Explain the construction and working of transistor
 
 
 
TRANSISTORS
 
A three terminal semiconductor electronic device is called transistor. Transistors are widely used in electronic appliances such as computers, radio, audio video equipment, bio medical instrument etc.
CONSTRUCTION
 
A transistor is a three layer semiconductor which consist a very thin central layer of one type of semiconductor material sandwiched between two relatively thick layer of second type.
TYPES OF TRANSISTORS
 
 
pnp-TRANSISTORS
 
In this type of transistors n-type semi-condutcor piece is sandwiched between two piece of p-type semiconductor layers.
npn-TRANSISTORS
 
In this type of transistors p-type semi conductor piece is sandwiched between two piece of n-type semiconductor layers.
ESSENTIAL PARTS OF TRANSISTORS
 
There are three essentials parts of a transistor
Base: It is the central layer denoted by b.
Emitter: It is the outer layer denoted by e.
Collector: It is the outer layer denoted by c.
WORKING
 
Consider any one of the transistors for example a pnp-transistor. Let the two p-end are connected to two batteries as shown in the diagram. The forward bias causes the holes in the p-type emitter to flow towards the base which constituent Ie current. These holes cross into the n-type base, they try to combine with electrons but the base is lightly doped and is very thin.
Therefore only few holes combine with electrons and the remaining holes cross into the collector and generates collector current Ic. In this way almost the entire emitter current flows in the collector circuit. From the above description it is clear that:
Ie = Ib + Ic
Thus there are two current paths through a transistor. One is the base-emitter path or input and the other is the collector-emitter path or output.
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