Sine-Reference Band (SRB)-Controlled Average Current Technique for Phase-Cut Dimmable AC-DC Buck LED Lighting Driver Without Electrolytic Capacitor

Abstract

This paper presents a phase-cut dimmable ac-dc buck LED driver for electrolytic capacitor-less LED lighting applications. In the driver, the sine-reference band (SRB)-controlled average current technique is proposed to perform rectified sine-average current control and phase-cut dimming control. The rectified sine-average current control can regulate the average value of sine-wave LED current, maintaining a high power factor (PF) over a wide range of ac input voltage and output LED load. The phase-cut dimming control not only makes the LED driver compatible with two types of phase-cut dimmers, namely, leading-edge and trailing-edge dimming types, but also eliminates visible dimming flicker at the ac line frequency. Fabricated in a 0.35 mu m CMOS process, experimental results show the line regulation of +/- 2.36% over 90 to 260 VAC and the load regulation of +/- 0.65% within the load range of 10 to 36 LEDs. The PF exceeds 0.95 under all conditions, and the peak efficiency of 90.7% is achieved. The analysis of the flicker frequency verifies that the proposed dimmable LED driver completely eliminates visible flicker owing to the phase dimming variations without an output electrolytic capacitor.