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PMP10871: Feedback loop

Part Number: PMP10871
Other Parts Discussed in Thread: TLV431, TEST

Hello!

it is possible to send me the step-by-step calculations to feedback loop design of PM10871?

I am using this reference design and I have a problem in the feedback loop, because I am using the optocoupler TLP181 (rank GB). With the original components of design of PM10871, the optocoupler are saturated. I changed the RLED to make the optocoupler operates in linear region but is not enough to put the Vfb inside the useful range and estabilizes the circuit. I read a lot of application notes with different circuits using the TLV431 and a optocoupler to external-error amplifier but any equal of used on PM10871.

Thanks for attention,

Best regards,

Diego

  • Hi Diego,

    The first thing you need to do is make sure the optocoupler is properly biased.  Here is an article that describes, step-by-step how to do that:

    www.edn.com/.../Make-sure-your-optocoupler-is-properly-biased

    The next thing you need to do is make sure you properly compensate the power supply based on the power stage and opto biasing.  Here is an article that describes how to do that:

    www.eetimes.com/author.asp

    Hope this helps.

    thanks,

    Brian

  • Hello Brian!

    Thanks for the tips. Actually, I found it these articles in my searches about the feedback circuit with TLV431, but I just looked around. :)

    Seizing the opportunity, maybe I have another problem. I did make a test removing feedback circuit and using a voltage divider with the Vref to FB pin to test regulation. First I tried Vfb with 3V but the output voltage not stabilizes. After I change the Vbf to 4,10 V and regulation seems good. Do you have some idea that what is happening?

    Sorry about these questions, this is the first power supply that I need debug.

    Best regards,

    Diego

  • Hi Diego,

    By removing the feedback circuit and using a divider from Vref to FB, you are running open-loop (un-regulated). You need to keep the feedback path from the output to maintain regulation.

    thanks,
    Brian