An electronic device includes a circuit protection unit providing over-current protection to a main circuit and including a series connection of first and second current limiting circuits, and a normally-open branch circuit coupled in parallel to the first current limiting circuit and operable to conduct when a voltage across the first current limiting circuit reaches a first predetermined threshold voltage not greater than an endure voltage of the first current limiting circuit. Prior to conduction of the branch circuit, the first current limiting circuit maintains a current flowing therethrough at a first limit value when a current flowing through the main circuit reaches the first limit value. Upon conduction of the branch circuit, the second current limiting circuit maintains a current flowing therethrough at a second limit value greater than the first limit value when the current flowing through the main circuit reaches the second limit value.