LED lamps also need intelligent control to get out of the differentiation circle

 LED has been very popular for such a long time, and more and more people are entering the LED industry. The wave of bankruptcies and mergers and acquisitions cannot change everyone's enthusiasm for LED. Those who make traditional lamps are doing LED lighting , those who make energy-saving lamps are doing LED lighting, and as long as the industry is related to lighting, they are all doing LED. In such an environment, let's take a look at the differentiated designs.

　　LED照明的出现改变了照明的使用方式，在LED灯具中加入智能控制及调色功能为设计人员开创了新的机会。LED效率高、具调光能力、寿命长等优势，能让可变色灯具的效率更高、更具成本效益并且更加容易取得。数码信号控制器(DSC)可驱动各种创新应用，能实现更高效率的LED驱动、更精确的色彩控制并与外部有著更良好的沟通。以上优势汇集使得设计人员拥有更大的自由开发高度差异化的LED照明灯具。

　　Low-power indicator LEDs are the basis of many products, and most engineers are familiar with their simple design. All they need is a voltage source and a series resistor of the correct value to keep the LED current at less than 5 mA. The LED can be flashed by connecting to a microcontroller's general-purpose input/output (GPIO) pin; however, connecting forward currents of more than 350 mA in series to form a high-brightness, high-current LED can become quite complex. Designers also face the challenge of current control in addition to temperature changes and the high temperature of the LED itself.

　　Figure 1: Using pulse current for dimming, the color change is not noticeable.

　　Figure 2: Buck technology for driving a single LED or LED string.

　　Current control

　　高亮度LED需维持在一个相对高的定电流来保持一定的亮度和颜色。LED的光通量与流经LED的顺向电流成正比，要达到一致的颜色和光线输出，关键是恒定的顺向电流。顺向电流会跟著电压源产生改变，造成LED发射出的光线变动。因此，需使用能主动调节顺向电流的电源供应器来驱动。

　　Temperature control

　　一般而言，LED的顺向电压会随著温度上升而增加，即使顺向电流是不变且经过调整的。高功率LED会产生热能，导致LED寿命缩减并提早发生故障。控制LED的顺向电流能让个别设计根据目标顺向电流及预估顺向电压来决定散热水平。使用温度感应器提供了一个监控温度状况的方法。

　　Color Control

　　LEDs can change their light output almost instantly, making them ideal for fixtures that need to change color quickly. By simply adjusting the brightness of each LED, any color can be created with strings of red, green, and blue LEDs. Increasing or decreasing the forward current of each LED is one way to do this, but changes in forward voltage not only change the brightness, but also slightly change the color of the LED. This can cause problems in applications that require precise color.

　　Another method is to use pulsed current, which can provide the same dimming effect without causing noticeable changes in color. The red dashed line in Figure 1 represents the brightness change that can be created by the average pulsed current while maintaining the consistency of the LED forward voltage. There will be no noticeable change in color.　　Digital dimming control

　　Using pulsed current technology for dimming, the design of digital signal controllers can be greatly simplified. The advanced pulse width modulation (PWM) module on the digital signal controller can be used to generate the PWM signal to control the power level of the LED . The PWM module has a reset input that can quickly and accurately turn off the PWM output to control the current to achieve LED dimming. The amount of dimming is a quantized number between the values ​​of all off (0) and all on (255). To set the LED brightness to 50%, the counter will count from 0 to 255 and turn off the PWM output at 128 (50%). At this time, no current will pass through the LED; when the counter reaches the maximum value of 255, it will return to 0 and the PWM will restart. Repeating this process continuously can generate the pulsed current required for LED dimming. Generally, a frequency of more than 400Hz is used to ensure that the LED flicker is not visible to the human eye.

　　Digital LED Driver

　　In addition to dimming control, the digital signal controller can also actively provide power to control the forward current flowing to the high-brightness LED. Buck and boost switch mode power supply technology (Switch Mode Power Supply; SMPS) can be used to power the LED.

　　If the forward voltage of the LED or LED string is less than the supply voltage, a buck technique can be used. As shown in Figure 2, in this technique, the PWM controls the switch (Q) and the voltage across the sense resistor (Rsns) corresponding to the LED forward current when the switch (Q) is off. The comparator of the digital signal controller is used to compare the voltage across the resistor (Rsns) with a configurable internal reference voltage, which is proportional to the forward current required by the LED. When the sense voltage is greater than the internal reference voltage, the analog comparator prevents the PWM from turning on the switch (Q), and the inductor (L) discharges the stored current to the diode (D) and the LED. At the beginning of the next PWM cycle, the switch (Q) is turned off; and the process repeats. The digital signal controller can actively adjust the forward current flowing to the LED without using any CPU resources.

　　Conversely, if the forward voltage of the LED or LED string is greater than the supply voltage, the forward voltage can be used. The PWM controls the switch (Q) and the forward current through the sense resistor (Rsns) is monitored. The analog-to-digital converter (ADC) module on the digital signal control module samples the voltage through the sense resistor, which corresponds to the forward current of the LED. This value is used by the proportional integral (PI) control loop, which is executed by the software of the digital signal controller to adjust the duty cycle of the switch (Q) based on the ADC reading and the software reference value corresponding to the required current. By implementing the PI control loop in software, the digital signal controller can provide the flexibility of using multiple control loop methods. Minimizing the CPU resources used by the PI control loop, the digital signal controller can control multiple LED strings and support additional functions.

　　Digital Communications

　　Digital signal controllers can control LED lamps in an intelligent way and can execute communication protocols without the need for independent communication control devices. For example, the DMX512 lighting control protocol uses standard one-way communication to send instructions to individual lamps through a master device and multiple slave devices at a 512-bit packet data rate and addressing each device or node separately. High-speed processing allows the digital signal processor (DSP) to quickly execute control loops, giving priority to controllers for boost converters, and running communication protocols such as DMX512. Because this communication is executed in software, it is not limited to a single protocol and can use a variety of communication methods to control lamps.

　　Shorten the learning curve

　　For designers, the learning curve of digital LED control is steep, and things will become easier by using the digital control LED lighting tool kit, reference design and application notes. Including free program source code, hardware files and interchangeable power stages to support different power topologies. Microchip's DM330014LED lighting development kit provides multiple LED driver daughter cards, allowing designers to experiment with multiple driver stages on the same board.

　　The high efficiency and instant dimming capability of LEDs will continue to drive the development of color mixing and other lighting applications. By adding the intelligent control and communication functions provided by digital signal controllers, designers will be able to add advanced functions and features to LED lighting fixtures, presenting the differences in lighting applications.

   Adding intelligent control to LED lights can better play the advantages of LED, and the energy-saving advantages will also be more fully utilized. Changing the color and brightness in different environments has become a fact. Intelligent control will be the future trend of LED.