Two-stage digitally controlled led driver based on buck-boost and DC/DC LLC resonant converter

In this study a digitally controlled Light Emitting Diode (LED) driver operating with high power factor, dimming capability and reduced DC-link capacitance is proposed. The proposed LED driver circuit topology, designed to supply a 100 W LED module, is composed by two independent stages. The Power Factor Correction stage is implemented with the buck-boost DC/DC converter, operating in Discontinuous Conduction Mode. This stage provide a high power factor and maintain the average bus voltage controlled in 400 V. Besides, a reduce DC-link capacitance with 25 μF is used, thus allowing the use of log lifetime film capacitors. The second stage comprises the DC/DC Half-Bridge LLC resonant converter, which is in charge to keep controlled the averaged LED current as function of the required dimming level. To avoid output luminous intensity modulation, the control loop of the second stage is designed in order to reduce the LED current ripple, arising from the low frequency bus voltage ripple. Experimental results are presented with the topology operating under output dimming and reduced DC-link capacitance.