Patent ID: 6919713

Claim:
A switching power supply unit comprising: a coil having a first terminal to which a DC input voltage is applied, a second terminal from which a first output voltage is outputted, and an intermediate tap from which a second output voltage is outputted; a first switch whose on-off state is controlled by an on-off control signal, which is connected between said intermediate tap or said second terminal and a common potential point; a first rectifying-smoothing circuit, which is connected to said second terminal, for rectifying and smoothing said first output voltage to output a first DC output voltage obtained by converting said DC input voltage; a second rectifying-smoothing circuit, which is connected to said intermediate tap, for rectifying and smoothing said second output voltage to output a second DC output voltage obtained by converting said input DC voltage; and control means for outputting said on-off control signal in order to control at least one of said first and second DC output voltages to be a constant voltage.