compensation of flyback
R813, R821, C819, C820, C822 FORMS A FEEDBACK LOOP STABILIZATION NETWORK FOR IC N804 (TL431 - PROGRAMMABLE REFERANCE), WHICH IS USED AS A VOLTAGE ERROR AMPLIFIER.
THIS CIRCUIT SENSES OUTPUT VOLTAGE OF A CONVERTER / POWER SUPPLY & GIVES A FEEDBACK TO THE PWM CONTROLLER VIA OPTO COUPLER, DUE TO THE LC COMPONENTS IN THE PATH THE OUTPUT SIGNAL FEEDBACK SIGNAL PHASE / GAIN HAS TO BE RESTORED OR STABILITY CRITERIA HAS TO BE MET & THIS NETWORK DOES THE JOB.
SIMILARLEY C825, C821, R822 ARE USED IN A CURRENT LIMIT FEEDBACK NETWORK. (C825 MIGHT BE USED TO FILTER THE RIPPLE CONTENTS OF C/L SIGNAL)