To provide a power-supply system which controls the timing of switching by maintaining inexpensive cost and versatility, and to provide a switching method of the system.
The switching power-supply system is provided with a transformer having a primary winding; a secondary winding and a control winding; a switching element for switching input to the primary winding; and a rectifier smoothing circuit for rectifying and smoothing output from the secondary winding and generating an output voltage. The system is also provided with a circuit, having a diode to which an anode is connected and in which a cathode is connected to one terminal of the control winding, and a resistor whose one terminal is connected to the anode of the diode and whose other terminal is connected to the other terminal of control winding. The system is also provided with a controller, having a zero-point detectipn part for detecting the voltage value of a cathode-side of the diode and a control part controlling timing for turning on the switching element, based on a detection result by the zero-point detecting part.
Haruko Sanwa
Kenichiro Ochiai