A power supply circuit for a motherboard includes a first resistor, a second resistor, a Schottky diode, and a direct current (DC) voltage source. The Schottky diode includes a first anode, a second anode, and a cathode. The first anode of the Schottky diode is respectively coupled to terminals of the first and second resistors, another terminal of each of the first and second resistors is respectively coupled to a power supply and ground. The second anode of the Schottky diode is coupled to the DC voltage source, the cathode of the Schottky diode is coupled to a south bridge.