Re: H bridge progress

Another important feature that is overlooked initially is the
fast acting over-current protection circuit. The constant
off-time or a syncrounous-off time circuit is described in the
application notes of the L2xx bridge part. Its a good
starting point. Also at the voltages you guys are playing with,
IGBT's may need come into play.

Discontinuities in the brush commutation on bigger DC servo motors
can add a impulse noise that can do strange things to a H-bridge. I
made a servo drive that I was testing to 180vdc. It worked fine at
voltages up to 80-90vdc, but then as the motor got loaded, you
could see massive ringing spikes(that varied with motor RPM that
seemed to rise quickly in proportion to the current especially
if the motor was near being stalled and above 90vdc. Since
this was my first drive design, I had overlooked the current foldback
features needed to keep the MosFETs in the safe operation region.
Needless to say I popped a few. The international rectifier appnotes
have some good tips on reducing the overshoots and protecting the
bridge drivers. It awfully dull reading however.

-Lee