Analysis of Temperature Dependencies of Eddy Current Loss and Residual Loss in Mn-Zn Ferrites for Power Supplies

摘要

The power loss and the hysteresis loss in Mn-Zn ferrites with a grain size of 5 mu m and 12 mu m were investigatied at various temperatures and up to 1MHz, 100mT for developing low loss materials. While the larger grain sample has the same temperature dependent residual loss as the hysteresis loss, which shows a minimum at T_(min) the finer grain shows small change. This discrepancy suggests that the residual loss is caused by the domain wall movement. The power loss caused by the domain wall movement is expressed by the product of a damping factor, beta, and velocity of wall movement, as Pr = beta centre dot upsilon~2 In this study, measurement of loss was carried out under sinusoidal excitation, so that the velocity of the wall movement was proportional to the frequency and the induction levels. Therefore, Pr must be proportional to f~2 centre dot Bm~2. The power alpha of Pr infinity Bm~(alpha) in the range from 10mT to 100mT shows 2.2 approx 3 dependent on the frequency. The power of Bm remarkably deviation from 2. This deviate from 2 is attributed to the contribution of the magnetic resonance as well as damping of the domain wall to the residual loss.