High-brightness light emitting diodes (HB-LEDs) are gaining immense attention from the angle of both residential and industrial applications, owing to their advanced futures of longevity, compact size, high efficacy and eco-friendly nature. To meet advanced future requirements, the LED driver should be robust and efficient. In addition, for HB-LED lighting applications, an ac-dc LED driver demands high-step-down conversion ratio, less source current harmonics, high power factor (PF) and to be cost effective. This work proposes a high-step-down coupled inductor-buck (HSD-CIB) based power factor correction (PFC) converter operating in discontinuous current mode (DCM) to attain high PF with low source current harmonics. Moreover, the proposed HSD-CIB can overcome the demerit of the existing single-stage ac-dc buck PFC converter in terms of highvoltage/current switching stress, gate-driver complexity, low conversion gain and low efficiency. This paper presents the detailed design and analysis of the proposed HSD-CIB PFC converter for an LED lighting system. A closed loop voltage mode control (VMC) is designed and implemented to study the line regulations of HSD-CIB converter at various loading conditions. The analysis of the proposed HSD-CIB topology is carried out using Matlab/Simulink simulation and validated experimentally with a prototype of 16 W.