Hello,
I have an H-bridge with two MP18851 under a 400VDC bus, as well as a power supply for the MOSFETs of 18V. The problem I encounter occurs every time I want to generate a 140V sine wave at approximately 50Hz with this DC bus. The current on my bus is then 2A, and the PWM signals are very clean.
The issue I have is that at a certain point (when the voltage reaches almost 140V), there is a very high overconsumption on the 18V line, which causes this bus to drop. I suspect the drivers because they are the only ones consuming from this bus. It seems that the fault occurs when I switch my signal from positive to negative or vice versa.
If I apply a purely negative or positive DC current, there is no problem. I don’t understand where this issue comes from… I followed the schematic from the MPF320810 application note to the letter for my application, I have just changed the MP18831 to MP18851. The schematic is available via this link: MPF32010GFP Reference Design.
For information, my PWM has a frequency of 9kHz, and I have increased the dead time to 250ns, which is huge considering I am using SiC. I have not observed any overvoltage during the ON->OFF or OFF->ON transitions.
Do you have any ideas?
BLUE : 18VDC
GREEN : LOW SIDE INPUT
YELLOW : HIGH SIDE INPUT