Optimal design methodology for the current-sharing transformer in a quasi-resonant (QR) flyback LED driver

In this paper, a quasi-resonant (QR) flyback converter with one current-sharing transformer (CST) to balance the output current for driving two-channel LEDs is analyzed. From the theoretical analysis, it shows that the parasitic capacitance of CST and its magnetizing inductance have a critical effect on the output current deviation and rectifying diode´s voltage stress. A design methodology for achieving the best current-sharing ability and the optimal CST in a Dc-Dc QR flyback converter is proposed. A 100W two-channel LED driver based on QR flyback converter is built up to verify the proposed methodology. According to the design guidelines, accurate balanced currents in two channels are achieved even at high voltage deviation between two LED strings.