Comparison of resonant converters for conversion of constant current to constant voltage

Four types of voltage-mode resonant power converters, which convert constant current to constant voltage are examined analytically and experimentally, and their static and dynamic characteristics are compared. The following results are reported: (1) the converters are experimentally confirmed to have power efficiency of about 80% at megahertz switching frequency for the load condition of 6 V and 1 to 2 A; (2) smaller output impedance means smaller variation of switching frequency for the load regulation-in the experiment, the class-E resonant converter has the smallest output impedance; (3) from the viewpoint of voltage ripple and switching noise, it is necessary for the converter to have both input and output LC filters-therefore Cuk type and class-E resonant converters are superior; and (4) in all these resonant converters, instability arises due to the phase lag of input and output filters when the loop gain is increased. Phase-lead compensation may be necessary in the feedback control loop