Patent ID: 7750504

Claim:
A power supplying apparatus to supply power to a system unit comprising one or more system components, the power supplying apparatus comprising: a power selecting unit connected directly to the system unit to select one of a plurality of inputs of power and output a selected power to the system unit; and a controller provided outside a power supply path between the power selecting unit and the system unit to control the power selecting unit to selectively output the power selected by the power selecting unit to the system unit according to a power switching signal received from an external source, wherein the power selecting unit comprises a plurality of switching control units each comprising an output to output a switching control signal, a plurality of power switching units each comprising a control input to receive the switching control signal from a corresponding one of the switching control units, a power input to receive a corresponding one of the inputs of power, and a power output to output the corresponding one of the inputs of power directly to the system unit according to the switching control signal received from the corresponding one of the switching control units, the controller generates an output control signal according to the power switching signal, and outputs the output control signal to the output of each of the switching control units to control each of the switching control units to selectively output the switching control signal according to the output control signal, and the controller comprises a first switching transistor having a base coupled to receive the power switching signal, via a first resistor, and an emitter connected to ground, and a second switching transistor having a base connected to a collector of the first switching transistor, via a second resistor, an emitter connected to cathodes of a first diode and a second diode arranged to supply one of the plurality of inputs to a first comparator and a second comparator, and a collector connected to outputs of the first comparator and the second comparator from which the switching control signals are outputted, via a first pull-up resistor and a second pull-up resistor, respectively, to supply the output control signal to the outputs of the first comparator and the second comparator from which the switching control signals are outputted.