A high power factor converter system comprises an input rectifier, a converter and a booster circuit. The input rectifier is configured for rectifying an input ac voltage. The converter is configured for generating an output voltage for the high power factor converter system. The converter comprises several converter switches and inverse parallel diodes. The booster circuit comprises an inductor and at least one converter switch and an inverse parallel diode of the converter. The inductor is coupled between the input rectifier and the converter. The booster circuit is configured for controlling the supply of a booster current through the inductor to be discontinuous when the instantaneous voltage level is less than a predetermined fraction of a dc voltage level across the converter and continuous when the instantaneous voltage level is greater than the predetermined fraction of the dc voltage level.