Patent ID: 7719284

Claim:
An apparatus for measuring a voltage of a cell while scanning a group of cells in a cell stack having a plurality of cells electrically connected in series, the apparatus comprising: a first switching device that is connected in series with a signal line carrying a voltage of a cell; a voltage detecting device for detecting the voltage of the cell, the voltage detecting device being electrically connected with signal lines that carry voltage of cells belonging to a group, wherein when the first switching device is electrically connected with an interface between two successive groups of cells, the first switching device is shared by the two groups; and a second switching device for selecting a line to be grounded from two signal lines which carry voltages of cells lying in interfaces on both sides of the group of cells, wherein the line to be grounded is alternately selected from two signal lines and grounded depending on whether an oddly or evenly numbered group is scanned, wherein the voltage detecting device detects the voltage of the cell when either of two lines is grounded, wherein the voltage detecting device comprises a differential amplifier, and wherein when the oddly numbered group is scanned, one of two signal lines which is a low voltage side in the oddly numbered group is selected to be grounded, and the differential amplifier adds a first offset voltage to an input voltage thereof, and when the evenly numbered group is scanned, one of two signal lines which is a high voltage side in the evenly numbered group is selected to be grounded, and the differential amplifier adds a second offset voltage higher than the first voltage to the input voltage thereof.