Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2000-11-01
2001-11-13
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
Reexamination Certificate
active
06316915
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a charge/discharge protection circuit provided in a battery pack that supplies power to mobile electronic equipment, the charge/discharge protection circuit protecting a rechargeable battery of the battery pack from being damaged when the battery is placed in an overcharge condition, an overdischarge condition or an overcurrent condition. Further, the present invention relates to a battery pack in which the battery and the charge/discharge protection circuit are provided.
2. Description of the Related Art
In recent years, the proliferation of mobile electronic equipment in the art is remarkable. In the mobile electronic equipment, a battery pack containing a secondary or rechargeable battery is commonly used as a power supply that supplies power to the mobile electronic equipment. When the voltage supplied to the mobile electronic equipment by the battery pack is excessively decreased after the use over an extended period of time, the battery in the battery pack is recharged with a charger, and the battery pack can be repeatedly used again as the power supply for the mobile electronic equipment.
As disclosed in Japanese Laid-Open Patent Application No.11-103528, a charge/discharge protection circuit for protecting a battery of a battery pack against damage is known. In the charge/discharge protection circuit disclosed in the above document, the circuit elements to which only the battery voltage is supplied are constructed in a low-voltage resistant structure, and the circuit elements (or part of the integrated circuit semiconductor device) to which the charger voltage is supplied are constructed in a high-voltage resistant structure.
In the above charge/discharge protection circuit, the high-voltage resistant structure is needed only for the specific circuit elements. The above charge/discharge protection circuit can avoid the damage of the battery when it is placed in an undesired condition, and it is useful to downsize the integrated circuit chip for mounting the charge/discharge protection circuit.
However, in the above charge/discharge protection circuit, some circuit elements for detection of undesired conditions of the battery are connected at their inputs directly to the terminal to which the charger voltage is supplied.
When an improper charger, which supplies an excessively large voltage, is connected to the battery pack, the large voltage from the improper charger will be supplied to the above charge/discharge protection circuit. The above charge/discharge protection circuit detects that an overcharge condition of the battery occurs, and cuts off the connection between the improper charger and the battery. At this time, the potential of the terminal connected to the minus electrode of the improper charger is lower than the potential of the terminal connected to the minus electrode of the battery. The voltage at the inputs of the circuit elements of concern in the above charge/discharge protection circuit is lower than the potential of the terminal connected to the minus electrode of the battery. If this condition is kept on for a long time, the threshold voltage of the circuit elements used for the detection of the undesired conditions of the battery will be significantly varied. As a result, the characteristics of the circuit elements used for the detection of the undesired conditions of the battery will be significantly varied.
Since the above charge/discharge protection circuit is configured such that some circuit elements are constructed in the high-voltage resistant structure and the others are constructed in the low-voltage resistant structure, the variation of the threshold voltage of the circuit elements is more considerable than in a charge/discharge protection circuit configured with all the circuit elements built in the same structure.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide an improved charge/discharge protection circuit in which the above-described problems are eliminated.
Another object of the present invention is to provide a charge/discharge protection circuit that is small in size and high-voltage resistant, and effectively prevents the variation of the threshold voltage of the circuit elements for detection of the undesired conditions of the battery even when an improper charger is connected to the battery pack over an extended period of time.
Another object of the present invention is to provide a battery pack in which a rechargeable battery and a charge/discharge protection circuit are provided, the charge/discharge protection circuit being small in size and high-voltage resistant, and effectively preventing the variation of the threshold voltage of the circuit elements for detection of the undesired conditions of the battery when an improper charger is connected to the battery pack over an extended period of time.
The above-mentioned objects of the present invention are achieved by a charge/discharge protection circuit for protecting a rechargeable battery of a battery pack from damage, which includes: a first terminal to which a negative electrode of a charger is connected; an internal detector unit which has an input connected to the first terminal; an improper charger detector unit which outputs a detection signal when an improper charger is connected to the battery pack, in response to a voltage supplied to the first terminal by the improper charger; and a connection cutoff unit which cuts off, when the detection signal is output by the improper charger detector unit, the connection between the internal detector unit input and the first terminal, so that, when the improper charger is connected to the battery pack, a voltage of the input of the internal detector unit is avoided from being lower than a voltage of a second terminal to which a negative electrode of the battery is connected.
The above-mentioned objects of the present invention are achieved by a battery pack which includes a rechargeable battery and a charge/discharge protection circuit, the charge/discharge protection circuit including: a first terminal to which a negative electrode of a charger is connected; an internal detector unit which has an input connected to the first terminal; an improper charger detector unit which outputs a detection signal when an improper charger is connected to the battery pack, in response to a voltage supplied to the first terminal by the improper charger; and a connection cutoff unit which cuts off, when the detection signal is output by the improper charger detector unit, the connection between the internal detector unit input and the first terminal, so that, when the improper charger is connected to the battery pack, a voltage of the input of the internal detector unit is avoided from being lower than a voltage of a second terminal to which a negative electrode of the battery is connected.
In the charge/discharge protection circuit of the present invention, when the detection signal is output by the improper charger detector unit, the connection cutoff unit cuts off the connection between the internal detector unit input and the first terminal, so that, when the improper charger is connected to the battery pack, a voltage of the input of the internal detector unit is avoided from being lower than a voltage of a second terminal to which a negative electrode of the battery is connected. The charge/discharge protection circuit of the present invention is effective in preventing the threshold voltage of the input transistors in the internal detector unit from being significantly varied when an improper charger is connected to the battery pack. Further, the charge/discharge protection circuit of the present invention is effective in avoiding the damage of the battery when it is placed in the undesired condition, and in downsizing the integrated circuit chip for mounting the charge/discharge protection circuit.
REFERENCES:
patent: 5493197 (1996-02-01), Eguchi et al.
patent: 5936384 (1999-08-01), Fukiwara et
Aota Hideyuki
Fujiwara Akihiko
Dickstein , Shapiro, Morin & Oshinsky, LLP
Ricoh & Company, Ltd.
Tibbits Pia
Wong Peter S.
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