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Optimal Control of a Wide Range Resonant DC-DC Converter

This paper presents an optimal control strategy for an immitance-network based resonant dc-dc converter capable of operating efficiently over wide input and output voltage ranges. The resonant network results in current-source property on the output side, together with zero-voltage switching of all the switching devices. On the inverter side, a pair of phase-shifted half bridge enables output current regulation using a combination of control signal phase-shifts designed to minimize losses. These features are well suited for automotive LED drivers supplied from a battery with wide input voltage range, and regulating output current through a string of LEDs, where the number of LEDs may vary, resulting in wide output voltage variation. Experimental results demonstrating operation with the optimal control strategy are shown for a 2 MHz converter prototype operating from an input voltage ranging from 8 V to 18 V, and delivering 0.5 A output current to a string of 1-15 LEDs, which corresponds to an output voltage range of 3-to-50 V. Using silicon MOSFETs, the prototype achieves a peak efficiency of 93.3%, and maintains greater than 87% efficiency across the wide output voltage range and for wide variations in input voltage.