[Amps] MOSFET ratings

[Steve Thompson]

OK Manfred.

Firstly, I should stress that you must not confuse me with someone 
who understands all about these MOSFETs :-) Your question spurred 
my interest.

I have been reading from my old (1987) IR catalogue, application 
note 966. This is describing the HEXFET III family, the first 
where diode dV/dt is specified. I have not had time to read it in 
full detail, but it refers to the diode recovery dV/dt limit 
applying "..as the diode recovers from conduction..." and 
describes a mechanism that occurs during the period that 
recombination is happening in the diode. If the value is too high, 
the bjt will conduct. I think the higher value is what will make 
the bjt conduct if the diode is fully 'off'.

I could not find AN-966 on line to give you a link - I can scan 
the article (7 x A4 pages, small print) for you if you wish.

Steve




> Steve,
> 
>> 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
> 
> Yes, that's right. But a MOSFET's internal diode is impossible to 
> separate from the MOSFET. So if the diode is limited to 5 V/ns slew rate 
> or so, then I can't see how the entire MOSFET could have a higher slew rate!
> 
> The data sheet of the STP4NK80Z claims 32ns for switching 400V with a 
> resistive load. That's 12.5 V/ns. If they mean to switch from 10% to 
> 90%, it would still be precisely 10 V/ns, but the data sheet gives a 
> maximum dv/dt of only 4.5 V/ns.