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Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
Finalizing my H-bridge design and wondered about current thinking regarding IGBT protection. I am running the CM300DY-24H brick, driven by GDT. First question on Gate-Emitter TVS diode? Would you recommend a breakdown voltage to match the max Vge (20v per data sheet) and the drive at 15v (again per spec)? Was thinking of the 1.5KE20CA.
Then what about C-E diodes? I have a 2uF, 1kv snubber connected, and I see others who use TVS (eg 1.5KE220) and some who do not. What is the suggestion for this?
Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
TVS diodes over C-E are pretty much useless with large igbt modules, the igbt module itself (actually co-pack diode) will act as zener diode and can dissapate muuuuch more power than dinky TVS diodes can ever :)
2µF film cap over power rails is ok as long as its mounted physically as close as possible to the igbt. Gate protection TVS diode voltage depends on your gate drive voltage. I have been using 30V bipolar diodes with 24V drive, seem to do the trick, no mysterious gate deaths.
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
Thanks - that is what I suspected. The snubber cap is the type that mounts directly to the brick, so I think I am good there.
The data sheet for the CM300Dy-24H says max Vge is 20v, so I would assume I should stay below that. Are you driving the CM300 on 24v? I have not used this particular brick before and don't want to destroy it !
Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
Its quite common to overdrive igbt gates in drsstc application. CM300s and CM600s are very commonly driven with 24V and even all the way up to 30V. I have always used 24V drive for larger 1200V bricks and had no issues at all.
EDIT:
As far as i have understood (correct me if im wrong here), the reason behind gate overvolting is to make sure that the igbt stays saturated even when we use them at several times their rated current. Its kind of like poor mans desaturation protection. Not industry standard method but good enough for tesla coils. In theory overvolting WILL reduce the life of the transistor but it has proven to be ok in tesla coil circuits. You are not going to need 1000s of hours of run time :)
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IGBT protection
