Hi,
For a full bridge I have been designing gatedrivers using TI ISO5451.
To get to see how the whole system works I did built up a small system with only one IGBT just for testing purpose:
First everything worked quite well. But after increasing input voltage to approximately 120 volts, the gate driver starts to shut down the IGBT shortly after the on-state has been reached, as you can see in the next picture (working voltage will be 560 volts, the IGBT has a rated voltage of 1200 volts).
Yellow: Gate Current Green: ISO5451 output voltage Blue: IGBT voltage Pink: IGBT current
When increasing input voltage even more, sometimes several turn-offs do appear at the gatedriver, the fault is repeating itself.
I have already tried the following steps:
- Shorten DESAT-protection to the emitter to avoid influences of the desat protection, the problem still exists
- Try a different gatedriver did not change anything
- Increase blocking capacity at the input of the gate driver which only slightly shifts the voltage at which the effect starts to appear
- Reduce or increase the gate resistor, no effect could be observed
- Remove load inductance (turn on at zero amps), this allows the IGBT to turn off faster and avoids the problem
- Increase the capacity of the 220 pF capacitor at desat protection
- Measuring at the input of ISO5451: Neither IN nor FLT indicate the turn-off
Actually the problem does not effect the final application as we will turn on zero current. Otherwise I still would like to know the cause of this problem and probably change my design to avoid further problems.
Best regards,
Yanick