Abstract: An exchanging converter includes a zero-voltage switching control circuit, which drives an output voltage filter capacitor to partially feed back storage energy to an input side thereof by means of the operation of a transformer (or storage inductor), and provides a complementary driving signal to switches in the exchanging converter when the switches reaching a zero-voltage switching control condition, so as to control turn off or turn-on time of the switches, enabling the switches to repeat the switching operation at zero-voltage again and again.

Abstract: A power factor correction circuit includes a series connection of a bridge rectifier, a first winding, a diode, and an electrolytic capacitor, a series connection of the electrolytic capacitor, a second winding, and a DC/DC converter, and a common core wound round by the first winding and the second winding. The diode is able to switch between a reverse bias and a forward bias by controlling the polarities of the windings such that an input current always flows to the electrolytic capacitor during each sinusoidal period of an ac voltage. Further, a dc ripple voltage of the electrolytic capacitor will not rise, and an output of the DC/DC converter will not be adversely affected by the 120 Hz ac voltage input. By utilizing this circuit, the power factor of a conventional switching power supply is significantly improved.