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PSFB circulating current problem

evs
Genius 5910 points
Other Parts Discussed in Thread: TMS320F28035, TIDM-PSFB-DCDC

I'm designing a TMS320F28035 controlled Phase shift full bridge.

I have some issues getting the power electronics stable.

I use a transformer with external serial inductor, that is diode clamped between the Vbus and gnd. Much alike the TIDM-PSFB-DCDC.

Only even at very light load these diodes are getting hot. I already replace them with SIC schottky diode. But still they are getting real hot. I don't understand where the energy is coming from . The total LS app. 15uH. Fs=133khz.

Any suggestion or documentation on this topic?

Thanks!

  • 0
    TI__Mastermind 31525 points
    Hi,

    We apologize for the delay.
    The module expert has been assigned to respond to your query. US sites are currently closed due to the Thanksgiving Holiday, so responses may be delayed.

    Thanks and Regards,
    Veena
  • 0 in reply to Veena Kamath
    Genius 5910 points
    I really like to chat to someone with extended knowledge of zero voltage switching and design choices for the resonance circuit. I think I messed up there and I still don't know where my problem is.
    I'm designing a 1500W 375/375V PSFB. @133khz . Getting the hardware right is taking way to much time. and I was thinking making the software was the hard part.

    - I think the diode is getting hot because the switching current is to low for zero voltage switching (Is this correct?}
    - lowing the current needed for Zero voltage switch is: make LR bigger. When th load become so big. The voltage at LR become the complete Vbus voltage. So there isn't any left for the transformer transfer. Is there a way around this or is this a design trade off?
    - When I construct the transformer in a way that Lr is part of the transformer. I got the problem is that Lr is acting like a boost converter. I assume this is the same problem as the first point. Any suggestion to suppress this?
    - Can you please tell me something about the impact of deadtime for zero voltage switching?
    - Any suggestion for construction the transformer? Design for the lowest C coupling? Ns1:Ns2::Np?

    Thanks!
    EVS