The hottest point is the high-power LED for the li

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High power LED driving power supply scheme for street and parking lot lighting

with the increasing awareness of energy conservation and environmental protection, the industry is paying more and more attention to the impact of energy consumption on the environment. In various ways of energy consumption, according to statistics, up to 20% to 22% of electric energy is used for lighting. Improving the energy efficiency of lighting applications and even further reducing their energy consumption will help to reduce carbon dioxide emissions and create a greener world. Therefore, energy-efficient lighting is becoming a focus of competition in the industry

from the perspective of application fields, lighting covers residential lighting, industrial lighting, street lighting and restaurant, retail and service lighting. In terms of power level, in addition to low-power lighting, it also includes high-power area lighting. Typical applications include outdoor lighting such as column lights, wall washing lights, exterior wall lights, tunnel lighting, street lights, parking lot and public safety lighting, industrial and retail lighting, as well as indoor lighting such as low ceiling lights, high ceiling lights, freezers/refrigerators and parking garages

there are many challenges in high-power area lighting, such as the lamps may be difficult to access, the light source failure may bring safety problems, and there are many extreme environmental conditions outdoors. In addition, it can not be ignored that the existing light sources (such as metal halogen lamp, high-pressure sodium lamp, linear fluorescent lamp and compact fluorescent lamp) applied to high-power area lighting have many limitations, such as poor color rendering of high-pressure sodium lamp (CRI is about 22), high loss of typical lamps of metal halogen lamp (40%), and the time from start to light to complete brightness may be as long as 10 minutes, and the cold temperature performance of linear fluorescent lamp is poor, Compact fluorescent lamps also start slowly

Figure 1: example of intelligent dual brightness LED street lighting

on the other hand, with the continuous improvement of high brightness white light emitting diodes (LEDs) in performance and cost, they are increasingly used for high-power area lighting, and provide advantages that traditional light sources do not have, such as less power consumption per lumen, better directional control, better color quality, environmental protection, and their opening and closing can be controlled more easily, It is convenient to automatically detect the ambient light to change the brightness; In addition, led reliability is also better, which is conducive to reducing maintenance costs and total cost of ownership

led area lighting application requirements

the main function of LED driver is to lower the current under a variety of conditions, protect the LED from surges and other fault conditions, and provide a certain level of safety to avoid (Electrical and/or mechanical) vibration and fire. For area lighting applications, the outdoor environment will bring temperature challenges to LED drivers, and may need to withstand AC input voltages higher than the standard voltage, such as 277 VAC, 347 VAC, or even 480 vac

LED drivers for area lighting applications may also need to meet certain specifications and standards related to power factor or harmonic content. For example, the IEC standard of the International Electrotechnical Union (IEC) of the European Union puts forward requirements for the harmonic content of lighting equipment (Class C) with a power of more than 25 W, which is equivalent to a total harmonic distortion (THD) of less than 35%; However, compliance with IEC class C harmonic content does not necessarily mean that the power factor (PF) is higher than 0.9. Some markets (such as the United States) often require pf higher than 0.9 and thd lower than 20%

many area lighting applications are outdoors, which may be subject to various strict temperature conditions, thus affecting the overall service life. The overall system design has an important impact on the service life, so it is very important to use a high-energy LED Driver with less internal heating and lower loss. In addition, the driver should be thermally isolated from the LED heat source in the design, so as to enhance the reliability of the system

led lighting control can also become more intelligent. Traditional streetlights come from the main control with timers or ambient light sensors. Using power line communication (PLC) or wireless control technology, it can provide highly flexible led regional lighting control, such as centralized control of light output level based on time, light emission level control based on traffic flow sensor, and regulation of downtown lighting according to detection of human and vehicle activities, taking into account pedestrian vehicles and street lighting. LED intelligent control technology can save electric energy without compromising safety. Typical applications are intelligent dual brightness level lighting, such as the lighting of parks, gas station ceilings, parking places, stairs and refrigerator boxes, which support the lighting of adjusting the brightness level according to needs. The LED can be turned on and off instantly, and the lighting level can be easily adjusted according to the action or activity in these applications, such as providing 20% - 40% brightness level when no activity is detected, and providing 100% brightness lighting when activity is detected. This will help to save a lot of additional power consumption

led area lighting power supply architecture and typical LED driving scheme

1) distributed/modular scheme suitable for linear lamps, trunking lamps and other applications

in high-power LED area lighting applications, a common power supply architecture is a three-stage architecture of "power factor correction (PFC) + constant voltage (CV) + constant current (CC)". In this architecture, after power factor correction and isolated DC-DC conversion, the AC input power supply outputs a fixed voltage of 24 to 80 VDC to the constant current LED module with built-in DC-DC step-down conversion circuit (see Figure 2). The design of this architecture provides a modular approach that can be upgraded on site. The number of LED light strips can be flexibly changed according to the actual needs, so as to increase or reduce the light output and meet the requirements of specific regional lighting applications. Under this architecture, AC-DC conversion and LED drive circuit are not integrated, but distributed configuration is adopted, which not only simplifies safety considerations but also enhances system flexibility. It is also called distributed scheme. Typical applications include linear lamp and trunking lamp

Figure 2: schematic diagram of typical modular led area lighting power supply architecture

under this modular approach, a design can be extended to a variety of light output levels. Moreover, with the enhancement of LED light output performance, the LED module needs to provide the same light output level, and the required light bar is better. Each light bar is equipped with a special DC-DC LED driver, such as the cat4201 high-energy step-down LED driver of Anson semiconductor. Cat4201 is specially optimized for driving high current LED, and adopts patented switch control algorithm to provide energy-efficient and accurate LED current stabilization (up to 350 MA). Cat4201 can be powered by up to 36 V power supply voltage and is compatible with 12 V and 24 V standard lighting systems. Figure 3 shows the high-voltage LED driver configuration of cat4201. The peripheral n-channel MOSFET supports high-voltage input: the LED power reaches 30 W at 100 V input voltage; LED power reaches 13 W at 50 V input

figure 3:cat4201 high voltage LED driver configuration

2) integral/single-stage scheme suitable for wall washing lamps, exterior wall lamps and other applications

not all regional lighting applications require distributed/modular schemes. With the rapid improvement of white LED performance, the new LED has been able to cooperate with the new LED driver design method. Leading LED manufacturers have introduced new LEDs that support higher current and have higher luminous performance, such as Cree's XP-G series LEDs (with a forward voltage drop of 3.3 V) that can provide 330 lumens of light output at 1 a current, and Seoul semiconductor's P7 series LEDs (with a forward voltage drop of 3.3 V) that can provide 400 lumens of light output at 1.4 a. Under this condition, a novel LED driver can be configured to directly drive a large current of 1 A to 3 a. For example, the ncl30001 power factor correction triac dimmable LED driver of Anson semiconductor can be used

ncl30001 is an integral/single-stage LED driving scheme, which integrates PFC and isolated DC-DC conversion circuit, and provides constant current to drive led directly. This scheme is equivalent to integrating the AC-DC conversion and LED drive circuits, both of which are located in the lighting fixtures, eliminating the linear or DC-DC converter integrated in the LED light bar. This integrated scheme has fewer power conversion sections, reduces the number of components (such as optical components, LEDs, electronic components, printed circuit boards, etc.), reduces system costs, and supports higher overall energy efficiency of LED power. Of course, this scheme has a higher power density, which may not be suitable for all regional lighting applications. Its optical pattern may be more suitable for low-power led. Typical applications include LED street lights, exterior wall lights, wall washing lights and refrigerator box lighting

ansenmey semiconductor has developed a single-stage high power factor led driver demonstration board with a power of 90 W, a current of 0.7 a to 1.5 A, and a voltage lower than 60 v. The demonstration board adopts ncl30001 LED driver and ncs1002 secondary terminal constant voltage and constant current (CVCC) controller with pulse width modulation (PWM) dimming function (see Figure 4), which is suitable for LED street lights and other regional lighting applications

Figure 4: 90 w LED driver demonstration board circuit based on ncl30001 LED driver and ncs1002 controller

the 90 w constant voltage and constant current demonstration board accepts an extended general input voltage of 90 to 265 VAC (305 VAC can be supported under the condition of replacing components), provides a constant current output range of 0.7 a to 1.5 A (which can be selected by slightly adjusting the resistance) and a constant output voltage range of 30 V to 55 V (which can be selected by the resistance divider), The maximum output power is 90 W, supports 50 to 1000 Hz dimming control, and includes a 6-pin interface that can be connected to an optional dimming card for intelligent dimming applications such as analog current regulation/dual brightness level digital dimming. In addition, the demonstration board also provides rich protection features such as short-circuit protection, open circuit protection, over-temperature protection, over-current protection and over-voltage protection. The test shows that the energy efficiency of this demonstration board is higher than 87% under the conditions of 50 W output power, 1000 mA output voltage/48 V forward voltage drop (see Table 1 for details), and the power factor is higher than 0.9 under the conditions of 50% to 100% load. At the same time, it meets the IEC class C equipment harmonic content standard

Table 1: energy efficiency test results of 90 w LED driver demonstration board based on ncl30001 and ncs1002

3) high energy efficiency LLC topology driving power supply for higher power regional lighting applications

in recent years, the industry has become increasingly interested in ultra-high energy efficiency LED lighting topology, and it is expected to provide high energy efficiency (such as higher than 90%) in higher power 50 W to 250 W led regional lighting applications. To provide such high energy efficiency, we need to adopt a high-energy power topology, such as resonant half bridge dual inductor plus single capacitor (LLC) topology, so as to give full play to the advantages of zero voltage switching (ZVS)

in such higher power led regional lighting applications requiring ultra-high energy efficiency, consumers are increasingly concerned about environmental protection. We can combine the ncp1607 PFC controller of ansenmey semiconductor and the ncp1397 dual inductor plus single capacitor (LLC) half bridge resonant controller for high-energy LED street lighting applications with power in the range of 50 to 300 W. Ncp1397 is a high-performance resonant mode LLC controller, which integrates a 600 V high-voltage floating driver, supports high-frequency operation from 50 to 500 kHz, and has built-in high-end and low-end drivers. It supports adjustable and accurate lowest frequency. It is elegant, convenient and fast, provides high energy efficiency, and has a variety of fault protection features

Figure 5: energy efficient LED power supply scheme for street lighting based on ncp1607 and ncp1397

protection scheme to enhance the reliability of LED strings

multiple strings of LEDs are usually used in regional lighting applications. Although the LED itself has high reliability, if one of the LEDs in the LED string is open circuit, the whole string of LEDs may be turned off, which should be avoided in street lighting and other applications, so as to reduce the later maintenance cost. Anson semiconductor introduced the nud4700 LED current bypass protector. This device is a

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