[jyanof]

i've missed a bunch of stuff! that's what i get for not checking the board in a while.

Paul - i've been helping 64jeep a bit with his controller and we did a similar setup for the 3 drivers.

each IGBT has its own VLA-503 driver and DCDC. We swapped out the NAND gate on the control board for a higher current version and use its output to drive the 3 optocoupler inputs to the VLA-503's in parallel (each has its own resistor in series built into the driver). i ended up disabling the desaturation detection on each driver instead of figuring out how to incorporate it into the control logic.

We were also worried about how the timing worked out when driving each IGBT like this. we ended up scoping the outputs of the drivers on a dual input scope and they were all really close, within a few ns or so of each other. a sample size of 1, but we're only building 1 =P

We also didn't optimize the gate resistors, so the switching times might be a little slower than ideal - I thought that might be a good way to accommodate deviations in switching. like, what's a few ns delay out of a few hundred ns total switching time? (or whatever the real times were). so, I forget what gate resistor we have in there now, it might be 5 ohm while the datasheet suggests going down to 3.3 ohm or something. Whatever we started out with, it seemed to work ok so we didn't mess with it.

so, it seems totally doable to have separate drivers. we haven't maxed out the current yet, but it's been good so far to 75% current. if you have have control of each PWM signal down to the counter, that's pretty slick.