Capacitor Symbol

Transistors are considered to have revolutionized electronics into what it is today. They are at the heart of all electronic circuit and chips there are. These handy little devices are switches that can be turned on or off with a single electronic signal.

There are two types of standard transistors, NPN and PNP, with different circuit symbols. The letters refer to the layers of semiconductor material used to make the transistor. Most transistors used today are NPN because this is the easiest type to make from silicon.

The leads are labeled base (B), collector (C) and emitter (E). These terms refer to the internal operation of a transistor but they are not much help in understanding how a transistor is used, so just treat them as labels!

The way a transistor works is it has an input (collector) and an output (emitter) which is divided by a dielectric. A dielectric is a neutral substance made out of positive and negative charges (protons and electrons) that cancel out each other's charge. Then you use an opposite charge with sufficient current and/or voltage to create a bridge that creates a temporary connection between the collector and emitter.

NPN transistors have a flow of negative charges that can flow through it and is activated by a positive charge input to the base. The way it works is that there are two terminals that allow negatively charged electrons to flow but it is blocked by the neutral charged dielectric.

Once a large enough positive charge current or voltage is seen on the base, it then attracts negative charges towards it which completes a bridge of negative charges, allowing a flow.

The same goes for PNP transistors that allow a positive charge flow through it and is activated by a negative charge current/voltage on its base lead.

Transistors are also occasionally considered amplifiers because the small base current controls the larger collector current.