Patent ID: 6961255

Claim:
A power control method for a switching power supply apparatus constructed by a transformer having at least first, second, and third coils as primary, secondary, and feedback coils, detecting means for detecting load voltage and/or a load current and a width of a pulse that is generated in the feedback coil, a switching device for controlling said load voltage and/or said load current, and negative feedback means connected in series with said switching device and said primary coil of said transformer and for applying a negative feedback corresponding to said detected pulse width to said switching device, comprising the steps of: detecting the load voltage and/or load current by said detecting means and a pulse width of said feedback coil; discriminating whether at least one of said detected load voltage and said detected load current is a value for making said negative feedback means operative or stopping the operation or not; making said negative feedback means operative if it is determined that at least one of said detected load voltage and/or said detected load current is a value for making said negative feedback means operative; and stopping the operation of said negative feedback means if it is determined that said at least one of said load voltage and/or said detected load current is a value for stopping the operation of said negative feedback means.