Transistor, pnp transistor, npn transistor
Transistors
Three terminals - Emitter, base, collector
Middle layer or sandwich layer
thin compare to outer layers
lightly doped, less free carriers
Can be looked as two diodes connected back
to back but does not behave like a diode. In
case of diode during reverse bias it behaves as
a switch in off condition
Transistor operation - pnp
Forward biased diode - pn junction, emitter-base
Base- collector is open circuit.
Depletion layer is reduced and behave like a normal diode
Reverse biased diode - np junction, base collector
Depletion layer is increased and behave like a reverse biased diode
Forward biased emitter-base, and reverse biased base collector Base is lightly doped, unable to handle large majority carriers. Diffuse to
collector which is reverse bias, ready to accept the diffused holes.
IC(majority) – Generally it is milliamp.
IC(minority) – Current when emitter
junction is open. Generally it is in
microamperes and sensitive to
temperature variation.
How a “NPN” Transistor works?
The base-emitter diode (forward) acts as a switch. when v1>0.7 it lets the electrons flow toward collector. so we can control our output current (Ic) with the input current (Ib) by using transistors.
Because of the electric field existing between base and collector (caused by VCE), the majority of these electrons cross the upper p-n junction into the collector to form the collector current, IC.
The remainder of the electrons recombine with holes, the majority carriers in the base, making a current through the base connection to form the base current, IB