I do not understood how you performed the shortcircui test, as you described. In my opinion the case 2 and case 3 are the same. If you shorted the load when has no voltage on the circuit, and, after this, you switched-on 110VDC and 8VDC, your load was a jumper (R=0, L=0) even if before the load was an inductor or a resistor. Or, you said
devura said:
Case 2:
If I switch OFF the 110V DC and the voltage at the IN pin, and then short-circuit the load and if I now switch ON the 110V DC, followed by switching ON the IN voltage, my IGBT is not getting protected...
Case 3:
If I change the load to resistive, i.e., if I connect a 300 Ohms resistance as load and repeat the test as described in the above two cases, the circuit works fine, i.e., the IGBT is protected from short circuit...
Who tells to circuit what before was in place of the jumper, inductor or resistor?
Another obs:
If the load is shorted when is no voltage (switch-off), and after this you apply the supply voltages, the charge pump circuit using 555 and asociated components, can NOT start, because, in the normal working, the 555 take supply voltage from the LOAD (load voltage) via resistor R75(56K/1W), this voltage charges the 100nF capacitor C42 connected between pins 8 and 1 of the 555 generating minus 15V referenced to pin 5 of the IR2125, necessary to prepare the auxiliary voltage for the bootstrap circuit. During the load is shorted, this voltage is zero, and the 555 is not working.
Another question:
Why you choosed like this expensive IGBT, 1200V/60A, if the supply voltage is 110VDC only, and load is 300 OHM? Do you have another suplimentar loads instead of DC-contactor coil? Why not MOSFET? (usually rated voltage of the IGBT is 600V and over, I never used IGBTs rated under 600V, maybe they are not available, I looked for it..) In the shortcircuit conditions, the load is about 20m wire (cable), or not? (You said the contactor is located at 10m distance from the PCB containing IGBTs).