“After more than ten years of industrial development, LED lighting has changed from an innovative technology to a mature technology and has entered millions of households. According to TrendForce’s latest report, LED lighting products are necessities for people’s production and life, and it is estimated to reach 44.3 billion US dollars in 2025. Lighting products are further developed to digital intelligent dimming and control lamps. It is believed that the future lighting industry will also pay more attention to the intelligent systemization of products, human-caused health lighting, and market demand for segmented applications.
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After more than ten years of industrial development, LED lighting has changed from an innovative technology to a mature technology and has entered millions of households. According to TrendForce’s latest report, LED lighting products are necessities for people’s production and life, and it is estimated to reach 44.3 billion US dollars in 2025. Lighting products are further developed to digital intelligent dimming and control lamps. It is believed that the future lighting industry will also pay more attention to the intelligent systemization of products, human-caused health lighting, and market demand for segmented applications. Traditional LED lighting solution technology is becoming more mature, and some market segments are still one of the key markets for the performance of power semiconductor solution providers due to their unique and more demanding technical characteristics. This article takes ADI in machine vision, car lights, stage and architectural lighting as examples to analyze how to meet the needs of LED lighting in market segments.
Support LED lighting design under machine vision
Before the large-scale application of collaborative robots, modern industrial assembly lines have already used machine vision to assist in automated optical inspections to ensure that fast-moving parts on the assembly line meet the defined specifications. Defective parts that fail the optical inspection are marked and automatically removed from the assembly line to ensure consistency between parts. The high-speed camera used as a visual sensor on this type of assembly line requires a camera flash system that can consistently reproduce a fixed on-time light pulse, and the variable off-time is determined by the speed of the assembly line. And the separation distance of the components.
Fast-moving conveyor belt uses machine vision system for fast labeling and defect detection
In this process, infrared and laser LED flashes are often used in machine vision for short-range and motion detection. The security system emits high-speed, imperceptible LED flashes to detect movement, capture and store security images. However, these machine vision camera flash systems all have a challenge, that is, to generate very high current and short-term (microsecond) LED camera flash waveforms. These waveforms may spread out over a long period of time, such as 100 ms to 1 s. above.
However, it is not easy to generate short-term LED flash square waves with longer intervals. When the driving current of the LED (or LED string) rises above 1 A, and the LED turn-on time is shortened to a few microseconds, the challenge becomes more difficult. Many LED drivers with high-speed PWM capabilities may not be able to effectively handle long off-time and short-time high currents without degrading the quality of the square wave required to properly process high-speed images.
In order to achieve the above functions, ADI’s high-speed LED driver LT3932 can provide machine vision camera flashes for LED strings up to 2 A. The off time can be as long as 1 second, 1 hour, 1 day or more, which perfectly solves this problem. problem. The special camera flash function of the LT3932 allows it to keep the output capacitor and control loop charged, even during long off-time. After sampling the state of the output and control loop capacitors, the LT3932 continues to trickle charge these components during the long off period to compensate for the usual leakage current, which is not considered by other LED drivers.
ADI’s LT3932 proprietary flash technology supports expansion, and the drivers can be connected in parallel to provide higher LED flash current. The required flash shape and integrity remain unchanged. The figure below shows that two drivers are connected in parallel to support 3 A camera flashes, even up to 4 A designs are possible.
Relative to the standard PWM dimming frequency, parallel LT3932 1.5A LED driver
Generate 3A machine vision LED pulse with long off time
One IC drives the entire LED headlight group
In vehicles, LEDs are mainly used for headlights, daytime running lights (DRL), side indicators and ambient lighting. The headlight group combines high beam and low beam lights, daytime running lights, and sometimes The signal light and the width indicator light are integrated into a single headlight group. The components of the lamp set will have very different driver requirements, including voltage and current requirements, topology, power levels, or unique dimming functions. Meeting various requirements often means adopting a separate drive solution. The use of multiple drives not only complicates the bill of materials (BOM) and production process, but also makes it difficult to meet EMI standards.
Although the headlights of each car style and model can be equipped with various creative LED currents and voltages, they usually reach a total value of up to 30W. Therefore, such a driver must have the following characteristics: Can accept a relatively wide battery Voltage range, and uses a buck-boost topology to convert it to a variety of lamp string voltages; it has the characteristics of small and versatile, so that it can be easily installed in the very limited space of the lamp group; it must produce extremely low EMI, so as to minimize the research and development workload and eliminate the need to add expensive EMI metal shielding enclosures; the last but very critical point, it should also be highly efficient. ADI’s synchronous, four-switch buck-boost LED controller LT8391A is unique in meeting all of the above requirements. It can drive the entire headlight group and still only uses a single controller.
Using LT8391A’s 2MHz demo circuit DC2575A to drive 16V LED with 1.5A
LED headlights can be both innovative and artistic. High beam and low beam can be “wrapped” together with stylish, beautiful and unique daytime running lights (DRL). Because the daytime running lights are only needed when the high and low beams are off, a single LED driver can be used to power the high and low beam LEDs or daytime running lights. This approach will only work if the LED driver has a flexible input-to-output ratio and can boost and buck the input-to-output voltage. The buck-boost design can meet this requirement.
The multi-beam LT8391A buck-boost LED driver can drive LED string voltages from 3V to 34V. This makes it possible to drive a low beam string and create a high beam by adding LEDs to the low beam string. After the same driver is switched, it can drive a DRL with a higher voltage but a lower current. Switching from low-beam only LED to low-beam/high-beam combined light string, there will be no spikes in the output voltage or LED current. The LT8391A can smoothly switch between boost, 4-switch boost, and buck working areas. For converters, changing from a light string with a small number of LEDs to a light string with a large number of LEDs will not generate LED spike pulses will be a thorny problem, but this multi-beam LED light circuit can easily do this.
LT8391A multi-beam LED headlight group solution for low beam, high beam and DRL lights
The LT8391A LED driver is specially designed for automotive headlights. It uses AEC-Q100 components and meets CISPR25 Class5 radiated EMI standards. In the demo circuit in the above figure, although the controller has a 2MHz operating frequency and 24W power, this buck-boost LED driver still meets the CISPR25Class5 radiation and conducted EMI specifications.
Color control of stage and architectural LED lighting
Red, green, and blue (RGB) LEDs can be used in architectural and stage lighting systems to form bright projection colors-sometimes white LEDs are added to the RGB combination to expand the color range in terms of hue, saturation and brightness. Regardless of the number of color components, the brightness of each color component must be accurately controlled in order to predict the color or compensate for the color difference between the LEDs.
A lighting system using a large number of RGBW LEDs requires a large number of drivers, and the control signal must be synchronized with these drivers. The best way to perform is to directly control each LED with a high-performance LED driver. Under this method, the PWM dimming and DC current and voltage of each LED can be controlled, the ripple can be reduced to a minimum level, and the predictability can be greatly improved. Using the dual step-down LED driver LT3964 controlled by a serial bus, this type of system can be easily implemented.
The LT3964 dual buck LED driver with I2C control and reporting is an ideal solution for driving multiple LEDs or LED strings with high current and high bandwidth through serial communication technology. The buck regulator has inherently high bandwidth. The LT3964 integrates two 36 V, 2 MHz synchronous and high-frequency buck LED drivers in a single package, as well as a 2 A switch, which can drive multi-channel high current relatively easily LED.
ADI pictures
The I2C serial communication function simplifies the analog and PWM dimming functions of the two independent high-current LED channels supported by each LT3964, with up to eight different LT3964 addresses on a single I2C bus. For example, the 2 MHz dual-channel 1A step-down LED driver example circuit in the figure above has high efficiency and ultra-small size. It can be changed to provide up to 30 V LED power for each channel through 34 V to 36 V input , The efficiency is higher than 90%.
Two LT3964 drivers are sufficient to drive a single or string of RGBW LEDs with 1 A (or more). Although RGBW color is usually controlled with 1:256, 8-bit resolution, LT3964 can provide up to 1:8192, 13-bit PWM dimming function and 1:10 analog dimming function for each channel-all controlled by I2C .
Cree XM-L RGBW high power LED can be driven by two LT3964 LED drivers
This direct drive method allows component RGBW LEDs to have large differences in brightness and voltage-each channel is completely independent. In this example, a single Cree RGBW LED is driven by four LT3964 channels, and each channel outputs 1A. By simply changing the digital register, the brightness and color control can be extended to 1:8192 PWM dimming, and 1/10 analog dimming can support each red, green, blue, and white LED. The only real limitation on color is the LED itself. In fact, such a powerful color mixing control capability allows color correction of LEDs if needed.
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