Techniques for input ripple current cancellation: classification and implementation

Switching power supplies, due to their high-frequency switching operation, draw a substantial amount of input ripple current, which manifests as undesirable electromagnetic interference (EMI). This paper discusses the cancellation methods, and classifies the basic circuit configurations for ripple current cancellation. The basis of discussion is a "nullification" process, which call be described effectively in terms of the ideal circuit element nullor. Both active and passive implementation examples are given and experimentally demonstrated.