| 摘要 |
A switching mode power supply (SMPS) with an active load detection function which supplies AC power input to a primary coil of a transforming element, then to a secondary coil of the transforming element, and then rectifies and outputs the AC power is provided. The SMPS comprises a controlling unit for controlling switching frequency by changing the time constant of a switching unit depending on the current and reducing the amount of power supplied to the primary coil of the transforming element. The current at a terminal of a resistor can be controlled under a cross condition, and the current flowing to the resistor can be controlled when in a normal state, thereby preventing energy loss which always occur in the resistor. The switching frequency during a standby state can be reduced to reduce switching loss.
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