Patent ID: 6198637
Filing Date: 2001-03-06
Classification: H02M

Abstract:
A switching power supply circuit comprising a transformer having a primary winding, a secondary winding, and a feedback winding, a switching element connected in series to a first end of the primary winding, a control circuit disposed between a control terminal of the switching element and the feedback winding, a starting circuit connected between a second end of the primary winding and the control terminal of the switching element, and a rectifying/smoothing circuit connected to the secondary winding;wherein the control circuit includes a first delay circuit for determining a time that elapses before the switching element is turned on by a voltage generated at the feedback winding, a control element driven to perform at least one of preventing the switching element from turning on and turning off the switching element, anda second delay circuit for changing a delay time such that, under rated load or under heavy load, the switching element is turned off by driving the control element after the switching element is turned on by the voltage generated at the feedback winding, and, under light load, the turn-on of the switching element is blocked by driving the control element before the switching element is turned on by the voltage generated at the feedback winding.