Digital Control For Metal Halide Electronic Ballasts

With the development of green lighting in the world, the High-Intensity-Discharge Lamps (HID) are used abroad for their high luminous efficacy, good color rendering, and long life. Metal halide lamps (MHL) have the best combination of the above properties and are considered the most ideal light sources. The electronic ballasts that drive light sources, must be high efficient and can prevent acoustic resonance.Due to the complex lamp start-up process and timing control requirements, control circuit built with conventional analog control is unavoidably cumbersome. The merits of digital control: simple hardware, no temperature drift, flexible control and easy to realize advanced arithmetic and etc. Products based on digital control are more credible and easier to realize in batches with lower costs and short development cycle than those based on analog control. So digital control will be one of the directions of electronic ballast development.At first, the development process of electronic ballast is introduced. The kinds of circuit topologies is sorted by methods which can eliminate acoustic resonance, are summarized and analyzed. The control strategies and dimming function of electronic ballast are also introduced. Secondly, the lighting principle of metal halide lamps are analyzed from the theory , and the start-up process of MHL is achieved. Thirdly, the control method of electronic ballast is presented , and the digital controller is designed based on the analysis of each step of the start-up process including the parameters of the main circuit and PI controller, then they are verified by simulation. At last, the thesis places emphasis on hardware, software and anti-interference design. A prototype for 250W metal halide lamps is presented, and the experimental results are displayed.