A controller for a PWM converter. The low frequency input impedance is an important parameter of PWM converters. In active power factor correction schemes, this impedance needs to resistive in order to keep the power factor near unity. The controller of the present invention will force the input terminals of a PWM converter, and in particular that of a Boost converter, to look resistive, or with a reactive component as desired. The advantages of the controller according to the present invention are simplicity, low cost, robustness and the fact that it does not require an analog multiplier and does not require sensing the input voltage.