Multi-channel LED driver with CLL resonant converter

This paper proposes a two-stage multi-channel LED driver, which contains a buck converter as the first stage and a multi-channel constant current (MC³) CLL resonant converter as the second stage. The forward current of one specific LED string is sensed for feedback control to regulate the bus voltage, which is also the input voltage of the MC³ CLL resonant converter. In contrast, the MC³ CLL is unregulated and always working around the resonant frequency point to achieve best efficiency. Therefore, this two-stage LED driver could achieve high efficiency within a wide load range. Furthermore, for the MC³ CLL resonant converter, the magnetizing inductance of the transformer can be as large as possible, so the current sharing among the transformer modules is very good, even under unbalanced load conditions. Meanwhile, the currents of two LED strings driven by the same transformer is balanced via a DC blocking capacitor. As a result, this two-stage LED driver can achieve good current balance even with a large load variation. Finally, the merits of this two-stage LED driver are verified by experiment.