Led lighting is a near-mainstream technology, and the replacement of led lights allows property managers and owners to enjoy the long working life and energy-saving characteristics of LEDs using traditional power infrastructure. Local area network (LAN), Power over Ethernet (PoE) technology provides unprecedented ability to dynamically monitor and control each LED light as well as intelligent led lighting/sensor concentrators.
The application advantages of LEDs are constantly evolving and mature, and will become the first choice for more and more traditional and new lighting applications. The advantages of LEDs include longer working life, higher energy efficiency and a small form factor. For example, LED lamps have a working life of 50,000 hours, far exceeding the typical operating life of incandescent lamps of 1,000 to 2,000 hours, and the life of compact fluorescent lamps (CFLs) of 5,000 to 10,000 hours. Therefore, LEDs are well suited for many commercial and industrial applications, and these industries have high requirements for energy efficiency.
The wavelength or color of the led illumination depends on the materials used in the LED construction. With the right driver, the LED will have greater design flexibility, allowing for dimming and changing the color of the illumination; when used with the appropriate controllers and sensors, the amount and color of the illumination can be adjusted according to changes in the environment. This capability makes it useful for indoor lighting as well as dimmable street lights and outdoor lighting, changing its brightness depending on ambient light changes. LED dimming saves about 1:1, which means that dimming the LED to 50% will save about 50% of the energy.
Designers continue to apply LEDs to a growing variety of lighting applications, and now discuss LED applications in both scenarios. Designers use led modules (such as MR16) in traditional luminaires. LEDs must work with existing power infrastructure to take advantage of LED lights. In contrast, Power over Ethernet (PoE) led lighting network or the parallel use of newer electrical infrastructure. Before discussing these applications, briefly review the led drive .
LED driver
The LED driver is a low voltage component that converts the input voltage (eg 120V, 220V or 277V) to the low voltage required by the LED, while these drivers also resolve the control signal, dim, brighten and change the color of the illumination (as shown in Figure 1). . LED drivers can be configured with constant current (eg 350mA, 700mA or 1050mA) or constant voltage (typically 12V or 24V), but these two types of drivers are not interchangeable. The luminaire manufacturer can choose the type and configuration of the drive to match the electrical requirements of the LED modules used in the luminaire. This article discusses 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. Designers can match the drive to the LEDs based on various combinations of application requirements, including the number of LEDs driven, the type of power supply, and the functional characteristics of the LED. Matching an improper LED driver actually shortens the operating life of the illuminator, causing unpredictable lighting problems, such as flicker.
If the amplitude 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 lamp is prone to flicker (cause of flickering) There are many, 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
LEDs can be used to replace other lighting technologies, especially incandescent and halogen lamps. When using LED lights for existing lighting infrastructure, there are two main challenges: First, the replacement lights must conform to the dimensions of conventional light sources; secondly, they must work without flicker in existing electrical infrastructure environments. Mounting LED lights to existing fixtures not only limits the size of the driver board, but also the thermal issues of the design itself.
Since LEDs emit only visible light and heat is higher than incandescent or halogen lamps, heat dissipation is one of the factors that limit the amount of illumination produced by the illumination. The LED technology used in today's replacement lamps almost does not reach the acceptable brightness level in the mainstream market. Increasing the brightness limit and improving the resulting thermal design are essential to designing a commercially successful product, but the thermal design will inevitably affect the life of the drive board. In order to emit more light, the illuminator must operate at a relatively high temperature (+80 ° C ~ +100 ° C), in this temperature environment, the driver circuit board that is easily affected by high temperature will limit the entire LED lamp life span.
In order to be able to work under existing electrical specifications, replacement LED lamps must work correctly with the infrastructure, but 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, the LED replacement lamp does not support the thyristor dimmer to work well because it does not provide the required starting current and does not provide the holding current. The result is that the dimmer does not start properly or is working. Turned off, causing the LED light to flicker.
The electronic transformer has its own design considerations: the load is required to be resistive, but the LED 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 lights is the need to develop 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 LED lamps to not work with the electronic transformer, and the dimmer further reduces the current, which exacerbates this difficulty. Maxim's MAX16840 LED driver solves this problem with its patented fixed-frequency, average current mode control method and is compatible with most electronic transformers and trailing edge dimmers.
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