Efficiency Improvement of Multichannel LED Driver With Selective Dimming
There is a widespread application of selective dimming of multichannel LED drivers. In this article, two new selective dimming methods to improve the efficiency of multichannel LED drivers are proposed. The proposed methods are based on a two stage multichannel LED driver that consists of an ac dc boost power factor correction converter at its front end and a dc dc non resonant converter at its second stage. Primary side digital peak current control method is applied to the dc dc converter to control the LED peak currents during selective dimming operation. The auxiliary back to back switches are connected across each transformer winding either at the primary side or secondary side to perform selective dimming. The duty ratios of these auxiliary back to back switches are varied at lower than switching frequency of dc dc converter to control the brightness of LED loads. The proposed topologies offer high efficiencies in both full load and during selective dimming operations, and meet the IEEE 1789 recommendation with 3 kHz dimming frequency. The design of the proposed dc dc converters, modes of operation as well as detailed theoretical analysis are presented in this article. A 150 W prototype of the proposed LED driver with a non DSP microcontroller is implemented to verify the feasibility of such LED drivers. Comparisons between the proposed methods and the converters reported previously are presented in the article.
IEEE Transactions on Power Electronics