Author: ◆ Cypress Semiconductor Product Manager / Adam Eades High-brightness LEDs are semiconductor components, and unfortunately, like all semiconductor components, even the components produced on the same wafer have different electronic characteristics. For LEDs, such differences can cause differences in color (or wavelength), luminous flux output, and forward voltage. LED manufacturers place these parts in specific bins based on productivity and performance. This binning categorization program will affect your product design load current and how much LEDs are used in your design. In order to solve this problem, some designers would rather pay a price to purchase a specific bin, but this still can not solve the color accuracy of the LED system, because the specific size of these bins is still +/-5nm visible to the naked eye. tolerance scope,. In terms of color mixing systems, such as theater lighting, building lighting, etc., the system color gamut specifications are quite important. The gamut is made up of LEDs used in the system. Color gamut refers to all possible colors that the system can output by individually changing the luminous flux of each LED output. When designing a system, first determine the color requirements, then select the LED. This will again cause a problem when dealing with manufacturing bin units. If you do not get the pre-planned LED specifications for your lighting system, your system gamut will deviate from the actual results and the output color will be different than expected. Output the color you want Design LED control mechanisms for your system, facing basic linear algebra. After getting the chromaticity coordinates of your LED, you must first create a matrix to find the delta value between the desired color points, as shown in Equation 1. The color subscript in the formula is the color of the LED, and the mix subscript represents the color you want to render. For accurate color output, it depends on the application you are designing. Whenever the end user notices a difference in the color output of the fixture (such as building lighting or effect lighting), it means that high color accuracy is required. However, in these two examples, color sensors are not an ideal solution. To find acceptable color accuracy, start with dynamic color changes that are derived from the effects of LED junction temperatures and their characteristics. This can be solved with a firmware or a thermostat. Color sensors are recommended for high color accuracy design. However, when trying to develop a color feedback system, there are many mechanical problems. The placement of the sensor is as important as the temperature sensor solution. The low-cost color sensor does not face the light of the LED, and the ideal placement of the color sensor is the input that can receive reflection or tightly combine light. In the ideal position of the color sensor, the same light input can be seen by the end user, so that the most desired feedback data of the system can be obtained. But when designing a color sensor, the most annoying problem is the effect of light noise or ambient light generated by the system on the color sensor. The color sensor requires two mechanisms to operate correctly; the first is the relationship between the color sensor and the individual intensity values ​​of the red, green, and blue LEDs; the second is the relationship between the color sensor and X, Y, and Z. All corrections must be made in the firmware, but the benefits of this type of feedback system will increase the robustness and precision. Many color system designs have different feedback methods and take months to develop firmware. Resolving bin adjustments, temperature compensation, or higher precision color feedback systems and calibrations requires knowledge of color science and accurate sensor readings. When developing any high-brightness LED design, it is highly recommended that you first understand these related terms. Fortunately, when you get to market, you can take advantage of Cypress Semiconductor's fast and easy PSoC Express 3.0 solution to help you get started quickly. All of these different feedback solutions, as well as the compensation mechanism for high-brightness LEDs, are included in an easy-to-use graphical interface that allows you to complete these designs with just a drop-down menu and various calibration techniques. The firmware described in this article is built into the PSoC Express software tool. This software tool also allows you to build a network for your system using DMX512 with only three variables defined. Dongguan Guancheng Precision Plastic Manufacturing Co., Ltd. , https://www.dpowergo.com
Traditional incandescent bulbs are now being phased out around the world. Not only government agencies, but also civilian users require more efficient lighting solutions. A sophisticated fluorescent bulb (CFL) is not the best solution to this problem. But it has won the incredible long life of incandescent lamps and higher efficiency, enough to make it a tempting solution to your problem. However, the mercury content of the CFL makes subsequent problems such as disposal and disposal more complicated. High-brightness LEDs (HB LEDs) or high-power LEDs (HP LEDs) are now considered the ultimate solution because of their higher power-saving efficiency (even beyond CFL) and longer life. These LEDs have been used in automotive lighting, building lighting, stage lighting, and certain indoor lighting applications. Many of these systems use multiple LEDs to achieve the desired color in a mixture of color and light; or in a white light application, a single or multiple LEDs to achieve the desired color rendering index (CRI) or relative color temperature (CCT) ). The complexity of these systems will increase, because your system will not only face many design constraints, but the LED itself will gradually lead to many problems. Solving these problems will require intelligent firmware, feedback mechanisms that depend on the required accuracy, and control of these lighting systems through communication networks such as DMX512 and DALI.
High-brightness LED design challenges
In addition to various manufacturing issues, LED characteristics such as luminous flux output and wavelength will also vary due to junction temperature and LED usage hours. Each colored LED is affected by temperature to varying degrees, depending on the material of the LED. The red and amber LEDs are most affected when the contacts are raised, while the blue and white LEDs are the least affected (see Figure 1). In these lighting systems, each LED is affected in a certain order because the desired color point or CCT is convertible unless your system is adaptable to changes in LED characteristics. The design sequence for aging effects requires extremely high color accuracy. Because when the LED ages, the luminous flux of the output will gradually decline.
The power topology is another issue that LED design has to solve, but it is beyond the scope of this article and it is related to the number of system LEDs and power components.
Build your color gamut
Defining your color gamut is not easy. The chromaticity coordinates of its LEDs are not provided in the specification data of most LED manufacturers. However, when you have chromaticity coordinates, you can easily mark the position of the LED in the color space, as shown in Figure 2. The triangle of the system gamut in the figure is overlaid on the CIE 1931 color space. The CIE 1931 color space represents all the colors that the human eye can see; outside the color curve is the wavelength, which depicts the chromaticity coordinates. In this figure, the Planckian locus is added, or a black body is colored, representing the coordinates of the black body in the color space as the temperature changes. In common terms, this coordinate represents the result of different types of white light passing through the CCT.
Equation 1: To find out the luminous flux that each LED should output, use the inverse matrix and multiply by the desired luminous flux output, as shown in Equation 2.
Equation 2: Luminous flux output per LED This applies only to a single bin environment. If multiple bins are used, the combination of each bin will have different strengths.
Choose your feedback mechanism
The junction temperature can be calculated by the temperature of the board, the divergence of the power of the LED, and the thermal resistance between the board and the LED. The relationship is shown in Equation 3.
Equation 3: Relationship between Contact Temperature and Board Temperature After obtaining the junction temperature of the LED, you can adjust the system and change the relative luminous flux output value of each LED based on the highest luminous flux output reset by the LED. One of the problems with temperature feedback is the distance between the thermostat and the LED. The closer the thermostat is to the LED, the more accurate the temperature feedback data will be. When you string many LEDs in one channel, the problem becomes more serious. In this case, the difference between the different LEDs will cause color continuity problems and the system will be affected.
By developing this graphical tool, Cypress allows developers to quickly enter the high-brightness LED market and develop more efficient lighting products.