Zero Voltage Switching of Two-switch Flyback- Forward Converter

FORWARD CONVERTER Jhao-Cyuan Huang, Yong-seng Wong, Kuo-Bin Liu, NSRRC, Hsinchu, Taiwan Abstract The traditional pulse-width-modulated flyback converter power switch has serious electromagnetic interference (EMI) and lower conversion efficiencies problems due to the hard-switching operations. This paper produces a zero voltage switching of flyback-forward converter with an active-clamp circuit, the traditional pulse-width-modulated flyback converter with a active clamp circuit to achieve zero-voltage-switching (ZVS) at both main and auxiliary switches, the active-clamp circuit can reduce most of switching loss and voltage spikes across the switches and improve the overall efficiency of the converter. The theoretical analysis of soft switching flyback-forward converter with an active-clamp circuit is verified exactly by a prototype of 50W with 100V input voltage, 5V output voltage and 30kHz operated frequency. INTRODUCTION The first Taiwan synchrotron light source situated at the national synchrotron radiation research center (NSRRC) has been operational for twelve years. Scientists from nationwide and all over the world have been swarming in to conduct pioneering scientific research, with remarkable growth in both research quality and quantity, levelled up to world standard. After Taiwan photon source (TPS) is completed, a bright source of X-rays will be provided to generate an exhilarating vision of our country’s scientific and technological development. So NSRRC research high efficiency and small volume power supply. Some scientists present forward-flyback converter[1-3], in order to get high efficiency and reduce high switch voltage stress of main switches, the paper uses active clamp techniques [4-6]. ZERO VOLTAGE SWITCHING OF TWOSWITCH FLYBACK-FORWARD CONVERTER Figure 1 shows two-switch active clamp flybackforward. In the figure, the primary has the transformer magnetizing inductance L , the resonant inductor L that is the sum of transformer leakage and external inductor, the two main switches S ,S and auxiliary switch S are N-channel power MOSFET whose output capacitances are denoted by C ,C and C . The flyback-forward of the active clamp circuit includes a clamp capacitance C , and an auxiliary switch S is used to achieve ZVS. The isolated forward secondary side has diode D 、D , output inductor L , output capacitor C ,and transformer winding turn N .The isolated flyback secondary side has diode D , and transformer winding turn N .