Transister

Transistor is an electronics devices which has wide range of applications in electronics and communication field .Before the discover of the solid state semiconductor transistor ,vacuum tube transistor or mercury value are used to make the transistor .It is bigger in size ,low accuracy or efficiency ,difficult to make it, high cost etc .So when semiconductor transistor is discovered in 1948 by American scientists .From this time above type of transistor was replaced by semiconductor because it overcome the drawback of those type of transistor.It contains P-type of semiconductor and N-type of semiconductor in proper quantity.There are two type of semiconductor transistors:

1. P-N-P type transistor
2. N-P-N type transistor

It is used in the place of triode.
In P-N-P type of transistor N-type semiconductor of thin slice is sandwich between P-type semiconductor crystals.In this transistor left P-region is emitter,middle plates is base and last P-region is collector.Emitter is connect to the positive potential and collector is connect to the negative potential with respect to base terminal.Here left side of PN junction is forward bias that means high resistance .The direction of current is as shown below.

In N-P-N type of transistor P-type semiconductor of thin slice is sandwich between N-type semiconductor crystals.In this transistor left N-region is emitter,middle plate is base and last N-region is collector .Here emitter is connected to negative potential where as collector is connected to positive potential with respect to base .It just opposite to the P-N-P type semiconductor .The direction of current is opposite to P-N-P transistor.