Patent ID: 8471526

Claim:
A protection device for use in a battery assembly containing a series of N secondary battery cells, “N” being a positive integer greater than one, the protection device comprising: a voltage detector having N or more sub-circuits each for monitoring a specific battery cell to output a detection signal when at least one of the battery cells outputs an abnormal voltage, each sub-circuit including: voltage dividing resistors to generate a voltage division signal by dividing an output voltage of the battery cell; a reference voltage generator to generate a reference voltage; and a comparator to compare the voltage division signal against the reference voltage, each comparator being powered with voltage across the battery cell associated with the sub-circuit; a selection terminal to output a selection signal specifying a number of battery cells connected to the protection device in the battery assembly; a load connected between a power supply terminal and a ground terminal of the protection circuit; N primary metal-oxide-semiconductor transistors connected in series with the load between the power supply terminal and the ground terminal, each to turn off in response to the detection signal output from the low voltage detector; and (N−1) or fewer secondary metal-oxide-semiconductor transistors each connected in parallel with one or more of the primary transistors and having a gate terminal connected to the selection terminal to deactivate and activate the one or more primary transistors by turning on and off in response to the selection signal, the protection circuit outputting a voltage detection signal other circuit at a node where the load connects to the series of primary transistors.