Patent ID: 7679330

Claim:
A protection circuit for protecting a battery pack having rechargeable batteries connected in series from overcurrents and overvoltages, the protection circuit comprising: a protection device having a heating resistor and a fuse element provided on a circuit board; and sensing means for detecting an overvoltage across any of the batteries in the battery pack and switching a current flowing into the heating resistor, wherein the fuse element is melted in an overcurrent condition, and in an overvoltage condition on any of the batteries, wherein the sensing means switches on the current flowing into the heating resistor wherein a voltage across the heating resistor is less than a voltage across a total number of batteries in the battery back, thereby causing the heating resistor to generate heat and the fuse element to be melted, and wherein the sensing means includes a FET, wherein a source terminal of the FET is connected between two batteries in the battery pack.