Application of electronic technology in LED lighting analysison January 4th, 2012 at 1:59 AM
Compared with the traditional way of lighting, LED bulb lighting has many unique places, mainly in: from the structural point of view, traditional lighting and lamps are separated, and LED bulb lighting in the structure can be achieved with light, heat and light of one design; from a functional point of view, only a small part of the traditional lighting can achieve dimming, and LED lighting not only able to adjust the brightness, but also to achieve the color and color temperature adjustment. In addition, LED lighting is more suitable than the traditional way of intelligent lighting and digital control, the composition of complex lighting systems.
LED-based lighting of these features can be roughly three models are given, respectively, for general LED lighting, LED lighting, smart control, LED lighting and solar wind with the design, stating that the electronic information technology in LED lighting in some applications.
Model I: Power + Light
Electric light the nature of modern work is to convert electrical energy into light energy, accompanied by a certain degree of heat. Therefore, LED general lighting model and light source on the only power of two parts. In this model, the switch can only be achieved lighting control, dimming lighting can not be achieved, communication, feedback and other functions.
Power specifically refers to the constant current type AC-DC switching power supply. AC-DC is AC to DC conversion, because the LED is actually a semiconductor diode, which is working in DC voltage. Another feature is the LED current approximation is an exponential function of voltage, voltage fluctuations can cause small changes in current huge, severe burn directly to LED, so LED to ensure the safety of the work, must make it a constant current . Usually the power is constant pressure appliances, LED it is to determine the characteristics of constant current power supply. In order to improve the reliability of LED work, we generally use isolated switching power supply, electricity grid of LED and the effective isolation. And the corresponding switching power supply, there is a class called linear power supply, is now rarely used, because the switching power supply volumetric efficiency and is more dominant. Now the switching power supply technology, can achieve 85% conversion efficiency even higher than 0.95 power factor, total harmonic less than 15%. We chose these indicators are also basic requirements of switching power supply.
Light source is LED chip, LED lighting, which is the core component. In addition to operating current, tube voltage drop and other electrical parameters, we are more concerned about its optical indicators, such as luminous flux, luminous efficiency, color temperature, color rendering index, the light fades, and so on. LED optical performance is closely related to its temperature, the temperature will cause lower luminous efficiency, color temperature drift, life loss and other problems, so in cooling technology in the LED lighting is especially important. Knowledge of thermodynamics tells us that the object of cooling only three ways: conduction, convection and radiation. As the LED chip is the issue of a fixed wavelength of visible light, infrared radiation, so there is no heat. In the LED, the main heat conduction, convection cooling is accompanied by some. Reducing the LED thermal conductivity and lower part of the thermal resistance of each link, if necessary, the use of forced air-cooled, are in thermal design considerations.
Model 2: Power + Control + Light
Model 2 than in more than one model of a control module, which greatly enriched the LED lighting function. If the model is a just a lighting product, model 2 can be a lighting system. As inclusion of the control module, power supply switching power supply becomes constant, but the LED light source of the work or need constant-current power supply, this part of the (constant-current drive) on the control module together we achieve. Here, we focus on analysis of LED lighting control system.
LED lighting control system, very flexible, feature-rich. Such as: wireless remote dimming system, lighting system, adjustable color temperature, RGB color dimming system, simulated daylight lighting system, with DALI protocol intelligent lighting system, based on ZigBee and GPRS wireless street light control systems. Look beyond the surface, all of these lighting control systems are the use of electronic technology in embedded technology, communication technology, sensor technology, computer technology and the development of power electronics technology to build up. Seemingly diverse and complex, in fact, based on evidence.
In order to clarify the context, we can control the LED lighting system is divided into eight levels, layer by layer elaboration. If we can do for each level of technology solutions, then any complex control system we can be like “building blocks” as easy to achieve.
LED lighting control system by the end of the eight levels up as follows: power level, drive level, light level, sensor layer, the proposed layer, letter layer for layer, the system implementation level.
Power level for the entire control system to provide efficient and stable DC power supply. Work with the LED light source of constant current power supply needs of different control systems needed to be a constant voltage supply. The power supply layer to obtain two ways: First, from the LED lighting on the constant voltage power supply on the acquisition, which is a DC-DC (direct current to direct current) conversion, because the lamp on the constant power supply voltage is usually high , while the low voltage control system, so do a step-down from DC to DC converter; the second is from the AC power to obtain, it is a AC-DC (AC to DC) converter, for safety, usually do into isolated switching power supply, because the control system power consumption is usually low, so here is a constant voltage supply requirements for the conversion efficiency is not high.
As mentioned earlier, the model II power supply is constant voltage source, and the LED light source of the work requires constant current source, therefore, in the control system to have a constant current driver module for the normal operation of the LED light source to provide constant current source. In the design of constant-current drive, typically using a dedicated driver chips, and with some of the external circuit.
Driver IC output is usually with a string of LED, the output current is constant LED current. The higher the output voltage range, the number of LED can be with the more. There are exceptions, output to multiple strings in parallel LED, then, we give each string of LED in series to achieve a small current shunt resistor. General there is a driver IC PWM (pulse width modulation) port, used to achieve dimming control, which is the basis for intelligent lighting. Constant-current drive pros and cons, is directly related to the reliability and service life of LED lighting. Therefore, the LED driver technology research, particularly important.
The reason is easy to implement LED lighting intelligent control, because it is easy to achieve dimming control. The embodiment of all intelligence functions are achieved through dimming. LED lighting dimming for understanding, not only adjust the brightness of light, including LED color temperature and color of the regulation. It is also able to subvert the traditional lighting LED lighting as a major factor. Dimming technology implementation, there are both analog and digital. Among them, mainly through digital dimming PWM (Pulse Width Modulation) technology, which is now the program’s main LED dimming means. PWM signal to the microcontroller can be programmed to produce different duty cycles, in order to achieve LED lighting dimmer. Design a LED “Three Keys” (brightness, color temperature, color) function integration scheme, is the focus of this level of study.
As mentioned above the driver layer and the dimming level is output from the system point of view of. Clearly, the sensor layer is the input of intelligent systems. It is like the eyes and ears of intelligent systems, can feel the changes in the external environment, and these changes into electrical signals passed to the intelligence system of the brain – the central processing, analysis and processing. Lighting control in the field, we are mainly concerned with sensors: light sensors, collecting information on the brightness of natural light; body sensors to detect whether someone close to the presence of light; temperature sensor, the temperature of the external environment information collection; still working on the system’s current voltage data collection and analysis.
No rules no standards. Intelligent lighting system to achieve the various modules within the orderly coordination, must have a sound “rules” used to convey instructions and perform operations. The system is intelligent system protocol. In the current lighting industry, there are two more mature protocol, one light communication in DALI (DigitalAddressablELightingInterface Digital Addressable Lighting Interface) protocol, and the other is to achieve RGB color control DMX512 protocol. Unfortunately, these two agreements are not tailored for LED lighting. LED lighting control related protocol for the study, now is a hot, still no uniform international standards. This is for us, may be an opportunity!
In the field of electronic information, the transmission protocol is based on communications technology for the carrier to achieve. LED lighting in traffic, there are three main ways: the bus way, way power line carrier and radio frequency methods. Bus mode, with its mature technology, high reliability, networking simple, moderate cost, etc., is currently the most widely used means of communication, such as the RS485 bus. Power line carrier method is to pass through the exchange of network protocols, eliminating the need for duplicate wiring costs, it should be said to be an excellent means of communication. However, its network of high quality requirements, given the current harmonic pollution in China is very serious, this approach is suitable for China’s national conditions, has yet to be verified. RF mode, now the most popular technology is ZigBee. It is an emerging short-range, low speed, low-power wireless network technology.
To achieve this level of user and system information exchange. Software for human-computer interaction design, simple operation and friendly interface, easy to maintain and upgrade, should be the primary consideration. In accordance with the application of different, and interactive software can be divided into two categories: one running on embedded systems; the other runs on a PC.
System implementation layer
At this level, we do a global control system analysis and design, the use of the previous seven-level research, to complete the whole system set up. In other words, the level design is based on the previous seven-level, is the former seven-level synthesis of research results.