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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Hi, As I've never used delay compensation circuits before, this was of no concern to me, because the IGBTs were always switching late Is it best to tune the switching transitions a bit after, bit before or exactly at the current zero crossing?
And the second question, with small ultrafast IGBTs which have the turn-off time in the ~100-150ns range, is a dead time needed or will a simple resistor-diode combination in series with the gate do the trick? I could check this by measuring the power consumption with no load, but i don't know if the cross conduction doesn't appear only with a load.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I adjusted the delay while looking at the H-bridge output voltage on a scope. There's a (quite narrow) setting where all of the ringing disappears and the waveform looks perfect. That's where I set mine. I think it corresponds to switching slightly before the zero crossings.
My driver has adjustable deadtime, but when using the Fairchild miniblocks, it worked fine with the deadtime set to minimum, about 100ns. I think it would still work at 0ns, and even if it didn't, you could easily add 100ns of deadtime with the resistor and diode.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Just one more question, is it really bad if the interrupter is not synchronised to turn off at current zero crossing? When running long ON times and low peak currents...
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Two DRSSTC tuning questions
Is it best to tune the switching transitions a bit after, bit before or exactly at the current zero crossing?
I think it corresponds to switching slightly before the zero crossings.