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Re: Smokin' gate drive chips on DRSSTC-2 board



Original poster: Sue Gaeta <sgsparky@xxxxxxxxxxx>

Hey, wait a sec! Let's take this a half cycle at a time, because I am confused now. I thought that when U34 and U35 (positive going pulses) go high, current will flow through C45 and C46 to the transformer, I think we agree for the first half cycle, but then that automatically means that the caps are in backwards right from the beginning according to SC2048 which shows positive pulses, but the plus signs of the caps are on the other side!

If that's not bad enough, here is where we seem to disagree. It's when U34 and U35 go low, and U36 and 37 go high. Now the current flow through the transformer reverses direction, and it's gotta go somewhere! Its gotta come back through C45 and C46 and either gets sinked throgh U36 & 37, or must get dumped through CR36. I tend to think that the drivers are the actual path.

Now if the driver transformer were center tapped to return, and those two bottom drivers actually were putting out negative 15 volt pulses (which they are not), then I might think that the current was only flowing in one direction through the tantalums.

If I am wrong, and there is some kind of return path that I am not seeing, then putting a diode in series with the two tantalums, cathode towards the driver transformer should have no effect on the operation of the circuit. I am afraid to try it though :-)

Sue



>I think they block DC voltage from pumping a lot of current in the
>transformer if the thing is not oscillating. The caps would normally
>charge in only one direction and discharge through the transformer so they
>would be perfectly fine as is.