High frequency gas discharge lamp dimming ballast

摘要

A high frequency dimming ballast dims to about 1 percent of rated output in a repeatable way so that parallel connected dimming ballasts will all produce the same light illumination when dimmed to a very low percentage of their rated light output. A first current sensor is connected in series with a semiconductor power switching device which is coupled to and controls power to the ballast. A second current sensor is connected directly to the lamp circuit to detect actual lamp current, particularly at low illumination conditions, for example at less than 10 percent of the rated light output. Lamp control under low illumination conditions is derived from the lamp current sensor and overrides control by the sensor in series with the transistor switch means.