ABSTRACT
The electromagnetic interference (EMI) filter requires what is termed a soft core. This really means that the core is driven into saturation slowly rather than abruptly, as required for pulse transformers and magnetic amplifiers. Inductors for EMI filters come in several styles: tape wound, toroids, C cores, and slugs. E cores, pot cores, and RM cores are rarely seen. There are several subgroups. For toroids, the styles are ferrite, powdered iron, molybdenum permalloy powder, high-flux , and Kool Mu. Ferrite toroids are used in EMI filters primarily for common-mode cores. They should not be used for inductors because they saturate too easily. Tape-wound toroids can be used for EMI filters, but they are primarily used for transformers. C cores are typically used within EMI filters for higher currents, as these are more than the powder cores are able to handle. The design of any inductor is often a challenge in many respects.
