The adjustable voltage monitor can be used to check whether the voltage in a circuit remains within a given range. If the dc voltage is less than the voltage at pin 5 of-Ul-B, then LED 1 will light. If the voltage is over 5V, LED2 will light. If the voltage is within the window set by R4 and R5, neither LED will light.
This circuit is useful as an under-or-over voltage monitor.