PoE technology surpasses IEEE802.3at standard
With the advent of IEEE80 2.3at (high-power standard), the Power over Ethernet (PoE) function is rapidly becoming the mainstream technology and used in many new products. PoE-enabled products provide users with extremely low installation complexity and high system flexibility. New PoE products can now support power supplies with power levels much higher than the existing IEEE80 2.3af / t standard, expanding the number of PoE-enabled products / devices.
PoE market development trend
It seems that fusing data and power on the same conductor has become a clear choice for intelligent system integration. In automotive, aerospace and industrial applications, proprietary standards have been used for decades. The emergence of the IEEE802.3 standard has spawned low-cost, high-data-rate agreements that support new concepts. The original IEEE802.3af standard supports up to 13.4W of power for the load, helping to promote the expansion of Internet Protocol (IP) phones and other similar data nodes in enterprise environments. These early-generation devices have clear and direct goals in form and function.
The expectations of data equipment users are not only a rich feature set and high performance, but also the physical appearance has the same high performance in terms of shape, usually eliminating the need for wall plug-in power transformers and their uncharacteristic power lines. This increase in performance inevitably leads to increased energy consumption. The IEEE802.3at standard (promulgated in 2009, also known as PoE +) is designed to cope with the increased demand for energy consumption, but as the market evolves, the standard is tending to lag behind the cutting-edge design field.
The energy consumption requirements of new products such as home / commercial automation panels, netbooks, and low-power laptops can be adapted to the power supply capability of the PoE IEEE802.3 at standard. Conceptually, this means that the docking staTIon can accept the shape of a single RJ45 connector. In home and commercial automation panels, the advantages of integrated PoE are very obvious, because there is no need to connect different power lines. The limitation of this special design field is that in addition to Ethernet cables, routers or switches that support PoE must also be supported. Due to the ease of integration, most homeowners and small business owners have adopted wireless connections, and companies will naturally promote the integration of PoE. Therefore, the installation is simple and easy, and consumes very little labor.
Information stations (informaTIon kiosk) have begun to appear in many public places, often used to accept orders, point-of-sale (POS) terminals, travel or customer service. This type of information equipment poses challenges to the power limitations of the IEEE802.3af / t standard, such as flat panel displays, printers, and computing platforms that increase large power budgets. Although many well-designed kiosks can operate at powers within 25W (50W when using standby line pairs), higher performance devices require higher power consumption. As the technology further gains market acceptance, the number of information terminals / stations supporting PoE functions will increase substantially.
The wireless design domain is the fastest growing segment of PoE. Access points (WiFi, WiMax, etc.) must be connected to a router, switch, or main network connection. The additional power provided by the IEEE802.3at standard enables all these devices to integrate PoE, making wireless access point installation or service extremely simple, requiring only a single RJ45 connector to be inserted.
The latest market segmentation for wireless design is small mobile access points, also known as femto cells or pico cells, which provide mobile access in non-traditional areas. The high-power version of this concept was originally used to provide better signal coverage for large buildings, and is now being used to replace large mobile base stations in densely populated areas. This will greatly simplify installation and provide a more attractive connection solution in physical size. The energy consumption of mobile base stations in small areas is quite high, much higher than the 25W supported by the existing PoE standard.
Beyond IEEE802.3at standard
The basic power limit of PoE is easy to understand. The maximum voltage limit imposed on an Ethernet cable is considered dangerous if it exceeds 60V. Most local and national electrical regulations establish strict rules and guidelines for conductors carrying elevated voltages. Therefore, for the sake of pragmatism, the voltage provided by the PD node is 57V. For a given system component, due to the square relationship and power dissipation (P = I2R), current is the main cause of energy efficiency losses.
If you want to increase the total power provided to the node, the analysis shows that the series resistance must be reduced first, and the thermal performance of the entire PoE system must also be considered. Most (fortunately not all) PoE devices only meet the standard industrial temperature requirements; if the power supply limits set by the PoE standard are exceeded, PoE devices may only provide marginal performance or even be affected by the shortened usable life. The result may be that the solution becomes More complicated.
PoE electronic devices must enable users to externally configure in-line current limits, and need to be manufactured using technologies that can support long-term operation without degradation of performance when the temperature increases. Most PoE power equipment (PoE-PD) and PoE power supply equipment (PoE-PSE) products support current limiting configuration, but only a few of them can provide true high temperature operation.
If "spare pairs" are used, it is easy to design a PD node with two PoE controllers and combine the outputs on the secondary side of the power transformer (see Figure 1). There are a few commercial products on the market that support PoE to provide up to 30W of power for each pair, while maintaining compliance with IEEE802.3af and IEEE802.3at standards, which can provide 60W of power to the load. If the power supply works with a higher current limit and expands the thermal performance of the selected PoE controller, each pair supports 40W of power, with a total power of 80W.
ONE's NCP1081 and NCP1083 and other 80W-powered PoE-PD can now provide enough power for more applications, including small mobile access points, network storage nodes, many laptops and small form factor computers.
Tradeoffs in size, cost and performance
The large number of PoE options on the market just illustrates that each design challenge involves different combinations of classic constraints such as size, cost, and performance. As PoE functionality becomes mainstream, all three conditions are more important. In consumer applications such as WiFi and data devices, size and cost are critical, but performance is shared by the entire platform. The most common performance measure is the total energy efficiency of the system during the workload cycle. Therefore, for size and cost-sensitive applications, simple but more durable PoE-PD modules need to be equipped with more advanced PSE circuits to provide superior performance. In designs that are less cost-sensitive, some newer PD controllers can be applied, but external software support must also be developed to provide high performance, but they can be used with less advanced PSE electronic devices.
Summary of this article
The continued expansion of the PoE market allows designers to optimize installation complexity and user experience with integrated high-power PoE functions. The recently released IEEE802.3at standard supports up to 25W of power for a single PoE node. PoE power supply can also be expanded to support power three times higher than the IEEE802.3 standard limit, thereby creating new market segments and maintaining backward compatibility. PoE integration will benefit a wide range of products that previously did not meet standard PoE power limits.
Figure 1: ON Semiconductor dual PoE-PD provides 60 to 80W of power for the load.
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