Análise da transferência de ondulação de baixa frequência em drivers de LEDs

Abstract

This work presents the analysis of low frequency ripple transmission from the bus voltage to the output current in LED drivers, in the power control stage. The buck, boost and buck-boost converters, operating in discontinuous conduction mode, are evaluated. The main goal is to check the maximum bus voltage ripple values allowed for the proposed topology, to follow the IEEE Std. 1789-2015 recommendations. This recommendation defines the current modulation levels in lighting systems to mitigate the effects of flicker on human health. To reach this condition, a mathematical approach to determine the low-frequency ripple transfer of the proposed topologies is presented, and is used to compare three different LED models. From these analyses, the LED load 3014, composed of 96 LEDs with rated power of 20W, is selected to be simulated and experimentally implemented in three operation points of bus voltage to each topology. The efficiencies of each experimental result are also measured. The buck-boost converter was the most flexible in ripple transfer because it presented a factor of 1.75 for the entire operating range evaluated, but it had the lowest efficiencies levels, between 90.7% and 92.7%, which reduces as the bus voltage increases. When it is possible to operate the converter with high bus voltages, the buck converter becomes a good alternative, with ripple transfer levels of around two times and efficiencies above 93.5%. When the bus voltage can be small, leading to a high relationship between the output voltage and the input voltage, the boost converter is an alternative, with a ripple transfers factor up to 2.4 times and efficiencies over 93.5%.