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Summary Last days,I bought a new house and I am considering how to decorate it. when thinking about wall-lighting sconces.My project is to place an array of LED strips on the walls,covered with translucent(or in some cases,opaque!) Yeah,Plexiglas plates mounted a few centimetres away. That's the plan anyway...   Preparation At first, I need a 18W power supplies small enough to fit into an electrical box.Finally,I chose a power supply.This product could provide a full 1.5A without collapsing.However,upon opening the cases,the component temperatures after rumming at full-throttle for a new minutes suggested otherwise.The switching transistor,output rectifier,and output capacitor were all far too hot for comfort.I imagine the 18W spec is only valid for one day of use. Figure 1  The 12V 18W PSU. Notice the 100% efficiency (IN & OUT are both 18W), and  the dire warning not to touch the surface of the plastic case because of high temperature   I also bought one PSU from Aliexpress.They behave differently than the first batch. From an external vantage point, they’ll only supply 1.3A as opposed to the former 1.5A. The output voltage collapses to 8V at 1.5A.Take it apart, and further differences appear. Most noticeably, the 12V output capacitor does not egregiously overheat at, say, 1.3A. Sure enough, the part has “Low ESR” printed on the case. The previous caps don’t. Figure 2  PSUs from AliExpress (top) and another, forgotten source (bottom). Note the  convenient dates at the bottom of the boards. Manufacture has transitioned from phenolic to fiberglass   The design appears to be a simple self-oscillating circuit. I measured the switching frequency to be about 100 kHz. The 12V output caps are at the upper-right of each board. Though the legend says “1000µF 25V”, the installed caps are 470µF.   After discovering the output cap heat problem (but before getting the second PSU batch), I sourced a bagful of quality capacitors – 270µF @ 35V, still more than enough capacitance for this circuit, but with a high ripple-current rating and low ESR. Both of the boards above have these new parts installed. They run cool as a cucumber, versus the slight temperature rise of the second PSU caps, and of course, the extreme rise of the first ones. Figure 3  The PCB bottoms reveal other minor design changes in the newer boards – mainly exposed copper to pick up current-fortifying solder   I’m constantly struck by the strange state of affairs at this level of Chinese manufacture. Clearly, there is some thought and skill put into design and production, yet we still end up with stupidities, like unsuitable parts, or wishful-thinking specs. As I mentioned, other parts get hot too. The switching transistor can get toasty at higher loads, but it was the output rectifier I focused my measurements on. At 1.33A, free-air TC registered 90°C. At 1.2A, 86°C. Figure 4  My test setup here at EDN Labs. Note the many safety protocols employed on the bench   Enclosed in its case, in an electrical box, I don’t think I’ll want to pull more than 1.1A from these PSUs. Hopefully, that will be enough for my LED lighting. Other options: Squeeze two PSUs into a box (possibly swapping the case for some shrink wrap or electrical tape), or, cut a hole in the case so I can bend the rectifier out and heat-sink it to the electrical box! Hmm. We’ll see.   Result I didn't realize my plan until now.I am so tangle should choose which one? The last one,there is an absence of an AC line filter on the board.The former, at least, has a line filter, and even if they also don’t meet their output-current spec, they will certainly be better than the PSUs I’m using. But…they don’t fit into an electrical box.How do you think about my plan? Anyaway,I will attempt it again when I am free.  

SummaryAs we all known,better knowledge of the absorption and scattering of light inside the LED,the performance of white LEDs can be improved.Yeah,LEDs can be made even more efficient and powerful.When in May,2017,researchers who from the University of Twente and Philips Lighting have developed a new method which can lead to efficiency improvement and powerful design tools. They found a detailed way to describe the light that stays inside the LED by absorption and scattering. This is very valuable information for the design process. The Theory about Light Sources From relatively weak light sources to strong lights at home and in cars, for example: since the blue and white LED were invented, we've seen a rapid development in possible applications. Low energy consumption and long lifetime are major advantages over existing lighting solutions. White LEDs consist of a semiconductor emitting blue light, with on top of that phosphor plates that turn the blue light into yellow. What we see then, is white light. The light will be scattered by the phosphor particles, but it is absorbed as well. What part of the light will exit the LED, is not easy to predict. Unless you look at absorption and scattering in another way, according to Maryna Meretska and her colleages. Theory from astronomy helps. Good Prediction is Difficult What makes good prediction particularly difficult: some of the light is absorbed, but re-emitted in another colour. One way is trying to define all possible light rays, and use a lot of computing time to get a result. This doesn't give much insight in what is actually happening. A theory that is often used for light propagation in a LED, is diffusion theory. In strongly absorbing media, however, this approach isn't valid anymore. Meretska therefore has built a setup to collect all the light around the phosphor plates, in the whole visual spectrum. Based on this, absorption and scattering can be deduced using the radiative transfer equation, well known in astronomy.  This results in a full description of light propagation inside and outside the phosphor plates. Compared to a description using diffusion theory, the absorption level is up to 30 percent higher. At the same time, the method is about 17 times faster than the numerical approach. ConclusionThis new insights leaded to powerful and predictive tools for LED designers.They help in further improving the efficiency and overall performance.The research has been done in the Complex Photonic System group of UT's MESA+Institute for Nanotechnology,together with Philips Lighting in Eindhoven. The University of Twente has a strong concentration of research groups and facilities within the rapidly growing field of photonics.  Article provided by University of TwenteArticle edited by kynix 

CCD image sensors still remain preferable in some specialised application.Today I would like to talk something about CMOS image sensor technology. As the development of image sensor,CMOS technology is widely used in most machine vision applications.What's excited,perhaps as the concepts behind industry 4.0 become adopted more broadly--the need for mre capable vision systems has grown sharply. This is a video of CCD vs CMOS sensors Catalog   Historical and modern CMOS Improve productivity, support high bandwidth   readout Inherent flexible available About the high resolution Design the right products Conclusion FAQ Machine vision systems use images to gather information on a system or process and to then make decisions based on the image captured.While such systems are dependent upon lighting and software,the camera-and the image sensor within it-is the key component in the overall operation of the system,as well as the ability to improve manufacturing quality and increase productivity.At a high-level,a typical machine vision application involves som combinaton of basic measurement,counting or inspection functions.Objects may be assessed to confirm the number of objects present,to determine the number and size of features or their quality level.So machine vision could be used to not only determine that the proper number of holes have been drilled into an item, but also to verify the spacing and shape of each hole. Similarly, the location of an object may be determined in order for it to be picked up by a robot arm or to determine whether a feature is in the correct place. Other functions include reading a barcode, performing character recognition or measuring the level of a fluid.So machine vision could be used to not only determine that the proper number of holes have been drilled into an item, but also to verify the spacing and shape of each hole. Similarly, the location of an object may be determined in order for it to be picked up by a robot arm or to determine whether a feature is in the correct place. Other functions include reading a barcode, performing character recognition or measuring the level of a fluid.   Historical and modern CMOS Historically, machine vision systems have required CCD image sensors because of their high image quality and performance.  Today, however, CMOS image sensors have jumped to the forefront for many machine vision applications. Advances in CMOS pixel design have made the imaging quality available from this platform sufficient for a variety of different end uses.Modern CMOS image sensor platforms, such as that used in ON Semiconductor’s PYTHON family, are based on a global shutter pixel design that enables the capture of moving objects without the introduction of motion artefacts. In-pixel correlated double sampling provides low readout noise, while on-chip fixed pattern noise correction helps preserve image quality. Combined with a 10bit A/D converter and a dynamic range of 60dB, these features allow machine vision systems to leverage the intrinsic advantages of a CMOS platform in their operation.   Improve productivity, support high bandwidth readout With many machine vision applications looking to operate at ever higher speeds in order to increase productivity, image sensors must support high bandwidth readout. The output architecture of the CMOS platform enables this as additional digital outputs can be added to increase the available bandwidth. For example, the use of up to 32 separate LVDS outputs enables high resolution PYTHON devices to realise bandwidths that exceed those of modern computer interfaces, including 10Gbit Ethernet or USB 3.1. The ability to output at up to 80frame/s from a 25Mpixel device is well beyond the capabilities of standard CCD designs. Inherent flexible available The inherent flexibility available in CMOS output designs allows the frame rate to be further increased when operating in Region of Interest (ROI) mode, where only a portion of the image sensor array is read out. With proper design considerations, the speed increase when operating in this manner can scale by both the x and y dimensions of the ROI, enabling faster frame rates than can be realised when using a more standard CMOS output design, which only scales the x dimension. Consider the frame rates from the PYTHON 5000 image sensor compared to theoretical frame rates from a similar 5Mpixel sensor using a standard CMOS output. At full resolution, both designs would provide approximately 100frame/s, but when reading out a 1280 x 720 pixel ROI, the the PYTHON device’s frame rate increases to almost 600frame/s, while the standard output design would increase to only 300frame/s. This can be an important differentiator.    About the high resolution While high resolution can provide finer detail, this must be balanced by making sure that too much information is not captured, which would slow data processing. In addition to having the right number of pixels, they need to be in the appropriate aspect ratio for the application. For example, an aspect ratios of 1:1 is often used in pick and place applications to maximise image capture across the full field of view. Different spectral sensitivities, such as colour, monochrome and extended near infrared (NIR), may also be required to optimise the imaging system for the application. In order to do this, a camera manufacturer will look for an integrated family of image sensor products that includes multiple resolution nodes and colour options to support a portfolio of products.The PYTHON family has more than 40 options, with resolutions ranging from VGA to more than 25Mpixel. These devices are available in multiple configurations, including monochrome, Bayer Color and extended NIR sensitivities. Selected devices are available in low-power configurations or with removable tape to protect the image sensor during the camera assembly process.   Design the right products Avent Silica offers a range of evaluation kits to help designers understand the performance available from the PYTHON family of image sensors.These kits include an image sensor,the appropriate sensor headboard,FPGA evaluation board and software and accessories.The Flexible design also allows the evaluation hardware to be use with other PYTHON devices by purchasing additional image sensors.After identifying the most appropriate image sensor, designers then need to consider the remainder of the camera design. Complementary products from ON Semiconductor include embedded boards, power and signal chain components that allow engineers to choose between modular solutions and the flexibility of a discrete design. If a machine vision system needs to be brought to market quickly, it may not be possible to build it from the ground up. For those applications, Avnet Silica products such as the PYTHON-1300-C camera module. Based on the PYTHON 1300 colour image sensor and featuring a 0.5in SXGA CMOS image sensor with a resolution of 1280 x 1024 pixels, the module can be combined with Avnet Silica’s MicroZed Embedded Vision Carrier Card and the Smart Vision Development Kit to provide a complete hardware design, leaving the designer to only write the application software. Conclusion Because of the combination of image quality,bandwidth,image flexiblity and configuration flexiblity available from MOS image sensors has accelerated adoption of this technology in machine vision applications.What's celebrating,The imaging capabilities of such devices has ushered in a new level of performance and functionality for industrial imaging and CMOS sensor based imaging is now suitable for use in almost every type of design.   FAQ   1. How does a CMOS image sensor work? Unlike CCD sensors that use high-voltage analog circuits, CMOS sensors employ a smaller digital circuitry that uses less power, and are in principle free from smear (vertical white streak in the image taken under bright light) and blooming (corruption of images such as white spots).   2. Which sensor is better CCD or CMOS? CMOS sensors have thousands. This means that CMOS cameras can read out incredibly fast, even 100X faster than a comparable CCD. For long-exposure applications that is not so important, but it is especially important for video cameras.   3. Is CMOS a full frame sensor? "Full frame" is a description of sensor size, sort of... "CMOS" is a name for semiconductor technology used to make sensors. So, they are definitely different, and not comparable.   4.What is CMOS sensor type? A CMOS sensor is an electronic chip that converts photons to electrons for digital processing. CMOS (complementary metal oxide semiconductor) sensors are used to create images in digital cameras, digital video cameras and digital CCTV cameras.   5. What is the function of image sensor? An image sensor is a device that allows the camera to convert photons – that is, light – into electrical signals that can be interpreted by the device. The first digital cameras used charge-coupled devices, facilitating movement of the electrical charge through the device so it could be modulated.   6. What is difference between CCD and CMOS? The biggest difference is that CCD sensors create high quality images with low noise (grain). CMOS images tend to be higher in noise. CCD sensors are more sensitive to light. CMOS sensors need more light to create a low noise image at proper exposure.   7. What CCD means? Charged Coupled Device. Stands for "Charged Coupled Device." CCDs are sensors used in digital cameras and video cameras to record still and moving images. The CCD captures light and converts it to digital data that is recorded by the camera. For this reason, a CCD is often considered the digital version of film.     8. What is CCD and CMOS? CCD (charge coupled device) and CMOS (complementary metal oxide semiconductor) image sensors are two different technologies for capturing images digitally. Each has unique strengths and weaknesses giving advantages in different applications.   9. Is CMOS sensor good? CMOS sensors traditionally have lower quality, lower resolution and lower sensitivity. CMOS sensors are just now improving to the point where they reach near parity with CCD devices in some applications. CMOS cameras are usually less expensive and have great battery life.   10. How does a CCD work? Fundamentally, a charge coupled device (CCD) is an integrated circuit etched onto a silicon surface forming light sensitive elements called pixels. Photons incident on this surface generate charge that can be read by electronics and turned into a digital copy of the light patterns falling on the device.  

SummaryA metamaterial developed by researchers at King's College London uses quantum effects to turn electrons flowing through a circuit into "hot electrons" and light in a highly controlled manner.According to the team,this has potential application in optoelectronics and sensing. BodyThe nanomaterial takes advantage of electron tunnelling to produce streams of particles which can have important applications, when properly controlled.   Accodring to the researcher Dr Pan Wang,this one tiny device offers several amazing applications: plasmon excitation, light generation and chemical reaction activation. And all this is achieved by a small, easy to produce material which only requires a small voltage to function. A voltage applied across the device causes electrons to flow from one material (eutectic gallium indium) to another (gold nanorods). These are separated by an air gap, which would usually stop the electron flow, but because the air gap is less than 1nm, the electrons can ‘tunnel’ through.Most of the tunnelling electrons arrive at the gold nanorod tips in the form of ‘hot electrons’, but a small proportion excite plasmons in the metamaterial to emit light whose wavelength is directly related to the applied voltage. According to the team, this conversion is usually inefficient, but the use of array gold nanorods provides 100billion tunnel junctions, improving electron-to-plasmon conversion and making the emitted light visible. While there are applications in sensing, the researchers point to a benefit in small scale electronics. Since light is generated by applying a voltage along a 10nm thick nanorod, it can be used to transmit information optically between or within chips. The metamaterial allows optical signals to be produced within a much smaller device, holding the potential of faster electronics. "We expected to generate some weak light which we thought should be enough for various nanophotonic applications when we began these studies," added King’s College Professor Anatoly Zayats ,"but But as sometimes happens in the research, the applications are much richer.” 

SummaryIt has been successfully demonstrated that a nanocrystal of of perovskite can serve as a quantum emitter of light, and, when coupled with a nanophotonic cavity, can dramatically improve the efficiency of the light emission by an international research team from the University of Maryland and ETH Zurich in Switzerland.  A new device features perovskite nanocrystals and a series of nanophotonic cavities. The arrows indicate the way that the UV laser used to excite the crystals, and the light  the crystals produce, move in and out of the device. Described in the Journal Applied Physics Letters ,the resulting device and method could be used to build nanolasers and optical devices that exhibit much faster response times than currently possible. Previously, there have been other quantum emitting materials that have been coupled to nanophotonic cavities. In this area, epitaxial materials such as quantum dots have garnered the most research interest. Distinct advantage to using PerovskiteHowever, the researchers believe there are some distinct advantages to using perovskite nanocrystals instead of epitaxial materials, which involve the fairly complex deposition of a crystalline layer on a crystalline substrate.Instead of the epitaxial techniques, the perovskite nanocrystals are synthesized using inexpensive colloidal chemistry techniques. This also makes it possible for these crystals to be placed on a broad range of substrates using simpler solution-deposition techniques when they are coupled to various photonic structures. The other main set of advantages for perovskites in light-emitting applications relates back to why they have become such a darling in photovoltaics: their optical and electrical properties. Perovskites exhibit a slow non-radiative decay rate and low densities of carrier-trapping defects, which contributes to their high photoluminescence efficiency at room temperature.In addition, the emission spectrum could cover the whole visible range by controlling the size and material composition, especially for the blue-green wavelengths that are otherwise difficult to access. The device operates by exciting the coupled system using a UV laser. This excites the perovskites to a higher energy level. Within a nanosecond, the exciton (an excited electron-hole pair) will decay to its ground state while transforming its energy in the form of an emitting photon. The cavity introduces more decay channels to the emitting materials, so a majority of the photons are coupled into the cavity and form the standing mode of the cavity. Finally, the researchers are able to detect the photons leaking away from the cavity, which is the emission signal. Difficult metThe problem that previous attempts have encountered in working with nanocrystal perovskites has been the material quality. “We need emitters with good photostability, so it can hold the performance when coupling to the cavities, said Yang. “Our collaborators from ETH provided perovskites that make this coupling possible.” In addition to nanolasers and faster optoelectronics, Yang believes the device they have made could increase the efficiency of existing perovskite emitting devices, such as LEDs, which could open up real-world applications in efficient illumination and displays. Before these aspirations can be realized, Yang concedes that they will need to further improve the performance and stability of the material itself. Second, it would be better to excite the material electrically rather than optically for practical use.Yang will try to realize similar devices spanning the whole visible range and the next step it to find ways to further improve and stabilize the performance and also utilizing electrical gates to excite the material in devices. Article source: Applied Physics LettersArticle edited by kynix