A self-power circuit for a protecting relay includes: a rectifying circuit section rectifying an AC current from an electric power system; a power source circuit section includes: a comparator comparing whether an output voltage from the rectifying circuit section exceeds a reference voltage and a semiconductor switch configured to be switched by an output from the comparator, and supply the output voltage from the rectifying circuit section, as a constant voltage to a microcomputer unit of the protecting relay; an inductor configured to, when a DC current supplied from the rectifying circuit section is rapidly increased, gradually increase the DC current to flow to thus have an increased voltage thereacross; and a bi-directional diode connected between the power source circuit section and a ground and turned on to form a bypass path of a current when a DC voltage supplied from the power source circuit section is rapidly increased.
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