Fundamental Physics/Electricity/Electric Conductor/NPN transistor

NPN transistor

NPN is one of the two types of bipolar transistors, in which the letters "N" and "P" refer to the majority charge carriers inside the different regions of the transistor. Most bipolar transistors used today are NPN, because electron mobility is higher than hole mobility in semiconductors.

A small current entering the base in common-emitter mode is amplified in the collector output. The arrow in the NPN transistor symbol is on the emitter leg and points in the direction of the conventional current flow when the device is in forward active mode

NPN Transistor Construction

NPN transistors consist of a layer of P-doped semiconductor (the "base") between two N-doped layers.

o--[N|P|N]--o

Symbol

Characteristics

Characteristic of PNP transistor is specified in I-V curve

Mode of operations

Transistor is OFF	$V_{B}<V_{d}$	$I<0$
Transistor is ON	$V_{B}=V_{d}$	$I=1mA$
Transistor	$V_{B}>V_{d}$	$I=Ae^{\frac {V}{V_{d}}}$
Transistor is saturated	$V_{B}>V_{d}$	$I=I_{S}$