Power MOSFET/IGBT Internal Gate Resistance Measurement

Discussion in 'General Electronics Chat' started by Bakez, Jul 14, 2013.

  1. Bakez

    Thread Starter Active Member

    Aug 21, 2012
    I am wondering if anyone has any good documents on the internal gate resistance of a MOSFET.

    I am searching for a way to measure it.

    We know it exists, but other than it being listed in the datasheet there doesn't appear to be much information on its behaviour:
    - how can we measure it?
    - what is its behaviour in circuit?
    - what are the material properties that influence it?
    - how does its value change with aging?

    The only good document I can find is this: http://www.st.com/st-web-ui/static/...ical/document/application_note/DM00068312.pdf

    But the conclusions this makes are fairly logical - a higher internal gate resistance means higher switching losses and higher chip temperatures.

    I would like to find a way to measure it when the MOSFET is in a converter. I have read this thread here: http://forum.allaboutcircuits.com/showthread.php?t=47432 and also methods that say I have to short the drain and the source, or use an LCR meter - but I don't think that helps me.

    These values are usually quite large, between 1to 10Ω from some datasheets i've just looked at. I think it should be possible to measure it. surely the peak gate current is related to it? I could just put a 2V (or something below threshold voltage) on the gate and measure the peak gate current and infer it from this? But then the parasitic capacitances and inductances also have an effect? I could also infer it using some modelling from actual switching waveforms (id imagine this would get complicated though)

    Ultimately I would like to find a way to do this while the MOSFET is in an operating converter

    Moderator Edit: Deleted post restored. Do not delete existing posts!
    Last edited by a moderator: Oct 1, 2013
  2. wayneh


    Sep 9, 2010
    I don't know how feasible that is, but with the gate disconnected from the circuit, couldn't you treat the MOSFET like a capacitor and measure the ESR? There are meters you can get to measure ESR, basically by applying an AC signal to the gate and looking at what happens.