The LED market is very hot. With the increase in energy costs, as well as the concern for climate change, the national government and industry began to promote efficient lighting solutions. LED with high efficiency and long life characteristics, and therefore is an excellent solution. Same time, LED technology is undergoing a period of rapid change and innovation process, and will continue to introduce a brighter and more efficient products, but this will make the most of the engineers is difficult to keep up with the pace of the latest products. Fortunately, assist in the selection of LED components, and product planning and design tool program has been very well, which will make the engineers in the choice of the appropriate LED and LED driver easier. Even with a powerful design tool, but engineers still need to know what are the parameters of choice will affect the LED can truly play the maximum effectiveness of the tool.
How to select LED
The first step is to choose the LED color. Variety of different colors of LED mainly because of the different dominant wavelength and wavelength in the ultraviolet to infrared range. The white LED is set for its color temperature warm white LED is usually a color temperature of 2800K to 3500K range, suitable for interior lighting. Compared with white LED, the traditional ordinary incandescent light bulbs color temperature range of about 3000K. The cold white LED color temperature range from 6300K to 7500K region, while the white LED is the middle of the range from 3600K to 6200K.
The individual high-brightness LED luminous flux value is usually less than 100 lumens (although the values are rapidly rising). Therefore, in most applications in the form of the LED into an array, in order to achieve higher brightness. Multiple LED lighting they use a combination of parallel string array, and a single current control driver to drive. However, a parallel may be because the LED forward voltage and flowing through each light string within the current, leading to string lights produce different brightness. Therefore, it is best to use a series of LEDs, the brightness and color to be consistent. However, the series voltage will be increased with the use of more of the LED, so will affect the drive topology, buck and boost.
led driver 120w is directional characteristics in different angles will show different brightness, the conditions of a certain perspective, we have observed the brightness may be reduced to 50%. Directional applications, the actual perceived brightness will be higher than the spherical luminous point light source. In other words, if some applications require using a spherical light-emitting way, you must design for the application corresponding to the array, you can use the optical diffusion or focus the light.
Lighting component efficiency measurement basis for the luminous efficiency in units of lumens / watt. Surge in the number of LED R & D and design, making a rapid increase of 75 lm / W luminous efficiency value component on the market recently he's begun with 115 lm / W LED. Luminous efficiency using the same criteria to compare different light sources, incandescent light bulbs about 17 lumens / watt, energy saving bulbs is about 60 lumens / watt, and 100 of the low-pressure sodium street light 200 lumens / watt.
Voltage and current
The LED forward voltage is a characteristic of the LED process, In general, yellow / orange / red LED forward voltage value in the range 2-3V, and blue / green / white LED along the voltage value the range of 3-4V. Flow through the LED current control LED brightness, also affect the rendering of color, the LED will operate in constant current mode. High Brightness LED will usually use 0.35A, 0.7A, 1.0A, 1.4A above the current. Also need to consider is the size and height of the LED. The products must be provided with cooling function, this function will be the key to high-current applications. Of course, cost is another key parameters need to be taken into account together.
Easier to choose the LED
Many LED Flood light 10W suppliers have launched online selection tool, LED selection easier. These tools can be compared a variety of solutions and provides graphical analysis, which allows the LED design engineers to quickly obtain the best solution.
LED temperature control
If the LED is so efficient, why do we need for temperature control and monitoring of the LED? LED operation temperature not lower than the incandescent light source? Proved, the LED with better efficiency than incandescent light bulbs, but still generated a lot of heat. Incandescent bulbs produce heat via infrared radiation, heat, However, the LED semiconductor diode structure in addition to production of heat, will produce photons. This heat does not belong to the radiation spectrum, by means of conduction and convection to exclude.
If the LED Spotlight 30W operation in hot conditions, certain problems may arise. LED brightness will darken as the temperature rises significantly. In addition, the LED color will change as the temperature changes, so may need to keep the color consistent application, such as the white light generated from the RGB. In the design of the drive circuit, should take into account the electronic properties of this type of LED forward voltage due to temperature change, change, if the LED current sharing in parallel configuration, the LED forward voltage changes may also be a problem. Long-term exposure to high junction temperature environment will accelerate the LED aging, and reduce its service life and reliability. Therefore, in designing the system, must make the LED temperature specifications within the scope of the operation. This is usually a heat sink to achieve their goals, such as a printed circuit board copper area, additional radiator, or use as heat-resistant / metal printed circuit board (PCB) to load the LED; can also be use of forced air flow.
However, fever or heat sink for abnormal climate change such as the failure accident situation, you can implement a fail-safe mechanisms to deal with. Most of the buck topology LED driver has a thermal shutdown feature, so if the drive beyond the specified temperature (usually 125 to 150 ° C), closes the drive LED. Boost topology drive will protect itself, and not loaded when in the closed circuit of the pry bar or other protective devices, so the need for the use of LED. In either case, the temperature of the LED may be higher than the temperature of the drive, so the LED itself needs its own temperature sensor and control circuit fail-safe protection device. This temperature sensor can reduce or turn off the LED current, open cooling fan, the alarm mechanism and the user or maintenance personnel.
LED Floodlight 80W temperature sensor type
In general, the accuracy of the temperature sensor must provide sufficient flexibility to be able to detect the temperature of overheating, while not in the normal operating temperature to trigger a fault warning. For example, if the system's normal operating temperature is 80 ℃, and the need to detect fault conditions does not exceed 100 ° C, then use the + / - 2 ° C accuracy temperature sensor system, can be allowed to set the value of 90 ℃ to 98 ℃ can be, but if use the + / -10 ° C accuracy temperature sensor system, will allow the value is set to the minimum value.