| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply unit for automatically performing switching between a normal mode and a standby mode without any malfunction. SOLUTION: This switching power circuit, including a transformer 1 having a primary winding and a secondary winding, a semiconductor switch 2 connected to the primary winding in series, a control circuit 3 for periodically turning on and off the semiconductor switch 2, and a rectification circuit 4 connected to the secondary winding, comprises a mode switching device 20 which integrates a flyback voltage generated at an auxiliary winding provided at the transformer 1 with an integrating circuit 30, detects an auxiliary winding integrated voltage obtained by the integration with an integrated voltage detection circuit 33 and switches an operating mode from the normal mode to the standby mode if the auxiliary winding integrated voltage is not larger than a preset voltage. COPYRIGHT: (C)2006,JPO&NCIPI
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