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UCC28610: Maximum Output Voltage of Flyback Converter

Conall Hill
Prodigy 20 points
Part Number: UCC28610

Hi,

I currently use the UCC28610 in a 16.5V 45W module, and was hoping to use the same controller for a new multiple-output module I am designing, with +60/+20/0/-20/-60 rails and a total 42W output power.

However, I notice that on some of the TI design tools the UCC28610 is limited to designs with output rails of 48V. I can't find this specification on the component's datasheet, and am wondering where it comes from. Is this an absolute maximum rating? If the 60V rail isn't beyond a maximum, I would prefer to use the UCC28610 as the BOMs of the two modules could be fairly well aligned for much of the primary-side components. 

Best Regards,

Conall

  • +1
    TI__Expert 3431 points

    Hi, Conall:

    It has no limitation for output voltage. UCC28610 is okay to use as output rail is 60V. 

    I thought what you mentioned about is the output voltage range (5V~48V) which shows in WEBENCH® Designer UCC28610, which is designed for most of applications. 

    Please use the calculation file which allows over 48V design as below link. 

    https://www.ti.com/lit/zip/sluc113

    Please note the UCC28610 is primary side regulation, it only regulates output voltage through auxiliary wilding. The cross regulation would be not as good as SSR flyback. So if output voltage ripple or output voltage regulation is concerned, please consider SSR topology. 

    Regards, 

    Wesley

  • 0 in reply to Wesley Hsu
    Prodigy 20 points

    Thanks Wesley,

    Thanks for your response, that is a very useful tool and I hadn't seen it!

    Using that calculator does help with 60V rail designs, but I am concerned that it forces the maximum frequency to drop quite a lot. Eg. When designing for 60V and max load of 0.9A and using recommended transformer parameters, I tried different values to see the effect of tolerances in inductance and the end-of-life capacitance of the bulk capacitor. At some combinations, the maximum frequency of the switching was limited to around 100kHz.

    Is this effect detrimental, or fine? Also, in these conditions it called for an Rmot of 110kOhms, which is above the 100K maximum in the datasheet. Should the Rmot be kept at 100K?

    Regards,

    Conall

  • 0 in reply to Conall Hill
    TI__Expert 3431 points

    Hi, Conall:

    Sorry for my late reply. 

    May I know what's your concerned about max frequency? 100kHz should be a normal value in flyback converter. I think you may have some special reason for this one. Would you mind to share me?

    For RMOT, please refer the figure as above, you may also find it on page 15 in datasheet, if the RMOT is over 100kHz, it would be a boundary to IC to decide the protection mode. Hence, to modify RMOT slightly through Lp adjustment would be suggested after the protection mode is chosen. 

    Also, it is a reference once the max on time is calculated based on the system requirements. 

    Regards, 

    Wesley

  • 0 in reply to Wesley Hsu
    Prodigy 20 points

    Hi Wesley,

    Really, its not the frequency itself that was worrying me, there's no problem with it dropping to 100kHz, I am only really worried that this might be symptom of some problem that my design could create (such as Rmot needing to be over 100kOhm)

    Modifying Lp would work, but I worry that in production we may only be able to specify it to +/-10%, so I don't want to rely too much on fine modifications to it. But I will take this approach and just make sure to find a range of Lp that works with 100kOhm Rmot. If the max frequency drops then that will be fine!

    Many thanks for your explanation.

    Kind Regards,

    Conall