In high frequency DC-DC converters for battery-powered applications, improving power supply efficiency is critical and can mean the difference between a device working when it needs to or not. Inductors play a large a role in this – perhaps as large as the circuit topology itself. Inductors filter out the AC ripple current superimposed on the DC output, smoothing the ripple to provide a pseudo-DC output. The goal of highest efficiency is met by selecting an inductor that provides sufficient inductance to smooth the ripple current while simultaneously minimizing losses. This application note examines core and winding losses and the impact they have on inductor – and overall power supply – efficiency.