A transistor is a semiconductor device used to amplify or switch electrical signals and power. The transistor is one of the basic building blocks of modern electronics. It is composed of semiconductor material, usually with at least three terminals for connection to an electronic circuit.
NPN: Not Pointing iN
Current: IE = IB + IC
Base current flows in to the trainsistor
PNP:
Current: IE = IB + IC
Base current flows out of transistor
β (beta), the gain or amplification factor of a transistor, normally is given when solving a circuit equation.
β = I C / I B
β = ( I E / I B ) – 1
It uses a small base current to trigger a large collector current on the NPN or large emitter current on PNP.
NPN Example
β =100
IB = 1mA
I C = ( 100 ) ( 1mA ) = 100mA
I E = 1mA + 100mA = 101mA
PNP Example
β =100
IB = 1mA
I C = ( 100 ) ( 1mA ) = 100mA
I E = 1mA + 100mA = 101mA