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Can the LNK564 offline flyback controller have output regulation by optocoupler?

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We intend to use LNK564 offline flyback controller for a flyback that switches off the 380VDC PFC bus.
It will supply a secondary of 5V, 200mA, and will have a 13V bias winding which gives some 100mA to the primary side circuitry.

Do you think we can do this via secondary side optopcoupler/TL431 regulation? (The opto transistor would be connected in emitter follower style from Bias winding to FB pin of LNK564).

Page 11 of the datasheet appears to say that regulation is a complicated function of the current into, and the voltage at, the FB pin.

Do you think its possible to do opto-based regulation of the LNK564?

Lnk564 datasheet:

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