Patent ID: 7865754

Claim:
A power budget monitoring circuit in a power sourcing equipment (PSE) for a Power over Ethernet system, the PSE including multiple power ports, the power budget monitoring circuit comprising: a differential amplifier having an inverting input terminal coupled to receive a reference voltage, an non-inverting input terminal coupled to a first node and an output terminal; a first transistor having a control terminal coupled to the output terminal of the differential amplifier, a first current handling terminal coupled to an input terminal of a current mirror and a second current handling terminal coupled to the first node; a first resistor coupled between the first node and a ground voltage and having a first resistance value, wherein the differential amplifier and the first transistor force a voltage equaling the reference voltage across the first resistor to establish a reference current as a function of the reference voltage across the first resistor and the first resistance of the first resistor, the reference current being indicative of a current value per unit power and being provided to a current mirror input device of the current mirror; a plurality of current mirror output devices in the current mirror functioning as variable current sources, each current mirror output device being associated with a power port of the PSE, each current mirror output device providing an output current indicative of the power demanded by the associated power port, the output currents from the plurality of the current mirror output devices being summed at a second node into a monitor current; a second resistor coupled between the second node and the ground voltage and having a second resistance value proportional to a maximum power budget of the PSE, wherein the second resistor receives the monitor current and a monitor voltage develops across the second resistor being indicative of a total power demanded by the power ports of the PSE; and a comparator comparing the monitor voltage to the reference voltage, the comparator providing a comparator output signal having a first state indicating that the total power demanded by the power ports does not exceed the maximum power budget of the PSE and a second state indicating that the total power demanded by the power ports has exceeded the maximum power budget of the PSE.