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Problem with L6566B in flyback power supply

MIInge_8
Associate

‎2025-10-16 4:33 AM - last edited on ‎2025-10-16 4:41 AM by Community manager

Greetings.

I am building a 24V, 240W power supply with the help of the ST eDesign Suite website. The problem I have is that before starting, it goes into a blinking mode. To start it, I have to measure with a multimeter on the ZCD pin. Then, suddenly, it enters the steady state and outputs a continuous voltage value. Before this, the Vcc voltage has a triangular shape in the power supply, reaching the minimum supply value of 10.4V and 12.5V.

Would anyone know what this is due to and how I can fix it?

I was wondering if it would be possible to obtain the Spice model to simulate the component.

Attached is the link to view the power supply design in eDesign Suit: L6566B QR FLYBACK AC/DC Converter | eDesignSuite | STMicroelectronics

I have also used two different transformers in case the problem was this. I am attaching them as well.

Greetings and thank you very much.

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Peter BENSCH
ST Employee

‎2025-10-17 5:22 AM

Welcome @MIInge_8, to the community!

The Turn-On threshold of the L6566B is min 13V, max 15V. If you want to achieve a safe start, you should therefore ensure that the voltage reaches at least 15V.

Regards
/Peter

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