早乙女 英夫

<p>  The dynamic magnetic loss in ferrites is obtained by subtracting the hysteresis loss, which is independent of the excitation frequency, from the iron loss. In the high frequency excitation region, the dynamic magnetic loss is the dominant component of the iron loss in ferrites. The iron loss in ferrite is temperature-dependent and this dependence has been described in product catalogs, where the hysteresis and dynamic losses are not separated. The catalog data are measured using sinusoidal wave voltage excitation, whereas ferrite cores are commonly used under rectangular wave voltage excitation in DC-DC converters. In this paper, the experimentally obtained temperature characteristics of the hysteresis and dynamic magnetic losses for rectangular wave voltage excitation are shown separately, and it is found that the two are different. This suggests that the physical mechanisms involved are different as well. Thus, it is important to consider the temperature characteristics of the dynamic magnetic loss to produce low-loss ferrites.</p>

The B-H loop of ferrites consists of two areas: one is the DC hysteresis loop and the other corresponds to the dynamic magnetic loss. The former is temperature dependent whereas the latter is temperature independent. The difference in the temperature dependence of these two areas suggests that the physical mechanism for the dynamic magnetic loss is different than that of the DC hysteresis loss. The eddy current loss in ferrite grains is a candidate for the dynamic magnetic loss. The conductivity of the ferrite grain was estimated from the experimental results of the dynamic magnetic loss. Based on the results, it was found that the conductivity is too large for iron oxide. This fact leads to some important suggestions.