Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2002-12-17
2004-07-27
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
Reexamination Certificate
active
06768288
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to detecting battery life on portable electronic devices, and more particularly to a system and method for detecting a low battery condition on a hand-held computer device such as hand-held calculators, personal digital assistant (PDA) or personal learning tool (PLT).
BACKGROUND OF THE INVENTION
Determining the amount of remaining battery life is an important aspect of many portable electronic devices. In some prior art devices, it was common to simply measure the voltage of the battery under load to estimate the remaining battery life. In other prior art devices, “gas gauges” are used to monitor the charge entering and leaving the battery in order to provide an accurate indication of remaining battery life.
Other prior art systems measures battery terminal voltage during each application of one or more constant power loads to the battery, and compares either the measured voltage, or an internal impedance calculated from the measured voltage, with a pre-characterization of the relationship between battery capacity and battery voltage or impedance for the given battery type and operating conditions. See U.S. Pat. No. 6,313,609.
In the prior art methods, the battery life determined by the voltage alone may be inaccurate for systems with a varying load. Further, in prior art methods that monitor battery charge, the battery life indication is not accurate if the battery is changed in the system. In other prior art methods it was necessary to compare measured voltages with known power loads, which may not be available or possible in some electronic devices.
SUMMARY OF THE INVENTION
The present invention provides a method to more accurately monitor remaining battery life under varying conditions. The problem in some prior art circuits was the changing and unknown current would not allow reference to a battery discharge curve to accurately estimate the remaining battery life. In embodiment of the present invention, the measured battery voltage is adjusted for the current load and then used to determine the remaining battery life according to the battery voltage discharge curve for the battery type and chemistry. The method is particularly advantageous in a system where the battery may be exchanged and where the load varies dramatically over time.
An advantage of an embodiment the present invention is remaining battery life can be determined despite fluctuations in the current due to a changing load.
Another advantage of an embodiment the present invention is remaining battery life can be determined without monitoring current flow so that the determination of battery life is independent of the battery charging process.
Another advantage of an embodiment the present invention is remaining battery life can be determined with a low cost circuit where much of the required hardware is already available on the electronic device.
REFERENCES:
patent: 4678998 (1987-07-01), Muramatsu
patent: 4888716 (1989-12-01), Ueno
patent: 5193067 (1993-03-01), Sato et al.
patent: 5341503 (1994-08-01), Gladstein et al.
patent: 6313609 (2001-11-01), Brink
Baker David D.
Rosenquist Russell M.
Brady III W. James
Petersen Bret J.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
Tso Edward H.
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