Unusual Effects Measured Under DC Bias Conditions on MnZn Ferrite Material

Switch mode power supplies are the predominant form through which power conversion is currently implemented in electronic equipment. Within such power supplies, ferrite cored magnetic components are commonly placed under dc bias conditions which, due to magnetomechanical effects, can result in higher than expected core losses. This paper presents measurements that show the impact of magnetomechanical effects on the losses of a MnZn ferrite core material under low ac excitation and high dc bias conditions. The measurements are made using an accurate measurement circuit, and the results show the impact on losses of magnetomechanical resonance. In addition distorted, figure-eight shaped
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loops are measured, which are also believed to manifest from magnetomechanical interactions. These
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loops show that, on a transient basis, magnetomechanical interactions may take place in a manner that is not only lossless, but returns energy back to the excitation supply.