I was doing some experiments using the following IGBT:
I used it to drive a load of ~4.7ish Ohm and ~140ish µH from a capacitor bank of 2350µF. Each experiment consisted of charging the capacitor bank to a certain voltage and then applying a single pulse of varying length to the gate driver (MCP1407, for schematic I replaced it by the next best thing I could find in the components list), Datasheet:
For maximal switching speed, I did not use a gate resistor, but used a 15.3V Zener soldered directly on the leads to protect the gate from eventual spikes. The inductive load had a diode across (near IGBT) to limit voltage after shut-off. The gate driver was powered by a 12V lead acid battery. I omitted decoupling caps from the schematic (1µF for the gate driver and 11.2nF parallel to the capacitor bank)
As I was increasing the voltage and pulse duration, the IGBT decided to suddenly identify as a 0 Ohm resistor (<3mOhm). All other components survived (except the flimsy wire to the load, which melted in one spot (deliberately chosen weak point)). The gate is now a 16 Ohm resistor.
I gathered the following data on the experiments:
last experiment before the boom: capacitor bank charged to 450V, a pulse of 500µs (or 5xxµs?, I'm not 100% sure the last 2 digits were 0, unfortunately that was the one number I forgot to write down and only re-added it afterwards from memory). The pulse discharged the capacitors to 432V, dumping ~19J at ~84.6A average current (assuming 500µs and capacitor ratings are accurate).
The next experiment of 720µs pulse duration @450V resulted in a boom. Interestingly, the IGBT has no visible damage and magic smoke only escaped from the wire. Afterwards, the capacitor bank had ~120V remaining.
Now the question: what happened? What did I do wrong? I thought the datasheet said 160A is fine, or is that the wrong value to look at? However, SSOA also states 480V 100A. Do the other conditions to that value matter/in which direction is a deviation from them safe? Or was the pulse duration of 720µs too long? How would I go about calculating the max duration from the thermal response data in the datasheet? Or is there such a thing as switching it too fast? Or were 12.5V for the gate driver too low? The data from 500µs does not show a dramatic voltage drop on the IGBT, at least not by my calculation: At an average 441V(-4V IGBT drop), expected would be 93A for a 4.7 Ohm resistor or 87.2A with the measured total resistance of wires, contacts and load (5.01 Ohm). Now add ~29µs inductive current ramp-up and a bit of cap ESR and the numbers match.
As I would not like to burn through more IGBTs finding out, I would like to know what I did wrong/what I can do so it does not happen again. Unfortunately, I don't have a DSO that could capture these events.