Patent ID: 8427003

Claim:
A power supply device comprising: an electric storage unit for storing electricity which a main power supply supplies to a load; a charging circuit for charging the electric storage unit with the electricity supplied by the main power supply; a voltage detection circuit for detecting a voltage (Vc) of the electric storage unit; a current detection circuit for detecting a current (Ic) of the electric storage unit; a discharge circuit for supplying electricity stored in the electric storage unit to the load; and a control circuit for controlling the main power supply and the charging circuit, and for reading a signal indicating the voltage (Vc) of the electric storage unit and a signal indicating the current (Ic) of the electric storage unit, wherein when the voltage (Vc) of the electric storage unit is a predetermined steady-state voltage (Vcs) of the electric storage unit, the steady-state voltage (Vcs) being lower than a steady-state output voltage (Vbs) of the main power supply and higher than a driving lower-limit voltage (Vfk) at which the electric storage unit can drive the load, the control circuit controls the charging circuit to charge the electric storage unit until the voltage (Vc) of the electric storage unit reaches a voltage (Vcu, Vcd) for determining whether or not the electric storage unit deteriorates in property by using at least one of a first internal resistance (R 1 ), a capacitance (C), and a second internal resistance (R 2 ) of the electric storage unit, where the first internal resistance (R 1 ) is calculated from a variation width (ΔVcr) of the voltage (Vc) of the electric storage unit before and immediately after the charge process is started, and from a current (Ic) of the electric storage unit, the capacitance (C) is calculated from a variation width (ΔVct) per unit time of the voltage (Vc) of the electric storage unit and from a current-time product (∫(Ic)dt) of the electric storage unit per unit time during the charge process, and the second internal resistance (R 2 ) is calculated from the variation width (ΔVcr) of the voltage (Vc) of the electric storage unit before and after the charge process is interrupted, and from the current (Ic) of the electric storage unit.