Surge Protection Circuit for Power Supply
Surge Protector circuit is simple with timer IC and it can give effective solution for protecting your valuable and sensitive electric/electronic systems. Surge typically occurs when power returns after a power-cut (blackout) and connected equipment receives a surge of electricity at an over-voltage level, which can be very damaging. Usually, power-back surges are created by the utility, when it restores supply at an above normal voltage level in order to compensate for the demand as connected equipment restarts at the same time. The author took this little circuit personally to protect numerous lab equipment.
The Surge Protector circuit is designed to be constructed in a small module structure with an onboard electromagnetic relay as the primary switching device. The design is centered around (again) the famed 555 timer, wired as a bi-polar latch switch with its two comparator inputs tied together and biased at 1/2 Vcc through a resistive-potential divider. Since the threshold comparator will trip at 2/3 Vcc and the trigger comparator will trip at 1/3 Vcc, the bias provided by the resistors are centered within the comparators trip limits. The module does need a source of external power for operation, and so a “clean” 5v dc supply is preferred here as the power supply for the entire circuit.