Field Effect Transistor


  • Often abbreviated as the FET:
    • The MOSFET is merely a type of FET:
      • It is the Metal-Oxide-Semiconductor Field-Effect Transistor:
        • This is the most commonly used FET.
        • Used for amplifying or switching electronic signals.
      • This superseded the JFET:
        • Junction gate Field-Effect Transistor.
      • But it is very susceptible to overload voltages and so needs careful handling during installation.
  • It is basically a transistor that relies on an electric field to control the conductivity between its drain and its source.
    • The FET has three terminals:
      • Gate (G) by applying voltage here it is possible to switch ON or OFF the larger current flowing through the Source and Drain terminals.
      • Source (S) is where conventional current is supplied to the FET:
        • It is the input rail and corresponds to the anode of thyristors and the collector of transistors.
      • Drain (D) is where the conventional current exits the FET:
        • It is the output rail and corresponds to the cathode of thyristors and the emitter of transistors.
  • They are commonly used as voltage amplifiers.
  • FETs are not latching unlike thyristors.
    • They also exhibit better thermal stability than BJTs (Bipolar Junction Transistor).
  • However they have a very low gain-bandwidth compared with normal BJTs.
  • FETs are unipolar (thus the drain and source terminals are somewhat arbitrary):
    • It only depends on majority current flow.
  • The pinout of FETs depends on the shape of the casing and so is variable.
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