High frequency electronic ballast for multiple lamp independent operation
 An electronic ballast with a voltage-fed, LC or LLC resonant inverter for multiple gas discharge lamp independent operation which maintains a substantially constant voltage to a lamp or lamps connected to the ballast even during a transition period when a lamp or lamps is ignited, extinguished, added or removed. The ballast includes a feedback loop that maintains a substantially constant phase angle between the voltage and the current in an LC or LLC tank circuit, which has the effect of the ballast providing the substantially constant voltage output. The feedback loop obtains a current feedback signal and a voltage feedback signal from the tank circuit, and provides a phase shifted signal as a feedback correction signal which is the current feedback signal phase shifted by the voltage feedback signal that tracks phase angle changes with one, some or all of the lamps of a set thereof connected to the ballast, and during the transition period. The feedback loop includes a phase-shift circuit which includes at least one differential amplifier stage that receives the current feedback signal at both inputs and the voltage feedback signal at one input so as to phase shift the current feedback signal at that one input. The ballast operates instant start or rapid start gas discharge lamps in various configurations, including dimming configurations. 
Philips Electronics North America Corporation
H H Y Y H H
H02M H05B Y02B Y10S H05B H05B
inventional inventional additional additional inventional inventional
Gert W. Chin
Bruning Chang