Dimmable Solid State Ballast With Integral Capacitive Occupancy Sensor

This paper describes and demonstrates an LED lighting system with an integral capacitive sensor that can detect occupancy both lighted and in the dark, and a driver (“ballast”) that is dimmable over a wide range. Sensing in the dark is accomplished by taking advantage of the logarithmic relationship between LED voltage and current. The ballast uses an inductor pre-charge technique to maintain efficiency during dimming, while maintaining relevant parameters for quality of lighting (e.g., chromaticity/color cast).