Switching power supply device and method of starting the same

A switching power supply device using a first power supply circuit for generating a first output power and a second power supply circuit for generating a second output power higher than the first output power, said device comprising:

• a switch circuit inserted between said first power supply circuit and said second power supply circuit and supplying/stopping, in response to a control signal, an electric power fed from said first power supply circuit to said second power supply circuit and required for starting said second power supply circuit;
• an operating/stop signal circuit for generating an operating signal or a stop signal;
• an external control circuit, responsive to the operating signal or the stop signal, for supplying the control signal to said switch circuit to turn on/off said switch circuit;
• a first detecting circuit for detecting the first output power of said first power supply device to produce a first output power detection signal;
• a first feedback circuit for feeding back the first output power detection signal as the first feedback signal to a primary-side circuit of said first power supply device;
• a second detecting circuit for detecting the second output power of said second power supply device to produce a second output power detected signal;
• and
• a second feedback circuit for feeding back the second output power detection signal as the second feed back signal to a primary-side circuit of said second power supply device;
• and
• detecting means for detecting at least one of the first and the second feedback signals to deliver a detected signal to said external control circuit.