NPN transistor

1) A P-type region lies between 2 N-Typed Semi Conductors . This kind of configuration is called NPN Transistor.

PNP transistor

2) An N-type region lies between 2 P-Typed Semi Conductors . This kind of configuration is called PNP Transistor.

It is equivalent to two nose-to-nose diodes, but as before, just connecting two diodes will not work. Generally, a PNP diode is identical to an NPN diode, but with all currents reversed.

I V Curve

Manufacturer's IV Graph specification tell transistor operation

Operation Modes

${\displaystyle V>V_{d}.I=0}$ . Transistor is OFF

${\displaystyle V=V_{d}.I=1mA}$ . Transistor is ON

${\displaystyle V<V_{d}.I=I_{o}e^{\frac {V}{V_{d}}}}$

${\displaystyle V=V_{S}.I=I_{s}}$ . Transistor is saturated

An electronics amplifier

${\displaystyle i_{b}>0}$

${\displaystyle i_{e}>\alpha i_{b}}$

${\displaystyle i_{c}>\beta i_{b}}$

Provided that, transistor should be turned ON with biased voltage at the base must be greater than diode's break over voltage

${\displaystyle v_{b}>v_{be}}$ . ${\displaystyle v_{be}=v_{d}}$

An electronics switch

Transistor is switch On when ${\displaystyle V_{b}>V_{be}}$

Transistor is switch Off when ${\displaystyle V_{b}<V_{be}}$

A buffer

${\displaystyle v_{c}=v_{b}}$