Instantaneous voltage drop protection device

The invention aims to provide an instantaneous voltage drop protection device which allows the repeated frequencies of charing and discharging of electrolytic capacitors to be reduced and enables longevity and small capacity of the electrolytic capacitors to be realized if the device is used in countries\regions where the voltage variation of commercial AC power is high. If an input AC voltage is in the range of 70% to 90% of a rate input voltage, an inverter is helped to carry out DC-AC conversion under a condition that the switch of a switching part is conducted, such that compensated power based on input AC power is generated and is added to input AC power via an injection transformer. Therefore, load can run with no time limit under an AC voltage of 90% of the rated input voltage without utilization of accumulated power of an electrolytic capacitor. If the input AC voltage drops to be 70% lower than the rated input voltage, the switch of the switching part is cut off, such that DC-AC conversion is carried