HK1182851B - Cable resistance determination in high-power poe networks - Google Patents

Abstract

The invention relates to a cable resistance determination in high-power PoE networks. An exemplary implementation of the present disclosure is a power sourcing equipment (PSE) for determining a resistance of a powered cable. The PSE includes a first supply voltage to cause a first current to flow through first and second output terminals of the PSE. The PSE also includes a second supply voltage to cause a second current to flow through third and fourth output terminals of the PSE. The PSE further includes a current modulation circuit offsetting the second current from the first current to create an offset voltage between the second and the first supply voltages to determine the resistance of the powered cable. The current modulation circuit can offset the second current from the first current utilizing a variable resistance switch to adjust the second current.

Description

Cable resistance determination for high power over ethernet networks

Technical Field

The invention relates to cable resistance determination for high power over ethernet networks.

Background

Power over ethernet (PoE) allows Powered Devices (PDs), such as Internet Protocol (IP) phones, wireless LAN access points, and secure network cameras, to receive power and data over ethernet cables. In a PoE network, a Power Sourcing Equipment (PSE) may be connected to one or more Powered Devices (PDs) via an ethernet cable. The PSE can allocate power to one or more PDs and transfer the power to the one or more PDs over the ethernet cable. An ethernet cable includes four pairs of wires, each pair of wires being a twisted pair for differential signals. In some PoE networks, only two of the four pairs of wires in the ethernet cable are used to transmit power to one or more PDs. However, four pairs of wires in an ethernet cable are increasingly commonly used to transmit power to one or more PDs. By using more than two pairs of wires, the PoE network can support higher currents with reduced cable losses.

In allocating power to one or more PDs in a PoE network, the PSE can determine power loss and thereby budget power allocation among the one or more PDs. Because the power loss cannot be accurately determined, for example, the PSE may estimate the power loss and stop transmitting power to one or more PDs based on the estimated power loss to maintain a desired power efficiency of the PoE network. As another example, the PSE may not allocate precisely less power to one or more PDs based on worst case scenarios. In PoE networks, ethernet cable resistance is a significant cause of power loss. Thus, the PSE estimates the ethernet cable resistance to determine power loss. For example, time domain reflectometry may be used with the average resistance per unit length of ethernet cable to estimate the resistance of the ethernet cable.

Disclosure of Invention

The present disclosure relates to cable resistance determination in a high power PoE network, substantially as shown in or described in connection with at least one of the figures, as set forth more completely in the claims.

One aspect of the present disclosure relates to a power supply apparatus for determining a resistance of a live cable, the power supply apparatus comprising: a first supply voltage to flow a first current through first and second output terminals of the power supply device; a second supply voltage for causing a second current to flow through third and fourth output terminals of the power supply device; a current modulation circuit that biases the second current from the first current to produce a bias voltage between the second supply voltage and the first supply voltage to determine the resistance of the live cable.

In the power supply apparatus according to the present disclosure, it is preferable that the current modulation circuit biases the second current from the first current with a variable resistance switch to adjust the second current.

In the power supply apparatus according to the present disclosure, it is preferable that the variable resistance switch includes at least one transistor that regulates Rdson.

In the power supply apparatus according to the present disclosure, it is preferable that the current modulation circuit forces the bias voltage to be maintained below a predetermined maximum value.

In the power supply apparatus according to the present disclosure, it is preferable that the power supply apparatus applies the first and second power supply voltages to a power receiving apparatus through the live cable.

In the power supply apparatus according to the present disclosure, it is preferable that the power supply apparatus is used for a power over ethernet network.

Another aspect of the disclosure relates to a method of determining the resistance of a live cable used by a power sourcing equipment in a power over ethernet network, the method comprising: applying a first supply voltage to cause a first current to flow through first and second output terminals of the power supply device; applying a second supply voltage to cause a second current to flow through third and fourth output terminals of the power supply device; biasing the second current from the first current to generate a bias voltage between the second supply voltage and the first supply voltage to determine the resistance of the live cable.

In the above method, the second current is preferably biased from the first current by a variable resistance switch to adjust the second current.

In the above method, preferably the variable resistance switch comprises at least one transistor with Rdson regulated.

In the above method, it is preferable to include forcing the bias voltage to be maintained below a predetermined maximum value.

In the above method, preferably, the first and second power supply voltages are applied to the power receiving device through the live cable.

In the above method, preferably, the current modulation circuit determines the resistance of the live cable with the bias voltage.

In the above method, preferably, the current modulation circuit determines the resistance of the live cable using the first current and the second current.

Yet another aspect of the present disclosure relates to a system for determining the resistance of a live cable, the system comprising: a power receiving apparatus; a power sourcing equipment applying a first power supply voltage to the powered device through the live cable and causing a first current to flow through first and second conductive pairs in the live cable; the power sourcing equipment applies a second supply voltage to the powered device through the live cable and causes a second current to flow through a third and fourth conductive pair in the live cable; a current modulation circuit to bias the second current from the first current to generate a bias voltage between the second supply voltage and the first supply voltage to determine the resistance of the live cable.

In the above system, preferably, the current modulation circuit biases the second current from the first current using a variable resistance switch to adjust the second current.

In the above system, preferably, the variable resistance switch includes at least one transistor that regulates Rdson.

In the above system, preferably, the current modulation circuit forces the bias voltage to be maintained below a predetermined maximum value.

In the above system, preferably, the current modulation circuit is located in the power supply apparatus.

In the above system, preferably, the current modulation circuit determines the resistance of the live cable with the bias voltage.

In the above system, preferably, the live cable is a live ethernet cable.

Drawings

Fig. 1 shows an exemplary flow chart of a method for determining a live cable resistance according to an embodiment of the present invention.

FIG. 2A shows an exemplary diagram of a system for determining the resistance of a live cable according to an embodiment of the invention.

FIG. 2B illustrates an exemplary diagram of a system for determining the resistance of a live cable according to an embodiment of the invention.

Detailed Description

The following description contains specific information pertaining to the embodiments of the present invention. It will be apparent to those skilled in the art that the present invention may be practiced in other specific ways than those specifically described herein. The drawings in the present application and their accompanying detailed description are directed to merely exemplary embodiments. Unless otherwise indicated, identical or corresponding elements in the drawings may be denoted by identical or corresponding reference numerals. Further, the drawings and figures in this application are diagrammatic and not drawn to scale and do not correspond to actual relevant dimensions.

Fig. 1 illustrates an exemplary flow chart 100 of a method for determining a hot cable resistance used by a Power Sourcing Equipment (PSE) in a power over ethernet (PoE) network. The methods and techniques illustrated in flowchart 100 are sufficient to describe at least one embodiment of the present invention, however, other embodiments of the present invention may utilize methods and techniques other than those illustrated in flowchart 100. Furthermore, although flowchart 100 is described with respect to power-over-ethernet (PoE) network 200 shown in fig. 2A and 2B, the disclosed inventive concepts are not limited to the specific features of PoE network 200 shown in fig. 2A and 2B. In addition, although various features are shown as being included within a particular element, these features may be present external to it in different embodiments. As an example, in various embodiments, the current modulation circuit 216 and/or the power supply 208 shown in fig. 2A and 2B may be disposed external to the PSE 202.

Referring now to flowchart 100 shown in fig. 1 and PoE network 200 shown in fig. 2A, flowchart 100 includes applying a first supply voltage to first and second conductive pairs of a powered ethernet cable to cause a first current to flow through first and second outputs (output terminals) of the PSE (170 in flowchart 100). PoE network 200 includes a resistor R for determining a live ethernet cable 206 (or more generally, "live cable 206")_CThe PSE 202.

As shown in fig. 2A, PoE network 200 includes PSE202, Powered Device (PD) 204, and powered ethernet cable 206. The PSE202 includes a power supply 208, a switch 210, a switch controller 212, a variable resistance switch 214, a current modulation circuit 216, and outputs 218a, 218b, 218c, and 218d (also collectively referred to herein as "outputs 218"). Live ethernet cable 206 includes conductive pairs (connectivepair) 220, 222, 224, and 226. Powered device 204 includes diode bridges 228 and 230 and load 232.

PSE202 can be used in PoE network 200 to provide power and data to PD204 over a powered ethernet cable 206. For example, the PD204 may be an IP phone, a wireless LAN access point, and a secure network camera. In PoE network 200, PSE202 is connected to PD204 through a powered ethernet cable 206. The PSE202 can distribute power to the PD204 and transfer the power to the PD204 through the powered ethernet cable 206.

In this embodiment, live ethernet cable 206 includes four pairs of wires (i.e., conductive pairs 220, 222, 224, and 226), each pair of wires being a twisted pair (twistedpair) for a differential signal (differential). For example, each output 218 utilizes a respective transformer within the PSE202 to generate a differential signal (differential), which is then combined by another transformer within the PD204 in a manner known in the art. It should be noted that although the present embodiment is described using a hot ethernet cable 206, an ethernet cable is not required according to embodiments of the present invention and may include more or less than four conductive pairs. Furthermore, in some embodiments, any conductive pair may be replaced by a single wire or more than three wires. Furthermore, differential signaling may not be used in some embodiments.

Applying a first V across conductive pairs 220 and 222 of live Ethernet cable 206_supplySo as to make the current I₁Flows through the outputs 218a and 218b of the PSE 202. FIG. 2A shows PSE202, which includes a first V_supplySo as to make the current I₁Flows through the outputs 218a and 218b of the PSE 202.

For example, as shown in FIG. 2A, PSE202 and PD204 are connected by a powered Ethernet cable 206. Conductive pair 220 of live ethernet cable 206 is connected to output 218a at one end and received by PD204 at the other end. As also shown in fig. 2A, output 218a is coupled to the positive terminal of power supply 208, and conductive pair 220 is received by input 234a of diode bridge 228. Load 232 is coupled to rectified positive rail (rectifiedpositive rail) 236a of diode bridge 228. Similarly, conductive pair 222 of hot ethernet cable 206 is connected at one end to output 218b and at the other end is received by PD 204. As also shown in fig. 2A, output 218b is coupled to the negative terminal of power supply 208 through switch 210, and conductive pair 222 is received by input 234b of diode bridge 228. Load 232 is also coupled to rectified negative rail 236b of diode bridge 230.

Thus, in PoE network 200, switch 210 can be used to form a current path to pass current I₁Flows through the outputs 218a and 218b of the PSE 202. For example, as shown in act 170 of the flowchart 100 of FIG. 1, the switch controller 212 enables the switch 210 to cause the power supply 208 to generate the first V across the output terminals 218a and 218b_supply. Thus, in the present embodiment, the current path is formed fromThe power supply 208 begins, enters the load 232 through the output terminal 218a, the conductive pair 220, and the diode bridge 228, and returns to ground through the diode bridge 228, the conductive pair 222, and the output terminal 218 b. As a specific example, the first V_supplyMay be about 48 volts.

Referring to flowchart 100 of fig. 1 and PoE network 200 of fig. 2A, act 172 of flowchart 100 discloses applying a second supply voltage across third and fourth conductive pairs of a powered ethernet cable to cause a second current to flow through first and second outputs of the PSE.

In act 172, a second V is applied across conductive pairs 224 and 226 of powered Ethernet cable 218_supplySo as to make the current I₂Flows through the outputs 218c and 218d of the PSE 202. FIG. 2A shows PSE202, which contains a second V_supplySo as to make the current I₂Flows through PSE202 outputs 218c and 218 d.

For example, as shown in fig. 2A, conductive pair 224 of hot ethernet cable 206 is connected to output terminal 218c on one end and received by PD204 on the other end. As also shown in fig. 2A, output 218c is coupled to the positive terminal of power supply 208 and conductive pair 224 is received by input 238a of diode bridge 230. Load 232 is coupled to rectified positive rail 240a of diode bridge 230. Similarly, conductive pair 226 of hot ethernet cable 206 is connected at one end to output 218d and at the other end is received by PD 204. As also shown in fig. 2A, output 218d is coupled to the negative terminal of power supply 208 through variable resistance switch 214, and conductive pair 226 is received by input 234a of diode bridge 230. Load 232 is also coupled to rectified negative rail 240b of diode bridge 230.

Thus, in PoE network 200, variable resistance switch 214 is used to form a current path to pass current I₂Flows through the outputs 218c and 218d of the PSE 202. For example, in act 172, current modulation circuit 216 enables variable resistance switch 214 to cause power supply 208 to generate a second V_supply. Thus, in this embodiment, a current path is formed from power supply 208, through output terminal 218c, conductive pair 224, and diode bridge 230, into load 232, and through diode bridge 230, conductive pair226 and output 218d return to ground. As a specific example, the second V_supplyMay be about 48 volts.

Fig. 2A shows PoE network 200 after performing acts 170 and 172 in flowchart 100. In some embodiments, acts 170 and 172 are performed simultaneously. In other embodiments, act 170 is performed prior to act 172. In other embodiments, act 172 is performed prior to act 170. In FIG. 2A, PSE202 applies a first V to PD204 over a live Ethernet cable 206_supplyAnd a second V_supply. Thus, as described above, the conductive pairs 220, 222, 224, and 226 are all used to transfer power to the PD 204. Thus, PoE network 200 supports high current and has low cable loss.

In allocating power to PD204 in PoE network 200, PSE202 can determine power losses and budget power allocation to PD204 accordingly. In PoE network 200, ethernet cable resistance is a significant cause of power loss. In this embodiment, the current modulation circuit 216 is able to determine the ethernet cable resistance and thus the power loss. In the illustrated embodiment, each wire of each conductive pair 220, 222, 224, and 226 has a resistance R_C(for simplicity). It should be noted, however, that the actual resistances may differ, and the PoE standard may require only a 3% resistance imbalance between the various conductive pairs.

In PoE network 200, resistor R_CCan be determined by the following equation 1:

wherein, I₁=（I﹣2*k）*（I₁+I₂) And I is₂=k*（I₁+I₂) K is the current I₁And I₂An imbalance constant between. However, after acts 170 and 172, power is transferred to the PD204 at the PSE202 with the conductive pairs 220, 222, 224 and 226, typically the first V_supply-a second V_supplyEqual or nearly equal to each other. Similarly, current I₁And I₂Typically equal or nearly equal to each other. In other words, in equation 1, k may be equal to or almost equal to 0.5. Thus, in FIG. 2A, equation 1 cannot be used to accurately determine the resistance R_C。

Referring now to act 174 in fig. 1 and PoE network 200 of fig. 2B, act 174 in flowchart 100 comprises offsetting (offset) the second current from the first current to generate an offset voltage between the second and first supply voltages, while optionally forcing a voltage offset to remain below a predetermined maximum value.

In act 174, current I₂From the current I₁Biased to be at a second V_supplyAnd a first V_supplyGenerates a bias voltage V between_offsetTo determine the resistance R_C. More specifically, in the present embodiment, the current modulation circuit 216 biases the current I₂To current I_2offset=I₂﹣I_offsetWhile current I₁=I₁+I_offsetAssume that the current flowing to the load 232 in fig. 2A remains substantially constant.

In the present embodiment, for example, the current modulation circuit 216 utilizes the variable resistance switch 214 to slave the current I₁Bias current I₂To convert the current I₂Regulated to current I_2offset. More specifically, the variable resistance switch 214 includes at least one transistor whose Rdson is regulated by a current modulation circuit 216. As an example, fig. 2B shows variable resistance switch 214 as a transistor connected between output 218d and ground. The current modulation circuit 216 is coupled to the gate G of the variable resistance switch 214 and can adjust Rdson of the variable resistance switch 214 by controlling the potential applied to the gate G. In certain preferred embodiments, the Rdson of the variable resistance switch 214 is driven from the current I₁Reduced to bias current I₂. However, in other embodiments, Rdson of the variable resistance switch 214 is driven from the current I₁Increase to a bias current I₂。

In the present embodimentOver-performing action 174, current I₂Is changed into a current I_2offsetAnd current I₁Is changed into a current I_1offset. In some embodiments, for example, switch 210 is also a variable resistance switch, such that current modulation circuit 216 employs a variable resistance switch to slave current I₁Bias current I₂To regulate the current I₁. For example, the current modulation circuit 216 is connected to the switch 210 instead of the switch controller 212. Furthermore, in some embodiments, the current modulation circuit 216 does not include the variable resistance switch 214. For example, switch 210 and variable resistance switch 214 are in slave current I₁Bias current I₂The roles in the processes may be reversed from those shown in the figures. Further, although the present embodiment is applied to the variable resistance switch slave current I₁Bias current I₂Other devices may also be used. For example, in various embodiments, a current source is used in conjunction with or in place of a variable resistance switch to derive the current I₁Bias current I₂。

By slave current I₁Bias current I₂So that a current I₂Is equal to current I_2offsetAnd current I₁Is equal to current I_1offsetThe imbalance constant k in equation 1 is adjusted away from 0.5. In addition, the adjustment is equal to the first V in equation 1_supply-a second V_supplyBias voltage V of_offsetAway from 0. Thus, the current modulation circuit can utilize, for example, the bias voltage V_offsetCurrent I_1offsetAnd current I_2offsetIs measured to calculate the resistance R_C. Thus, in some embodiments, the current modulation circuit 216 uses a bias voltage V_offsetCurrent I_1offsetAnd current I_2offsetDetermining resistance R of live Ethernet cable 206_C。

As shown in fig. 2A and 2B, the current modulation circuit 216 includes inputs 244 and 246. Input 244 is coupled to conductive pair 222 through output 218b of PSE202, and input 244 is coupled to conductive pair 226 through output 218d of PSE 202. Thus, the current modulation circuit 216 may measure the current I using the input 244_1offsetMeasuring current I using input 246_2offsetAnd measuring the bias voltage V using inputs 244 and 246_offset. It should be appreciated that the inputs 244 and 246 are shown to demonstrate the measurement capability of the current modulation circuit 216. Thus, in this embodiment inputs 244 and 246 sink (sink) negligible current.

Furthermore, in other embodiments, the current modulation circuit 216 measures the first V alone_supplyAnd a second V_supplyAnd calculating the bias voltage V_offset. In other embodiments, the current I_1offset+ Current I_2offsetMeasured from one line. Furthermore, a first V_supplySecond V_supplyCurrent I_1offsetAnd current I_2offsetMay be estimated, predetermined and/or calculated using equation 1. Further, it should be appreciated that equation 1 is merely exemplary and that other suitable equations may be used to calculate or otherwise determine the resistance R_C。

Greater bias voltage V_offsetCan ensure that the resistance R is calculated more accurately_C. However, a first V may be desired_supplyAnd a second V_supplyRemain within a certain range of each other to ensure that PoE network 200 is functioning properly. In some embodiments, the current modulation circuit 216 is driven from the current I₁Bias current I₂To be at the second V_supplyAnd a first V_supplyGenerates a bias voltage V between_offsetThereby determining the resistance R of the live ethernet cable 206_CWhile forcing a bias voltage V_offsetBelow a maximum value V_maxWhich is a predetermined maximum value.

For example, in the present embodiment, the current modulation circuit 216 incrementally varies the current I from the current I₁Bias current I₂Until a maximum value V is reached_max. In one embodiment, at each increment, the current modulation circuit 216 obtains a corresponding bias voltage V_offsetOr in other embodiments a different measurement is obtained, e.g. a second V_supplyAnd a firstA V_supplyAt least one of). The current modulation circuit 216 stops the slave current I based on the measurement result₁Increasing bias current I₂Generating a bias voltage V_offset. In one embodiment, the maximum value V_maxAbout 0.5 volts. It should be appreciated that the current modulation circuit 216 may use other factors in addition to or in place of the above measurements to determine when to stop the slave current I₁Bias current I₂. For example, in some embodiments, the current modulation circuit 216 also forces the current I_2offsetAbove and/or below a predetermined value. Fig. 2B shows PoE network 200 after performing act 174.

Referring to act 176 in fig. 1 and PoE network 200 in fig. 2B, act 176 of flowchart 100 comprises determining a resistance of the powered ethernet cable using the bias voltage, the first current, and the second current.

For example, in this embodiment, the current modulation circuit 216 uses a bias voltage V_offsetCurrent I₁And current I_2offsetDetermining resistance R of live Ethernet cable 206_C. To determine the resistance R of a live Ethernet cable 206_CThe current modulation circuit 216 calculates the resistance R based on equation 1_C. It should be appreciated that different equations may be used to calculate the resistance R_C. Then resistance R_CMay be used, for example, to determine power loss in PoE network 200.

Thus, as described above, the current modulation circuit 216 derives the current I from the current₁Bias current I₂To be at the second V_supplyAnd a first V_supplyGenerates a bias voltage V between_offsetThereby determining the resistance R of the live ethernet cable 206_C. By measuring bias voltage V_offsetCurrent I_1offsetAnd current I_2offsetEmbodiments of the present invention may use these measurements to accurately determine the resistance R_C。

Further, as described above, PSE202 applies a first V to PD204 over powered Ethernet cable 206_supplyAnd a second V_supply. As such, embodiments of the present disclosure advantageously determine the resistance R while receiving high power from the PSE202_C. In PoE network 200, resistor R_CMay change as the temperature of powered ethernet cable 206 changes. The temperature of the live ethernet cable 206 typically increases significantly when power is transmitted as compared to non-transmitted power, which may, for example, cause the resistance R_CUp to 50%. In this way, current modulation circuit 216 is able to determine resistance R as PSE201 transfers power to PD204_CResistance R_CMay be used to accurately determine power loss during operation of PoE network 200. By accurately determining the power loss, the PSE202 can exhibit greater accuracy in budgeting power allocations between one or more PDs.

From the foregoing description, it is manifest that various techniques can be used for implementing the concepts described herein without departing from their scope. Additionally, although concepts have been described with specific reference to certain embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the concepts. Thus, the described embodiments are to be considered in all respects only as illustrative and not restrictive. It should also be understood that the application is not limited to the particular embodiments described herein, but is capable of various rearrangements, modifications, and substitutions without departing from the scope of the invention.

Claims (10)

1. A power supply apparatus for determining the resistance of a live cable, the power supply apparatus comprising:

a first supply voltage to flow a first current through first and second output terminals of the power supply device;

a second supply voltage for causing a second current to flow through third and fourth output terminals of the power supply device;

a current modulation circuit that biases the second current from the first current to produce a bias voltage between the second supply voltage and the first supply voltage to determine the resistance of the live cable.

2. The power supply apparatus of claim 1, wherein the current modulation circuit biases the second current from the first current with a variable resistance switch to adjust the second current.

3. The power supply apparatus of claim 2 wherein the variable resistance switch comprises at least one transistor with Rdson regulated.

4. The power supply apparatus of claim 1 wherein the current modulation circuit forces the bias voltage to remain below a predetermined maximum value.

5. The power supply apparatus according to claim 1, wherein the power supply apparatus applies the first and second power supply voltages to a powered apparatus through the live cable.

6. The power sourcing equipment of claim 1, wherein the power sourcing equipment is for a power over ethernet network.

7. A method of determining the resistance of a live cable used by a power sourcing equipment in a power over ethernet network, the method comprising:

applying a first supply voltage to cause a first current to flow through first and second output terminals of the power supply device;

applying a second supply voltage to cause a second current to flow through third and fourth output terminals of the power supply device;

biasing the second current from the first current to generate a bias voltage between the second supply voltage and the first supply voltage to determine the resistance of the live cable.

8. The method of claim 7, wherein the power supply device comprises a current modulation circuit configured to determine the resistance of the live cable from the bias voltage, the first current, and the second current.

9. A system for determining the resistance of a live cable, the system comprising:

a power receiving apparatus;

a power sourcing equipment applying a first power supply voltage to the powered device through the live cable and causing a first current to flow through first and second conductive pairs in the live cable;

the power sourcing equipment applies a second supply voltage to the powered device through the live cable and causes a second current to flow through a third and fourth conductive pair in the live cable;

a current modulation circuit for biasing the second current from the first current to generate between the second power supply voltage and the first power supply voltage

Generating a bias voltage to determine the resistance of the live cable.

10. The system of claim 9, wherein the current modulation circuit is located within the power supply device.