NPN

The symbol of an NPN BJT.

NPN is one of the two types of bipolar transistors, (or BJTs), the second being PNP. The letters "N" and "P" refer to the majority charge carriers inside the different regions of the transistor. Most transistors used today are NPN, since this is the easiest and most cost effective to make from silicon.

NPN transistors consist of a layer of P-doped (the doping agent is often boron) semiconductor (the "base") between two N-doped (often made with arsenic) layers. NPN transistors are commonly operated with the emitter at ground and the collector at a positive voltage.

A helpful mnemonic for recognizing an NPN BJT symbol is to look at the Emitter region. If the arrow is pointing away from the Base region, (i.e. Not Pointing iN), then it is an NPN BJT. If the arrow is pointing to the Base region, then it's a PNP BJT.

A small current entering the base will allow a large current to travel across the collecter-emmitor.

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