Mutchus

This circuit is a voltage monitor which operates on fixed testes ± 5 VDC and ± 12 VDC, and is easily constructed as shown in Fig. It is considerably simpler than the normal display using comparators and AND gates. The circuit is not intended to indicate the level of entries. If one of the testes fail, for example, -5 V line fails, the transistor Q3 remains on but the base-emitter junction of T2 is not, so that this transistor is cut off. When this happens, there is no current through D, which then turns off. Monitor voltage + and - 5VDC + and - 12VDC Circuit Diagram

The circuit diagram shows the over voltage protection as a feature of LM317 linear voltage regulator.Over voltages come from several source or factors which are usually in the form of transients. Transients are represented in spikes which are short and fast disturbance or change in the voltage and current component. It only occurs in circuits containing conductance and capacitance. The causes are typically from power outages, short circuits, tripped circuit breakers, lightning spikes, inductive spikes and other malfunctions from power company.  As an example using a 12V battery source, the LM317 voltage regulator can be used to obtain 6 Volts. To protect any device from over voltage, there are ways such as adding relays or a zener diode. A relay switch functions by opening or closing under the command of another circuit. But finding a relay that would limit the output from 6 V to 12 V is not easy. Fortunately, zener diodes are more abundant. A 6.2V zener diode rating can be used t...