Switching power-supply device having wide input voltage range

摘要

Provided is a highly-efficient switching power-supply device having a wide input voltage range. The switching power-supply device includes: a first series circuit including first and second switching elements and a second series circuit including third and fourth switching elements, which are connected in parallel with a power supply; a series resonance circuit including a primary coil and a capacitor connected in parallel with the second switching element; a reactor connected between a connection point of the third and fourth switching elements and the capacitor; a transformer having the primary coil and a secondary coil; and a control circuit that turns on-and-off the first and second switching elements, alternately, and turns on-and-off the third and fourth switching elements, alternately. The control circuit switches the first and second series circuits when an input voltage is low and switches only the first series circuit when the input voltage is high.