A current detecting circuit for use in a power converter having a control circuit, a switching circuit, a transformer and an energy storage element is disclosed. The current detecting circuit comprises a filter, a rectifier and a differentiator. The filter is electrically connected to the energy storage element for receiving a voltage signal from the energy storage element and filtering the voltage signal to obtain an alternating voltage change value. The rectifier is electrically connected to the filter for rectifying the alternating voltage change value to obtain a half-sine wave voltage change value. The differentiator is electrically connected to the rectifier and the control circuit for performing a differential operation on the half-sine wave voltage change value to obtain a current change value of the energy storage element. The current change value is compared with a predetermined reference value stored in the control circuit so as to dynamically control the switching status of the switching circuit according to the comparing result.