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Voltage spike across Primary mosfets in phase shift ZVS converter

Newdesigns power electronics
Prodigy 20 points
Other Parts Discussed in Thread: UCC28950

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 :

  • 0
    Prodigy 205 points

    Hi 

    i'm working too on thing like this, i advice to use a snubber "RDC". Please keep in mind that this snubber will decrease signficanftly spikes but it will affects the respense time to a step of load. also pay attention to additionnal losses !! 

    best regards!