An electric power saver with a shunt winding protection function extends the lifetime of the electronic apparatus by providing a constant power to a load and reduces power consumption by preventing unnecessary overvoltage from being supplied. An external power is inputted to an input terminal(10). An output terminal(20) supplies the electricity to a load side. A first transformer part(30) is composed of a series winding between the output terminal and the input terminal. A by-pass switching unit(40) is installed in parallel to the first transformer part and installed between the input terminal and output terminal in order to switch the bypass path about the first transformer part. The bypass switch is circuit-shorted in case the voltage above the standard set by the input terminal is inputted to the input terminal. The shunt winding(45) supplies the voltage to the output terminal after the voltage is induced to one or more shunt windings inductively coupled in the first transformer and is dropped. A resist portion(50) is connected in parallel with the down transformer part in order to prevent the damage to the electric power apparatus while preventing the inversion of the high voltage induced from the load side when the power source induced to the first transformer is induced to the down transformer part by the turn-on operation of the bypass switch. A transfer switch(60) interrupts the contact point of the resist portion and a down transformer part by being automatically switched by the bypass switch and interlock system.
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