Power LED Lighting Design
Whether power or small power LED lighting applications, generally consists of power supply, LED drivers, LED, lens and substrate sections, one of the key components is the LED driver, it must provide a constant current output in order to ensure the LED emits The light does not flicker, not occur LED color cast phenomenon, it is generally accepted 24V-48V DC voltage input, but also has some advanced LED driver can be directly accepts AC input of 220V electricity. Most customers require the use of high-performance LED driver to meet the PF value> 0.9 and +85 efficiency LED lighting specification forthcoming .
The main design challenges for LED lighting applications include the following aspects: heat, high efficiency, low cost, dimming, flicker-free, wide range dimming, reliability, security, and eliminate a color cast. These challenges require integrated use of appropriate power system topology architecture, drive circuit topology and mechanical design to solve.
Diodes, Asia Pacific Marketing Director, said: "For a designer, the biggest technical challenge is the high efficiency requirements, optical design, thermal management, and improve the reliability of some applications, such as high-brightness LED streetlights. Beam after the right we now offer series of LED lighting solutions covering applications from 0.1W to 250W.
"In addition to selecting the right LED products, LED lighting system, a complete LED lighting design but also including optical design, thermal design, product design and electrical drive design LED low-voltage devices, high-voltage AC power supply converted to LED using low voltage constant current driver will be faced with many challenges. "before the ON Semiconductor China area senior application manager Zheng were pointed out:" further said that, in order to ensure the advantages of LED lighting, LED electrical drive must be reliable, efficient, safety and low-cost. therefore, for a variety of LED lighting applications, you first need to select the correct driver circuit topology. "ON Semiconductor now from 1W to 500W power range of LED lighting solutions can provide.
In order to drive rapid take-off of the LED lighting market, National Semiconductor Corporation (NSC) has recently targeted an enormous incandescent direct replacement market, which uses LED lights directly replace incandescent lamps in existing home or other application markets, and launched a a direct mains for the market to enter the LED chip LM3445.
However, the NSC Asia Pacific product marketing manager for power management incandescent lamp has been available for many years, for many of the texts for the technical standards, our home lighting system has also followed many of the texts for the technical standards, the Wu Zhimin, said: not overnight can be changed over. example, based on issues such as cooling and lighting angles, the original old-fashioned lamp socket or device is not appropriate to install LED bulbs but in addition to the technical problems, the cost-effectiveness is also LED lights can not The popularity of the biggest causes of the price of incandescent light bulbs and neon tubes of about US $ 0.6-0.7/Klm, but the price of LED lights still up to U.S. $ 40-50/Klm. "
As mentioned above, the LED lights must be able to be installed within the original old socket, therefore the heat is a must overcome. But strictly speaking, it can take advantage of mechanical engineering technology to solve the problem, the responsibility of the LED system manufacturers to develop new technologies, maximize the LED brightness (lumens amount) per unit of power generated. Wu Zhimin said with confidence: "We can provide the efficacy of the most efficient LED driver to ensure that the entire lighting system to minimize the amount of heat."
The relatively high cost of LED lighting market is still difficult to scale take-off of the main obstacles. For example, Infineon power management business unit director of product marketing Alexander Sommer said: "the majority of less than 25W typical LED lighting applications marker lamps, marker lamps, as well as replace standard incandescent and halogen lamps but with compared to existing fluorescent and incandescent technology, LED initial cost is still a major obstacle to enter the mass market. "
Cytech products and design department engineers Xu Rui package also agree that the cost of major commercial challenges. He said: "various power LED lighting systems are on the circuit can be achieved, the technical challenges from the requirements of end-use applications, used in automobiles, for example, to take into account the optical design and the overall thermal design. Commercially deploy challenges mainly from the LED the cost. "
Thermal considerations LED lighting design
25W of LED lighting systems are generally designed for spotlights like reading lamps, corridor lights, living room, family dining lamps in applications such as customers generally want this type of application design is the more compact as possible, so the PCB can be placed The design space is relatively small, so the temperature inside the packaging space when used for a long time may be very high. Designer unlikely to install a cooling fan within its thermal design becomes very critical and important.
"Most of less than 25W low power LED lighting applications require a certain degree of miniaturization, which often leads to higher power density, despite power is not great. Adequate thermal management measures must be provided by an improved mechanical structure. Addition, high electrical efficiency helps reduce power consumption. "Alexander Sommer noted that" If the need to further reduce the thermal resistance, which can be electrically isolated to do, because it can achieve a maximum efficiency of heat transfer. These methods also allow to achieve optimized lumens output. "
The idea is to prevent LED long work overheat problem of another dimming solutions. Fairchild's high voltage IC product marketing manager, said: SangCheol Her compared to fluorescent and incandescent lamps, dimming solutions is an important way to reduce the LED power consumption, the use of such programs dimming controller. Especially for small 25W of LED driver solutions, thermal problem is inevitable, due to the small PCB size package space is limited, so the program is more important. "
In fact, in this power range, the LED lights will replace halogen lamps and compact fluorescent lamps (CFL). In addition, advanced technology, in order to get rid of the heat problem, you must remove sensitive to temperature changes, passive components, such as electrolytic capacitors. However, most LED driver solutions are derived from the power supply topologies and on this basis, it should take into account the temperature limits, because most products are usually based on commercial standards, but the lights must ensure that can adapt to the harsh environment, such as industrial environments.
LED lighting design of the architecture of choice for
LED lighting systems architecture of choice depends on your design goals is a low-cost, high-efficiency, or the smallest PCB area. In general, less than 25W of LED lighting system does not require power correction, so you can take a simple topology architecture, such as PSR or Buck topology. 25W-100W LED lighting applications require power correction, it is generally a single-stage PFC and quasi-resonant (QR) PWM flyback topology. More than 100W LED lighting applications generally use efficient LLC topology and two-stage PFC.
Less than 25W power LED lighting solutions the PSR or Buck topology can be used, mainly because this power range for small design, the emphasis on the simplicity of the design solutions for medium power (25W-100W) suitable for single-stage PFC quasi-resonant ( QR) PWM, flyback topology. "SangCheol of Her high power solutions (> 100W) suitable LLC, QR PWM, flyback topology design. LLC and QR better performance from the point of view of efficiency, ; PSR program without secondary feedback, simple design, the size is also smaller than other programs. "
Cheng Chung also said: "The main applications of less than 25 W LED lamps in indoor lighting, they are mainly low-cost flyback topology. Transformation of ON Semiconductor NCP1015 and NCP1027 monolithic integrated circuit integrates a built-in high-voltage MOSFET and PWM control can effectively reduce PCB area and the volume of the lamp, provide a maximum power output of 25W (230V AC input). "
Less than 25W LED lighting applications for non-isolated input to output conversion ratio is low, so simple buck converter can be the choice of a low-cost and small size. Isolated valued efficiency topology architecture, like quasi-resonant devices Infineon CoolSET ICE2QS Series flyback topology is a good choice. "Alexander Sommer said. Infineon is the first company to offer digital quasi-resonant flyback controller IC suppliers.
25W-100W power range typical LED lighting applications, street lighting (district roads) and in public places such as parking. Power conversion efficiency, cost-effective implementation of PFC function and high color quality is the most important of the three major technical challenge. For example, commercial lighting and street lighting applications, longer service life and lower maintenance costs resulting is helping to overcome the higher initial cost of entry barriers. 25W to 100W LED lighting applications power factor requirements, and therefore need to increase the power factor correction circuit.
"This circuit can be used to the traditional two-stage structure, the active non-continuous mode power factor correction (PFC) circuit plus a DC-DC PWM conversion circuit, such as power factor correction controller ON NCP1607, NCP1607 external circuit is very simple and can provide very good performance. "Zheng were before", it is recommended for high efficiency, low cost and small size LED program is a single-stage PFC circuit, it can simultaneously achieve low voltage DC power factor and isolation output, and has significant cost advantages, will become the mainstream of the medium-power LED lighting program. Semiconductor NCP1652 optimal control scheme for single-stage PFC circuit. "
Shenzhen Shiqiang Telecommunications is using the Silicon Labs C8051F3XX series of 8-bit MCU to be implemented in software PFC. The company assistant market manager Huang Feng Sun said: "our home city electric (180V-260V) input 10W-30W low power LED lighting applications developed all-digital LED lighting program, available software controlled manner to achieve up to 0.95 of PFC value. Hardware PFC compared with the set of software solutions in the premise to guarantee the same performance indicators, and also has a higher flexibility, adaptability, and scalability. "The program uses LED driver MIC3230 maximum output current of 350mA maximum drive 12 1W LEDs, can well meet the needs of indoor lighting.
Alexander Sommer said: "For the efficiency and performance of 25W-100W power LED lighting application requirements in a very wide input and / or load range (dimming) has recommended an independent with the PFC stage quasi-resonant flyback topology. typically can achieve up to 90% efficiency. "
100W or more applications, including the main road and highway lighting (It should be up to 20K lumens brightness or more, and a 250W power supply input) and professional applications, such as stage lighting and architectural floodlighting. A key driving force in high-power applications using LED reliability and low power consumption of the low cost of ownership. For example, the system efficiency can be compared with a metal halide and low pressure sodium lamps. The initial cost is more likely to continue in the short term barriers to entry in the market.
Cheng Chung pointed out: "For more than 100W of LED application, we will use the active non-continuous mode power factor correction circuit and half bridge resonant DC-DC converter circuit. Launched a new integrated controller, which integrates active non-continuous mode power factor controller and high-voltage driver half-bridge resonant controller. "
The half-bridge resonant controller operates at a fixed switching frequency and a fixed duty cycle, and the circuit does not require output side of the feedback control loop. This makes the resonant half-bridge DC-DC converter circuit ZVS and ZCS state at the highest efficiency. The DC output voltage will follow the output of the power factor correction circuit.
Alexander Sommer stressed: "higher power level of 100W or more LED lighting applications, the efficiency becomes more important, it is recommended to use the LLC resonant topology, it can achieve more than 90% efficiency, we recommend that you use Infineon's new 8-lead pin devices ICE1HS01. "
Regardless of how the output power of the LED lighting system, the selection of the LED drive circuit will largely depend on the input voltage range, the accumulated voltage drop of the LED string itself, and sufficient current required to drive the LED. This has led to a variety of different possible LED driver topologies, such as buck, boost, buck - boost and SEPIC type.
Linear Technology Power Products Division, Product Marketing Director Tony Arm strong, pointed out: "each topology has its advantages and disadvantages, which standard buck converter is the most simple and easiest to implement programs, boost followed by a buck - boost converter, SEPIC converter is the most difficult to achieve, because it uses a complex magnetic design principles, and designers need to have a a superb switch mode power supply design expertise. "
All in all, the end product application determines the topology of the LED, then according to the topology of the LED and the input power again reasonable choice Buck, Boost, SEPIC, or Buck-Boost structure. "In general, 25W choose Buck more power tend to choose Boost structure. Efficient both general can do more than 85%, LT3755 can be done up to 97% efficiency. Consider driving part BOM cost more should consider the overall system cost. "says Xu Rui package," As competition intensifies, from time to time there will be a lower BOM cost of the program, but not necessarily the most appropriate design products in accordance with this standard does not recommend PCB area is mainly controlled by the main components, a low-power LED lights maximize the use of high integration programs. To choose the technology of high-power high integration products and simple external circuit. discussed here are DC-DC solution. "
Beam after the right also pointed out that: "In order to achieve high efficiency requirements, should consider the use of the switch-mode LED driver, the majority of these customers prefer to choose the buck LED driver, because the total efficient from a lowest BOM cost perspective to consider switching type LED converter is not the cheapest of these customers may try to use linear constant current LED driver which can provide the lowest BOM cost efficiency may not like the switch-mode LED driver as high as from the smallest PCB board area of the viewpoint, usually optional switch mode converter, because they generate less heat, and even the related components will be smaller volume. "
Analog, PWM and TRIAC dimming scheme
LED dimming solutions and norms have been changing, and until now has not been fixed, so now the market there are three dimming PWM, analog and SCR (TRAIC) program. PWM and analog method is relatively simple, but need to build the infrastructure of dimming and dimming controller.
Analog dimming scheme, the drawback is that the adjustment range of the LED current is confined between a maximum value to the maximum of about 10% (10:1 dimming range). As the LED's chromatography with current, so this method is not suitable for certain applications.
The PWM dimming solution is based on a certain fast enough to cover up the visual flicker rate (usually higher than 100MHz) to switch between zero current and maximum LED current. The duty cycle change the effective average current, which can achieve up to 3000:1 dimming range (limited only by the minimum duty cycle). As LED current either is at a maximum, or off, so that this method has the advantages of the LED color misregistration occurs can be avoided in the current changes in the analog dimming such LED color misregistration phenomenon is very common.
SangCheol Her optimistic about the market prospects TRIAC dimming program thyristor (TRIAC, 2 lines dimming) will become a very popular solution, because this technology can fully use the traditional system without any changes, he said: Moreover, it can also be extended to 3-line dimming in order to avoid the defects associated with the low power factor values. "
TRIAC dimmer today is a very hot topic of the industry, initially, TRIAC dimmers designed for incandescent, but most users want the same TRIAC dimmer alternative LED lights dimming. Leung said after the right: Diodes Zetex currently available to provide customers with full dimming solutions (including PWM, analog and TRIAC), ZXLD1362 LED driver Used ADJ pin to analog and PWM dimming, which brought to customers a great deal of design flexibility. "
However, Cheng Chung before that, TRIAC dimmer applications on the market should only be transitional, in the long run, you should use PWM dimming. He said: "The main point decisive factor as follows: 1) PWM dimming from zero to the most light, there will not be flashing phenomenon. 2) the performance will be better. Dimming output power with a power factor correction circuit , which is in line with the mandatory requirements of the global lighting power factor, although generally from 25 W, but the United States need a mandatory power factor correction circuit lights starting at zero watts such as the TRAIC dimming sacrifice power factor and increase the complexity of the circuit. Therefore, using the PWM dimming can provide the best performance of the selection, the future trend. 3) costs will be better with the duty cycle of the PWM adjustment, does not require much additional control circuit cost. "
Alexander Sommer also optimistic about the PWM dimming scheme prospects, he said: "analog dimming LED's PWM dimming method has the following advantages: 1) more efficient; 2) regardless of the degree of dimming allows LED has been optimization and constant current getting off work group; 3) LED color tone consistent throughout the dimming range (color shades like lumen output with LED operating current change). "
Xu Rui package frankly: "personal feel, the modulation choice should not be determined by the power of the LED. Should decide on the application requirements of the end products. Example, the display backlight or LED decorative lights may choose PWM dimming color consistency and high brightness level but for general home lighting or commercial lighting, analog dimming or TRIAC can also choose, but will produce a color cast, and the dimming level will be low. "
Beam after right said: "In order to achieve continuous dimming, flicker-free, most customers prefer to choose the PWM dimming, because it provides greater dimming range and better linearity. Depends on you are using dimmer frequency flicker can be minimized. analog dimming easier to achieve, because it requires only a DC voltage, flicker-free dimming of the LED. Generally speaking, dimming range narrower. "
Constituted by a plurality of high power LED lighting applications, ensure that each LED has a uniform brightness without any flicker has also become a major obstacle to the design, but the PWM method is easy to solve the blinking problem dimming. "If the duty cycle of the PWM modulator can be maintained constant, handy, there should not have the problem of uneven brightness of the lights." Said Wu Zhimin, "National Semiconductor's LED driver can not only ensure that the output current uniform size, but also to ensure screen high brightness contrast from these aspects, our LED drive than its class on the market better and winning. "Tony Armstrong pointed out that, in short, the end-user dimming method used in very a large extent, by the end use of LED itself to decide. For example, the LED for the back lighting to display the car infotainment system, ambient lighting brightness range is very wide, both sunny extremely bright, but also whether the January night darkness, can be described as vastly different. Because the human eye is extremely sensitive to slight variations of the ambient lighting conditions, and therefore need a wide dimming range of 3000:1. This will require the LED driver circuit using PWM dimming method.
However, he added: "LED street lamps either in the ON state or in the off state, and therefore need only a limited range of dimming can. In this case, the only use of a kinds of simple analog dimming method will be able to meet the requirements. "
As mentioned earlier, less than 25W of LED lighting applications replace standard incandescent and halogen lamps. In this power range, an application is the most likely alternative to TRIAC (TRIAC) gradually cut into the wall dimmer control incandescent or energy-saving lamps. Market leading and trailing edges cut dimmer overall compatibility challenges, from the perspective of EMI TRIAC dimming poor to.
DCM PFC single-stage PFC flyback topology like Infineon TDA486 3G is an appropriate choice. "Alexander Sommer think," 25W and above power range of LED lighting applications that require the best cost-effective non-dimming applications, oriented to the professional market. dimming control method selection will depend on the replacement or new installation type digital lighting control (such as DALI or wireless solutions) allows more precise control dimming level, and more more functionality, such as sunlight down light duty cycle induction. replacement installation may be required to be compatible with the old analog 1-10V dimming controller. "
The main design challenges for LED lighting applications include the following aspects: heat, high efficiency, low cost, dimming, flicker-free, wide range dimming, reliability, security, and eliminate a color cast. These challenges require integrated use of appropriate power system topology architecture, drive circuit topology and mechanical design to solve.
Diodes, Asia Pacific Marketing Director, said: "For a designer, the biggest technical challenge is the high efficiency requirements, optical design, thermal management, and improve the reliability of some applications, such as high-brightness LED streetlights. Beam after the right we now offer series of LED lighting solutions covering applications from 0.1W to 250W.
"In addition to selecting the right LED products, LED lighting system, a complete LED lighting design but also including optical design, thermal design, product design and electrical drive design LED low-voltage devices, high-voltage AC power supply converted to LED using low voltage constant current driver will be faced with many challenges. "before the ON Semiconductor China area senior application manager Zheng were pointed out:" further said that, in order to ensure the advantages of LED lighting, LED electrical drive must be reliable, efficient, safety and low-cost. therefore, for a variety of LED lighting applications, you first need to select the correct driver circuit topology. "ON Semiconductor now from 1W to 500W power range of LED lighting solutions can provide.
In order to drive rapid take-off of the LED lighting market, National Semiconductor Corporation (NSC) has recently targeted an enormous incandescent direct replacement market, which uses LED lights directly replace incandescent lamps in existing home or other application markets, and launched a a direct mains for the market to enter the LED chip LM3445.
However, the NSC Asia Pacific product marketing manager for power management incandescent lamp has been available for many years, for many of the texts for the technical standards, our home lighting system has also followed many of the texts for the technical standards, the Wu Zhimin, said: not overnight can be changed over. example, based on issues such as cooling and lighting angles, the original old-fashioned lamp socket or device is not appropriate to install LED bulbs but in addition to the technical problems, the cost-effectiveness is also LED lights can not The popularity of the biggest causes of the price of incandescent light bulbs and neon tubes of about US $ 0.6-0.7/Klm, but the price of LED lights still up to U.S. $ 40-50/Klm. "
As mentioned above, the LED lights must be able to be installed within the original old socket, therefore the heat is a must overcome. But strictly speaking, it can take advantage of mechanical engineering technology to solve the problem, the responsibility of the LED system manufacturers to develop new technologies, maximize the LED brightness (lumens amount) per unit of power generated. Wu Zhimin said with confidence: "We can provide the efficacy of the most efficient LED driver to ensure that the entire lighting system to minimize the amount of heat."
The relatively high cost of LED lighting market is still difficult to scale take-off of the main obstacles. For example, Infineon power management business unit director of product marketing Alexander Sommer said: "the majority of less than 25W typical LED lighting applications marker lamps, marker lamps, as well as replace standard incandescent and halogen lamps but with compared to existing fluorescent and incandescent technology, LED initial cost is still a major obstacle to enter the mass market. "
Cytech products and design department engineers Xu Rui package also agree that the cost of major commercial challenges. He said: "various power LED lighting systems are on the circuit can be achieved, the technical challenges from the requirements of end-use applications, used in automobiles, for example, to take into account the optical design and the overall thermal design. Commercially deploy challenges mainly from the LED the cost. "
Thermal considerations LED lighting design
25W of LED lighting systems are generally designed for spotlights like reading lamps, corridor lights, living room, family dining lamps in applications such as customers generally want this type of application design is the more compact as possible, so the PCB can be placed The design space is relatively small, so the temperature inside the packaging space when used for a long time may be very high. Designer unlikely to install a cooling fan within its thermal design becomes very critical and important.
"Most of less than 25W low power LED lighting applications require a certain degree of miniaturization, which often leads to higher power density, despite power is not great. Adequate thermal management measures must be provided by an improved mechanical structure. Addition, high electrical efficiency helps reduce power consumption. "Alexander Sommer noted that" If the need to further reduce the thermal resistance, which can be electrically isolated to do, because it can achieve a maximum efficiency of heat transfer. These methods also allow to achieve optimized lumens output. "
The idea is to prevent LED long work overheat problem of another dimming solutions. Fairchild's high voltage IC product marketing manager, said: SangCheol Her compared to fluorescent and incandescent lamps, dimming solutions is an important way to reduce the LED power consumption, the use of such programs dimming controller. Especially for small 25W of LED driver solutions, thermal problem is inevitable, due to the small PCB size package space is limited, so the program is more important. "
In fact, in this power range, the LED lights will replace halogen lamps and compact fluorescent lamps (CFL). In addition, advanced technology, in order to get rid of the heat problem, you must remove sensitive to temperature changes, passive components, such as electrolytic capacitors. However, most LED driver solutions are derived from the power supply topologies and on this basis, it should take into account the temperature limits, because most products are usually based on commercial standards, but the lights must ensure that can adapt to the harsh environment, such as industrial environments.
LED lighting design of the architecture of choice for
LED lighting systems architecture of choice depends on your design goals is a low-cost, high-efficiency, or the smallest PCB area. In general, less than 25W of LED lighting system does not require power correction, so you can take a simple topology architecture, such as PSR or Buck topology. 25W-100W LED lighting applications require power correction, it is generally a single-stage PFC and quasi-resonant (QR) PWM flyback topology. More than 100W LED lighting applications generally use efficient LLC topology and two-stage PFC.
Less than 25W power LED lighting solutions the PSR or Buck topology can be used, mainly because this power range for small design, the emphasis on the simplicity of the design solutions for medium power (25W-100W) suitable for single-stage PFC quasi-resonant ( QR) PWM, flyback topology. "SangCheol of Her high power solutions (> 100W) suitable LLC, QR PWM, flyback topology design. LLC and QR better performance from the point of view of efficiency, ; PSR program without secondary feedback, simple design, the size is also smaller than other programs. "
Cheng Chung also said: "The main applications of less than 25 W LED lamps in indoor lighting, they are mainly low-cost flyback topology. Transformation of ON Semiconductor NCP1015 and NCP1027 monolithic integrated circuit integrates a built-in high-voltage MOSFET and PWM control can effectively reduce PCB area and the volume of the lamp, provide a maximum power output of 25W (230V AC input). "
Less than 25W LED lighting applications for non-isolated input to output conversion ratio is low, so simple buck converter can be the choice of a low-cost and small size. Isolated valued efficiency topology architecture, like quasi-resonant devices Infineon CoolSET ICE2QS Series flyback topology is a good choice. "Alexander Sommer said. Infineon is the first company to offer digital quasi-resonant flyback controller IC suppliers.
25W-100W power range typical LED lighting applications, street lighting (district roads) and in public places such as parking. Power conversion efficiency, cost-effective implementation of PFC function and high color quality is the most important of the three major technical challenge. For example, commercial lighting and street lighting applications, longer service life and lower maintenance costs resulting is helping to overcome the higher initial cost of entry barriers. 25W to 100W LED lighting applications power factor requirements, and therefore need to increase the power factor correction circuit.
"This circuit can be used to the traditional two-stage structure, the active non-continuous mode power factor correction (PFC) circuit plus a DC-DC PWM conversion circuit, such as power factor correction controller ON NCP1607, NCP1607 external circuit is very simple and can provide very good performance. "Zheng were before", it is recommended for high efficiency, low cost and small size LED program is a single-stage PFC circuit, it can simultaneously achieve low voltage DC power factor and isolation output, and has significant cost advantages, will become the mainstream of the medium-power LED lighting program. Semiconductor NCP1652 optimal control scheme for single-stage PFC circuit. "
Shenzhen Shiqiang Telecommunications is using the Silicon Labs C8051F3XX series of 8-bit MCU to be implemented in software PFC. The company assistant market manager Huang Feng Sun said: "our home city electric (180V-260V) input 10W-30W low power LED lighting applications developed all-digital LED lighting program, available software controlled manner to achieve up to 0.95 of PFC value. Hardware PFC compared with the set of software solutions in the premise to guarantee the same performance indicators, and also has a higher flexibility, adaptability, and scalability. "The program uses LED driver MIC3230 maximum output current of 350mA maximum drive 12 1W LEDs, can well meet the needs of indoor lighting.
Alexander Sommer said: "For the efficiency and performance of 25W-100W power LED lighting application requirements in a very wide input and / or load range (dimming) has recommended an independent with the PFC stage quasi-resonant flyback topology. typically can achieve up to 90% efficiency. "
100W or more applications, including the main road and highway lighting (It should be up to 20K lumens brightness or more, and a 250W power supply input) and professional applications, such as stage lighting and architectural floodlighting. A key driving force in high-power applications using LED reliability and low power consumption of the low cost of ownership. For example, the system efficiency can be compared with a metal halide and low pressure sodium lamps. The initial cost is more likely to continue in the short term barriers to entry in the market.
Cheng Chung pointed out: "For more than 100W of LED application, we will use the active non-continuous mode power factor correction circuit and half bridge resonant DC-DC converter circuit. Launched a new integrated controller, which integrates active non-continuous mode power factor controller and high-voltage driver half-bridge resonant controller. "
The half-bridge resonant controller operates at a fixed switching frequency and a fixed duty cycle, and the circuit does not require output side of the feedback control loop. This makes the resonant half-bridge DC-DC converter circuit ZVS and ZCS state at the highest efficiency. The DC output voltage will follow the output of the power factor correction circuit.
Alexander Sommer stressed: "higher power level of 100W or more LED lighting applications, the efficiency becomes more important, it is recommended to use the LLC resonant topology, it can achieve more than 90% efficiency, we recommend that you use Infineon's new 8-lead pin devices ICE1HS01. "
Regardless of how the output power of the LED lighting system, the selection of the LED drive circuit will largely depend on the input voltage range, the accumulated voltage drop of the LED string itself, and sufficient current required to drive the LED. This has led to a variety of different possible LED driver topologies, such as buck, boost, buck - boost and SEPIC type.
Linear Technology Power Products Division, Product Marketing Director Tony Arm strong, pointed out: "each topology has its advantages and disadvantages, which standard buck converter is the most simple and easiest to implement programs, boost followed by a buck - boost converter, SEPIC converter is the most difficult to achieve, because it uses a complex magnetic design principles, and designers need to have a a superb switch mode power supply design expertise. "
All in all, the end product application determines the topology of the LED, then according to the topology of the LED and the input power again reasonable choice Buck, Boost, SEPIC, or Buck-Boost structure. "In general, 25W choose Buck more power tend to choose Boost structure. Efficient both general can do more than 85%, LT3755 can be done up to 97% efficiency. Consider driving part BOM cost more should consider the overall system cost. "says Xu Rui package," As competition intensifies, from time to time there will be a lower BOM cost of the program, but not necessarily the most appropriate design products in accordance with this standard does not recommend PCB area is mainly controlled by the main components, a low-power LED lights maximize the use of high integration programs. To choose the technology of high-power high integration products and simple external circuit. discussed here are DC-DC solution. "
Beam after the right also pointed out that: "In order to achieve high efficiency requirements, should consider the use of the switch-mode LED driver, the majority of these customers prefer to choose the buck LED driver, because the total efficient from a lowest BOM cost perspective to consider switching type LED converter is not the cheapest of these customers may try to use linear constant current LED driver which can provide the lowest BOM cost efficiency may not like the switch-mode LED driver as high as from the smallest PCB board area of the viewpoint, usually optional switch mode converter, because they generate less heat, and even the related components will be smaller volume. "
Analog, PWM and TRIAC dimming scheme
LED dimming solutions and norms have been changing, and until now has not been fixed, so now the market there are three dimming PWM, analog and SCR (TRAIC) program. PWM and analog method is relatively simple, but need to build the infrastructure of dimming and dimming controller.
Analog dimming scheme, the drawback is that the adjustment range of the LED current is confined between a maximum value to the maximum of about 10% (10:1 dimming range). As the LED's chromatography with current, so this method is not suitable for certain applications.
The PWM dimming solution is based on a certain fast enough to cover up the visual flicker rate (usually higher than 100MHz) to switch between zero current and maximum LED current. The duty cycle change the effective average current, which can achieve up to 3000:1 dimming range (limited only by the minimum duty cycle). As LED current either is at a maximum, or off, so that this method has the advantages of the LED color misregistration occurs can be avoided in the current changes in the analog dimming such LED color misregistration phenomenon is very common.
SangCheol Her optimistic about the market prospects TRIAC dimming program thyristor (TRIAC, 2 lines dimming) will become a very popular solution, because this technology can fully use the traditional system without any changes, he said: Moreover, it can also be extended to 3-line dimming in order to avoid the defects associated with the low power factor values. "
TRIAC dimmer today is a very hot topic of the industry, initially, TRIAC dimmers designed for incandescent, but most users want the same TRIAC dimmer alternative LED lights dimming. Leung said after the right: Diodes Zetex currently available to provide customers with full dimming solutions (including PWM, analog and TRIAC), ZXLD1362 LED driver Used ADJ pin to analog and PWM dimming, which brought to customers a great deal of design flexibility. "
However, Cheng Chung before that, TRIAC dimmer applications on the market should only be transitional, in the long run, you should use PWM dimming. He said: "The main point decisive factor as follows: 1) PWM dimming from zero to the most light, there will not be flashing phenomenon. 2) the performance will be better. Dimming output power with a power factor correction circuit , which is in line with the mandatory requirements of the global lighting power factor, although generally from 25 W, but the United States need a mandatory power factor correction circuit lights starting at zero watts such as the TRAIC dimming sacrifice power factor and increase the complexity of the circuit. Therefore, using the PWM dimming can provide the best performance of the selection, the future trend. 3) costs will be better with the duty cycle of the PWM adjustment, does not require much additional control circuit cost. "
Alexander Sommer also optimistic about the PWM dimming scheme prospects, he said: "analog dimming LED's PWM dimming method has the following advantages: 1) more efficient; 2) regardless of the degree of dimming allows LED has been optimization and constant current getting off work group; 3) LED color tone consistent throughout the dimming range (color shades like lumen output with LED operating current change). "
Xu Rui package frankly: "personal feel, the modulation choice should not be determined by the power of the LED. Should decide on the application requirements of the end products. Example, the display backlight or LED decorative lights may choose PWM dimming color consistency and high brightness level but for general home lighting or commercial lighting, analog dimming or TRIAC can also choose, but will produce a color cast, and the dimming level will be low. "
Beam after right said: "In order to achieve continuous dimming, flicker-free, most customers prefer to choose the PWM dimming, because it provides greater dimming range and better linearity. Depends on you are using dimmer frequency flicker can be minimized. analog dimming easier to achieve, because it requires only a DC voltage, flicker-free dimming of the LED. Generally speaking, dimming range narrower. "
Constituted by a plurality of high power LED lighting applications, ensure that each LED has a uniform brightness without any flicker has also become a major obstacle to the design, but the PWM method is easy to solve the blinking problem dimming. "If the duty cycle of the PWM modulator can be maintained constant, handy, there should not have the problem of uneven brightness of the lights." Said Wu Zhimin, "National Semiconductor's LED driver can not only ensure that the output current uniform size, but also to ensure screen high brightness contrast from these aspects, our LED drive than its class on the market better and winning. "Tony Armstrong pointed out that, in short, the end-user dimming method used in very a large extent, by the end use of LED itself to decide. For example, the LED for the back lighting to display the car infotainment system, ambient lighting brightness range is very wide, both sunny extremely bright, but also whether the January night darkness, can be described as vastly different. Because the human eye is extremely sensitive to slight variations of the ambient lighting conditions, and therefore need a wide dimming range of 3000:1. This will require the LED driver circuit using PWM dimming method.
However, he added: "LED street lamps either in the ON state or in the off state, and therefore need only a limited range of dimming can. In this case, the only use of a kinds of simple analog dimming method will be able to meet the requirements. "
As mentioned earlier, less than 25W of LED lighting applications replace standard incandescent and halogen lamps. In this power range, an application is the most likely alternative to TRIAC (TRIAC) gradually cut into the wall dimmer control incandescent or energy-saving lamps. Market leading and trailing edges cut dimmer overall compatibility challenges, from the perspective of EMI TRIAC dimming poor to.
DCM PFC single-stage PFC flyback topology like Infineon TDA486 3G is an appropriate choice. "Alexander Sommer think," 25W and above power range of LED lighting applications that require the best cost-effective non-dimming applications, oriented to the professional market. dimming control method selection will depend on the replacement or new installation type digital lighting control (such as DALI or wireless solutions) allows more precise control dimming level, and more more functionality, such as sunlight down light duty cycle induction. replacement installation may be required to be compatible with the old analog 1-10V dimming controller. "
