LED area lighting drive architecture and typical design

From the application field, lighting covers different categories such as residential lighting, industrial lighting, street lighting and restaurant, retail and service lighting. In terms of power level, in addition to low-power lighting, high-power area lighting, typical applications such as column lights, wall washers, exterior wall lights, tunnel lighting, street lights, parking lots and public safety lighting, industrial and retail lighting, etc. Outdoor 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 possibility that the luminaire may be difficult to access, the safety problem may occur when the light source fails, and there are many extreme environmental conditions in the outdoor. In addition, it should not be overlooked that existing light sources (such as metal halide lamps, high pressure sodium lamps, linear fluorescent lamps, and compact fluorescent lamps) used in high-power area lighting have many limitations, such as poor color rendering of high-pressure sodium lamps (CRI is about 22), the typical luminaire loss of metal halide lamps is higher (40%) and the time from start to illuminate to full brightness may be as long as 10 minutes, the cold temperature performance of linear fluorescent lamps is poor, and the starting speed of compact fluorescent lamps is also higher. SLOW.

On the other hand, as high-brightness white light-emitting diodes (LEDs) continue to improve in terms of performance and cost, they are increasingly used for high-power area lighting and offer advantages not found in traditional light sources, such as emitting light per lumen. It consumes less power, has better direction control, better color quality, is environmentally friendly, and can be more easily controlled by turning it on and off, allowing automatic detection of ambient light to change brightness; in addition, LED reliability is better, which is beneficial to the LED. Reduce maintenance costs and total cost of ownership.

First, LED area lighting application requirements

The main function of the LED driver is to flow at a lower limit of various conditions and to protect the LED from surges and other fault conditions, as well as to provide a level of safety against vibration and ignition (electrical and/or mechanical). For regional lighting applications, outdoor environments present temperature challenges to LED drivers and may require AC input voltages higher than the standard voltage of 277 Vac, 347 Vac, or even 480 Vac.

LED drivers for regional lighting applications may also need to meet certain specifications for power factor or harmonic content. For example, the European Union's International Electrotechnical Union (IEC) IEC61000-3-2 standard requires harmonic content of lighting equipment (class C) with a power exceeding 25 W, equivalent to a total harmonic distortion (THD) of less than 35%; However, compliance with IEC61000-3-2 Class C harmonic content requirements does not necessarily mean that the power factor (PF) is higher than 0.9. In some markets (such as the United States), PF is generally required to be higher than 0.9 and THD is less than 20%.

Many regional lighting applications are outdoors and may withstand a variety of stringent temperature conditions, which can affect overall service life. While the overall system design has a significant impact on service life, it is important to use an energy-efficient LED driver with less internal heat generation and lower losses, and to thermally isolate the driver from the LED heat source in the design to enhance system reliability.

The control of LED lighting can also become more intelligent. Traditional street lights come from the main control with a timer or ambient light sensor. The use of power line communication (PLC) or wireless control technology can provide highly flexible LED area lighting control, such as time-based light output level centralized control, vehicle flow sensor based lighting level control, and control based on detection of people and vehicle activity. Downtown lighting, taking care of walking cars and street lighting. LED intelligent control technology saves energy and does not compromise safety. Typical applications include smart dual-brightness lighting, such as parks, gas station ceilings, parking lots, stairs, and refrigerator cabinet lighting that support lighting levels that adjust brightness levels as needed. LEDs can be turned on and off instantly, allowing for easy adjustment of lighting levels based on motion or activity in these applications, such as providing 20%-40% brightness levels when no activity is detected and 100% when activity is detected Brightness lighting. This will save a lot of extra power consumption.

Second, LED area lighting power supply architecture and typical LED driver solution

1) Distributed/modular solutions for applications such as linear lamps and trunking lamps

In the high-power LED area lighting application, a common power supply architecture is a three-stage architecture of "power factor correction (PFC) + constant voltage (CV) + constant current (CC)". In this architecture, the AC input power supply is subjected to power factor correction and isolated DC-DC conversion, and a fixed voltage of 24 to 80 Vdc is output to the constant current LED of the built-in DC-DC buck converter circuit. Module (see Figure 2). The design of this architecture provides a modular approach to field upgrades that can flexibly change the number of LED strips as needed to increase or decrease the light output to meet specific area lighting application requirements. In this architecture, AC-DC conversion and LED driver circuits are not integrated, but distributed configuration, which simplifies security considerations and enhances system flexibility. It is also called distributed solution, typical application. Including linear lights and trunking lights.

In this modular approach, a design can be extended for multiple light output levels. Moreover, as the LED light output performance is enhanced, the LED module must provide the same light output level, and the required light bar is better. Each strip has a dedicated DC-DC LED driver, such as the CAT4201 high-efficiency buck LED driver from ON Semiconductor. Optimized for driving high current LEDs, the CAT4201 features a patented switching control algorithm that delivers energy efficient and accurate LED current regulation (up to 350 mA). The CAT4201 can be powered from a supply voltage of up to 36 V and is compatible with 12 V and 24 V standard lighting systems. Figure 3 shows the high-voltage LED driver configuration of the CAT4201. The peripheral N-channel MOSFET supports high-voltage input: LED power is 30 W at 100 V input voltage and 13 W at 50 V input.

2) Integrated/single-stage solution suitable for applications such as wall washers and exterior wall lamps

Not all regional lighting applications require a distributed/modular approach. With the rapid improvement of white LED performance, new LEDs can be used with the new LED driver design method. Leading LED manufacturers have introduced new LEDs that support higher currents and higher luminosity, such as CREE's XP-G series LEDs (with a forward voltage drop of 3.3 V) delivering 330 lumens at 1 A. Seoul Semiconductor's P7 series LEDs (3.3 V forward voltage drop) provide 400 lumens of light output at 1.4 A. Under these conditions, a novel LED driver can be configured to directly drive a large current of 1 A to 3 A. For example, an NCL30001 power factor corrected TRIAC dimmable LED driver from ON Semiconductor can be used.

The NCL30001 is a monolithic/single-segment LED driver solution that integrates a PFC and isolated DC-DC converter circuit and provides a constant current to directly drive the LED. This solution is equivalent to converting AC-DC with The LED driver combines the two parts of the circuit, all located in the lighting fixture, saving the linear or DC-DC converter integrated in the LED strip. This monolithic solution has fewer power conversion segments, reduces component usage (such as optical components, LEDs, electronic components, and printed circuit boards), reduces system cost, and supports higher overall energy efficiency of LED power supplies. Of course, this solution has higher power density and may not be suitable for all area lighting applications. Its optical pattern may be more suitable for lower power LEDs. Typical applications include LED street lights, exterior wall lights, wall washers and refrigerator cabinets. Lighting, etc.

The 90 W constant voltage constant current demo board accepts an extended universal input voltage of 90 to 265 Vac (supports 305 Vac for component replacement) and provides a constant current output range of 0.7 A to 1.5 A (selectable with a micro-amplitude resistor) And a constant output voltage range of 30 V to 55 V (selectable by resistor divider), maximum output power of 90 W, support for 50 to 1,000 Hz dimming control, and 6-lead connection to an optional dimming card Foot interface for analog dimming applications such as current regulation / dual brightness level digital dimming. In addition, the demo board provides a wide range of protection features such as short circuit protection, open circuit protection, over temperature protection, over current protection and over voltage protection. Tests show that the demo board has an energy efficiency of more than 87% at 50 W output power, 1,000 mA output voltage / 48 V forward voltage drop (see Table 1 for details), and power factor is higher at 50% to 100% load. 0.9, in line with IEC61000-3-2 Class C equipment harmonic content standards.

3) Energy-efficient LLC topology drive power for higher power area lighting applications

In recent years, the industry has become increasingly interested in ultra-high-efficiency LED lighting topologies, expecting to provide energy efficiency (eg, above 90%) in more powerful 50 W to 250 W LED area lighting applications. To provide such high energy efficiency, an energy-efficient power supply topology, such as a resonant half-bridge dual inductor plus single capacitor (LLC) topology, is required to take advantage of zero voltage switching (ZVS).

In this type of ultra-high-power LED area lighting application that requires ultra-high efficiency, it can be combined with ON Semiconductor's NCP1607 PFC controller and NCP1397 dual inductor plus single capacitor (LLC) half-bridge resonant controller for power generation at 50 Energy efficient LED street lighting applications in the 300 W range. The NCP1397 is the latest high-performance resonant mode LLC controller with integrated 600 V high voltage floating driver, supports high frequency operation from 50 to 500 kHz, built-in high-end and low-end drivers, supports adjustable and accurate minimum frequencies, and provides extremely high energy efficiency. And a variety of fault protection features.

Third, enhance the protection scheme of LED string reliability

Multi-string LEDs are often used in area lighting applications. Although the LED itself is highly reliable, if one of the LED strings is open, the entire string of LEDs may be turned off, and this situation should be avoided in applications such as street lighting. Reduce post-maintenance costs. ON Semiconductor has introduced the NUD4700 LED current bypass protector. This device is a shunt device. If an LED in the LED string is open, it will provide current bypass to ensure that the entire LED will not turn off under the condition of a certain LED failure; and it can also support proper heat dissipation. Large currents greater than 1 A.

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