An over-current protection circuit for limiting a power current flowing through a switch device, which generates the power current according to a control signal of a control node, is provided. The over current control circuit includes a voltage control circuit, a current sense unit, a conversion circuit, and a control switch. The voltage control circuit provides the control signal to a gate terminal of the switch device according to a limit signal. The current sense unit senses the power current flowing through the switch device to generate a sense voltage. The conversion circuit converts the sense voltage into a conversion voltage. The control switch generates the limit signal according to the conversion voltage.