SEPIC converter includes: a control unit (10); a transformer (23) having a primary winding (15), an auxiliary winding (16), and a secondary winding (20); a work capacitor (17) between the primary winding (15) and the auxiliary winding (16); a main switch (18) and a recovery switch (30), both controlled by the control unit (10) and connected respectively between the primary winding (1.5) and an input terminal (7b), and between the work capacitor (17) and the input terminal (7b); a main diode (28) and a recovery diode (31) parallel to the main switch (18) and the recovery switch (30) respectively. The control unit (10) is configured to close the main switch (18) and the recovery switch (30) respectively when the main diode (28) conducts and when the recovery diode (31) conducts.