To seek the miniaturization of the size as a power unit, cost down, and efficiency improvement by obviating the necessity to make circuit parts the ones of high breakdown strength.
The primary winding NP of a transformer T1 is provided with a middle tap TP, and a series circuit composed of an inductor L1, a diode D1, a primary winding Np2, and a switching element TR1 is connected between the output ends of a full-wave-rectifying circuit DB. Then, a series circuit composed of primary windings Np2 and Np1 and a switching element TR1 is connected in parallel with a smoothing capacitor C1, and a series circuit composed of an inductance L1, a diode D2 for discharge, and a smoothing capacitor C1 is connected between the output terminals of the full-wave-rectifying circuit DB. Then, the voltage of the smoothing capacitor C1 is restrained from going up when load Z is light, by reducing the excitation energy of the inductor L1.
OBA TSUNETOSHI
MURABAYASHI YOKO
OMRON TATEISI ELECTRONICS CO