I connected the circuit below, a transistorized ignition circuit, and it worked for a couple minutes, then it stopped working (engine quit, wouldn't restart). When it stopped working, I couldn't feel anything that had clearly overheated on the board, and didn't observe any smoke.
I took the board into the lab, hooked it up to a power supply and tested the voltages at various nodes for the points breaker switch being open and closed. I used a 20 ohm load in place of the coil.
I found that the TIP31 was turning on correctly when the points switch was open such that \$V_c=.02V\$ (collector voltage of the BJT/gate voltage of the IGBT) and Q1's base voltage = .63V, so the TIP31 appears to be working properly. The IGBT should be "Off" with a gate voltage of 0.02V, but instead I'm measuring a 4.3V drop across the 20 ohm load resistor (which is in place of the Coil shown in the schematic), meaning the IGBT is conducting .21A given a 20ohm load.
I can only speculate why the IGBT failed, and I'm hoping someone that has experience can give me a better idea. I was to understand that IGBT's were very well suited for inductive load switching. Did I choose an IGBT that was poorly suited for this application? Could it have just overheated and burned out without me noticing? Most importantly, is poor conduction a typical failure mode of IGBT's?