battery voltage detection

[0123456rohit]

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...

 

[alijamali74]

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

 

[Ogu Reginald]

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.

 

[Audioguru]

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.

 

[BradtheRad]

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.

 

[Venkadesh_M]

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..............

 

[Audioguru]

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.

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.