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LM5161: Topology with 9 isolated outputs

Stefano Infante
Expert 2320 points
Part Number: LM5161
Other Parts Discussed in Thread: LM5160

Hello,

I have to design a power scheme including a non-isolated 3.3 V rail and 9 individually isolated 3.3 V rails.

In the past I used LM5161 in fly-buck topology in order to generate 4 individually isolated rails with buck converters used to bring voltage down to 3.3 V, but with this new topology I'm not able to find a single transformer that does the job. Is there a way to generate all 9 isolated rails without using two or more converters?

I see there are many 6 1:1 windings isolated transformers on the market. I think I could take a couple of them and use their two primary windings in series as the non-isolated inductance of an LM5161, but what voltage should I expect on the 10 secondary windings?

Is there another simplest way to get the job done?

Thanks in advance.

Regards,

Stefano

  • 0
    TI__Mastermind 23845 points
    Hi,

    With 9 isolated outputs, please be aware the current capability of LM5161. The Flybuck current secondary is related to (1-D) therefore it could be limited. I would use 2 converters just in case because the flybuck regulation on the secondary is quite poor unless you have another LDO on the secondary.

    Thanks
    -Arief
  • 0 in reply to Arief Hernadi
    Expert 2320 points

    Hi Arief,

    yes, I surely will use LDOs (or buck converters, depending on the voltage I will obtain) on all 9 secondary sides. I know the current limitations of LM5161, but, if needed, I could switch to LM5160 which has more available current, so I don't think current will be an issue.

    So, do you think I can use a single LM5161 (or LM5160)? Or should I always prefer using two parts?

    By the way, my main issue is to find a suitable transformer... what if I use two 6-windings transformers with a single LM5160? How could I arrange my power scheme?

    Thanks again.

    Regards,

    Stefano

  • 0
    TI__Mastermind 40060 points
    Hello Stefano,

    You may want to consider the Versa pak from Coiltronics, or the Hex pak from Coil craft, I believe they have 6 winding's in total. you can use two transformers and one converter provided you do not exceed the max current rating of the converter? Place the primary's in parallel and the secondary's in series. hope this helps?

    Kind regards,

    David.
  • 0 in reply to David Baba
    Expert 2320 points
    Hi David,
    I think this could be the best choice for me. I just have to take into account the different turns ratios generated by the parallel primary windings, but it should be ok.
    Thanks for your help.

    Regards,
    Stefano