Supply voltage monitor

In much equipment, such as computers, amplifiers, and the like, where high tolerance components are used, it is important to know at all times whether the supply voltage is within specification. The circuit presented here was designed to show just that. It does so by eomparing two d.c. voltages. As soon as there is a difference of more than 10 mV between these. the indicator LED goes out to signal that something is amiss. lt is, therefore, neeessary to use a very accurate reference voltage, corresponding to the required voltage level.