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Anyone have success with these bricks in a DRSSTC?

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williamn

Thu Aug 17 2006, 04:56AM

Registered Member #55 Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149

I have been slowly converting my medium DRSSTC to run on one of these bricks. It has a measured Fres of 83Khz. I am using Steve Ward's new high side brick driver circuit. Here is a picture of the setup, in it you see the Toshiba brick, gate drive PSU and the two driver boards. The scope shot is a pic of the IGBT gate being driven at 83Khz with +30, -10V. What do you guys think?

Steve Ward

Thu Aug 17 2006, 05:24AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Looks good to me Will. For 83khz, those waveforms look very promising.

You might want to look carefully at sizing the turn ON resistance. I think i ended up with 10 ohms for my CM300 drivers. This results with the gate voltage sitting in the miller region for about 400nS. Yes, its far longer than it could be if the resistance was 0 ohms, but i found it greatly reduced voltage spikes caused by reverse diode recovery (which is related to the opposing IGBT turning ON). Then again, my snubbers reduced voltage spikes a lot too until they blew up (over-stressed 500V cap to 800-900V). Now the coil works fine with no snubbers

. So maybe those short little voltage spikes caused by diode recovery dont really do much harm to the IGBTs. My old gate driver didnt have any gate R, and that seemed to work fine too. But be careful about shoot-through! So the turn on resistance is at least useful for that, and if you need some delay anyway, why not soften that diode recovery at the same time?

williamn

Fri Aug 18 2006, 02:58AM

Registered Member #55 Joined: Thu Feb 09 2006, 04:56AM
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Posts: 149

I used 10 ohm resistors for the gate resistor so we should be fine there. Here is a pic of both gates being driven at 83khz. I am getting ready to fire it up on a low voltage tuning run here in a few minutes and will report back.

Here is a pictute of the coil next to my small DRSSTC for size comparason. I think I need to go to a 6" secondary that 4.5 looks kinda skinny.

Only a few minutes from running time!

UPDATE: No problems during the test run, the coil works. I only went up to about 65V on the variac and no more than 50usec on time to tune, the coil seems to like 4 turns, when the calculator predicted 5.5-6. I don't think I am near the proper spot becuase it took up to 50V or so to get some decent spark. I did notice though that once I bumped it up to 65 the sparks got much bigger. I dont really want to eyeball this one so I will hook up a Ct and see if I can find the sweet spot. Prior to the test run I addded another string of caps because according to wintesla I needed it for my 5.8 turn primary (mmc= .375uf 4kv). Details, details, the coil does work and I have had about 12" streamers so far.

Will

Reaching

Fri Aug 18 2006, 12:34PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

nice william

good to see those bricks working in a drsstc, i have 2 of this sorta bricks but never got round to use them in a drsstc, more in a quick wired up induction heater etc.

and 12" for 65volt input, not bad, wait to see some pics of this nice little beast

williamn

Sat Aug 19 2006, 07:46PM

Registered Member #55 Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149

Thanks Reaching. I am just about finished tuning the coil, I just need to tweak it a bit here and there. I am going to set it up outside tonight and have its first full power run. I will take some pictures and videos for posting. I hope to prove that these bricks are a viable IGBT to use in DRSSTCs, they are cheap and plentiful on ebay and I have 19 left

UPDATE:Its been raining outside and I did not want to take the chance of having a shower pop up while I was testing (Houston is notoriuos for that) so I set everything up in my garage. The IGBTs work great, I have flogged this coil pretty hard and they are still fine. I am having troubles with my OCD circuit though. Even at max setting (1000A) it still engages at about 75% vin with an ontime setting of 50usec or higher. I increased the coupling a bit to see if that helped which it did. I would think the IGBT would pop at 1KA so its more than likley noise. I am sure once I figure it out I should be home free. So to anwer the question wether or not these bricks are any good I would have to say YES deffinately.

williamn

Sun Aug 20 2006, 11:02PM

Registered Member #55 Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149

I figured out the OCD problem and fixed it, I also increased coupling a bit more as I wasnt having any racing sparks so why not. I have run the coil for most of the day and by the end of the last run (10minutes) the .25" copper tubing was HOT, I have been trying to break it

Here is a picture from a video I took today. I will upload it to my website in an hour or so. This is a 40" strike to a grounded target. Pretty good!

HV Enthusiast

Sun Aug 20 2006, 11:09PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

Looks good.

Also, what was the OCD problem and how did you solve it? This information would be good for others that would have similar problems.

williamn

Mon Aug 21 2006, 12:41AM

Registered Member #55 Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149

Thanks! To fix my noise issues with the comparator I put a 10uf Tantalum cap across its supply rails and also added a 100pf mica cap across the inverting input to ground. This seems to have done the trick as now it engages at the proper current levels. Here is the video that I took that snapshot from: http://www.texaslightning.4hv.org/DRSSTC-Toshiba.wmv

Terry Fritz

Mon Aug 21 2006, 01:52AM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi,

Also, what was the OCD problem and how did you solve it? This information would be good for others that would have similar problems.

For the record, here is what I did to fix my 'many' OCP problems:

Schematics here:

Here is the video that I took that snapshot from:

)))))

Don't worry about the "frequency" specs in the data sheets. As Steve mentioned, switching time is all that matters to "us". At a 5% duty cycle, the switching loss and heating is just not a problem we neet to worry about like that...

Cheers,

Terry

JimG

Mon Aug 21 2006, 03:26AM

Registered Member #52 Joined: Thu Feb 09 2006, 04:22AM
Location: Austin TX
Posts: 57

With these things showing up on ebay relatively cheap it's cool to see that someone has gotten around to testing them above the speculated 20 KHz.

How hot does the bridge get after a run?

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