具有偵測內部電阻補償電路及平穩控制技術的鋰離子電池快速充電器之研究設計

Abstract

在科技日益進步的這幾年之間，可攜式產品已經成為了人人不可或缺的必備工具，諸如手機、PDA或是數位相機等，都成為了市場上主要的消費產品。而在這許多的應用之中，限制其使用的最主要原因就是電池的效能。 配合可攜式產品的發展，可充電電池的重要性亦大幅增加。如何安全並且快速的充電，就成為了一項很重要的議題。近幾年間，充電電池都採用了定電流-定電壓(CC-CV)充電法。當充電器對一顆放電完畢的電池充電時，會先以小電流對電池進行儲能的動作。當電池電壓上升至一個較高的位準時，充電器便以大電流進行快速的充電。當電池充至一個預先的額定電壓位準(ex: 4.2V)時，便進入了定電壓模式。然而因為電池本身以及充電器上的寄生電阻，會讓電池的能量並未完全儲滿。為了令電池達到最大的儲能量，在定電壓模式中充電器提供了一個漸漸下降的電流來補足能量。當電流下降至足夠微小時，便停止充電，此時就完成了一個完整的充電週期。 在充電過程中，定電流模式跟定電壓模式的轉態點以及定電壓模式的時間決定了充電的週期長短。在定電流以及定電壓的轉態過程中，若是採用數位控制便容易產生電池電壓震盪而處於不穩定的狀態。同時在定電壓的衰減電流充電過程中，亦會相對延長充電時間。為了改善此兩項缺點，本篇論文提出一個包含了SCC以及BRC的充電器架構。不僅令充電器能平順的切換工作模式，同時加速了充電週期。本論文使用了TSMC 0.35μm2P4M製程，而實驗結果亦顯示了出明顯的改善。

A built-in resistance compensator (BRC) to speed up the charging time of the lithium-ion (Li-Ion) battery is presented and experimentally verified in this paper. Based on the physical properties of the battery cell, the charger charges the cell with three stages, which are trickle current (TC), constant current (CC), and constant voltage (CV) stages [1], [2]. When the battery is under the low voltage, ex: 2.5V, the structure of the battery system pack is easy to be damaged from the large charging current. That is the reason the charger charges the Li-Ion cell by trickle current but prolongs the whole charging process. Once the voltage of battery reaches the specified value, 2.5V, the charger then switches to the constant current stage and charges the battery in larger current to fasten the charging speed. At the end of the constant current stage, the battery reaches the rated voltage (ex: 4.2V) and the charger enters the constant voltage stage. A smooth control circuit (SCC) is proposed to ensure the stable transition from the CC stage to the CV stage. The charger keeps the voltage of the battery in stable level until the charger stops the whole charging process. However, due to the external parasitic resistance of the Li-Ion battery pack system, the charger circuit switches from the CC stage to the CV stage without fully charging the cell to the rated voltage value. The Li-Ion cell is needed to be charged by a degrading current at the CV stage to avoid overcharging. The longer the cell stays at the CV stage, the longer the charging time is owing to the degrading current. The BRC technique can dynamically estimate the external resistance of the battery pack system to extend the period of the CC stage. The test chip was fabricated in TSMC 0.35-μm technology. Experimental results show that the period of the CC stage can extended to about 40% that of the original design. The charging time can be effectively reduced.