Low-Battery Indicator Is Low Cost, Highly Efficient, and Environmentally Friendly

Abstract: This application note presents a circuit that uses a low-power CMOS comparator to provide an LED visual indication of a low-battery condition. This LBO (low-battery-indicator) is achieved by pulsing the LED at a low frequency and low duty cycle. The circuit accomplishes this without draining excessive battery current that can lead to permanent battery damage and, ultimately, hazardous waste disposal. This circuit also helps conserve battery current in the off cycle by placing the comparator in shutdown. Equations and circuit analysis are included for determining duty cycle and comparator trip points.