Patent ID: 7205808

Claim:
A power supply switching circuit, comprising: an input terminal for receiving a signal from a motherboard; an output terminal to output a control signal; a stand-by power supply terminal and a system power supply terminal; a first Bipolar Junction Transistor (BJT), a base of the first BJT being connected to the input terminal via a base bleeder circuit, a collector of the first BJT being connected to the stand-by power supply terminal via a collector resistor, and an emitter of the first BJT being grounded; and a second BJT, a base of the second BJT being connected to the collector of the first BJT, a collector of the second BJT being connected to the system power supply terminal via another collector resistor, the collector of the second BJT being connected to the output terminal, and an emitter of the second BJT being grounded; wherein the signal from the motherboard indicates a status of the motherboard, the signal has a particular logic low range and a particular logic high range, and an average of a highest value of the logic low range and a lowest value of the logic high range is adopted as a turnover voltage of the power supply switching circuit.