Selecting the best core geometry for a given application can be challenging given all the options available. For high-frequency applications using ferrite and other low loss materials, many different shapes are available from core manufacturers. For power electronics applications, frequencies are not constrained to power line frequencies leading to more complex core designs. Proximity effects, nonlinear core excitation, and sensitivity to frequency are just some effects to consider for good designs. Whether designs are intended for 50 Hz or 100 kHz, the basic design equations are the same.