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

M

#### Mook Johnson

Jan 1, 1970
0
Gents,

I've seen several app notes showing using complementery N/P channel fets to
drive a brushless DC motor with a low bus voltage (say 12 - 80VDC).

I have an application that has a 150Vbus. Is there any reason I could not
use a 250 - 400 watt P-channel with appropriate currnet rating?

Id the appnote stop at 80 volts because the P-channel devices of the time
were wimpy and not desired?

I know I could use all n-channels but the floating gate drive is getting to
be problematic due to the long duty cycles. It can be done and I'm
investigating a small footprint solution.

My problem is that the application is at very high temperature (>150C) and
the standard "easy" answers don't work. (IR2110 or optocouplers). The next
step is gate drive driving a carrier through the transformer and
demodulating it on the other side.

Seems like if it could work, a P-channel high side drive would be a better
choice.

What are your opinions on complememtary motor drive for a 150Vbus brushless
motor driver.

R

#### Robert Latest

Jan 1, 1970
0
Mook said:
I have an application that has a 150Vbus. Is there any reason I could not
use a 250 - 400 watt P-channel with appropriate currnet rating?

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.
What are your opinions on complememtary motor drive for a 150Vbus brushless
motor driver.

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

J

#### John Larkin

Jan 1, 1970
0
Gents,

I've seen several app notes showing using complementery N/P channel fets to
drive a brushless DC motor with a low bus voltage (say 12 - 80VDC).

I have an application that has a 150Vbus. Is there any reason I could not
use a 250 - 400 watt P-channel with appropriate currnet rating?

Id the appnote stop at 80 volts because the P-channel devices of the time
were wimpy and not desired?

I know I could use all n-channels but the floating gate drive is getting to
be problematic due to the long duty cycles. It can be done and I'm
investigating a small footprint solution.

My problem is that the application is at very high temperature (>150C) and
the standard "easy" answers don't work. (IR2110 or optocouplers). The next
step is gate drive driving a carrier through the transformer and
demodulating it on the other side.

Seems like if it could work, a P-channel high side drive would be a better
choice.

What are your opinions on complememtary motor drive for a 150Vbus brushless
motor driver.

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 W #### Winfield Jan 1, 1970 0 This approach is a bit more complex, but popular and very inexpensive. 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.

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.

J

#### John Larkin

Jan 1, 1970
0
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

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