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Author: search.filters.author.Inoue, TakahiroSubject: search.filters.subject.Power converters

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    A step-down switched-capacitor AC-DC converter for energy harvesting system using vibration-based energy
    (2011-07-01)
    Eguchi, Kei
    ;
    Pongswatd, Sawai
    ;
    Tirasesth, Kitti
    ;
    Fujimoto, Kuniaki
    ;
    Sasaki, Hirofumi
    To realize battery-free operation employing energy harvesting, a step-down switched-capacitor-based converter has been used as a vibration-to-electricity converter. In this paper, to improve power efficiency, an AC-DC converter realizing 1/N× (N = 2; 3,...) step-down is designed by using switched-capacitor techniques. Although conventional converters offer a DC output by regulating the stored energy in a big capacitor, the proposed converter generates a DC output by realizing AC-DC conversion. Thus, the proposed converter can improve power efficiency. To clarify effectiveness of the proposed converter, theoretical analysis is performed concerning power efficiency and equivalent circuit. When the AC input is a rectangular-wave voltage, the theoretical results obtained by the theoretical analysis are consistent with SPICE simulated results. Furthermore, SPICE simulation results show that the proposed converter can improve power efficiency about 32 % from the conventional converter when R<inf>L</inf> = 100Ω. Next, the validity of the circuit design is confirmed by experiments. The experiments show that the proposed converter can offer stepped-down DC voltage from sinusoidal voltage. © 2011.
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    A switched-capacitor-based serial DC-DC converter using clean energy power supplies
    (2011-06-01)
    Eguchi, Kei
    ;
    Pongswatd, Sawai
    ;
    Tirasesth, Kitti
    ;
    Sasaki, Hirofumi
    ;
    Oota, Ichirou
    Aimed at mobile back-lighting applications, a switched-capacitor-based serial DC-DC converter is proposed in this paper. By using battery energy and solar energy, the proposed converter generates the stepped-up voltage to drive white LEDs. Unlike conventional multiple-input parallel converters, the output voltage of the proposed converter is generated by adding the output voltage of the SC-based circuit to the voltage of solar-cells. For this reason, the proposed converter can realize not only small hardware-cost but also wide input-range. Concretely, in comparison with the conventional parallel converter using 1.5 × step-up SC converters, the proposed converter can achieve 20% reduction of hardware cost and 16% extension of input range. The characteristics of the proposed converter are clarified by theoretical analyses. Furthermore, SPICE simulations and experiments show the validity of circuit design, where theoretical results correspond well with simulation results. For this reason, derived theoretical formulas can provide basic information to design serial SC DC-DC converters. The proposed converter will be useful as a LED driver circuit for display back-lighting. © 2011 ICIC International.
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    Optimal design of a single-input parallel DC-DC Converter designed by switched capacitor techniques
    (2010-01-01)
    Eguchi, Kei
    ;
    Pongswatd, Sawai
    ;
    Tirasesth, Kitti
    ;
    Sasaki, Hirofumi
    ;
    Inoue, Takahiro
    In the design of parallel-connected power converters, theoretical analysis to clarify the influence of process fluctuation is important, because the characteristic of a converter which consists of many circuit components is strongly influenced by the fluctua-tion of those components. Concerning parallel-connected switched-capacitor (SC) DC-DC converters, 1. the optimal setting of a duty factor to achieve best efficiency and 2. the change in characteristics caused by fluctuation of circuit components are analyzed in this paper. The validity of the theoretical analyses is confirmed by SPICE simulations and experiments. The results of this study are as follows: 1. The optimal setting of duty fac-tor D can be derived by the proposed theoretical formulas, because the theoretical results correspond well with the simulated results. 2. The fluctuation of on-resistances affects power efficiency in proportion to the decrease of output load RL. The value of the total SC resistance is important in power efficiency η, for example, an increase of 20 % in the total SC resistance causes a decrease of 2.2 % in efficiency when R<inf>L</inf> = 5ω. 3. When fluctuation of input voltages is caused, the influence on power efficiency η increases ac-cording to output load R <inf>L</inf>. 4. In the case of the fluctuation of capacitance, the influence of ripple factor R depends on fluctuating directions of capacitances. © 2010 ISSN.