Analysis of the asymmetrical half-bridge for street LED-lighting applications

High-Brightness Light Emitting Diodes (HB-LEDs) are considered as a remarkable lighting device due to their high reliability, chromatic variety and increasing efficiency. As a consequence, a high number of solutions for supplying LED strings are coming out. One-stage solutions are cost-effective, but their efficiency is low as they have to fulfill several purposes with only one converter: Power Factor Correction (PFC), galvanic isolation (in some cases) and current regulation. Two-stage and three-stage solutions have higher efficiency as each stage is optimized for only one or two tasks and they are the preferred option when supplying several strings at the same time. In this paper, a two stage solution is proposed. The first stage is the well-known PFC Boost converter. The second stage, on which is focused this paper, is the Asymmetrical Half Bridge (AHB). Its design has been optimized taking into account the needs and characteristics of LED-based street lighting applications. The proposed transformer design (with asymmetrical secondary windings) minimizes the conduction losses. Experimental results obtained with a 40-W prototype show an efficiency as high as 94.5% for this second stage and validate the use of this topology.