Here I have attached SMPS design circuit, I am not confident about the selected values for R15 and R16.
Can you please help me if the values are correct or needs to be changed, or is there any formula for it.

 

hi SG,
This is what LTspice shows for TL431 circuit, a problem.
E

Ref PDF Page #24

 

I am not confident that the circuit in post #1 works as intended. I am guessing that it is intended to be a 12.0 volt power supply able to deliver up to 300mA.
Given that TI and others have published reference designs available on line, along with detailed explanations, it makes sense to see what is offered there for free.

 

I am not confident that the circuit in post #1 works as intended. I am guessing that it is intended to be a 12.0 volt power supply able to deliver up to 300mA.
Given that TI and others have published reference designs available on line, along with detailed explanations, it makes sense to see what is offered there for free.

It is intended to work for 12V/300 mA.
It works very well for full load operation
But sometimes it fails input resistor of R6 actual shown is 33E but practically i use 100E blows up.

 

hi SG,
This is what LTspice shows for TL431 circuit, a problem.
E

Ref PDF Page #24

I don’t see anything wrong with that feedback circuit. it should regulate to 12.07V with those values, so there won’t be any LED current at 12V because there is only 2.48V on the adj pin.