Self exciting type switching power supply circuit

A switching power supply circuit comprising:

• a DC voltage source;
• a transformer having a primary winding, a secondary winding and a couple of auxiliary windings, one terminal of said primary winding being connected to one terminal of said DC voltage source;
• a switching transistor through which another terminal of said primary winding is connected to another terminal of said DC voltage source and which is turned on and off at a predetermined frequency;
• switching means for turning on and off a closed circuit comprising said DC voltage source, said primary winding and said switching transistor;
• an integrating circuit provided between one of said auxiliary windings of said transformer and the base of said switching transistor for supplying a current to the base of said switching transistor, a waveform of the current being similar to a waveform of collector current, during a period in which said switching means is turned on;
• and
• a differentiating circuit, provided between another one of said auxiliary windings of said transformer and the base of said switching transistor in parallel with said integrating circuit, for operating only immediately after said switching means is turned on to supply a current of a predetermined magnitude to the base of said switching transistor.