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

[John]

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
https://ec.irf.com/v6/en/US/adirect/ir?cmd=catProductDetailFrame&productID=IRFP2907PBF

The IRFP90N20D is spec'd at 39S at 50Vds, 56A
https://ec.irf.com/v6/en/US/adirect/ir?cmd=catProductDetailFrame&productID=IRFP90N20DPBF

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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[leo123]

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, 125Ahttps://ec.irf.com/v6/en/US/adirect/ir?cmd=catProductDetailFrame&prod...

The IRFP90N20D is spec'd at 39S at 50Vds, 56Ahttps://ec.irf.com/v6/en/US/adirect/ir?cmd=catProductDetailFrame&prod...

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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.....

 

[John Larkin]

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
https://ec.irf.com/v6/en/US/adirect/ir?cmd=catProductDetailFrame&productID=IRFP2907PBF

The IRFP90N20D is spec'd at 39S at 50Vds, 56A
https://ec.irf.com/v6/en/US/adirect/ir?cmd=catProductDetailFrame&productID=IRFP90N20DPBF

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

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

John

 

[John]

Look at the transfer curve, the curve of Id versus Vg. The derivative
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. <grrrrr> 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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