A Single-Stage Integrated Buck–Boost and Resonant Converter with Automatic Current Balancing for High-Power LEDs

A novel single-stage driver configuration that combines a modified buck–boost converter with a Class-D series resonant topology is implemented for high-power LED applications. Operating in the discontinuous conduction mode (DCM), the integrated buck–boost stage inherently guarantees a high power factor (PF) alongside minimized total current harmonic distortion (THDi). To power four independent LED strings, the resonant stage interacts with a 1:1 transformer, which successfully delivers autonomous current-balancing capabilities without requiring auxiliary current control loops. The proposed architecture effectively mitigates stage-to-stage conversion losses. Furthermore, soft-switching performance is achieved across all components, featuring zero-voltage switching (ZVS) during turn-on for active switches and zero-current switching (ZCS) during turn-off for diodes. The steady-state behavior of the topology is thoroughly analyzed, followed by the formulation of mathematical equations to guide component selection. To validate the theoretical framework, a 100 W experimental prototype was constructed and evaluated. Initial assessments under rated loading conditions—consisting of four parallel channels, each containing twenty-five series-connected 1 W LEDs—demonstrated a PF of 0.996, a THDi of 5.58%, and an overall power conversion efficiency of 89.6%. Subsequent robustness tests utilizing asymmetrical string arrangements (23, 24, 26, and 27 LEDs per channel) confirmed nearly uniform current distribution across all branches, thereby substantiating the self-governing current-sharing mechanism of the proposed circuit.