I am working on a 6KW charger design using UCC28950. My design is mostly similar to TI's reference design PMP6712 Dual-Channel Isolated Full-Bridge but the controller moved to the secondary side. input voltage range is120vdc to 240vdc and the output capable of charging 48v batteries.
As I increase the input voltage above 200v primary FETs A and D start getting hot rapidly while other transistors remain cold. basically the transistor B is under 40 degree while A and D are around 100 degree.
I changed a little the DELAB, DELCD and DELEF resistors, supposed that I have some shoot-through at the secondary bridge but it doesn't make any change. Even single channel tests shown no difference, it always start to heat up when the input voltage goes over 200v.
I was doing my tests under 3KW output load on all above tests.
Does anybody have any idea why I see so much temperature difference between primary FETs and why it happens when input voltage goes high?
Thanks,
Payam
