• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 64 subscribers
  • Views 91 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TL431LI-Q1: TL431 For flyback converter feedback loop

Karthik karri
Prodigy 215 points
Part Number: TL431LI-Q1
Other Parts Discussed in Thread: TL431

Tool/software:

Hi Ti team,

I have a query regarding Vka voltage of TL431 in the feedback loop of dc-dc converter,

What is the VKA voltage value , is it same as Vef=2.5V??

From the above formula formula i am getting VKA=28.029V which is higher that my converter output voltage and and Rin i am getting  negative value which is wrong .

For Rpullup or Rin=(Vout-VD-Vka)/ILED.I considered this formula for calcuation.because of VKA  28.2V value i am getting negative resistance value .There could be some mistake in my approach.

Can you please check and suggest me proper approach.

  • 0
    TI__Intellectual 910 points

    Hi Karthik,

    Thank you for your question!

    Vref has some inaccuracies that are not apart of this simplified equation which is the cause for this solution. In general, this error would require designers to slightly lower the Vref voltage and design slightly above 28V in order to achieve 28V at the output.

    The full equation and design process for a flyback converter feedback loop can be found in section 2 in the application note below:
    https://www.ti.com/lit/an/snoaa00a/snoaa00a.pdf

    I hope this helps!

    Best Regards,

    Andrew Li