| 摘要 |
A switching power supply device comprises: a series resonance circuit that is formed by a leakage inductance of an insulating transformer (T) and a capacitance (C); a first switching element (Q1) that is driven by a drive control circuit performing a separately-excited oscillation operation and is used for applying a DC input voltage (Vin) to the series resonance circuit; and a second switching element (Q2) that is connected to the series resonance circuit in parallel and is driven to be turned on by the voltage generated in an auxiliary winding (P2) of the insulating transformer when the first switching element is off. The switching power supply device is especially characterized by being provided with a threshold setting circuit for appropriately setting the turn-on timing of the first switching element (Q1) by changing a winding threshold voltage (VWth) according to the DC input voltage (Vin), said winding threshold voltage (VWth) being set in a winding detection circuit for detecting a polarity inversion of the voltage generated in a third winding (P3) of the insulating transformer and outputting a winding detection signal. |
