To meet the increasingly stringent product requirements of the home LED lighting application market, the new generation of off-line LED drivers feature electrical isolation, high efficiency, power factor correction and Triac dimming, and provide well-regulated current to maintain consistent brightness. At the same time, various protection functions also improve system reliability.
In the past few years, display backlighting applications have been a major factor driving the growth of the light-emitting diode (LED) market. However, LED general-purpose lighting is increasingly attractive in the commercial and residential markets, and it has further accelerated the growth of the LED market. According to a research report by LEDinside, a market research institute, the commercial high-lumen LED lighting system has experienced rapid growth in 2010. This is because home LED lighting is still too expensive for most consumers. On the other hand, for commercial areas such as parking lots, offices, factories, warehouses, etc., LED lighting can bring long-term benefits such as energy saving and environmental protection, and related tax reduction policies, so the LED lighting usage in these application areas will grow substantially.
Home LED lighting market will accelerate growth
LED lamps can not only replace high-pressure sodium lamps, halogen lamps and incandescent lamps, but also replace energy-saving fluorescent lamps (CFLs) and fluorescent lamps in some fields. LED commercial lighting will grow rapidly and be widely adopted, while 2012 is a key year for home LED lighting.
In commercial buildings, lighting typically accounts for 25 to 40% of total energy use, so it is not surprising that commercial applications have begun to switch to LED lighting. Since such applications require high intensity, long-term lighting, the economic return from saving energy is relatively short-term. In addition, the LED accessory has a long life, thus greatly reducing the replacement cost of the LED lamp. The replacement cost includes not only the cost of the lighting fixture itself, but also the labor cost of hands-on replacement, which is usually high in some applications, such as the disassembly and assembly of high-end lighting applications, which require professional-level labor costs.
Overall, from the perspective of most consumers, GM's home LED lighting is still too expensive, but in the future, with the decline in the price of LED accessories and wider supply of LEDs, the lighting market will also appear in the residential sector. growing up. Most analysts expect the residential market to accelerate growth after 2012.
LED driver IC design considers multi-faceted and multi-faceted
As mentioned earlier, the main driver behind the high growth rate of the LED lighting market is its ability to significantly reduce power consumption. If the same amount of light output (in lumens) is provided compared to incandescent lighting, the LED requires less than 20% of the incandescent lamp. As shown in Table 1, LED lighting has more advantages, but there are more challenges. The advantages of LEDs include longer lifetimes than incandescent lamps, which greatly reduces replacement costs; especially in the residential lighting market, the ability to dim LEDs with previously installed bidirectional silicon-controlled rectifier (Triac) dimmers is also a major advantage. The LED light can be turned on in real time, without the warm-up time like the CFL, and the LED light is not sensitive to the power cycle, which is also different from the CFL lamp. In addition, the LED lighting accessory does not contain any toxic materials that need to be controlled or handled, while the CFL operates with toxic mercury vapor. Finally, LEDs can achieve new and very flat form factors, which is impossible with other technologies.
These new LED lighting applications cover a wide range of applications, from 4 watt (W) screw-in replaceable incandescent bulbs to 100W street lights to high shed lights requiring hundreds of watts of power. Most of these LED lights rely on existing AC (AC) off-line power supplies (typically 90 to 265 VAC depending on the geographic location of the end application. To obtain an off-line power from the AC) The ability to efficiently drive LEDs has created some fairly unique LED driver IC design challenges.
LED drivers must not only provide the highest efficiency to ensure power savings, but also provide electrical isolation for safety reasons. In addition, LED drivers are also required to provide power factor correction (PFC) and low harmonic distortion performance for a variety of applications. Not only that, but in many residential applications, LED drivers must also provide the ability to dim with existing Triac dimmers. Finally, the solution must be cost-effective and the overall area should be small enough to allow the attachment to have enough room to accommodate the solution to attract commercial and residential users to replace existing lights with LED lights. All in all, LED driver ICs that meet these requirements are available, which is critical to the widespread adoption of LED lighting applications.
LED power saving still has room for improvement
One of the main driving forces behind the rapid growth of the LED lighting market is that LED lights can save more power than incandescent or even CFL lighting. So, look at the power savings from using existing LEDs and how their power will be further saved in the next few years.
Current 60W incandescent lamps provide approximately 800 lumens and can be converted to 13.3 lumens per watt (lm/W). Existing LEDs have an efficiency of between 50 and 170 lm/W for commercial products. Future LEDs will provide efficiencies ranging from 200 to 230 lm/W. However, the maximum theoretical efficiency is about 250 lm/W.
For lighting purposes, a 100 lm/W LED can be considered. The electric power required for the LED itself is 8W. However, the efficiency of AC-to-DC (AC-DC) LED drive electronics must also be taken into account, which is 85% for high performance LED drivers. Therefore, the total power required for off-line power supplies is 8W/0.85=9.4W, resulting in a power savings of 84% compared to incandescent lamps. If you use a more conservative figure of 65 lm / W, the LED power can be reduced by 75% compared to the power consumed by incandescent lamps. Looking ahead, power will be saved as much as 92% when 200 lm/W LEDs are available. In order to meet the current ENERGY STAR requirements, compared to standard incandescent lamps, the power of LED lamps must be reduced by at least 75% in order to replace incandescent lamps.
Off-line power supply design is difficult
The ability to drive LEDs with off-line power supplies can increase applications faster and faster, as power supplies of this type can be easily and easily obtained in commercial buildings and homes. Although the attachment of the LED lamp is relatively simple and the end user is very easy to install, the requirements for the LED driver IC are greatly improved. Because the LED requires a well-regulated constant current source to provide a constant light output, powering the LED with an AC input source requires some special design methods and meets some special design requirements.
For example, in different parts of the world, off-line power parameters may vary, typically between 90 and 265 VAC, and frequencies between 50 and 65 Hz. Therefore, in order to manufacture a LED accessory device for the general global market, it is preferable to have such a circuit design that the LED can be used anywhere in the world without modification. To achieve such a goal, a single LED driver IC can be processed to handle a variety of input voltages and Frequency function.
In addition, there are many off-line LED applications that require electrical isolation between the LED and the driver circuit. This is primarily due to safety considerations and is strictly required by several regulatory agencies. Electrical isolation is typically performed by an isolated flyback LED driver architecture that uses a transformer to isolate the primary and secondary ends of the driver circuit.
The power required to use LED lighting comes from the fact that the power required to provide a specific light output can be greatly reduced, so it is imperative that the LED driver IC provide the highest efficiency. Because the LED driver circuit must convert the high voltage AC supply to a lower voltage and a well regulated LED current, the LED driver IC must be designed to provide efficiencies greater than 80% so as not to waste power.
And in order to match the widespread use of Triac dimmers in residential applications where LEDs are widely available, LED driver ICs must work efficiently with these dimmers. Triac dimmers are designed to work well with incandescent and halogen lamps, which are ideal resistive loads. However, LED driver circuits are generally non-linear and are not electrically pure resistive loads. Its input bridge rectifier typically absorbs high-intensity peak currents when the AC input voltage is at its positive and negative peaks. Therefore, the LED driver IC must be designed to "simulate" a purely resistive load to ensure that the LEDs are properly activated without any significant flicker and that a Triac is used for proper dimming.
PFC left and right drive circuit performance
In terms of LED lighting, PFC is an important performance specification. In short, if the current drawn is proportional to the input voltage and in phase, the power correction factor is one. Because incandescent lamps are an ideal resistive load, the input current and voltage are in phase and the PFC is 1. PFC is particularly important because it relates to the electrical power that local power suppliers need to provide.
In other words, in a power system, a load with a low power factor can draw more current than if a load with a high power factor is the same. Because of the higher current required, the energy lost in the power distribution system is also increased, requiring thicker wires and other transmission equipment. However, larger equipment and energy waste increase costs, so power companies typically charge higher fees for industrial or commercial customers with lower power factors. International standards for LED applications are still under development, but most believe that for LED lighting applications, PFC > 0.90 will be required.
LED driver circuits (including a large number of diodes, transformers, and capacitors) do not behave like a purely resistive load, and their PFC can be as low as 0.5. In order to increase the PFC to above 0.9, active or passive PFC circuits must be designed into the LED driver circuit. In addition, high PFC is especially important in applications that use hundreds or more 50 watt LED lamps, in which case a high PFC (>0.95) LED drive design is beneficial.