PURPOSE:To obtain the prescribed output by a simple circuit by connecting an inductance coil and a transistor between a DC power source and a load, and providing taps at the inductance and the secondary winding connected to the inductance or tertiary or higher windings. CONSTITUTION:A transistor 3 and an inductance coil 34 are connected in series between a DC power source 21 and a load 2. The secondary winding 34a, 34b are provided at the secondary side of the inductance coils 34. Taps are respectively provided at the coil 34 and the secondary windings 34a, 34b, and switched by switches 35, 35a, 35b. When the switches 35, 35a, 35b are switched, the inductance values of the inductance 34, and the secondary windings 34a, 34b are switched to the value within a range that the output DC level is held constantly.
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