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Registered Member #1535
Joined: Wed Jun 11 2008, 11:37PM
Location: Northeastern Pennsylvania - USA
Posts: 117
Ouch. Yes, it was real. :( What can I say, it's my most epic fail. This was before my "first light" obviously. If you check my YouTube page, you can clearly see that I've gotten out of that stage. Hehehehe
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Steve Ward wrote ...
Here's one related to DRSSTCs:
On a clone of my DRSSTC-2 system a ringy gate drive circuit caused a CM300 failure, but not in the normal sense of "my waveforms look ringy!". The issue was that at the end of the drive cycle, the GDT was to shut off and be at 0 output, but instead the GDT would ring at around a few volts. This was enough to turn the IGBTs back on momentarily when the currents were still quite high. I suspect hard switching of 1200A or so to be the reason for failure. The IGBT failed just seconds after ramping up the power to maximum.
The fix: adding a parallel 50 ohm resistor with the DC blocking cap on the GDT to damp out this ringing (which is caused by GDT leakage inductance and blocking capacitor). With a clean turn off gate signal at the end, that system went on to run for years without ever failing another IGBT, eventually that whole drive was scrapped/recycled for an upgraded set of electronics, though the same CM300 modules were used and continue to work.
Woah sir, thanks for this information - I'm designing a GDT based driver for CM300 DRSSTC, and I would hate to have this happen to me as well! Are you 100% sure this was the cause of failures though? I remember you had problems with your early isolated gate drive, but I never thought you had problems with gdt's.
Steve Conner first suggested this resistor since his Mjollnir the DRSSTC, but he told me it's not a critical part and mainly serves to damp the ringing imposed on the top of the waveform during on-time. Apparently your issue is much more important.
Boozer: well, look at the bright side - you can always cut the secondary into several small coils for various uses!
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
TheBoozer wrote ...
Ouch. Yes, it was real. :( What can I say, it's my most epic fail. This was before my "first light" obviously. If you check my YouTube page, you can clearly see that I've gotten out of that stage. Hehehehe
Rich
So you never achieved breakout from that coil? A pity, I hoped for some spark pics at least!
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