Efficient LED back-light power supply for liquid-crystal-display

A highly efficient light-emitting-diode back-light power supply is proposed for liquidcrystal display. The proposed power supply consists of a bridgeless boost rectifier for power-factor correction and the asymmetrical half-bridge flyback converter with synchronous rectifier (SR) for DC-DC power conversion. In the proposed bridgeless boost rectifier, the diode reverse-recovery losses are reduced by achieving zero-current turn-off of the output diodes, as well as zero-current turn-on of the additional diodes. The reverse-recovery transients of the diodes are improved by a simple passive snubber circuit. For a DC-DC converter, the asymmetrical half-bridge flyback converter operates under zero-voltage switching for the power switches, and the SR switch operates under zero-current switching. The analysis of the proposed converter is presented and its design considerations are discussed in detail. Experimental results based on 28 V, 300 W back-light power are provided to demonstrate the performance of the proposed converter.