Patent ID: 8836240
Filing Date: 2014-09-16
Classification: H05B

Abstract:
1. A ballast, comprising: a rectifier to receive an alternating current (AC) voltage signal from an AC power supply and to produce a direct current (DC) voltage signal therefrom; a buck converter circuit connected to the rectifier to receive the DC voltage signal, wherein the DC voltage signal has a magnitude that is substantially constant, the buck converter circuit has a duty cycle to generate a lamp voltage output signal from the DC voltage signal, the lamp voltage output signal applied to a lamp to energize the lamp, wherein the lamp voltage output signal has a magnitude that is varied by the duty cycle to energize the lamp at a plurality of lamp lighting levels; and a controller connected to the buck converter circuit, the controller configured to receive a dim input signal that is indicative of a selected lamp lighting level, to provide a control signal to the buck converter circuit as a function of the dim input signal, the control signal indicating a particular duty cycle for the buck converter circuit, the control signal configured such that, during an initial start-up period, the control signal indicates at least a minimum duty cycle for the buck converter circuit, and thereafter the control signal indicates a duty cycle for the buck converter circuit that corresponds to a lamp voltage output signal having a magnitude for energizing the lamp at a selected lamp lighting level from the plurality of lamp lighting levels; wherein in response to the buck converter receiving the control signal, the buck converter circuit adjusts the duty cycle according to the control signal to produce the lamp voltage output signal having the magnitude to energize the lamp at the selected lamp lighting level.