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AC/DC with Flyback controller

Other Parts Discussed in Thread: UCC28722, UCC28910, UCC28880, LM5021

Hi all,

Would you mind if we ask AC/DC with Flyback controller?
Please refer to the following file which we wrote some questions.

20150330_ACDC_FlybackController.pdf

Kind regards,

Hirotaka Matsumoto

  • Hi team,

    We guess that your days are so busy, but could you let us know?
    Of cource, if you say that there are no recommended devices, we will accept it.

    Kind regards,

    Hirotaka Matsumoto

  • Hi Hirotaka, there are several TI controllers which could be used for this application, but the power stage will need to be changed for the different input parameters.

    The UCC28722 is a primary side regulated device which is designed for use with a BJT as the main switch which is cheaper than a MOSFET. The Vdd is charged via a resistor from Vin at startup so it can be used down to the 24V input range.

    It can also be used up to the 500Vac input, but the power stage will require additional circuitry on the primary side to handle the higher voltage. Either a clamp to reduce the voltage to below the rating of the bulk cap, or two bulk caps in series and a higher rated switch.

    Alternatively the UCC28910 can be used, it has an integrated MOSFET which saves BOM cost and PCB footprint and can start directly from the input voltage, but I'm not sure what voltage it needs on the drain pin to charge Vdd. The drain is only rated to 700V so the input voltage in the 240Vac - 500Vac range would need to be clamped.

    Both of these devices are valley switched and primary side regulated as desired, but as you mention, with isolated outputs there will be some cross regulation. If one output is lightly regulated and the other output is heavily regulated, the lighter loaded output is likely to regulate high. The cross regulation will depend on the max and min load on each output.
    This effect can be reduced if the outputs share a common ground, but apart from good transformer design little can be done where the two are isolated.

    For opto coupled Feedback you could use the UCC28880 or LM5021 as you mention.

    Thanks

    Billy

  • Billy san

    Thank you for your reply and excellent cooperation. 

    We'd like to confirm following content;
    "but the power stage will need to be changed for the different input parameters."

    UCC28722 can be used with multiple different AC/DC for control, but the power stage as transformer needs to be changed.
    In order to correspond for several input conditions(AC24V to 60V,,, AC250V to 500V), it needs to be changed number of transformer's turns.
    Is our recognition correct?

    Kind regards,

    Hirotaka Matsutmoto

  • Hi Hirotaka, pretty much but to be clear, for an optimised design, you will probably need to change several of the power components, like the input bulk cap,  the primary MosFET, the secondary rectifier, the transformer turns as you say, and maybe some others.

    Thanks

    Billy

  • Hello, all

    Now we have one inquiry regarding UCC28880 isolated Flyback use.
    In datasheet page 26 Fig.26 .
    Customer requires turn off optionally.
    Please give me an additional cuircuit idea which can control the secondery output 0v temporarily.

    Best regards,