Closed-Loop Control of LCL-T Resonant DC-DC Converter Operating as Automotive LED Driver

This paper presents an automotive LED matrix driver with improved dynamic performance, based on an LCL-T resonant network and a π filter. This LED driver can efficiently deliver a constant current to an LED matrix string with a fast-changing number of LEDs. This is achieved by the inherent current source nature of the LCL-T resonant converter and a π filter with smaller filtering elements. High efficiency is achieved by maintaining zero-voltage and near zero-current switching of all transistors. The performance of this converter is further enhanced by closed loop control of the LED current. A 2-MHz prototype LCL-T resonant converter, designed to drive 1-15 series connected LEDs with a constant current of 0.5 A, is built and tested. The overshoots and undershoots in LED current during load transients are greatly reduced from 90% to 10%. This prototype achieves a peak efficiency of 94% and maintains an average efficiency of 91% over its 15:1 output voltage range (3.3 V to 49.5 V).