Battery charger for preventing both overshoot charging current and overcharged battery voltage during charging mode transition

A battery charger for charging a battery through controlling a charging regulation circuit, comprising:

• a current sensing unit, configured to monitor a charging current applied to the battery when the battery charger operates under a constant current mode, thereby generating a first regulation signal to control the charging regulation circuit to regulate the charging current at a predetermined current level;
• and
• an operational amplifier, configured to compare a battery voltage of the battery with a first reference voltage to generate a first comparison result, wherein when the battery charger operates under the constant current mode, the operational amplifier generates the first comparison result to control a charging mode transition of the battery charger from the constant current mode to a constant voltage mode, and when the battery charger operates under the constant voltage mode, the operational amplifier generates the first comparison result to act as a second regulation signal, and utilizes the second regulation signal to control the charging regulation circuit to regulate the battery voltage applied to the battery.