Analysis of Low Frequency Ripple Transmission in LED Drivers

This paper presents an analysis of LED drivers applied to reduce low frequency current ripple in LED loads. This current ripple is the result of the pulsing power at the input of the power factor correction (PFC) front-end converters, which originates a bus voltage ripple at the output. The ripple transmission attenuation from the bus voltage to the LEDs' current has to attend some desired goals in lighting systems, namely reduction of the PFC bulk capacitance, enabling the employment of long-life film capacitors, preventing flicker and assuring high luminous efficacy and life span. The present analysis about the ripple transmission is performed by comparing the series-resonant converter and the Buck converter, operating in continuous and discontinuous conduction mode. These converters are among the simplest and most efficient topologies used as LED drivers. These converters were analyzed in open loop, without any ripple compensation technique, supplying three different LED lamps, using mid power LEDs, chip-on-board LED, and high-power LEDs. While the series-resonant converter provides a great reduction of the low frequency current ripple, the Buck converter presents higher ripple values. Experimental results from the three converters to supply an LED lamp are presented in order to validate the proposed analysis.