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Registered Member #795
Joined: Mon May 21 2007, 06:04PM
Location: Bocholt, Germany
Posts: 35
Hi!
I have a thread about my big DRSSTC in the projects board, but I think for posting a question this new thread is better. At the moment I rectify the 230V AC from 3 lines with a M3 configuration (halfwave rectified here is the scematic (M3) (sorry, german)). So now I get about 320V DC. My IGBTs can handle up to 600 Volts. I a B6 configuration I would get about 560V DC. I have read in the forum that you should only push your IGBTs to about 2/3 of the maximum voltage. The Voltage peaks seem to be pretty small in operation. So if I am shure that the voltage peaks do not exeed 600 V, is it good to let the IGBTs work so near to their absolute maximum voltage, beside the problem of a hit of a streamer into the primary coil? Beside, the IGBTs are 2MBI600NT. (datasheet included)
What voltage would you prefer in my case?
Any ideas?
Thanks for the answers! (hope you can understany my english)
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
How do you know that the voltage transients are small? Whenever i probe my large IGBT bridges, the voltage transients from switching are usually 50 to 75% overshoot, so i would have to keep the bus voltage to just a little more than 50% of the IGBT rating.
Tell me more about how you are measuring your voltage transients on the IGBTs. In general i would say 560V is too close to the rating.
Registered Member #795
Joined: Mon May 21 2007, 06:04PM
Location: Bocholt, Germany
Posts: 35
Thank you for the fast answer.
I asked this question, because up to now I get over 2.3m sparks, and I think i can make a lot more.. This coil is still under construction, and I thougt about what would bring more sparklength. Then I thought of a higher supply voltage.
I measured the voltage with an scope. But just with small power, because measuring near the running TC is not that easy ;)
How would (do) you measure it?
I think the voltage overshoot appears just (or most) when the complete coil is running, so measuring it without the secondary coil is not recommended, am I right?
I have not spent much time into measuring, but I will now... I think in the next days (when the weather is not that bad as it is now) I will measure and post a few pictures of the scope.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
I measure my voltage spikes with just the primary circuit hooked up. My probes can only handle a few hundred volts, so im limited in that respect, but i can usually run it at about 200VDC on the bridge and measure the transients. As far as i know, this should be pretty much the same when the secondary is connected. My transients had a frequency of 10MHz or so, so be sure your scope has enough bandwidth to measure this.
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Question about voltage on IGBTs
