Design and Implementation of a Microcontroller-Based High Power Factor Electronic Ballast to Supply Metal Halide Lamps

The analysis, design and implementation of a microcontroller-based electronic ballast to supply metal halide lamps are presented. The proposed power scheme is based on the integration of the buck and flyback converters. The former providing power factor correction and the latter controlling lamp power by supplying the lamp with a low frequency square-waveform current, which is a convenient way to avoid acoustic resonances in high intensity discharge (HID) lamps. Both converters operate in discontinuous conduction mode, thus allowing the use of only one high-frequency switch and simplifying the control. The electronic ballast is digitally controlled by using a low cost microcontroller PIC16F684. The microcontroller performs all the necessary tasks during starting, heating and steady state, including closed loop control of lamp current and protections. Experimental results for a 35 W metal halide lamp are presented