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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
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Pongswatd, Sawai
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Tirasesth, Kitti
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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
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Pongswatd, Sawai
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Tirasesth, Kitti
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Sasaki, Hirofumi
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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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Synthesis and analysis of a dual-input parallel DC-DC converter designed by using switched capacitor techniques
(2011-04-01)
Eguchi, Kei
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Oota, Ichirou
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Pongswatd, Sawai
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Julsereewong, Amphawan
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Tirasesth, Kitti
As a building block of mobile equipments, single-input switched-capacitor (SC) power converters have been used. However, the single-input converter is difficult to improve battery runtime by adjusting a voltage conversion ratio, because the ratio of the voltage conversion is predetermined by circuit structure. To solve this problem, a dual-input parallel-connected converter designed by the SC technique is proposed in this paper. Although the conventional single-input converter uses a lithium battery as an input energy source, the proposed dual-input converter uses not only a lithium battery but also solar cells. For the conventional SC converters, the energy conversion of clean energy is difficult, because the voltage of clean energy sources such as solar cells is sensitive to weather condition. To adopt the change in the voltage of clean energy input, the proposed converter provides the multi-state step-up conversion. By converting clean energy, the proposed converter realizes long battery runtime. Moreover, to design the multiple-input converter, the theoretical analysis to clarify circuit characteristics is required, because detailed analyses concerning multiple-input SC DC-DC converters have not been performed yet. Therefore, concerning circuit characteristics of the proposed dual-input converter, handy theoretical formulas are given in this paper. Through SPICE simulations, theoretical analyses and experiments, the validity of the proposed converter is confirmed. The theoretical results correspond well with SPICE simulation results. Therefore, the proposed analysis technique can be extended to the circuit design of other multiple-input SC DC-DC converters. Furthermore, the experimental results show that the proposed converter can generate the stepped-up voltage in spite of the change in the voltage of solar cells. Therefore, the proposed converter can realize long battery runtime. ICIC International © 2011.
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Design of 3 ×/4× step-up AC-DC converters for RFID tags
(2010-12-01)
Pongswatd, Sawai
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Eguchi, Kei
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Sugimura, Tatsuya
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Watanabe, Toshiya
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Tirasesth, Kitti
In this paper, two types of step-up AC-DC conveners for RFID tags are proposed: the 3× step-up converter and the 4× step-up converter. The proposed converters consist of 2 charge-pump type AC-DC converters with opposite polarities. Unlike conventional converters, the proposed converters can offer higher output voltages. Furthermore, as for the 3× step-up converter, the circuit size of the proposed converter is almost the same as that of the Cockcroft-Walton type AC-DC converter. The characteristics of the proposed converters are clarified by theoretical analyses. Furthermore, the SPICE simulation and the experiment showed the validity of theoretical formulas and circuit design. ICIC International © 2010 ISSN 1881-803X.
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Optimal design of a single-input parallel DC-DC Converter designed by switched capacitor techniques
(2010-01-01)
Eguchi, Kei
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Pongswatd, Sawai
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Tirasesth, Kitti
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Sasaki, Hirofumi
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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.
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Design of a multiple-input parallel SC DC-DC converter and its efficiencyestimation method
(2009-09-01)
Eguchi, Kei
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Sugimura, Tatsuya
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Pongswatd, Sawai
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Tirasesth, Kitti
;
Sasaki, Hirofumi
A multiple-input parallel SC (Switched Capacitor) DC-DC converter and itsefficiency estimation method are proposed in this paper. The proposed parallelconverter consists of two different kinds of converter blocks: 1. a 1.5×step-up SC DC-DC converter employing an input voltage from a lithium battery and2. a novel step-up converter employing an input voltage from clean energysupplies. Since the proposed step-up converter can achieve not only a largestep-up conversion ratio but also a wide input range, the proposed parallelconverter enables us to extend battery runtime, reduction of heat, and so on.Furthermore, concerning the proposed converter, theoretical analyses areperformed to estimate power efficiency. The proposed analysis technique can beextended to the circuit design of other SC DC-DC converters. The validity ofcircuit design and theoretical formulas is confirmed by SPICE simulations.ICIC International © 2009.

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