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

Discussion in 'Electronic Design' started by Mook Johnson, Apr 16, 2007.

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  1. Mook Johnson

    Mook Johnson Guest


    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

    What are your opinions on complememtary motor drive for a 150Vbus brushless
    motor driver.
  2. 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

  3. John  Larkin

    John Larkin Guest

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

    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.

  4. Winfield

    Winfield Guest

    This approach is a bit more complex, but popular and very
    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.
  5. John  Larkin

    John Larkin Guest

    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.

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