Intelligent and efficient LED driver design

Lighting power is an important source of global energy consumption. According to calculations, China's lighting electricity consumption accounts for about 12% of the total electricity consumption in the society. Among the various lighting fixtures, the use of incandescent lamps with a long history but low energy efficiency is still very extensive. If the use of energy-efficient light sources is limited, and the use of more energy-efficient and environmentally-friendly light sources is vigorously promoted, energy conservation will be facilitated.

Therefore, including China, many countries in the world have formulated policies to phase out incandescent bulbs. For example, China plans to phase out all the incandescent bulbs used for general lighting above 60W in 2015. Fluorescent lamps and compact fluorescent lamps (CFLs) have higher energy efficiency than incandescent lamps and have been used in the market for many years. However, fluorescent lamps contain highly toxic mercury, causing more and more environmental concerns.

In comparison, LED performance in various aspects, such as luminous efficiency, has been continuously improved, and it has also become an environmental protection and long-life characteristic, and has received increasing attention. In fact, LED downlights and retrofit bulbs already have higher energy efficiency than incandescent, halogen, or CFL lighting technologies. In terms of cost, the study found that compared with 2010, the price of LED has accelerated (falling 13% to 24% each year) and is expected to continue to decline in the next few years, which will help reduce the cost of LED bulbs and lamps.

Therefore, all countries in the world are optimistic about and promote the development of LED lighting industry. For example, the National Development and Reform Commission of the People's Republic of China issued the “Semiconductor Lighting Energy-Saving Industry Plan” and planned that by 2015, the market share of LED functional lighting products will exceed 20%, and the output value of LED lighting energy-saving industries will increase by 30% annually. In 2015, the output value will reach 450 billion RMB. Yuan ($72 billion).

LED general lighting applications and development prospects

In addition to the widespread use of mobile devices, medium-size liquid crystal display (LCD) backlights, and LED signage, LEDs are also increasingly used for interior/exterior lighting in LED cars, such as headlights, fog lamps, and taillights. , Parking lights, dashboard backlight, roof lights, reading lights and atmosphere lights, as well as LED lighting for residential lighting and architectural lighting and other general lighting.

LED general lighting applications cover a wide range of power, as low as 3W to 15W LED residential lighting, medium power such as 15W to 75W commercial and architectural decorative lighting, up to 75W to 250W outdoor and infrastructure lighting, typical lighting products like MR16/GU10 lamp, E27/A19 lamp, ballast, downlight, T8 lamp, street lamp, etc.

LED general lighting applications have great development prospects. Among the various LED general lighting fixtures, in the near term, the development momentum of LED bulbs (such as A19 LED bulbs) is staggering. According to statistics, global LED bulb shipments reached 735 million in 2012 and is expected to grow to 1.225 billion in 2013; it is estimated that by 2014 it will usher in the tipping point of the LED bulb market, when the price of LED bulbs will drop to US$10. In the following, shipments are expected to increase by approximately 85% from 2013 to 2.27 billion; and by 2015 shipments will further increase to 3.9 billion.

Energy-efficient driver is the focus of LED general lighting

To maximize the energy-saving features of LED lighting, high-efficiency LED drivers are required. We use LED bulbs as an example. Typical LED bulbs include LED arrays, drive circuits, diffusers, heat sinks, and screw caps. In terms of drive circuits, energy-efficient LED Driver ICs are undoubtedly the focus. The right half of Figure 2 shows a typical LED light bulb driver circuit using a typical stand-alone LED driver.

To take advantage of the high efficiency of LED general lighting, LED drivers present multiple challenges. The first is that energy efficiency is crucial. LED bulbs, for example, have a fixed shape and limited heat dissipation. The use of energy-efficient LED drivers can help convert more electrical energy into light energy and help dissipate heat. Second, LED bulbs have limited space and require a larger Heat Sink area, especially for larger power bulbs. In addition, LEDs are rapidly changing, offering a variety of options that pose challenges for the choice of LED drivers. Due to the limited space of the LED light bulb, the size of the driving electronic circuit must be reduced to increase the remaining space and cooperate with heat dissipation. LED general lighting covers different power levels, so LED driver selection must be optimized to match different lighting and power requirements. For safety, LED selection and other factors, the designer must also consider whether to use isolated or non-isolated topology, which also affects the choice of LED driver.

ON Semiconductor's Driver Solution for LED Universal Lighting

ON Semiconductor actively promotes energy-efficient innovation, including energy efficient electronic innovations such as LED lighting, involving many segments of LED lighting, such as mobile devices, LCD backlighting, LED signage, automotive and general lighting as mentioned above. Among them, LED general lighting is now ON Semiconductor's focus in the lighting market. In the LED general lighting market, ON Semiconductor's strategy is to make full use of the company's broad array of analog power ICs, discrete devices, and advanced micro packages to provide differentiated, energy-efficient LED driver solutions.

ON Semiconductor supplies LED driver solutions covering a wide range of power and different topologies. The drivers that ON Semiconductor can use for low-power LED general-purpose lighting applications include the NCL30000, NCL30002, and NCL3008x series. Among them, the NCL30000 is a single-stage power factor correction (PFC) LED driver that supports TRIAC dimming. It uses a secondary-side controller to support flyback/buck/buck-boost topology. The NCL30002 is also a single-stage power factor correction LED driver that supports a buck topology and provides ±3% current margin. The NCL3008x family currently includes devices such as the NCL30080, NCL30081, NCL30082, and NCL30083, and is a new high-efficiency quasi-resonant controller for low-power LED lighting applications.

It is worth mentioning that the NCL3008x series uses the primary side regulation (primary-side control) technology (also called primary-side control or primary-side control), which eliminates the need for secondary-side control circuits and optocouplers. Constant current stabilization of the LED current from the primary side helps simplify PCB layout, save board space, improve energy efficiency, and simplify safety analysis. In addition, it has many advantages such as high current stability, support for wide forward voltage drop (Vf) range, low electromagnetic interference (EMI), and integrated robust protection features. This series of devices provides a power factor of 0.8 to 0.9, in line with the United States "Energy Star" power LED lighting greater than 5W power factor requirements (PF "0.7).

ON Semiconductor also developed a reference design for the compact A19 LED light bulb based on the NCL30082. This reference design is optimized for isolating a flyback or non-isolated buck-boost topology and is optimized for 10W LED lighting applications. It uses a valley fill PFC to meet the "Energy Star" power factor above 0.7. The target size of the PCB and components is a 22x60mm cylinder. Tests have shown that this reference design provides high energy efficiency, high power factor, and high stability.

In terms of medium-power and high-power LED lighting, ON Semiconductor also provides a rich product portfolio to meet customers' different application needs. It includes both single and combined controllers as well as traditional two-stage (PFC + DC-DC) controllers covering a wide power range from 15W to 400W.

In medium-power LED general lighting applications, single-stage power factor correction LED controllers such as the NCL30000 and NCL30001 can be used; in high-power applications, energy-efficient combination controllers such as NCL30051 and NCP1910 can be used. Take the NCL30051 as an example, this is a power factor correction (PFC) and resonant half-bridge combination controller optimized for off-line LED lighting applications that provide constant voltage for step-down DC-DC converters/LED drivers. The device integrates a critical conduction mode (CrM) PFC controller and a half-bridge resonant controller with a built-in 600V driver optimized for off-line power applications with all the features needed to achieve high efficiency, small form factor designs .

In addition to the above-mentioned single-stage solution, designers can also choose the traditional two-stage (PFC segment + DC-DC conversion segment) solution according to application requirements. Specifically, optional controllers for the PFC segment include NCP1653, NCP1631, NCP1611/NCP1612, and NCP1608. Among them, NCP1611/2 is an enhanced energy-efficient PFC controller based on an innovative current-controlled frequency reverse- going (CCFF) architecture. When the PFC inductor current exceeds a set value, the circuit usually operates in the critical conduction mode (CrM). When the current is lower than the preset value, the switching frequency is linearly reduced to about 20 kHz, at which time the current is zero. The CCFF architecture simultaneously maximizes rated load operation energy efficiency and light load energy efficiency, especially minimizing standby losses. Typical applications include flat panel TVs, all-in-one computers and high-power adapters, and LED lighting power supplies and drivers. Dimmable fluorescent ballasts, etc.

In the DC-DC section, optional devices include NCP1398, NCP1380, NCP1288, and NCL30105. In addition to these devices, ON Semiconductor is also developing more new production devices to meet customers' wider application needs.

Intelligent LED lighting advantages and development forecast

The emerging LED intelligent lighting is another important point in the LED general lighting market, and it is also an important development direction. The so-called "smart lighting" is often combined with intelligent dimmable LED drivers, wireless receivers, infrared receivers, ambient light sensors, and passive infrared occupancy sensors.

LED intelligent lighting will make LEDs easier to control and dimming. LED smart lighting electronic circuit will enhance a variety of new features, such as occupancy sensors or ambient light sensors with dimming control and power saving. For example, a built-in occupancy sensor can be used to detect and determine whether a lighting area is occupied, typically for room entrance or exit, enabling safe lighting control and power saving. Most of these sensors use passive infrared (Ir) sensors, and other sensor options include ultrasound and motion sensors.

In addition, silicon photoelectric sensors are used in electronic circuits, which can be used for different applications such as measuring ambient light to collect sunlight, and for sensing the light output of a lamp to perform LED lighting control. Typical ambient light sensors are, for example, ONA Semiconductor's NOA1211/2 with linear output and NOA1305 with dual output. Ambient light sensors combine energy with outdoor (dusk/dawn) and indoor (daylight collection) dimming. By controlling the LED light source in a closed loop, the specific light output under different temperature and time conditions can be adjusted. In addition, constant light output adjustment with LED output light feedback can save and extend the life of the driver.

Smart lighting will also be more flexible, allowing the use of low-power wireless interfaces such as IrDA infrared, Zigbee, and Bluetooth LE without changing the switches or cables. But this requires wireless control standards in place, such as Zigbee Light Link.

LED driver ICs must be designed to work with LED "smart" lighting and can easily be designed to work with both analog and digital (ie, PWM) dimming. For example, ON Semiconductor's NCL30082 LED controller with intelligent dimming interface enables analog dimming, digital dimming, or simultaneous analog and digital dimming with a single control pin, providing wide dimming from 0 to 100% range. The device is easy to connect to analog sensors or microcontroller (MCU) general-purpose input/output ports (GPIOs) for increased design flexibility.

With the cooperation of these technologies, intelligent LED light bulbs and LED modules will soon emerge. By combining standardized wireless control technology, Ethernet and the Internet, people are expected to use smart phones to remotely control LED light bulbs. The new solution also addresses thermal management, optics, and modular/substitution issues. The commercial/industrial segment is expected to lead the adoption of smart lighting solutions.

summary

In the tide of environmental protection and the promotion of various policies and regulations, LED lighting is rapidly developing. To take full advantage of the high efficiency of LED general lighting, the use of energy-efficient LED drivers is essential. This article describes the challenges faced by general-purpose lighting LED drivers and the LED driver solutions that ON Semiconductor has overcome these challenges and applied to different LED general-purpose lighting applications. ON Semiconductor offers a broad lineup of complementary solutions, including smart dimming LED drivers and related sensors, to help promote and welcome the dawn of LED intelligent lighting.