Patent ID: 7737664

Claim:
A device for protecting a battery from overcharging and overdischarging, comprising: a first semiconductor device with a first plurality of parallel switch elements configured to control a discharge current from the battery; a second semiconductor device with a second plurality of parallel switch elements configured to control a charge current to the battery; a control circuit configured independently to control an ON/OFF state of each of switch elements of the first and second semiconductor devices, in response to a signal that reflects a characteristic of a current in the semiconductor device that is indicative of an overdischarged or overcharged state of the battery, the control circuit being configured selectively to exert said control over said first or second plurality of parallel switch elements according to whether the current to be controlled is the discharge current or the charge current, the first and second semiconductor devices being interposed in series with each other, so that current discharged from the battery passes through the first and second plurality of switch elements in one direction and current charging the battery passes through the first and second plurality of switch elements in an opposite direction; a charge current detector, coupled to said control circuit and configured to detect the charge current according to a voltage drop on the first semiconductor device when the battery is in the overdischarged state; a discharge current detector, coupled to said control circuit and configured to detect the discharge current according to a voltage drop on the second semiconductor device when the battery is in an overcharged state; an overdischarge detecting circuit, coupled to said control circuit and configured to detect the overdischarged state of the battery; and an overcharge detecting circuit, coupled to said control circuit and configured to detect the overcharged state of the battery, wherein the control circuit is configured to turn the first plurality of parallel switch elements ON when the overdischarge detecting circuit does not detect the overdischarged state of the battery, and to turn at least one of the first plurality of parallel switch elements ON and the rest of said first plurality of parallel switch elements OFF according to the charge current detected by the charge current detector when the overdischarge detecting circuit detects an overdischarged battery condition, and wherein the control circuit is further configured to turn the second plurality of parallel switch elements ON when the overcharge detecting circuit does not detect an overcharged state of the battery, and to turn at least one of the second plurality of parallel switch elements ON and the rest of said second plurality of parallel switch elements OFF according to the discharge current detected by the discharge current detector when the overcharge detecting circuit detects an overcharged battery condition.