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Re: [Amps] MOSFET ratings

Subject: Re: [Amps] MOSFET ratings
From: Steve Thompson <>
Date: Sun, 17 Jul 2011 23:11:16 +0100
List-post: <">>
One cross reference for the IXYS transistor you mention is 
STP4NK80Z. If you look at the ST datasheet, it shows the lower 
dV/dt as applying to the MOSFET diode and two different circuits 
for test/measurement of the main switching dV/dt and the diode 
recovery. Does that help? I guess you would need to find some more 
general data about the FETs to get detail about what the diode 
slew rate limit means in practice.


> For example, take the data sheet for the IXFP3N80. This transistor is 
> rated for a rise time of 14 ns, to slew from zero to 400V, under certain 
> conditions of base drive and drain current. Assuming that the voltage 
> ramp is linear, that would be a dv/dt of 28 V/ns. If the ramp is 
> nonlinear, the peak dv/dt would be even larger. But this same 
> transistor, in the same data sheet, is rated for an absolute maximum 
> dv/dt of only 5 V/ns!
> The same discrepancy happens in the data sheets of many other MOSFETs. I 
> don't know what I'm misunderstanding here, if perhaps that low absolute 
> maximum dv/dt rating is valid under totally different conditions, or if 
> these data sheets are simply wrong! I notice that many manufacturer 
> specify either 5 or 10 V/ns of absolute maximum dv/dt, for transistors 
> that actually seem to have very different rise times. Could it be that 
> these dv/dt ratings are simply copied from one data sheet to the next, 
> and do NOT reflect the true capability of each transistor?

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