Patent ID: 6798671
Filing Date: 2004-09-28
Classification: H02M

Abstract:
A self-excitation type switching power supply unit comprising:a transformer serving to output a D.C. voltage inputted to a primary winding as a flyback voltage through a secondary winding and having an auxiliary winding in which a feedback voltage from the primary winding and the secondary winding is induced; a main switching element for switching input of a D.C. voltage to the primary winding; and an output portion for rectifying and smoothing the flyback voltage outputted through the secondary winding to output a D.C. voltage, wherein: an inductance of the primary winding of the transformer in a high input voltage and in a light load is set high within a range of not exceeding a rated value of the main switching element; and an inductance of the auxiliary winding and values of a control resistor and a capacitor of the main switching element in a low input voltage and in a heavy load are set low within a range of not deteriorating the oscillation characteristics of the main switching element.