ZVS-PWM Flyback Converter With An Auxiliary Circuit

Among dc/dc converters, the flyback topology have been also widely used in industry because of its relatives simplicity when compared with other topologies used in low power applications such as its high power capability, fast transient response and ease of control.The flyback"transformer"serves as dual purpose of providing energy storage as well as converter isolation.The power switches in the flyback converter must suffer the relatively high voltage and current stress. An addition, the high surge voltage across the power switches is always caused by the parasitic oscillation between the transformer leakage inductance and switch capacitance to break the power switches. Theses are the facts of detriment to increasing output power.To reduce the size and weight of the magnetic element in the converter, the general practice is to increase the switching frequency. However, it will result in the more switching losses and electromagnetic interference (EMI), and amplify the adverse effects created by the parasitic circuit elements, such as the leakage inductance of the transformer.The volume of the power converter reduced and the power density increased with the enhancement of the switching frequency, the losses of the converter increased on the contrary. Soft switching technique could improve the circumstance of the power switch, reduce the losses and increase the efficiency of the converter.By using similar concept, a novel ZVS-PWM flyback dc/dc converter with a simple auxiliary circuit is presented in this paper. The main switch and the other semiconductor devices in proposed converter are operated at zero-voltage-switching turn-on and turn-off condition off except auxiliary switch. The auxiliary switch operates at zero-current-switching turn-on and turn-off condition. Besides operating at constant frequency and reducing commutation losses, the proposed ZVS-PWM flyback dc/dc converter have no additional current stress in comparison to the hard switching flyback dc/dc converter counterpart. The energy used to assist in the ZVS operation of the main switch is not dissipated, but is instead delivered to the input dc bus.Analysis on topological nature, operational principle and commutation process are given in detail with effectiveness confirmation of mathematical equations, numerical simulation results and experimental waveforms.