Circuit and device for protecting secondary battery

DETAILED DESCRIPTION I claim: 1.
A battery protective circuit incorporated in a rechargeable battery, comprising: a charge/discharge circuit including: a first switching means for protecting the rechargeable battery from overcharging; and a second switching means for protecting he rechargeable battery from overdischarging connected in series with the first switching means in the charge/discharge circuit of the rechargeable battery; a main protective circuit for: detecting a battery voltage between positive and negative electrodes of the rechargeable battery; turning on the first switching means when the battery voltage is below a charge-prohibiting voltage, above which charging of the rechargeable battery must be prohibited; and turning off the first switching means when the battery voltage is detected to be higher than said charge-prohibiting voltage, and maintaining the OFF state of the first switching means until the detected voltage becomes below a charge-permitting voltage that is lower than said charge-prohibiting voltage; and a sub-protective circuit for: detecting the battery voltage between the positive and negative electrodes of the rechargeable battery; turning on the second switching means when the battery voltage is below a second charge-prohibiting voltage which is higher than the first charge-prohibiting voltage; and turning off the second switching means when the battery voltage is detected to be higher than the second charge-prohibiting voltage.
2.
The battery protective circuit according to claim 1, wherein the sub-protective circuit maintains the OFF state of the second switching means until a second charge-permitting voltage, which is lower the second charge-prohibiting voltage, is detected.
3.
The battery protective circuit according to claim 1, wherein the sub-protective circuit fixes the OFF state of the second switching means after the second charge-prohibiting voltage has been detected.
4.
The battery protective circuit according to claim 1, wherein the first switching means and second switching means include power MOSFETs having parasitic diodes therein, wherein said first switching means and second switching means are connected such that the forward direction of the parasitic diodes is the discharge direction of the rechargeable battery