LED environmental lighting leads the rapid development of interior lighting in the future
While pursuing enhancing the value of products and increasing the attractiveness of automobiles, automotive OEM interior designers are also committed to creating a positive driving experience and increasing brand awareness. These factors have laid the foundation for the rapid development of LED environmental lighting solutions. Electronic equipment continues to be the fastest-growing part of automotive components, and its development rate exceeds mechanical devices, pneumatic devices and hydraulic devices. As the number of LED ambient lighting applications continues to increase (from cluster backlights to cup holder lights, to map lights, footpath and mood lighting for door trims, and ceiling lights), automotive OEMs have adopted white and colored LED ambient lighting Differentiate the solution. In fact, research shows that lighting can enhance the driver's vision. In order to match application requirements and achieve a cost-effective design with a shorter time to market, it is still critical to choose the right embedded solution. This article will introduce the following in depth: 1. Trade-offs between methods of controlling LED ambient lighting solutions 2. Use control algorithm to achieve effective pixel combination, dimming and temperature compensation for LED colors 3. By changing the color and brightness of the LED array to create a lighting scene preferred by the driver As the demand for networked lighting modules continues to grow, best practices for implementing LIN communications in LED ambient lighting solutions can help reduce development costs and shorten development cycles. Because LED consumes less energy and takes up less space, car fuel efficiency will be enhanced, and designers can use the advantages of LED packaging to extend their creativity into lighting, thereby improving the in-car experience. Overall, LED ambient lighting solutions give OEMs the opportunity to create a comfortable atmosphere for drivers and passengers. LED ambient lighting is much more than its novelty. In the past few years, research on the impact of interior lighting has not received attention, and the focus of research and development has been on exterior lighting. This situation is changing. With the rapid development of LED technology in recent years, OEMs can not only provide more colorful interior lighting, but also provide user-adjustable lighting. In this way, the driver can adjust the lighting according to personal emotions or tastes. In addition, interior lighting has greater potential. In future models, interior lighting is very likely to become part of the advanced driver information system. This innovative idea is to adjust the interior lights according to driving conditions. For example, when a car is driving in a city, on a country road, or on a highway, the color of the lights in the car will be different. The red interior light can improve the driver's alertness in the city, while the yellow interior light helps the driver relax when driving on the highway. The lighting in the car can even remind the driver that an accident is about to happen. In many cases, flicker-free interior lighting is linked to the high-value positioning of car manufacturers to make their products stand out in an increasingly competitive environment. Drive LED The LED must be driven with a constant current source. Most LEDs have a specified current level at which the LED can reach maximum brightness without premature damage. The light output of the LED is proportional to the current passed. There are two ways to control the LED brightness in the circuit. One is to change the LED drive current. LED drive current can be controlled by variable resistance or variable voltage power supply. Another method is to apply pulse width modulation (PWM) or PWM with variable frequency but fixed duty cycle to the LED drive current. The first method has two main disadvantages: as the current decreases, the LED efficiency may also decrease. Moreover, in high-power white LEDs, lower current levels may cause color deviation. PWM dimming technology always drives LEDs with full current. Therefore, problems such as reduced efficiency and color deviation can be eliminated. In order to produce different color combinations, the duty cycle of the PWM output needs to change over time. Color control method Using embedded single-chip technology, the color components of the light source can be detected and actively controlled. Active color control can be used to generate specific light colors, and can also be used to generate mixed colors. For example, a variety of composition colors can be mixed to produce a specific quality of white light. Using three color values ​​for red (R), green (G), and blue (B) and another value for brightness can produce the desired color. It can be implemented with three PWM channels, or with four PWM channels (three of which represent three colors and the additional fourth channel represents brightness). The latter is simpler and more efficient. The latter method is adopted by Ford Motor Company's latest models that provide situational lighting. The method of using three channels to uniformly control color and brightness usually requires 14-bit to 16-bit resolution and a powerful single-chip microcomputer (MCU). The same quality can also be achieved with four channels with a resolution of 10 bits each, which are usually provided in low-cost 8-bit MCUs. In the four-channel scheme, the product of color and brightness is calculated by an external hardware circuit. On the low-cost 8-bit MCU, the power function approximation method can also be used to accurately achieve the typical logarithmic gradation required for brightness control (see Figure 1). Figure 1 Block diagram of a solution using 3 and 4 PWM channels LED temperature is one of the factors that has a significant influence on the color of the LED. Therefore, the effect of temperature needs to be compensated. An inexpensive and simple and effective method of temperature compensation is to use an on-chip comparator of the microcontroller and a low-cost negative temperature coefficient (NTC) thermistor located near the LED. Another way to achieve LED temperature control is to measure its forward voltage drop. The resolution of the 10-bit analog-to-digital converter (ADC) integrated into the microcontroller is sufficient to accomplish this task. The forward pressure drop measurement has certain advantages because no additional external components are required. Lighting network Color correction, temperature compensation, color change, color mixing, brightness control, and automobile manufacturers' expectations for various lighting scenarios are bound to use microcontrollers, such as PIC® MCUs with nonvolatile memory. In addition, the need for networking of RGB lighting nodes in the car and the requirements for diagnosis require appropriate low-cost communication protocols. The first generation of interior lighting uses separate wiring, while the latest generation and newly developed interior lighting of OEM uses the well-known and cost-effective LIN / J2602 communication bus. The LIN communication speed is 19.2k baud, which is enough to support color changes and lighting scenes, and will not have a significant impact on drivers and passengers. Recently, some car manufacturers are considering using LIN communication with automatic addressing for such applications. There are many known automatic addressing methods, and each method has its own advantages and disadvantages (see Figure 2). The commonality of all methods is that the cost of silicon is increased compared to standard LIN communication. However, this additional cost will reduce the logistics costs of OEMs and Tier 1 suppliers. Figure 2 Block diagram of a LIN transceiver with and without automatic addressing Addressing space limitation Typical interior lighting applications are subject to very large space constraints. Light nodes are embedded in switches, cup holders, door handles, dashboards, seats, reading lights, footrest areas and top consoles. The available space of electronic equipment is usually compressed to 10 mm x 20 mm or less, which promotes the application of small packaging solutions such as SSOP, QFN and DFN. In this environment, semiconductor devices with low power dissipation and extended operating temperature range of -40 ° C to 125 ° C require careful thermal management of the ambient temperature and self-heating. Normally, the node is connected to terminal 30, so very low standby current is required, well below 100 µA. Bark Stop Collar,Best Bark Control,Remote Pet Training Collar,No Shock Bark Collar Elite-tek Electronics Ltd , https://www.aetertek.ca
