Transistor and LED

 1 Transistor 

There are two types of transistors.

• NPN Transistor

• PNP Transistor

NPN Transistor consist on three semiconductor materials in which two are N type and one is P type semiconductors. 

There are three regions of NPN transistor. 

• Emitter

• Base

• Collector

(1) Emitter 

The region to the one side of base is called emitter.

It has greater concentration of impurity then collector.

(2) Base 

The central region is very thin of the order of 10-6m is called base. 

(3) Collector 

The region to the other side of base is called collector. It is larger than emitter. Both emitter and collector have large impurity concentration than base. 

The arrow point on the emitter terminal shows the NPN transistor. We use NPN transistor in our project because it is most c ommonly and easy to deal with it.

 2 LED

LED stand for light emitting diodes. 

Light emitting diodes are made from special semi-conductors such as gallium arsenide and gallium arsenide in which the potential barrier between the P and n sides in such that when an electron combine with a hole during forward bias conduction , a photon of visible light is emitted . These diodes are commonly used as small light source e.g. indicators etc.LED emits light whenever current flow through it otherwise it remains off. In a semiconductor material which making LED emits energy in the form of photon when electrons recombine with holes.