Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
1999-12-29
2001-01-16
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C320S137000
Reexamination Certificate
active
06175215
ABSTRACT:
BACKGROUND OF THE INVENTION
1 Field of Invention
This invention relates to battery charging systems. Specifically, the present invention relates systems and methods for charging a cellular telephone battery over a cable and interface that have linear or nonlinear properties.
2 Description of the Related Art
As the demand for cellular telephones and general consumer electronics increases so does the need for efficient batteries, power supplies, and battery charging mechanisms. Efficient charging mechanisms are particularly important for batteries used in cellular telephones where the batteries are often charged daily.
The batteries of cellular telephones are often charged via an accessory that enables use of the phone while it is being charged. The accessory may include a charger that is connected to a power source in a car horn or other location and that supplies current to a battery in a cellular telephone via a cable. Additional electronic interfaces are often located in the phone between the cable and the phone battery. The charger supplies current to the battery until the voltage drop across the battery, as measured from the output terminals of the charger, reaches a predetermined voltage indicative of a charged battery. Many conventional charging power supplies however, fail to account for voltage drops across the cable and any electronic interfaces. As a result, such power supplies typically fail to fully charge the battery.
Many newer battery charging circuits attempt to account for the voltage drop across the cable and electronic interfaces by incorporating an additional constant voltage factor representative of an estimated voltage drop across the cable and electronic interfaces. For example, if the estimated voltage drop is 0.2 volts and the battery reads 4.0 volts when it is fully charged, the charging circuit will charge the battery until the voltage between the charging circuit terminals is approximately 4.2 volts. However, this method may result in an overcharging of the battery if the estimated voltage drop is larger than the actual voltage drop.
The voltage drop across the cable and any additional electronic interfaces is often a nonlinear function of current and temperature. As a result, the estimated voltage drop, i.e., the constant voltage factor, quickly becomes inaccurate as the current from the power supply changes or as the temperature of the cable and interface changes. This may result in an overcharging or an undercharging of the phone battery.
Alternatively, power supplies may contain control circuits that reduce current flowing through the cable as the battery becomes fully charged. By reducing the current flowing through cable and any associated interface, the voltage drop across the cable and interface is reduced, which reduces charging error caused by the voltage drop. However, as the current flowing through the cable and interface decreases, the time required to fully charge the battery increases. For example a standard desktop charger having no cables or electronic interface between the battery and charging terminals may take two hours to fully charge a phone battery, while a comparable charging accessory that charges the battery through linear or nonlinear cables or phone interfaces may take four hours. The additional required charging time is an inconvenience and may still result in an overcharging of the battery.
Hence, a need exists in the art for a system and method for quickly and accurately charging a battery while accounting for any voltage drop across linear or nonlinear circuitry between the charger and the battery.
SUMMARY OF THE INVENTION
The need in the art is addressed by the system for charging a battery over a linear or nonlinear circuit of the present invention. In the illustrative embodiment, the inventive system is adapted for use with cellular telephone battery and includes a first mechanism for receiving a feedback signal and providing a charging signal to the battery over a first electrical path when the feedback signal indicates that the battery is not fully charged. A second mechanism measures a voltage state of the battery via second and third electrical paths and provides the voltage state as the feedback signal to the first mechanism in response thereto. The voltage state accounts for voltage drops occurring over the linear or nonlinear circuit.
In the specific embodiment, the first mechanism is a power supply having a mechanism for adjusting an output voltage and the second mechanism is a sensing circuit. The sensing circuit includes a subtractor circuit for subtracting a voltage on the second electrical path from a voltage on the third electrical path and providing the feedback signal in response thereto. The second electrical path includes a wire corrected between a first terminal of the subtractor circuit and a positive terminal of the battery. The second electrical path also includes a first resistor connected between an output of the power supply and the first terminal of the subtractor circuit. The first resistor has a resistance that is orders of magnitude larger than a resistance of the linear or nonlinear circuit and that is orders of magnitude less than the input impedance of the subtractor circuit. The third electrical path includes a wire connected between a second terminal of the subtractor circuit and a negative terminal of the battery. The third electrical path includes a second resistor connected between a ground and the second terminal of the subtractor circuit. The second resistor has a resistance that is orders of magnitude larger than a resistance of the linear or nonlinear circuit and orders of magnitude less that an input impedance of the subtractor circuit.
The novel design of the present invention is facilitated by the use of the first and second resistors that facilitate a determination of the voltage drop occurring across the linear or nonlinear circuit. This voltage drop is accounted for at the inputs of the subtractor circuit, which provides, as output, an accurate measurement of the voltage state of the battery to the power supply. The power supply halts the charging of the battery when the voltage state reaches a predetermined level. This allows the battery to be accurately and quickly charged without the risk of overcharging or undercharging.
REFERENCES:
patent: 4134056 (1979-01-01), Fukui et al.
patent: 5444378 (1995-08-01), Rogers
Fitzgerald Joseph R.
Simmons Edmund V.
Werner David E.
Brown Charles D.
Edwards Christopher O.
Qualcomm Incorporated
Tso Edward H.
Wadsworth Philip R.
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