An Alternative Approach to LED Driver Design Based on High-Voltage Driving

This paper discusses an alternative approach to designing LED drivers based on high-voltage operation. Compared with the conventional approach of driving LEDs with low voltage and high current, the alternative approach aims to deliver the same power to LED load with high voltage and low current so that small and nonelectrolytic capacitor can be used. High-voltage operation also facilitates the use of simple PFC preregulators such as boost or SEPIC converters as single-stage LED drivers. This paper begins with the derivation of the relationship between the nominal output voltage and output capacitor's size of a PFC preregulator for achieving a given output voltage ripple's size, followed by a review of the recently emerged high-voltage LED packages suitable for the proposed application. This paper also discusses the flicker and colorimetric performances of LED light sources under the influence of large current ripple when nonelectrolytic capacitor is used. The method of third-harmonic current injection to the input current of LED drivers is also incorporated as an option for further reducing the output capacitor's size while meeting a specified flicker limit. Finally, a design example of high-voltage LED driver based on a boost PFC preregulator with third-harmonic current injection is presented and verified experimentally.