Evolution of Basic Topologies for the Power Stage of Switching Power Converters(Part3)DC-DC High Frequency Soft-Switching Conversion Technologies

Generally,high-frequency power conversion offers high power density and fast transient response. However,to operate at higher frequencies,it is necessary to minimize switching losses.In past years,a number of techniques and circuits which reduce switching losses have been proposed.These techniques can be broadly classified into two categories:resonant-type(including resonant,quasi-resonant and multi-resonant techniques)and soft-switching PWM techniques(including ZVS/ZCS-PWM,ZVT/ZCT-PWM and full bridge phase-shifted ZVS-PWM or ZVZCS-PWM techniques). Significantly,higher voltage and/or current stresses on power semiconductor devices(compared with those in the conventional PWM technique)and variable-frequency control are the main characteristics of resonant-type techniques. The distinctive features of soft-switching PWM techniques are constant-frequency duty-cycle control with simultaneous reduction of switching losses for the same,or only slightly greater,voltage and current stresses on power semiconductor devices.