With the continuous improvement of LED application technology and the gradual decline in cost, LED lamps have been closer to the large-scale application of mass-produced vehicle systems after preliminary design stages such as technical verification and concept car display in automotive electronics in recent years. Good prospects. Starting from the full use of LED lights in the Audi R8 electronic system, to Mercedes-Benz, BMW, Cadillac, Toyota and other companies have also launched their own LED lights to replace the traditional incandescent, HID lamp car models, a variety of colorful LED lamps for the new car Less, attracting the attention of consumers, at the same time, it also provides a new bright spot for future car design, I believe that soon more car manufacturers will use LED lights as the first choice for automotive lighting, instructions, backlighting and decoration.
LED is suitable for various lighting applications of automotive electronics, including headlights (high beam and low beam), fog lights, tail lights, brake lights, turn signals, daytime running lights, pedal lights, interior lights, display Wide lights, navigation, entertainment systems, instrument backlights and indicator lights, etc. The application of LED lights in automotive systems mainly has the following advantages: first, high color saturation, which makes the output light clearer and softer, in line with the characteristics of automotive headlight applications; second, long service life, durable, strong shock resistance , Can exceed 10,000 hours, and the life of traditional halogen lamps is generally around 300 hours; third, high efficiency, less additional losses, compared to the complex heat dissipation system of traditional lamps, it can be seen that the heat loss of LED lamps is much smaller, The conversion efficiency can reach more than 85%, which is especially suitable for the design concept of future cars that pay attention to energy saving; fourth, fast response, unlike traditional incandescent light, HID lamps require a longer driving lighting delay, more real-time reflection of vehicle and road conditions, leave Give drivers longer time to judge and reduce car safety accidents; Fifth, small size and light weight, can achieve more compact and exquisite lamps, saving more space for other car designs; Sixth, LED lights belong to the color A light source with good performance, no other infrared rays, ultraviolet rays and other light, little heat and radiation, suitable for automotive interior lighting and backlight applications.
The use of LED lights in automobiles is currently mainly focused on the use of headlights, tail lights, lighting lights, car GPS backlights, etc., especially tail lights, accounting for about 10% of the entire market.
Five technical challenges
The scale of domestic automotive LED currently accounts for only a small share of about 10% of the automotive light source market, and is currently mainly concentrated in high-end automotive applications. Although the cost of LED lamps continues to decline, it must be gradually improved in quality and output in order to be comparable to traditional light sources in order to reduce LED costs and expand the market share of LED automotive electronics.
High cost is not the only factor to delay the application of LED lamps in automotive electronics. Some technical performance problems also need to be solved. For example, the illumination intensity of a single LED is still insufficient, which cannot reduce the number of LEDs to reduce the size of the lamp. At the same time, the smaller size is not conducive to the heat dissipation of the light source, which requires LED manufacturers to do a good job of thermal management of products, in order to give full play to the advantages of LED, no matter how long the LED life or color rendering can provide a better state, otherwise It can only be counterproductive and reduces the quality of the product; the conversion efficiency of the LED drive system is also a key problem at present. In high-power applications, many solutions take into account the cost while the conversion efficiency is not high; there are currently LED lights in China. Automotive electronics are all high-end cars, and most of the high-end cars are controlled by foreign car manufacturers. The selection and certification of LED suppliers by foreign manufacturers are very harsh. It is difficult for domestic LED companies to enter their supply chain; there is LED light production in China. Most of the level still stays within the requirements of civilian products, and it is difficult to meet automotive-level application standards, even if it meets automotive Some manufacturers of high-level applications may not be enough in terms of production capacity and product consistency, and it is difficult to meet the high-volume and high-quality requirements of mass-produced cars.
Therefore, if you want to speed up the share of the entire car light source, LED lights must first solve these problems, such as the thermal management problems, production costs, and product consistency issues mentioned above.
Automotive requires discrete LED drive power
Driving with a constant voltage source cannot guarantee the consistency of LED brightness, and affects the reliability, lifespan and decay of LEDs. Therefore, the LED must be driven with a constant current source. Most LEDs have a specified current value, which can be driven by a linear regulator configured as a constant current source. The linear regulator has the advantages of reducing the number of parts and reducing electromagnetic interference (EMI), but in terms of efficiency and heat consumption There are serious drawbacks in that it is not suitable for high-power applications, and switching power supplies (SMPS) are more suitable for various applications.
At present, the LED drive power supply using SMPS mode is the mainstream of the market, and it is also divided into separate device combinations and IC integration methods. IC integration modes such as Taiwan Macroblock, Zetex (Diodes), TI and NSC, etc. The main feature is the built-in MOSFET And its driving circuit, and some integrated multi-channel driving, automatic dimming and various protection functions, etc., the application circuit is simple, the volume is small, and the cost is easy to control, but because of the small driving current of this application, the design is not flexible enough, and the control accuracy High, unable to realize the boost mode and other reasons, it has great limitations in most automotive electronics applications, and the separation mode realized by the PWM control chip and external MOSFET can achieve high power, high efficiency and high stability in automotive electronics Application, it can achieve the overall goal of the system through different topologies, combined with the LED's voltage, current and power requirements. The cost will gradually decrease with the usage.
Mainstream solutions for the European front-loading market
At present, the MCU + MCP1630 solution is widely used in Europe, accounting for more than 70% of the European front-loading market. It is mainly used in headlights (high beam lights), tail lights, flash lights and other applications. The chip has high reliability and high performance. Efficiency, flexible functions, and high cost performance have established a good reputation in the application of automotive electronic LED drivers, and are the first choice for LED drivers of some large foreign manufacturers. At the same time, with the continuous increase in usage, the cost advantage of MCP1630 is also increasing Obviously, it can be applied in low-end and middle-end models to better solve the problems of thermal management, efficiency and product consistency in LED drivers.
MCP1630 is a high-speed pulse width modulator that can be used to develop smart power supplies. The MCP1630 can reach a frequency of 1MHz in peak current mode. The CMOS output driver can directly control the MOSFET driver or the low-end N-channel MOSFET. It can provide an external reference power supply and flexibly implement the output voltage and current regulation settings; internal high-speed comparator, high-speed bandwidth / The error amplifier can achieve faster and more accurate current detection, and also integrates over-temperature protection and under-voltage lockout functions to better achieve better thermal management. When working with a single chip microcomputer, it can provide a stable output voltage or current by controlling the duty cycle of the power supply system. The single chip microcomputer is used to adjust the output voltage or current, switching frequency, maximum duty cycle and other characteristics that can improve the intelligence and adjustability of the power supply system.
In the LED drive system, if the power supply voltage exceeds the total LED voltage, a buck converter is required. If the voltage of the LED group exceeds the supply voltage, a boost converter is required. In automotive power systems, the LED voltage may be higher or lower than the power supply voltage. In this case, power topology technologies such as buck / boost or single-ended primary inductance converter (SEPIC) should be used. MCP1630 can realize the above various topological design needs. At the same time, adhering to the consistent style of Microchip products (high stability and product consistency), so that LED production costs and quality have been improved. Taking the high-speed PWM chip MCP1630 from Microchip as an example, the applicability of this scheme in automotive electronics applications is explained through the SEPIC topology.
Microchip has introduced the SEPIC topology using PIC12F1823 + MCP1630 for automotive taillight / flash light application DEMO, which can achieve an input voltage of + 9V to + 16V, with a maximum output voltage of 55V @ 350mA, driving 10 1.5W LED lights, and achieving graded adjustment Light, under voltage, over temperature protection and other functions, the conversion efficiency reaches more than 85%.
In this application, the MCP1630 can control the load current of the LED to a pre-designed level under the influence of various factors. The circuit sends a reference voltage or current signal Vref and the LED load voltage or current signal FB into the signal control module. In comparison, the error signal is processed and sent back to the primary control IC for processing. When the load current changes due to various factors, the primary control IC can control the switch to return the load current to the original design value. Through feedback and over-temperature detection, thermal management can be well achieved.
In terms of the topology used, although the efficiency of the SEPIC converter is not as good as a buck regulator or a boost regulator, it also has its advantages. SEPIC has both boost and buck capabilities, which is particularly suitable for automotive cold start At this time, the voltage may be as low as about 4.5V. On the other hand, in the case of automotive overload, the voltage will suddenly rise to more than 40V. Another advantage that is very concerned by automotive applications lies in the middle of its circuit. Capacitor, it can provide very effective isolation between input and output. Of course, the SEPIC converter also has an obvious disadvantage that it requires two inductors to operate. In this application, the two inductors are wound into two separate components in a concentric circle, which saves both cost and volume. At the same time, due to the presence of a high-speed comparator in the peak current mode, the MCP1630 can respond quickly within 12 ns to achieve fast and high-precision current closed-loop. At the same time, PIC12F1823 can also realize voltage detection through AD detection and achieve high efficiency control.
In addition to being used as a SEPIC topology application, the MCP1630 can also be used in a separate boost / buck circuit, mainly used in automotive headlights and daytime running lights, etc. It can achieve LED series connection for more efficient control applications
In addition to MCP1630 applications, Microchip has also launched low-cost MCU integrated LED driver application solutions, such as PIC12HV615, PIC16HV785, which integrates a high-voltage regulator, high-speed hardware PWM module, comparator, ADC, op amp, voltage reference, etc., It can achieve boost or buck control, and is used in low-power applications such as vehicle equipment backlights, instrument backlights, brake lights, etc., and converts traditional CCFL backlights into LED backlights. The rich resources of MCU can realize more intelligent functions. The highly integrated application reduces the cost, simplifies the design, saves space, and also helps to overcome thermal management and improve efficiency. But this application is not yet suitable for high-power applications.
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