[SOLVED] Simple H-bridge MOSFET Drive Problem

[azadfalah]

Hi friends,

According to the schematic below, I made a 12 to 220 volt inverter

Normally everything works fine

The problem started when the DC bus voltage exceeded 310 volts
A strange shape is seen in the one of the high side H-Bridge MOSFET gate voltage
just in one side of high side MOSFET
And I do not know why this wave is created and how to solve it?

I have used FDPF18N50 in H-Bridge

if DC BUS under ~ 310V Gate Wave is ok

if DC BUS voltage Over ~ 310 volt we have this shape

 

[dick_freebird]

I'd start with the gate drive, which could be marginal
or mis-built and allow high dV/dt switching to induce
on-state oscillation in the power FET. At least follow
the bad side back toward the control IC, until it starts
looking the same as the "good" side. Then you'll have
bounded the problem area, at least.

 

[FvM]

Despite of other possible problems of the driver circuit. MMBTA42 has maximum rating of 300V, clearly exceeded.

 

[azadfalah]

Despite of other possible problems of the driver circuit. MMBTA42 has maximum rating of 300V, clearly exceeded.

Sorry, I forgot to mention that this part has been replaced with KSP44

 

[Easy peasy]

We cannot see the layout - but the clever money is on RFI getting into your control from the hard switching on the pri side coupled with the hard reverse recovery of the diodes on the sec -

remedies: - slow the fet turn on

- put snubbers on the fets & diodes

--- Updated Oct 11, 2021 ---

the current spikes into C13 will be significant too

 

[azadfalah]

Despite of other possible problems of the driver circuit. MMBTA42 has maximum rating of 300V, clearly exceeded.

thanks a lot your answer made me doubt them
and yes the KSP44s were fake and their breakdown voltage was lower