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.