A 1.9 kW FB-ZVS phase shifted high power density DC/DC converter for off-line applications

This paper describes the main design efforts that have been done during the design of a high power density 1.9 kW DC/DC converter prototype for off-line applications. A phase shifted ZVS full bridge topology was selected because it helps to achieve high efficiency and high power density. Attention has been paid to the design of the magnetic elements, especially to thermal constraints, because they are the major limitation for the reduction of their size. It is shown that a small increment in the power losses of that component can pay back an impressive reduction in their volume. Solutions for improving heat evacuation outside the transformer are presented and a discrete elements based model is given for calculating the temperature of the hottest spot of the transformer and for the study of its thermal stability. A special method for constructing large current toroids for output filter inductance is also presented. The control functions are performed by a UC 3825 PWM controller from UNITRODE and a logic circuit implemented into an EPLD (erasable programmable logic device) from ALTERA, which synthesizes the phase shifted control waveforms and the time delays that must be left for allowing for the resonant transitions to take place