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Low Battery Level Monitor Using Op-Amp 741

Low Battery Level Monitor Using Op-Amp 741


Parts Used:

Resistors: (All are 1/4 Watts)

R1 – 1M

R2 – 470K

R3 – 8.2K

R4 – 680E

Diodes:

D1 – 5.1 Zener (500mW)

D2 – IN4148

L1 – LED (any color)

IC:

U1 – Op-Amp 741

Battery:

BT1 – 12V

Switch – On/Off

Circuit Description:

A 741 op-amp is employed as a voltage comparator. The non inverting input is connected to zener reference source. Reference volt is 5.1V. R2 is adjusted so that the voltage at the inverting input is half the supply voltage. When the supply voltage i greater than 10.2V, the LED will not light. When the supply falls just below the 10.2V, the IC’s inverting input will be slightly negative of the non inverting input and the output will swing fully positive. The LED will light, indicating that the supply voltage has fallen to the preset threshold level. The LED can be made to light at other voltages by adjusting the resistor R2.

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