Research On Suppression Secondary Voltage Ringing By Clamp Circuit For Phrase-shift Full-bridge

Switching power supply has the advantages of high efficie ncy, small size, and higher working frequency and so on. DC/DC converter is the most important part in switching power supply. As we all know, the societ y is suffering from energy crisis which make the phase-shift full-bridge(PS-FB) to be a hot research. The PS-FB can use parasit ic to achieve soft switching and has the advantages of simple control, small switching voltage stress. In this paper, the zero voltage switching PS-FB DC/DC converter is studied.Working modes of PS-FB are analyzed and the reason of voltage overshoot and ringing in rectifier are determined. This is verified in saber. The excessive ringing cause EMI and increase the rat ing of rectifier devices. Several solutions to this problem are suggested. One simplest solut ion is to use a separate leakage and to clamp the voltage in the primary. Another attempt is to use active snub ber. Their working principle is analyzed and their performance is compared in simulat ion software. In order to reduce conduct ion losses, synchronous rectificat ion is adopted. Different drive timing of synchronous rect ification and select ion principle o f MOSFET used in synchronous rect ificat ion are introduced.A converter is designed including main parameter. D ead time has influence on ZVS. According to PS-FB dut y cycle loss, small signal modeling for PS-FB is established and open loop transfer function is compensated. Finally, drive circuit is designed and PS-FB circuit is bulited to verify the analysis.