Patent ID: 6956754

Claim:
A switching power supply apparatus for supplying a voltage and a current to a connected load, comprising: a transformer constructed by at least primary, secondary, and feedback coils; detecting means, having a first current detecting circuit and a second current detecting circuit, for detecting a voltage and/or a load current; a switching device for controlling said voltage and/or load current, said switching device having a first resistor and a second resistor in series circuit with said switching device; negative feedback means connected in series with said switching device and primary coil of said transformer and for supplying a negative feedback to said switching device; a switch circuit provided in parallel with said first resistor; control means, in circuit with said switch circuit, for controlling an ON/OFF operation of said switch circuit, and an operation circuit responsive to said first current detecting circuit to turn on said switch circuit through said control means, and a canceling circuit responsive to said second current detecting circuit to turn off said switch circuit through said control means, wherein said control means makes said negative feedback means operative when said detecting means detects the load voltage and/or the load current in which it is possible to determine that a value of the load is equal to or less than a predetermined value.