Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2000-03-23
2001-09-04
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C320S159000
Reexamination Certificate
active
06285166
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to battery chargers and, more specifically, to a battery charger with improved overcharge protection mechanism and method of charging a battery with such charger.
BACKGROUND OF THE INVENTION
Cordless telephones have become a staple in today's homes. They offer nearly the portability of a cellular telephone, but cost no more to use than a wireline telephone.
Cordless telephones consist of a base and a handset, each containing a wireless transceiver. The base plugs into a wireline telephone jack and derives its power from a wall outlet. The handset is battery-powered. The base often provides a cradle for the handset to allow the handset to be conveniently stored and recharged.
The number of cordless telephones is and has been rapidly increasing due to user demands for higher mobility and broader general utility. This has resulted in a higher demand for improved performance from the rechargeable batteries to allow the telephones to be operationally available for a greater percentage of the time. Conventional battery charging and monitoring systems are focused on simplicity of operation, regardless of any degenerative impact that the systems may have on the batteries themselves. For example, a conventional battery charging and monitoring system may provide a fixed charging current during the charging period. This fixed charging current is typically maximized to assure that the batteries are charged quickly. Alternatively, a battery may be charged only by a trickle current, which may not damage the battery, but requires an unacceptably long period of time to charge a fully discharged battery.
In spite of these problems, an even more critical problem exists. Batteries quick-charged for faster availability are often at risk of being overcharged. Overcharging a battery usually results in partial, or even permanent, damage to the battery. In addition, overcharging results in a waste of electricity.
To address this problem, prior art battery chargers attempted to detect when the battery was fully charged so they could prevent overcharging and damaging the battery. Designers of such battery chargers noticed that batteries tend to exhibit a small, but detectible, drop in their terminal voltage when they reach a full charge.
Unfortunately, not all batteries exhibit a detectible voltage drop. In fact, some batteries exhibit no drop whatsoever. To complicate matters, battery characteristics change over time. Batteries that may have exhibited detectible drops at one time, now no longer may. These facts kept prior art battery chargers from being able to detect full charges reliably for all batteries that they may be called upon to charge.
Accordingly, what is needed in the art is a battery charger, and related method, that can more reliably determine when a battery is fully charged. In addition, what is needed in the art is a cordless telephone set that incorporates the charger or the method.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides a battery charger with improved overcharge protection mechanism and method of charging a battery with such charger. In one embodiment, the charger includes: (1) a voltage sensor for sensing a voltage of a battery that the battery charger is charging and (2) a controller, coupled to the voltage sensor, that adjusts (or terminates) a charge mode (such as a quick charge mode) of the battery charger when samples of the voltage taken over a predetermined period of time are within a predetermined range thereby to prevent overcharging of the battery.
The present invention rests on the recognition that batteries do not always exhibit a dramatic voltage drop when they reach full charge. Instead, they sometimes simply maintain a relatively constant voltage. Prior art battery chargers that quick-charge until they detect the voltage drop continue to quick-charge after the battery has been fully charged, wasting power, generating heat and potentially harming the battery. The present invention instead recognizes the substantial constancy of the voltage as indicating a full charge and adjusts (or completely terminates) the charge mode in response. The present invention enjoys substantial utility in avoiding the waste of power, generation of heat and risk of battery damage that the prior art realizes.
In one embodiment of the present invention, the predetermined period of time is at least 10 minutes. In an embodiment to be illustrated and described, the predetermined period of time is 30 minutes. Six samples taken at five-minute-long periodic intervals are filtered, smoothed or compared to a range of allowable reference voltages to determine whether the sensed voltage is constant enough to recognize that the battery has been fully charged and terminate quick-charging as a result.
In one embodiment of the present invention, the controller enters a trickle charge mode of the battery charger when the samples taken over the predetermined period of time remain within the predetermined range. Those skilled in the art are familiar is with quick charge and trickle charge modes for battery chargers. The present invention makes advantageous use of such known modes and improves substantially upon the conditions under which such modes are selected. Of course, later-discovered quick charge and trickle charge modes fall within the broad scope of the present invention.
In one embodiment of the present invention, the controller alternatively terminates the quick charge mode when the voltage drops by at least a predetermined amount between successive ones of the samples. As stated above, some batteries do not exhibit a voltage drop upon attaining full charge; others do. Accordingly, in one embodiment to be illustrated and described, the battery charger looks for either voltage constancy or drop, taking either as an indicator of full charge.
In one embodiment of the present invention, the controller alternatively terminates the quick charge mode upon expiration of a predetermined maximum charge time. This watchdog function ensures that the quick charge mode does not continue indefinitely. In an embodiment to be illustrated and described, the predetermined maximum charge time is about four hours.
In one embodiment of the present invention, the controller takes the samples at periodic intervals. Of course, the controller may take samples aperiodically. The present invention does not require a certain number of samples, a particular period of time or periodicity in sampling.
In one embodiment of the present invention, the battery charger is part of a cordless telephone base and the battery is part of a cordless telephone handset. Those skilled in the pertinent art will realize, however, that the present invention will find wide-ranging use in a variety of applications that employ rechargeable batteries.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
REFERENCES:
patent: 4118661 (1978-10-01), Siekierski et al.
Agere Systems Guardian Corp.
Tso Edward H.
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