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Flyback PSR, CV/CC with PFC?

Logic Nibble
Prodigy 40 points
Other Parts Discussed in Thread: UCC28700, TPS92310, UCC28810, UCC28811

Hi!

I am developing a LED driver (12W) with 2 stages:

1-AC/DC isolated flyback with PSR and CV/CC to generate a constant voltage output.

2-DC/DC converter for constant current output and LED driver

I am using for stage 1 the UCC28700 which suits me nicely, but it lacks PFC which it's needed for LED lighting.

I've been checking the TPS92310 Led lighting with PFC. Can I use it to create a constant voltage output? Or is there a way to control PF with UCC28700?

Thanks

  • 0
    TI__Intellectual 855 points

    For a 2-stage design you could use the UCC28810/UCC28811 for PFC/flyback followed by LM34xx DC/DC.  The TPS92310 would work if you are ok with a single-stage design.  You could also design a valley fill circuit for the UCC28700 to add some passive PFC.  The challenge with this though is the number of valley fill stages needed to get to 0.7 or 0.9 (depending upon your target value) and resulting efficiency drop due the valley fill circuit itself.

  • 0 in reply to Prasad Dhond
    Prodigy 40 points

    The reason I need 2 stages is because I want to do parallel FET dimming for groups of leds. with all leds connected in series.

    I have a 4th winding to generate 5V for a MCU which drives the FETs for dimming.

    If I used the TPS92310 (single-stage) and only needed 1 led on (Vls low), the Vlaux, as well as the 4th winding voltage, would be too small (linked with the Ls voltage) and the whole system would shutdown (I guess).

    That being said, I don't understand how the UCC28810 would work, provided that is also a constant current controller. And I would like to avoid opto-couplers and use Primary-Side Regulation.

  • 0 in reply to Logic Nibble
    TI__Intellectual 2540 points

    Hi,

    It is a little bit clearer what you are trying to do now.  With respect to adding PFC to UCC28700, you might get some inspiration from the PMP4342 (http://www.ti.com/tool/pmp4342) reference design which has valley fill and PF>0.7.  Of course, this assumes 0.7 is sufficient. 

    The UCC28810/1 can do either voltage or current control; however, you are correct in that it relies on secondary side feedback.  An opto-coupler is needed to maintain isolation.

     

    John