A power factor correction circuit utilizes a digital controller string
comprised of an analog-to-digital converter, which is input to a digital
compensator followed by a pulse width modulation circuit for generating a
switching pulse. The loop current in a regulator circuit such as a boost
regulator is sensed and input to one side of a differential
analog-to-digital converter, the other side thereof providing a digital
reference current. This digital reference current is derived from
comparing the input AC voltage to the regulator with the DC output
voltage and processing these two voltages with a PFC algorithm to provide
this reference voltage.