SMPS H-Bridge trouble Answered
I've built a 1kW SMPS designed to take a 350V unsmoothed DC input and convert it to 3kV @ 300mA. The circuit is basically Uzzors2k's design seen here minus the overcurrent protection and smoothing capacitor (for now), however I accidentally wired the GDT outputs backwards so the gate resistors (33ohm 2W) are on the source. I have used alternate MOSFETs the latest attempt with FDPF16N50T's.
I've had various problems with the circuit, primarily the MOSFET's exploding seemingly from overvoltage (evidence of flashover in some cases despite no evidence of secondary leakage (i dismantled the transformer to check)). During my last test I had a flashover between the drain and source pins of one of the FET's, in addition all of the gate resistors were smoking hot after, seems the gates had all been shorted (first time this happened, other occurrences were from case to ground). This happened despite the variac only being turned up to 40% which should be well well below the pin spacings maximum voltage tolerance.
I have checked the drive signals, they are quite nice square waves at about +-15V with some oscillation on their rise.
I have built SMPS's before, one is currently working with similar MOSFETs using a half bridge at 300W.
Does anyone have any suggestions as to why these troubles are occurring or have any suggestions to fix it or have any alternative circuits that may be less troublesome (is a h-bridge easier to manage?)?
I just gave it another test with a H-bridge instead and the source of one of the FET's blew so it appears that there is just FET failure and maybe not arcing between drain and source.