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This article will introduce you some basic information of LEDs, you will learn what is LED, what are its characterics, how to and where to use it, how many kinds of LEDs are there, and so on. Catalog I. What is LED? 1.1 Brief Introduction 1.2 LED Structure 1.3 LED Limiting Parameters 1.4 LED Electrical Parameters 1.5  LED Optical Parameters II. LED Material III. LED Polarity IV. LED Characteristics V. LED Types VI. LED Trends VII. LED Application VIII. LED Light Decline Reasons IX. Complement: Blue LED FAQ I. What is LED? 1.1 Brief Introduction A tutorial on the basics of using LEDs (light emitting diodes). Polarity, forward voltage and current are discussed. A light-emitting diode (LED) is a kind of semiconductor electronic component that can convert electric energy into light energy. The electronic component appeared as early as 1962, emitting only low-light red light at an early stage, and later developed versions of other monochromatic lights, which now has light throughout visible light, infrared and ultraviolet light, and the luminosity has increased to a fairly high degree. With the development of technology, light-emitting diodes have been widely used in display, TV lighting decoration, and lighting sources. With the rapid progress of LED technology in the 1990s, its luminous efficiency exceeded the incandescent lamp, the intensity of light has reached the candlelight level, but also the color has covered the whole visible spectrum range from red to blue. This technological revolution from LED levels to beyond general-purpose light sources has led to new applications such as automotive signals, traffic lights, large outdoor panchromatic displays, and special lighting sources. The light-emitting diode is abbreviated as LED. It is made of a compound containing Ga, As, P, N, and so on. The making principle of LED is when the electrons and the holes are combined, the visible light can be radiated. It is one of the semiconductor diodes that can convert electrical energy into light energy. Compared with ordinary diodes, light-emitting diodes are composed of a PN junction and have unilateral conductivity. When a forward voltage is applied to the light-emitting diodes, the holes injected from the P region to the N region and the electrons injected from the N region to the P region are combined with the electrons and holes in the N region and the P region in the vicinity of the PN junction, respectively, to produce spontaneous emission fluorescence. The energy states of electrons and holes in different semiconductor materials are different. So when their electrons and holes are combined, the energy released is different, and the more energy is released, the shorter the wavelength of light.  Commonly used light-emitting diodes are red, green, or yellow. The reverse breakdown voltage of light-emitting diodes is greater than 5V. Its forward volt-ampere characteristic curve is steep, it must be used in a series current limiting resistor to control the current through the diode. The current limiting resistance R can be calculated using the following formula: R= (E－UF) / IF E is the power supply voltage, the UF is the forward voltage drop of the LED, and the IF is the normal operating current of the LED. The core portion of the light-emitting diode is a crystal sheet composed of a P-type semiconductor and an N-type semiconductor, and a transition layer is formed between the P-type semiconductor and the N-type semiconductor, referred to as a PN junction. In the PN junction of some semiconductor materials, if the injected minority carriers are combined with the majority carriers, the rest will be released in the form of light, that is, the electric energy is directly converted into light energy.  When the reverse voltage is applied to the PN junction, and the minority carriers are difficult to inject, so that no light is emitted. When the current flows from the LED anode to the cathode, the semiconductor crystal emits light from ultraviolet to infrared colors, and the intensity of the light depends on the current. 1.2 LED Structure In the following, a common LED white light as an example to illustrate the structure of the LED. As shown in Fig. 1 , the LED is mainly composed of the following parts: Fig. 1 LED structure Chip ( light emitting) Support: including substrate and heat dissipation base, pin, etc. (heat dissipation, conduction) Gold wire (conductive) Transparent resin (protecting grains, transmittance) 1.3 LED Limiting Parameters 1) Allowable power (PM): The positive DC voltage added to both ends of the LED and the maximum value of the current that flows through it. Beyond this value, the LED will be heated and damaged. 2) Maximum forward DC (IFM): Maximum positive DC current allowed to be added. Exceeding this value will damage the diode. 3) Maximum reverse voltage (VRM): Maximum reverse voltage allowed. If this value is exceeded, the LED may be corrupted. 4) Working temperature: Making a temperature range based on the requirement that LED works with. When exceeding this range, the LED will not work properly and will greatly reduce efficiency. 1.4 LED Electrical Parameters Fig. 2 wavelength of LED light 1) Spectral distribution and peak wavelength: Light generated by light-emitting diodes is not a single wavelength, and its wave growth body is shown in Fig. 2. It can be seen from the diagram that the intensity of λ =100 wavelengths is the largest, and the wavelength is the peak wavelength. 2) The luminous intensity of IV: Light-emitting diodes usually refers to the light intensity in the normal line direction (for cylindrical light-emitting diodes, the axis is its axis). Due to the luminescence intensity of normal LED is 2, the luminescence intensity is usually candela (MCD). 3) The spectral half-width (1/2): It indicates the spectral purity of the light-emitting tube. It refers to a difference between the two wavelengths corresponding to the peak intensity of the light in Fig. 3. Fig. 3 angular distribution of the luminous intensity of two different types of LED 4) The half-value angle θ1/2 and the angle of view: θ1/2 is the angle between the direction of light intensity value and the axial direction (normal direction) of the axial intensity value, and the half-value angle is twice the angle of view (or half-power angle). Fig. 2 shows the angular distribution of the luminous intensity of two different types of LED. The coordinate of the vertical (normal) AO is the relative luminous intensity, that is, the ratio of the luminous intensity to the maximum luminous intensity. Obviously, the relative luminous intensity of the normal direction is 1, and the larger the angle of the normal direction, the smaller the relative luminous intensity.  And this graph can get a half-value angle or an angle of view. 5) The forward working current (IF): It is the positive value of LED when it is normal. In practice,  you should select an IFM below 0. 6. 6) The forward operating voltage VF: Obtain the working voltage in the parameter table at a given forward current. In general, it is measured under IF=20mA. In VF, the forward voltage of the LED is 1.4 ~3V. And when the external temperature rises, the VF drops. 7) V-I characteristics: The relation between the voltage and current of the LED is shown in Fig. 4. When the forward voltage is less than a certain value (called threshold), the current is very small and does not emit light. When the voltage exceeds a certain value, the forward current increases rapidly with the increase of the voltage and is illuminated. The forward voltage, reverse current and reverse voltage of the LED can be obtained from the V-I curve. The reverse leakage current of the forward light emitting tube is lower than 10μA. Fig. 4 relation between voltage and current of LED Light-emitting diodes can be divided into four types: transparent, colored, and colorless. In addition, scattered light-emitting diodes are used to guide lights. (8) Main wavelength λD(nm): LED usually uses wavelength to represent color. The main wavelength is equivalent to the corresponding wavelength of the color seen by the human and is different from the peak wavelength of the luminous wavelength. The unit is nm (nanometer). The following are the wavelength parameters for the various luminous colors LED: Purple: 400～435nm Yellow-green: 560～580nm Blue: 435～480nm Yellow: 580～595nm Blue-green: 480～500nm Green: 595～610nm Green: 500～560nm Red: 610～760nm White: It is usually represented by the color coordinates below, or simply showed with warm white, right white, cold white. (9) Chromaticity diagram x and y It refers to the actual value of the LED glow color in the 2D orthogonal coordinate systems x and y, as shown in the following illustration: Fig. 5 chromaticity coordinate diagram 1.5 LED Optical Parameters Several important aspects of optical parameters of LED are: luminous flux, luminous efficiency, luminous intensity, light intensity distribution, wavelength. Luminous efficiency and luminous flux The luminous efficiency is the ratio of the luminous flux to the electric power, and the unit is generally lm/ W. The luminous efficiency represents the energy-saving characteristic of the light source, which is an important index to measure the performance of the modern light source. Luminous intensity and distribution The intensity of LED luminescence is a characterization of its intensity in a certain direction. Since the intensity of LED varies greatly in different spatial angles, we have studied the intensity distribution of LED. This parameter is of great practical significance and directly affects the minimum viewing angle of the LED display device. For example, the large-scale LED color display in gymnasiums and stadiums, if the distribution range of LED single tube is very narrow, then the audience facing the larger angle of the display screen will see the distorted image. And traffic signs also require a wider range of people to identify. Wavelength For the spectral properties of LED, we mainly look at whether its monochromatic property is good, and we should note that the main colors such as red, yellow, blue, green, white LED are pure or not. Because in many cases, such as traffic lights, the color requirements are relatively strict, but it is observed that in some LED lights, in reality, green looks blue and red is dark red. From this point of view, it is necessary and meaningful to study the spectral properties of LED. II. LED Material Generally, the five main raw materials of LED are wafer, bracket, silver glue, gold wire, epoxy resin. In 1993, at that time, Shuji Naka mura, who worked at Nichia Corporation in Japan, invented a blue light LED with commercial application value based on wide-gap semiconductor material nitride (GaN) and silicon nitride (InGaN), which was widely used in the late 1990s. In theory, the blue LED combined with the original red LED and the green LED can produce white light LED, but the white light LED is rarely made in that way. Most of the current white-light LED is made by covering the blue LED (near-UV, wavelength 450nm~470nm) with a yellowish phosphor coating, this yellowish phosphor is usually made by grinding the cerium-doped yttrium aluminum garnet (Ce3: YAG) crystal into powder and mixing it in a dense adhesive. When a LED chip emits blue light, some of the blue light is efficiently converted by this crystal into a mostly yellow light with a wider spectrum (the spectral center is about 580nm). Since the yellow light can stimulate the red and green light receptors in the naked eye, with the blue light, so that it looks like white light when these colors mixed, and its color is often referred to as moonlight. The method of making a white light LED was developed by Nichola Corporation and used in the production of white light LED from 1996. To adjust the color of the light yellowish light, it is possible to replace the Ce doped with the Ce3 +: YAG with other rare-earth elements, or even in a manner that replaces part or all of the aluminum in the YAG. Based on the characteristics of its spectrum, red light and green light are not as obvious as the broad-spectrum light source illuminated. In addition, due to the variation of the production conditions, the color temperature of the finished product of the LED is not uniform, therefore, the characteristics of the finished product should be distinguished during the production process. Another method of making a white LED is like a fluorescent lamp. An LED that emits near-ultraviolet light is coated with a mixture of two phosphors, one is europium which emits red light and blue light, and the other is copper and aluminum-doped with ZnS which emits green light. However, the epoxy resin in the adhesive will be cracked and deteriorated caused by the ultraviolet rays, the production difficulty is high, and the service life is also shorter. In contrast to that first method, it is less efficient (producing more heat) but its spectrum is better and the light looks better.  III. LED Polarity One of the longers of the two leads of the light-emitting diode is the positive pole, which should be connected to the positive pole of the power supply. Some LED leads are the same length, but there is a convex tongue on the shell, the lead near the small tongue is positive. LED Unidirectional Conductivity The LED can only be turned on in one direction, called forward bias, when the current flows, electrons, and holes recombine to emit monochromatic light, which is an electroluminescent effect, and the wavelength of the light and the color is related to the type of semiconductor material used and the element impurities to be incorporated. It has the advantages of high efficiency, long service life, difficult breakage, high switching speed, high reliability, and so on. The light-emitting efficiency of the white LED has been obviously improved in recent years. IV. LED Characteristics Compared with the incandescent bulb and the neon lamp, the light-emitting diode is characterized in that the working voltage is very low, and the working current is small, the impact resistance and the anti-seismic performance are good, the reliability is high, and the service life is long. The intensity of the light-emitting can be conveniently modulated by the intensity of the current passing through the modulation. Due to these features, the light-emitting diode is used as a light source in some photoelectric control devices and is used as a signal display in many electronic devices. Voltage LED uses a low-voltage power supply, the supply voltage is between 3~24V DC, depending on the product requirement, there are a few DC 36V or DC 40V, so it is a safer power supply than the use of high-voltage power supply, especially suitable for public places. Energy consumption The energy consumption is 80% less than the incandescent lamp with the same light efficiency and 40% less than the energy-saving lamp. Applicability Because of its small size, each unit of LED is a square of 3~5mm, so it can be fabricated into devices of various shapes and is suitable for the variable environments. Stability 100,000 hours, light attenuation is 50% of the initial. Response time The response time of the incandescent lamp is milliseconds and the response time of the LED lamp is nanosecond. Pollution No harmful metal mercury, etc. Color The red, yellow, green, and blue-orange multicolor luminescence can be realized by adjusting the energy band structure and the bandgap of the material conveniently through chemical modification. The operation voltage of the red light tube is small, and the operation voltage of red, orange, yellow, green, and blue light-emitting diodes is increased in turn. V. LED Types 1. Depending on the different packaging of the LED, the luminous surface and characteristics of the LED can be roughly divided into the following types: 1) Plug-in LED Plug-in LED, in addition to the common two-terminal monochrome LED, also includes three-terminal dual-color LED and four-terminal RGB full-color LED. 2) Surface-mount LED A surface-mount LED is usually available in 0402, 0603, 0805, 1206, and so on, in monochrome, two-colour, and RGB full-color type. 3) High power LED This type of LED is usually used for lighting source, and most of it is white-emitting LED. 4) LED digital tube By making more than one LED into each field and forming a characteristic letter or combination, you can display the 0/9 or English letters) or the bar-type to indicate progress or scale. 5) LED matrix screen The matrix form of LED can display Chinese and English letters. For example, the manufacturer's LED display screen is composed of these dot matrix screen modules. According to color, it can be monochrome, double color or RGB full-color type. 6) Smart LED This type of LED includes not only a LED core, but also a control circuit, IC, for specific functions, such as blinking flash. Or bus addressing controls the color of each point, and so on. 7) Special LED This kind of LED emits lights that are invisible to human eyes, such as infrared, ultraviolet, and so on. In daily life, we use the remote control as this kind of LED lamp. 2. Light-emitting diodes can also be divided into ordinary monochromatic light-emitting diodes, high brightness light-emitting diodes, ultra-high brightness light-emitting diodes, chronotropic light-emitting diodes, scintillation light-emitting diodes, voltage-controlled light-emitting diodes, infrared light-emitting diodes, and negative resistance light-emitting diodes, etc. There are two control modes of LED: constant current and constant voltage, and there are many dimming modes, such as analog dimming and PWM dimming. Most of the LEDs are controlled by constant current, so that the current of LED can be kept stable, and it is not easy to be affected to extend the service life of LEDs. Ordinary monochromatic light-emitting diode Ordinary monochromatic light-emitting diodes have the advantages of small volume, low operating voltage, small working current, uniform and stable luminescence, fast response speed, and long service life, and can be driven by various DC, AC, and pulse power sources. It belongs to the current-controlled semiconductor device, it needs to be connected to an appropriate current limiting resistor. The light-emitting color of ordinary monochromatic light-emitting diodes is related to the wavelength of light-emitting, and the wavelength of light-emitting depends on the semiconductor materials used in the manufacturing process. The wavelengths of red light-emitting diodes, amber light-emitting diodes, orange light-emitting diodes, and yellow light-emitting diodes are generally 650~700nm, 630~650nm, and 610~630nm respectively, and yellow light-emitting diodes are usually 585nm, green light-emitting diodes typically have a wavelength of 555~570nm. High brightness monochromatic light-emitting diode The semiconductor materials used in high brightness monochromatic light-emitting diodes and ultra-high brightness monochromatic light-emitting diodes are different from those of ordinary monochromatic light-emitting diodes, so the intensity of light-emitting is also different. Typically, high brightness monochromatic light-emitting diodes use materials such as gallium arsenide (GaAlAs) and ultra-high brightness monochromatic light-emitting diodes use phosphonium gallium arsenide (GaAsInP), etc. Common monochromatic light-emitting diodes use gallium phosphide (GaP) or phosphogallium arsenide (GaAsP). Variable color light-emitting diode The variable color light-emitting diode is a light-emitting diode capable of converting light-emitting colors. The color type of the variable color light-emitting diode can be divided into two-color light-emitting diodes, three-color light-emitting diodes, and multi-color (red, blue, green, and white) light-emitting diodes. According to the number of pins, the variable color light-emitting diode can be divided into two-terminal variable color light-emitting diode, three-terminal variable color light-emitting diode, four-terminal variable color light-emitting diode, and a six-terminal variable color light-emitting diode. Flashing light-emitting diode The flashing light-emitting diode is a special light-emitting device consisting of a CMOS integrated circuit and a light-emitting diode, which can be used for alarm indication and under-voltage and overvoltage indication. When using, the flashing light-emitting diode does not need to be externally connected with other components, so long as the appropriate direct-current working voltage is added at the two-end of the pins to flash and emit light. Voltage-controlled light-emitting diode Ordinary light-emitting diodes belong to current-controlled devices, and the current-limiting resistors with appropriate resistance values should be connected to each other when used. Voltage-controlled light-emitting diode integrates light-emitting diode and a current limiting resistor, which can be connected directly to both ends of the power supply when it is used. Infrared emitting diode  Infrared light-emitting diodes, also known as infrared emitting diodes, are light-emitting devices that can directly convert electrical energy into infrared light (invisible light) and can radiate it out. It is mainly used in various optical control and remote control emission circuits. The structure and principle of infrared light-emitting diodes are similar to those of ordinary light-emitting diodes, but the semiconductor materials used are different. Infrared light-emitting diodes are typically made of gallium arsenide (GaAs), gallium arsenide (GaAlAs), in a fully transparent or light blue, black resin package. VI. LED Trends With the development of the industry, technological breakthroughs, and the application of vigorously promote, LED lighting efficiency is also increasing and the price is constantly lower. The emergence of new combined tube sets also increases the power of a single LED. Through the continuous research and development of the same industry, the breakthrough of new optical design, the development of new lamps, the single product situation is also expected to be further improved. The improvement of control software also makes the use of LED lighting more convenient. LED, known as the fourth generation light source, has the characteristics of energy-saving, environmental protection, safety, long-life, low power-consumption, low heat, high brightness, waterproof, micro, shock proof, easy dimming, beam concentration, easy maintenance, and so on. It can be widely used in all kinds of the pilot light, display, decoration, backlight, general lighting, and other fields. Advantages of LED: high electro-optic conversion efficiency (close to 60%, environmental protection, long life (up to 100000 hours), low working voltage (about 3V), lossless life of repeated switches, small volume, less heat, high brightness, rugged and durable, easy dimming. The color is varied, the beam is concentrated and stable, and the start-up has no delay. Disadvantages of LED: high starting cost, poor color rendering, low efficiency of high power LED, constant current drive (special drive circuit required). In contrast, there are certain defects in traditional lighting. Incandescent lamp: low electro-optic conversion efficiency (about 10%), short life (about 1000 hours), high heating temperature, single-color, and low color temperature. Fluorescent lamps: low electro-optic conversion efficiency (about 30%), harmful to the environment (including mercury and other harmful elements, about 3.5-5mg/pic), non-adjustable brightness (low voltage can not start to glow), ultraviolet radiation, flicker phenomenon, large size, slow start, The increase in the price of the raw materials (the ratio of phosphors to costs increased from 10% to 60%~70%), the repeated switching affects the life. High-voltage gas discharge lamp: large power consumption, unsafe use, short life, heat dissipation problems, mostly used for outdoor lighting. VII. LED Application 1) LED display screen Since the mid-1980s, monochrome and multicolor displays have been introduced, most are text screens or animation screens at first. In the early 1990s, with the development of computer technology and integrated circuit technology, the video technology of LED display screen was realized. TV images can display directly on the screen, especially in the mid-1990s, the blue and green ultra-high brightness LED was successfully developed and put into production rapidly, which greatly expanded the application of outdoor screens with areas ranging from 100m to 300m. At present, LED display screen has been widely used in stadiums, squares, avenues, and even streets and shopping malls. 2) Traffic light Navigation lights have been using LED as a light source for many years, and the present work is to improve and perfect. Road traffic lights have made great progress in recent years, the technology is developing rapidly, and the application is developing rapidly. Its advantages are long life, power-saving and maintenance-free effect are obvious. At present, the peak wavelength of red LED is  630nm, yellow is 590nm and green is 505nm. It should be noted that the driving current should not be too large, otherwise the high temperature in the summer will affect the life of LED. 3) Automobile light Ultra-bright LED can be used as brake lamp, tail lamp, and direction lamp of the automobile, and can also be used in instrument lighting and in-car lighting. It has obvious advantages over an incandescent lamp in vibration resistance, power-saving, and service life. In addition, when it used as a brake light, the response time is 60ns, much shorter than the incandescent (140ms), which increases a safe distance of 4m to 6m on a typical highway. 4) LCD backlight As the backlight of liquid crystal display, LED can not only be used as green, red, blue, white, but also as a color-changing backlight. And many products have entered the production and application stage. 5) Decorative lighting Due to the increase in brightness of light-emitting diodes and the decline in price, coupled with the long life, power saving, easy drive and control than neon lights, and it can not only flash, but also change color during lighting, so it is made of various ultra-high brightness LEDs to decorate the tall buildings, bridges, streets and squares and other landscape in the cities, presenting a colorful, starlight and streamer scene. 6) Lighting source LED lamp has the advantages of anti-vibration, suitable for battery power supply, solid structure, and portability. It will have a great development in special lighting source. As lawn lights, buried lights, microscope field lighting, flashlights, medical lighting, museum or painting exhibition lighting, and reading table lamps. Application of monochromatic LEDs At first, LED was used as the indicator light source of the instrument. Later, various kinds of light-colored LEDs were widely used in traffic signal lights and large-area display screens, resulting in good economic and social benefits.  Automobile signal lamp is also an important field of the LED light source application. Due to the fast response speed (nanosecond level) of the LED, the driver of the trailing vehicle can be informed of the driving condition as soon as possible, thus reducing the occurrence of car rear-end collision accidents. In addition, LED lights in outdoor red, green, blue full-color display, key button miniature flashlight, and other fields have been used. VIII. LED Light Decline Reasons A. Quality issues of LED products 1) LED chip used in the physical condition is not good, and the brightness decay is faster. 2) There are defects in the production process. The heat dissipation of the LED chip can not be well derived from the pins, which leads to the increase of the attenuation of the chip because of the high temperature of the LED chip. B. Applying Problem 1) The LED is a constant current drive, and some of the LEDs are driven by the voltage to cause the LED to decay too fast. 2) The driving current is greater than the rated driving value. Advantages Small size: LED is basically a very small chip encapsulated in epoxy resin because it is very small and light. Low voltage: The power consumption of the LED is quite low, and generally speaking, the operating voltage of the LED is 2~3.6V, that is, only a very weak current is required to light normally. Long service life: The service life of the LED can be up to 100,000 hours under the proper current and voltage. High brightness, low heat: The LED uses cold light-emitting technology, which produces much lower heat than ordinary lighting lamps and lanterns of the same power. Eco-environment: LED is made of non-toxic materials, unlike fluorescent lamps containing mercury will cause pollution, and LED can also be recycled. IX. Complement: Blue LED Blue LED is a blue-emitting LED. In 2014, Yuji Nakamura and Hiro Amano won the Nobel Prize in physics for "inventing high-brightness blue light-emitting diodes, bringing energy-saving and white light sources." The invention of blue LED enables humans to gather together a three-primary colors LED, that emits trichromatic light so that it can produce enough bright white light with LED. The invention of the white LED lamp greatly improves the lighting efficiency of human beings. Principle Two breakthroughs in the late 1980s laid the foundation for the invention of blue LED: one was the development of epitaxial technology of gallium nitride and the another was the doping of P-type semiconductors. Blu LED contains several different (GaN) layers of gallium nitride. The lighting efficiency, adding indium (In) and aluminum (Al) in LED, is greatly improved. Meaning and controversy The invention of the blue LED enabled humans to use LED to produce white light that was bright enough, and the efficiency of the white LED is much higher than that of the incandescent lamp. White LED promotes the invention of all kinds of the LED display screen and also promotes the improvement of lighting efficiency. In particular, the latter makes it possible for humans to reduce carbon emissions and combat climate change. There are also concerns that blue light emitted by blue LEDs could do harm to the human eye because blue light can cause macular degeneration. Related Info: Triacs are at the heart of dimming controls for LED lighting. Triacs used in dimmers have normally been characterised and specified for incandescent lamp loads, which have high current ratings for both steady-state conditions and initial high in-rush currents, as well as very high end-of-life surge current when a filament ruptures. LEDs have much lower steady-state current than incandescents, and their initial turn-on current can be much higher for a few microseconds of each half-cycle of AC line voltage. Therefore, a spike of current can be seen at the beginning of each AC half-cycle. Typically, the current spike for an AC replacement lamp is 6 to 8A peak; the steady-state follow current is less than 100mA. An LED flood lamp for a recessed ceiling fixture designed to replace a typical filament unit that produces 750 lumens consumes only 13W in contrast with the old filament unit, which normally draws 65W. Designing an AC circuit for controlling LED light output is very simple when using the newest triac designs, such as the Littelfuse Q6008LH1LED or Q6012LH1LED Series, because the only components required are a firing/triggering capacitor, a potentiometer, and a voltage breakover triggering device. Two inverse parallel sensitive gate silicon-controlled rectifiers (SCRs), such as the Littelfuse S4X8ES1, can be used as the voltage breakover triggering device, allowing the controlling circuit to produce a wide range of light level outputs. Also, using these components as the triggering device allows achieving a low hysteresis control because two SCRs form a full breakback trigger.  If the application doesn’t demand a wide control range and low hysteresis, a simple variable light control may be designed using quadrac devices, such as the Littelfuse Q6008LTH1LED or Q6012LTH1LED Series (Figure 1). (A quadrac device is a special type of thyristor that combines a diac and a triac in a single package.) The circuit shown in Figure 2 minimises the component count by combining the diac triggering device and an alternistor triac in a single TO- 220 isolated mounting tab package. This control circuit allows a little lower full turn-on voltage due to higher VBO switching of the diac trigger device but offers a light dimming function that operates from 175° to <90° of each AC half-cycle. FAQ 1. What led means? light emitting diode. LED stands for light emitting diode. LED lighting products produce light up to 90% more efficiently than incandescent light bulbs. 2. What is LED used for? Made popular by their efficiency, range of color, and long lifespan, LED lights are ideal for numerous applications including night lighting, art lighting, and outdoor lighting. These lights are also commonly used in electronics and automotive industries, and for signage, along with many other uses. 3. How do LED lights work? An LED bulb produces light by passing the electric current through a semiconducting material—the diode—which then emits photons (light) through the principle of electroluminescence. Don't let that big word scare you! ... In contrast, an incandescent light bulb works by passing electricity through a small wire, or filament. 4. Why is it better to use LED lights? LED is highly energy efficient – Less heat, more light, lower cost. Use less electricity for the same light output - 85% less electricity when compared to conventional lighting and around 18% less electricity compared to CFL. ... LED can make a big impact on your energy use. 5. Why do LEDs fail? Temperatures are too high (or too low).When heat can't dissipate from the heat sink, it can cause lamps to fail prematurely. Also keep the surrounding environment in mind. ... Because LEDs emit light that decreases exponentially as a function of time and temperature. 6. What do LED light colors mean? The lower the color temperature, the warmer the light will appear, or the redder it will appear. The higher the temperature, the cooler the light will appear, or the bluer it will look. 7. What should be the biasing of LED? The LED works when the p-n junction is forward biased i.e., the p- side is connected to the positive terminal and n-side to the negative terminal. 8. Why are LED lights used mainly for lighting nowadays? Additionally, unlike Compact Fluorescent Lights (CFLs), LED lights do not contain mercury that can spill if dropped, making them a safer choice for household use. LEDs, which stand for Light Emitting Diodes, burn light 90 percent more efficiently than incandescent bulbs. 9. What are the disadvantages of LEDs? High up-front costs. Transformer compatibility. Potential color shift over lamp life. Performance standardization has not yet been streamlined. Overheating can cause reduced lamp life. 10. Why do my LED lights burn out so fast? The most common reasons for LED blowing out are high voltage, bad contacts, use of incompatible dimmer switch, or recessed lighting. Other causes include overheating due to not using the right fixtures, or simply a bad batch of lightbulbs! You May Also Like: Design LED strips on My House Walls Product Recommendation: LTL-4251NHBP LM3080N VC1510145UY3

A new type of electronic sensor that might be used to quickly detect and classify bacteria for medical diagnostics and food safety has passed a key hurdle by distinguishing between dead and living bacteria cells.Conventional laboratory technologies require that samples be cultured for hours or longer to grow enough of the bacteria for identification and analysis, for example, to determine which antibiotic to prescribe. The new approach might be used to create arrays of hundreds of sensors on an electronic chip, each sensor detecting a specific type of bacteria or pinpointing the effectiveness of particular antibiotics within minutes."We have taken a step toward this long-term goal by showing how to distinguish between live and dead bacteria," said Muhammad Ashraful Alam, Purdue University's Jai N. Gupta Professor of Electrical and Computer Engineering. "This is important because you need to be able to not only detect and identify bacteria, but to determine which antibiotics are effective in killing them."Findings are detailed in a research paper appearing this week in Proceedings of the National Academy of Sciences. The paper was authored by doctoral student Aida Ebrahimi and Alam. The droplet sensor evolved from a device originally designed to detect small concentrations of negatively charged DNA molecules in research that began about four years ago, Ebrahimi said."We did not anticipate that the sensor could be used to tell live and dead bacteria apart -- it was a chance observation that eventually led us to this elegant way of measuring cell viability," she said.As described in the PNAS paper, the sensor works by detecting changes in electrical conductivity in droplets containing bacteria cells. (A Youtube video about the research is available at https://youtu.be/QN019bQJCb8?). "To see if someone is alive," Alam said, "we can either count the grandchildren many generations later, which is analogous to the traditional growth-based techniques. Or, we can directly measure the person's pulse, analogous to the proposed 'osmoregulation-based' detection of bacteria. Needless to say, immediate physiological measurement is faster and far superior."Bacteria cells maintain the proper internal pressure through osmoregulation, a process in which water, salts and other molecules move across the cell membrane. As a droplet begins to evaporate on the sensor, bacteria cells contained in the droplet detect the increasingly salty environment, triggering emergency valves called osmoregulatory transporters in the cell membrane. The cells then either take in or release water and charged molecules including salts, changing the electrical conductivity of the surrounding fluid in the droplet, which is measured by electrodes. This change in electrical conductivity varies according to whether a bacteria cell is dead or alive and also might be used to identify specific types of bacteria because they use fundamentally different osmoregulatory channels."Aida proved the hypothesis by using genetically mutated cells that do not have those osmoregulatory channels and therefore are less effective in regulating the pressure differential," Alam said.The sensor's surface was designed specifically to maintain the shape of a droplet, which is critical for the technology to work. Two other advances making the sensor possible are the ability to measure the changing electrical conductivity in the droplet and harnessing a cell's osmoregulation as the basis for detection."In the end you want to provide a new tool for medicine and food safety, so you need to be able to quickly identify bacteria and the right antibiotics to treat infection," Alam said. "That requires an understanding of the dynamics of the cell membrane."The technology, which was tested with low concentrations of living and dead forms of E. coli, Salmonella and S. epidermidis bacteria, is said to be label-free because it does not require that samples be treated with fluorescent dyes, making it a potentially practical tool for medicine and food safety. Much of the research was performed at the Birck Nanotechnology Center and Bindley Bioscience Center in Purdue's Discovery Park.Source from by Purdue University 

"What Capacitor Types Should I Choose?" - Complete Guide 2025This is a question asked by many beginners and even experienced engineers. I will give you a comprehensive answer to this question, covering all the essential details you need to know. After reading this updated guide, you should be able to confidently select the right capacitor for your project. Understanding why one capacitor type might be better than another is crucial because there are many factors (temperature characteristics, package size, ESR, lifetime, etc.) that can make a specific type of capacitor the optimal choice for your application.2025 Update: This guide has been updated to include the latest capacitor technologies, including advanced ceramic capacitors, solid polymer electrolytes, and new packaging formats that have emerged since 2016.I What is a Capacitor?A capacitor is a passive two-terminal electronic component that stores electrical energy in an electric field. The effect of a capacitor is known as capacitance. While some capacitance exists between any two electrical conductors in proximity in a circuit, a capacitor is a component specifically designed to add capacitance to a circuit. The capacitor was originally known as a condenser or condensator, and this original name is still widely used in many languages, though not commonly in English.The physical form and construction of practical capacitors vary widely, and many capacitor types are in common use. Most capacitors contain at least two electrical conductors, often in the form of metallic plates or surfaces separated by a dielectric medium. A conductor may be a foil, thin film, sintered bead of metal, or an electrolyte. The nonconducting dielectric acts to increase the capacitor's charge capacity. Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, mica, air, vacuum, and various oxide layers. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy, though real capacitors have some energy loss.When two conductors experience a potential difference, for example, when a capacitor is attached across a battery, an electric field develops across the dielectric, causing a net positive charge to collect on one plate and a net negative charge to collect on the other plate. No current actually flows through the dielectric; however, there is a flow of charge through the source circuit. If the condition is maintained sufficiently long, the current through the source circuit ceases. However, if a time-varying voltage is applied across the leads of the capacitor, the source experiences an ongoing current due to the charging and discharging cycles of the capacitor.II Capacitor Functions1. Blocking DC (DC Blocking): The function is to prevent the passage of DC current while allowing AC signals to pass through. This is fundamental to AC coupling applications.2. Bypass (Decoupling): Provides a low impedance path for AC signals, effectively bypassing certain components in AC circuits. This is crucial for power supply decoupling and noise reduction.3. Coupling: Acts as a connection between two circuits, allowing AC signals to pass while blocking DC components. This enables signal transmission to the next stage while maintaining DC isolation.The purpose of using a capacitor as a coupling element is to transmit the AC signal from one stage to the next while preventing DC bias voltages from affecting subsequent stages. This makes circuit design simpler and performance more stable.Without coupling capacitors, AC signal amplification would still occur, but the DC operating points of all stages would need to be carefully coordinated. The interaction between stages makes this extremely difficult, especially in multi-stage amplifiers.4. Filtering: This is critically important for circuits, especially those behind CPUs and power supplies. Capacitors filter out unwanted frequency components.The impedance of a capacitor decreases with increasing frequency (Z = 1/(2πfC)). At low frequencies, the capacitor presents high impedance, allowing signals to pass. At high frequencies, the capacitor presents very low impedance, effectively shorting high-frequency noise to ground.5. Temperature Compensation: Improves circuit stability by compensating for temperature-dependent variations in other components.Analysis: Since the timing capacitor's value determines the oscillation frequency, it must remain stable across temperature variations. Capacitors with positive and negative temperature coefficients can be combined for temperature compensation.When operating temperature increases, one capacitor's value increases while another decreases. Since they're connected in parallel, the total capacitance remains relatively stable. Similarly, when temperature decreases, the opposite occurs, maintaining stable oscillation frequency.6. Timing: Used with resistors to determine circuit time constants in RC timing circuits.When a signal transitions from low to high and passes through an RC circuit, the capacitor's charging characteristics prevent the output from changing immediately. Instead, there's a gradual transition, creating a time delay that depends on the RC time constant.7. Tuning: Used in frequency-selective circuits such as those in mobile phones, radios, and televisions for channel selection and filtering.8. Switching/Rectification: Controls the switching of semiconductor components at predetermined times in power conversion circuits.9. Energy Storage: Stores electrical energy for release when needed. Examples include camera flash units, defibrillators, and backup power systems. Modern supercapacitors can store energy approaching the levels of small lithium batteries.III Capacitor TypesThere are several different types of capacitors that vary by polarity, performance, cost, and application. Below are the most common capacitor types: aluminum electrolytic, ceramic, tantalum, film, mica, and polymer capacitors, along with their features, applications, and selection criteria.1. Aluminum Electrolytic CapacitorAluminum electrolytic capacitors use aluminum foil electrodes separated by electrolyte-impregnated paper. The thin aluminum oxide layer acts as the dielectric. Due to the oxide film's unidirectional conduction properties, these capacitors are polarized.Advantages: High capacitance values, can handle large ripple currents, cost-effective for bulk energy storage.Applications: Power supply filtering, energy storage, motor starting, audio coupling.Disadvantages: Large tolerance (typically ±20%), significant leakage current, limited high-frequency performance (typically below 100kHz), temperature sensitivity, finite lifetime due to electrolyte evaporation.2025 Update: Modern aluminum electrolytics now feature improved electrolytes with operating temperatures up to 150°C and lifetimes exceeding 10,000 hours at rated temperature.2. Ceramic CapacitorCeramic capacitors use ceramic materials with high dielectric constants, such as barium titanate, formed into discs, tubes, or chips. Silver electrodes are applied through firing processes.Available in two main classes:Class 1 (C0G/NP0): Temperature-stable, low loss, used in precision timing and filteringClass 2 (X7R, X5R, Y5V): Higher capacitance density but with temperature and voltage dependenceApplications: High-frequency circuits, decoupling, bypass, timing circuits, RF applications.Advantages: Excellent high-frequency characteristics, low ESR, small size, non-polarized, good temperature stability (Class 1).Disadvantages: Voltage and temperature dependence (Class 2), microphonic effects in some types, limited capacitance values in stable types.2025 Update: Multi-layer ceramic capacitors (MLCC) now achieve capacitance values up to 1000µF in small packages, with improved temperature stability and reduced acoustic noise.3. Tantalum CapacitorUses sintered tantalum powder as the anode with tantalum pentoxide as the dielectric and manganese dioxide or conductive polymer as the cathode.Advantages: Excellent temperature and frequency characteristics, low leakage current, stable capacitance, long service life, high capacitance-to-volume ratio, low ESR (polymer types).Applications: Mobile devices, computers, automotive electronics, medical equipment, aerospace applications.Disadvantages: Higher cost, susceptible to voltage transients, can fail catastrophically if overvoltaged.2025 Update: Polymer tantalum capacitors now offer ESR values below 10mΩ and improved surge current handling, making them ideal for high-performance applications.4. Film CapacitorStructure: Film capacitors use plastic films such as polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), or polycarbonate as dielectrics, with metal foil or metallized film electrodes.Common types include:Polyester (PET): General purpose, good stabilityPolypropylene (PP): Low loss, high frequency capabilityPolystyrene (PS): Excellent stability, low temperature coefficientPolycarbonate: Good temperature stability (now less common)Advantages: Non-polarized, high insulation resistance, excellent frequency characteristics, low dielectric loss, self-healing properties (metallized types).Applications: Power electronics, motor drives, lighting ballasts, audio equipment, power factor correction, snubber circuits.2025 Update: New film capacitor technologies include improved polypropylene films for electric vehicle applications and enhanced metallization techniques for better self-healing properties.5. Mica CapacitorStructure: Uses natural mica sheets as the dielectric with silver electrodes, assembled in a stacked configuration and encapsulated in epoxy or molded plastic.Characteristics: Extremely stable, low temperature coefficient, high Q factor, excellent frequency characteristics up to several GHz.Applications: RF circuits, oscillators, filters, precision timing circuits, test equipment, military and aerospace applications.Advantages: Outstanding stability, low loss, predictable temperature coefficient, radiation resistant.Disadvantages: Higher cost, limited availability, larger size compared to ceramic alternatives.6. Polymer CapacitorStructure: Uses conductive polymers as the cathode material, available in both aluminum and tantalum versions. The polymer provides better conductivity than traditional liquid electrolytes.Advantages:Extremely low ESR (as low as a few milliohms)High ripple current capabilityStable capacitance over frequencyNo voltage derating required within ratingsFail-safe behavior (no catastrophic failures)Long operational lifeApplications: CPU power supplies, graphics cards, high-frequency switching converters, automotive electronics, telecommunications equipment.2025 Update: Hybrid polymer capacitors now combine the benefits of wet and polymer electrolytes, offering improved performance across temperature ranges and extended lifetimes.IV Capacitor Value Marking Methods1) Direct Marking MethodUses letters and numbers to directly mark values on the component body. For example, 1µF denotes 1 microfarad. Some capacitors use "R" to denote decimal points, such as R56 for 0.56 microfarads.2) Character-Symbol MethodCombines numbers and characters where symbols represent units: p (pico), n (nano), µ (micro), m (milli), F (farad). Examples:p10 = 0.1 pF1p0 = 1 pF6P8 = 6.8 pF2µ2 = 2.2 µFTolerance markings for values less than 10pF: B=±0.1pF, C=±0.2pF, D=±0.5pF, F=±1pF.3) Color Code MethodSimilar to resistor color codes, uses colored bands or dots to indicate capacitance, tolerance, and voltage rating.4) Numerical Code MethodThree-digit system where the first two digits are significant figures and the third digit is the multiplier (power of 10). Examples:272 = 27 × 10² = 2700 pF473 = 47 × 10³ = 47000 pF105 = 10 × 10⁵ = 1,000,000 pF = 1 µF2025 Update: QR codes are now being used on some capacitors to provide detailed specifications and traceability information accessible via smartphone apps.V Capacitor Characteristics(1) Capacitance and Tolerance: The maximum allowable deviation between actual and nominal capacitance. Standard tolerance grades include:Grade I: ±5%Grade II: ±10%Grade III: ±20%Precision grades: ±1%, ±2%, ±0.5%, ±0.1%(2) Rated Working Voltage: The maximum continuous voltage a capacitor can withstand while maintaining reliable operation. Higher voltage ratings generally require larger physical sizes for the same capacitance.(3) Temperature Coefficient: The relative change in capacitance per degree of temperature change. Smaller temperature coefficients indicate better stability.(4) Insulation Resistance: Indicates leakage current levels. Higher insulation resistance means lower leakage. Typical values range from megohms to teraohms depending on capacitor type and size.(5) Dielectric Loss: Energy dissipated as heat during operation, usually expressed as loss tangent (tan δ) or dissipation factor (DF).(6) Frequency Characteristics: How electrical parameters vary with frequency. Different capacitor types have different frequency limitations:Small mica capacitors: up to 1 GHzCeramic capacitors: up to several GHzFilm capacitors: up to 1 MHz (depending on type)Electrolytic capacitors: typically below 100 kHz2025 Update: New measurement techniques now allow characterization of capacitor behavior up to millimeter-wave frequencies, important for 5G and beyond applications.VI Capacitor Electrical SymbolsHere are the standard schematic symbols for various capacitors:(1) ①: Basic capacitor symbol for non-polarized types (ceramic, film, mica)(2) ②-⑥: Polarized capacitor symbols (electrolytic, tantalum) - curved plate indicates negative terminal(3) ⑦: Variable capacitor symbol(4) ⑧: Adjustable (trimmer) capacitor symbolStandard Capacitor ValuesCapacitors are available in standard values following the E-series. Here are the most commonly found values:Standard Capacitor ValuespFpFpFpFµFµFµFµFµFµFµF1.01010010000.010.11.0101001000100001.51515015000.0150.151.5151501500150002.22222022000.0220.222.2222202200220003.33333033000.0330.333.3333303300330004.74747047000.0470.474.7474704700470006.86868068000.0680.686.868680680068000VII How to Choose Capacitors Correctly?7.1 Selection Requirements1) Application-Based Selection:Power Supply Filtering: Aluminum electrolytic or polymer capacitorsHigh-Frequency Decoupling: Ceramic capacitors (MLCC)Precision Timing: C0G/NP0 ceramic or film capacitorsAudio Coupling: Film or non-polarized electrolytic capacitorsMotor Starting: Film capacitors rated for AC operationEnergy Storage: Supercapacitors or high-capacity electrolytics2) Voltage Rating Selection: Choose capacitors with voltage ratings 1.5-2 times the maximum expected voltage. For pulsed applications, consider peak voltages. In high-temperature environments, derate voltage further.3) Temperature Considerations: Select capacitors rated for the expected operating temperature range. Consider both ambient temperature and self-heating effects.4) Frequency Response: Match the capacitor's frequency characteristics to your application requirements. High-frequency applications require low-ESR types.5) Lifetime Requirements: Consider operational lifetime, especially for electrolytics. Calculate expected life based on temperature and ripple current.6) Environmental Factors: Consider humidity, vibration, shock, and chemical exposure in the operating environment.7.2 Advanced Selection Criteria1) Frequency-Based Selection:DC to 1 kHz: Aluminum electrolytic, tantalum1 kHz to 1 MHz: Film capacitors, low-ESR electrolytics1 MHz to 100 MHz: Ceramic capacitors (X7R, X5R)Above 100 MHz: C0G/NP0 ceramic capacitors2) Temperature Stability Ranking:C0G ceramic ≥ Film ≥ Solid tantalum ≥ Mica ≥ X7R ceramic ≥ Aluminum electrolytic3) ESR Performance Ranking:Ceramic ≥ Film ≥ Polymer ≥ Solid tantalum ≥ Wet tantalum ≥ Aluminum electrolytic4) Ripple Current Capability:Film ≥ Polymer ≥ Aluminum electrolytic ≥ Ceramic ≥ Tantalum2025 Update: New selection tools include AI-powered capacitor selection software that considers multiple parameters simultaneously and suggests optimal components based on application requirements.7.3 Common Selection Mistakes to Avoid1. Voltage Derating: Always provide adequate voltage margin. A 10V capacitor should not be used in a 10V circuit.2. Temperature Effects: Consider both ambient temperature and self-heating. Electrolytic capacitors lose significant capacitance at low temperatures.3. Frequency Mismatch: Using electrolytics in high-frequency applications or ceramics in precision low-frequency circuits.4. Ignoring ESR: High ESR can cause excessive heating and poor performance in switching applications.5. Lifetime Calculations: Not considering the impact of temperature and ripple current on electrolytic capacitor lifetime.6. Mechanical Stress: Ignoring thermal expansion, vibration, and mechanical mounting stress.2025 Update: Modern design software now includes comprehensive capacitor models that account for parasitic effects, aging, and environmental factors, helping prevent common selection errors.VIII Emerging Capacitor Technologies (2025)1. Supercapacitors (EDLC/Ultracapacitors)Supercapacitors bridge the gap between traditional capacitors and batteries, offering:Capacitance values from 0.1F to over 3000FHigh power densityLong cycle life (>1 million cycles)Fast charging/dischargingWide temperature range operationApplications: Energy harvesting, backup power, automotive start-stop systems, renewable energy storage, IoT devices.2. Solid-State CapacitorsNew solid-state electrolyte technologies offer:Improved safety (no liquid electrolyte)Extended temperature rangeBetter reliabilityReduced size3. Graphene-Enhanced CapacitorsGraphene electrodes provide:Ultra-low ESRHigh frequency capabilityImproved thermal managementEnhanced durabilityIX ConclusionCapacitor technology continues to evolve rapidly, with improvements in materials science, manufacturing processes, and design techniques leading to better performance and lower costs. Whether you're beginning a new design or updating an existing one, it's essential to stay current with the latest capacitor technologies and selection criteria.The key to successful capacitor selection lies in understanding your application requirements and matching them to the appropriate capacitor characteristics. Consider not just the basic electrical parameters, but also environmental factors, lifetime requirements, and cost constraints.Modern design tools and simulation software can help optimize capacitor selection, but fundamental understanding of capacitor behavior remains crucial for successful circuit design.Frequently Asked Questions (FAQ)1. What is a capacitor used for?A capacitor is a passive electronic component used to store electrical energy in an electric field. Common applications include power supply filtering, signal coupling, timing circuits, energy storage, and frequency tuning.2. What is the difference between polarized and non-polarized capacitors?Polarized capacitors (like electrolytics and tantalums) have positive and negative terminals and must be connected correctly. Non-polarized capacitors (like ceramics and films) can be connected either way.3. How do I choose the right voltage rating?Select a voltage rating at least 1.5-2 times higher than the maximum voltage in your circuit. For critical applications or harsh environments, use even higher derating factors.4. What's the difference between ESR and ESL?ESR (Equivalent Series Resistance) represents resistive losses, while ESL (Equivalent Series Inductance) represents inductive effects. Both affect high-frequency performance.5. Can I replace an electrolytic capacitor with a ceramic one?It depends on the application. Ceramics offer better high-frequency performance but may not provide sufficient capacitance for power supply filtering. Consider the specific requirements of your circuit.6. How long do capacitors last?Lifetime varies by type: ceramic and film capacitors can last decades, while electrolytic capacitors typically last 2,000-10,000 hours at rated temperature. Actual lifetime depends on operating conditions.7. What causes capacitor failure?Common failure modes include overvoltage, overtemperature, aging (especially in electrolytics), mechanical stress, and manufacturing defects. Proper selection and derating minimize failure risk.8. Are supercapacitors better than regular capacitors?Supercapacitors excel in energy storage applications but have lower voltage ratings and higher cost per farad. They're complementary technologies rather than direct replacements.9. How do I measure capacitor performance?Key parameters include capacitance, ESR, leakage current, and temperature coefficient. Specialized LCR meters and impedance analyzers provide accurate measurements.10. What's the impact of temperature on capacitor performance?Temperature affects capacitance value, ESR, leakage current, and lifetime. Different capacitor types have varying temperature sensitivities, with C0G ceramics being most stable.2025 Update InformationLast Updated: November 2025

LM4910LQ belonging to the Boomer series of National Semiconductors is an integrated stereo amplifier primarily intended for stereo headphone applications. The IC can be operated from 3.3V ans its can deliver 0.35mW output power into a 32 ohm load. The LM4910LQ has very low distortion ( less than 1%)   and the shutdown current is less than 1uA. This low shut down current makes it suitable for battery operated applications. The IC is so designed that there is no need of the output coupling capacitors, half supply by-pass capacitors and bootstrap capacitors. Other features of the IC are   turn ON/OFF click elimination, externally programmable gain etc. Stereo headphone amplifier LM4910LQCircuit diagram of the LM4910LQ stereo headphone amplifier is shown above.C1 and C2 are the input DC decoupling capacitors for the left and right input channels. R1 and R2 are the respective input resistors. R3 is the feed back resistor for left channel while R4 is the feed back resistor for the right channel. C3 is the power supply filter capacitor. The feedback resistors also sets the closed loop gain in conjunction with the corresponding input resistors. Notes:The IC is available only  in SMD packages and care must be taken while soldering.The circuit can be powered from anything between 2.2V to 5V DC.The load can be a 32 ohm headphone.Absolute maximum supply voltage is 6V  and anything above it will destroy the IC.A logic low voltage at the shutdown pins shut downs the IC and a logic high voltage at the same pin activates the IC. 

The current memory landscape spans from venerable DRAM to hard disk drives to ubiquitous flash. But in the last several years PCM has attracted the industry's attention as a potential universal memory technology based on its combination of read/write speed, endurance, non-volatility and density. For example, PCM doesn't lose data when powered off, unlike DRAM, and the technology can endure at least 10 million write cycles, compared to an average flash USB stick, which tops out at 3,000 write cycles. This research breakthrough provides fast and easy storage to capture the exponential growth of data from mobile devices and the Internet of Things. Applications IBM scientists envision standalone PCM as well as hybrid applications, which combine PCM and flash storage together, with PCM as an extremely fast cache. For example, a mobile phone's operating system could be stored in PCM, enabling the phone to launch in a few seconds. In the enterprise space, entire databases could be stored in PCM for blazing fast query processing for time-critical online applications, such as financial transactions. Machine learning algorithms using large datasets will also see a speed boost by reducing the latency overhead when reading the data between iterations. How PCM Works PCM materials exhibit two stable states, the amorphous (without a clearly defined structure) and crystalline (with structure) phases, of low and high electrical conductivity, respectively. To store a '0' or a '1', known as bits, on a PCM cell, a high or medium electrical current is applied to the material. A '0' can be programmed to be written in the amorphous phase or a '1' in the crystalline phase, or vice versa. Then to read the bit back, a low voltage is applied. This is how re-writable Blue-ray Discs store videos. Previously scientists at IBM and other institutes have successfully demonstrated the ability to store 1 bit per cell in PCM, but today at the IEEE International Memory Workshop in Paris, IBM scientists are presenting, for the first time, successfully storing 3 bits per cell in a 64k-cell array at elevated temperatures and after 1 million endurance cycles. "Phase change memory is the first instantiation of a universal memory with properties of both DRAM and flash, thus answering one of the grand challenges of our industry," said Dr. Haris Pozidis, an author of the paper and the manager of non-volatile memory research at IBM Research - Zurich. "Reaching three bits per cell is a significant milestone because at this density the cost of PCM will be significantly less than DRAM and closer to flash." To achieve multi-bit storage IBM scientists have developed two innovative enabling technologies: a set of drift-immune cell-state metrics and drift-tolerant coding and detection schemes. More specifically, the new cell-state metrics measure a physical property of the PCM cell that remains stable over time, and are thus insensitive to drift, which affects the stability of the cell's electrical conductivity with time. To provide additional robustness of the stored data in a cell over ambient temperature fluctuations a novel coding and detection scheme is employed. This scheme adaptively modifies the level thresholds that are used to detect the cell's stored data so that they follow variations due to temperature change. As a result, the cell state can be read reliably over long time periods after the memory is programmed, thus offering non-volatility. "Combined these advancements address the key challenges of multi-bit PCM, including drift, variability, temperature sensitivity and endurance cycling," said Dr. Evangelos Eleftheriou, IBM Fellow. The experimental multi-bit PCM chip used by IBM scientists is connected to a standard integrated circuit board. The chip consists of a 2 × 2 Mcell array with a 4- bank interleaved architecture. The memory array size is 2 × 1000 μm × 800 μm. The PCM cells are based on doped-chalcogenide alloy and were integrated into the prototype chip serving as a characterization vehicle in 90 nm CMOS baseline technology. Source from IBM

A new highly efficient power amplifier for electronics could help make possible next-generation cell phones, low-cost collision-avoidance radar for cars and lightweight microsatellites for communications.Fifth-generation, or 5G, mobile devices expected around 2019 will require improved power amplifiers operating at very high frequencies. The new phones will be designed to download and transmit data and videos faster than today's phones, provide better coverage, consume less power and meet the needs of an emerging "Internet of things" in which everyday objects have network connectivity, allowing them to send and receive data.Power amplifiers are needed to transmit signals. Because today's cell phone amplifiers are made of gallium arsenide, they cannot be integrated into the phone's silicon-based technology, called complementary metal-oxide-semiconductor (CMOS). The new amplifier design is CMOS-based, meaning it could allow researchers to integrate the power amplifier with the phone's electronic chip, reducing manufacturing costs and power consumption while boosting performance."Silicon is much less expensive than gallium arsenide, more reliable and has a longer lifespan, and if you have everything on one chip it's also easier to test and maintain," said Saeed Mohammadi, an associate professor of electrical and computer engineering at Purdue University. "We have developed the highest efficiency CMOS power amplifier in the frequency range needed for 5G cell phones and next-generation radars."Findings are detailed in two papers, one to be presented during the IEEE International Microwave Symposium on May 24 in San Francisco, authored by former doctoral student Sultan R. Helmi, who has graduated, and Mohammadi. They authored another paper with former doctoral student Jing-Hwa Chen to appear in a future issue of the journal IEEE Transactions on Microwave Theory and Techniques.The amplifier achieves an efficiency of 40 percent, which is comparable to amplifiers made of gallium arsenide.The researchers created the new type of amplifier using a high-performance type of CMOS technology called silicon on insulator (SOI). The new amplifier design has several silicon transistors stacked together and reduces the number of metal interconnections normally needed between transistors, reducing "parasitic capacitance," which hinders performance and can lead to damage to electronic circuits."We have merged transistors so we are using less metallization around the device, and that way we have reduced the capacitance and can achieve higher efficiencies," Mohammadi said. "We are trying to eliminate metallization between transistors."The new amplifiers could bring low-cost collision-avoidance radars for cars and electronics for lightweight communications microsatellites.The CMOS amplifiers could allow researchers to design microsatellites that are one-hundredth the weight of today's technology.