Problems

LED lighting has a huge energy-saving effect, which will replace the traditional light source, thus triggering the fourth revolution in the history of human lighting, greatly improving the living environment of human beings, and alleviating the increasingly severe global energy crisis. While LED is shining brilliantly, LED driving power supply is the guarantee for the development of LED industry chain. The quality of LED power supply directly restricts the reliability of LED product application. Therefore, the LED industry chain is gradually improved, The development and maturity of LED drive power supply is also crucial.

Because LED is a characteristic sensitive semiconductor device and has negative temperature characteristics, it needs to be stable and protected in the process of application, resulting in the concept of drive. LED devices have almost strict requirements for driving power supply. Unlike ordinary incandescent bulbs, LEDs can be directly connected to 220V AC mains power. LED is driven by 2~3V low voltage. It is necessary to design complex conversion circuit. LED lamps with different purposes should be equipped with different power adapters. In the international market, foreign customers have very high requirements for the efficiency conversion, effective power, constant current accuracy, power life and electromagnetic compatibility of LED drive power supply. These factors must be taken into consideration when designing a good power supply, because the role of power supply in the whole lamp is as important as that of human heart. In 2009, although the financial crisis had a great impact on the world economy, the demand for high-power LED power supply in Europe and the United States and other international markets was still large, and the export volume of corresponding high-end LED products was less affected by the financial crisis. In 2008, the output value of China's LED application products has exceeded 45 billion yuan. LED demonstration application street lights, LED full-color display devices, solar LED, landscape lighting, consumer electronic backlight, signal, indication and other applications are still the main application fields. However, in the context of a prosperous market, the quality of LED products is mixed, the requirements for driving power are chaotic, and the LED products in the market are in full swing. As for LED driving power enterprises, they are facing several challenges. First of all, the overall life of the drive circuit, especially the life of key components such as capacitors at high temperature, directly affects the life of the power supply. Secondly, LED drivers should challenge higher conversion efficiency, especially when driving high-power LED, because all power not output as light is dissipated as heat, and the low power conversion efficiency affects the exertion of LED energy-saving effect. Third, the LED can be dimmed efficiently with a large dimming ratio, and the color characteristics can be kept constant at high and low brightness. At the same time, to reduce the cost, in applications with low power (1~5W), the proportion of the cost of constant current drive power supply has been close to 1/3, which has been close to the cost of light source, and has affected the market promotion to a certain extent.

Development trend

China's LED industry started in the 1970s.

After more than 30 years of development, China's LED industry has initially formed a relatively complete industrial chain, including the production of LED epitaxial chips, the preparation of LED chips, the packaging of LED chips, LED power supplies and LED product applications.

Driven by the "National Semiconductor Lighting Project", seven national semiconductor lighting industrialization bases have been formed in Shanghai, Dalian, Nanchang, Xiamen, Shenzhen, Yangzhou and Shijiazhuang.

The Yangtze River Delta, the Pearl River Delta, the Fujian Delta and the northern region have become the gathering places for the development of China's LED industry.

China's semiconductor lighting industry is developing well. The development of epitaxial chip enterprises is particularly rapid, the scale of packaging enterprises continues to maintain rapid growth, and lighting applications have made great progress.

In 2007, the output value of LED application products in China has exceeded 30 billion yuan, and has become the world's largest producer and exporter of LED full-color display, solar LED, landscape lighting and other application products. The emerging semiconductor lighting industry is taking shape.

China has formed certain characteristics in the field of lighting, among which outdoor lighting has developed the fastest, with hundreds of LED street lamp enterprises and dozens of demonstration roads built. However, China is still lagging behind in large LCD backlight and automobile headlights.

The centralized display of LED lighting at the 2008 Beijing Olympic Games has given people a new understanding of LED and has strongly promoted the development of China's semiconductor lighting industry.

At present, China's semiconductor industry is large but not strong, and its core competitiveness still needs to be further improved.

For domestic enterprises, strengthening the scale and improving the product quality and technical level is the primary task, or gradually breaking through core patents through research and development.

Due to the advantages of environmental protection, long service life and high photoelectric efficiency, LED applications in various industries have developed rapidly in recent years, and LED driving power supply has become a focus of attention. Theoretically, the service life of LED is more than 100000 hours, but in the actual application process, LED is extremely vulnerable to damage due to improper design of driving power supply and selection of driving mode.

At present, many manufacturers produce LED light products (such as guardrail, lamp cup, projection lamp), which use resistance and capacitance voltage reduction, and then add a voltage regulator diode to stabilize the voltage to supply power to the LED. This way of driving the LED has great defects. First of all, it is inefficient, and consumes a lot of power on the voltage reduction resistance, which may even exceed the power consumed by the LED, and cannot provide high current drive, because the greater the current, The more electric energy is consumed on the step-down resistor, so many LED products do not dare to adopt the parallel mode, but adopt the series mode to reduce the current. Secondly, the ability to stabilize the voltage is extremely poor, and it is impossible to ensure that the current through the LED does not exceed its normal working requirements. When designing products, the voltage at both ends of the LED will be reduced to supply power and drive, which is at the cost of reducing the brightness of the LED. The LED is driven by resistance and capacitance voltage reduction. The brightness of the LED cannot be stable. When the power supply voltage is low, the brightness of the LED will become dark. When the power supply voltage is high, the brightness of the LED will become brighter.

The future way is to integrate constant pressure and then linear constant current. The voltage is guaranteed to meet the load demand within a certain range. According to the different Vf values of LED between 3 and 3.6V, the lowest value can be calculated by multiplying the actual number of LEDs by 3V, and then the maximum possible voltage value can be calculated by multiplying the 3.6V voltage by the number, finally determining the voltage range to be adjusted for the power supply. The rear end of the linear constant current source can be used in parallel with multiple constant current sources, or the use of multiple single constant current sources can be increased. The front-end voltage source part samples and detects the voltage difference of constant current source, adjusts the appropriate load demand voltage, so as to achieve efficient and flexible drive line requirements. The constant current source needs a low voltage differential linear constant current device. The linear constant current source has a good current error and will also have a good gray scale performance. There can be a voltage difference of 1~3V at low current, and a low voltage difference of 200~300V at high current is required to have high efficiency, so the linear constant current source needs additional power supply. In fact, each drive mode has its advantages and disadvantages. According to the requirements of LED products and application occasions, the key is to select LED drive mode reasonably and accurately design the drive power supply.