An energy-saving control device is disclosed. The control device is connected with an integrated circuit (IC) and a secondary winding of a transformer of a power converter. A primary winding of the transformer receives energy, and then the energy is discharged from the secondary winding and an energy signal of the energy is generated. And the energy signal comprises a high-frequency part and a low-frequency part thereafter. The energy signal is received by the energy-saving control device to control the operation of the IC according to a ratio of the low-frequency part to the high-frequency part.