Patent ID: 8541908

Claim:
A powered device, the powered device being connected to a local power source and a power sourcing equipment, the powered device, comprising a first conversion circuit comprising a first input and configured for converting a voltage input to the first input into the rated working voltage of the powered device; a first diode, wherein the positive terminal of the first diode is connected to the local power source for normal power supply and the negative terminal of the first diode is connected to the first input; a second diode, wherein the positive terminal of the second diode is connected to the power sourcing equipment for temporary power supply via power over Ethernet technology and the negative terminal of the second diode is connected to the first input, the voltage of the local power source exceeding that of the power sourcing equipment; a constant current source, the constant current source being configured for drawing at least 10 mA direct current from the power sourcing equipment when the powered device is powered by the local power source; wherein the constant current source comprises a sixth resistor, a fourth npn transistor, a fifth npn transistor, and a seventh resistor, the collector of the fourth npn transistor being connected to one of the connection terminals of the power switch, the base of the fourth npn transistor being connected to the connection terminal the power switch via the sixth resistor, the emitter of the fourth npn transistor being connected to ground through a seventh resistor, the collector of the fifth npn transistor being connected to the base of the fourth npn transistor, the base of the fifth npn transistor being connected to the emitter of the fourth npn transistor, the emitter of the fifth npn transistor being grounded.