Patent ID: 6532159
Filing Date: 2003-03-11
Classification: H02M,Y02B

Abstract:
A switching power supply unit comprising:a transformer having a primary winding, a secondary winding and a bias winding; a main switching element connected to the primary winding, the main switching element receiving an output of the bias winding as a feedback signal so as to operate in self-excitation oscillation; a rectifying smoothing circuit connected to the bias winding; a mode switching circuit to be turned on and off depending on an output voltage of the rectifying smoothing circuit; and a delay circuit coupled to the mode switching circuit and connected between the main switching element and the bias winding and delaying the output of the bias winding and applying the delayed output to the main switching element, the delay circuit lengthening a turn-on delay time when the mode switching circuit detects an output voltage of the rectifying smoothing circuit which has a predefined relationship to a threshold voltage.