FET Cheat Sheet

    FETs are available in variety of flavors. This reference provides a quick overview of common FET types along a few important characteristics for each type.

    FETs differ from BJTs (Bipolar Junction Transistors) in one key way. The conduction through a FET’s channel, from drain to source, is controlled by a voltage applied to the gate while BJTs are controlled by the transistor’s base current. In addition to this basic distinction, FETs are available in a number of different flavors, so to speak, while BJTs are available in two.

    One of the primary differentiators in FET characteristics is whether the drain to source channel is in conduction (on) with a 0V gate to drain voltage or off. In addition, the specific FET type may need either a positive gate voltage or a negative gate voltage to bring it in or out of conduction. While many FETs are able to control a bidirectional current (from drain to source or vice versa), other types have an inbuilt diode which only allows control of the current flow in one direction because the diode will conduct current when it is forward biased.

    The following table provides a schematic symbol for each type of FET (Symbol), its name (Name), an indication if the FET is in conduction or not with a 0V gate (0V gate), whether the FET can control current flow in one direction or both (Channel cur.), and if requires a negative or positive gate voltage to bring the FET into or out of conduction (Gate polarity).

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