Patent ID: 8089740

Claim:
A power supply adapted for receiving an input voltage from a power source and for outputting an output voltage, said power supply comprising: a voltage generating unit adapted to be coupled to the power source for receiving the input voltage therefrom so as to output a working voltage; a monitoring unit operable so as to generate a first signal indicating whether said power supply is operated in an ON mode, where said power supply outputs the output voltage, or an OFF mode, where said power supply does not output the output voltage, and a second signal indicating whether said power supply is to output the output voltage; a control unit for receiving the working voltage from said voltage generating unit so as to output the output voltage; a clamp unit adapted to be coupled to the power source and said voltage generating unit for receiving the input voltage and the working voltage therefrom, and coupled to said monitoring unit for receiving the first and second signals therefrom and for outputting a clamp signal in response to the first and second signals from said monitoring unit; a clamp switch coupled between said voltage generating unit and said monitoring unit, and having a control end coupled to said clamp unit for receiving the clamp signal therefrom, said clamp switch being operable between an ON-state and an OFF-state in response to the clamp signal from said clamp unit; and a coupling unit coupled among said clamp switch, said voltage generating unit, said monitoring unit and said control unit; wherein, when said clamp switch is in the ON-state, said coupling unit is operable, in response to the second signal from said monitoring unit, so as to establish electrical connection between said voltage generating unit and said control unit such that said control unit receives the working voltage from said voltage generating unit through said coupling unit; and wherein, when said power supply is switched from the ON mode to the OFF mode, said clamp switch is switched from the ON-state to the OFF-state in response to the clamp signal from said clamp unit such that said coupling unit interrupts electrical connection between said voltage generating unit and said control unit, said control unit outputting the output voltage that drops to a low level after a warning time period in response to electrical disconnection between said voltage generating unit and said control unit.