Low Cost High Density AC-DC Converter for LED Lighting Applications

Inhalt:
Low cost, high power density designs of LED ballasts are not readily available on today’s market. With every new generation the LED technology itself is becoming more efficient and the devices are becoming smaller. This leads to an increased demand for smaller lamps. Thus, a compact design of all components in a luminaire is becoming increasingly important. This is the main motivation to focus on miniaturizing the electronics, in order to facilitate small lighting fixtures. As this market is very competitive and thus price sensitive, the cost must be kept at a minimum. This paper presents an extensive topology evaluation and comparison followed by a size and cost optimized design of an AC-DC converter for LED lighting applications. The basis of this work is a comparison of more than twenty different topology combinations. On the set of the five most promising solutions more detailed analyses has been carried out. It turned out that for the given specifications a two-stage design achieves the best performance. It consists of a BCM (boundary conduction mode) Boost PFC as an AC-DC stage and an LLC converter providing galvanic isolation and output regulation. This solution allows high frequency operation, up to 1 MHz, which reduces the size while keeping the switching losses low, owing to zero voltage switching over the entire range of operation. On a prototype for an industrial application the analytical and simulation results were verified by measurements. This project was generously supported and funded by Tridonic GmbH & Co KG.