Patent ID: 6631079
Filing Date: 2003-10-07
Classification: H02M

Abstract:
A switching power supply apparatus comprising:a transformer having a primary winding and at least two secondary windings; an inductor and a capacitor connected in series with the primary winding; a first switching element having an on-time and an off-time, the first switching element connected in series with the primary winding; a series circuit comprising a second switching element, connected in parallel to a series circuit comprising the inductor, the capacitor, and the primary winding; a rectification circuit for rectifying at least two outputs from the secondary windings and providing at least two output voltages; a control circuit for controlling at least two different outputs from the at feast two secondary windings by control of the on-time of the first switching element, wherein the control circuit turns the first and second switching elements on and off, alternately, so as to sandwich a time-period when both of the first and second switching elements are off, and controls the on-time of the switching elements, whereby the outputs are controlled; an output detection circuit for detecting the at least two output voltages and providing a control signal for control of the on-time to the control circuit; and wherein the output voltage detection circuit comprises: a control signal formation circuit in which the control signal for control of the on-time is formed, corresponding to a voltage at a voltage comparison terminal; plural voltage detectors connected between the at least two outputs of the secondary windings and the voltage comparison terminal, respectively; and whereby the at least two different outputs from the at least two secondary windings are stabilized in dependence on a predetermined control ratio for the outputs.