DRSSTC Update

gentoo_daemon, Wed May 09 2007, 05:31AM

I finished that half bridge DRSSTC. I ended up going with 15 strings of 4 of the CDE caps. Everything worked fine. The ti drivers actually drove the bigger IGBTs. Resonant freq was about 41 kHz

here is a photo of the coil and my project partner, Leslie.

Link2
Link2

I ran at 1/3 power for a while. ( got small arcs). Everything was fine until i turned up the power to max. That's when I think an arc struck my MMC terminal and there was a flash by the IGBTs. :( Now I had a short on the input of my coil. So i took my bridge apart to find that the IGBTs were indeed shorted across emitter and collector. Is this usually the case when you overvoltage them?

I had the driver board well protected, but the half bridge and the mmc were pretty much exposed.

I'm going to upgrade to the pwrx cm600 IGBTs, a full bridge this time.

Re: DRSSTC Update
Steve Ward, Wed May 09 2007, 06:29AM

Well, these things do tend to blow up when everything isnt perfect (and even still when they might be). I doubt it was simply an arc between the MMC and bridge... its never *that* simple. The flash you saw was very likely just the IGBT failing (unless your MMC was mounted with .25" of the IGBTs). I hope you didnt have the impression that these things were easy amazed .

Anyway, good luck with the trouble shooting. Larger IGBTs might just be what you need. You should be measuring your primary current during these tests to make sure things arent wildly out of control. Being out of tune will make small sparks yet run enourmous current through the IGBTs.
Re: DRSSTC Update
gentoo_daemon, Wed May 09 2007, 02:23PM

Steve Ward wrote ...

Being out of tune will make small sparks yet run enourmous current through the IGBTs.

Yeah I noticed that when i first turned it on. I had the OCD pot set to 2 volts, and my LED was blinking constantly yet there wasn't really any output. After it was tuned, this went away.


Re: DRSSTC Update
gentoo_daemon, Wed May 09 2007, 04:41PM

Steve Ward wrote ...

I doubt it was simply an arc between the MMC and bridge...

I meant there was an arc from the toroid that struck the mmc terminal since it was sticking out quite a bit.

Re: DRSSTC Update
Steve Ward, Wed May 09 2007, 05:19PM

I meant there was an arc from the toroid that struck the mmc terminal since it was sticking out quite a bit


Oops, i just misread your post. That could indeed cause the failure. So the sparks were that long already huh? Sounds good!