Abstract
Due to the advantages of high luminous efficiency, ruggedness, long life and compact size of LEDs, solid state lighting has now become a main trend to replace the traditional lamps. However, the corresponding driver performance such as efficiency and output current ripple remain to be a topic for further improvement. In this thesis, a novel single-stage single-switch AC/DC converter with universal input and dimming control is first proposed for LED drivers. The new single-stage topology requires only one active switch and one diode to reduce the conduction loss and achieve better efficiency. Also, the input capacitor is designed and operated in the discontinuous voltage mode to achieve unity power factor for an universal input power. Meanwhile, due to the small capacitance value and the quasi-resonance characteristic, the proposed converter can achieve rather high step-down voltage ratio easily. Second, theoretical analysis of the proposed converter is made and some design guidelines are given. Due to high dimension of the proposed converter model, proper approximations are made to derive the voltage gain and the boundaries between continuous conduction mode (CCM) and discontinuous conduction mode (DCM) for input inductor current, resonant inductor current and input capacitor voltage respectively. Third, a low cost low dropout regulator IC (AMC7140) is employed for implementing the dimming control of LEDs. Finally, a prototype with 100W rating, 90Vrms ~ 265Vrms AC input, 24V DC output is constructed to verify the validity of the proposed LED driver. It is seen that the resulting power factor is higher than 0.99, and the efficiency is greater than 90% in the output power range of 20W ~ 120W. Also, the input current harmonics regulation of IEC 61000-3-2 Class C is well satisfied and the maximum efficiency is about 92.8%. The dimming control range is from 10% ~ 100% with an output voltage ripple being less than 1.54%.