Compared with the traditional lighting, LED lighting has many unique places, mainly in: from the structural point of view, the traditional lighting of the light source and the lights are separated, and LED lighting in the structure can achieve light distribution, cooling and lighting one Design; from the functional point of view, only a small part of the traditional lighting can achieve dimming, and LED lighting can not only achieve the brightness of the adjustment, but also to achieve color and color temperature adjustment. In addition, LED lighting than traditional lighting is more suitable for intelligent and digital control, composed of complex lighting system.
Based on these characteristics of LED lighting, we can give three kinds of models, which are aimed at LED general lighting, LED lighting intelligent control, LED lighting and solar energy combined design, indicating that electronic information technology in LED lighting in some applications.
Model 1: Power + Light Source
Modern electric light source is the essence of the work of electricity into light energy, accompanied by a certain degree of heat. Therefore, LED general lighting model only includes the power and light source in two parts. In this model, can only achieve the lighting switch control, can not achieve the lighting dimming, communication, feedback and other functions.
Power refers specifically to AC-DC constant current switching power supply. AC-DC refers to AC to DC conversion, because the LED is actually a semiconductor diode, it is working in the DC voltage. LED also has a characteristic that its operating current approximation is the exponential function of the operating voltage, the small fluctuations in voltage will cause a great change in current, serious will burn directly to the LED, so to ensure the safety of the LED work, must make its current constant The Usually household appliances are constant voltage, LED characteristics determine it to use constant current power supply. In order to improve the reliability of LED work, we generally use isolated switching power supply, LED and power grid to achieve effective isolation. And switch power corresponding, there is a class called linear power supply, now has been rarely used, because the switching power supply in the efficiency and volume more dominant. Now the switching power supply technology, can convert efficiency to 85% or more, power factor 0.95 or more, the total harmonic within 15%. These indicators are also the basic requirements of our choice of switching power supply.
Light source is the LED chip, which is the core of LED lighting components. In addition to operating current, tube pressure drop and other electrical parameters, we are more concerned about its optical indicators, such as luminous flux, light efficiency, color temperature, color rendering index, light failure and so on. LED optical properties and its temperature is closely related to the temperature rise will cause light efficiency, color temperature drift, life expectancy and other issues, so the cooling technology in LED lighting is particularly important. Thermodynamics tells us that the heat dissipation of the object is only three ways: conduction, convection and radiation. As the LED chip is fixed only issued a wavelength of visible light, so there is no infrared radiation heat. In the LED, the main conduction heat, accompanied by a certain convection heat. Reduce the thermal conduction of LED links and reduce the thermal resistance of each link, if necessary, forced air cooling, cooling design considerations are.
Model 2: Power + Control + Light Source
Model two more than a model of a control module, which greatly enriched the LED lighting function. If the model is a lighting product, then the model two can be said to be a lighting system. As a result of the control module, the power supply becomes a constant voltage switching power supply, but the work of the LED light source still need constant current power supply, this part (constant current drive) we put together in the control module to achieve. Below, we focus on the analysis of LED lighting control system.
LED lighting control system, can be small, feature-rich. Such as: wireless remote control dimming system, color temperature adjustable lighting system, RGB dimming color system, analog daylighting system, with DALI protocol intelligent lighting system, based on ZigBee and GPRS wireless street light control system. Through the nature of the phenomenon, all of these lighting control systems are built using the embedded technology, communication technology, sensor technology, computer technology and power electronics technology in the field of electronic technology. Seemingly complicated, in fact, according to follow
In order to sort out the context, we can LED lighting control system is divided into eight levels, layer by layer. If we can do a good job of each level of technical solutions, then any complex control system we can like "building blocks", easy to achieve.
LED lighting control system of the eight levels from the bottom up in order: power supply layer, the drive layer, optical layer, the sensor layer, the layer, the letter layer, for the layer, the system layer.
Power supply layer
The power supply layer provides an efficient and stable DC power supply for the entire control system. Unlike the constant current power supply required for LED light source operation, the control system requires constant voltage power supply. Power supply layer power supply has two ways: First, from the LED lighting on the constant voltage power supply, which is a DC-DC (DC to DC) conversion, because the lamp on the constant voltage power supply voltage is usually high, And the control system voltage is very low, so to do a DC to DC from the buck conversion; the second is from the AC utility access, which is an AC-DC (AC to DC) conversion, in order to safety, Isolated switching power supply, because the control system power consumption is usually very low, so here the constant voltage power supply on the conversion efficiency requirements are not very high.
As mentioned earlier, the power supply part of the model II is a constant voltage source, and the operation of the LED light source requires a constant current source. Therefore, there must be a constant current drive module in the control system to provide a constant current source for the normal operation of the LED light source. Constant current drive in the design, the general use of a dedicated driver chip, and with a certain external circuit.
The output of the driver chip is usually with a string of LED, the output of the constant current is the LED current. The higher the output voltage range, the more the number of LEDs that can be taken. There are exceptions, the output side to parallel multi-string LED, then, we have to give each string of LED in series to achieve a small current shunt. Driver chip generally also has a PWM (pulse width modulation) port, used to achieve dimming control, which is the basis for the realization of intelligent lighting. Constant current drive the merits of the program, directly related to the reliability of LED lighting and service life. Therefore, the LED drive technology research, is particularly important.
LED lighting is easy to achieve intelligent control, because it is easy to achieve dimming control. All the intelligent function of the embodiment, are achieved through the dimming function. For LED lighting dimming understanding, can not be limited to adjust the brightness of light, but also on the LED color temperature and color adjustment. This is also the LED lighting can subvert the traditional lighting of a major factor. Dimming technology to achieve the way, there are two analog and digital. Among them, the digital dimming is mainly through the PWM (pulse width modulation) technology to achieve, it is now the main means of LED dimming program. PWM signal can be programmed through the microcontroller to achieve a different duty cycle, in order to achieve LED lighting dimming. Design an LED "three tone" (brightness, color temperature, color) function of the integrated program, is the level of research focus.
The driver layer and the dimming layer mentioned above are analyzed from the perspective of system output. Obviously, the sensor layer is the input of the intelligent system. It is like the eyes and ears of the intelligent system, can feel the changes in the external environment, and these changes into electrical signals, passed to the intelligent system of the brain - the central processor, for analysis and processing. In the field of lighting control, we care about the main sensors are: photosensitive sensors, the natural light to collect the brightness of information; human sensors, detect the presence of light near the people; temperature sensor, the external environment to collect temperature information; Voltage and other data collection and analysis.
No rules, no standards. To achieve the intelligent lighting system within the various modules of the orderly coordination between the work must be a set of perfect "rules and regulations", used to convey the instructions and the implementation of operations. This system is the agreement of the intelligent system. In the current lighting industry, there are two more mature agreement, one is the lighting communication DALI (DigitalAddressablELightingInterface digital addressable lighting interface) protocol, the other is to achieve RGB color control DMX512 protocol. Unfortunately, these two sets of protocols are not tailored for the LED lighting. LED lighting control for the relevant agreement, is now a hot spot, there is no uniform international standards. It may be an opportunity for us!
In the field of electronic information, the transmission of the agreement is based on the communication technology as the carrier to achieve. LED lighting communication, there are three main ways: bus mode, power line carrier mode and radio frequency mode. Bus mode, with its technology is mature, high reliability, simple network, the advantages of moderate, etc., is currently the most widely used means of communication, such as RS485 bus. Power line carrier mode, through the AC power grid to pass the agreement, eliminating the cost of repeated wiring, it should be said is a good means of communication. However, it is a high quality requirements of the grid, in view of the current power grid pollution is very serious, this approach is suitable for China's national conditions, remains to be verified. Radio frequency, now the most popular technology is ZigBee. It is a new short-range, low-speed, low-power wireless network technology.
This level implements the user and the system information exchange. For human-computer interaction software design, simple operation, user-friendly, easy to maintain and upgrade, should be the primary consideration. Depending on the application, the interactive software can be divided into two categories: one is running on the embedded system; the other is running on the PC.
System implementation layer
At this level, we are on the control system to do the overall analysis and design, the use of the previous seven levels of research results to complete the entire system structures. In other words, this level of design is based on the previous seven levels, is the first seven levels of research results of the integrated.