Patent ID: 8044606

Claim:
A power supply, having an alternating current (AC) output for supplying power to a lamp, the power supply comprising: an energy transfer element, comprising an energy transfer input end and an energy transfer output end coupled to the output of the power supply; a power control circuit comprising a energy control circuit coupled to the energy transfer element; a dimming circuit comprising a switching element and a dimming control circuit, in which the switching element is coupled to the power control circuit, the dimming control circuit is coupled to the switching element and receives a dimming signal, and switches the switching element in response to the dimming signal, the power control circuit increases a frequency of the AC output to a frequency range in response to switching of the switching element, and turns off the power supply when the frequency exceeds a pre-determined value; a photo coupler coupled to the switching element and the power control circuit, in which the photo coupler generates a coupling signal in response to turn-on mode of the switching element, the power control circuit increases the frequency of the AC output to the frequency range in response to the coupling signal, and turns off the power supply when the frequency exceeds the pre-determined value; and an over-current detect circuit coupled to the output of the power supply and the photo coupler, driving the photo coupler to generate the coupling signal in response to the output of the power supply.