AN966| Application Note
Maxim > App Notes > POWER-SUPPLY CIRCUITS Keywords: battery monitor, comparators, low battery outputs, lbo, power regulator, dc regulator, voltage monitor
Jul 09, 1998
APPLICATION NOTE 966
Low Battery Monitor Delays System Shutdown
Abstract: A simplified approach of using a dual comparator to act as a battery monitor. Using both low battery outputs (LBO), an application circuit is shown monitoring both the battery voltage and the output of a DC regulator. One of the comparators provides an early warning signal to shut off key components before turning off the power regulator in order to prevent system problems. The circuit of Figure 1 gives an early warning of declining battery voltage. Then, to allow a controlling processor time for emergency housekeeping chores such as the storage of register data, the circuit delays system shutdown by a specified time interval (rather than waiting for battery voltage to decline further, to a specified lower level). Circuit components are chosen for low quiescent current, which protects discharged cells by minimizing the battery drain during shutdown: IC1 draws 1uA, IC2 draws 3uA, and R1/R2 draw 3uA, for a total shutdown current of about 7uA.
Figure 1. This 12V regulator issues a warning when the battery voltage is low, and shuts itself down
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