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From: firstname.lastname@example.org (Adam Seychell)
Subject: Re: Problems with MOSFET drivers
Date: 16 Nov 2002 17:39:52 -0800
NNTP-Posting-Date: 17 Nov 2002 01:39:52 GMT
Mike Poulton wrote in message news:...
> I would also note that this is far from the first time I've built a
> switching power supply containing a mosfet H-bridge. This is the
> highest frequency and highest power I have tried to switch, though --
> both by an order of magnitude. It is also the first time I have tried
> to switch a high voltage load with a full bridge, thus requiring
> complete isolation of the gates from the driver circuit.
You say that the drivers blow only when you connect the feed back
You have not said what's exactly coming out from this winding. The
drivers should be driven with fast square waves. It would be helpful
for us if you explained more about your transformer configuration and
what wave forms you observed during bench tests with function
generator and no bridge voltage. I'm interested in how you made a 600
KHz 1:1.5 gate drive transformer for 4 large die FETs ?
If it were me building it I'd use four twisted pairs around a u ~ 3000
ferrite and take one wire from each pair and parallel them to make the
primary. The other wire form each of the pairs goes directly to the
MOSFETs. Its much easier to make a low leakage 1:1 transformer than
You probably need something more clever like a phase locked VCO to
control the bridge. That way you can guarantee 50% duty cycle and
frequency can never accidentally get out of range to cause everything
going up in smoke but rather just quietly oscillates out of tune.
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