Switching power supply device

A switching power supply device, comprising:

• a transformer including:
• a primary winding to one end of which an input voltage is applied;
• a secondary winding;
• and
• an auxiliary winding provided on a primary-winding side;
• a switching element provided in a path of the primary winding;
• an output capacitor having a potential at one end thereof fixed;
• a rectifying element provided between another end of the output capacitor and one end of the auxiliary winding, with a cathode of the rectifying element on an output-capacitor side;
• a control circuit controlling the switching element between ON and OFF, the control circuit including:
• a power terminal connected to the other end of the output capacitor;
• a HIGH-voltage terminal connected to an input side of the input voltage;
• and
• a start-up circuit provided between the power terminal and the HIGH-voltage terminal, the start-up circuit passing a first current for charging the output capacitor via the power terminal;
• and
• a current supplementing circuit receiving the input voltage and connected to the HIGH-voltage terminal, the current supplementing circuit passing a second current to the output-capacitor side based on the first current,
• wherein a load is connectable to the other end of the output capacitor, and
• wherein the current supplementing circuit includes:
• a resistor element to one end of which the input voltage is applied and to another end of which the HIGH-voltage terminal is connected;
• and
• a transistor of which a control end is connected to the another end of the resistor element, the transistor having the input voltage applied to a current-in end thereof, the transistor having a current-out end thereof connected to the other end of the output capacitor, and
• wherein when, as a result of the output capacitor being charged, a voltage at the power terminal exceeds a first threshold voltage, the start-up circuit shuts off the first current, and
• in response to the first current being shut off, the current supplementing circuit makes the second current substantially zero.