A multi-channel light-emitting diode(LED) current sharing method utilizing the charge balance of block capacitors was proposed to solve the current sharing issue when LED strings are paralleled. The block capacitors are in series with the corresponding secondary side windings of the transformer. By coupling the block capacitors in series, plus with amp-second balance, accurate current sharing among output LED strings is achieved. A four-output LLCC LED driver was constituted by combining the block capacitors and the LLC topology in primary side. The operating modes in one switching cycle are presented. The current sharing principle was also analyzed. By merging four outputs into one, the characteristic gain curves could be concluded for the circuit design guidance. A 150 W four-channel output prototype with 0.35 A/channel was built up. The amplitudes of the current waveforms in secondary side windings were identical and the phases were identical or opposite in the current sharing range, thus accurate current sharing was realized.
HU Chen, WU Xin-ke, PENG Fang-zheng, QIAN Zhao-ming. Multi-output LED driver with charge balance in multi-capacitors. JOURNAL OF ZHEJIANG UNIVERSITY (ENGINEERING SCIENCE), 2014, 48(12): 2202-2209.
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