Can i test a mosfet with a multimeter??

Discussion in 'The Projects Forum' started by onlyvinod56, Jun 18, 2009.

  1. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
    1
    Hi everyone.

    I found some testing methods in the datasheets of the mosfets conecrned.
    But can i test it with a multimeter whether the mosfet dead r not.

    Im thinking that, if a mosfet is dead means, the multimeter must show a conduction between drain to source & source to drain.
    Am i right?
    And again i have performed another test. see the attachment.
    There are three different types of results i got here.
    Can anybody clear this.........:(
     
  2. franzschluter

    Active Member

    Jun 1, 2009
    95
    0
    Case two and three is broken MOSFET.
    There is a better way to test these MOSFETS..

    Apply 20V gate voltage and let it drive a lamp...

    http://www.4qdtec.com/mostest.htmly.

    Hehe it seems you've blown some MOSFETS already :D
    Before plugging them in you should first have an oscilloscope ready and a couple of multimeters.. To test if the firing sequence is correct..Upper and Lower must never turn on same time :D
    Then lastly install the MOSFET once you see proper 20V voltage at the gate to source.

    Cheers
    Franz
     
  3. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    I would think that anytime you leave a gate floating you leave the door open for very erratic results.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    A meter test is possible. There should be a PN junction between the drain and source leads in reverse polarity to the normally applied voltage. An N channel FET should conduct From the drain to the source, for instance.

    All other leads should show no conduction.
     
  5. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    If you look carefully at the datasheet there is a built in diode going from the source to the drain.

    http://www.vishay.com/docs/91291/91291.pdf

    I would expect that if you put the positive lead of you tester on the source and the negative lead on the drain that your LED would light when the part it good.
     
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,699
    907
    For an N-channel mosfet, that only shows that the intrinsic diode may be good.

    For N-channel, with your meter in the diode check or low ohm position, put the positive lead on drain, negative on source. There should be no conduction. If there is conduction, ground or touch the gate. If it continues to conduct with gate grounded, it is bad. If it does not conduct, then you can test gate operation by briefly touching the positive lead to the gate -- leave negative attached. In doing that, you charge the gate. Then test drain to source conduction. If the mosfet is good, you should see conduction. I then discharge the gate by touching it just to confirm it is working.

    John
     
  7. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    See corrected link in quote.
     
  8. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    With the gate of the Mosfet floating, it could have the gate capacitance charged and the Mosfet should conduct. Or it can have the gate capacitance discharged and the Mosfet should not conduct.
     
Loading...