Input filter design for TRIAC dimmable LED lamps

This paper presents input EMI filter and damping circuits for phase dimmable LED lamps. An input EMI filter is implemented as part of LED lamp power supplies to comply with conducted emission standards set by regulatory agencies. The use of conventional EMI filter configurations are limited in this application due to the absence of earth (chassis) connection and the presence of stringent mechanical size constraints. This paper describes alternative EMI filter topologies suitable for 2-wire input connections present in Edison or Bayonet sockets. Criteria for achieving dimmer compatibility are introduced and the impact of an EMI filter on phase dimming operation is studied. The influence of different damping networks on transient performance of systems is analyzed using pole-zero mapping techniques and minimum damping requirements are established. A step-by-step procedure for EMI filter and damping network design is outlined and verified for a 16 W, 230 V_AC LED power supply example based on a discontinuous conduction mode (DCM) Flyback topology.