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TL431: tl431

M M86
Prodigy 50 points
Part Number: TL431
Other Parts Discussed in Thread: UCC28600,

I have a question about the loop design with tl431. I designed a flyback with the ic ucc28600 and I'm searching for a guide, how to realize the feedback loop. I found a guide from ti (slua671) but I'm not sure, if this guide is correct. In this article a type 2 compensation network is described. But they use a C and a RC combination in the opamp circuit. In some other documents (e.g. "The TL431 in the Control of Switching Power Supplies" from OnSemi and literature there is only one condensator instead and the solution is very different from the ti literature. Furthermore in the literature of onsemi the pole depends on the capacity of the optocoupler. Which solution is correct?

  • 0
    TI__Genius 12630 points
    M M86,

    Both solutions are correct. There are many different types of compensation that can be used to still produce stable operation. The main point with loop design is that your phase margin, gain margin, and bandwidth produced by your compensation is producing a stable output. The TI version C1 + R1 // C2 vs other compensation with C1 + R1 only will both work, the additional C2 will provide an slightly different frequency response and can add some DC gain. There is a lot of literature out there for designing loop compensation so there is no single correct answer. Some designs will be OK with only one cap and one resistor while other designs may require more complex compensation. I hope this answers your question.

    Other literature that help visualize the generic types of compensation in Op Amps on the frequency response, specifically the pole placement, can be seen here: www.ti.com/.../slva662.pdf

    -Michael