Analysis and Design of LLCC Resonant Four-Channel DC-DC LED Driver with Current Sharing Transformer

By utilizing the charge balance in one capacitor, the current in two LED strings can be balanced in the LLCC resonant converter [1]. In order to balance four LED strings, a new LLCC resonant converter with two secondary side windings in main transformer, two secondary resonant capacitors in and an additional current sharing transformer (CST) is proposed. Each secondary resonant capacitor can balance the currents in one pair of outputs. And it bears the DC output voltage difference between two outputs of each pair. Meanwhile, the CST is used to balance currents of two pairs. The circuit operation principle, steady state characteristic and design considerations are discussed. A prototype of 140W four-channel LED driver is built to verify the proposed current sharing circuit.