Hi i am designing 72V (100V max) to 12 V, 1Kw DC-DC converter using ucc28950. My converter is working well but the voltage spike across the primary mosfet (turn off spike) was very high (>140V @ 60V input and 60 Amp output load).
Due to this voltage spike i am not able to use 150V mosfet and if i increase the mosfet voltage rating i won't get the required efficiency.
Possible root causes: I think the spike may be due to the CT (series inductance) between input mosfets and input filter capacitors.
Question 1: Can i place my CT in series with the transformer
Question 2: Please see the below picture (Ch1 : gate signal Ch2: Mosfet voltage) and suggest me how can i
reduce the voltage spikes.
See the below picture for my ZVS ( 200 ns dead time)
My primary current :