Fundamental Physics/Electricity/Electric Conductor/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.
Characteristic of PNP transistor is specified in I-V curve
Mode of operations
Transistor is OFF Transistor is ON Transistor Transistor is saturated