High-Performance Megahertz-Frequency Resonant DC-DC Converter for Automotive LED Driver Applications

This paper introduces a megahertz-frequency resonant dc-dc converter that inherently achieves a load-independent output current while maintaining high efficiency across a wide output voltage range. These properties make the proposed converter well-suited for automotive LED driver applications, where a varying number of LEDs need to be driven with a constant current. The proposed converter achieves load-independent output current by utilizing an LCL-T resonant network, and achieves high efficiency by operating at a fixed switching frequency with optimized magnetics. This LCL-T resonant converter is also capable of regulating its output current at any desired value by utilizing phase-shift control. The performance of the LCL-T resonant converter is theoretically and experimentally compared with the recently proposed (LCL)-L-3 resonant converter. For the experimental comparison, the prototypes of the LCL-T and the (LCL)-L-3 resonant converters are designed for 2-MHz operation across an output voltage range of 3 V to 50 V (corresponding to a string of 1 to 15 LEDs) while supplying a constant 0.5 A output current to the LEDs. The LCL-T resonant converter prototype achieves a peak power stage efficiency of 94.5%, which is 1% higher than the peak efficiency of the (LCL)-L-3 converter prototype. Furthermore, the LCL-T converter prototype maintains 1.5% higher average efficiency over its output voltage range relative to the (LCL)-L-3 converter prototype.