Abstract: The present invention is to provide a flyback converter by utilizing harmonic effect generated by a transformer thereof, after transferring electric energy in the transformer in a boundary mode, through cooperating with a simple control circuit to draw the charges stored in a main switch thereof out and enable the main switch to perform a zero voltage switch under a variety of loads in the boundary mode, which not only greatly reduces switch loss thereof, but also effectively limits an operating frequency of the main switch in a predetermined range to greatly decrease peak value of voltage caused by inductance leakage and have the advantages of high efficiency, high switching frequency and low noise without increasing the manufacturing cost.

Abstract: The present invention relates to an electronic ballast of fluorescent lamp, which comprises an resonant element being parallelly connected to a lamp at a distal side from a power source for participating in starting the lamp or preheating electrodes thereof to achieve the purposes of providing an appropriate current for preheating electrodes in starting and substantially reducing or eliminating the current of electrodes after the lamp being turned on, so that an undesirable power consumption in electrodes is avoided.

Abstract: A ring-free zero-voltage switching technique for use in a switching power converter having a zero-voltage switching circuit to achieve high-performance and high-density zero-voltage switching and a transformer to produce an oscillatory L-C circuit at the primary side thereof during zero-voltage switching of the switching power converter, the technique includes the step of short-circuiting the current at inductance means of the L-C circuit upon the occurrence of ringing, and to suppress the voltage at capacitor means of the L-C circuit, so as to eliminate parasitic ringing produced by the zero-voltage switching circuit, to effectively reduce power loss and lower the reverse voltage rating requirement to the secondary side rectification component, to greatly increase the working frequency and power density, to eliminate EMI noises, to minimize the size of the heat sink required for dissipating heat energy from the power MOSFETS, and to let the switching power converters meet the requirements of international EM

Abstract: A ring-free zero-voltage switching technique for use in a switching power converter having a zero-voltage switching circuit to achieve high-performance and high-density zero-voltage switching and a transformer to produce an oscillatory L-C circuit at the primary side thereof during zero-voltage switching of the switching power converter, the technique comprises the step of short-circuiting the current at inductance means of the L-C circuit upon the occurrence of ringing, and to suppress the voltage at capacitor means of the L-C circuit so as to eliminate parasitic ringing produced by the zero-voltage switching circuit, to effectively reduce power loss and lower the reverse voltage rating requirement to the secondary side rectification component, to greatly increase the working frequency and power density, to eliminate EMI noises, to minimize the size of the heat sink required for dissipating heat energy from the power MOSFETS, and to let the switching power converters meet the requirements of international EM

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.