Efficient lighting has been a hot topic in recent years. With the elimination of incandescent lamps, compact energy-saving lamps are becoming more and more accepted by everyone. According to the International Energy Agency (IEA) report, global electric lighting accounts for about 19% of total generating capacity. In addition, ENERGY STAR® also plans to set standards for home and commercial lighting. However, in these news, it is ignored that about 70% of lighting energy consumption is outside the home, including shops, factories, schools, hospitals and district lighting; regional lighting covers such as street lighting, parking lots and parks. And other applications of public space.
Regional lighting must also address public safety, operating environment, design and aesthetics, energy efficiency, system reliability, and maintenance costs while providing lighting. The most common area illumination sources are high voltage discharge (HID) types, such as high pressure sodium lamps, metal halide lamps, and low pressure sodium lamps and high pressure mercury lamps. Advanced HID lamps, such as metal halide lamps, have a high energy efficiency of more than 80 lm/W and a reasonable life of 10,000 to 15,000 hours. The standard is 4,000 hours per year and the life expectancy is about 2 to 4 years. However, due to the difficulty of replacement, it is quite expensive in terms of maintenance time or labor cost, and it is a big problem in tunnels or bridges. In addition, most HID lamps contain mercury, so they must be handled with care after replacement to avoid environmental problems.
High-brightness white LED technology continues to advance, providing a promising solution for energy-efficient lighting applications. The most important reason for the popularity of high-brightness white LEDs is their long life and luminous efficiency. When its brightness is maintained at 70%, the life span can reach 50,000 hours, and the outdoor area lighting can reach 12 years of running time. Amplify subsequent maintenance and replacement costs. High-power white LEDs that have been commercialized at present can achieve a luminous output of 80 to 120 lumens per lamp with an efficiency of approximately 80 lm/W. As a reference, a 100 W metal halide HID lamp can produce approximately 8000 lumens of output, and the luminosity of the HID tube. The output is omnidirectional, so there is a lot of loss in the light projection path, but the LED does not have this problem, because it has directivity, about 110 LEDs per package can replace the lumen output of the 100WHID lamp.
LED lighting can be composed of one or more LED arrays, which converts AC power into a control circuit for the current used by the LEDs. Therefore, it is possible to consider a modular design that includes a string of LEDs and drive circuits. The advantage of this concept is the same circuit. The design can be reused by adding more arrays to different lighting needs. In addition, due to the use of multiple arrays in the illumination source, if there is a problem with a single LED, only a portion of the LEDs will cease to function, and the entire illumination source will still provide a lower brightness illumination output. LED lighting sources must also comply with industry and international harmonic standards. In the European Union, such products are subject to IEC61000-3-2 and other power line harmonic distortion (power factor) specifications, although not used in the United States and other places, However, the power company will also require a power factor of at least 0.9 for area lighting that is not metered.
Another consideration is the security of isolation. For area lighting sources that are not easily replaceable, non-isolated designs are quite common. The main advantage of non-isolated designs is the replacement of bulky transformers with lower cost inductors. The actual demand considerations for driving LEDs are also very important. Although LEDs require constant current drive, this current does not necessarily need to be pure DC, so it can also be driven by pulsed DC waveforms, as long as the average and maximum current values ​​match the LED itself. The specified current specification is sufficient. Therefore, we can use ON Semiconductor's NCP1216 control chip with a high-power MOSFET, an inductor, and a few external passive devices to implement a simple and energy-efficient PFC and constant current converter on a single-power stage circuit. The output usually does not need to filter out the frequency component of the 100/120 Hz main power supply, so it is not necessary to use large electrolytic capacitors in the circuit, which not only can reduce the circuit size, but also improve the reliability of the overall power supply. The following is the circuit diagram of the relevant circuit. .
Figure 1: Circuit design of 115 Vac, 350 mA configuration
This circuit diagram shows the most basic implementation of a non-isolated converter circuit. It is a buck converter circuit that rectifies AC power from D1 to D4 and then through inductor L1, MOSFET-Q1, output capacitor C4, and controller. In this particular circuit with a 90 to 135 Vac input, a simple feedback network consisting of a parallel current sense resistor R4, integrating circuits R6 and C6, and a photocoupler allows the circuit to operate in a constant current output mode. Usually, a photocoupler is not needed in a non-isolated design, but it is used here to shift the current sensing signal at the top of the LED string. The special implementation of this circuit enables it to provide high power factor and constant current. Output, buck input capacitor C2, also commonly referred to as buck capacitor, must have high impedance to the 120 Hz full-wave rectified waveform appearing on the input bridge rectifier circuit, otherwise the power factor will appear as a capacitive input filter In the case of significant degradation, this capacitor typically has a value in the range of 0.1 μF to 0.47 μF, depending on the target output power of the circuit. The inductance of L1 should be low enough to allow the buck converter to operate in discontinuous conduction mode, which is important for the high power factor of the circuit. In the discontinuous conduction mode, the value of C4 can also be quite small, about 1 to 5 μF, because it only needs to be used to filter out the high frequency switching components in the current waveform, and a low ESR polypropylene film capacitor should be used.
Figure 2: Input voltage and current waveforms
Vin = 115 Vac, Vf = 31 V, Iout = 350 nom
Figure 3: Relationship between power factor and current regulation versus LED forward voltage
Vin = 115 Vac
As can be seen from the above, ON Semiconductor has developed an optimized high power factor single-stage LED driver circuit that can be used to drive LED arrays. Although the operating voltage of the circuit in the example is 115 Vac, we can change the value of the device. For 230 Vac applications, the number of drive LEDs can be multiplied.
The use of LED arrays in regional lighting applications has received global attention. Many government organizations also understand the advantages of LED technology. This is evident from the extensive introduction of traffic signals. They also understand that long-life products do not require the same maintenance costs. . For example, in the city of Raleigh, North Carolina, the 140 120W high-pressure sodium lamps in the parking lot were replaced by LED lighting devices, reducing energy consumption by 40%, and there is almost no annual maintenance cost. In the future, more LEDs will be applied to more regional lighting, especially for lower power lighting applications requiring only a small number of LEDs and for the design where the photometric output can be adapted to the specific needs of the application. For these applications, optimizing the driver circuit to meet power and specification requirements, as well as the flexibility to meet changing LED configurations, can achieve the widely adopted economic cost targets.
Electirc Healthy Teapot,Glass Teapot,Electric Teapot,Multi Function Health Teapot
Shaoxing Haoda Electrical Appliance Co.,Ltd , https://www.zjhaoda.com