Patent ID: 7719235

Claim:
A charge/discharge protection circuit, comprising: a double-throw semiconductor switching device provided between an external terminal and a secondary battery; and a charge/discharge control circuit for controlling charging/discharging of the secondary battery by monitoring a voltage of the secondary battery and turning on and off the double-throw semiconductor switching device, wherein the charge/discharge control circuit comprises: a first terminal connected to the double-throw semiconductor switching device; a second terminal for detecting which one of a charger and a load is connected to the external terminal; a VDD terminal connected a positive electrode of the secondary battery; a first resistor and a first switch connected in series between the VDD terminal and the second terminal; and a second resistor and a second switch connected in series between a ground terminal of the charge/discharge control circuit and the second terminal, wherein the charge/discharge control circuit, when detecting an overcurrent at the external terminal based on a voltage of the second terminal in a charging state, is configured to monitor a voltage of the second terminal by turning off the double-throw semiconductor switching device and turning on the first switch through an output of the first terminal, wherein the charge/discharge control circuit, when detecting an overcurrent at the external terminal based on a voltage of the second terminal in a discharging state, is further configured to monitor a voltage of the second terminal by turning off the double-throw semiconductor switching device and turning on the second switch through an output of the first terminal, and wherein the charge/discharge control circuit is configured to turn off the double-throw semiconductor when a difference of a voltage across the second terminal and the ground terminal minus a voltage across the VDD terminal and the ground terminal is greater than or equal to a first preset value.