Why Ferrites? To start, there are two components to a transformer; a ferrite core and a winding or windings around that ferrite core. This is true whether that core is toroidal, a rod, an RM core, or something to be designed into the printed circuit board or other unique application. Based on Faraday’s Law of electromagnetic and mutual induction, a transformer needs a core to act as a support to the windings of the transformer in that it provides a low resistive path for the magnetic flux to flow. On the suppression side of things, electromagnetic emissions need to be either blocked for low frequency noise or absorbed for high frequency. This is mainly needed to keep in line with EMI compliance.