TRANSISTOR

Monday, 17 June 2013
Transistor:
Transistor is an electronic device that can be used as an amplifier or as a switch.Transistor is the next version to diode.Diode can simply pass through current in uni direction and can act as switch,but transistor can also amplify.They can control a large current flowing through 2 regions of semiconductor like si to a small current applied to a middle region.There are many kinds of transistors typical is bipolar transistor. Transistor has 3 layers. Transistor is designed by appending another region on diode(PN-diode) either left or right,so the transistor configurations are PNP,NPN . The layers are Emitter,Collector and Base.In transistor current flow from Emitter to Collector and that flow is controlled by current applied to middle terminal called Base.

Demonstration:  
When current is applied to Emitter electrons cross over to P-type base filling the electrons holes ,when holes are filled resulting negative charges so repell further electrons to come from Emitter and transistor doesnt conduct.But a small amount of current is applied to base that will produce additional holes ,this will further invite much electrons from Emitter to pass through base to collector because Emitter to Collector flow is several 100 times more than Emitter to Base thus making transistor a power amplifier.
As base current is controlling the amplification process transistor is a current controlled voltage source.
Transistor is also called Bipolar junction transistor.since both holes and electrons are operating this is a bipolar device and since junction is present between PN and NP.This is referred as bipolar junction transistor.

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