SWITCHING POWER SUPPLY DEVICE

PROBLEM TO BE SOLVED: To generate a drive signal to a synchronous rectifier with small number of components and at low cost, so as not to increase loss as a device as much as possible without winding an auxiliary winding on a transformer. SOLUTION: Currents flowing in synchronous rectifiers SR1, SR2 (or diodes 10, 11) and the primary side current or the secondary side current of a transformer 3 are in the same phase. Using only a resonant current detection signal from a current detection means 33 that detects a resonant current by a current resonant circuit 12, drive signals DS1, DS2to the synchronous rectifiers SR1, SR2 synchronizing with the resonant current and consequently the primary side current or the secondary side current of the transformer 3 are generated from the results of comparisons by inputting the resonant current detection signal and a reference voltage to comparators C2, C7. Then, the drive signals DS1, DS2to the synchronous rectifiers SR1, SR2 can be generated without winding the auxiliary winding to the transformer 3. COPYRIGHT: (C)2008,JPO&INPIT