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UCC29950: Isolated PFC needed for 100-300W app

douglas Sudjian
Prodigy 190 points
Part Number: UCC29950
Other Parts Discussed in Thread: UCC28180, UCC25600

Hi People,

I have a new power supply design (100W to 300W) with a linear regulator section  that is at least 92% efficient.

But it need an isolated 30 to 50V DC input with a floating gnd from 115Vac.

Fly-back with PFC would be great but I have not looked at that too closely. I don't see a TI part using both pieces.

The UCC29950 LLC PFC  looks similar to a fly-back.

Why don't people apply PFC after a step-down transformer? Then a simple buck, boost, or  buck/boost PFC would suffice at these lower voltages.

Switching losses would be low. Would the transformer cause too much havoc with emissions, even with EMI filtering?

My goal is to pick a part even if I have to add hardware around it, then macro-model it before I connect anything to the POWER LINE Serpent waiting to bite us.

Thanks

Doug

  • 0
    TI__Mastermind 34465 points

    Hello Doug,

    A step down transformer with a 300W rating is a very big and heavy part. It is also more expensive than the alternative electronic solution.
    If your application is 300W you should be looking at the CCM type pfc controllers such as the UCC28180 followed by a DC/DC converter such as an LLC (UCC25600) 
    Or you could consider the UCC29950 combo controller.
    A flyback controller is unsuitable at 300W because of the high peak currents involved.

    If you wish to model your design before building any hardware the UCC28180 and the UCC25600 do have models of reference designs on their web pages.

    Regards

    John

  • 0 in reply to John Griffin1
    Prodigy 190 points
    Hi John,
    Thanks for your opinions. I can macro-model the Boost PFC section in simulation very well, excluding startup.
    I will check out the other part numbers as well.
    Doug
  • 0 in reply to John Griffin1
    Prodigy 190 points
    Hey John,
    You were spot on with your recommendation. From a simulation point of view LLC seems easy. Seems easy on paper too.
    But I have a lot of reading to do before I implement the best solution here.
    But you got me in the ballpark with a big bat.
    Just another example of TI staying in business all these years.
    Doug