Analysis and design of digital SEPIC converter with programmed dimming and current sharing for automobile LED headlights application

This paper presents an automobile LED headlight system with load current sharing and programmed dimming features. The presented system consists of the automobile power net, two sets of SEPIC converter, and two sets of LED headlamp. The I–V characteristics of the high power white LED array adopted in the study is addressed first. The steady state analysis and design of the SEPIC converter is then presented. Two coupled inductors are used in the converter to reduce component counts and share LED currents. While the digital proportional-integral control algorithm is used to regulate the converter, the current mode pulse-width-modulation approach is programmed to dim the headlights when the automobile is running at zero speed. To verify the theory and design, two prototype SEPIC converters with rated power 40W for each have been built and tested. Each converter drives 6 LED arrays consisting of 2 parallel strings with 3 arrays connected in series. Digital signal processor TMS320F28035 is utilized to realize the system. As a result, the experimental results well confirm the theoretical prediction. The LED currents are shared with difference less than 0.5% in strings The converter efficiency measured at full load is 90.11% and 94.9% at half load. The better efficiency at half load implies that more energy can be saved from the LED headlight dimming operation.