A Novel Double Integrated Buck Offline Power Supply for Solid State Lighting Applications

A single stage offline power supply for LED lighting applications, based on the integration of a buck PFC and a tapped buck DC/DC converter, is presented in this paper. Besides the high step-down capability and output current regulation, the proposed topology effectively provides power factor correction, so as to comply with the harmonic injection and energy saving standards EN 61000-3-2 and Energy Star. The low BUS voltage level, resulting from the use of an input step-down PFC stage, actually allows the use of film technology capacitors, instead of short lifetime electrolytic capacitors, to filter the BUS voltage and reduce the LED current ripple component at twice the line frequency. Thanks to the high reliability, the simple structure, the good line side spectral performance and the low component count, the proposed topology effectively results to be very suitable for medium power solid state lighting applications, as in the case of LED down-lighting. The issues related to the operation of the presented solution and to its design optimization will be carefully discussed. A prototype of the proposed AC/DC converter has been built and tested. The main experimental results will be described.