Abstract: An over-voltage protection circuit is provided herein for protecting a load from an over-voltage condition, and that does not cause a reverse voltage. The over-voltage protection circuit includes a first switch circuit and a second switch circuit. The first switch circuit is for outputting a switch-on signal when the input voltage is lower than or equal to a predetermined value and a switch-off signal when the input voltage is higher than the predetermined value. The second switch circuit for conducting the input voltage to the load when receiving the switch-on signal. An over-voltage protection method is also provided.

Abstract: A battery charging system for receiving an AC voltage and charging a rechargeable battery is provided herein. The battery charging system includes an adapter for rectifying an AC voltage into a first DC voltage; a controller for receiving a battery voltage of a rechargeable battery and outputting a control signal; and a DC switching convertor for converting the first DC voltage into a second DC voltage to recharge the rechargeable battery according to the control signal, wherein the second DC voltage changes according to the battery voltage. A charging method is also provided.