PROTECTION CIRCUIT

A protection circuit is provided, which protects a battery pack from overcurrents and overvoltages using sensing means and a protection device having a heating resistor and a fuse element provided on a circuit board. This protection circuit allows for sharing a protection device regardless of the current rating and the voltage rating of the battery pack, thereby being manufactured at low costs.A protection circuit 1A protects a battery pack 5 having serially connected rechargeable batteries 6 from overcurrents and overvoltages. The protection circuit 1A includes a protection device 2A having heating resistors 3 and fuse elements 4 provided on a circuit board, and sensing means 7 for detecting an overvoltage across any of the batteries in the battery pack 5 and switching a current flowing into the heating resistor 3. The protection circuit 1A allows the sensing means 7 in an overvoltage condition to switch on the current flowing through the heating resistor 3. This allows the voltage across a predetermined number of the serially connected batteries in the battery pack 5 to be applied to the heating resistor 3, thereby causing the heating resistor 3 to generate heat and the fuse element 4 to be melted.