Using the loss-free resistor concept to design a simple ac-dc HB-LED driver for retrofit lamp applications

Currently acknowledged, as a rapidly emerging technology, High-Brightness Light-Emitting Diodes (HB-LEDs) are considered the true alternative to many mature technologies (i.e., incandescent bulbs, compact fluorescent lamps, etc.) due to their high efficiency, low maintenance and durability. It is evident that the HB-LED driver must be durable and efficient to achieve these advantages. Moreover, in the case of replacing incandescent bulbs, the ac-dc HB-LED driver needs to be low cost and to have a high enough Power Factor (PF) to comply with international regulations. This paper presents a new proposal to design a simple, low-cost ac-dc HB-LED driver for retrofit lamps. The proposed solution originates from a very simple concept: the use a Switching Mode Power Supply (SMPS) acting as a Loss-Free Resistor (LFR) connected in series with the mains to shape the line input current. For the proposed application, it is obvious that the LFR needs to have a very simple topology to be economical. However, efficiency cannot be ignored. This paper proposes the flyback converter working as a LFR connected in series with the mains, operating in Boundary Conduction Mode (BCM) in order to improve its efficiency. First, a static analysis of the proposed concept will be presented. A distortion analysis of the input current of the proposed ac-dc HB-LEDs driver will then be carried out to test compliance with international regulations. Finally, a 12 W experimental prototype has been built and tested in order to validate the theoretical results presented in this paper. These results show the proposed ac-dc HB-LED driver to be a low-cost, high efficiency, sinusoidal input current option for designing retrofit lamps.