Re: An extremely good MOSFET driver

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Original poster: "S Gaeta by way of Terry Fritz <twftesla-at-qwest-dot-net>" <sgtporky-at-prodigy-dot-net>

Hi Ken,

Those MOSFETs were switching 400V! They used another switch bank to boost
the rectified and filtered line to 400VDC using the "Boost" topology. IRFP
460s were used for that, as well as for the inverter. 400 volts was used for
the inverter to keep the transformer small for that power level (probably
for other reasons too, that only engineers understand!) It's like stepping
back in time to when you had to worry about getting bit by B+ voltage!. I
don't really see how the PWM chip could possibly care, or have any idea
about what the MOSFETS are switching, since the gate(s) is/are all that that
the driver sees. Unless, of course the MOSFETS fail, which happened a bit
too often for my poor frail nerves! If the inverter fets blew, sometimes the
bias supply(L.V. which powered the blowers, among other things, including
the PWMs) continued to function, and the blowers would sometimes cause the
flames to come shooting out from the front of the supply. Any time the fets
blew, it would take out their driver, and made the PWMs look like an
EPROMs(It made almost perfect holes in the middle of the IC). At only 1KW,
these supplies humbled even the toughest technicians that work there! Of
course it was always funny when it happened to someone else :-). Everyone
knew not to stand in front of those things. Sometimes one of the only
components left intact was the fuse!

Sue

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, August 10, 2002 3:24 PM
Subject: Re: An extremely good MOSFET driver


> Original poster: "K. C. Herrick by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <kchdlh-at-juno-dot-com>
>
> Sue (& all)-
>
> Thru-hole ICs--DIPs--for sure:  My old eyes are too poor to dream of
> fussing with SMTs!
>
> I checked the UC3865Q's data sheet: it appears to be for low-voltage use
> only--& it includes a VCO which I would not have use for.  No charge pump
> since it is not intended to drive a high-side MOSFET that is at any V.
> higher than 22 or so.  Those IR 2110-type devices' charge pumps are
> evidently quite high-impedance circuits.  Big electric fields mess them
> up--at least, that's what I think I learned the hard way.
>
> Ken