Electronic ballast for discharge lamps

Abstract

An electronic ballast operates a gaseous discharge lamp. The electronic ballast includes a filter circuit for removing noise from an electrical power signal. The power factor of the filtered power signal is adjusted by a power factor correction circuit. The power factor correction circuit includes a programmable inductor circuit having a plurality of selectable inductance values for varying the amount of power factor adjustment to accommodate operation of different lamp types and/or different lamp wattages. A power supply circuit converts electrical power received from the filtered power signal to provide low level power for operating the electronic ballast. An output circuit receives the corrected power signal produced by the power factor correction circuit and produces an electrical signal to ignite and operate the discharge lamp. The output circuit includes an ignition circuit for producing an oscillating voltage signal to ignite the lamp, and an operating circuit produces an oscillating current signal which operates the discharge lamp after ignition. A control circuit controls the operation of the electronic ballast. A current monitor is used to determine when the lamp is ignited. The ability of the electronic ballast to accommodate different lamps is enhanced by providing the ignition circuit with a programmable inductor circuit to oscillate the voltage signal at different frequencies. A similar effect is achieved by providing the operating circuit with a programmable resistor circuit having a plurality of programmable resistance values.