As seen in the last slide, power supplies typically contain multiple magnetic components working in concert to achieve efficient power conversion, the required operating frequency, and the desired impedance. Here is a brief overview of the primary uses of inductors in power supplies. First, as a circuit filter or choke - Inductors are commonly used to filter or choke (attenuate or cut) unwanted noise out of a circuit by choking high frequencies and alternating current and allowing lower frequencies and direct current to pass. Second, for resonant circuits or frequency tuning - Inductors are one of the three primary passive components of a resonant circuit (R-C-L). Resonant circuits are a very important building block in many electrical circuits, as they enable the designer to “tune” the circuit and operate within a specific frequency range. Third, for energy storage - Inductors are used to store and release energy from their magnetic field.  Last, for impedance matching – Inductors can also be used to help match source and load impedance. Maximum power transfer efficiency is achieved when the impedance of a load is equal to the impedance of the source.