Patent ID: 8773075

Claim:
A battery monitoring circuit that monitors voltages of n (n≧2) secondary batteries connected in series with each other, comprising: a first switch element connected to a first terminal at a first end, the first terminal being intended to be connected to a positive pole of a first secondary battery; a second switch element connected to a second terminal at a first end and to a second end of the first switch element at a second end, the second terminal being intended to be connected to a negative pole of the first secondary battery and a positive pole of a second secondary battery; a (n+1)-th switch element connected to a (n+1)-th terminal at a first end and to the second end of the first switch element at a second end, the (n+1)-th terminal being connected to a ground and intended to be connected to a negative pole of a n-th secondary battery; a first output capacitor connected to the second end of the first switch element at a first end; a first output controlling switch element connected between a second end of the first output capacitor and the ground; an AD converter that analog-to-digital converts a signal responsive to a voltage at an output terminal between the second end of the first output capacitor and the first output controlling switch element and outputs the resulting digital signal; and a controlling circuit that controls turning on and off of the first to (n+1)-th switch elements and the first output controlling switch element and controls operation of the AD converter.