For users of the IEEE 802.3af/t POE (Power over Ethernet) standard, the benefits are obvious: anyone who can pull a Category 5 or Category 6 cable can open an electrician and use it for networking applications where there is no AC plug. Install the power port and data port. Users can simply add a typical $39.95 POE power supply to a network equipment cabinet and connect it to a Category 5 twisted pair. Compare this scenario to the cost of a new power plug (up to $2,000, including labor and parts costs) and the time wasted with the electrician. A POE network has two main components : a PSE (powered device) such as a network switch or a central router; a PD (powered device), such as a VOIP phone or a wireless access point, connected to a network that provides power and data. Networks equipped with non-POE switches can still take advantage of POEs, adding mid-span power supplies (such as enabling power supplies in network equipment cabinets) that are independent of switches or routers to inject power into the network. Using the UPS as a backup for the PSE ensures that network devices, including VOIP phones, continue to operate even in the event of a power failure in the office. VOIP phones and wireless access points consume less power. The current POE IEEE standard is IEEE 802.3af, and its developers consider the above types of applications to set the PD's power limit to 12.95W. However, 13W power is not sufficient for many types of devices, such as multi-port wireless access points and PZT (shake/zoom/tilt) cameras in the field of building security and surveillance. The standards committee has begun to develop a second edition, 802.3at, or POE Plus. This version is currently in draft form, adding 25W to the maximum power that the PD can consume. Semiconductor manufacturers have introduced a number of draft-based POE ICs with the goal of enabling higher power POE PDs (Figure 1). However, 25W is still not enough for some applications, they may require much more than 30W of power. Figure 1 POE-PD interface chip can handle IEEE802 The IEEE 802.3at standards committee set the limit to 30W at first, and later reduced it to 25W, because the test data showed that when the installer buried the Category 5 or Category 6 cable in a large bundle of cables, and it carried up to At 750 mA, its temperature rises significantly. The committee is not worried about safety because the possibility of a fire is negligible in this case, but rather that when the Category 5 or Category 6 cable temperature exceeds 60 ° C, its signal quality will degrade. However, the cables required for applications requiring higher power are not always bundled together. For example, PZT security cameras with low temperature heaters, IR (infrared) lamps, steerable microphones, etc. are often located outdoors and have dedicated cables. System designers of these applications can consider using non-standard versions of POE, which follow all 802.3at parameters, with the exception of maximum PD power. Focusing on these non-standard applications, all POE interface ICs for POE Plus support more than 25W. Deviating from industry standards can be a daunting move, but if PD needs more than 25W of power, then people may have no choice. However, people can take steps to reduce the risks associated with non-standard pathways. First, make sure that the device design does require more than 25W of power. In the past, PD had a common feature of almost all electronic devices. It appeared before the energy price soared: energy efficiency was low. Five to ten years ago, the power efficiency of power supplies was often only 80% or less. People should now be able to buy or design a power supply that is more than 90% efficient, and the extra power it provides may be large enough that the design does not have to exceed the 25W limit of the standard. However, if the PD has a high-efficiency power supply and still needs more than 25W of power, then people may consider the Network Cable later. Will people's applications have to work with the lowest standard cable? If this is the case, one must take into account the relatively high losses in the cable system. On the other hand, if one can specify cables for their own equipment, they can switch from Category 5 to Category 6, which typically has a larger wire diameter and correspondingly lower resistance and wasted power. Mike McCormick, product manager for POE at Texas Instruments, said: "As time passes, cables will degrade when they carry more power because Ethernet cables are not really power delivery cables. They are not solid cables. Their main use is signal transmission. Therefore, when we use them to provide power, they are not the best conductors. You must be aware of which type of cable your customers will use, provided you use some sort of excess Something. If your device is not a standard type, then using a standard cable might not make sense." When using non-standard and therefore more expensive cables, be sure to get approval from the marketing department, as the parameters are often determined by the department. McCormick said: "I have met some customers who are designing for outdoor cable installations. Their marketing department said, 'No, we must adopt the most common cable standards'." However, the wiring installation base for outdoor data communication clients not good. It may not make sense to limit your product to "standard" cables for different environments. [U2] Figure 2 Old-fashioned Ethernet system can include POE capability if adding mid-span power. The power supply POE voltage into the network. Phihong's single-port POE60U-560G provides 60W for $62. Another option is to use only two pairs, but use four pairs of cables, which is also allowed by the POE standard. Keith Hopwood (Fig. 2), vice president of marketing for Phihong Power, a mid-span power manufacturer, said that although he had heard of several installations in Europe using two pairs of cables, he never encountered any four pairs of cables. Installation case. With four pairs of cables, you can increase the amount of power available to the PD and minimize heat in the cable. At some point, if wiring and installation costs become large, it is necessary to evaluate whether it is possible to use an AC plug. For non-standard installations, the problem of resistive cable loss can also be a surprising thing, because the power available at the PD guaranteed by this standard no longer shelters people's designs. This standard guarantees 13W per PD and it also limits the cable extension length to 100m. Once a non-standard approach is taken, one must calculate the power and the voltage drop caused by the cable and determine the available power at the PD. If people are designing PSE capabilities into switches for standard or non-standard systems, they must ensure that the switch actually uses the power it allocates for the PD. Harmik Singh, business development manager for POE products at Maxim, emphasized the importance of power budgeting for PSE. He said: "Power is very valuable, you don't want to allocate more power than PD actually." If the PD identifies itself as a POE Plus device that will require 25W or more, but only consumes 10W, then the PSE should It has the ability to determine this so that it does not allocate unused power. For example, Maxim's MAX5952 PSE control IC measures the actual current that the PD is consuming, digitizing the PD's power consumption and reporting it in real time, allowing the system controller to allocate actual power usage. Since non-standard POE installations cause so much concern, it is necessary to ask: Why not develop a specification for higher power equipment? TI's McCormick provided the answer: "In the networking world, every optional feature will eventually become a requirement." Compared to a design that must provide 25W per port, a 96-port switch that must supply 50W per port is A more complicated and expensive design, the special reason is that although the high-power PD on the market is quite large, it is likely to not dominate the market. For example, for an 8-port router, if 50W is provided per port, the router will be charged 400W, and most applications will not use such a large amount of power. While POEs make Ethernet more attractive in offices and factories, its combination of power and data also makes it attractive in outdoor applications such as security cameras and sensor networks. However, once electronic communication systems come outside, their susceptibility to power surges will rise dramatically. Lightning is most likely to be the source of catastrophic surges, but other random events can also send destructive surges over the network. The Ethernet cable acts as an antenna and actually receives any surges, discharges, or transients. The PD interface control IC comes with various protection schemes. TI's product family is equipped with minimal internal protection, making it easy for designers to tailor their designs for the final application. McCormick said: "In terms of voltage suppressors and diodes, we think you'd better go to the protection device manufacturer." He pointed out that people can get higher voltage ratings, and these devices can handle much higher power than mixed-signal devices. . Other IC vendors also offer integrated surge protection. For example, ON Semiconductor's NCP108X POE-PD interface controller provides 3kV cable ESD protection because the company uses automotive mass-grade high-voltage processes to assemble the device. Akros Silicon's AS1135 PD controller provides higher than 16.5kV air-gap discharge, 8kV contact discharge, 6kV surge on-chip protection, and a very low ground impedance path.
A high frequency cable is a cable for transmitting high frequency signals. Since the cable has a distributed capacitance and a distributed inductance, filtering the high-frequency signal will attenuate the high-frequency signal, so for the transmission of the high-frequency signal, a cable with a distributed capacitance and a small distributed inductance is required. The following describes one of the high frequency cables: high frequency symmetrical cables.
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Features: high frequency, same resistance to ground, two identical wires, transmission loop