Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2002-01-23
2003-02-11
Toatley, Jr., Gregory J (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C320SDIG011
Reexamination Certificate
active
06518728
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a secondary battery device comprising an overdischarge protective unit and a method of protecting an overdischarge of the secondary battery.
2. Description of the Related Art
A secondary battery device comprises, e.g., a plurality of unit batteries connected in series. In such a secondary battery device, some of the unit batteries can be overcharged or overdischarged due to variation of the capacity or internal impedance of the unit batteries. For example, when a lithium ion battery as a unit battery is overcharged beyond a tolerance voltage, the decomposition reaction of an organic electrolyte proceeds. On the contrary, when the lithium ion battery is overdischarged, it shows an increase of internal resistance or the like, causing the deterioration of performance or safety thereof.
Thus, a battery device normally comprises a protective circuit incorporated therein. The group of unit batteries is electrically connected to an external circuit, such as load and charger, through the protective circuit. The protective circuit individually detects the terminal voltage of each of the unit batteries. When one of the unit batteries shows a terminal voltage of higher than a predetermined reference voltage, the protective circuit causes an FET element or the like to disconnect the battery device from the external circuit so that charge or discharge is forced to suspend. Therefore, the overcharge and overdischarge can be prevented, thereby protecting the unit batteries.
A potable personal computer or the like is subject to defectives, such as troubles in hard disk, when the power supply is forced to be turned off while CPU is in a predetermined operation state, such as reading of data. Such a forced suspension of discharge should be avoided as much as possible. It is inconvenient also for cellular phone that the power supply is forced to be turned off during communication.
In the conventional secondary battery device, when the terminal voltages of the unit batteries show a great variation, the protective circuit causes the suspension of discharge to an apparatus such as main body of personal computer to prevent one of the unit batteries from being overdischarged, even if the total battery voltage of the secondary battery device falls within a normal range which allows the supply of electric power high enough to operate the apparatus. As a result, it is much likely that the power supply can be forced to be turned off even when CPU of personal computer is in a predetermined operation state or cellular phone is communicating. Of course, it is necessary that the unit batteries be protected against overdischarge or the like. However, there are many cases where the continuation of predetermined operation state of load should be given priority.
SUMMARY OF THE INVENTION
An object of the invention is to provide a secondary battery device and a method of protecting an overdischarge of the secondary battery, which is subject as little as possible to defectives, such as disconnection of power supply in a predetermined operation state of load.
In order to accomplish the object above, the following means are adopted. The secondary battery device according to a first aspect of the invention comprises a secondary battery, a load state judging unit, and an overdischarge protective unit connected to the secondary battery. The secondary battery supplies electric power into a load circuit. The load state judging unit judges the operation state of the load circuit. The overdischarge protective unit detects the discharged state of the secondary battery, and breaks the discharge from the secondary battery when the secondary battery reaches a predetermined discharged state. When the load state judging unit judges the load circuit stays in a predetermined operation state requiring the protection of power supply, the supply of electric power into the load circuit is allowed to continue without breaking the discharge from the secondary battery.
The “a predetermined operation state of the load circuit requiring the protection of power supply” as used herein may be set to stay in any of the following states (1), (2). The predetermined operation state of the load circuit may be arbitrarily set by the user or may be previously fixed to the definite conditions by the manufacturer.
(1) State where the load circuit or various instruments connected thereto can be subject to defectives when the power supply is forced to be disconnected
In some detail, when the secondary battery device according to the invention is applied, e.g., to a portable personal computer or the like, the load circuit may be set to stay in any of the following states (i) to (iv):
(i) State where a hard disk is driven;
(ii) So-called active state where CPU performs an application program on the basis of an input signal inputted by key operation while the application program is being started;
(iii) Processing awaiting state where a successive input signal is awaited after the termination of the foregoing active state while the application program is being started; and
(iv) Processing awaiting state with low power consumption, i.e., so-called sleep state which suppresses the power consumption when the processing awaiting state continues for a predetermined period of time.
(2) State where the load circuit or various instruments connected thereto cannot be used, even though not going so far as defective in the state (1), when the power supply is forced to be disconnected.
Specific examples of this state include:
(i) Calling state where a calling operation is effected upon the reception of communication signal, and communicating state between off hook and on hook when the secondary battery device according to the invention is applied to cellular phone; and
(ii) State where communication with the base station is conducted when the secondary battery device according to the invention is applied to data communication terminals.
In accordance with the present invention, the overdischarge protective unit allows the supply of electric power into the load circuit to continue without breaking the discharge from the secondary battery when the load state judging unit judges that the load circuit stays in the predetermined operation state requiring the protection of power supply. Accordingly, the occurrence of defectives such as sudden disconnection of power supply can be prevented as much as possible when the load circuit stays in the predetermined operation state requiring the protection of power supply, such as state where the hard disk of personal computer is driven or communicating state of cellular phone.
The risk of overdischarging to an extent such that the terminal voltage of the secondary battery falls below a predetermined reference voltage can be eliminated by providing the secondary battery device with an overdischarge preventive function on the load circuit side thereof. The secondary battery device may be overdischarged when the load circuit stays in a predetermined operation state. However, it is thought that the load circuit stays in a predetermined operation state requiring the protection of power supply for a short period of time. Accordingly, the operation of the load circuit is normally terminated as early as possible by the use of a mechanism which informs the exterior of the fact that the secondary battery is overdischarged. For example, the mechanism informs to the exterior by means of displaying on the display of the personal computer or sounding an alarm. By doing so, the secondary battery device cannot reach an abnormal state developed by the continuation of overdischarge and thus can be recovered to its normal terminal voltage after being charged.
The secondary battery may be a plurality of unit batteries connected in series. The unit battery includes not only a single battery cell but also a plurality of battery cells connected in parallel.
A secondary battery device according to a second aspect of the invention comprises a secondary battery, a load stat
GS-Melcotec Co., Ltd.
Toatley Jr. Gregory J
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