Ethernet interface circuit

Abstract

The invention relates to the field of Ethernet power supply, in particular to an Ethernet interface circuit capable of preventing high voltage produced by lightning stroke from affecting the resistance between power supply line pairs when the high voltage enters from non power supply line pairs. The Ethernet interface circuit comprises a first isolating transformer, a second isolating transformer, a third isolating transformer, a fourth isolating transformer, a second capacitor and a fifth capacitor, wherein the secondary coil output ends of the first isolating transformer and the second isolating transformer are the power supply line pairs respectively, and the secondary coil output ends of the third isolating transformer and the fourth isolating transformer are the non power supply line pairs respectively; one end of the second capacitor is connected with a center tap of a secondary coil of the second isolating transformer, while the other end is grounded through a sixth capacitor; center taps of secondary coils of the third isolating transformer and the fourth isolating transformer are grounded through the sixth capacitor; and one end of the fifth capacitor is connected with a center tap of a secondary coil of the first isolating transformer, while the other end is grounded.

Description

technical field [0001] The invention relates to the field of Ethernet power supply, in particular to an Ethernet interface circuit. Background technique [0002] POE (Power Over Ethernet, Power over Ethernet) technology is a method of transmitting DC power while transmitting data through Ethernet cables. Wherein, the POE system includes: power supply equipment (Power Source Equipment, PSE) and power receiving equipment (Powered Device, PD). In a POE system, the device that provides power is called the power supply device, and the device that receives the DC power provided by the PSE device is called the powered device. In the POE system, the Ethernet interface circuit is generally used to connect the PSE and PD, such as figure 1 The structure diagram of the POE system is shown. The CABLE SIDE (cable side) of the Ethernet interface circuit is one end of the cable, which is connected to the remote PD load through the cable; the PCB SIDE (physical layer) end of the Ethernet i...

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Problems solved by technology

In this way, the equivalent resistances of C1 and C2 are not infinite, but may be tens of K or tens of K. Therefore, during the detection process of the PSE supplying power to the remote load, because the equivalent resistances of C1 and C2 are not infinite, According to the equivalent resistance R=1 / (1 / Rab+1 / Rpd) between the PD load power supply line pair, R≠Rpd, therefore, in the PSE detection process, it is possible to make Rpd that originally complies with the IEEE802.3af standard , the detection result becomes inconsistent with the IEEE802.3af standard, so the PSE will misjudge the PD load, affecting the power supply of the remote PD load by the PSE

For example: when C1 and C2 are broken down, the equivalent resistance of C1 and C2 is 25K, that is, Rab=25K, and the standard PD Rpd=20K, then the PD equivalent resistance between power supply lines after parallel connection is R=1(1 / 25+1 / 20)=11.1K, and the resistance value of a standard PD is 19K≤Rgood≤26.5K, so the PD that originally complied with the IEEE802.3af standard will become non-compliant, that is, the PSE is detecting During the process, the PD load was misjudged, which affected the power supply of the PSE to the remote PD load.

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