Patent ID: 7400517

Claim:
A power factor correction circuit comprising: an ac input configured to receive a first ac signal; a zero crossing detector configured to receive the first ac signal and generate a detect signal representing a zero crossing of the first ac signal; a switching output configured to control a power switch to regulate an output voltage to a target value within a range of values that includes a first value that is greater than the target value and a second value that is less than the target value; a sample and hold circuit configured to receive a feedback signal that is representative of the output voltage, to store a value of the feedback signal on a storage element, to couple a stored value of the feedback signal to an output of the sample and hold circuit responsively to the detect signal, and to couple the feedback signal to the output of the sample and hold circuit responsively to the feedback signal increasing to a third value that is greater than the first value or decreasing to a fourth value than is less than the second value; and an error amplifier configured to receive a first signal that includes a second signal from the output of the sample and hold circuit and responsively provide an error signal.