Systems and methods for regulating output current of power conversion system

Systems and methods for regulating the output current of a power conversion system are disclosed. An example system controller comprises a first controller terminal and a second controller terminal. The first controller terminal is configured to receive a first signal associated with an input signal of a primary winding of the power conversion system. The second controller terminal is configured to output a drive signal to a switch to affect a first current flowing through the primary winding of the power conversion system. The drive signal is associated with the turn-on time period, and the switch is closed during a turn-on time period. The system controller is configured to adjust the duration of the turn-on time period based at least on information associated with the first signal.