• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

low battery

Status
Not open for further replies.

sreekanthm

New Member
How do battery operated instruments check low battery condition and give indication ?
If schematic is there it will be more helpful.
 

kpatz

New Member
You could do it with a fixed voltage reference and a comparator.

For example, if your circuit runs at 9V and you want it to warn you when the battery drops below 7V, use a zener circuit to feed (7/2)=3.5V into one input and a voltage divider to feed Vbat/2 into the other input. When (Vbat/2) < 3.5V (meaning battery voltage is below 7V), the comparator output would switch and you can use the output to indicate a good or bad battery status (e.g. light up a low battery LED, or feed the status into a microcontroller).
 

MikeMl

Well-Known Member
Most Helpful Member
I have a simple circuit using a TL431 (or LM431). As shown, it was optimized for a 12V lead-acid battery, and trip point is adjustable from 10.7V to 11.6V. If you want a different trip point, the LED lights when the voltage on the REF input to the TL431 is less than 2.500V, so recalculate the voltage divider consisting of R8, R6 and the 1K trimpot (R3 & R4 in the simulation).

The Plot shows the total current drawn by the circuit as the input voltage sweeps from 10V to 12V for different positions of the Trimpot wiper (0<k<1000). Note that the current drawn by the circuit when the input voltage is above the trip point is less than 1mA. For the value of R5 shown, the LED current is about 6mA when the input voltage is less than the trip point. If you want more LED currrent or change the operating range, you might have to adjust R5
 

Attachments

Last edited:
Status
Not open for further replies.

EE World Online Articles

Loading
Top