A mathematical design procedure is presented in this paper
for choosing the values of the resonant tank parameters
of an APWM half-bridge DC-DC resonant converter for a
certain maximum allowable duty ratio. It is evident that,
when designed for minimum input voltage and maximum
load at maximum allowable duty ratio, the converter ensures
zero voltage turn-on of the two primary-side switches and
zero current turn-off of the secondary-side switch irrespective
of load conditions. Moreover the circulating current in the
primary-side is decreased significantly by operating the converter
exactly at resonant frequency, as well as by minimizing
the magnetizing current with the use of the additional switch
at the secondary side of the transformer. Thus the designed
converter achieves very high efficiency over a wide load range.