A power factor correction circuit for driving a switch of a boost type converter circuit having an AC line frequency input, comprising a sense circuit for sensing and comparing the output voltage of the boost type converter circuit to a reference voltage, a circuit responsive to the output of the sense circuit for providing a drive signal for driving the switch, wherein the drive signal comprises a pulsed signal comprising a pulse grouping during each half cycle of the AC line frequency comprising at least one pulse wherein the number of pulses and frequency of the pulses of the pulse grouping changes with the output of the sense circuit up to a threshold value with the pulse width of the pulses being substantially constant; and when the output of the sense circuit has reached the threshold value, the pulse width of the pulses of the pulse grouping are varied in accordance with the output of the sense circuit.