I have a Tesla coil driver, designed around a UCC21520 isolated gate driver. It is operating as a fixed 50% duty cycle half bridge switcher. The frequency is varied from 150kHz to 250kHz. It is driving a ~20uH inductor loosely coupled to a Tesla coil secondary.
Issue: Repetitively the high side portion of the gate driver dies, seemingly randomly as I am adjusting frequency.
It has yet to die when it is at resonant frequency of the coil. Only when I'm off resonance, and the effective impedance of the load should be highest. The system is currently only switching +- 30V and is on an isolation transformer, so I can safely measure whatever I need to.
I have examined the following:
- Soldered coax directly to each gate/source of the FETs being driven. There is minimal ringing, just ~1Vpp on falling edge. I don't believe 1V below ground is killing the driver...
- The power supply and half bridge I added multiple 0.1uF MLCC capacitors added, but regardless there seems to be no ringing there either.
- Drive and FETs remain cool. Even immediately after the driver dies, it is cool. I just hear a buzzing sound indicating it has died.
I'm at a loss, any input would be appreciated. I have an analog scope so that is why I have no images of the scope shots. When I get more driver chips, I can try to take some.