Ethernet: First control LED lighting and also intended for BEMS

As PoE achieves power supply of about 100W, the application scope of Ethernet is expanding. Among them, the control of LED lighting is the most concerned. In the future, it may become a key component for the popularization of BEMS.

The use of "Power over Ethernet (PoE)" using Ethernet power supply is expanding (Figure 1). In fact, the application scope of PoE has been expanding since the standard specification "IEEE802.3af" was established in June 2003. The maximum voltage of IEEE802.3af is 57V, and one port can output 15.4W of power, which can supply 12.95W to the receiving side. Later, in June 2009, the "IEEE802.3at (PoE+)" standard was established, which can receive 25.5W of power per port, and the number of supported models has further increased. Currently, the use of IP phones, surveillance cameras and wireless LAN access points used in office buildings is increasing.

Figure 1: PoE promotes large-scale power

The IEEE standard PoE generally outputs 15.4 to 34W of power per port, but now there are technologies that can supply more power, such as Cisco's UPoE and Linear Technology's LTPoE++.

Recently, PoE technology that can supply more than 25.5W of power specified by IEEE802.3at has been put into practical use. Among them, the "LTPoE++" of Linear Technology Corporation of the United States can supply a large power of about 100W. One port on the power supply side can output 125W and receive 90W of power.

IEEE802.3af and IEEE802.3at use 2 pairs of the 4 twisted pairs in the Ethernet cable. LTPoE++ uses all 4 pairs to increase the power supply (Figure 2). As the power increases, the company has introduced the function of detecting voltage and current values ​​in the power supply control IC to improve reliability. In addition, in order to reduce the heat generated, an external standard that can select low-loss MOSFET is adopted. According to Linear Technology, as the power increases, it can be used for small base stations for mobile communications. It is expected that small base stations equipped with LTPoE++ PoE control ICs will be unveiled from the end of 2012 to 2013.

Figure 2: Using four twisted pairs to supply high power

The specification that can output more than 34W of power per port utilizes all 4 twisted pairs in the Ethernet cable.

No AC-DC converter required

Among the applications that have expanded with the increase in power consumption of PoE, LED lighting has attracted the most attention . This is because PoE has two major advantages that make it suitable for driving LED lighting equipment.

First, there is no need for an AC-DC converter to drive LED lighting. LED lighting products are more efficient than light bulbs and fluorescent lamps, and have a longer lifespan, so in order to reduce the environmental load, LED lighting has begun to replace other lighting products.

Unlike conventional fluorescent lamps, LED lighting is generally driven by direct current. Therefore, an AC-DC converter must be used, and the AC-DC converter "sometimes causes LED lighting to flicker" (Cisco Systems Japan). PoE uses direct current to supply power, so it is easy to avoid such problems.

Another advantage of PoE driving is that it can send and receive control signals. PoE can easily control the brightness of LEDs through the exchange of data signals, which is expected to reduce power consumption.

Due to these two advantages, some leading companies have begun to promote the practical use of PoE systems that support the driving and control of LED lighting. Among them, Cisco Systems of the United States took the lead.

The company has developed "Universal PoE (UPoE)" that can supply 60W of power to one port on the power supply side and receive 51W of power on the power receiving side, and products supporting UPoE, such as network switches, were launched in the fall of 2011. Cisco has developed an LED lighting system that uses UPoE and has introduced it to the Osaka office of its Japanese subsidiary, Cisco Systems Japan (Figure 3).

Figure 3: Controlling LED lighting products via PoE

Cisco Systems Japan has introduced an LED lighting control system using PoE in its Osaka office. The LED lighting fixtures are powered by "UPoE", which can supply 60W of power with one Ethernet cable, and control signals are sent to adjust the brightness of the LEDs (a). In addition to IP phones connected to PoE, the LED lighting fixtures can also be controlled by tablet terminals (b).

This system was proposed in Japan and developed jointly by Cisco Systems Japan and Japanese companies. It can be said that this is a product that can only be born in Japan, which is promoting the popularization of LED lighting. It uses control servers from DEP and Sanki Industry and DEP's DC-DC converter for LED lighting.

The PoE-enabled LED lighting system introduced in the Osaka office can adjust the brightness of the LED lighting in three levels: 0% (off), 50% and 100% through tablet terminals connected by wireless LAN and IP phones driven by PoE. For example, dimming or turning off the LED lighting during times when there are fewer employees or during the day can reduce power consumption. Since employees can operate it at their fingertips, it is convenient to adjust the brightness at any time.

Not only is LED lighting easy to control, but by introducing high-efficiency DC-DC converters, power consumption is reduced by approximately 70% compared to conventional fluorescent lighting.

Becoming the infrastructure for power management

Currently, the LED lighting brightness of Cisco Systems Japan's Osaka office is manually controlled by employees, but it can be automated using data obtained from illuminance sensors and human presence sensors. DEP has trial-produced a dimming system that combines UPoE-driven LED lighting products with human presence sensors and illuminance sensors.

Cisco plans to further increase the number of electronic products that can be powered by PoE in the future. These include laptops and thin client terminals. This will allow IP phones and laptops on desks to be wired with Ethernet cables only. In addition, by enabling power management for these products, PoE is expected to become popular as the infrastructure for building energy management systems (BEMS).

The reduction of power consumption of office equipment has also promoted the popularization of PoE. For example, although the thin client terminal of HP in the United States is an all-in-one machine, its maximum power consumption is only about 13W, which can be fully driven by the conventional PoE. In the future, with the popularization of about 100W PoE and the reduction of power consumption of ordinary notebook computers and desktop personal computers, it will also be possible to power these products.

The luminous efficiency of LED lighting products is also constantly improving, so more LED lighting products can be driven with the same supply power. The power consumption of the 120cm long LED lighting products installed in the Osaka office of Cisco Systems Japan is about 25W per tube. One UPoE port can drive two tubes. By improving the efficiency of LED lighting, if the power consumption is reduced to 17W at the same brightness, one UPoE port can drive 3 LED lighting tubes.

Low labor cost

In addition to energy saving, the introduction of PoE also has advantages in terms of labor costs. For example, in Japan, wiring must be done by professionals with qualifications such as "electricians", which increases labor costs. However, PoE does not require special qualifications.

"After comparing the wiring and PoE, a company chose PoE for reasons such as low construction costs" (Cisco Systems Japan). The same is true overseas. "In places like Singapore, some office buildings do not have wiring, and companies that move in must wire their own. In this case, some companies consulted about PoE because of its low introduction cost" (DEP).

PoE is also used in vehicles

Although PoE is mainly popularized in offices, its application scope will continue to expand as the application fields of Ethernet expand. As a new use of Ethernet, the most popular one is the automotive field. The automotive industry has also begun to take action to use Ethernet in the network connecting ECUs and electrical components in cars, that is, the in-vehicle LAN standard.

When using Ethernet for transmitting images from a vehicle camera, consider using PoE to power the camera module. This eliminates the need for wires, which can reduce costs and vehicle weight. Currently, a single twisted pair cable can achieve a maximum data transmission rate of 100Mbit/s while supplying 5-6W of power (Figure 4), which is enough to drive a camera module. (To be continued, reporter: Makoto Nezu, Nikkei Electronics)

Figure 4: Automotive Ethernet can also use PoE

PoE is also being considered for in-vehicle LAN Ethernet. For example, Broadcom's "BroadR-Reach" can use a twisted pair cable to supply 5 to 6W of power, which can drive an in-vehicle camera. The photo shows a demonstration of the action made public by a mainland company at the "ESEC" held in May 2012.