LED lighting seeks to break through price barriers in the home market

Cost is the biggest obstacle to LED entering the home market

Piero Bianco, Business Line Manager, HBLED Product Line, Maxim

Compared with commercial lighting applications, a huge consumer base makes the LED home lighting market extremely attractive, but the home market is extremely sensitive to cost, which leads to its slow development. Piero Bianco, business line manager for Maxim's HBLED product line, points out, “The key factor that restricts LED lighting from entering home applications is cost. To compete for market share with other technologies (fluorescent lamps are its main competitors), the price of LED lamps must be controlled at 10 to US$15 or less.” Liu Xuechao, a senior technology market development engineer at Texas Instruments, agrees. “Although the cost of LEDs is gradually decreasing, there is still a certain price gap compared to traditional CFL energy-saving lamps.”

Texas Instruments Advanced Technology Market Development Engineer Liu Xuechao

The high cost of LED light bulbs comes mainly from three aspects, including high-power LED light sources, LED control chips, and bulb housing materials used to achieve good heat dissipation. One of the effective ways to reduce the cost of the entire LED system is to reduce the cost of the driver. According to Maxim's PieroBianco, using a single-stage conversion driver to directly use an AC power supply can effectively reduce costs. Another way is to avoid the use of electrolytic capacitors in the driver as much as possible. Because the operating temperature of the LED lamp is high, an advanced electrolytic capacitor must be used to maintain sufficient drive circuit life. Therefore, if there is no need to use electrolytic capacitors in the driver, the corresponding cost will be saved. The company has introduced a single-stage conversion LED lamp drive solution that does not require electrolytic capacitors.

Undoubtedly, the improvement of technology 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, reliability, etc., the market appeal and application value of LED lighting will continue to increase, and it will be adopted in homes. The rate will also gradually increase. In addition to price, in order to be truly competitive in the home market, high-brightness LED lighting solutions must also provide dimmable options. By adding the dimming function so that the user can adjust the brightness of the lamp according to actual needs, it also helps to reduce power consumption.

Reliability and Thermal Design Challenges

ON Semiconductor Lighting & Smart Grid Marketing Director Zheng Lekang

The key challenge that engineers must deal with when designing an LED lighting system is to maintain high reliability while reducing costs. Zheng Lekang, director of marketing for lighting and smart grid marketing at ON Semiconductor, said that in order to reduce the cost of home LED lighting systems, design engineers tend to use lower-level components such as lower-temperature rated capacitors or lower-accuracy resistors. If a lower rated temperature capacitor is used in the electronic driver part of a household LED lighting system, these lower rated capacitors are likely to fail after being used for several years (3 to 5 years). Then, the final situation will be LED life in the LED lighting system itself is up to 50,000 to 100,000 hours (15 to 20 years), but the electronic drive can only survive for 3 to 5 years due to reliability issues. Therefore, engineers cannot design at the expense of reliability, and should ensure that the reliability and lifespan of the electronic driver matches the reliability and longevity of the LED.

Su Ji, Deputy Manager, Accumulation Technology LED Lighting Product Line Project

Good thermal management and efficient drive circuits are important guarantees for achieving efficient LED lighting systems. “Otherwise there will be potential for system reliability degradation, light decay, and even product failure. Efficient thermal management is also required for the drive part. By increasing the conversion efficiency, it is possible to reduce losses and thereby reduce the heat output. From the design of the controller to the selection of the components, care must be taken.” Su Xing, deputy manager of the LED lighting product line at Taiwan Accuchip, stressed. Improper heat treatment will accelerate brightness decay, 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 LED driving power supply has become a design difficulty.

The shift from traditional general lighting to LED lighting must also meet consumer demand for high quality products. According to Liao Guangbin, a senior project manager at Liqi Technology, “The demand for LED lighting is different from that for traditional lighting products. Therefore, a power supply design scheme developed specifically for LED lighting is necessary. These requirements include constant current output and support for Triac. Dimming, single input multi-string output design, low output power, high PF, new architecture to meet high power and low cost requirements, etc."

Intersil Senior Applications Engineer Tamara Schmitz

Tamara Schmitz, Intersil's senior applications engineer, said, "Consumers demand that designs have a power factor of at least 90 and over 80% efficiency. In DC applications, the maximum input voltage can exceed about 40V. In AC applications, the input voltage may be 120V or 240V (maximum 277V) High-brightness LED must be driven by PWM running at 120Hz frequency to minimize any visible interference, sometimes need to change the frequency.In addition to these design constraints, depending on the application, you can use isolation And non-isolated design." Therefore, there is no one solution that fits all applications. Each solution is specifically defined based on the number of LEDs and the current through the LEDs. Depending on changes in magnetics, selected power components, and output capacitors, adjustments must be made to the solution.

LED driver ICs need to achieve high efficiency and dimmable

Bill Weiss, Senior Product Marketing Manager PowerIntegrations

Unlike traditional switching power supplies, LED driver power supplies need to consider issues such as heat dissipation, efficiency, and dimming, thus placing many different requirements on driver ICs. Bill Weiss, senior product marketing manager at Power Integrations (PI), pointed out that "the technology development trend for AC/DC driver ICs is high reliability, high efficiency, high power factor, dimmable and small size."

According to Maxim's PieroBianco, LED applications put forward two key requirements for AC/DC driver ICs, which is exactly the difference between them and traditional power ICs. First of all, the use of triacs to achieve dimming is very complex and requires dedicated mature technology. Flickerless dimming is a major challenge for driver design. It is still difficult to find a solution that can meet this requirement. Second, unlike power circuits, LED drivers must operate at high temperatures due to high power consumption in LED lighting. . The development of a driver capable of long-term operation 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 architecture to drive the LEDs. This solution allows the triac to adjust the brightness without flicker, as it does not require the use of electrolytic capacitors and can be made smaller. Dimensions, and help to extend the service life. Devices can be configured as isolated (flyback) and non-isolated (buck) architectures with a power factor better than 0.9.

ON Semiconductor's latest 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-stage topology, thereby saving one DC / DC conversion section. Typical applications include LED downlights, LED driver power/drivers, and TRIAC dimmable LED-based light bulb replacements. The device is compatible with leading-edge TRIAC and tail-edge transistor dimmers. Depending on the dimmer used, the LED output can be controlled below 2%.

Intersil's hottest HBLED driver, the ISL6745A, features "dead-time" with adjustable switching frequency, adjustable soft-start, over-temperature protection, and precise regulation, and can be used for isolated or non-isolated, as well as adjustable or non-dimmable applications.

TI's new TPS99210 is an LED driver chip with PFC function. It uses a fixed ON-TIME time-slicing Flyback architecture to achieve 5W ~ 90W power LED driver, and with SCR dimming, suitable for A19/E27, GU10, Design of isolated LED drivers such as PAR30/38. The TPS92010 is a complete LED lighting driver reference board from TI and Lemnis Lighting, which helps solve three major problems: cost, dimming and efficiency. The TPS92010 LED lamp reference board uses TI's general-purpose LED lighting semiconductor technology and Lemnis Lighting's dimmable lighting application expertise to help accelerate the promotion of energy-efficient LED light bulbs.

Su Shisui, Project Manager of AXElite's Strategic Marketing Department, said that in the future, high-power LED driver ICs will move toward highly-integrated SoCs and multi-chip packages. In addition to stability and low power consumption, they should also achieve consistent brightness. The constant current technology, pulse width modulation (PWM) technology with integrated brightness adjustment, and high-voltage characteristics for indoor lighting. In addition, the driver output is independent, which can effectively prevent overheating problems; digital soft-start function; cycle-by-cycle current limiting; short-circuit protection, over-voltage protection and over-temperature detection are also essential basic functions.

The design of the LED driver also requires the design engineer to balance among numerous technical parameters, repeatedly weighing the performance and making decisions. To this end, PI provides a rich reference design library and supports comprehensive LED driver design optimization through online power supply design tools, helping design engineers accelerate the time to market for their products. Experts’ efforts have enabled the technology to be further improved and the vision for development is better.