UCC28950: QA and QB are overheating in my design using UCC28950

There seems to have been some sort of error with my post. I'll repost it here: Hello everyone,


My full bridge circuit is very similar to the one in the UCC28950 Application sheet slua560c except that my output is 180V and output power is 1kW.


My device is regulating just fine and everything is working fine other than the fact that QA and QB overheat quickly and are causing me efficiency issues. Is there any reason why QA and QB would be prone to

overheating and not QC or QD. (Note: I am not using synchronous rectification, nor am I using a shim inductor).


The MOSFETs I am using for all four switches is the FCH067N65S3 and I am driving it with +-13V. When I look at the waveforms, the rise time is about 10-19% of the total on time.


Any help is much appreciated.

I have decided to add a capacitor in parallel with the two leading leg MOSFETs to lower dv/dt. I will also try adding an external parallel SiC diode to lessen the Qrr loss. This technique is referenced in a few articles I've managed to find. I will update this post with whether or not this works.

I am using similar application, 150V 800W. I am not yet testing the temperature but I see that Qa and Qb need higher output current to reach ZVS, around 2-3.8A output but Qc and Qd would reach ZVS at lower output current of 0.1 - 0.4A. Do you experince this?