"Each topology has its advantages and disadvantages, of which the standard buck converter is the simplest and easiest to implement the program, boost and buck - boost converter followed by the SEPIC converter the most difficult to achieve, because it uses a sophisticated magnetic design principles, but also the designer has a superb switch-mode power supply design expertise. "
All in all, the end product of the application determine the topology of LED, LED and then according to the topology and the input power and then a reasonable choice of Buck, Boost, SEPIC, or Buck-Boost structure. "In general, 25W the following selection of Buck's more. More power tend to choose Boost structure efficiency, then the two can generally be more than 85%, LT3755 can be as high as 97% efficiency. Consider driving part BOM cost should be considered when the overall system cost. "Rui Xu package says," As competition intensifies, there will be always lower BOM cost of the program, but not necessarily the most appropriate and we do not recommend the product in accordance with the standard design . PCB area is mainly affected by the main components of the control, low-power LED lights maximize the use of highly integrated solutions. high-power highly integrated program to use technology products and simple external circuit. are discussed here refer to DC-DC the solution. "
Liang also pointed out right after: "In order to achieve high efficiency requirements, should consider a switch mode LED driver, most of these customers prefer the step-down LED drivers, because the total efficiency is higher if the lowest BOM cost from the point of view, switch type LED converter not the cheapest. Such customers may try to use a linear constant current LED driver, which can provide the lowest BOM cost, but may not be as efficient switch mode LED driver as high as from the smallest PCB board area of the point of view, usually use switch-mode converters, because they produce less heat, and even the volume-related components will also be smaller. "
Analog, PWM, and TRIAC dimmer program
LED dimming solutions and standards are constantly changing, until now, has not yet fixed, so now there on the market PWM, analog, and SCR (TRAIC) three kinds of dimming solutions. PWM and analog method is the more simple, but need to build new infrastructure and dimming dimming controller.
Analog dimming scheme drawback is, LED current adjustment range limited to a maximum value to the maximum value of about 10% (10:1 dimming range). As the LED current chromatography and related, so this method is not suitable for some applications.
PWM dimming scheme is based on a visual fast enough to cover up the flashing rate (usually higher than 100MHz) and the zero-current switching between maximum LED current. The duty cycle changes the effective average current, which can achieve up to 3000:1 dimming range (limited only by the minimum duty cycle). Since the maximum LED current is either in, or is turned off, so this method also has to avoid changes in the current advantages of LED color cast, and in the analog dimming LED color cast when this phenomenon is very common.
SangCheol Her program is optimistic about the TRIAC dimming prospects for the market, he said: "thyristor (TRIAC, 2-wire dimming) will become a very popular solution, because this technology can fully use the traditional system without any change . Moreover, it can be extended to 3-wire dimming, to avoid the low power factor values associated with the defect. "
TRIAC dimming the industry today is a very hot topic, initially, TRIAC dimmers designed for incandescent lamps, but most users want the same TRIAC dimmer can replace the LED lamps on dimming. Liang said right after: "Diodes Zetex now provide customers with full dimming solutions (including PWM, analog, and TRIAC). For example, ZXLD1362 LED drives use an ADJ pin to analog and PWM dimming, which offers customers a great deal of design flexibility. "
However, Zheng were before that, the market TRIAC dimmer applications should only be transitional in nature, in the long run, you should use PWM dimming. He said: "The main determinant of the three: 1) use PWM dimming from zero to the most light, there will not be flickering 2) performance will be better because the dimming output power with a power factor correction circuit This is in line with the global use of the light power factor requirements are mandatory, although generally from 25 W started this requirement, but requires light from the United States has to be mandatory since the zero-watt power factor correction circuit, such as dimming the expense of using TRAIC power factor and increase the complexity of the circuit, therefore, the use of PWM dimming option provides the best performance, but also the future trend. 3) the cost would be better. adjustment by PWM duty cycle, not much extra control circuit cost. "
Alexander Sommer PWM dimming options are also optimistic about the prospects, he said: "Compared with analog dimming, LED PWM dimming method has the following advantages: 1) efficient; 2) regardless of how much dimming level, allowing the LED to remain in the optimization and constant current getting off work groups; 3) in the whole range LED dimming consistent color hue (color tone as the same lumen output LED current with changes). "
Rui Xu package frankly said: "Personally think that the choice of modulation should not determine the power of the LED, while the end product should be determined by application requirements, such as display backlight or LED decorative lights may choose to use the PWM dimming , color, consistency, and high brightness levels, but for general household lighting or commercial lighting, analog TRIAC dimming or you can choose, but will have a color cast, and the dimming level will be low. "
After the beam power, said: "In order to achieve continuous dimming without flicker, most customers prefer PWM dimming, because it offers greater dimming range and better linearity. Depends on what you are using the dimmer frequency, flicker can be minimized. Analog dimming is easier to achieve because it requires a DC voltage can be flicker-free dimming of the LED, but generally speaking, narrower dimming range. "
For constituted by a number of high-power LED lighting applications, ensuring uniform brightness of each LED has a flashing without any design has become a major obstacle, but the PWM dimming method is very easy to solve when the flicker problem. "If the duty cycle of the PWM modulator can be kept constant, there should not have a light handy uneven brightness problems." Wu Zhimin said, "The United States National Semiconductor's LED driver output current is not only to ensure uniform size, but also to ensure very high contrast screen brightness from to these terms, we drive the LED on the same level than the market superior products better. "
Tony Armstrong said, in short, the end user dimming method used by the LED itself is largely determined end use. For example, in the LED display is used to provide backlighting automotive infotainment systems, changes in ambient lighting brightness range is very wide, both very bright and sunny when, but also on whether the dark night, can be described as different. Because the human eye for slight changes in ambient lighting conditions are extremely sensitive, requiring a wide dimming range of 3000:1. This will require the use of LED driver circuit PWM dimming method.
However, he added: "In the LED lights, because this light is often either in the connected state or in the off state, thus only a limited dimming range can be in this situation, the only use of a kinds of simple analog dimming method can meet the requirements. "
As mentioned earlier, less than 25W of LED lighting applications mainly replace standard incandescent and halogen lamps. In this power range, the most likely application is to replace the one based on TRIAC (TRIAC) is gradually reduced into the wall dimmer control of incandescent or energy-saving lamps. There are currently on the market leading and trailing edges cut dimmer, which challenges the overall compatibility, because the perspective of EMI TRIAC dimming is poor.
"For the best price for non-dimming applications, use TDA4863G such as Infineon's single-stage PFC DCM PFC flyback topology is an appropriate choice." Alexander Sommer think, "25W power range and above the surface of LED lighting applications to the more professional market. dimming control method will depend on the choice of alternative or new it is mounting. digital lighting control (such as DALI or wireless solution) to allow a more precise level of dimming control, and more features such as solar light duty lower induction. alternative installation may require compatibility with older analog 1-10V dimming control. "
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