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UCC256304: Is it possible to operate LLC converter in open loop topology?

John11513
Expert 5490 points
Part Number: UCC256304
Other Parts Discussed in Thread: UCC28951, UCC256404

Hi expert,

My customer is developing an isolated inverter module, to deliver isolated 110V/25Hz/1kW output from 220VAC input. The system structure they are considering is: 220VAC --> PFC --> isolated DC/DC --> DC/AC inverter. For isolated DC/DC stage, I am thinking, since its input is regulated output from PFC, and its output is not required for tight regulation (since the DC/AC stage can provide output regulation), to simplify the design is it possible to implement an unregulated, isolated DC/DC stage? such as open loop PSFB or LLC topology?

Thank you!

John

  • 0
    TI__Expert 8210 points

    John

    Yes, what you propose should work.  The one challenge that will come up though is that the double line frequency ripple on the output of the PFC will pass thru the open loop isolated DC/DC stage, so you will need to insure that your DC/AC inverter stage can filter it out enough to meet any THD, PF or harmonic requirements.  Since this double line frequency is only 100Hz or 120Hz, this should not be difficult to achieve.

    At 1kW we recommend using PSFB with UCC28951.  Our LLC controller UCC256404 and previous generations use a half bridge, so their performance will be more limited at 1kW power level.  The full bridge that the PSFB topology has allows for higher performance at 1kW.

    Best Regards,

    Eric