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Sakib816 , 09-26-2025, 05:37 AM

I have some question ...
For SMPS power supply design , in many application the TL431 voltage reference is used. so for some example circuit i saw that a bias resistor is used when using optocupler PC817.

i do not understand why this bias resistor is used ? can any one tell me the reason ..

Note : red circle indicate the bias resistor R6...the smps output is 12V DC