Abstract
Due to the advantages of high luminous efficacy, ruggedness, long life hours and compact size of LED, it has now become a main trend to replace the traditional lamps in many applications. Therefore, the main objective of this thesis is focused on developing a LED driver with low cost and high efficiency. The major contributions of this thesis may be summarized as follows. First, a novel dimmable LED driver topology with low voltage switching (LVS) is proposed. Compared with the conventional buck converter, only one additional resonant inductor is needed which results in low cost and high reliability. Both the low voltage switching of the active switch and the zero current switching (ZCS) of the diode can reduce switching losses and raise the efficiency rather significantly. Also, the wide duty ratio operating range of the proposed driver renders much higher dimming resolution for active load cases such as LED dimming application. Secondly, theoretical analysis of the proposed LED driver is made and some design guidelines are given. The mathematical models of the proposed LED driver are derived based on reduced-order average modeling technique and full-order average modeling technique for the design of the closed-loop control. Although the former can result in a more simplified model, however, the latter can provide better accuracy. Thirdly, in addition to the duty ratio feedback control, the switching-frequency control can also be coordinated in the closed-loop controller simultaneously to improve greatly the transient response of the driver. Finally, a 50W prototype is constructed for verifying the effectiveness of the proposed LED driver. Experimental results show that the maximum efficiency is up to 96.06% and high dimming resolution is available which makes the proposed LED driver suitable for LED dimming application. Keywords: LED Driver, LVS, ZCS, Reduced-Order Average Modeling, Full-Order Average Modeling, Switching-Frequency Control.