Patent ID: 8147138

Claim:
A power supply circuit for a motherboard, comprising: a control circuit configured for receiving a working mode signal; a self-locking circuit comprising: a first switch comprising a control terminal receiving a power supply on signal from a power supply, a power terminal connected to a standby power, and a voltage output terminal; and a second switch comprising a control terminal connected to the voltage output terminal of the first switch, a power terminal connected to the control terminal of the first switch and the standby power, and an output terminal connected to the control circuit; and an unlocking circuit comprising: a delay circuit connected to the standby power; a third switch comprising a control terminal connected to the delay circuit, a power terminal connected to the output terminal of the second switch and the control circuit, and a grounded terminal; and a fourth switch comprising a control terminal receiving a power ok signal from the power supply, a power terminal connected to the delay circuit, and a grounded terminal; wherein upon the condition that the motherboard is placed in an energy-saving mode, there is no signal output from the control circuit in response to the working mode signal; when the computer is turned off, the power ok signal is at a low voltage level to turn off the fourth switch, the third switch is turned on after a delay of the delay circuit, there is no voltage at the voltage output terminal, and the second switch and the first switch are turned off, thereby the standby power cannot be sent to the voltage output terminal.