Patent ID: 8890488

Claim:
A power supply apparatus comprising: a battery connected to an electric load through a power supply circuit and which supplies electric power to the electric load; the power supply circuit including a first switch whose contacts are connected between one of positive and negative terminals of the battery and the electric load, a second switch whose contacts are connected in parallel to the first switch, a resistor connected in parallel to the first switch and in series to the second switch, and a controller for selectively opening and closing the first switch and the second switch to control supply of electric power to the electric load; a power supply voltage detecting unit for detecting a power supply voltage between the battery and the power supply circuit; a system voltage detecting unit for detecting a system voltage between the power supply circuit and the electric load; and an internal resistance detecting unit for detecting an internal resistance of the battery; wherein when the first switch is in an open state, the controller switches the second switch from an open state to a closed state, and thereafter switches the first switch from the open state to a closed state depending on a voltage difference between the power supply voltage detected by the power supply voltage detecting unit and the system voltage detected by the system voltage detecting unit; and if the controller detects that the internal resistance of the battery detected by the internal resistance detecting unit is relatively high, the controller switches the first switch from the open state to the closed state using a first threshold value with respect to the voltage difference, and if the controller detects that the internal resistance of the battery detected by the internal resistance detecting unit is relatively low, the controller switches the first switch from the open state to the closed state using a second threshold value which is smaller than the first threshold value.