Patent ID: 7777456

Claim:
An electric storage device, comprising: an input terminal; a direct current power source connected to the input terminal; a charge element connected to the input terminal and limiting a direct current from the direct current power source; a charging current detection unit connected to the charge element and detecting the charging current; a storage element connected to the charging current detection unit; a discharge element connected to the storage element; an output terminal connected to the discharge element; a voltage detection unit detecting a voltage to be applied to the storage element; a control unit connected to the voltage detection unit and controlling the charge element and the discharge element; a voltage comparison unit connected to the voltage detection unit and the control unit; and a variable reference voltage source connected to the voltage comparison unit, and its magnitude is adjusted therefore, wherein, when an inter-terminal voltage of the storage element exceeds the variable reference voltage source, an overvoltage of the storage element is detected and the charge element is controlled through the control unit to halt the charging current or to limit a magnitude of the charging current, so as to prevent deterioration of the charge element, and wherein the variable reference voltage source is adjusted based on a current value detected by the charging current detection unit.