SWITCHING POWER SUPPLY UNIT

摘要

A switching power supply unit providing a DC output comprises a DC power supply; a transformer having a primary winding; a main switching element for connecting in series to the primary winding; and an auxiliary switching element for performing ON/OFF operations in synchronism with or opposite to ON/OFF operations performed by the main switching element; wherein an auxiliary switching element drive winding for generating a voltage turning on/off the auxiliary switching element is disposed in the transformer; and a first impedance circuit including a first resistor, a first capacitor being connected in series with the first impedance circuit, and a differentiating circuit for determining the timing for turning on the auxiliary switching element and the ON time thereof is connected to the auxiliary switching element drive winding.