A New Technique for Measuring Ferrite Core Loss Under DC Bias Conditions

It is well known that the measurement of ferrite core losses is difficult, particularly under low power factor conditions for which the excitation VA drawn is large relative to the power dissipated in the ferrite core. This paper proposes a new technique, called mutual inductance neutralization, which overcomes this difficulty by compensating for the reactive power drawn by the circuit through the use of an air cored mutual inductor. Based on the technique, circuits are presented which are appropriate for core loss measurement in the absence, and the presence of a dc bias. Measured results are presented which verify the accuracy of the technique, and results are also presented showing the effect of dc bias conditions on the losses of the ferrite core under test.