PLC810 loop stability

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Hello, I want to design a resonant power supply with one high-power bipolar output (±25V) and one low-power unipolar output (+18V) using PLC810. I don't want to use the PFC module of the IC, so I just leave open the ISP, GATEP, VCOMP, GNDP pins, connect the FBP pin to a resistive divider. Look at the Fig. 1 and tell me if it is a correct way to obtain dynamic stability. In practice this circuit shows instability at heavy loads: 200-300 hz oscillations are generated.

Hi,

C9 should be connected to the opamp output instead of the optocoupler LED anode.

Please review the design guide for HiperPLC product which includes a detailed section on control loop analysis and design. I am providing a link below for your reference.

(Specifically pages 18,19 and 20)

http://www.powerint.com/sites/default/files/product-docs/an46.pdf

Regards

PI-Sarek

Sarek, do you know what difference between positive and negative feedback is? What you advised me to do is to make positive feedback obviously! Take a look at the Fig. 1 carefully, the transistor Q1 inverts the signal from the opamp so that the feedback becomes negative. Nevertheless, I tested your suggestion and made sure that I was right. I'd read the design guide before I started to design my project, I tried these methods, combined them, but my power supply is still sounding changing its tone with load varying. Sarek, could you give me the pcb-files of the power supply described in PLC810 datasheet (http://www.powerint.com/sites/default/files/product-docs/hiper_family_datasheet.pdf) including the pcb-file of the standby supply? Send it to my email if possible.
Best wishes!

Hi,

I apologize for the oversight. I did not realize that the operational amplifier inputs are flipped as compared to a conventional implementation in which the reference is tied to the non-inverting terminal and the inverting terminal is tied to the feedback divider network.

We make mistakes sometimes but I believe I do understand the difference between negative and positive feedback. You were right and I was wrong in this instance and there was oversight on my part which probably caused you inconvenience. I thank you for your understanding.

We have the following information available for reference which includes board layout and other relevant details.

http://www.powerint.com/sites/default/files/PDFFiles/rdr189.pdf

http://www.powerint.com/sites/default/files/PDFFiles/der212.pdf

I hope you find this useful. This is the only information we have available for HiperPLC that I can share with you.

Regards

PI-Sarek