Method to reduce bus voltage stress in a single-stage single switch power factor correction circuit

An apparatus for providing operating frequency modulation of the switch in a single-stage single-switch converter for reducing voltage stress, comprising:

• a capacitor having a capacitance and coupled to a controller associated with said switch;
• a resistance coupled to said controller and cooperable with said capacitor for determining an operating frequency for the switch, wherein said resistance determines the charging current applied to said capacitor;
• and
• a frequency foldback device adapted to reduce said determined operating frequency and having an input for receiving an indication of the bus voltage of said converter for comparison to a threshold and an output coupled to one of said capacitor and said resistance and operable to reduce said charging current applied to said capacitor responsive to a threshold detection.