Elimination of electrolytic capacitor in LED power supplies by two-phase driving approach

A two-phase driving approach for light-emitting-diode (LED) applications is proposed in this paper. In the approach, two rectangular AC sources are employed so that the output current ripple can be significantly reduced. It leads to the elimination of electrolytic capacitor from the driver circuit. The approach is realised by a dual asymmetrical half-bridge converter with LEDs as the load. Considering the mandatory lighting standard for an AC/DC LED driver, the half-bridges are preceded by a valley-fill circuit for meeting the input power factor (PF) and current harmonic distortion requirements. Unlike other existing interleaved LED drivers that can only obtain low current ripples in certain operating points, the proposed approach can maintain a constant output current at all times even under large duty cycle dynamics due to the use of a valley-fill circuit. To validate the feasibility of the proposed approach, a 13 W prototype is built and tested experimentally.