Abstract
The metal halide lamps (MHL) are widely used in many lighting applications due to their attracting properties such as high luminous efficiency, good color rendering, and long life time. However, for proper operation, an electronic ballast is required for driving the MHLs from starting up to steady state. In order to enhance the performance and extend the life time of MHLs, fully digital implementation and constant power control are two important factors considered for future development. Hence, in this thesis, the major objective is to choose a low cost commercial digital signal controller (DSC) to implement a fully digital electronic ballast and achieve a more accurate constant power control for gaining longer life time for MHLs. Basically, the contributions of this thesis can be summarized as follows. First, a single digital signal controller (DSC), namely, dsPIC30F4011, is chosen to accomplish fully digital control and simplify the circuit. The digital signal controller is used to deal with both feedback signal processing and control signal output together with combining multiple peripheral module functions, such as High Speed Analog to Digital Converter (A/D) Module, Output Compare Module, Motor Control PWM Module, and the Timer Module with interrupt function. As a result, it can simplify greatly the complexity of the whole ballast circuit. Also, a resonant ignition technology is adopted in this thesis. Compared with the traditional pulse ignition starting, resonant ignition method has the advantage of having fewer elements and more possibility of successful ignition. Second, in order to extend the life time of lamps, a constant power control is also implemented. By using the proposed digital signal controller, the resulting electronic ballast can achieve much more accurate constant power control in spite of large variation of the equivalent resistance due to aging effect. Third, in this thesis, a dsPIC30F4011 designed by MICROCHIP company is adopted as the control center to realize the overall control of the electronic ballast. Finally, a prototype ballast is also constructed for driving a 70W metal halide lamp. Experimental results show that the proposed fully digital control can indeed achieve the desired performance.