LED lighting is a near-mainstream technology. The replacement LEDs allow property managers and owners to take advantage of the traditional power infrastructure to enjoy the long working life and energy efficiency of LEDs. Local area networks (LANs) are installed in these environments, and Power over Ethernet (PoE) technology provides unprecedented ability to dynamically monitor and control each LED light as well as intelligent LED lighting/sensor concentrators.
In 2015 and beyond, LED will definitely drive the design of lighting systems
A light emitting diode (LED) is a semiconductor device that emits light when passing current. The application advantages of LEDs are constantly evolving and maturing, making them the first choice for more and more traditional and new lighting applications.
The advantages of LEDs include longer working life, higher energy efficiency (lumen/watt) and a small form factor. For example, LED lamps have a working life of 50,000 hours, far exceeding the typical working life of 1,000 to 2,000 hours for incandescent lamps, and 5,000 to 10,000 hours for compact fluorescent lamps (CFLs). Therefore, LEDs are well suited for a wide range of commercial and industrial applications, where energy efficiency is required, and contact/safety risks and high labor costs are not conducive to replacing lamps. The brightness of a 10W LED lamp is equivalent to about 60W incandescent lamp, which makes the LED lamp use and maintenance cost much lower. LEDs can be used with conventional luminaires such as the MR16; they are ideal for replacing these pedestals, providing longer time and more energy efficient lighting.
The wavelength or color of the LED illumination depends on the materials used in the LED construction. With the right driver, LEDs offer greater design flexibility for dimming and changing the color of the luminescence. When used with suitable controllers and sensors, the amount and color of the light can be adjusted according to changes in the environment. This capability makes it ideal for indoor lighting as well as applications such as dimmable street lights and outdoor lighting, changing its brightness depending on ambient light changes. LED dimming saves about 1:1, so dimming the LED to 50% will save about 50% of the energy.
Designers continue to apply LEDs to a growing variety of lighting applications. We discuss LED applications in two scenarios. Designers use LED modules in traditional luminaires, such as the MR16, which must work with existing power infrastructure to take advantage of LED lights. In contrast, Power over Ethernet (PoE) LED lighting networks use new or parallel power infrastructure. Before discussing these application spaces, let's briefly review the LED drivers.
Figure 1: LED driver converts the input voltage to the level required by the LED
LED driver
The LED driver is a low voltage component that converts the input voltage, such as 120V, 220V or 277V, to the low voltage required by the LED. These drivers also parse the control signals, dim, brighten, and change the illuminating color (Figure 1). The LED driver can be configured with a constant current (eg 350mA, 700mA or 1050mA) or a constant voltage (typically 12V or 24V). These two types of drives are not interchangeable. The luminaire manufacturer selects the drive type and configuration to match the electrical requirements of the LED modules used in the luminaire. In this paper, we discuss the constant current driver as an example.
The constant current driver supports Pulse Width Modulation (PWM) and Constant Current Dimming (CCR) to regulate the output current during LED dimming. LED applications require a constant current to ensure that the LED lamp output remains constant as the input voltage fluctuates. LED drivers not only drive high-end and low-end illumination, but are also responsible for continuous or step dimming. The designer matches the drive to the LED according to various combinations of application requirements, including the number of LEDs driven, the type of power supply, and the functional characteristics of the LED. Matching or poorly implemented LED drivers can actually shorten the operating life of the illuminator, causing unpredictable lighting problems, such as flicker.
If the amplitude and/or frequency of the LED illumination is periodically modulated or fluctuated (unpredictable), the human eye will sense it. If the input current changes rapidly and the LED lamp output changes rapidly, the LED is prone to flicker. There are many causes of flicker, including power supply noise, control noise, component tolerance, and LED driver circuit design issues.
A good LED driver design should consider all internal and external factors to provide a constant, non-oscillating current to the LED for flicker free dimming.
Renovation
The longer life and higher efficiency of LEDs make them ideal for replacing other lighting technologies, especially incandescent and halogen lamps. There are two main challenges when using LEDs for existing lighting infrastructure. First, the replacement lamp must conform to the dimensions of a conventional light source; secondly, it must work correctly without flicker in an existing electrical infrastructure environment.
Mounting the LED to an existing form factor, such as the MR16 (Figure 2), not only limits the size of the driver board, but also the thermal issues of the design itself.
Figure 2: MR16 size luminaires are retrofitted to LED versions
Since the LED emits only visible light, the heat conduction heat dissipation is higher than that of an incandescent lamp or a halogen lamp. Heat dissipation is also one of the factors that limit the amount of illumination produced by an illuminator. The LED technology used in today's replacement lamps is almost impossible to reach the acceptable brightness level in the mainstream market. Increasing the brightness limit and the resulting thermal design are essential to designing a commercially successful product. An inevitable result of heat dissipation is the service life of the drive board. To emit more light, the illuminator must be operated at a relatively high temperature (+80 ° C to +100 ° C). In this temperature environment, the driver circuit board that is susceptible to high temperatures limits the operating life of the entire LED lamp.
In order to work properly with existing electrical specifications, replacement LED lamps must work correctly with the infrastructure, including chamfering (triac/leading or trailing edge) dimmers and magnetic or electronic transformers. Each infrastructure has its own technical problems.
For halogen lamps, the dimmer works very well because the current consumption is high enough to keep the dimmer on. However, LED replacement lamps do not support thyristor dimmers to work well because they do not provide the required startup current and provide hold current. The result is that the dimmer does not start properly or is turned off during operation, and the LED light flickers.
Electronic transformers have their own design considerations: the load is required to be resistive, but the LED MR16 lamp is not a resistive load. Therefore, it is necessary to change the load characteristics to prevent the electronic transformer from being turned off. One of the biggest obstacles in the design of LED MR16 lamps is the development of lamps that are flicker-free and compatible with electronic transformers. Electronic transformers are much smaller than traditional magnetic transformers. When the current required by LED lamps is low, it is an arduous design problem. The lower LED current causes most LEDs to not work with electronic transformers. The dimmer will further reduce the current, which exacerbates this difficulty.
Maxim's MAX16840 LED driver solves this problem with a patented fixed-frequency, average-current mode control method that is compatible with most electronic transformers and trailing edge dimmers.
Power over Ethernet (PoE)
LED lighting is a near-mainstream technology. In addition, LEDs work easily with sensors, wireless communication modules, and embedded processors. This versatility allows LED luminaires to become intelligent network sensor concentrators, and with an isolated local embedded processor, the lighting system can save energy. Connect smart LED lights/sensor concentrators to a local area network (LAN), allowing installed LED concentrators to quickly support and take advantage of new features emerging on IoT (Internet of Things) without the need to replace expensive lights to provide future growth Technology (Figure 3). PoE is ideal for powering, connecting, and controlling smart LED concentrators over a LAN. The PoE technology is subject to the IEEE 802.3 standard. The standard specifies that a single standard network cable (such as cat 5) directly supplies power to the network port of the connected device and performs data communication. Using PoE reduces the cost of deploying and installing compatible IP devices, including LED lights and sensor concentrators. Since only one data cable needs to be routed, the wiring cost is low; no separate power cable is required. Since data network cabling does not require the employment of a licensed, qualified electrician, the installation cost is lower. The PoE network supports better overall network power management by enabling discrete control over the power of the connected equipment and providing power backup using only network connections during power outages. PoE supports 10BASE-T, 100BASE-TX and 1000BASE-T networks.
The original PoE standard was issued in 2003 and updated in 2009. Power is supplied through a power supply unit (PSE) on the switch/hub. The IEEE 802.3 standard allows PSE to be used in mid-span mode to plug power into the network. This method supports traditional networks and provides better control over the network being powered. A connected device that receives power is often referred to as a powered device (PD).
To support legacy equipment, the PSE can be powered by two pairs of wires. When using Category 3 or better cables, the maximum power is 15.4W and the voltage range is 44VDC to 57VDC. This standard also specifies PSE when using Category 5 or better cables. Available in 30W (through two pairs of wires) or 60W (through four pairs of wires) with voltages ranging from 50VDC to 57VDC. For these three power scenarios, the PD is limited to a maximum power of 13.0W, 25.5W or 51W (considering Power loss to the worst operating conditions in the cable) - all in the 37VDC to 57VDC voltage range.
Figure 3: LEDs with integrated sensors become intelligent network concentrators
During the initial connection, the PD negotiates its power level with the PSE. All PDs have a 25kΩ resistor on their supply pair, allowing the PSE to detect when the PD is connected to the network and when it is disconnected from the network.
PoE does not affect the data communication performance, but actually prevents the network device from being overloaded by the power consumption negotiation between the PoE unit and the connected device. Power is only supplied to compatible devices to prevent power from being supplied to incompatible legacy devices. This approach allows users to mix traditional devices and PoE-compatible devices casually and securely on their network.
In the PoE configuration, each LED luminaire can be a standard RJ45 connector plug-and-play device with its own IP address and can be independently addressed. A smart LED concentrator (integrated sensor and wireless access point) is connected via PoE to power each LED concentrator that is illuminated. The PoE connection also supports each LED concentrator to collect information from its various sensors and send the data back to the controller (Figure 4). Information collected may include ambient light, temperature, humidity, and anonymous room usage data. For example, an inductive sensor can be used to ensure that the light is turned on only when someone enters the room. When the sensor does not detect anyone, the illumination is automatically turned off. Alternatively, ambient light sensors support daylight harvesting because LED lighting is automatically adjusted when daylight is insufficient to maintain illumination.
Through PoE operation, the LED lighting system becomes an information network, so users can control the lighting and temperature in their vicinity. The system has access to other building services (such as through smart phones), such as proximity sensors to discover the nearest free meeting rooms; it also enables property managers to better measure, monitor, and control other building systems, such as real-time heating and ventilation. Property managers can now use this data for historical trend analysis to identify opportunities to improve energy efficiency and operational efficiency. Opportunities to improve efficiency include adjusting temperature, lighting, and developing a cleaning plan based on the user's actual behavior. CAT 5e/6/6A CABLE DIMMER PATCH PANEL MOTION SENSORS
Figure 4: Networked lighting and sensors bring new features to any area that uses lighting
The PoE LED network offers additional benefits for future growth as LED lighting (and integrated smart sensor concentrators) has been deployed where people gather. If the property manager wants to add new sensors or communication modules, such as distributed short-range wireless access points, it can be implemented at a lower profit cost because power and data are already connected to the most advantageous location.
PoE is the future of LED lighting. Maxim LED drivers support a wide range of voltages (MAX16832: 6.5V to 65V) and output current (MAX16832: 1A), ideal for supporting PoE applications. These devices support analog and PWM control for smooth flicker-free dimming. The device integrates a variety of external components, including MOSFETs, to meet small size requirements.
to sum up
Replacing LED lights allows users to enjoy the benefits of LED lighting work and control while using traditional power infrastructure. PoE supports LED lighting networks that use installations, maintenance, and retrofits that are simpler and less expensive than traditional power infrastructure. The PoE-powered LED lighting network provides the ability for property managers and building owners to dynamically monitor and control each LED light like never before. Because PoE-powered LED lighting networks are easily integrated with other components, such as sensors and wireless communication modules, they provide a way to adapt to the future and easily support new features that are emerging in IoT.
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