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Old 11-29-2009, 03:00 PM   #2658 (permalink)
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One thing to mention. upgrading to the better diodes can be done, but would be a pain. You would have to have a good desoldering station, or a $6 solder sucker from Ebay, like I use. I've replaced individual mosfets like that before. It was not what I would call fun. It's what I would call, "anger time".

By the way, I just now tested the pwm outputs in complementary mode on the new dsPIC. I was able to control them with a throttle circuit that inputted into one of the A/D channels! The A/D converter was initialized correctly! hurray!!! At this point, I could actually take the piece of garbage breadboard circuit sitting on my desk and run some sort of synchronous rectification controller! It would probably blow up, but it would work at least for a little while. Really I need to add the hardware overcurrent stuff and all that other crap. REally what I'm going to do is just modify the Rev. 2c circuit for this microcontroller. Then I'll already have all the protective stuff all done! I think that it's relatively minor what needs to happen to make it work. For the high side drive, I'm just using a second 12v-12v DC to DC brick that will power a 2nd mosfet driver for the high side mosfets. The DC-DC has an isolation of 3kV for 1minute, so I think it will be fine.

The neat thing about the synchronous rectification is that it more efficient until you get to really really high currents. It's like using freewheel diodes with a 0.2 or 0.3v drop until you get to like 400 or 500amps. Then it's up into the 0.6 range, and a little higher, it gets crappier, but I'm not going to be pulling 230 amps per device. I have a family and I want to see my son grow up.

The PWM outputs have a dead time of 2 us and are the NOTs of each other. hurray!
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