Patent ID: 8604758

Claim:
A control circuit for a switching power supply of an electronic device, comprising: a power controller measuring a current flowing from the switching power supply, and converting the current to a voltage, for indicating working status of the electronic device; a comparator comprising an inverting terminal receiving the voltage from the power controller, and a non-inverting terminal connected to a reference voltage; a first electronic switch comprising a control terminal connected to an output terminal of the comparator, a first terminal connected to a first power supply through a first resistor, and a second terminal grounded; a second electronic switch comprising a control terminal connected to the first terminal of the first electronic switch, a first terminal connected to a second power supply through a second resistor, and a second terminal grounded; a third electronic switch comprising a control terminal connected to the first terminal of the first electronic switch, a first terminal connected to the second power supply through a third resistor, and a second terminal grounded; a fourth electronic switch comprising a control terminal connected to the first terminal of the second electronic switch, a first terminal connected to the first power supply, and a second terminal connected to the switching power supply; and a fifth electronic switch comprising a control terminal connected to the first terminal of the third electronic switch, a first terminal connected to the second power supply, and a second terminal connected to the switching power supply; wherein when the electronic device is operating with light load, a voltage received by the inverting terminal of the comparator is less than a voltage received by the non-inverting terminal of the comparator, such that the output terminal of the comparator outputs a signal with a high level, the first and fourth electronic switches are turned on, and the second, third, and fifth electronic switches are turned off, the first power supply is outputted to the switching power supply; and wherein when the electronic device is operating with heavy load, the voltage received by the inverting terminal of the comparator is greater than the voltage received by the non-inverting terminal of the comparator, such that the output terminal of the comparator outputs a signal with a low level, the first and fourth electronic switches are turned off, and the second, third, and fifth electronic switches are turned on, the second power supply is outputted to the switching power supply.