How to judge if a MOSFET is good or fault?

[RoboColor]

I am meeting a problem that the MOSFET I bought is bad one that can never work. Maybe they are pulled down by dealer from some old PCB board. So I want to know how to judge if they are good one or fault one with help of some simple tool, eg. multi-meter.

Thanks a lot!

 

[s_cihan_tek]

Well, the easiest way is to measure its terminals with a multimeter ( in diode test or resistance mode) and compare the measurements with a reliable one. If you don't have any other MOSFET's in your hand, then you can make these tests with the multimeter:

1 - Most of the time, a faulted MOSFET has at least two of its terminals short circuited. This is the first thing you need to check. But before making this test, make sure that the gate capacitance of the MOSFET is discharged. Or you could see a short circuit in D-S even if the MOSFET is good, since the MOSFET would be on.

2 - D-S should behave like a diode.
In diode test mode, the multimeter should show a value like 0.XXX volts in one direction and infinity in the other. In resistance measurement mode, it should show some value in one direction and show infinity in the other direction.

3 - The resistance between G-D and G-S should be infinite


But if i were you, i would simply build a circuit with a lamp and try to trigger the MOSFET to see if it works or not.

 

[RoboColor]

Thank you very much. Because the resistance between pins of MOSFET is very large, except the diode terminal, so I think I'd better test the MOSFET with a lamp.

Thank you again!