> FWIW, at the meeting last night I discussed the switching FETs slated
> for the new gizmocopter PWM motor drivers. They use a case which
> is somewhat like the TO-220, but a bit larger (TO-247). Here's a link to
> the package spec:
>
> http://www.irf.com/package/hexfet/to247.pdf
> <http://www.irf.com/package/hexfet/to247.pdf>
>
> The datasheet for the transistor is here:
>
> http://www.irf.com/product-info/datasheets/data/irfp054.pdf
> <http://www.irf.com/product-info/datasheets/data/irfp054.pdf>
>
> The snubber diode I'm considering is here:
>
> http://www.irf.com/product-info/datasheets/data/hfa30pb120.pdf
> <http://www.irf.com/product-info/datasheets/data/hfa30pb120.pdf>
>
> I believe if we attach one set of these components (one FET and one
> diode) to each arm of gizmocopter -- directly under each propeller, then
> cooling won't be a problem.
That's the way it looks to me. Pdiss from FET on-resistance and max current is 30A x 30A x 0.014 Ohm = 12.6W. Then, junction to case thermal resistance gives junction temp. rise -- 12.6W x 0.65 deg. C/Watt = 8.19 C above ambient.
We'll still want to mount them on a metal plate, just because metal is easier to work with. But I don't think a heat sink will be needed.
> The FETs can drive up to 70 Amps continuously, but I
> can't imagine we're going to even get close to those conditions. The
> diodes are rated for just 30 Amps continuous, but 90 Amps repetitively
> pulsed, so I believe they'll do alright in their roll as snubbers. I may
> want to reconsider these particular diodes as their reverse breakdown
> voltage is much much higher than would occur in our 12 VDC system.
Unless diodes with a lower PRV are much less expensive than these, I say buy them. When you're a diode, you can never have too high a PRV. Even at 1200V.
But why do you need external snubber diodes when the IRFp054 has one built in?
Chris
_______________________________________________ ERPS-list mailing list [EMAIL PROTECTED] http://lists.erps.org/mailman/listinfo/erps-list
