Problem with PWM voltage at MOSFET gate in three-phase inverter

[dompa]

Hello.

I have designed and made my own three-phase inverter and I am currently testing it with a regulated DC supply, but recently one of the MOSFETs failed.


I replaced the MOSFET and checked the gate signals with a scope.
When I checked the signal on the bottom MOSFET gates, I see a constant PWM signal of 12V, independent of the DC supply, which is good.



ET gates, the peak voltage PWM keeps rising when I rise the DC supply!!
I got almost to 20V peak with 10V DC supply.



That's why the MOSFET died the first time.
So, my question is, what could be the reason the gate voltage keeps rising?

Thanks in advance.

 

[barry]

You don't show what's driving the gate, but ask us to figure out why the voltage there is too high? I'll pass.

 

[schmitt trigger]

Hello.



ET gates, the peak voltage PWM keeps rising when I rise the DC supply!!
I got almost to 20V peak with 10V DC supply.

.

I agree that driving a Mosfet above 20 volts will certainly destroy the gate.

But as Barry mentioned, you are not showing the complete top-gate driving circuitry, and without that information any ideas that we could provide, will be only speculation.

 

[KlausST]

Hi,

The absolute voltage at the gate is not of interest.
Measure the "gate-to-source" voltage.

Klaus

 

[barry]

It's not clear, but if your bottom plot is supposed to be the top gate drive, it looks like you might have a situation where both top and bottom FETS are on simultaneously. Not a good thing to do. POST YOUR SCHEMATIC and post both top and bottom gate signals together. That plot doesn't look right...