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Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Are you perhaps forward biasing your TVS diode strings when the IGBT wheeling diode is supposed to be conducting? Check the voltage drop of the TVS diodes in forward mode to find out.
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
Hi dude_500 nice work I also hate using gate derive transformers for bricks. one of the problem is that the electronics have delay and I think that yhey may not switching on zero cross. do you have a dead time adjust. I use plastic fiber and IXDD414ci drivers and seperate power supplies for my bricks and I think one of the problems I have is delay problems. have you added some phase leading or some sort of digital compinsation. bar component failure you design looks good on the surfsce . transorbs have a tendancy to short when a failure ocurs but if you have a acurate zero cross thet may not be necisary
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I did a quick comparison of the datasheets for the CM600HA-24H and the device we're discussing here.
One thing that jumps out at me is, the reverse recovery charge of the CM600's diode is quoted as 4.46uC, but for the other device it's 110uC: 20x worse. (The Eupec datasheet quotes the charge in "microamp-seconds", but those are the same as microcoulombs.)
So, your reverse diodes could be blowing out simply because they're really slow.
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
teravolt, yes I do have phase lead compensation on this coil.
I'm building a CM600 bridge now, I no longer approve of these big slow bricks I was using for tesla coil use. The recovery diodes in them just fail at life.
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
if you build a big tesla the secondary Fo may be low enough for you say 50 khz. I tried driving the piss out of those bricks and got a full bridge up to 100khz with dead time using 2 ixdd414ci in parallel with 20v at half an ohm.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
teravolt wrote ...
if you build a big tesla the secondary Fo may be low enough for you say 50 khz. I tried driving the piss out of those bricks and got a full bridge up to 100khz with dead time using 2 ixdd414ci in parallel with 20v at half an ohm.
The problem is the deadtime (when the freewheeling diodes turn on) needs to be at least 10uS long, so you'd be looking at sub 10KHz operation.
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
bwang, the doides wont turn on if there is soft switching typicaly you don't need more than +- 5% of dead time from zero. the switch times that in the data sheets are about 450ns on the fall and a 700ns rise plus about 100ns for dead time. 100khz is 10 us so I know that a tesla of 50k to 75k should be doable.
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