Patent ID: 7944663

Claim:
An over-current protection circuit for use with a constant voltage circuit that converts an input voltage to a predetermined output voltage and that outputs the predetermined output voltage, the over-current protection circuit comprising: an output current detecting circuit configured to output an output current detecting voltage proportional to an output current outputted from the constant voltage circuit; an output current control circuit configured to control the output current outputted from the constant voltage circuit according to the output current detecting voltage outputted from the output current detecting circuit; an output voltage detecting circuit configured to output at least an output voltage detecting voltage according to the output voltage of the constant voltage circuit; a conversion rate altering circuit configured to alter a conversion rate of the output current to the output current detecting voltage of the output current detecting circuit according to the output voltage detecting voltage outputted from the output voltage detecting circuit; and a switch device that is capable of operating the output voltage detecting circuit when the output current is greater than a predetermined current value, wherein the switch device includes a first transistor that is connected to the input voltage and the output voltage detecting circuit, the first transistor having a same conductivity type as an output control transistor of the constant voltage circuit that controls the output voltage of the constant voltage circuit, wherein a source and a gate of the first transistor are connected to a source and a gate of the output control transistor respectively, and wherein a threshold voltage of the first transistor is greater than a threshold voltage of the output control transistor.