Quote:
Originally Posted by Pdelcast
That's close -- but the actual FET damage during braking is actually caused by current, not by voltage. It's an effect of voltage, but the damage is done by current.
What happens is this -- the voltage rises until the FETs avalanche -- that is, they start acting like a zener diode. On the MMM the FET avalanche voltage is around 44V-48V. When the FETs avalanche, they provide a low resistance path for current, and the instantaneous currents can be thousands of amps. This can (rarely) be high enough to damage the interconnects inside the FET itself.
We RARELY see this type of damage on an MMM though-- because the FETs on the MMM are tough enough to handle repeated avalanche currents without failing.
Much more often we see a power supply issue, where a part in one of the power supplies fails from voltage stress. We have been (and continue to) toughen up the power supplies on the MMM to help prevent these issues.
Patrick
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And by power supplies are you talking about the drivers for the fets or the BEC, or something else?
Thanks,
Jeff