Power MOSFET/IGBT Internal Gate Resistance Measurement

Thread Starter

Bakez

Joined Aug 21, 2012
31
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/active/jp/resource/technical/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!
 
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wayneh

Joined Sep 9, 2010
16,398
Ultimately I would like to find a way to do this while the MOSFET is in an operating converter
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.
 
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