Hello,

I've been designing a voltage comparator to check battery voltage using LEDs.
This is the schematic:

The circuit works fine when powering it with 4V, but won't pull the output high (turn the LEDs off) when powering it with 3V.
Any suggestions or things I missed?
Thanks in advance!

 

The TS391 has a n open collector output so it can never drive the drive the output high. You provide a pull-up to bring the output high.
If I understand your circuit, one TS391 input is at 2V but what is the voltage on the other input when the circuit doesn't work?

 

I shoud've noticed that, weird that is does work at 4V though.
When I measure the zener voltage is ~2.18V (inverting input) and the non-inverting input is 3.4V.

 

I shoud've noticed that, weird that is does work at 4V though.
When I measure the zener voltage is ~2.18V (inverting input) and the non-inverting input is 3.4V.

Make sure that the inputs are never higher than the supply voltage minus 1.5V if you want the output to be correct.

 

Thanks, this really helped me out! I'll remember to pay more attention to these specs (this is my first time designing a comparator schematic).