Patent ID: 6433443
Filing Date: 2002-08-13
Classification: H02M,Y02B

Abstract:
A switching power supply having two or more DC outputs comprising:a DC power supply; a transformer having a primary winding, at least two secondary windings, and a feedback winding; a main switching element having an off-state period and an on-state period, connected in series to the primary winding and to be turned on by a voltage generated in the feedback winding, the main switching element having a control terminal and a threshold voltage to turn the main switching element on; and a rectifying circuit connected to each secondary winding, a starting circuit which initially turns on the main switching element at startup of the power supply and a switching circuit provided between the two DC outputs, and wherein, when the switching circuit is turned on, a voltage across both secondary windings attains the voltage level of the lesser of the two secondary windings, a voltage generated in the feedback winding is lowered during the off-state period of the main switching element and a voltage to be applied to the control terminal of the main switching element is controlled so as to be less than the threshold voltage, and the main switching element is turned on by the starting circuit.