Patent ID: 8335092

Claim:
An isolated switching power supply apparatus having a main transformer including a primary coil and a secondary coil and that transmits a power from a primary side to a secondary side; at least one power switch that is connected in series to the primary coil of the main transformer and that interrupts a current flowing from a DC input power supply to the primary coil of the main transformer; a rectifier that rectifies a voltage generated in the secondary coil of the main transformer; and a smoothing circuit that smoothes the voltage rectified by the rectifier; wherein energy is stored in the main transformer during an ON period of the power switch and the stored energy is released to the secondary side during an OFF period of the power switch; the isolated switching power supply apparatus comprising: a ramp wave generating circuit that generates a ramp wave based on a change of magnetic flux generated in the main transformer; a comparing device that compares a reference voltage on which the ramp wave is superposed with an output voltage which has been smoothed by the smoothing circuit, and outputs a timing signal to invert a magnitude relation; a timing signal transmitter that transmits the timing signal output from the comparing device from the secondary side to the primary side; and a switching controller that controls a turn-off timing of the power switch by using the timing signal transmitted by the timing signal transmitter to control an ON time of the power switch.