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Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
I've noticed a lot of people use much-higher-than-datasheet voltages to drive the gate of IGBTs, usually in DRSSTCs, and get away with it (as opposed to mosfets, where it busts the gate structure)
My question is, how much can you overdrive the gate by? I'm struggling to find any actual figures, and would rather not blow one up to find out. Also, is it safe to swing the gate negative by the same amount?
I don't have the part number on hand for my IGBTs, but they are about about 60 amp pulsed in a TO247 package, just to give an idea.
Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
Thanks, I'll ramp it up to 30V and see what happens, I think if it survives 30V I'll just leave it at that anyway (datasheet states +-20V absolute max)
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
IGBT gates aren't any less sensitive to destruction than MOSFET ones, so we try not to use any more voltage than really needed. The most I ever used was 24V on the big brick IGBTs, and I managed to push about 3-4 times the maximum pulsed current through them without trouble.
When I used smaller devices on my DRSSTC I only ran them at +/-15V, since I wasn't looking for much more than the datasheet maximum pulsed current of 400A.
As far as I know, swinging the gate negative isn't any different from a damage perspective than swinging it positive. I did design my latest driver to swing from +24 to -12 to save on the total amount of swinging that needs done.
Registered Member #358
Joined: Sat Apr 01 2006, 06:13AM
Location: UCSB
Posts: 28
My old DRSSTC ran 37v on the gate, and it hasn't caused any problems (I had a likely explanation for every explosion that didn't involve too much gate voltage )
I was able to run my CM150DU-12H IGBTs up to 1700 amps with no problems at this gate voltage, which is 5.67x the rated peak current.
Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
So I take it that the IGBT's ability to work at several times it's rated peak current is just due to the fact that you are getting much faster switching times by overvolting the gate. (less time in linear, less heating)
I have quite a few of these little 60 amp peak devices, I think I'll throw together a little drsstc when I get around to it. If I could get twice the pulsed rating I'll be happy!
Registered Member #85
Joined: Thu Feb 09 2006, 01:22PM
Location:
Posts: 21
Actually the reason for the high gate voltage is to keep the igbt saturated when turned on. Otherwise if the current is too high and the gate voltage too low it is in linear mode the whole time it is on. There are some graphs in igbt datashets showing the maximum current for saturation in relation to the gate voltage, but they usually stop at 15V so you have to extrapolate a bit.
While this method works very well in drsstcs(soft switching), dont expect it to work with hard switching. There is nothing to my knowledge that can be done to improve the maximum turn off current of igbts. Please correct me here if i am wrong.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
There is nothing to my knowledge that can be done to improve the maximum turn off current of igbts. Please correct me here if i am wrong.
There will be 2 limitations here, power dissipation and voltage limitations. The first is caused by the fall time, where you have an overlap of voltage and current (power) across the device. The voltage problem is related to V=L*di/dt. You can help fix both problems with a snubber which 1) clamps the voltage excursion, and 2) if its the right snubber, can give zero voltage switching (assuming a special snubber that starts with 0V on the capacitor initially). Of course, there are still parasitic inductances that will slightly ruin this ideal situation, but it can still be pretty good. My large boost converter uses such a method to take care of both problems, leading to a far more efficient design.
Registered Member #85
Joined: Thu Feb 09 2006, 01:22PM
Location:
Posts: 21
That sounds good. So do you think i could improve the maxiumum turn off current of my igbts that have a turn off safe operating area as in the following picture by making them switch off at zero voltage with a snubber?
I am rather pessimistic about that because the soa does not show higher currents for lower voltages
I already bought 100 of those igbts for paralleling them to get a decent current for my coilgun, but it would be cool to boost the maximum current some more
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Steve Conner wrote ...
IGBT gates aren't any less sensitive to destruction than MOSFET ones, so we try not to use any more voltage than really needed. The most I ever used was 24V on the big brick IGBTs, and I managed to push about 3-4 times the maximum pulsed current through them without trouble.
When I used smaller devices on my DRSSTC I only ran them at +/-15V, since I wasn't looking for much more than the datasheet maximum pulsed current of 400A.
As far as I know, swinging the gate negative isn't any different from a damage perspective than swinging it positive. I did design my latest driver to swing from +24 to -12 to save on the total amount of swinging that needs done.
Well, quite few IGBT's have defined 'pulsed' gate voltage, like 30V for 30N60; so it seems that it completely safe to operate with +-30V in DRSSTC's. (and even little more than that, according to jimmy ).
I didn't yet see a 20V IGBT that popped on anyone when overdriven like this; it seems that this depends a lot on how device is constructed internally.
If somebody had destroyed an IGBT that way, I hope he'l be interested in thread..
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'Overdriving' IGBT gate
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