overvoltage protection - for use with most power supplies

for use with most power supplies Although the circuit described uses an SCR (silicon-controlled rectifier) as protection device, it does not depend on direct crowbar action: instead the SCR causes a fuse to blow. A 723 voltage regulator, used as locked comparator and SCR driver, provides an internally generated reference voltage of 7.15 V at pin 6. This voltage is divided by two (R4/R5) and applied to the inverting input (pin 4) of the comparator. The voltage to be protected (at point A) is divided in R1, P1, and R2 and then applied to the non-inverting input of the comparator (pin 5). The trigger level may be set between 4.5 . . . 17 V with P1. Points B, C, and D are all connected to the unregulated power supply line. Note that the voltage at pin 12 of the 723 should not be less than 9.5 V. If the unregulated line is lower than this value, pin 12 (point B) must be connected to an auxiliary voltage of not less than 9.5 V. When the voltage at point A exceeds a value predetermined b...