Transistor ‐ electronic component made of semiconductor material, capable of controlling a significant current in the output circuit from a small input signal. Transistors are widely used to amplify, generate, switch, and convert electrical signals. Currently, the transistor is the basis of circuitry for the vast majority of electronic devices and integrated circuits.
Usually the transistor has three pins, but sometimes there is a fourth pin connected to the case, the substrate or a second gate in a double gate field effect transistor.
Classification by transistor structure
| Transistors | |||||||||||||||||||||||||||||||||||||||||||||
| Bipolar (BJT) | Field-effect transistors | ||||||||||||||||||||||||||||||||||||||||||||
| p-n-p | n-p-n | With p-n junction gate (JFET) | With insulated gate (MOSFET) | ||||||||||||||||||||||||||||||||||||||||||
| n-channel | p-channel | Depletion-mode | Enhancement-mode | ||||||||||||||||||||||||||||||||||||||||||
| n-channel | p-channel | n-channel | p-channel | ||||||||||||||||||||||||||||||||||||||||||
Symbols for transistors in circuits
Bipolar transistors
The key difference in the principle of operation from field-effect transistors: they are controlled by the current flowing through the base (in the most common case).
Field effect transistors
The key difference in operating principle from bipolar transistors: they are controlled by the voltage supplied to the gate.