Choice of size and power LED lighting solutions

Whether it is high-power or low-power LED lighting applications, it is generally composed of power supply, LED driver, LED, lens and substrate. The key component is the LED driver, which must provide a constant current output to ensure the LED is emitted. Light will not be flickering and LED color shifting will not occur. It generally accepts 24V-48V DC voltage input, but there are also some advanced LED drivers that can directly accept 220V mains AC input. Most customers require high-performance LED drivers to meet upcoming LED lighting specifications such as "PF Value" 0.9" and "+85 Efficiency."

The main design challenges for LED lighting applications include the following: heat dissipation, high efficiency, low cost, dimming without flicker, wide dimming, reliability, safety, and elimination of color cast. These challenges need to be addressed by a combination of appropriate power system topology, drive circuit topology, and mechanical design.

Liang Houquan, director of technology marketing for Diodes Asia Pacific, said: "The biggest technical challenge for designers will be high efficiency requirements, optical design, thermal management and improved reliability of certain applications, such as high-brightness LED street lights. We now offer A range of LED lighting solutions cover applications from 0.1W to 250W."

“In the application of LED lighting systems, in addition to selecting the right LED products, a complete LED lighting design also includes optical design, thermal design, product design and electrical drive design. Since LED is a low voltage device, it converts high voltage AC power. The low-voltage constant-current drive used for LEDs will face many challenges.” Zheng Zongqian, senior application manager of ON Semiconductor China, pointed out: “Further, in order to ensure the advantages of LED lighting, LED electrical drives must be reliable, efficient, and safe. And low cost. Therefore, for different LED lighting applications, the first choice is to choose the correct drive circuit topology.” ON Semiconductor now offers all LED lighting solutions from 1W to 500W.

In order to quickly push the LED lighting market off, National Semiconductor Corporation (NSC) recently targeted a very large incandescent lamp to directly replace the market, using LED lights to directly replace incandescent lamps in existing home or other application markets, and launched A direct mains input LED driver chip LM3445 for this market.

However, Wu Zhimin, marketing manager of NSC Asia Pacific Power Management Products, said: "The incandescent lamp has been available for many years. For many years of unresolved technical standards, our home lighting system has been using many unresolved technical standards for many years. The situation may not change overnight. For example, based on heat dissipation and lighting angles, the original old lamp socket or device is not suitable for installing LED bulbs. However, in addition to technical problems, the cost effectiveness is also unable to make LED lights The biggest reason for the popularity. Tungsten bulbs and neon tubes are priced at about US$0.6-0.7/Klm, but the current price of LED lamps is still as high as US$40-50/Klm.”

As mentioned above, heat dissipation is a big problem that must be overcome because the LED light must be able to fit within the original old socket. Strictly speaking, this can be solved by mechanical engineering techniques. The responsibility of LED system manufacturers is to develop new technologies and try to increase the brightness of LEDs (ie the amount of lumens per unit of power). Wu Zhimin said with confidence: "We can provide the most efficient LED driver to ensure that the heat dissipation of the entire lighting system can be minimized."

The relatively high cost of LEDs is a major obstacle to the large-scale take-off of the LED lighting market. For example, Alexander Sommer, Director of Product Marketing, Power Management Business Unit, Infineon Technologies, Inc. said: "The typical LED lighting applications that are less than 25W are sign lights, sign lights, and alternative standard incandescent and halogen lamps. But now The initial cost of LEDs is still a major obstacle to entry into the mass market compared to fluorescent and incandescent technology."

Xu Ruibao, engineer of Cytech's product and design department, also agrees that the main commercialization challenge is cost. He said: "At present, LED lighting systems of various powers are achievable on the circuit. The technical challenges come from the requirements of terminal applications, such as automotive applications, taking into account optical design and overall thermal design. Commercial deployment The challenge comes mainly from LED costs."

Thermal considerations for LED lighting design

LED lighting systems below 25W are generally designed for applications such as reading desk lamps, corridor lights, living room spotlights, home dining lights, night lights, etc. Customers generally expect such applications to be designed as small as possible, so their PCBs can be placed in a design. The space is relatively small, so the temperature inside the package space may be high when used for a long time. Since the designer is unlikely to install a cooling fan inside it, its thermal design becomes critical and important.

“Most of the low-power LED lighting applications that are less than 25W require a certain amount of miniaturization. This often results in higher power density, although the power consumption is not very large. Sufficient thermal management measures must be provided by an improved mechanical structure. Electrical efficiency helps reduce power consumption,” Alexander Sommer points out. “If you need to further reduce thermal resistance, this can be done by electrical isolation because it enables the most efficient heat transfer. These methods also allow for optimized lumen output. ."