LED Driver Based on Input Current Shaper Without Electrolytic Capacitor

Abstract

This paper presents a high-power-factor light-emitting diode (LED) driver implemented by using an input current shaper technique. A flyback converter operating in DCM is placed between the main rectifier and dc bus, in order to increase the conduction angle of the rectifier diodes and to decrease the current harmonics injected to the mains. A buck converter performs the LED power control stage, which is integrated with the flyback by sharing the same active switch, thus presenting reduced component count. The use of a flyback converter operating as a loss-free resistor provides reduced power processing, increasing the converter's overall efficiency. The two-stage configuration allows bus capacitor reduction, owing to the effect of low frequency filtering provided by the second stage. In this way, electrolytic capacitors can be avoided, thus increasing reliability of the LED driver. An analysis of the effects of the bus voltage ripple caused by the capacitance reduction is performed. The driver also presents dimming capability. Analysis and design example of the proposed converter are presented. Experimental results of the proposed converter supplying an LED luminaire of $\text{50}\, \text{V}/\text{2.1}$ A LEDs are shown. The prototype presented high power factor, ${\text{PF}} = \text{0.97}$ , harmonic distortion of input current satisfying the IEC 61000-3-2 requirements, THD = 22.3%, and high efficiency, $\eta = \text{91.1}\% $ .