In　general,　Boost　circuit　is　widely　used　as　PFC　circuit　to　achieve　high　power　factor　(PF),　but　the　power　supply　needs　to　add　a　Buck　circuit　in　the　case　of　low-voltage　output　applications.　Two-stage　circuit　requires　more　components　and　two　control　circuits.　On　the　other　hand,　as　the　power　levels　increase,　the　full-bridge　diode　rectifier　reduces　the　converter　efficiency　due　to　the　large　conduction　losses.　This　paper　presents　a　novel　single-stage　(SS)　bridgeless　Boost&Buck　circuit.　Boost　circuit　serves　as　a　PFC　stage　and　Buck　as　a　DC/DC　stage.　Bridgeless　structure　can　reduce　conduction　losses　effectively,　and　improve　the　efficiency　of　the　converter　in　low-input　voltage　&　high-input　current　conditions.　The　proposed　DCM　+　CCM　control　strategy　is　used　to　achieve　high　PF,　high　efficiency　and　step-down　capabilities.　At　last,　a　prototype　with　85　similar　to　135V(rms)　input　and　75Vdc/150W　output　was　set　up　to　verify　the　theoretical　analysis.