Single-stage high-power-factor electronic ballast for multiple fluorescent lamps

An Electronic ballast with series-resonant parallel-load half-bridge inverters for multiple fluorescent lamps is developed. The ballast can be loaded with the desired number of lamps by connecting the corresponding number of the load resonant circuits. Each lamp is controlled by its associated active power switch and thus can be operated independently. To improve the input power factor, a boost converter for power-factor-correction is integrated in to the ballast by commonly using the active power switches of the inverters. By asymmetrical pulse-width-modulation, a high efficiency on the ballast-lamp circuit and a high power factor at the line input can be retained.