This overvoltage protection or crowbar protection circuit is used where we need protection against high voltage surge. The circuit has a few components, it is very easy to build and will protect your electric equipment againg overvoltages. The crowbar circuit must be mounted between power supply and the protected device.
The over voltage protection circuit is based on brute force: when the power supply voltage increases too much a thyristor shortcircuit the output. This mean that the overvoltage is quickly removed from equipment power terminals and F1 fuse will burn.
The voltage at which the crowbar protection starts is set between 5V and 25V with P1:
The overvoltage (crowbar) circuit is now set. Replace the wire bridge with a fuse (5A). In repaos state the circuit take 1 mA.