment.
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