How does this power supply monitor work?

[rinaishlene]

Hi

Anyone can explain in details about the circuit operation in Figure 9.14 (as attached0 in terms of how each components involved function?

Thank you

 

[barrybear]

Re: Power supply monitor

The LM358 zener sets a standing voltage on the 2 comparitors. The other inputs to the comparitors are both positive and negative causing the outputs to switch in oposing directions . The transistor and led reflects the state of the outputs of the comparitors providing an on and off bias for the base of the transistor.
It will give you a small window off voltage when the comparitors provide bias to turn the transistor on and off