Patent ID: 8179704

Claim:
An electronic device comprising: a rectifying unit adapted to be coupled to an external power source for receiving and rectifying a voltage input therefrom, and generating a rectified output; a main circuit coupled to said rectifying unit and receiving the rectified output generated by said rectifying unit; and a circuit protection unit for providing over-current protection to said main circuit such that a current flowing through said main circuit does not exceed a threshold current value, said circuit protection unit including a series connection of first and second current limiting circuits coupled to said main circuit, each of said first and second current limiting circuits having a respective endure voltage, said first current limiting circuit being operable to maintain a current flowing therethrough at a first limit value when the current flowing through said main circuit reaches the first limit value, said second current limiting circuit being operable to maintain a current flowing therethrough at a second limit value that is greater than the first limit value when the current flowing through said main circuit reaches the second limit value, and a normally-open first branch circuit coupled in parallel to said first current limiting circuit, and operable to conduct when a voltage across said first current limiting circuit reaches a first predetermined threshold voltage that is not greater than the endure voltage of said first current limiting circuit; wherein the first limit value serves as the threshold current value prior to conduction of said first branch circuit, and the second limit value serves as the threshold current value after conduction of said first branch circuit.