LED lighting seeks to break through price barriers

Cost is the biggest obstacle for LEDs to enter the home market

PieroBianco, Business Manager, HBLED Product Line, Maxim

Compared to commercial lighting applications, the huge consumer base has made the LED home lighting market extremely attractive, but the home market is extremely sensitive to cost, which has led to its slow development. PieroBianco, Maxim's HBLED product line business manager, pointed out that "the key factor that restricts LED lighting into home applications is cost. In order to compete with other technologies (fluorescent is its main competitive product) for market share, the price of LED lamps must be controlled at 10 to Less than $15." Liu Xuechao, a senior technology market development engineer at Texas Instruments (TI), agrees. "Although the cost of LEDs is gradually decreasing, there is still a price gap compared to traditional CFL energy-saving lamps."

Texas Instruments senior technology market development engineer Liu Xuechao

The high cost of LED bulbs comes from three main sources, including high-power LED light sources, LED control chips, and bulb housing materials for good heat dissipation. Reducing drive cost is one of the effective ways to reduce the cost of the entire LED system. According to Maxim's PieroBianco, the use of a single-stage conversion driver, directly powered by AC power, can effectively reduce costs. Another way is to avoid using electrolytic capacitors in the driver as much as possible. Because LED lamps have a higher operating temperature, advanced electrolytic capacitors must be used to maintain sufficient drive circuit life. Therefore, if electrolytic capacitors are not required in the drive, the corresponding cost will be saved. The company has introduced a single-stage, LED lamp driver solution that eliminates the need for electrolytic capacitors.

Undoubtedly, the improvement of the technical level will help promote the successful application of LED lighting in the home. The luminous efficiency of high-brightness LEDs has been greatly improved in the past few years. With the continuous improvement of luminous efficiency, service life and reliability, the market appeal and application value of LED lighting will continue to increase, and adoption in the home. The rate will also gradually increase. In addition to price, high-brightness LED lighting solutions must also offer dimmable options in order for products to be truly competitive in the home market. By increasing the dimming function, the user can adjust the brightness of the lamp according to actual needs, which also helps to reduce power consumption.

Reliability and thermal design challenges

Zheng Lekang, Marketing Director, Lighting and Smart Grid, ON Semiconductor

The key challenge engineers must address when designing LED lighting systems is to maintain high reliability while reducing costs. According to Zheng Lekang, director of marketing for lighting and smart grids at ON Semiconductor, design engineers tend to use lower-level components, such as lower-rated capacitors or lower-precision resistors, to reduce the cost of home LED lighting systems. If a lower rated temperature capacitor is used in the electronic driver portion of a home LED lighting system, these lower temperature rated capacitors are likely to fail after several years (3 to 5 years) of use. Then, the final situation will be that the life of the LED itself in the LED lighting system is as long as 50,000 to 100,000 hours (15 to 20 years), but the electronic driver can only last for 3 to 5 years due to reliability problems. Therefore, engineers should not be designed at the expense of reliability and should ensure that the reliability and longevity of the electronic driver match the reliability and lifetime of the LED.

Deputy Manager of Accumulation Technology LED Lighting Product Line Project

Good thermal management and efficient drive circuit are important guarantees for efficient LED lighting system. "Otherwise, it may cause system reliability degradation, light decay or even product failure. For the drive part, efficient thermal management is also necessary. By increasing the conversion efficiency, the loss can be reduced, thereby reducing the heat output. From the design of the controller to the selection of components, attention needs to be paid." Su Ying, deputy manager of the LED lighting product line project of Taiwan Accumulation Technology, stressed. Improper heat dissipation will accelerate the attenuation of brightness, which in turn reduces the brightness and lifetime of the product. In addition, due to the harsh working environment of LED lighting (lightning strike, high temperature, etc.), improving the efficiency and reliability of the LED driving power supply has become a design difficulty.

Switching from traditional general lighting to LED lighting must also meet the high quality requirements of consumers. Liao Guangbin, senior project manager of Liqi Technology, believes that “the demand for LED lighting is different from that of traditional lighting products. Therefore, the power supply design developed specifically for LED lighting is very necessary. These requirements include constant current output and support for Triac. Dimming, single-input multi-string output design, low output power, high PF value, new architecture to meet high power and low cost requirements."

Intersil Senior Application Engineer TamaraSchmitz

Intersil senior application engineer Tamara Schmitz said, "Consumers require designs with power factors of at least 90 and over 80% efficiency. In DC applications, the maximum input voltage can exceed approximately 40 V. In AC applications, the input voltage can be 120V or 240V (maximum 277V). High-brightness LEDs must be driven by PWM running at 120Hz to minimize any visible interference. Sometimes the frequency needs to be changed. In addition to these design constraints, isolation can be used depending on the application. And non-isolated designs." Therefore, there is no solution for all applications. Each solution is specifically defined by the number of LEDs and the current through the LEDs. Depending on the magnetic component, the selected power component, and the output capacitor, the solution must be adjusted.

LED driver ICs need to achieve high efficiency and dimming

BillWeiss, Senior Product Marketing Manager, PowerIntegrations

Unlike traditional switching power supplies, LED driver power supplies require considerations such as heat dissipation, efficiency, and dimming, and thus place many different requirements on the driver IC. Bill Weiss, senior product marketing manager at PowerIntegrations (PI), points out that "the technology trends in AC/DC driver ICs are high reliability, high efficiency, high power factor, dimming and small size."

According to Maxim's PieroBianco, LED applications place two key requirements for AC/DC driver ICs, which is how they differ from traditional power ICs. First, the use of triacs for dimming is very complex and requires specialized, proven techniques. Flicker-free dimming is a major challenge for drive design. It is still difficult to find a solution that can meet this requirement. Secondly, unlike power supply circuits, LED drivers must operate in high temperature environments due to high power consumption during LED lighting. . Developing a driver that can operate for a long time in a high temperature environment is a special requirement for LED drivers.

The AC input (120VAC and 230VAC) lighting solutions developed by Maxim use a single-stage conversion structure to drive the LEDs. This solution allows the brightness to be adjusted by the triac without flicker, which can be achieved by eliminating the need for electrolytic capacitors. The dimensions and helps to extend the life. The device can be configured as an isolated (flyback) and non-isolated (buck) architecture with a power factor better than 0.9.

ON Semiconductor's new NCL30000 is a power factor corrected dimmable LED driver that uses a critical conduction mode (CrM) flyback architecture to provide a high power factor (>0.95) in a single-segment topology, saving one DC /DC conversion segment. Typical applications include LED downlights, LED driver power/drivers, and TRIAC dimmable LED-based bulb replacement. The device is compatible with leading edge TRIAC and trailing edge transistor dimmers. The LED output can be controlled to less than 2%, depending on the dimmer used.

Intersil's most popular HBLED driver, the ISL6745A, features "dead time" with adjustable switching frequency, adjustable soft-start, over-temperature protection, and precision adjustment for isolated or non-isolated, and adjustable or non-dimmable applications.

TI's new TPS99210 is a PFC-enabled LED driver chip that uses a fixed ON-TIME time-scaled Flyback architecture to drive 5W to 90W power LEDs with thyristor dimming for A19/E27 and GU10. Isolated LED driver design such as PAR30/38. TPS92010 is a complete LED lighting driver reference board jointly developed by TI and LemnisLighting to help solve the three problems of cost, dimming and efficiency. The TPS92010 LED light reference board uses TI's general LED lighting semiconductor technology and LemnisLighting dimming lighting application expertise to help accelerate the promotion of energy-efficient LED bulbs.

Su Xingsui, project manager of AXEL ite's strategic marketing department, said that in the future, high-power LED driver ICs will move toward highly integrated SoC and multi-chip packages. In addition to stability and low power consumption, they should have consistency. Constant current technology for brightness, pulse width modulation (PWM) technology with integrated brightness adjustment function, high voltage resistance for indoor lighting, etc. In addition, the driver output is independent, which can effectively prevent overheating; digital soft start function; cycle-by-cycle current limit; short circuit protection, over voltage protection and over temperature detection are also essential functions.

The design of LED drivers also requires design engineers to balance among the many technical parameters, weigh the performance and make decisions. To this end, PI offers a rich library of reference designs and supports comprehensive LED driver design optimization through online power design tools to help design engineers accelerate their time to market. The efforts of experts have allowed the technology to be further innovated and the vision for development to be better.

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