Two-frequency electronic ballast system having an isolated PFC converter

A ballast system for a lamp, comprising:

• rectifier means for rectifying AC input power having a first frequency and producing a pulsating DC current;
• a DC-DC converter for converting said pulsating DC current into a substantially constant DC voltage, said DC-DC converter including an isolation transformer having a primary side and a secondary side and a power factor correction circuit provided on said primary side of said isolation transformer, said power factor correction circuit including an inductor and an energy storage capacitor;
• second converter means provided on said secondary side of said isolation transformer for converting said constant DC voltage into an AC output current having a second frequency, said second frequency being higher than said first frequency;
• and
• power application means responsive to said AC output current for powering the lamp;
• wherein said power factor correction circuit and said DC-DC converter include, in common, a first switching means for regulating conduction of current through said inductor and transfer of energy stored in said inductor to said energy storage capacitor, and first control means for operating said first switching means at a first switching frequency, and for modulating the switching frequency of said first switching means to effect power factor correction.