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LM5180-Q1: Transformer Suitability Inquiry for LM5180 Quasi-Resonant Flyback Design

Fikret Yildirim
Prodigy 105 points

Part Number: LM5180-Q1
Other Parts Discussed in Thread: LM5180

Tool/software:

I hope this message finds you well.

In my current design, I am using the LM5180 quasi-resonant flyback controller. The input voltage range is 30 V to 10 V, and I aim to generate two independent isolated 5 V outputs from this single converter. For this purpose, I have considered using the Würth Elektronik transformer with part number 750313974.

One of the outputs is expected to supply 400 mA, and the second output will supply approximately 100 mA. I would like to confirm whether this transformer is suitable for such a configuration and whether the output voltages can remain stable under these load conditions.

Additionally, I would appreciate your guidance on the following:

  • Are minimum loads required on the secondary outputs to maintain regulation?

  • Would you recommend an alternative transformer that may be better suited for this dual-output 5 V isolated design with the LM5180?

Thank you in advance for your support. I look forward to your insights

  • +1
    TI__Genius 15646 points

    Hi Fikret,

    Yes, 750313974 is a good choice for LM5180 converter with 10V<Vin<30V and Vout1: 5V/0.4A VOut2: 5V/0.1A. 

    Are minimum loads required on the secondary outputs to maintain regulation?
    [MA]: Regarding min. load, LM5180 is a PSR (Primary Side Regulation) Flyback converter that switches at a fsw_min=12kHz. This means that the converter delivers a min power at the output side regardless of how small the output load is. That is why we recommend using a zener diode connected at each output with a zener voltage of at least 10% higher than Vout set point. You can also use a dummy load.

    Would you recommend an alternative transformer that may be better suited for this dual-output 5 V isolated design with the LM5180?

    [MA]: 750313974 is a good choice. For alternative options, please contact transformer manufacturers such a Wruth Elektronik or Coilcraft.

    Finally, please find attached the Calculator Tool that I prepared for your case. Calculator tool helps you with the schematic/component selection design.

    Thank you

    LM(2)518x PSR flyback converter quickstart tool revB_AspilsanEnergy.xlsx

  • 0 in reply to Manuel Alva Hernandez
    Prodigy 105 points

    Hi Manuel Alva,

    Thank you very much for your detailed support and for sharing the calculator tool.
    Your guidance on the transformer selection and output regulation considerations has been extremely helpful for my design process. I truly appreciate your time and expertise.

    I will proceed with the suggested approach and consider contacting transformer manufacturers for further optimization if needed.