P-Channel high side gate drive for 150Vbus BLDC motor drive

I'm sure you mean volt, not watt.

A quick look at Farnell's site (which isn't the best-stocked, but has all the jellybean stuff) shows a single 250V P-Channel MOSFET, and that's a TO92 device. After that they havbe only 100V parts.

I don't know what makes it so hard to make decent P-channel power MOSFETs. Maybe it would be possible today, but there's no market because everybody has settled for N-channel only with floating high-side drivers.

Go bipolar? Oh... just checked. Not much luck there either.

My hunch is that even if there are high-power, high-voltage PMOS or PNP devices out there, they might be single-sourced and expensive. Personally, I'd definetely opt for all-NMOS and somehow wiggle my way around the other problems.

robert

High power, high voltage N-channel fets are cheaper and more available.

Drive is easy: use a cheap potted dc-dc converter to get floating power, then an optoisolator and a chunky gate driver; maybe $12 for the whole thing.

John

This approach is a bit more complex, but popular and very inexpensive.

There are some reasonably-good 400 to 500V p-channel power MOSFETs, but as you say, they aren't as good as n-channel (e.g. a poorer Rds-on * price, etc., figure-of-merit). But if the O.P. feels the need... He may think p-channel-drive circuits are more simple, but after he's added the ability to drive high currents into the p-MOSFET gates, I dunno.

Yup, I'm still using lots of the 300-watt Ixys parts you suggested. They're on the heatsink beast whose photo I posted to abse last week.

But it seems to me that there wouldn't be much difference in gate drive complexity. You wouldn't want to capacitively couple directly into a p-channel gate, not with the source that far off ground. I guess if you had multiple p-fets working off the + rail, h-bridges maybe, you could share the dc-dc converter.

Oh, did you ever used the drift step-recovery gadgets I sent? The project is dead on my end (ie, all the lawsuits are pretty much settled) so I don't consider the stuff to be secret any more.

John