Driving multiple high-power LEDs in a switch mode and achieving uniform brightness, dimming, and power factor compensation is not a straightforward task, yet for a professional power designer it takes only a day to satisfy the full design Claim. What we mean by "driving LEDs" is "designing the right power supply." But if you are not a professional power design engineer, then this design can be a big challenge.
Do not be intimidating
In recent years, demand for LED lighting solutions is strong. No matter what your level of competence, you have access to a large selection of power solutions. If your goal is to design the entire lighting fixture, you can refer to many other designs, including thermal management and optics. This article will focus on power design.
Before carrying on the power design, must solve the power load problem first. To do this, there are several factors to consider:
Power Requirements - How many LED lights do you want to drive? Is 1W, 3W or 5W LED lights? Is there a fixed amount of LED lights on each series line, or is it necessary to adjust the power supply based on the output voltage range? How do you expect the power brightness? Cree provides an excellent online tool to help engineers determine the number of LED lights needed for their application design.
Connection Schemes - Do you want to drive LED lights in series, parallel or in combination? If you want to make all the LED brightness of each group consistent, the proposed series configuration. However, if there is a problem with the output voltage, it is recommended to use parallel mode.
Forward Voltage (VF)) - Not only the VF values ​​of the LED lamps in the circuit are different, but also the typical LED forward voltages of different colors and different chip technologies are different. The following is the Avago ASMT-Ax00 1W series of equipment, the relevant data:
LED light color Chip type VF, minimum VF, specification value VF, maximum current
Warm white InGaN2.83.23.5350mA
Red AlInGaP 1.72 .12.3350 mA
Blue-green InGaN3.03.43.8350mA
Features - Features such as dimming and power factor compensation all add to the complexity of the design. By continuously changing the forward current of the LED or a pulse width modulation (the PMW) can implement dimming function; and a PWM output, using low-cost micro controller can control and for maximum flexibility, but must be a power supply circuit For precise integration. For power factor compensation (PFC), you have other options if traditional PFCs can not be implemented due to size or budget constraints. For example, ON Semiconductor offers a single-stage high power factor based on the NCL3000 critical conduction mode controller LED driver program.
Topology - No one wants to be biased, including myself, but as I grow up in the semiconductor space I inevitably tend to design everything by using the switch mode (I have some good friends who are linear designers) . One of the biggest selling points for LED lighting and switching mode power supplies is energy efficiency, so why not design a power supply here? If you decide to use LED lighting and switch mode, then you need to consider the following questions: Your lighting applications are DC or off-line? If offline, is it necessary to isolate or universal input? Do you want LED lights to be synchronous or asynchronous? Each topology has its own strengths and weaknesses in implementing your application requirements.
The last important issue to consider before starting a power supply design is determining your level of competence. Professional power designers find it easy to design their power supply from scratch, but few of us are really power designers. You can according to their own design goals, respectively, refer to the following three programs:
Buy finished power
Although using a power scheme designed by others is often less of a rewarding accomplishment, it is the easiest way for engineers to build LED lighting. Even in this case, engineers have some great options. Off-line LED power supply provided by Ming Wei Company of Taiwan is exquisitely packaged and suitable for indoor and outdoor applications. In addition, it has the functions of dimming, comprehensive protection, PFC and universal AC input. In industry, it is the "full-featured" little guy. If you have other functional requirements, the company can also provide more basic options.
Modify the mature reference design
If you are inexperienced in power supply design, this may be the best approach for you, especially if you are limited to a proprietary design. Semiconductor giant companies such as Texas Instruments and STMicroelectronics have released complete reference designs on their websites, including original schematics, bill of materials and application notes, and even Gerber files. You can get a solid resource for starting product designs by looking at reference designs from vendors such as TI, STMicroelectronics and Linear Technology. In addition, try to be modest and gentleman, that is, when you modify a vendor's reference design, you should purchase that vendor's product throughout the design, prototyping, and manufacturing process.
put all one's eggs in one basket
If you want to design your own power supply from scratch, then you will not have any obstruction, you may occasionally irritated charred fingertips or hair with smoke. It is important that you understand that the so-called desperate does not mean being "alone." Life is too short, and one can not design alone in a vacuum. You need to find a community of fellow members who gather with peers or experts, such as the community of the Community of the point of contact for advice and exchange of ideas.
If you use a reference design for product development, you'd better first look at the supplier that offers that reference design. As mentioned above Cree, it can provide some useful design guidelines; Texas Instruments provides module diagrams and online PowerLab? Reference design database; and Linear Technology is in its official website for designers to provide a variety of applications and design notes and reference circuits. In addition, STMicroelectronics, NXP and ON Semiconductor also provide similar resources to help designers carry out LED power supply design.
Even luckily, you get some great, affordable graphics capture and layout software for power supply design. And when you do all the preparatory work and begin to build the program, you can easily get the price is real
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