A Dual-Input DC-DC Converter Using Clean Energy Power Supplies

Abstract

For small color displays in portable devices, white LEDs have been used to provide one of the most ideal back-light solutions. To drive white LEDs in portable devices, switchedcapacitor (SC) DC-DC converters (Bong (2009); Chung (2009); Doms (2009); Eguchi (2009a; 2010a;b); Gregoire (2006); Min (2002); Myono (2001); Park (2009); Starzyk (2001); Tanzawa (1997); Wei (2008); Yamada (2004); Yamakawa (2008)) have been used, because the capacitorbased converter can be designed without a magnetic element. Although the power efficiency of capacitor-based converters is inferior to that of inductor-based converters such as buck converters, boost converters, etc., inductor-less design enables capacitor-based converters to realize thin circuit composition, light-weight, no flux of magnetic induction, and so on. In previous studies, single-input SC converters realizing step-up conversion (Chung (2009); Eguchi (2010b); Min (2002); Myono (2001); Park (2009); Starzyk (2001); Tanzawa (1997); Wei (2008)) have been used as a driver circuit of white LEDs. However, the single-input SC power converter is difficult to improve power efficiency by adjusting a voltage conversion ratio 1 , because the ratio of voltage conversion is predetermined by circuit structure. Therefore, the single-input SC converter is difficult to realize long battery runtime. To solve this problem, multiple-input parallel converters (Eguchi (2009b); Ishikawa (2007); Kabe (2007); Qiu (2006)) using battery power supplies and clean energy power supplies have been proposed, where solar energy is usually used in mobile devices as a clean energy source. By converting solar energy, the multiple-input parallel converter can achieve long battery runtime. However, the hardware-cost of the parallel converter increases in proportion to the number of converter blocks although the parallel converter can be designed easily by connecting single SC DC-DC converters. Moreover, the parallel converter which consists of same converter blocks is difficult to achieve the wide range of clean energy inputs, because the ratio of the voltage conversion is predetermined by circuit structure although the value of input voltages from solar-cells changes depending on the weather conditions. To utilize solar energy for back-lighting applications effectively, the SC DC-DC converter which can realize not only small hardware-cost but also wide input-range is required. In this chapter, a switched-capacitor-based serial DC-DC converter is proposed. The converter consists of 2 converter blocks, where the Block-1 is the step-up/step-down SC DC-DC