LinkSwitch Feedback Pin

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Hello,

 

I am trying to design a non-dimmable non-isolated 700 mA LED driver using LNK420 (this'll be my first experience using PI's chips).

 

I read the datasheet, the AN-249 and RDR-257... but I can't understand how the feedback divisor is calculated. 

 

PIXls gives values but not the formulas.

 

I read (RDR-257, page 9) that Ifb = k . Vout, but to choose a "k" value, I would need to know what is the Ifb min. and max... 

 

This question probably sounds stupid, but would you please tell me what I missed ? 

 

Best regards

Jérémy Hervé 

The output voltage of LED driver using LinkSwitch-PH is regulated by the FB current as shown in DER-297, IFB = K x Vout.

The feedback circuit in DER-297 is the level shifted voltage controll current circuit using PNP transistor.