Patent ID: 6469913
Filing Date: 2002-10-22
Classification: H02M

Abstract:
A switching power supply device comprising:a first switching circuit comprising a parallel connection circuit having a first switching element, a first diode, and a first capacitor; a second switching circuit comprising a parallel connection circuit having a second switching element, a second diode, and a second capacitor, the first and second switching circuits forming a series circuit; the series circuit being connectable to an input power source; a transformer including a primary winding and a secondary winding; the primary winding, an inductance, and a series capacitor forming a series circuit, one end of the series circuit being connected to a junction of the first switching circuit and the second switching circuit and the other end thereof being connectable to the input power source; a rectifying and smoothing circuit including a rectifying element, the rectifying and smoothing circuit being connected to the secondary winding of the transformer; energy being accumulated in the primary winding and the series capacitor during an ON-period of the first switching element and an output being obtained from the secondary winding during an OFF-period of the first switching element, an ON-time of the first switching element being controlled so that an output power is controlled; a first driving winding included in the transformer to generate a voltage substantially proportional to a voltage of the primary winding and for turning on the first switching element; a second driving winding included in the transformer to generate a voltage substantially proportional to a voltage of the primary winding and for turning on the second switching element; and switching control circuits alternately turning on and off the first and second switching elements. the switching control circuits alternately turning on the first and second switching elements after periods during which the switching elements are both turned off, the switching control circuits alternately turning off the first and second elements before periods during which the switching elements are both turned off, the first switching element being turned on after the second switching element and the rectifying element are both turned off, so that a self-excited oscillation is performed.