Panasonic television User Manual

Page of 98
PFC Circuit
Pin 16 of IC501 also goes low when pin 23 is “high”. When pin 16 goes “low”, the diode within the photo-coupler 
IC401 emits light to turn on the photo-transistor.
Pin 4 of IC401 goes “low”. This “low” is applied to the gate of Q401 turning it on to apply 12V to pin 8 of PFC 
circuit.
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