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UCC28630 Secondary side regulation

Mahesh KC03
Intellectual 1360 points
Other Parts Discussed in Thread: UCC28630, UCC28610, UCC28740, LM5023, UCC28600, UCC28C44, UC2844, UCC28730, UCC28700

Hi,

One of customer is planning to use the UCC28630 for a universal AC input to DC converter. UCC28630 employs a primary side regulation through feedback bias winding to control the output voltage. I wanted to know whether the same controller will work with an opto-coupler feedback from  the secondary side? Is it possible? Would it not affect the over-voltage and loop compensation portion.

If it is possible, what are the changes we need to do? 

  • 0
    TI__Expert 8210 points
    The UCC28630 is a PSR controller, so you will need to use one of our SSR controllers if you'd like to use an optocopuler based feedback.

    Based on the part you already selected I recommend looking at UCC28600 first, then LM5023 and UCC28740 third. If the power level is always between 12-65W UCC28610 would be a good fit as well.

    If you provide the AC input range, DC output voltage/current and any key requirements (i.e. standby power consumption, size, cost) I can help further reduce that list to the best SSR controller for their application.
  • 0 in reply to Eric Faraci
    TI__Intellectual 1360 points

    Hi Eric,
    Thanks for the quick reply.
    The Input is 85V to 265V AC at 50/60Hz. The output is 12V,65W regulated DC. The customer has already chosen UCC28630 but he said that he will make provision for a secondary side feedback in his circuit. So, I wanted to check if the same device can be operated with opto feedback.
    I will recommend him to use UCC28600/UCC28610 if we wants an SSR.

  • 0 in reply to Mahesh KC03
    Prodigy 140 points
    Hi Mahesh,

    As Eric told you, can't use SSR in PSR mode. As you will look in bolck diagram of UCC28630 , you will find the answer that at Vsense pin of UCC28630 and there is not only Error amplifier placed. There are multiple sampling section for loop compensation and protection. So you can not feed Via opto-coupler, u should have to feed output proportional PWM there to operate all functions.
    You can use SSR mode Ics as Eric suggested, also UCC28C44 or UC2844 are for such SSR Flyback converter.
  • 0 in reply to Parth3989
    TI__Intellectual 1360 points
    Hi Arjun,
    Correct. The VSENSE pin in UCC28600 does more than just feedback regulation.
    Thank you for the help
  • 0 in reply to Mahesh KC03
    TI__Intellectual 1360 points

    Hi Arjun, Eric
    The customer has to design two power supplies; one with the PSR and other with SSR. But he wants to use the same controller for both the operations. In case of a not so tightly regulated and efficient supply, he wants to use PSR and SSR in case of higher regulated supply.
    I went through the UCC28740 controller and saw that it has both PSR for CC and SSR for CV. Can i suggest this controller for his application? Or Do we have a better fit device?
    The input is 36 to 72V DC, 12V output,65W.

  • 0 in reply to Mahesh KC03
    TI__Expert 8210 points
    Mahesh K C

    The UCC28740 is an SSR controller and cannot work in a PSR design. We do not offer a controller that can operate as a PSR and a SSR. CV/CC regulation is independent of PSR or SSR, and we have PSR and SSR controllers that both have CV/CC control.

    We do offer PSR flyback controllers and SSR flyback controllers that have similar performance. Based on those operating conditions UCC28740 is a good SSR controller option, and I'd recommend looking at UCC28730 for a PSR controller option.

    Eric
  • 0 in reply to Mahesh KC03
    Prodigy 140 points
    Hi Mahesh,

    Using UCC28740, you can't regulate using PSR. It firmly made for SSR.
    In datasheet of UCC28740, description saying for both PSR and SSR. But it does meant that in SSR mode you can get functionality of PSR. Such like Line sense, Valley switching, Current regulation, PWM timing detection.

    For PSR you can go ahead with UCC28730, UCC28700.

    Arjun.
  • 0 in reply to Eric Faraci
    TI__Intellectual 1360 points

    Hi,
    Thanks for the confirmation. Since UCC28740 and UCC28730 are pin to pin, it should be easy to replace it in the same design with appropriate feedback mechanism.
    But the datasheet of UCC28740 says it enters CC mode when operating in PSR and controls the valley switching. In this case, the CV mode is lost(page 15, 7.4.2). How does it transit between CC and CV? Are both of them essential for the regulation?

  • 0 in reply to Mahesh KC03
    TI__Expert 8210 points
    When the measured current at CS reaches the Iocc limit the converter switches over to a constant current regulation of the output at Iocc. Not all converters have this feature.
  • 0 in reply to Eric Faraci
    TI__Intellectual 1360 points
    Thanks Eric. I realized that the control voltage to modulate the gate drive is actually generated using the current at the FB which is converted to VCL in case of UCC28740. In case of UCC28730, the VS pin is used to derive the VCL.