Switching power supply unit having sub-switching element and time constant circuit

摘要

A switching power supply unit providing a DC output has a DC power supply; a transformer having a primary winding and a secondary winding; a main-switching element for connecting in series to the primary winding; one or more sub-switching elements for performing ON/OFF operations in synchronism with or opposite to the ON/OFF operations of the main-switching element; a sub-switching-element drive winding disposed in the transformer for generating voltage turning the sub-switching element on; a turn-off switching element for turning the sub-switching element off; and a time-constant circuit for controlling the turn-off switching element.