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A distributed structure of step-up/step-down DC-DC converters using power saving techniques
(2014-01-01)
Eguchi, Kei
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Komatsu, Daisuke
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Pongswatd, Sawai
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Sasaki, Hirofumi
Improving power efficiency is one of the most important issues in DC-DC converters, because cooling of inefficient power converters is difficult and expensive. To reduce parasitic power losses caused by stray parasitic capacitances, a distributed structure of switched-capacitor (SC) step-up/step-down DC-DC converters using power saving techniques has been proposed in this paper. Unlike conventional converters, the proposed converter consisting of two converter blocks has two conversion processes: 1) charging and transferring process; and 2) charge reusing process. In each converter block, the charging and transferring process and the charge reusing process are repeated alternately, where the energy stored in parasitic capacitances is reused in the charge reusing process. Therefore, by alleviating parasitic losses, higher power efficiency can be achieved by the proposed converter. The results of the simulation program with integrated circuit emphasis(SPICE) simulation showed that more than 5% of the power efficiency was improved by the proposed converter when the output load is 10kΩ. © 2014 ISSN 1881-803X.
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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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Design of a dual-input SC DC-DC converter realizing negative outputs
(2011-01-01)
Eguchi, Kei
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Pongswatd, Sawai
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Tirasesth, Kitti
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Sasaki, Hirofumi
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Zhu, Hongbing
Aimed at a back-lighting application, a dual-input switched-capacitor (SC) DC-DC converter with battery charge process is proposed in this paper. The proposed converter can realize -1/N× (N = 2,3,.) step-down conversion as well as (N + 1)/N× step-up conversion. By converting clean energy such as solar energy, the proposed dual-input converter not only drives light-emitting diodes (LEDs) but also recharges the battery, although conventional single-input converter only consumes battery energy. In the proposed converter, the -1/N× stepped-down voltage is generated to drive the LED's cathode when the input voltage is insufficient to drive a 1× transfer mode. Furthermore, unlike conventional converters, the battery is charged by the (N + 1)/N× stepped-up voltage when the LED back light is in standby mode. Hence, the proposed converter can realize long battery run time. The validity of circuit design is confirmed by theoretical analyses, simulations, and experiments. The derived theoretical formulas will be helpful to estimate circuit characteristics, because the theoretical results correspond well with the simulation program with integrated circuit emphasis (SPICE) simulation results. © 2011 Institute of Electrical Engineers of Japan.
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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 SC DC-DC converter realizing long battery runtime
(2010-01-01)
Eguchi, Kei
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Pongswatd, Sawai
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Julsereewong, Amphawan
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Tirasesth, Kitti
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Sasaki, Hirofumi
A multiple-input switched-capacitor DC-DC converter which can realize long battery runtime is proposed in this letter. Unlike conventional converters for a back-lighting application, the proposed converter drives some LEDs by converting energy from solar cells. Furthermore, the proposed converter can charge a lithium battery when an output load is light. The validity of circuit design is confirmed by theoretical analyses, simulations, and experiments. Copyright © 2010 The Institute of Electronics, Information and Communication Engineers.
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A white LED driver using a buck-boost converter
(2010-01-01)
Eguchi, Kei
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Pongswatd, Sawai
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Watanabe, Toshiya
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Pannil, Pittaya
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Tirasesth, Kitti
For mobile backlighting applications, a white LED (WLED) driver using a buck-boost converter is proposed in this letter. Unlike conventional converters using boost converters, 2×/1.5× charge pumps, and so on, the proposed converter offers the negative stepped-down voltage to drive the LED's cathode only when the input voltage is insufficient to drive a 1× transfer mode. Furthermore, unlike the LED backlight using charge pumps, the proposed converter can adjust the output voltage by controlling the duty factor of the clock pulse. Thus, the proposed converter can realize high power efficiency. The validity of the proposed converter is confirmed by simulations and experiments. © 2010 Institute of Electrical Engineers of Japan.
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A multiple-input SC DC-DC converter with battery charge process
(2009-12-01)
Eguchi, Kei
;
Pongswatd, Sawai
;
Zhu, Hongbing
;
Tirasesth, Kitti
;
Sasaki, Hirofumi
Aimed at a backlighting application, a multiple-input switched-capacitor (SC) DC-DC converter with battery charge process is proposed in this paper. Unlike conventional SC power converters such as a Dickson-type converter, etc., the proposed converter drives some LEDs by converting energy from solar cells when solar cells offer enough energy. Furthermore, the proposed converter can charge a lithium battery when an output load is light. Hence, the proposed converter enables us to realize long battery runtime. The validity of circuit design is confirmed by theoretical analyses, simulations, and experiments. The derived theoretical formulas will be helpful to estimate circuit characteristics, because theoretical results agree well with SPICE simulation results. © 2009 IEEE.

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