Patent ID: 7705561

Claim:
A car power source apparatus comprising: a battery array having a plurality of series connected batteries; and a voltage detection circuit to detect the voltage of the batteries that make up the battery array; wherein the voltage detection circuit is provided with: an isolation transformer having its primary side connected to battery connection nodes; a switching device connected in series with the primary side of the isolation transformer; an isolated input circuit that switches the switching device ON and OFF with a given periodicity; and a secondary voltage detection section that detects output voltage from the secondary side of the isolation transformer when the switching device is switched ON and OFF by the isolated input circuit; and in the battery voltage detection circuit, the primary side of the isolation transformer and switching device series input circuit is electrically connected to a pair of measurement nodes at the battery for voltage detection, the isolated input circuit switches the switching device ON and OFF with a given periodicity to output a voltage at the isolation transformer secondary side corresponding to the primary side input voltage, and the secondary side output voltage is detected by the secondary voltage detection section to determine the voltage at one pair of measurement nodes in the battery array.