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UCC28951: Paralleling two PSFB in master slave configuration with interleaving using sync pin of UCC28951

AJIT JAIN
Prodigy 185 points
Part Number: UCC28951
Other Parts Discussed in Thread: PMP6712

Tool/software:

Hi Team,

We are planning to design two 6.6 kW PSFBs  (400V input, 60V output) and interleave them in master slave configuration using sync pin of UCC28951. Was concerned about the circulating current phenomenon in the secondary side. Found two different configurations of PSFB secondary side. What are the advantages/disadvantages of each configuration?

Two different configurations -

1) Two output inductor configuration - PMP6712 PMP6712 Schematic

2) One output inductor configuration -An Interleaved Phase-Shift Full-Bridge Converter with Dynamic Dead Time Control for Server Power Applications

What are the aspects to be taken care while doing the paralleling/interleaving of two PSFBs ? How bad the circulating current problem can be even after interleaving ?

Thank you

Ajit

  • 0
    TI__Guru* 86206 points

    Hello,

     

    The first design you mentioned has two separate output power stages with their own output LC filters.  The second design has one common LC filter.

     

    When interleaving using two separate inductors on the output should have less of a magnetic volume due to inductor ripple current cancelation and distributed power.

     

    It is possible to design a single output filter in the output stage per the white paper that you mentioned.   This power design will have a large inductor compared to the reference design that you mentioned.

     

    In both designs the current that leaves a transformer needs to return the transformer it came from.  In regards to the white paper that you referenced.  There are detailed figures showing the secondary current paths in figure 4 that should help you figure out the circulating current paths.

     

    Regards,