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Battery Low Detection With "Open Circuit" Test

IP.com Disclosure Number: IPCOM000041340D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 3 page(s) / 33K

Publishing Venue

IBM

Related People

Lakin, P: AUTHOR [+4]

Abstract

In a system in which a main power supply is provided with a battery to supply back-up power to bridge main power supply failure, a battery test circuit that will register battery failure or disconnection automatically, without undue battery drain, and which can be queried to distinguish between a weak battery and a disconnected battery can be implemented as shown in the figure. It is assumed that a load 1 is powered by a primary voltage source 2 backed up by a non-rechargeable battery 3 via a diode-OR circuit 4. The voltage due to the primary source 2 is tapped at 5 and divided by resistors 6 and 7 to provide a reference voltage at mid-point 8 to voltage comparator 9, setting the battery acceptability voltage threshold.

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Battery Low Detection With "Open Circuit" Test

In a system in which a main power supply is provided with a battery to supply back-up power to bridge main power supply failure, a battery test circuit that will register battery failure or disconnection automatically, without undue battery drain, and which can be queried to distinguish between a weak battery and a disconnected battery can be implemented as shown in the figure. It is assumed that a load 1 is powered by a primary voltage source 2 backed up by a non-rechargeable battery 3 via a diode-OR circuit 4. The voltage due to the primary source 2 is tapped at 5 and divided by resistors 6 and 7 to provide a reference voltage at mid-point 8 to voltage comparator 9, setting the battery acceptability voltage threshold. The voltage due to the battery 3 is tapped at 10 and ultimately supplies the other input to voltage comparator 9 via path
11. Connected to path 11 are two branch paths: one comprising resistor 12 and optional gate 13, and the other containing resistor 14, diode 15 and gate 16. The output 17 of the voltage comparator 9 supplies the battery test results, and the optional resistor pair 18 and 19, one in path 11 and the other bypassing the voltage comparator, provide hysteresis, if required. Optional gate 13 if disabled, disables the test circuit and further discussion will ignore elements 13 (assumed enabled) 18 and 19 (assumed absent). The component sizes are chosen so that the voltage on path 11, if gate 16 is disabled, is greater than the voltage at mid-point 8 with the primary voltage source 2 operating correctly; is less than the mid-point voltage if the battery is weak or defective; and is less than the mid-point voltage, whatever the battery state, on the surge when gate 16 is temporarily enabled. Assuming that the output of the tester is latched in such a way that the latch is reset if the voltage on path 11 is greater than the voltage at mid-point 8, battery defects will result in the latch being set at the time the battery becomes defective or disconnected and remaining set, providing unattended monitoring of the battery. For an attended test, which assumes the latch being in its reset state, temporarily enabling of gate 16 will set the latch on the surge, the latch remaining set for a weak battery state since the surge will drain the ...