A Robust Switch-mode Li-Ion Battery Charger with Bootstrap Detector and Soft-start Embedded in Type Ⅲ compensation Technique

• Main Author: 陳雅萍
• Other Authors: 陳科宏
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/32955274556394674647

碩士 === 國立交通大學 === 電控工程研究所 === 100 === 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.