battery voltage detection

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0123456rohit

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I want to make circuit which can automatically detect if the battery voltage has become lower then a certain setpoint.
For example- For a 9V battery, I want to detect the condition when the voltage becomes less than 5V.
Please help...
 

hi
ho do u want to design ur circuit? with microcontroller or not?
does the circuit have a seprate surce?
 

Just use an operational amplifier for the task. As we know, apart from the power pins of an op amp, it has inverting, non-inverting and an ouput pin.

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Please I am explaining op amp operating on single rail.

When the voltage at the inverting input is higher than the voltage at the noninverting input, the op amp outputs a logic zero but when the volatge at the voltage at the non inverting input is higher than the voltage at the inverting input, the op amp produces a logic one.
 

you need an opamp that works from a single low voltage supply PLUS a 5V voltage reference.
Use an LM10. It has a low voltage opamp and an adjustable voltage reference in an 8-pins package.
 
Here is a low battery monitor made from two NPN transistors. It can be powered by the same battery it is measuring.



It drains 3 or 4 mA continually while the battery is above 5V, therefore it may not suit.

It's still a good question whether some other method would use less power.
 

Hi use a comparator with a Opamp and a 3.1V zener..... choose the high resistance for voltage divider and zener series resistor values so that It wont drain much power....

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change the Zener diode with 3.1V..............
 
Venkadesh_M said:
Hi use a comparator with a Opamp and a 3.1V zener..... choose the high resistance for voltage divider and zener series resistor values so that It wont drain much power.
Click to expand...
Many lousy old 741 opamps DO NOT WORK with a supply voltage as low as 5V and their supply current is fairly high.
The LM10 opamp/voltage reference IC I recommended works fine from a supply voltage as low as 1.1V (and its maximum allowed supply is 45V) and its typical supply current is only 0.3mA.
 
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