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Battery Charging System - PDF

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Description: PRIORITY CLAIM The present application claims benefit of priority under 35 U.S.C. .sctn..sctn.120, 365 to the previously filed Japanese Patent Application No. JP2007-169013 entitled, "Charging system, electronic device, and charging method" with a prioritydate of Jun. 27, 2007, which is incorporated by reference herein.BACKGROUND OF THE INVENTION 1. Technical Field The present invention relates to charging systems in general, and in particular to a charging system that can maintain a high-setting voltage of a battery charger while maintaining a low-setting value of an overvoltage protection circuit withrespect to a battery cell. 2. Description of Related Art Most rechargeable batteries for portable computers take the form of a battery pack having multiple battery cells composed of a lithium ion rechargeable battery with a high-energy density. Upon charging/discharging the lithium ion rechargeablebattery, it is necessary to precisely control charging/discharging current and voltage. In particular, it is necessary to strictly control the charging voltage in a constant-voltage control period. Therefore, a processor is usually provided within abattery pack having lithium ion rechargeable batteries. The battery pack generally employs a smart battery in which a processor monitors an internal state of the battery pack during charging and discharging in order to send information to a portablecomputer or to activate a protection circuit. The smart battery is a battery device that is compliant with the standards called smart battery system (SBS) initiated by Duracell Inc. and Intel Inc. A battery pack compliant with the SBS standard is alsocalled an intelligent battery. In an intelligent battery, an electric circuit portion having a processor, a current measurement circuit, a voltage measurement circuit, a temperature sensor, and a rechargeable battery, all mounted on a substrate contained within a housing. The processor is operable to communicate with an embedded