Power supply circuit and electronic apparatus

A power supply circuit comprising:

• a series circuit of a choke coil connected to one terminal of a DC power supply from which a pulsating flow is obtained and a first diode;
• a converter transformer having a primary winding, an auxiliary winding which is serially connected to said primary winding and wound in phase therewith and a second winding which is wound in counter phase with said primary winding;
• a pulse width modulation control circuit;
• and
• a first capacitor,
• wherein said one terminal of said DC power supply is connected to a connection mid point of the primary winding and the auxiliary of said converter transformer by means of said series circuit of the choke coil and the first diode, one terminal of the auxiliary winding of said converter transformer is connected to the other terminal of said DC power supply through said first capacitor and at the same time the other terminal of said primary winding is connected to the other terminal of said DC power supply through a switching device, said secondary winding of said converter transformer is connected to a DC voltage output terminal through a rectifying circuit, said DC voltage output terminal is connected to an input side of said pulse width modulation control circuit, and an output terminal of said pulse width modulation circuit is connected to a control electrode of said switching device.