Your fets not good for Phase shift full bridge (PSFB). They have much Cds capacitance, and also, the internal diode is relatively slow…and you make this worse by paralleling them…..so there are two to reverse recover….and also…..you use two, so there is even less I(FET)*Rdson voltage to reverse recover the intrinsic diodes with.
For PSFB, you must use FETs which are specifically for PSFB useage, eg by infineon or st.com or Fairchild etc….paralleling is not really a good idea for PSFB.
IRF540 datasheet
**broken link removed**
- - - Updated - - -
The below references tell you the true horrors(!!!) of FET failure in the PSFB…this is why you must only use FETs which specifically are for PSFB…and they will have a low trr diode in them, and also they tell you the Cds value you have to use to do the calculation with so as to ensure ZVS. (or rather, the datasheet tells you , i meant to say)
https://www.fairchildsemi.com/application-notes/AN/AN-7536.pdf
https://www.microsemi.com/document-...itions-in-welding-br-and-similar-applications
https://www.st.com/st-web-ui/static...ical/document/application_note/CD00171347.pdf
https://www.infineon.com/dgdl/s30p5.pdf?fileId=5546d462533600a401535748559c3fcd
- - - Updated - - -
Also, you have no diode snubbers
Your diode is nice and fast, but you can get faster still, why dont you?
STTH30R06 datasheet:
https://www2.st.com/content/ccc/res...df/jcr:content/translations/en.CD00045268.pdf
- - - Updated - - -
Also, i dont think that 100R should be across the secondary
- - - Updated - - -
Also, i think you should use a sim transformer without the ideal transformer "thing" and just put the Lp and Ls values in there to correspond to the turns ratio.
- - - Updated - - -
Also, i think you should use a sim transformer without the ideal transformer "thing" and just put the Lp and Ls values in there to correspond to the turns ratio. Anyway, regarding the scope shot, did you use a probe with a dangling ground lead, ...just use a bit of coax, because the ringing looks like probe noise......unhook the probe and short the ground clip to tip and see if you still see the ringing...if so, then its "pickup"..which it probably is.
- - - Updated - - -
you see this fet, it tells you the effective output capacitance of the fet cds, "TIME related", and this is the value that you use to calculate your dead time in your PSFB
Coolmos fet for PSFB
https://www.infineon.com/dgdl/Infin...N.pdf?fileId=db3a30432e0bea21012e14e6178c6e0a
- - - Updated - - -
Notice also how the coolmos fet has a large gate charge figure.......this is good because a slow switch on of a PSFB FET reduces instances of "latchup" in the PSFB FET...and you can get a slow switch on easier with a high Qg