A Single-Stage Power Converter for a Large Screen LCD Back-Lighting

Abstract

This paper presents a single-stage power converter for driving any number of power Light-Emitting-Diodes (LEDs) from a high AC input voltage. The power converter converts a high AC input voltage into a DC current source directly by using a proposed single-stage power converter. The DC output voltage can be higher or lower than the peak of the AC input voltage level. In addition, the AC input current is synchronized with the AC input voltage so that AC input power factor is close to unity. The LED current is controlled based on a current-regulated PWM method. Hence, both a Power Factor Correction (PFQ feature and LED current regulation are obtained by using a single-stage power converter. Furthermore, there are no DC bulk capacitors in the DC-link and AC-rectified line voltage or current sensors. A current sensor at the MOSFET source-side is employed only to regulate the power LED current. With the proposed scheme based on a single power conversion stage, higher efficiency with a very simple, low-cost power LED driving system is implemented. Experimental results show that the total efficiency is over 90 [%] with PF /spl ges/ 0.9 in a wide LED current control range. The experimental results for the maximum output power of 90 [W], I/sub o/=500 [mA] and V/sub o/=180 [V] are provided.