METHOD AND APPARATUS FOR CURRENT SENSING IN POWER OVER ETHERNET (PoE) SYSTEMS

A method for power control in a system, the system including a first transistor having a drain coupled to a first conductor and a source coupled to a current sensor, and a second transistor having a drain coupled to a second conductor and a source coupled to the current sensor, comprising:

• detecting a drain voltage of the first transistor;
• detecting a drain voltage of the second transistor;
• adjusting a gate voltage of the first transistor and a gate voltage of the second transistor to keep the detected drain voltages of the first and the second transistors approximately equal;
• detecting a current through the current sensor;
• and
• adjusting the gate voltage of the first transistor and the gate voltage of the second transistor to limit the detected current to a current limit.

A power source equipment (PSE), comprising:

• a power source;
• a first transistor;
• a second transistor;
• an interface configured to couple a drain of the first transistor to a first pair of wires of an Ethernet cable, to couple a drain of the second transistor to a second pair of wires of the Ethernet cable, and to couple the power source to a third pair of wires of the Ethernet cable;
• a current sensor coupled to a source of the first transistor and a source of the second transistor;
• and
• a current management circuit configured to detect a drain voltage of the first transistor, to detect a drain voltage of the second transistor, to adjust a gate voltage of the first transistor and a gate voltage of the second transistor to keep the detected drain voltages of the first and the second transistors approximately equal, to detect a current through the current sensor, and to adjust the gate voltage of the first transistor and the gate voltage of the second transistor to limit the detected current to a current limit.