8/27/2023 0 Comments Low battery indicator![]() Off-time is derived from the equation for time-varying voltage across a discharging capacitor: On-time is derived from the equation for time-varying voltage across a charging capacitor: The MAX9030 then turns on, causing the LED to flash in accordance with the following analysis: Note that LBO (active high) is usable as shown, but an active-low warning (active-low LBO) requires the optional circuitry shown in the box. Operating this low-battery-warning LED at low frequency and low duty cycle saves power and extends battery life. The device remains in shutdown while the battery voltage is at normal operating levels it asserts LBO when battery voltage falls below a preset threshold.įigure 1. The MAX9030 is a small, inexpensive comparator with shutdown capability in a 6-pin SC70 package. ![]() You can greatly reduce the LED's power consumption by operating it at a low frequency and a low duty cycle.Īn existing low-battery output (LBO) like that found on DC-DC converters offers a convenient way to light the LED (Figure 1). By drawing current, however, the LED exacerbates the low-battery condition. The usual method for implementing the low-battery warning featured in most battery-operated equipment is to illuminate an LED. Equations and circuit analysis are included for determining duty cycle and comparator trip points. This circuit also helps conserve battery current in the off cycle by placing the comparator in shutdown. The circuit accomplishes this without draining excessive battery current that can lead to permanent battery damage and, ultimately, hazardous waste disposal. This LBO (low-battery-indicator) is achieved by pulsing the LED at a low frequency and low duty cycle. This application note presents a circuit that uses a low-power CMOS comparator to provide an LED visual indication of a low-battery condition.
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