This voltage monitor circuit is designed using LM393 operational amplifier and it has two has two light-emitting diode (LED) indicators that switch on if the monitored supply voltage falls below separate threshold levels.
This voltage monitor circuit can be used to monitor the DC supply voltage, and it will then give a warning if the supply voltage drops to an inadequate level due to a malfunction.
With the specified components values the circuit provides threshold potentials of 10V and 12V.
The voltage monitor circuit can be set at any potentials from about 3.5V to 30V, but the supply voltage to the monitor circuit must never exceed 36 volts.
This circuit has a typical current consumption of around 0-6mA under standby conditions and increases by about 4mA per LED when the circuit is activated.
The ICL8069 used in the IC1 position is a highly accurate and stable voltage reference chip, and not a simple Zener diode (it will operate efficiently at currents as low as 50uA).
The threshold voltage of the detector based on IC2a is determined by the values of resistors R1, R2, and R3.
This resistance is fractionally more than 1200k (1-2 megohms), giving a threshold voltage of 12V.
The switching voltage of the other comparator is controlled by the values of resistors R6, R7, and R8. With fractionally more than 1000k (1M) of resistance through the potential divider this gives a threshold potential of 10V.