Hello,
I am writing with reference to the LT1509 PFC/PWM controller.
****LINK TO LT1509 DATASHEET.
http://www.linear.com/pc/downloadDocument.do?
navId=H0,C1,C1003,C1142,C1138,P1516,D1119
I believe that the equation for control_to_output (voltage loop) at the bottom (left) of page 7 of LT1509...