Transistor is a three terminals (namely emitter, collector, base) three layer and two junction semiconductor device. It is used to amplify or process an electrical signal. A transistor consists of two two pn junctions formed either P type or N type semiconductor between a pair of opposite types. There are two types transistor.
- PNP Type Transistor
- NPN Type Transistor
PNP Type Transistor
In this type, the N type is sandwiched between two P-type layers. A PNP transistor composed of two p-type semiconductors separated by thin section of n-type semiconductor. PNP transistor shown in figure
NPN Type Transistor
In this type, the P-type is sandwiched between two N-type layers. A NPN transistor composed of two n-type semiconductors separated by thin section of p-type semiconductor.
Symbol of Transistor
There are three terminals in transistor, called emitter, collector and base. We have discussed above the transistor has three different layers or sections. The all layers or sections are different in size and having different doping level. According to this, different terminals are explained below:-
The emitter is heavily doped and moderate in size. Emitter supplies a large number of majority carries. The emitter is always forward biased w.r.t to base. So that it can supply a large number of majority carries to its junction with the base.
The other outer layer of the transistor that collects the majority carries supplied by the emitter is called collector. The collector-base junction is always reverse biased.
It is moderately doped and larger in size, so that it can collect most of the majority carries supplied by the emitter.
The middle of the transistor of the transistor. The base is lightly doped and small in size so that it can pass most of majority carries supplied by the emitter to the collector. The base forms two circuits.
Connections of Transistors