3. introduction
• A transistor is a semiconductor device used
to amplify and switch electronic signals and electrical
power. It is composed of semiconductor material with
at least three terminals for connection to an external
circuit. A voltage or current applied to one pair of the
transistor's terminals changes the current flowing
through another pair of terminals., a transistor
can amplify a signal. found embedded in integrated
circuits.
4. Transistor
• Transistor are electrical device, which utilize a
sandwich of p and n type of semi conductor
materials.
• It can be NPN or PNP types
5. Transistor
• It has got 3 parts :
• emitter
• Base
• Collector.
6. • One of the n type at the left is emitter
• Right is collector
• And central p type is the base
7. • When contact is being made between
materials in case of NPN transistor PD
develops at their junction and the emitter and
collector being positive relative to the base.
8. Transistor
• When the device is connected to a source of
EMF, with the emitter negative and the
collector positive, no current flows unless the
EMF exceeds the critical value, as the
electrons are unable to pass from the negative
p-type to the positive n-type semiconductor,
so cannot cross the base collector junction.
9. Transistor
• A second source of EMF is connected to the
base and the emitter, the base being positive
relative to the emitter.
• The electron can pass from the negative n
type to the positive p-type
• So the current flows across the base collector
junction.
10. Transistor
• In the circuit’ there is a thick layer of n-type
semiconductor, a thin layer of p-type
semiconductor’ so the current consist largely
of the movement of electrons from the
emitter soon pass into the base
11. Transistor
• The base has now an adequate supply of
electrons, and as it is very thin these come
close to the base collector junction, and are
attracted into the collector, to replace those
that had migrated into the base.
12. Transistor
• This reduces the barrier effect across the
base-collector junction, and current flows
across the transistor.
• Thus a current fed into he base current,
causes greater variation of current flowing
across the transistor.
13. Transistor
• In this respect the current fed into the base of
the transistor has an effect, comparable to
that of a positive charge applied to the grid of
a triode valve.
14. Transistor
• Uses of transistor
• Transistor are used in preference to the valve
in most modern equipment, as they are
durable, have a long life, consume less power
and need no heating device.
• As the power output is limited they are
suitable for use in the production of low
frequency but fail to produce high frequency
currents e.g. SWD
