The feedback winding is used by LinkSwitch-CV for output regulation and completely eliminates the need for an optocoupler for output isolation. This solution is very low cost and highly accurate. The feedback (FB) pin of the LinkSwitch-CV device uses an AC coupled signal through a voltage divider to sense the output voltage and thus regulate the output.
The feedback winding components dialog allows for the fine tuning of the feedback resistors. Any changes made to feedback components will be reflected in the BOM and schematic.