Introduction A large number of switching power supply inductors with extended high frequency characteristics have recently been developed. The reason for this is the increase in the switching frequency to reduce size of switching power supplies which are being built using electronic components which are more compact than are conventional compo- nents. However, if components which are not suitable for high frequency are used, the increase in the frequency lowers the efficiency of the switching power supply and creates electrical noise. Consequently, lower noise components and circuits for use at higher frequencies must be developed for future switching power supply designs. Inductors are one of the easiest components to reduce in size by raising the frequency and will require the development of low-loss, low leakage cores. The development and production of such inductors requires DC current biased inductance measurements to evaluate the inductance characteristics under actual operating conditions. This application note describes DC current biased inductance measurements that are more accurate and made over a wider frequency range than was previously possible.