PHASE SHIFTED, ZERO VOLTAGE TRANSITION DESIGN CONSIDERATIONS and the UC3875 PWM CONTROLLER

Abstract

This Application Note will highlight the design considerations incurred in a high frequency power supply using the Phase Shifted Resonant PWM control technique. An overview of this switching technique including comparisons to existing fixed frequency non-resonant and variable frequency Zero Voltage Switching is included. Numerous design equations and associated voltage, current and timing waveforms supporting this technique will be highlighted. A general purpose Phase Shifted converter design guide and procedure will be introduced to assist in weighing the various design tradeoffs. An experimental 500 Watt, 48 volt at 10.5 amp power supply design operating from a preregulated 400 volt DC input will be presented as an example. Considerations will be given to the details of the magnetic, power switching and control circuitry areas. A summary of comparative advantages, differences and tradeoffs to other conversion alternatives is included.