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Registered Member #1535
Joined: Wed Jun 11 2008, 11:37PM
Location: Northeastern Pennsylvania - USA
Posts: 117
In regards to driving the high side transistors, it was just as Steve Ward said. Use isolated power supplies to drive the opto's or build a bootstrap design. Bootstrap seems easy. An extra diode and capacitor, but the high side opto's only get their power capacitor charged up when the corresponding lower transistor fires. This could lead to complications. I made one. It works. I blew it up several times. I've abandoned that. I still have one design I've built with isolated power supplies. Haven't blown that one yet. These have advantages, but it certainly costs more...
Registered Member #883
Joined: Sat Jul 07 2007, 01:02PM
Location:
Posts: 16
ok, so why is there an issue with using drsstcs fed with voltage doublers? most optos ive seen are rated to stand off 3.5kv to 5kv. surely there is not that much voltage floating around in the tank circuit is there. the switches are only rated up to like 1200v
Registered Member #1739
Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261
Steve McConner wrote ... I also designed a GDT-based driver that overcomes the disadvantage that Lithiumlord mentioned, and I think others have done the same.
You mean which one - the size or the unipolar-exponential signal shape or the current? It all can be done with a GDT of course (even the signal shape), so basicly it all depends on your own preference - there's no absolute solution ;)
BSVi wrote ...
I have blown 6n137 up. The reason i found for this is high CM noise in drsstc. I use GDT since and have no problems )
Didn't check that concept for DRSSTCs, however in my ISSTC the coupler-based drive works well, the only two blows I had were after some serious overpower causing one overcurrent failure and one interference issue in the feeding circuits on the early test build. Other than those two accidents I had no blows at all, running like 2kW burst average power with sparks hitting a 60cm-away glass in smoothed-DC interrupted mode for a really long time already (both per-day and total work time) - even had a few flashovers on the early builds without any failure, so seems like at least that particular driver concept is a success.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I mean the drivers described in this thread:
They use a MOSFET driver stage after the GDT, which just carries a control signal, and another similar transformer to supply HF power to the driver. The driver switches between -12 and +24V and never hangs around at 0.
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optoisolators vs GDTs
