A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit.
Transistor come in two basic types, NPN and PNP. Both are used as solid state switches and amplifiers.
MPN, are the easiest type to make and the most used, they derive from silicon.
The three legs on the transistor are called BASE,COLLECTOR and EMITTER.
The legs are labelled:
base (B)
collector (C)
emitter (E).
If the BASE has a small amount of current flowing through it, it allows the COLLECTORto have current too. The COLLECTOR current will be proportional to the BASE current, but higher.
This proportional relationship allows the transistor to work as an amplifier. This proportional relationship lasts until the base current is high enough that the COLLECTOR current reaches its maximum.
The design of a transistor allows it to function as an amplifier or a SWITCH. This is accomplished by using a small amount of electricity to control a gate on a much larger supply of electricity, much like turning a valve to control a supply of water.
The base is the gate controller device for the larger electrical supply. The collector is the larger electrical supply, and the emitter is the outlet for that supply. By sending varying levels of current from the base, the amount of current flowing through the gate from the collector may be regulated. In this way, a very small amount of current may be used to control a large amount of current, as in an amplifier. The same process is used to create the binary code for the digital processors but in this case a voltage threshold of five volts is needed to open the collector gate. In this way, the transistor is being used as a switch with a binary function: five volts – ON, less than five volts – OFF.
That’s it for today, this was part 3 of the Basic components, on part 4 we will talk of Integrated Circuits and Timers.
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