Patent ID: 7310251

Claim:
A control circuit of a power supply comprising: a switching circuit coupled to an output terminal of the power supply to generate a switching signal for regulating the output of the power supply, in which the switching signal is used to switch a transformer of the power supply; a protection circuit generating a inhibit signal transmitted to the switching circuit to disable the switching signal in response to the fault conditions; and a detection circuit having a first threshold, a second threshold and a third threshold to generate a start signal and an on/off signal transmitted to the protection circuit and the switching circuit to turn on/off the circuits of the control circuit in accordance with an input voltage of the control circuit, in which the first threshold is higher than the second threshold and the second threshold is higher than the third threshold, the start signal and the on/off signal are enabled to turn on the circuits of the control circuit once the input voltage is higher than the first threshold, the on/off signal is disabled to turn off the circuits of the control circuit once the input voltage is lower than the second threshold, the start signal is disabled when the input voltage is further lower than the third threshold; wherein the control circuit consumes a first operating current when the circuits of the control circuit are turned on, the control circuit consumes a second operating current once the circuits of the control circuit are turned off, the control circuit only consumes a start-up current when the start signal is disabled, in which the first operating current is higher than the second operating current and the second operating current is higher than the start-up current.