Quote:
Originally Posted by MPaulHolmes
Sorry, I was away getting pinewood derby supplies for my 3 year old. "He's" going to enter the competition on Nov. 20th. hahaha.
I'm using 10 stth6002c diodes.
If you use a diode and resistor in series, the mosfet drain voltage will pulse MUCH higher than if you don't have a resistor in series with the diode, assuming paths are already at a minimum length. I also simulated that, but I haven't posted it. With a resistor it was 300v at the mosfet, and without the resistor it was about 140v at the mosfet.
I think your layout is the reason you are observing different results. I think you should have each diode/capacitor/mosfet loop as small as possible, because that loop has the fastest changing current on it. Everything else is a slop fest (meaning the other stuff can be relatively long).
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I realize that by using a resistor and diode in series, the voltages will be higher. How much higher is dependent upon the size of the resistor, of course. This is the reason I have been experimenting with the combination of zeners, capacitors and diodes. If I could duplicate your results and obtain waveforms with limited peak voltages and also control excessive ringing with the conventional flyback design, I would simply opt to use flyback diodes alone. I will try shortening some of the connections again but I can't commit to a design when I can't reproduce the results and feel safe my mosfets will be protected.