High power factor electronic ballast with fully differential circuit topology

In an electronic ballast circuit for driving a gas discharge lamp from a mains voltage signal supply, a ballast bridge unit having an upper and lower signal line comprises:

• a storage capacitor divider coupled across said upper and lower bridge unit signal lines said capacitor divider forming a reference voltage common terminal;
• an input converter bridge having at least two switches coupled in series at an input common terminal, wherein an upper switch of said input converter bridge is coupled to the upper signal line of the ballast bridge unit and the lower switch of said input converter bridge is coupled to the lower signal line of the ballast bridge unit;
• an output converter bridge having at least two switches coupled in series at an output common terminal, wherein an upper switch of said output converter bridge is coupled to the upper signal line of the ballast bridge unit and the lower switch is coupled to the lower signal line of the ballast bridge unit, wherein a first differential voltage signal is formed between said common input terminal and said reference voltage common terminal and a second differential voltage signal is formed between said common output terminal and said reference voltage common terminal;
• and
• a high-frequency generator that is configured to alternately switch the at least two switches of the output converter bridge to form the second differential voltage signal for driving the gas discharge lamp.

In a ballast circuit for driving a gas discharge lamp from a mains voltage supply line, said ballast circuit having a ballast bridge unit having an input converter bridge coupled in parallel with an output converter bridge and a reference voltage signal bridge, a method for operating said ballast circuit comprising the steps of:

• forming a voltage bus signal Vbus across a capacitor disposed in parallel with said signal bridges;
• forming an average voltage signal level at a common input terminal of said input converter bridge;
• shifting an average voltage signal at a common output terminal between two desired levels so as to form an ac current for driving the gas discharge lamp;
• and
• forming a reference voltage signal at a common terminal of said reference voltage signal bridge via a high speed switching within the reference voltage signal bridge at a switching frequency that is substantially higher than a frequency of the mains voltage, so as to form a first differential voltage signal between the common input terminal voltage signal and the reference voltage signal and to form a second differential voltage signal between the common output terminal voltage signal and the reference voltage signal for driving the gas discharge lamp.