ELECTRONIC BALLAST FOR A HIGH INTENSITY DISCHARGE LAMP

摘要

An electronic ballast for a discharge lamp is capable of dimming the lamp over a wide range, yet minimizing a color temperature deviation. The ballast includes a power converter which converts an input DC voltage into a lamp power for driving the lamp, and a dimmer providing a dimmer command of a varying dimming ratio in order to reduce the lamp power to a greater extent as the dimming ratio decreases. A controller controls the power converter to supply a high frequency AC current and a low frequency rectangular waveform alternatively to the lamp in response to the dimmingratio decreasing to a predetermined level, and to reduce an RMS value of the high frequency Ac current as the dimming ratio decreases past the predetermined level. A color temperature sensor is included in order to monitor the color temperature while dimming.