Device for protecting a secondary battery from overcharge and overdischarge
First Claim
1. A device for protecting a rechargeable secondary battery from overcharge and overdischarge, comprising:
- first normally ON switching means serially connected to a charge/discharge path of the secondary battery, and for causing a current to flow in a charging direction when turned on or blocking said charge/discharge path in the charging direction when turned off, said first switching means including a parasitic diode having a polarity so as to permit conduction in a discharging direction when said first switching means is turned off;
second normally ON switching means serially connected to a charge/discharge path of the secondary battery, and for causing a current to flow in the discharging direction when turned on or blocking said charge/discharge path in the discharging direction when turned off, said second switching means including a parasitic diode having a polarity so as to permit conduction in a charging direction when said second switching means is turned off;
control means for detecting a voltage of the secondary battery, and turning off said first switching means when said voltage of the secondary battery rises above a first reference voltage higher than a predetermined voltage close to a full-charge voltage or turning off said second switching means when said voltage of the secondary battery drops below a second reference voltage lower than a predetermined voltage close to a full-discharge voltage;
a first diode connected in parallel with said first switching means and conductive in a same direction as said parasitic diode of said first switching means wherein said first diode is a bypass for causing a current in the discharging direction to bypass said first switching means; and
a second diode connected in parallel with said second switching means and conductive in a same direction as said parasitic diode of said second switching means wherein said first diode is a bypass for causing a current in the charging direction to bypass said second switching means.
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Accused Products
Abstract
A device for protecting a secondary battery from overcharge and overdischarge has two switches and two diodes respectively connected in parallel with the switches. Each diode is conductive in the same direction as a parasitic diode included in the associated switch. When one of the switches is turned off, a current flows through the diode connected to the switch prior to the parasitic diode of the switch. This prevents a current from flowing through the switch in the opposite direction. The switches are, therefore, free from deterioration and damage and allow the protection device to surely operate without being damaged. Alternatively, a charge path and a discharge path may be connected in parallel with each other, and each may have a serial connection of a switch and a diode opposite in direction to a parasitic diode included in the switch. In this case, when one of the switches assigned to the respective paths is turned off, a current flows through the other path prior to the parasitic diode of the switch turned off.
204 Citations
14 Claims
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1. A device for protecting a rechargeable secondary battery from overcharge and overdischarge, comprising:
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first normally ON switching means serially connected to a charge/discharge path of the secondary battery, and for causing a current to flow in a charging direction when turned on or blocking said charge/discharge path in the charging direction when turned off, said first switching means including a parasitic diode having a polarity so as to permit conduction in a discharging direction when said first switching means is turned off; second normally ON switching means serially connected to a charge/discharge path of the secondary battery, and for causing a current to flow in the discharging direction when turned on or blocking said charge/discharge path in the discharging direction when turned off, said second switching means including a parasitic diode having a polarity so as to permit conduction in a charging direction when said second switching means is turned off; control means for detecting a voltage of the secondary battery, and turning off said first switching means when said voltage of the secondary battery rises above a first reference voltage higher than a predetermined voltage close to a full-charge voltage or turning off said second switching means when said voltage of the secondary battery drops below a second reference voltage lower than a predetermined voltage close to a full-discharge voltage; a first diode connected in parallel with said first switching means and conductive in a same direction as said parasitic diode of said first switching means wherein said first diode is a bypass for causing a current in the discharging direction to bypass said first switching means; and a second diode connected in parallel with said second switching means and conductive in a same direction as said parasitic diode of said second switching means wherein said first diode is a bypass for causing a current in the charging direction to bypass said second switching means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A device for protecting a rechargeable secondary battery from overcharge and overdischarge, comprising:
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first normally ON switching means connected to a charge path of the secondary battery, and for causing a current to flow in a charging direction when turned on or blocking said charge path in the charging direction when turned off, said first switching means including a parasitic diode having a polarity so as to permit conduction in a discharging direction when said first switching means is turned off; second normally ON switching means connected to a discharge path of the secondary battery, and for causing a current to flow in the discharging direction when turned on or blocking said discharge path in the discharging direction when turned off, said second switching means including a parasitic diode having a polarity so as to permit conduction in a charging direction when said second switching means is turned off; control means for detecting a voltage of the secondary battery, and turning off said first switching means when said voltage of the secondary battery rises above a first reference voltage higher than a predetermined voltage close to a full-charge voltage or turning off said second switching means when said voltage of the secondary battery drops below a second reference voltage lower than a predetermined voltage close to a full-discharge voltage; a first diode serially connected to said first switching means so as to have a conduction direction opposite to that of said parasitic diode of said first switching means; and a second diode serially connected to said second switching means so as to have a conduction direction opposite to that of said parasitic diode of said second switching means; said charge path and said discharge path branching, in parallel, from between the secondary battery and one of input/output terminals of said charge path and said discharge path. - View Dependent Claims (11, 12, 13, 14)
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Specification