hey, I just designed this circuit to cut off battery power when the 6xAAA cells get below 6v. I used a bc547 as an inverter after the tl431 to trigger an LMC555 to go high when the voltage goes below 6v, which then shuts off the p-channel mosfet (IRF4905). I have V+ going to an led circuit like this one: https://circuitdigest.com/electronic-circuits/darkness-detector-circuit-using-ldr . I used a trimpot to divide the battery's voltage and it's not shutting off the led's after turning it below 6v.

 

Why such a complex circuit (Rube Goldberg design school )?

All you need is the TL431 and a P-MOSFET (below):

(One of the errors in your circuit is that the MOSFET is backwards).

 

First question is what voltages have you measured? Start with the base and collector voltages of the transistor, to verify that the circuit is working as designed. (Assuming that you had a set of actions in mind when creating it.) The first step in failure analysis consists of learning what any system is supposed to do, and then learning what it is doing instead.
That simple scheme made me rather successful in the diagnostics and repair realm. It works for almost everything, not just electronics.

 

Why such a complex circuit (Rube Goldberg design school )?

All you need is the TL431 and a P-MOSFET (below):

(One of the errors in your circuit is that the MOSFET is backwards).

View attachment 332612

nice, I'll try this out (with the IRF4905). What software do you use to simulate? is it free?

 

What software do you use to simulate? is it free?

Several of us on these forums use the free LTspice from Analog Devices.
It's good at finding most bugs in your circuits before you build them.
Chances are, if it doesn't work in the simulation, it won't work in real life.

It has a somewhat steep learning curve, but there are many tutorials and example circuits to help with that, along with help from us here.