Patent ID: 6956749

Claim:
A switching power supply circuit, comprising: switching means including a main switching element for interrupting and outputting a direct current input voltage fed to said switching means; a high-voltage generating transformer including a primary winding and a plurality of secondary windings wound on one magnetic leg of a solid core having two magnetic legs each formed with a gap of a predetermined distance to form a closed magnetic path and a secondary low-voltage winding on the other of said two magnetic legs of said solid core, wherein said primary winding and said plurality of secondary windings are coupled in a closely coupled state, and said primary winding and said secondary low-voltage winding are coupled in a loose coupling state; a primary capacitor for cooperating with said primary winding of said high-voltage generating transformer to form a primary resonance circuit; direct current low-voltage production means for rectifying an alternating voltage obtained from said secondary low-voltage winding to obtain a direct current low-voltage; direct current high-voltage production means having a plurality of diodes corresponding respectively to said plurality of secondary windings each for rectifying a high voltage obtained by said plurality of secondary windings and each for stepping up the rectified voltage to obtain a direct current high voltage; and fixed-voltage control means for performing frequency control of said main switching element in response to a level of the voltage produced by said direct current high-voltage production means to perform fixed voltage control.