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How can I compare MOSFET transconductance specs when test currents are different?

I was looking at the specs for two MOSFETs, the IRFP2907 and IRFP90N20D, and was wondering how I could compare their transconductances?

The IRFP2907 is spec'd at 130S at 25Vds, 125A

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The IRFP90N20D is spec'd at 39S at 50Vds, 56A

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How can I tell which one has the lower transconductance in the 0A-25A range at 0Vds-55Vds?

It seems that I'd use one of the drain-source voltage vs. drain current curves for the Vgs I'd be using? I could derive a couple of di/dv numbers to get the transconductance? But, those curves are such low resolution that the numbers aren't very useful.

And since IR's datasheets don't have transconductance vs. drain current curves, how can I find out the lower drain current transconductance values for these FETs?

Thanks! John

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Reply to
John
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125A
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56A
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Reply to
leo123

Look at the transfer curve, the curve of Id versus Vg. The derivative (slope) of this curve is the transconductance.

John

Reply to
John Larkin

OK, cool.... To get the most accurate data, I'm guessing I should try to find the smallest "slice" of the transfer curve (in the region for my target drain current) when calculating the slope.

IR has some really lousy, low-res graphics for their transfer curves though. Why can't they just post the transconductance curves like so many other companies. :-)

Thanks again for your help John!

John

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John

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