mosfet testing

Discussion in 'Homework Help' started by jody, Dec 29, 2014.

  1. jody

    Thread Starter Member

    Nov 12, 2012
    39
    0
    im having trouble testing a mosfet. its an n channel STP7NK80Z diode protected. i have been trying to learn how to do the simple test with a multimeter set on diode test. as i understand it i put the positive lead to the drain and the negative lead to the source. i should get no reading.now if i touch the drain and gate together it should let the mosfet conduct. if i measure with the red lead on the source and the black on the drain i get a reading which i believe is the reading of the protection zener diode.
    am i doing this right as i have tried 2 mosfets now and cant get them to conduct. is there something different with this being a diode protected one??
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    You cannot read the resistance from Drain to Source with the gate floating, because there is no way to tell if the charge stored on the Gate is sufficient to turn the device on, or not.

    Shorting Gate to Source should show open when red lead is on Drain, and a forward biased Schottky diode if you reverse the Ohmmeter leads.

    Connecting Gate to Drain, you cant say anything because the Ohmmeter's open-circuit voltage may be enough to begin to turn on the NFET or not...
     
  3. jody

    Thread Starter Member

    Nov 12, 2012
    39
    0
    hi
    i gave in and bought a mosfet tester. great little piece of kit
     
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