This thesis presents the work performed by the author on the application of resonantmode
techniques to commercially-orientated off-line converters. An extensive review of
resonant-mode topologies leads to the development of a method of categorisation of these
topologies which allows a greater comprehension of their properties. The categories of
converter thus obtained are the conventional resonant converter, the quasi-resonant
converter, and the gap-resonant converter. The gap-resonant converter is selected for
further investigation. An analysis reveals the limited load and input voltage capabilities
of this converter, and hence leads to the introduction of a pre-regulating converter to
improve reliability and commercial viability.
High-frequency techniques are explored and reported, and new techniques are developed
in several areas in order to extend the concept of the gap-resonant converter to a realworld
practical design. Subjects explored include the high speed driving of power
MOSFETs, MOSFET and diode switching losses, high frequency magnetic materials and
core losses, and skin and proximity effects. The techniques developed are used in the
design of a 30OW, off-line converter with an input voltage range of 165V to 380V after
rectification, and a ten-to-one output load range.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.