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Subject: Re: Problems with MOSFET drivers
NNTP-Posting-Date: Fri, 15 Nov 2002 19:13:59 GMT
Organization: AT&T Broadband
Date: Fri, 15 Nov 2002 19:13:59 GMT
Mike Poulton, analog wrote:
>> Yes. The feedback waveform is both delayed and not symmetrical
>> about the input threshold of the driver ICs. This will lead to an
>> improperly phased, non square output waveform to the gate drive
> Good call. You're right. The phase feedback phase is incorrect,
> and it needs to be shifted. That should help quite a bit with the
> lack of (proper) oscillation. However, it won't stop the exploding
> driver IC's.
Actually it just might. As it is your circuit is forced to operate
with unbalanced drive waveforms at the wrong frequency, possibly in
a non linear fashion (relaxation mode) that may lead to the drive
transformer saturating enough to either cause reverse currents into
the driver ICs in excess of their ratings (leading to immediate
failure) or to the average output current exceeding the 2A(?) limit
of the driver ICs (leading to a slightly delayed thermal failure).
You might be able to prevent blow up by shunting the driver IC
outputs with a pair of beefy Schottky diodes to Gnd and Vcc.
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