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I'm using a logic-level N-Channel MOSFET, specifically the FQP30N06L. It doesn't appear to work in my circuit, so I decided to attach a DMM to it for test. My test was as follows:

  • DMM to ohm / diode test mode
  • Negative (COM) Lead to the source pin
  • Positive (INPUT) Lead to the drain pin

The results are showing 570k ohms resistance between the two. Is my test flawed, or is this MOSFET bad?

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    \$\begingroup\$ Did you leave the gate floating for this test? Static electricity could produce pretty much any behavior in that case, from very high to pretty low resistance measured for the channel. \$\endgroup\$
    – The Photon
    Commented Apr 26, 2019 at 16:24
  • \$\begingroup\$ @ThePhoton - Indeed. I just connected the gate to GND and I'm still seeing 541k ohms \$\endgroup\$
    – t3ddftw
    Commented Apr 26, 2019 at 16:26
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    \$\begingroup\$ Probably best is to connect it to the source. \$\endgroup\$
    – The Photon
    Commented Apr 26, 2019 at 16:27
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    \$\begingroup\$ Is the FET still connected to the rest of the circuit, or did you remove it from the circuit? \$\endgroup\$
    – The Photon
    Commented Apr 26, 2019 at 16:32
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    \$\begingroup\$ Sounds like a bad FET, given the leakage current spec is 1 uA with 60 V applied drain to source. \$\endgroup\$
    – The Photon
    Commented Apr 26, 2019 at 16:34

1 Answer 1

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Connect drain to source and measure the resistance to the gate. it should be infinite (much more than 1 Meg) with both meter polarities.

Connect gate to source and measure source measure to the drain. it should look like a diode

The data-sheet says up-to 1μA leakage with the gate connected to source depending on your meter that could be the 500kΩ reading you are seeing.

Logic level MOSFETs don't turn off as hard (with Vgs=0) as regular MOSFETs do due to the threshold being closer to 0V

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