Transistor is a semiconductor device that is used as a switch
or an amplifier (amplify weak electrical signals). A transistor is made up of a
semiconductor material with three pins (base, collector and emitter) which is
connected to external circuit. A current or voltage applied to one pin mostly
the base of the transistor terminal controls the current through another pin or
pair of terminals. Transistor is the fundamental building block of modern
electronic devices.
The most usefulness of a transistor is its ability to use a
small signal applied between its base or gate to control to control a much
larger output signal. This property is called gain. It can produce a
stronger output signal, a voltage or current which is proportional to a weak input
signal (base); that is, it can be used as an amplifier. Alternatively, the
transistor can also be used as an ON and OFF switch in a circuit. It low input
signal (voltage) can be used to switch ON or OFF a high voltage.
There are two types of transistor in a circuit which are BJT (bipolar junction transistor), and FET
(field effect transistor). There also the MOSFET (metal oxide semiconductor field effect transistor). A BJT
transistor has three terminals labeled the base,
collector, and emitter. A small current that is flowing between the base
and emitter, can control or switch a much larger current between the collector
and emitter. For a FET, the
terminals are labeled gate, source, and
drain, and a voltage at the gate can control a current between its source
and drain. The diagram below shows the circuit symbol of a BJT and MOSFET. The
resistor RL represents the load resistance.
(a) (b)
(c) (d)
From the diagrams above, (a)
represent BJT circuit symbol transistor, (b) represent MOSFET circuit symbol (C)
represent the circuit diagram of using transistor as a switch while (D)
represents the circuit diagram of using transistor as an amplifier.
We shall reveal more information
about transistors on our next post, and how to test various transistors.
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