| 摘要 |
A switching power supply that can accurately detect a period during energy is supplied from a primary side to a secondary side of a transformer with a simple circuit configuration is provided. A first switching element and a second switching element are serially connected to opposite output ends of a full-wave rectifier rectifying an AC voltage from an AC power source. A current resonant capacitor, a resonant reactor, and a primary winding of a resonant transformer are serially connected to opposite ends of the first switching element. A rectifying and smoothing circuit rectifies and smoothes a voltage of a secondary winding, a control circuit alternately turning on and off the first switching element and the second switching element based on an output voltage of the rectifying and smoothing circuit, and a resonant period detection circuit detects a period, during which energy is transmitted from a primary side to a secondary side, based on a voltage of an auxiliary winding tightly coupled with the secondary winding, and outputs a resonant period detection signal.
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