Can you check a MOSFET transistor?

fredster

New member
Joined
Mar 28, 2009
Messages
128
Reaction score
1
Location
Tennessee
Can you check a MOSFET transistor like a regular transistor with a multimeter diode check?

I have this one that may be causing a problem, and I don't have a replacement. It's a Fairchild 11N40. Where I get transistors doesn't have them, you have to buy 1000 of them at .64 apiece to get them.
 
Last edited:
First, identify the gate, drain and source pin. Once you have located each pin of the fet, then use your analog meter set to times 10K ohm range. If you are measuring an n-channel fet then place the black probe to the drain pin. Then touch the gate pin with the red probe to discharge any internal capacitance in the fet. Now move the red probe to the source pin while the black probes still touching the drain pin. Use your finger and touch the gate and drain pin together and you will see the analog meter needle will kick forward to the middle range of the meter's scale. Removing the red probe from the source pin and touching it back again to the source pin, the needle will still remain at the center of the meter's scale. To discharge it, you have to remove the red probe and touch one time on the gate pin. This will discharge the internal capacitance again. Now, using the red probe to touch on the source pin again, the needle will not move at all because you already discharged it by touching the gate pin.
 
Thanks. I did find the 11N40, but I want to check the one that was it there to see if was really bad or not. I know you couldn't use the standard diode check test.

I'm looking for that behavior if it's N type (it is) to see if it's good. Will it short on one of these tests if it's bad?

I think I still have my old analog multimeter. Any way to check it with a digital multimeter?
 
I've seen problems turning "on and off" the mosfet, and shorted legs as well.
 
In the past, if I had a known good one, I'd use both the ohms setting and diode check to make comparisons between the two.
 
Back
Top Bottom