My experiment with the series inductor went all wrong, as in loud
bangs and smoke
Still not sure what exactly went wrong. I would have expected the
inductor to just discharge properly through the 'freewheeling diode'.
Somehow however it demolished the diode together with an identical
diode in the snubber and three of the IGBTs. Most of the noise and
smoke came from some resistors that blew up and a 1sq mm wire that was
used to connect the freewheeling diode that completely vaporised. The
diodes are rated 1.2KV 150A continuous and 3000 amps for 6mS so they
should have easily taken the strain. That vaporised wire seems to be
telling me that a much larger current flowed, though where that could
have come from remains a bit of a mystery.
Anyway, I will just file that under 'bad ideas' and move on.
I'm struggling to design a PCB with a better driver to IGBT ratio.
Here's a jpeg of the schematic:
http://lister6520.googlepages.com/photographicflash
Not sure if it will help, but I am hoping it will at least remove any
doubts about the suitability of the gate drive. Any comments and
suggestions about the schematic would be appreciated.
The resistors in the supply lines to the gate drivers are intended to
provide decoupling both between the drivers as well as from grounbd
bounce and such ills that the very large current flowing in the
immediate vicinity are likley to cause.
The values of those resistors as well as the gate and emitter
resistors are at best a good guess (perhaps not even a good one). For
the decoupling resistors I'm looking for sufficient decoupling while
avoiding excesive voltage drop.
The gate resistors are probably too low as the gate driver can source
a maximum of 2 amps, so I may be changing them with 33 ohm or
thereabouts instead but I'm not sure yet.
