Patent ID: 7973534

Claim:
A protection device for an assembled battery including a plurality of secondary batteries connected in series, the protection device comprising: a sampling unit which includes a plurality of sample switches and individually samples voltages of the batteries using the sample switches to generate a plurality of sampled voltages; a holding unit which holds the sampled voltages to generate a plurality of holding voltages; a multiplexer which sequentially reads the holding voltages and outputs each voltage to a common output node; a measuring unit configured to measure the individual voltages and a state of charges of the batteries based on a voltage of the common output node in a measuring period within a constant measuring cycle; and a control unit configured to turn on/off the sample switches at the same time within the measuring period and repeatedly turn on/off at least one sample switch selected from the plurality of sample switches in accordance with the state of charge in a term other than the measuring period, wherein the sampling unit further includes a plurality of discharge switches for discharging charges of a plurality of capacitors, and wherein the control unit includes a determining unit to determine an overcharged cell based on the individual voltages of the batteries and a selecting unit to select at least one sample switch corresponding to the overcharged cell from the plurality of sample switches in the term other than the measuring period and turns on the selected sample switch, turns off the selected sample switch, turns on the discharge switch which discharges a charge of a capacitor corresponding to the overcharged cell, and turns off the discharge switch in that order.