Electrical computers and digital processing systems: support – Computer power control – Having power source monitoring
Reexamination Certificate
1999-10-01
2002-10-08
Lee, Thomas (Department: 2185)
Electrical computers and digital processing systems: support
Computer power control
Having power source monitoring
C713S300000, C713S320000, C713S330000
Reexamination Certificate
active
06463545
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
FIELD OF THE INVENTION
The present invention relates generally to portable computers and particularly to battery operated portable computers. More particularly, the present invention relates to automatically calibrating batteries in portable computers.
BACKGROUND OF THE INVENTION
Effective battery design has been at the forefront of computer systems development in recent years. Batteries store electric charge, which is gradually released to power the computer circuitry. Laptop computers in particular are designed to operate on battery power, allowing the computer to be used in virtually any location. Because the user is limited to a finite number of hours of computing time before the battery runs out, a longer lasting battery generally provides the user with a more fulfilling and productive experience. The exact amount of operating time that a battery provides depends on a number of factors, including the charge storage capacity of the battery, the operating speed of the computer, and the number of transistors in the computer. Higher operating speeds and more transistors, which generally permit higher performance, generally draw more power. Thus, power requirements continue to increase as computer manufacturers strive to improve performance, increasing the demand for higher battery capacity. Increasing battery storage capacity usually increases the size and weight of the battery, however, and large, heavy batteries are not feasible for laptop computers due to inherent size and weight restrictions.
Manufacturers have employed a variety of techniques to extend battery operating time, including modifications to computer hardware, special power-saving software algorithms, and improvements in battery technology. Many computer components, especially in laptop computers, are designed to shut down after a period of inactivity, even while the rest of the computer continues to operate. The display screen, for example, may darken or turn off if the user fails to type on the keyboard or move the mouse after a predetermined period of time. Similarly, the disk drive may shut off if not accessed for a period of time. Many computer systems are capable of entering a special “sleep” mode in which virtually the entire computer shuts down, including the central processing unit (CPU), although the memory contents are retained so that the computer can return to normal operation within a few seconds. Older computers relied on instructions stored in the computer hardware known as the Advanced Power Management (APM) to determine when to shut down selected components. Newer computer designs which conform to the Advanced Configuration and Power Interface (ACPI) standard, developed by Intel, Microsoft, and Toshiba, rely on the operating system (e.g., Windows 98) software to turn individual components on and off. Power control, through either hardware or software, extends the battery life by drawing power only as needed.
Recent improvements in battery design have extended battery life, as well. Previously, battery voltage would gradually decrease as the charge drained, eventually dropping below the required operating voltage of the computer. Although some electric charge would remain, these batteries could not regain the required operating voltage without being recharged. Newer by contrast, tend to remain at the required operating voltage until the charge is almost completely gone. When the battery output voltage drops below the desired operating voltage, modem computers typically have about four to eight seconds of operation time left before power completely vanishes, terminating computer operation. Thus, modem batteries last longer by operating more efficiently.
In order to prevent the computer from suddenly shutting down due to a drained battery, possibly resulting in data loss, computer software continuously tracks the battery level and notifies the user of the remaining battery power. Some computers, upon nearing complete discharge, prevent data loss by automatically saving the memory contents to disk and then shutting the computer down. The user then must recharge the battery, insert another computer battery, or plug the computer into a wall socket to resume computing.
Accordingly, it is desirable to know how much battery charge remains. Typically, the amount of remaining charge is determined by continuously measuring battery output current, beginning after the battery is recharged. Because the exact amount of charge after recharging is difficult to measure accurately, the battery monitor assumes that the battery charges to full capacity after each recharge, where the capacity represents the highest theoretical level of charge that the battery can store. The remaining battery level then is determined by subtracting the spent charge from the total battery charge capacity.
Because of the nature of battery chemistry, however, accurately determining the amount of charge stored in the battery after recharging can prove difficult. Many rechargeable batteries exhibit a phenomenon known as the “memory effect,” in which the battery cannot charge to full capacity unless first being completely discharged. If a battery is discharged to 90% of its initial charge level and then recharged, for example, then recharging the battery will not succeed in filling the battery to 100% of its charge capacity. Instead, the battery will stop recharging before reaching full capacity. Repeated charge/discharge cycles enhance the memory effect, causing the battery to reach successively lower levels of charge after each recharge. Whenever the memory effect prevents the battery from charging to capacity, the battery monitor reflects a higher level of charge than the battery actually stores. The memory effect thus can reduce the accuracy of a battery monitor by increasing the difference between the battery capacity and the actual charge level after recharging. Accordingly, the battery monitor may indicate that there is charge remaining when the battery reaches complete discharge. If the computer fails to save the contents of memory before the battery actually discharges, then data loss may occur.
To compensate for the battery monitor inaccuracy, the computer typically saves memory and shuts down when the charge level falls below a predetermined cutoff point. The cutoff point, which typically represents a percentage of the total battery capacity, is set sufficiently high to prevent unexpected loss of power. Though effective in preventing unexpected shut down, this early shut down technique reduces the amount of operating time for the user. In addition, because the battery never reaches complete discharge, the memory effect circumvents accurate measurement of the charge level by preventing the battery from fully recharging again. For this reason, batteries often must be calibrated by completely charging and then discharging the battery. After recharging the battery from a complete discharge, the battery can store the full charge capacity, and battery charge level measurements can be made accurately.
Discharging the battery, however, can be challenging and inconvenient for many users. Discharging the battery typically requires idling the computer for long periods, waiting for the battery to drain. While waiting for the battery to drain, the user may use the computer, although not without risking data loss when battery discharge causes the computer to shut down. In addition, many users experience difficulty when built-in power management features interfere with the discharging procedure. As explained above, for instance, some power management features force the computer to shut down before the battery completely drains, preventing the battery from fully recharging. Other power management features emit warning beeps or other indicators when the battery is nearly drained. Many inexperienced users turn the computer off, believing the beep indicates that the battery has fully drained. Further, some users
Fisher Andrew J.
Holehan Steven D.
James Jonathan E.
Liu Jon H.
Pham Thomas T.
Compaq Information Technologies Group L.P.
Conley & Rose & Tayon P.C.
Lee Thomas
Patel Nitin C.
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