How to design series resistor with optocoupler in TL431 feedback?

Posted by: alireza10471 on 06/12/2014

could you please tell me what is the design procedure for choosing the value of series resistor with optocoupler, in TL431 feed back?

Is there any formola for choosing the value of this resistor?

I am using TOPSWITCH-HX (TOP262EN) and I want to know how much current should Control pin (C) have?

Comments

Your question does not have a straight answer. Every engineer will give you a different answer. I think what you need to do is to understand more about TL431. Then from there you can deduce the value for the resistor. See the below link for you to understand more about the TL431

http://www.onsemi.com/pub_link/Collateral/TND381-D.PDF

Thanks for your answer

could you please tell me what is the nominal values of control pin current to opearate TOPSwitch for maximum and minimum duty cycle operation? Which data in datasheet have this information?

Datasheet for JX Family

Take a look to figure 6 and the top part of page 25

You can use 5 ma as a base number to run calculations