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Registered Member #55
Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149
You will want some sort of transient protection. IGBTs tend to be really sensitive to spikes, I found out the hard way. Especially if you are going to use doubled mains. I use the omnidirectional TVS across each IGBT. My first coil I couldnt wait for my TVS diodes to come in so I ran it without. It worked fine for about 1 minute, then I blew all four IGBTs. :-@
Registered Member #154
Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260
For DRSSTC coils,i put both zeners and TVS protection in parrallel with the gates of the IGBT's, along with TVS on the bus rail of the H-bridge. also a 1-10uf cap across each half bridge is essential for spike suppression. I also have Active Over Current Detection. Had no IGBT failure since.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Problem is - no TVS supressors, if I get some I'l put them in schematic.
I was thinking about gate resistor, steve ward's schematic didnt use it (i was suprised too). Il put 4,7ohm resistors to gates. Decoupling caps will not be a problem, schematic 5uF (maybe not too visible) and probably lot more later.
Overcurrent protection also doesnt seem to be some great trouble, same current transformers + graetz + comparator.
Im still waiting for lots of parts to arrive at last....
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I never use TVS suppressors- I just don't see the point of them. Pretty much all MOSFETs and IGBTs are avalanche rated now, which is to say that they have transzorb-like behaviour built in between the drain and source (collector and emitter if it's an IGBT)
I don't use TVSs between gate and source (emitter?) either, because they have very high capacitance. Some models are almost as high as the gate capacitance of the device they're protecting, so it adds up to a bit of a waste of gate drive. I just use regular zener diodes here.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I never use TVS suppressors- I just don't see the point of them. Pretty much all MOSFETs and IGBTs are avalanche rated now, which is to say that they have transzorb-like behaviour built in between the drain and source (collector and emitter if it's an IGBT)
Yep and then you show us pictures of blown igbts on topic near Joking, i rather think some precautions are needed and TVS are always a good idea...
And I did put two zeners antiparalell on gate, resistors and diodes hav to be added also. I dont see why is there some capacitance problem, TVS is actually zener designed for handling short high-power pulses (its unneeded at gate but if someone has them they can do instead of zeners).
Registered Member #123
Joined: Fri Feb 10 2006, 12:58PM
Location:
Posts: 162
Hi Firkragg, well tvs are not needed if you use back to back zeners on the gates. The resistors and diodes you mention offer no protection as such just a resistor to slow turn on so it can match turn off when passing through diode. The capacitance is a valid point also and to most gate drives this is the last thing you want. To be honest gate overvoltage is not usually the failure cause it's usually over current. better to spend time and parts there Cheers Colin
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First DRSSTC
