JPS645355A - Switching power circuit - Google Patents

Abstract

PURPOSE:To stabilize an output voltage and cut down the cost of a circuit by forming a self-oscillated feedback circuit via a coupled circuit and a saturable transformer. CONSTITUTION:In a switching power circuit, a switching element 3 by MOS-FET is connected with one end of the primary winding L1 of a main transformer and is turned ON and OFF according to an input voltage Vin. Then, the voltage of a secondary winding L2 is rectified by a diode D1 and supplied to a load. Said transformer 1 is provided with a feedback winding Lb, which is connected with a saturable transformer 2 via a coupled circuit 15 composed of a series circuit of a parallel circuit of a first capacitor C3 and a first resistance R3, and a diode D4, and of a second resistance and the like formed of a second capacitor C4 and a series circuit of a resistance R4 and a variable resistance VR to make a loop circuit to form a self-oscillated feedback circuit. Thus, the constant of said coupled circuit 15 varies with the direction of an electric current to improve the linearity of an ON-time variation.