Light-emitting diode (LED) lighting is becoming the industry's preferred technology, especially in harsh environmental conditions, LED solutions are durable and never completely fail, but the amount of light will indeed diminish over time. Using automatic dimming to measure the LED light output, while adjusting the power supply, can effectively maintain a constant light output throughout the life of the bulb. In this way, it can maintain stable brightness under different manufacturing methods and greatly extend the life of the lamp. This article will explain how to use various sensor technologies to operate and suitable for street, office and factory lighting circuit examples.
System-level ecological design must be comprehensive
As far as ecological design (Ecodesign) is concerned, for specific applications, extending the service life is always desired, because it is directly related to ecological impact (Ecological Impact). This is not as easy as imagined, because innovation never stops, the possibility of new standards and new applications must be taken into consideration, and new functions need to be implemented. The important thing is not to only implement the minimum standards, but also to build better products that are preloaded with various new features and at the same time bring some flexibility. The NASA's "Mars Rover" is a good example. A lot of technical support has helped the introduction of this project and made the project start-up time greatly advanced.
In addition to flexibility, the possibility of LEDs having such a long life is also important. For this, there are three types of effects that need to be considered: the effects of rapid changes (such as turn-on current), the effects of slow changes (such as drift), and external influences.
For all applications, the on-current is an important stress. The large bus capacitors in the power supply are the main cause of this stress. In addition, the ambiguous state when the power is turned on may put stress on the application. To avoid these conditions, you should use failure mode and effects analysis (FMEA) throughout the design stage to carefully analyze the circuit performance. In the completed application design, it is also necessary to check the current and temperature during the turn-on and turn-off process. In the design stage, two points may not be noticed, and the result often causes field failure in the later stage.
Figure 1 shows the temperature change of a power input bridge rectifier caused by the on-current. At this time, although the other components are in a cold state, the temperature of the rectifier is significantly increased, which may affect the service life of the product. Many applications developed 20 to 30 years ago use circuit technology that avoids drift-induced failures. Since many components used later have larger tolerance levels and greater drift, circuits that rely less on component characteristics have been developed. In order to prolong the service life of an application product, many of these technologies are not considered in today's ecological design, thus increasing the complexity of circuit design and increasing the number of components. The environmental impact of electronic circuits is usually lower than the impact caused by working energy consumption, and the extended service life can make up for the increased complexity.
Figure 1 Temperature change of power input bridge rectifier caused by on-current
Power electronics is an important part of all applications and products, especially in ecological design considerations, because the subsystem affects the environmental performance through efficiency and other characteristics, such as lower efficiency means that the application products must use greater heat dissipation Film, which consumes more energy during production and application, and must use more energy for transportation and recycling. Therefore, it is recommended that designers can consider the use of the highest efficiency and a larger input voltage range in order to reduce the number of components and obtain maximum flexibility, because this part cannot be changed in the future, such as the use of software modifications.
In lighting applications, the use of LED solutions is the general trend. In addition to having higher efficiency, the LED itself also has a long service life, and the LED drive electronic device should be designed to take advantage of the long-term service life of the LED. Figure 2 is a schematic diagram of such a lighting scheme.
Figure 2 Schematic diagram of LED lighting scheme
Street lighting is a special example of this type of lighting solution. There is no other lighting application combined with diversified requirements, such as temperature, humidity, vibration and other changing environmental factors, as well as high efficiency, high reliability and low power consumption requirements. All are within the considerations of lighting solutions, but also must consider mass production and bear the corresponding price pressure. As the power consumption of the lamp changes, the temperature will change from -40 ° C to 85 ° C, causing the temperature to rise significantly. It is important to note that each (daily) conduction cycle will trigger a temperature cycle, which means that at the system level, the bulb will have nearly two thousand temperature cycles in 5 years, which will bring great stress to the system .
Since the cost of street lighting is an important part of the urban budget, people pay special attention to the ability of high efficiency in order to help reduce the operating cost of street lamps. The goal is to use the least electrical energy to provide sufficient brightness for streets or sidewalks. This does not include the subsequent maintenance costs. If the lamp has a short service life, the maintenance cost will be more considerable. A rough estimate of the number of streetlights used by a certain population is based on the ratio of one streetlight for every six inhabitants. According to this ratio, there are about 13.3 million streetlights in Germany, and the energy saving potential is very alarming. Therefore, it is not surprising that many cities and communities have switched to using these new LED lighting solutions, partially replacing the entire bulb, or replacing the lamp head.
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