Transistor
From Physical Programming
A transistor is a small electronic component that has at least three electrical contacts – the input (source), trigger (gate) and output (drain) set inside the non-conductive body (substrate). The trigger is made up of semiconductor material that conducts a voltage from the input to the output to close the switch.
Transistors are used in a circuit for amplification, detection, or as high-speed switches for electronic signals. In the 1960s and ‘70s single transistors were superseded by integrated circuits and today computer chips contain millions of them. Transistors are used in virtually all electronic devices. They are very durable, very small, have a high resistance to physical shock, and are very inexpensive.
There are two main types of transistor, the bipolar junction transistor (BJT) and the field-effect transistor (FET). The bipolar junction transistor was the first type of transistor to be mass-produced. It has a higher transconductance than the FET and can be made to conduct by exposure to light. Transistors designed for this purpose have a transparent window to allow light in and are called phototransistors. Field-effect transistors can be produced in either depletion-mode and enhancement-mode type. Depletion-mode reduces the current in the output, enhancement-mode has the opposite effect.
