battery level indicator

crutschow

Joined Mar 14, 2008
34,389
Can someone please help me design a circuit that will glow the LED when the supply is less than 3V (AA batteries are used)
My circuit mentioned by sparky1 turns off the LED when the voltage goes low.
Are you sure you want to keep draining the battery with the LED after its voltage is low?
 

Dodgydave

Joined Jun 22, 2012
11,300
Minimum voltage for a red led is 1.8V, that only leaves 1.2V until the battery is too low, a TL431 zener is a good start.
 

Thread Starter

MRUNAL123456789

Joined Oct 18, 2023
7
My circuit mentioned by sparky1 turns off the LED when the voltage goes low.
Are you sure you want to keep draining the battery with the LED after its voltage is low?
My circuit mentioned by sparky1 turns off the LED when the voltage goes low.
Are you sure you want to keep draining the battery with the LED after its voltage is low?
yes actually I want to design a circuit that would check the battery levels of a television remote, and when the switch is turned on if the voltage is less than 3v the LED will glow, indicating an alert to change the batteries
Is it possible to design the circuit using LM76x without using any external supply?
 

crutschow

Joined Mar 14, 2008
34,389
I want to design a circuit that would check the battery levels of a television remote, and when the switch is turned on if the voltage is less than 3v the LED will glow, indicating an alert to change the batteries
The typical voltage of an AA alkaline is 1.5V.
The aren't normally considered discharged until the drop to below 1.2V or 2.4V for two in series, so why do you want to detect when they drop below 3V?

Below is a TLV431 circuit that turns the LED ON below the low-level battery voltage (here selected to be 2.5V).
So when the battery voltage (green trace) drops below 2.5V, the MOSFET turns on and powers the LED (red trace)
It only draws 100µA from the battery when the voltage is above that and the LED is not lit.
M1 can be just about any logic-level N-MOSFET (max Vgs threshold voltage <2V).

1697863107053.png
 
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