A Power Factor Correction (PFC) system providing near unity power factor for an AC power source (VAC) connected to a complex load. The system includes a bridge rectifier, boost or buck-boost converter, complex load, and pulse width modulation (PWM) controller to provide pulses with variable duty cycle to a power switch. The invention is a constant pulse proportional current (CPPC) PWM controller that generates trains of pulses constant in frequency and duty cycle for one semi-cycle of the VAC. The duty cycle of the driving signal is modified by applying open-loop correction signals to summing nodes of PWM circuits. Since the PWM provides a constant train of driving pulses with constant duty cycle for one semi-cycle of the VAC, the current absorbed by the converter is contingent and linearly proportional to the voltage. Thus, the output current follows the voltage resulting in a power factor of near unity.
