Download Low Battery Indicator - Hobby Circuits and Projects

Battery Monitor
This is an ideal solution to protect rechargeable batteries from deep discharge. It gives an LED
indication when the voltage level in the battery drops below5.1 volt
CA 3140 Op Amp is used as a comparator with a zener to fix voltage in its non inverting input.
Preset VR1 set the voltage level just below 5.1 volt at the inverting input. When the battery
voltage is above 5.1 volt, zener provides regulated 5.1 volt to pin3 of IC and its output goes
high to light LED. It indicates that battery is full. If the voltage in the battery drops below 5.1
volt, output of IC turns low to switch off LED.
R1 330 R
3
2
ZD 5.1 V
1W
7 IC1 CA 3140
6
4
6V BATT
R2 100 R
VR1 10K
LED
Red
If input voltage is more than 5.1V, output of IC goes
high lighting the LED. Adjust VR1 to get a reference
voltage of 5.1 V to pin 2.
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