A power factor correction (PFC) circuit (10) includes a pulse width modulator (31) operating in response to a clock signal (CLK) for switching a coil current (ICOIL) over a charging period (TCHG) to correct a power factor at a node (32). The coil current discharges over a discharging period (TDSCHG) to develop an output voltage (VOUT) at an output (30). An oscillator (35) generates the clock signal to have a clock period (TCLK) longer than the sum of the charging and discharging periods, thereby operating in a discontinuous mode, and has an input (39) for sensing the input signal to modify the clock period.