High Frequency Wide Range Resonant Converter Operating as an Automotive LED Driver

This article introduces an immittance network-based wide-range LCL-T resonant dc–dc converter, where two control variables, a phase shift between two inverter half-bridges, and a phase shift between inverter and rectifier half-bridges, are utilized to achieve output current regulation while minimizing losses over wide ranges of input and output voltages. A practical control strategy is developed to adjust the phase shifts so that zero voltage switching of all devices is achieved while minimizing conduction losses. Efficiency improvements over a standard LCL-T converter are demonstrated by loss modeling and by experiments. The features of the proposed WR-LCL-T converter are well suited for automotive LED drivers. Experimental results demonstrating operation with the loss minimizing control strategy are shown for a 2-MHz converter prototype operating from an input voltage ranging from 8 to 18 V, and delivering 0.5-A output current to a string of 1–14 LEDs, which corresponds to an output voltage range of 3–45 V. Using silicon MOSFETs, the prototype achieves a peak power stage efficiency of 92.4% and maintains greater than 86% power stage efficiency across the wide input and output voltage ranges.