 Parallel IGBTs current sharing during switching transitions
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Steve Conner
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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
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Interesting app note!
I've always put the gate protection directly between gate and emitter. I figure that the closer it is to the gate, the better it can clamp gate voltage spikes. My DRSSTCs and OLTCs have a 100% reliability record. 
I use ordinary Zener diodes. I found that the 1.5KE series TVS have huge capacitance, more than the IGBT gate.
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Marko
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Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
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Hey guys
For parallel devices (mosfets at least) it's often highly advised to use ferrite beads in series with every gate, along with a small series resistor to provide some damping at lower frequencies. However, some appnotes even advise removing the resistor completely if a suitable bead can be selected - the devices have some internal gate resistance which may provide enough damping on it's own.
Ferrite beads have impedance proportional to their frequency and seem to do really well at damping HF oscillations. They are rated by their impedance in ohms at 100Mhz, and I'm not yet certain which to select for what type of device... this would require some testing with many various beads.
Marko
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