Yes, the led lights up with the tl431, the transistor turns on when the led is lit inside, it shorts the Collector and Emitter together, just like a normal one.

Do you have a sample circuit diagram for this? I think it suits the best as per the requirements.. and also the Reference voltage should be kept at 0V at my case for TL431?

 

Here is a smpsu using the same technique, the right side of the diagram uses the Tl431 and opto..


http://danyk.cz/s_atx06c.png

 

This thread is closed. No kidding.