近年來人們開始提倡綠能發展，除了增加再生能源的利用之外，能源回收也是一直是被大家所廣泛討論的課題；問題在於現今的可攜式發電機不論是機電轉換的發電機還是小型太陽能板，其共通的特點為能量來源微小且不穩定，而本論文提出一種適用於可攜式發電機之切換式鋰離子電池充電晶片，其特色在於Buck架構本身擁有良好的功率轉換效率，再加上良好的穩定度設計，使其克服了可攜式發電機能量來源微小且不穩定的問題。
依照鋰電池的化學特性關係，本論文的充電晶片採用三種階段的充電模式，依序為穩定小電流充電、穩定大電流充電以及穩定電壓充電，其定電流模式是利用簡單的電流鏡架構自動偵測正半週期的充電電流，並透過PWM控制duty cycle，將充電電流上限設定在鋰電池所能忍受的合理值，如此一來前方的能源蒐集器如果蒐集較少的能源時(所能提供的充電電流不足上限值)，duty cycle將為100%，相對的如果能源蒐集器蒐集過多的能量時(所能提供的充電電流超越上限值)，充電器也能調控duty cycle將充電電流穩在電池所能忍受的上限值，以維持最佳的充電效率。
此晶片使用TSMC 0.35μm CMOS 2P4M標準製程實現，模擬結果顯示充電效率能達到90%左右，其量測的結果效率也達到86.1%，符合能源回收的高效率表現。

Nowadays, the development of green energy systems becomes more and more important. In addition to renewable energy, energy harvesting is another way to replace conventional fuels. There are two popular portable generators to derive energy: a mechanical-to-electrical generator and a portable solar board. Nevertheless, the source of power is small and unstable in both cases. Thus it is hard to collect the generated energy efficiently. As a result, this work proposed a Buck Li-ion battery charger IC for portable generators which overcomes the problems of efficiency and stability.
According to the chemical characteristics of Li-ion battery, there are three different charging modes correlating with battery voltage, namely the trickle current (TC) mode, the time varying energy from portable generators makes the charger difficult to maintain an efficient CC mode. In this work, a current mirror in the charger circuit is utilized to sense the charging current during positive duty cycle and maintain its value by using a pulse width modulator (PWM). Once a charging routine begins, if the portable generator provides suitable charging current, then the duty cycle is incremented to100% by the pulse width modulator. Conversely, if the portable generator provides too much power, then the duty cycle is decremented to limit the excessive current.
This chip was fabricated in a TSMC 0.35μm CMOS technology. The simulation results show that the charging efficiency is about 90% and the measured performance indicates that the charging efficiency is 86.1%. The IC is suitable for energy harvesting applications.

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