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Method for Determining a Low Battery Condition

IP.com Disclosure Number: IPCOM000115724D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Gladstein, L: AUTHOR [+4]

Abstract

Disclosed is the determination of a low battery condition in a portable device by measuring a derivative of the voltage output of the battery with respect to time. Accurately determining this condition is particularly important in a portable computing device, since such a determination affords an opportunity to store data in non-volatile storage before a power failure causes a loss of data.

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Method for Determining a Low Battery Condition

      Disclosed is the determination of a low battery condition in a
portable device by measuring a derivative of the voltage output of
the battery with respect to time.  Accurately determining this
condition is particularly important in a portable computing device,
since such a determination affords an opportunity to store data in
non-volatile storage before a power failure causes a loss of data.

      Fig. 1 is a graph showing the typical variation of the output
voltage of a battery used in a portable device.  After the voltage
remains relatively flat over an extended portion 1 of the useful
battery life, a rate of voltage decrease increases rapidly as the
battery goes through a "critical knee" portion 2 of the curve.
Following this portion 2, the voltage declines rapidly in a portion
3, indicating a need for battery recharging or replacement.

      Fig. 2 is a schematic diagram showing an analog circuit
converting the battery voltage, supplied at input terminal 4, to a
second derivative of this voltage at logic output terminal 5.  The
values of resistors 6, capacitors 7, and reference voltage 8
associated with operational amplifier circuits 9 are set for unique
conditions of the battery and device to optimize the sensitivity of
the detection circuit.

      Fig. 3 is a flow diagram of a using a digital signal converted
from the battery voltage in step 10 and read over a preset period of
time in step 11. ...