具有自舉電壓偵測電路及軟啟動功能結合補償電路技術的強健切換式鋰離子電池充電器之研究設計

Abstract

在現今社會，可攜式產品已經成為人人不可或缺的必備工具。隨著電子產品的蓬勃發展，鋰離子電池也成為目前最適合可攜式產品使用的行動電源。因此，如何以最理想且安全的方式將能量傳遞到電池對電池進行最快速也最有效率的充電是一個重要的課題。基於鋰離子電池的化學特性及安全性，充電策略分為細流充電模式、定電流充電模式與定電壓充電模式。由於切換式充電器在應用上較線性充電器廣泛且在快速充電階段也較有效率，本篇論文提出一個強健的鋰電池充電器，以切換模式為主之充電器來取代線性模式充電器。為了確保充電器在定電流充電模式與定電壓充電模式皆能保持穩定且平穩切換，本切換式充電器將定電流充電迴路與定電壓充電迴路並聯，且兩迴路之穩定度僅僅利用同一組補償電路即達到。在應用上為了能符合可移動的電池使用，確保整體充電系統無論輸出端電池存在與否皆能避免突然的過充電流發生，充電系統軟啟動之功能也是必要的。基於面積以及成本的考量，切換式充電器之功率電晶體皆選用N型電晶體。為確保功率電晶體之等效阻值皆在合理範圍內以維持高效率且防止電晶體燒毀爆炸之危險，電晶體之閘-源極電壓必須維持在足夠的導通電壓值以上。 本篇論文完成一具有自舉電壓偵測電路及軟啟動功能結合補償電路技術的健全切換式鋰離子電池充電器，利用自舉電壓偵測電路來偵測自舉電路中自舉電容之跨壓以維持充電器之功率電晶體導通電壓保持在一定位準之上，保護充電器之安全，維持整體效率。此外，提出一軟啟動功能結合補償電路之技術，利用補償電路原有的元件來達成軟啟動之目的，不僅僅節省了晶片面積降低整體成本，也減少了軟啟動電路所需耗的功率。

Bootstrap detector and soft-start embedded in Type Ⅲ compensation are implemented in the switch-mode lithium-ion charger to achieve robustness and high efficiency. 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]. How to deliver power to charge battery in an optimal and safe way is important for fast charging. Switch-mode charger is able to guarantee high efficiency regardless of the applications and provides higher current capability to accelerate charging process. To ensure the stability of both CC stage and CV stage, the switch-mode charger employ one Type Ⅲ compensation circuit to two parallel loop CC loop and CV loop. For applications with removable battery packs, a soft-start mechanism is necessary to ensure the operation of charger system and prevent inrush current whether battery is connected or not. Considering area and cost, two N-type power MOSFETs is adopted in the switch-mode charger. For appropriate turn-on resistance to maintain high efficiency and prevent the power MOSFET to burn out, the gate-source voltage of the N-type power MOSFET should be large enough. The proposed BSD monitors the voltage across the bootstrap capacitor, which is the source applies the high side power MOSFET driving voltage to avoid low efficiency and serous burning problem in both synchronous and non-synchronous charging mode. Furthermore, soft-start embedded in type Ⅲ compensation technique employs the compensation elements and the error amplifier of the type Ⅲ compensation circuit to achieve soft-start function without any external components and auxiliary circuits to greatly minimize the chip and footprint areas.