How to check N-Channel enhancement mode transistor

I know this is probably basic to most of you, by I don't remember exactly how this type transistor operates, and therefore not sure how to check if it is good. Can I do a diode check on it like a regular npn/pnp transistor? Thanks to all.

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Unfortunately not, but you can check it for shorts. These are very high impedance devices so there's not much a multimeter can tell you about them in the conventional way.

I'm no FET expert but I believe these are the type which operate a bit like a bipolar NPN transistor- they are usually 'off' and require the gate to be more positive than the source to turn them on.

If you connect one multimeter probe to the drain and one to the source (which probe to which will depend on how your multimeter is designed- some supply positive to the black probe!) then touching the gate with a finger should give a reading due to their extremely high gate impedace, but really the best way is to build a little tester for them.

The source to ground, drain through a resistor and LED to positive, and the gate touched by the finger should light up the LED. If it doesn't, a 10M resistor from gate to positive should do the trick. A finger between the positive and gate usually does the trick as well.


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Dave D

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