Design principles for high frequency power transformer materials

To meet the size and weight requirements of modern switching power supplies new ferrite materials with low losses in a 100kHz-1MHz frequency range are needed. Examplary the development of an improved version of the well known material N49 [1] designated as N49i is discussed. The development of this new material results substantially in the reduction of the con losses (by about 20%) compared with the conventional one within the frequency range around 500kHz at operating temperature area around 80 degrees C. In connection with N49 considerations important design principles in high performance power ferrites are discussed generally. This is concerned with a derailed lineup of suitable materials for the frequency range from 100kHz up to 1MHz. The performance of power ferrites N87 N49 and N59 is judged by its maximum fxB-product for a given dissipation level, a good measure for the attainable throughput power for a design. It is shown that the improved N49 version leads to an optimized gradation between the materials N87. N49 and N59. Furthermore the correlations between frequency dependent maximum of performance factor, grain size and AC-resistance behaviour are analysed.