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UCC28951: Secondary side synchronous rectification using full bridge instead of center tap

Erik Wallebom
Prodigy 60 points
Part Number: UCC28951

Tool/software:

Hi,

I plan to build a switching converter with high voltage output (200-270VDC out). I will try to avoid center tapped transformer because of high voltage reflection on the "unused" side of the secondary winding. My idea is to drive the gates of the secondary full bridge using the OUTE and OUTF outputs of the UCC28951. I will turn on the mosfets diagonally and using small DC/DC converters and isolated gate drivers in order to power the upper switches.

What worries me is I find several posts in this forum saying it should not be done in that way. The problem stated is that OUTE and OUTF are both high at the same time during freewheeling period. I don't fully understand why this would be a problem with a full bridge and not with a center tapped solution, although I am not 100% familiar with the controllers switching algorithm.

I do find this demo board from Toshiba: 1 kW Full-Bridge DC-DC Converter | Toshiba Electronic Devices & Storage Corporation | Asia-English

This demo board seems to do what I plan to do. It uses four mosfets on the secondary side and drives them with OUTE and OUTF.

This should work, right? Am I missing something? Any comments appreciated. Thanks.

Regards,

Erik

  • 0
    TI__Guru* 86266 points

    Hello,

     

    Since those posts we have had customers use out E and out F to drive half bridge drivers to drive H Bridges on the secondary.   At the time it was thought was all H Bridge FETs being on at the same time would short out the transformer.  However, that did not happen because during freewheeling the HBridge FETs on the primary are already shorting out the transformer during the freewheeling period.

     

    Regards,