Patent ID: 7035121
Filing Date: 2006-04-25
Classification: H02J,H02M,Y02B

Abstract:
1. A switching power supply apparatus, having: a rectifying circuit for converting an AC voltage into a DC voltage; a switching device for intermittently turning on and off the DC voltage obtained from the rectifying circuit through a primary winding of a transformer; a secondary winding and a tertiary winding for inducing powers in accordance with the turning on and off operations of the switching device; power converting means for rectifying and smoothing the power that is output from the secondary winding and supplying the rectified and smoothing power to a load circuit on the secondary side; control signal detecting means for driving the power obtained from the tertiary winding with the rectified and smoothened DC voltage and controlling the power supplied from the secondary winding to the load circuit for predetermined voltage and current; and a controlling circuit having an oscillating portion and a PWM modulating portion for controlling an ON period of the switching device in accordance with a control signal detected by the detecting means so that the power supplied on the secondary side becomes a predetermined value, the switching power supply apparatus comprises: comparing means for comparing the DC voltage obtained from the tertiary winding with a reference voltage; and a circuit for supplying a control signal of the detecting means to the controlling circuit, wherein the DC voltage of the tertiary winding is designated to equal to or higher than the minimum operation voltage of the controlling circuit, wherein when the load circuit is abruptly turned off, the oscillation stops, and wherein when the DC voltage becomes equal to or lower than the minimum operation voltage, the oscillation stop state of the controlling circuit is cancelled in accordance with a signal that is output from the comparing means.