Honeywell International Inc.
Current measurement and voltage control approach

Abstract:

A circuit that indicates a warning of low battery life so that an instrument supported by a battery, may have the battery replaced before the battery dies. A switch and series resistor may be connected between the battery and a capacitor. The switch may turn on when the voltage on the capacitor is below a first predetermined voltage limit, and the switch may be turned off when the voltage at the capacitor is above a second predetermined voltage limit. When the switch is on, a voltage on the resistor can be measured and current consumption can be calculated with measured voltage, resistor value and duty cycle of the switch. When the battery is discharged, its internal resistance and then its duty cycle may increase. When the duty cycle hits 100 percent, the battery may be nearly dead but with enough life for the circuit to issue the low battery warning.