Frequency-Based Active Ripple Compensation Technique to Reduce Bulk Capacitance in Integrated Offline LED Drivers

In order to increase the power density and the lifespan of light-emitting diodes (LED) drivers, several studies have proposed active ripple compensation (ARC) techniques for minimizing the converter bulk capacitance. However, a common side effect of the ARC method is the increase in the total harmonic distortion (THD) of the converter input current. In this context, a frequency-based ARC technique is proposed as an alternative to the conventional ARC methodology, in which the duty cycle is modulated. The analyses presented in this article show that the frequency-based ARC approach applied to resonant converters has a better performance than the one used in hard-switching converters, since it allows for a huge capacitance reduction with a small THD increase. Furthermore, this article presents a generalized analysis of ARC techniques applied to integrated offline LED drivers, which reduce the number of components and the overall LED driver cost. The input current harmonic content and the output ripple reduction have been theoretically predicted for several converters. Experimental results gathered from a 96-W laboratory prototype supplied from a 127-V 60-Hz grid attested the superior performance of the frequency-based active ripple compensation, since a capacitance reduction of 66.6% has been obtained with an increase of only 0.9% in the THD.