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High Efficiency Operation for H-Bridge DC-DC Converter
K. Okura,T. Nabeshima,T. Sato,K. Nishijima,H. Yajima 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
This paper presents two methods of switching operation for higher conversion efficiency and seamless control for wide range of the input voltage in a H-Bridge DC-DC Converter. This converter consists of buck and boost blocks and a feedforward control from the input voltage is employed for the boost block to realize seamless transition between step down and step up operation mode. From the view point of the conduction loss and the switching loss, two methods of the desirable duty ratio of the boost section and different switching frequencies are examined. As a result, higher efficiency was obtained by minimizing the duty ratio of the boost block for wide range of the input voltage and by decreasing the switching frequency of the buck block without increasing output ripple voltage.
NiZn Ferrite Coating for Electrical Insulation of MnZn Ferrite Cores
Kitamoto, Y.,Yajima, H.,Nakayama, Y.,Abe, M. The Korean Ceramic Society 2001 한국세라믹학회지 Vol.38 No.6
The ferrite plating with applying power ultrasound waves of 19.5 kHz and 600W enabled us to encapsulate entirely MnZn ferrite cores for transformers with Ni$\sub$x/Zn$\sub$y/Fe$\sub$3-x-y/O$_4$coating. Supplying a NH$_4$OH solution during the plating broke the limit of the solubility of Ni ions to ferrite-plated films. The electrical resistivity of the NiZn ferrite coating increased with increasing the Ni and Zn content, reaching 2.3${\times}$10$\^$5/Ωcm at the composition of Ni$\sub$0.24/Zn$\sub$0.30/Fe$\sub$2.46/O$_4$. The saturation magnetization was 540 emu/㎤. As a result, the MnZn ferrite cores were successfully encapsulated with the NiZn ferrite coatings for an insulation layer.