Frequency Dither Circuit for Electronic Ballast EMI Reduction

摘要

Electronic ballasts include switched-mode circuits that can generate a high amount of electro-magnetic interference (EMI). This EMI can conduct through various paths within the electronic ballast circuit and eventually reach the AC mains voltage as conducted noise. To block this noise, an L-C filter is typically placed at the input of the circuit. These filters can be difficult to design due to their second-order nature, and, can be a significant overall cost increase due to the size and the multi-winding requirements of the filter inductor. This paper describes a novel frequency dithering circuit used to spread and reduce the amount of EMI and therefore reduce the size and cost of the EMI filter. This paper introduces the designer to the main circuit blocks of an electronic ballast, presents the new frequency dither EMI reduction circuit, and provides the complete electronic ballast circuit driving a single 26W compact fluorescent lamp with experimental results.