View Single Post
Old 11-06-2015, 01:00 PM   #2298 (permalink)
MPaulHolmes's Avatar
Join Date: Feb 2008
Location: Maricopa, AZ (sort of. Actually outside of town)
Posts: 3,832

Michael's Electric Beetle - '71 Volkswagen Superbeetle 500000
Thanks: 1,368
Thanked 1,163 Times in 757 Posts
turning the IGBTs off and on only takes the 8 or 12 amps for less than a microsecond with a duty of maybe 1%. Those pnp and npn transistors are rated for 8 amps continuous, so I think you could do just about any old current you want for very short bursts. Probably 10 Ohm resistors would be fine, and that would be around 7.5amp peak for 3 of them. But I doubt 4.7Ohm gate resistors would cause a problem.

I don't think you need local checking for desat detection. It was just mechanically convenient for me to have 3 local spots connected to 3 separate B+'s. I'm not sure how well the desat detection converts to mosfets though. IT's designed for IGBTs. Do mosfets have a 5 or 10uS short circuit capability ever? And would a drain to source on voltage of like 6 or 7 volts destroy the part before it had a chance to shut off? Now that I think about it, I bet it would work OK. A lot of these parts can dissipate several hundred watts. So, 600 or 700 watts (7volts * 100amp) probably would be OK for 1 or 2 microseconds. crap... Let's say the RdsON was 10mOhm. I don't know what it would really be. Then, to get to the required 7v desat on voltage, it would take 700amps. That would be 4900 watts. haha. Maybe desat isn't practical in that case. I don't know. I do know I've tested it on accident with IGBTs, and it works very nicely. It shuts off before the hardware overcurrent circuit from the LEM Hass current sensor. So, it's quicker than 3uS.

Yes, if you want -5v, just use a 5v zener. But if you are push-pulling with 24v, it will only be around 19v down to -5v. And yes, I think you could reduce the duty so that you could control the output voltage. Right now it is 50%.
kits and boards

Last edited by MPaulHolmes; 11-07-2015 at 10:59 AM..
  Reply With Quote
The Following User Says Thank You to MPaulHolmes For This Useful Post:
e*clipse (11-06-2015)