Digital Control For Metal Halide Electronic Ballasts

The High-Intensity-Discharge Lamps (HID), are notable 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 network etc, make products based on digital control more credible and easier to realize in batches with lower costs and short development cycle. So digital control will be one of the orientations of electronic ballast development.At first, the development process of ballast is introduced. All kinds of circuit topologies sorted by methods which can eliminate acoustic resonance, are summarized and analyzed. And the control strategies are also introduced. Secondly, The transient and steady state characteristics of metal halide lamps are analyzed from the theory and experiment. Then a lamp start-up process of MHL is gained by experiment. Thirdly, based on the analysis of each step of the start-up process, the control method of electronic ballast is presented and the digital controller is designed. Fourthly, the parameters of the main circuit and PI controller are designed, and then 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.