AN834 Datasheet, PDF (1/3 Pages) Silicon Laboratories – ALKALINE BATTERY LOW-VOLTAGE INDICATOR

AN834
ALKALINE BATTERY LOW-VOLTAGE INDICATOR
1. Overview*
In many battery-powered systems, a user would like to know when it is time to replace the batteries before they are
completely discharged, causing the device being powered to fail completely. Alkaline batteries have an open cell
voltage of about 1.5 V. As they are discharged, the voltage slowly drops as shown in Figure 1. When the cell
voltage reaches about 1.25 V, they have delivered about 90% of their stored energy.
Constant Load 8.25 k
Starting Drain 181.8 µA
Temperature 20 °C
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0
200
400
600
800
Time [h]
Figure 1. Alkaline Battery Voltage Discharge Characteristic
The circuit shown in Figure 2 monitors the voltage of two alkaline cells in series and begins flashing an efficient red
LED when the total battery voltage drops below 2.5 V, alerting the user that the batteries need to be replaced.
*Note: This application note has previously been published on the Discover Circuits web site and is republished here with the
permission of the author, David Johnson of Discover Circuits.
Rev. 1.0 1/15
Copyright © 2015 by Silicon Laboratories
AN834