LM5156: Issues with Flyback Converter Design Using LM5156

Francesco Rizzotto

Prodigy 85 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

6 months ago

0 Hassan Jamal 6 months ago

TI__Expert 4090 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 Francesco Rizzotto 6 months ago in reply to Hassan Jamal

Prodigy 85 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 Niklas Schwarz 6 months ago in reply to Francesco Rizzotto

TI__Mastermind 30280 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

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LM5156: Issues with Flyback Converter Design Using LM5156