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LM5156: Issues with Flyback Converter Design Using LM5156

Francesco Rizzotto
Prodigy 50 points
Part Number: LM5156

Tool/software:

Hi,

I designed a flyback converter utilizing the LM5156 with the following specifications:

  • Input Voltage: 22-36V
  • Output Voltage: Up to 125V (regulated with current injection)
  • Maximum Output Power: 125W

I've encountered an issue when attempting to increase the output current.

At a certain point (around 6A), the primary winding current begins to flatten out.

I've experimented with different homemade transformers, but the results have been consistent.

Specifically, I tried using 20µH and 10µH transformers with a turns ratio of 1:1.5, employing ferrite core materials 61 and 67.

Attached is an image illustrating the problem:

  • CH1: MOSFET Gate
  • CH2: Secondary Side Transformer Voltage
  • CH3: Primary Side Transformer Voltage
  • CH4: Primary Side Current

I would appreciate any insights or suggestions you may have.

Thank you

  • 0
    TI__Intellectual 1300 points

    Hi Francesco, 

    Thanks for using the E2E forum.

    Can you please attach the schematic of your design?

    Moreover, share the saturation current rating of the transformer used.

    Best Regards,

    Hassan 

  • 0 in reply to Hassan Jamal
    Prodigy 50 points

    Hello,

    Thank you for your reply.

    May I send you the schematic privately?

    I also tested it with the Wurth transformer (model 750311783), which has a saturation current of 16A, and obtained the same result.

  • 0 in reply to Francesco Rizzotto
    TI__Mastermind 26290 points

    Hi Francesco,

    Thanks for the feedback.
    You can share the schematic via direct messaging on e2e.
    Just click on Hassans profile and click on "send private message".
    As Hassan may not be available today, you can send the files to me instead, and I will review the design until beginning of next week.

    Thanks and best regards,
    Niklas