The invention provides a conversion circuit for converting an input voltage into an output voltage, including: a first full-wave rectifier circuit including a first branch and a second branch connected in parallel, each including a winding and a rectifier switch connected in series to form a midpoint; a first switch branch including a first switch and a second switch connected in series to form a first connection node; and a first resonant unit connected between the first connection node and a midpoint of the second branch, wherein the first resonant unit is not connected in series to the windings of the transformer. The conversion circuit of the invention improves conversion efficiency while maintaining smaller voltage stress on switches.