Increasing efficiency of an DSP-controlled converter by on-the-fly changing of the gate drive method

This paper demonstrates how bypassing the MOSFETs body diodes in a full bridge application by freewheeling of the transformer current through the MOSFETs of one input leg decreases the power losses, depending on the operating point. A gate drive control via a modern digital signal processor is described that allows an on-the-fly change of the gate drive method so that freewheeling is activated or deactivated as required to obtain lowest losses in a wide operating range. Unlike other approaches to bypass the MOSFETs body diodes, this technique requires no additional circuit parts (e.g. external freewheeling diodes). The effect of freewheeling on power losses is illustrated by measurements of the current and voltages run, MOSFET temperatures and the characteristic curve of power losses