Today, with the rapid development of semiconductors, there is no research and development in the field of electromagnetic radiation. There is a kind of electromagnetic wave radiated by a device that can be observed by human eyes. It has made great progress in the field of light needs. Excellent performance makes us have no reason. Rejected, that is the new semiconductor solid state device - LED (Light Emitting Diode). The development and application of LED solid-state light source, which is called the new lighting revolution, has become one of the key development goals of this century. In particular, the official launch of the â€œNational Semiconductor Lighting Projectâ€ jointly organized by the Ministry of Science and Technology, the National Development and Reform Commission and the Ministry of Information Industry and other relevant departments marks that Chinaâ€™s high-brightness LED industry has entered an accelerated development stage, marking the Chinese LED industry. Encountered a rare opportunity for development.
The LED is a solid light source. When a forward voltage is applied across it, minority carriers and majority carriers in the semiconductor recombine, and the excess energy emitted will cause photon emission. Different materials can be used to make LEDs of different colors. As a new light source, in recent years, major companies and research institutes are in the ascendant to research LEDs, which has greatly improved their light efficiency. Lumiled has developed and produced white LEDs with luminous efficacy up to 90Lm/W, which has reached incandescent lamps. s level.
With the further study of LED, its light efficiency will be further improved, and its cost will be further reduced. In the near future, LED will replace incandescent lamps and even fluorescent lamps and become a major lighting source in the 21st century. trend. Unlike electronic ballasts for fluorescent lamps, the main function of the LED driver circuit is to convert the AC voltage to a constant current source and simultaneously match the voltage and current of the LED.
The digital model of the volt-ampere characteristics of the LED can be expressed by the following equation. VF=Vturn-on+RsIF+(Î”VF/Î”T)(T-25Â°C)(1) where Vturn-on is the starting voltage of the LED Rs represents the slope of the volt-ampere curve T ambient temperature Î”VF/Î”T is the LED forward voltage The temperature coefficient is typically -2V/Â°C for most LEDs.
From the volt-ampere curve and digital model of the LED, the small change of the forward voltage of the LED after the forward conduction will cause a large change of the LED current, and the environmental temperature, LED aging time and other factors will also change the electrical influence of the LED. performance. The light output of the LED is directly related to the LED current, so the LED driver circuit can preferably control the LED current when the input voltage and the ambient temperature change. Otherwise, the light output of the LED will change with factors such as input voltage and temperature, and if the LED current is out of control, long-term operation of the LED at high current will affect the reliability and life of the LED, and may fail.
1, the use of LED drive power
Standard lights are undergoing a revolution. In order to protect energy and respond to global warming, some states in the United States and other countries have begun to ban the use of energy-efficient incandescent bulbs. A variety of new technologies are being used to replace incandescent bulbs, with compact vacuum fluorescent lamps (CFLs) being the primary alternative. Although this CFL lamp consumes only 20% of the incandescent lamp, it contains toxic mercury. In contrast, LED lights provide a more efficient and environmentally friendly solution.
The original commercial application of LEDs appeared in the 1970s, but because of its extremely low light output, the range of applications is limited to areas such as indicator lights and calculator displays. Today, high-power LEDs that produce white light continue to increase in efficiency and prices are declining year by year, making it one of the choices for mainstream lighting applications. It is expected that with the development of LED technology , its luminous efficiency will reach 150 lm/W by 2012, and the cost of 1000 lumens will be less than US$5 (source: OIDA). At that time, LED is expected to become the main source of indoor lighting .
Rectifier bridge is to seal the rectifier tube in a shell. Points full bridge and half bridge. The full bridge connects the four diodes of the connected Bridge Rectifier circuit together. The half bridge is half of four diode bridge rectifiers, and two half bridges can be used to form a bridge rectifier circuit. One half bridge can also be used to form a full-wave rectifier circuit with a center-tapped transformer. Select a rectifier bridge to consider. Rectifier circuit and operating voltage.
Bridge Rectifier,Original Bridge Rectifier,Full Bridge Rectifier ,Diodes Bridge Rectifier,Single Phase Rectifier Bridge, Three Phase Bridge Rectifier
YANGZHOU POSITIONING TECH CO., LTD. , http://www.yzpst.com