I'm developing a buck converter. I need to to change its supply from 9 V to 12 V. I also need to get more power in it (up to 10 A). I do it by reducing the load resistor.
My problem is that when I try to gradually increase the voltage from 9 to 12, everything stops working at around 10 V. By stops working, I mean no PWM anymore, a lot of noise, and then no voltage at all at my probes.
Here is a picture of the voltage at the gate of the high-side mosfet (yellow) and source of the high-side mosfet (pink) at 9 V, when everything is still more or less working.
Theoretically, all my components are able to handle a voltage of 12 V.
I tried varying the output capacitor value, but it didn't seem to have any impact at all on my problem. When I decrease the load to smaller values, on the other hand, the circuit stops working with smaller voltage already. That's the reason I think it's less an issue of too high a voltage and more a problem of too high a power.
I searched for stability checks and calculation for buck converters, but all I found is literature about the stability of the converter in a feedback control. I do not have such a thing yet, my PWM is fixed. Plus, my output capacitance is pretty high, specifically to avoid problems with
So, here is my question: Why does my buck converter stops working when I try to transfer more power through it, although all elements are supposed to be able to handle it, and I shouldn't have a stability problem per lack of feedback?
Edit: I also wasn't able to reproduce the problem in LTSpice