Systems and methods are provided for regulating a power conversion system. An example system controller includes: a detection component configured to receive an input voltage related to a diode connected to an inductor and output a first signal at a first logic level in response to the input voltage being larger than a predetermined threshold, a control logic component configured to receive the first signal, process information associated with the first signal, and output a modulation signal related to a modulation frequency in response to the first signal being at the first logic level, and a driving component configured to receive the modulation signal and output a drive signal to open and close a first switch at the modulation frequency.