The Kynix Blog

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 

This blog is about GPS and inertial sensors for driverless cars. GPS is an essential technology for today's driving locations. However, due to the error, multi-path, and low update frequency of GPS, we cannot rely on it for positioning. Inertial sensors have a high update frequency and can be used in conjunction with GPS. CatalogI Self-driving car positioning technologyII Introduction to GPSIII Introduction to inertial sensorsIV GPS and inertial sensor fusionV GPS vs inertial sensor & GPS vs   inertial sensor fusionVI ConclusionFAQI Self-driving car positioning technologyDriving location is one of the core technologies of Driverless cars. Global positioning system (GPS) also plays a very important role in driverless positioning. However, unmanned vehicles are driving in complex dynamic environments, especially in metropolitan areas, where GPS multipath reflections can be significant. This GPS positioning information is very easy to produce an error. Such errors are likely to cause traffic accidents for cars traveling at high speed over limited widths. Therefore, we must rely on other sensors to assist positioning and enhance the positioning accuracy. In addition, due to the low frequency of GPS update (10Hz), it is difficult to provide accurate real-time positioning when the vehicle is driving fast.The inertial sensor (IMU) is a high-frequency (1KHz) sensor that detects acceleration and rotational motion. After the inertial sensor data is processed, we can get the displacement and rotation information of the vehicle in time. However, the inertial sensor itself also has the effect of deviation and noise . By using Kalman filter-based sensor’s fusion technology, we can integrate GPS and inertial sensor data to achieve better positioning results. Because unmanned driving’s requirements for reliability and safety are very high, positioning based on GPS and inertial sensors is not the only way to locate. We also match LiDAR with high-precision map, or position by visual odometer, so that a variety of positioning method will be adopted to correct each other in order to achieve more accurate results.II Introduction to GPS Global Positioning System (GPS) is an indispensable technology for current driving location and plays a very important role in driverless positioning. The GPS system includes 32 GPS satellites in space, 1 master control station on the ground, 3 data injection stations and 5 monitoring stations, and a GPS receiver as a subscriber station. With at least three of these satellites, the location and altitude of the client on Earth can be quickly determined. Now civilian GPS can reach about 10 meters positioning accuracy. The GPS system uses low-frequency signals and maintains considerable signal penetration, even in poor weather. Following i will analysis GPS operating principle and technical flaws.Figure 1. GPS three-way measurement of positioning2.1 Trilateration methodAs shown in Figure 1, GPS positioning system is the use of satellite basic triangulation Principle, utilizing GPS receiver to measure the transmission time of radio signals to measure the distance. From the location of each satellite, the distance between each satellite and the receiver can be measured to calculate the coordinates of the three-dimensional space of the receiver. Users receive the device as long as the use of three satellite signals received, you can set the user's location. In practice, GPS receiving devices use more than four satellite signals to locate the location and height of the user. Triangle positioning works as follows:Assuming that we measure the distance of the first satellite to 18,000 km, we can limit the current range of possible locations to 18,000 km above the surface of the Earth from the first satellite.Next, suppose we measure a distance of 20,000 km from the second satellite, and then we can further limit the current location to an intersection of 18,000 km from the first satellite and 20,000 km from the second satellite.Then we will measure the third satellite again and locate the current position through the intersection of the three satellites. Normally, the GPS receiver uses the location of the fourth satellite to confirm the position measurements of the first three satellites for better results.2.2 Distance measurement and precise time stampingIn theory, distance measurement is a simple process, and we only need to multiply the signal propagation time by the speed of light to get the distance information. But the problem is that the measured propagation time, any error, will result in a huge distance error. There is a certain amount of error in the clock we use every day. If we use quartz clock to measure the propagation time, there is a big error in GPS-based positioning. To solve this problem, atomic satellites are installed on each satellite to achieve nanosecond-level accuracy. In order for the satellite positioning system to use a synchronous clock, we need to have atomic clocks installed on all receivers as well. But atomic clocks cost tens of thousands of dollars, making it impractical for every GPS receiver to install such an expensive thing. In order to solve this problem, atomic clocks can still be used on every satellite, but ordinary quartz clocks often need to be calibrated at the receiver. Receivers receive signals from four or more satellites and calculate their own errors to adjust their own clock to a uniform time value.2.3 Differential GPSAs mentioned above, there are problems such as errors caused by satellite clocks and delays in satellites' distance measurement. Using differential technology, we can eliminate or reduce these errors, so GPS to achieve higher accuracy. The principle of differential GPS operation is quite simple: if both GPS receivers are fairly close to each other, the signals from both will have almost the same error. If the error of the first receiver can be accurately calculated, The results of the two receivers are corrected.Figure 2. Differential GPSHow to accurately calculate the error of the first receiver? We can place the reference receiver reference station at a known and accurate location. As shown in Figure 2, the GPS receiver installed on the reference station can observe three satellites and perform three-dimensional positioning to calculate the measurement coordinate of the base station. Then we can calculate the error by comparing the measured coordinates with the known coordinates. The reference station then sends the error value to a differential GPS receiver within a radius of 100 km to correct their measurement data.Figure 3. Multipath problem2.4 Multi-path problemAs shown in Figure 3, the multipath problem refers to the error of the signal propagation time caused by the reflection and refraction of GPS signals, which leads to positioning errors. Especially in urban environments, there are many suspended media in the air that reflect and refract GPS signals, and signals that reflect and refract on the outer walls of tall buildings, all of which cause confusion in distance measurements. The current high-precision military differential GPS, in the static and "ideal" environment can indeed achieve centimeter-level accuracy. The "ideal" environment here means that there is not too much suspended medium in the atmosphere, and the GPS has a stronger received signal when measured. However, unmanned vehicles are driving in a complex and dynamic environment, especially in large cities, GPS multipath reflections will be more obvious. This GPS positioning information is very easy to have a few meters of error, is likely to lead to traffic accidents.Even with all sorts of problems, GPS is still a relatively accurate sensor, and GPS errors do not increase over time. However, one problem with GPS is the low update frequency, which is around 10Hz. Due to the speed of unmanned vehicles, we need real-time precise positioning to ensure the safety of unmanned vehicles. Therefore, we must rely on other sensors to assist positioning and enhance the positioning accuracy.III Introduction to inertial sensorsThe inertial sensor (IMU) is a sensor that detects acceleration and rotational movement. The basic inertial sensors include accelerometers and MEMS gyroscope. This article focuses on MEMS-based six-axis inertial sensors, mainly by the three-axis acceleration sensor and three-axis gyroscope components.Here is a video introducing Inertial Sensor in detail：Inertial sensor introductionMEMS inertial sensors are divided into three levels: Low-precision inertial sensors are mainly used in consumer electronics products, smart phones, such sensors priced at 50 cents to a few dollars, but the measurement error will be relatively large. Intermediate inertial sensors are mainly used in automotive electronic stability systems and GPS-assisted navigation systems, such sensors priced at hundreds to thousands of dollars, relative to the low-end inertial sensors, intermediate inertial sensors in the control chip measurement error correction, So the measurement result is more accurate. However, after a long period of operation, the cumulative error will increase. High-precision inertial sensors as a military-grade and space-grade products, requiring high-precision, temperature zone, shock and other indicators. Mainly used for communications satellite wireless, missile seeker, optical aiming system and other stable applications. Such sensors are priced in the hundreds of thousands of US dollars range, even after a long run, such as transcontinental intercontinental missiles, still can achieve the rice level accuracy.Unmanned aerial vehicles are generally low-level inertial sensors. It is characterized by high update frequency (1KHz), can provide real-time location information. But the fatal disadvantage of an inertial sensor is that its error increases over time, so we can only rely on inertial sensors for positioning in a short period of time.Figure 4. Accelerometer3.1 AccelerometerFigure 4 shows the MEMS accelerometer, which works by virtue of the inertia of the moveable part of the MEMS. Because of the large mass of the intermediate capacitor plate and its cantilever configuration, the inertial force it receives exceeds the force that holds or supports it when the speed or acceleration is large enough, at which point it moves, keeping it up and down The distance between the plates will change, the upper and lower capacitors will change accordingly. Capacitance changes with the acceleration is proportional to. Depending on the measurement range, the strength or spring constant of the cantilever structure of the intermediate capacitor plate can be designed differently. And if you want to measure the acceleration in different directions, the structure of this MEMS will be very different. Capacitor changes will be another piece of dedicated chip into a voltage signal, and sometimes the voltage signal will be amplified. The voltage signal is digitized and processed through a digital signal that is output after zero and sensitivity correction.Figure 5. MEMS gyroscope3.2 MEMS gyroscopeFigure 5 shows the MEMS gyroscope, which works on the principle of conservation of angular momentum. It is a non-rotating object whose axis of rotation does not change with the rotation of the support carrying it. Similar to the working principle of an accelerometer, the upper active metal of the gyroscope forms a capacitance with the underlying metal. As the gyroscope rotates, the distance between the gyro and the underlying capacitive plate changes, and the upper and lower capacitances change accordingly. The change in capacitance is proportional to the angular velocity, so we can measure the current angular velocity.3.3 Inertial sensor problemDue to the production process, inertial sensor measurements usually have some error. The first error is the offset error, ie, the gyroscope and accelerometer will have non-zero data output even without rotation or acceleration. To get the displacement data, we need to integrate the accelerometer's output twice. After two integrations, even a small offset error will be magnified and as time progresses, the displacement error will accumulate, ultimately resulting in no further tracking of the UAV's position. The second error is the ratio error, the ratio between the measured output and the change in the sensed input. Similar to the offset error, after two integrals, the error caused by the displacement will accumulate over time. The third kind of error is the background white noise that, if not corrected, can also prevent us from tracking the location of the UAV.In order to correct these errors, we must calibrate the inertial sensor, find the offset error, the proportional error, and then use the calibration parameters to correct the original data of the inertial sensor. But the complication is that the error of the inertial sensor will also change with the temperature. Even if we make the best adjustments, as time goes on, the displacement error will continue to accumulate, so it is very difficult for us to use inertial sensors to locate UAV alone.IV GPS and inertial sensor fusionAs mentioned above, GPS is a relatively accurate positioning sensor even with multi-path problems. However, the update frequency is low and can not meet the requirements of real-time calculation. The inertial sensor positioning error will increase with the running time, but because it is a high-frequency sensor, in a short period of time can provide stable real-time location updates. Therefore, as long as we find a way to combine the advantages of these two sensors, each director, you can get more real-time and accurate positioning. Below we discuss how to use the Kalman filter to fuse the two sensor data.4.1 Introduction to Kalman FilterKalman filter predicts the position coordinates and velocity of an object from a set of observations that contain a limited set of noise-containing object positions. It has strong robustness. Even if there is an error in the observation of the object's position, we can accurately estimate the position of the object based on the historical state of the object and the current observation of the position. The Kalman filter is mainly divided into two phases: the prediction phase predicts the current position based on the position information of the previous time point; the update phase updates the position of the object by correcting the position prediction by observing the current position of the object.To give a concrete example, suppose you have a power outage without any light and you want to walk back to the bedroom from the living room. You know the relative position of the living room to the bedroom, so you walk in the dark and try to predict the current position by counting steps. Halfway through, you touch the TV. Since you know in advance the approximate location of the television in the living room, you can correct your prediction of the current location by the location of your television set, and then continue to rely on the calculated steps based on the more accurate adjusted position estimate Several to the bedroom forward. Relying on the calculation of the number of steps and touch the object, you eventually dark from the living room back to the bedroom, the truth behind this is the core principle of Kalman filter.Figure 6. GPS and IMU sensor fusion positioning4.2 Multi-sensor fusionAs shown in Figure 6, the fusion of inertial sensors and GPS data using a Kalman filter is very similar to the example given above. Inertial sensor here is equivalent to a few steps, and GPS data equivalent to the location of the reference TV. First of all, based on the last position estimation, we use the inertial sensor to predict the current position in real time. Before getting new GPS data, we can only predict the current position by integrating the data of inertial sensors. However, the positioning error of inertial sensors increases with runtime, so we can use this GPS data to update the current position prediction as new, more accurate GPS data is received. By constantly implementing these two steps, we can take the director of both to accurately locate the unmanned vehicle in real time. Assuming that the frequency of the inertial sensor is 1 KHz and the frequency of the GPS is 10 Hz, we can use 100 inertial sensor data points for position prediction between every two GPS updates.V GPS vs inertial sensor & GPS vs inertial sensor fusionThis article describes the principle of using GPS and inertial sensors to accurately position a vehicle in an unmanned location. The system consists of three parts, a relatively accurate but low-frequency update GPS, a high-frequency update but increasingly unstable precision inertial sensors over time, and a Kalman filter-based mathematical model to fuse both Sensors, take the director, in order to achieve fast and accurate positioning effect. However, since driverless reliability and safety requirements are very high, in addition to GPS and inertial sensors, we often use positioning methods such as LiDAR and high-precision map matching, visual odometer and the like to make various positioning France correct each other in order to achieve more accurate results.VI ConclusionThis article focuses on GPS and inertial sensors for driverless applications. GPS is an indispensable technology for current driving location.But due to GPS error, multipathing and low update frequency, we can not rely on GPS for positioning. The inertial sensor has a high update frequency that can complement with GPS. Using sensor fusion technology, we can integrate GPS and inertial sensor data in order to achieve better positioning results.FAQ 1. What is GPS and its uses?The Global Positioning System (GPS) has been developed in order to allow accurate determination of geographical locations by military and civil users. It is based on the use of satellites in Earth orbit that transmit information which allow to measure the distance between the satellites and the user. 2. What GPS means?Global Positioning System. The Global Positioning System (GPS) is a U.S.-owned utility that provides users with positioning, navigation, and timing (PNT) services. 3. How does the GPS work?GPS is a system of 30+ navigation satellites circling Earth. We know where they are because they constantly send out signals. A GPS receiver in your phone listens for these signals. Once the receiver calculates its distance from four or more GPS satellites, it can figure out where you are. 4.What is importance of GPS?Why GPS is Important? GPS includes space-base satellites, computers and receivers which provide your location information in every weather conditions anywhere at any time in the world. It was originally made for the US military to locate their troops in deserted areas and forests. 5. How is GPS useful in our daily life?Using GPS tracking systems, you can manage employee transportation fleet and improve its efficiency. You can save time and fuel, thereby minimizing expenses. While travelling, the feature in the GPS could track the luggage, laptop, and important personal belongings. 6. What is an IMU sensor?An IMU is a specific type of sensor that measures angular rate, force and sometimes magnetic field. ... Technically, the term “IMU” refers to just the sensor, but IMUs are often paired with sensor fusion software which combines data from multiple sensors to provide measures of orientation and heading. 7. How does an inertial device work?How Does an IMU Work? IMUs can measure a variety of factors, including speed, direction, acceleration, specific force, angular rate, and (in the presence of a magnetometer), magnetic fields surrounding the device. IMUs combine input from several different sensor types in order to accurately output movement. 8. How do you use the IMU sensor?An IMU sensor unit working can be done by noticing linear acceleration with the help of one or additional accelerometers & rotational rate can be detected by using one or additional gyroscopes. Some also contain a magnetometer which can be used as a heading reference. 9. Why magnetometer is used in IMU?The third component of our IMU is the magnetometer. This is where I have seen people facing difficulties. It is a device capable of measuring magnetism. It is able to help us find orientation using the earth's magnetic field, similar to a compass. 10. How do I choose an IMU sensor?Some of the aspects we have to consider when we have to select an IMU are performance, underlying technology, SWaP (Size, Weight, and Power) and Cost. Besides, another important factor in UAVs is the ruggedness of the IMU. In harsh UAV applications, vibrations can reach a high level and different temperatures. 

Dealing with a malfunctioning dc to dc converter can feel overwhelming. Voltage drops, overheating, or irregular performance can disrupt your projects or equipment. You need to identify the root cause to restore functionality. Troubleshooting and repair ensure the converter operates efficiently and reliably. By learning practical techniques and using expert advice, you can tackle common issues with confidence. Addressing problems early also helps prevent long-term damage, saving time and money.Common Issues in DC to DC ConvertersVoltage IrregularitiesVoltage irregularities are among the most common problems you may encounter in a DC-to-DC converter. These irregularities can manifest as sudden drops, spikes, or fluctuations in the output voltage. Such issues often stem from degraded components, poor soldering connections, or external factors like electromagnetic interference.When voltage irregularities occur, the converter's performance becomes unreliable, potentially damaging connected devices. Fault prediction methods often focus on single component degradation, which limits their ability to address the broader impact on the converter's overall performance. Additionally, detecting fault signals can be costly and challenging, especially when interdependencies between components are not considered.Tip: Regularly inspect solder joints and capacitors for signs of wear or damage. Ensuring a stable connection can help minimize voltage fluctuations.Current Delivery ProblemsA DC-to-DC converter may also face current delivery problems, where it fails to provide sufficient current to the load. For example, users have reported cases where the output voltage remains stable at around 5V, but the current is limited to just a few milliamps. This low current issue can arise from factors like inductor saturation, improper output capacitor values, or issues with the enable (EN) pin.To address such problems, you should first check the inductor's saturation level and ensure it matches the converter's specifications. Adjusting the output capacitor values can also improve current delivery. However, if these adjustments fail, the issue might lie deeper within the circuit.Common causes of current problems:Saturated inductorsIncorrect capacitor valuesFaulty enable pin configurationNote: Always use components that meet the manufacturer's specifications to avoid compatibility issues.Component FailuresComponent failures are inevitable in any electronic device, including DC-to-DC converters. These failures can occur at different stages of the converter's lifecycle, as illustrated by the reliability bathtub curve. Most failures happen during the early "infant mortality" phase, often within the first 24 hours of operation. Over time, the failure rate stabilizes before increasing again during the end-of-life phase.Metrics like Mean Time Between Failures (MTBF) and Mean Time To Failure (MTTF) help quantify the reliability of a converter. Commonly failed components include capacitors, inductors, and MOSFETs. Identifying and replacing these components promptly can prevent further damage to the circuit.Tip: Perform a thorough inspection during the initial hours of operation to catch early failures. This proactive approach can significantly extend the lifespan of your converter.Overheating concernsOverheating is a critical issue that can compromise the performance and lifespan of your DC-to-DC converter. Excessive heat can damage components, reduce efficiency, and lead to complete failure. Identifying the causes of overheating and addressing them promptly is essential for maintaining reliable operation.Common Causes of OverheatingSeveral factors contribute to overheating in DC-to-DC converters:Poor ventilation: Limited airflow around the converter traps heat, causing components to overheat.High ambient temperature: Operating the converter in a hot environment increases the risk of thermal stress.Excessive load: Running the converter beyond its rated capacity generates more heat than it can dissipate.Faulty components: Malfunctioning capacitors, inductors, or MOSFETs can produce abnormal heat levels.Tip: Place your converter in a well-ventilated area and avoid exposing it to direct sunlight or heat sources.How to Detect OverheatingYou can identify overheating issues by observing the following signs:Physical symptoms: Components may feel hot to the touch or emit a burning smell.Performance drops: The converter may fail to deliver stable voltage or current.Thermal shutdown: Some converters include built-in protection mechanisms that shut down the device when it overheats.Using a digital thermometer or thermal imaging camera can help you measure the temperature of individual components.Preventing OverheatingPreventive measures can help you avoid overheating problems:Install heat sinks: Heat sinks dissipate excess heat and keep components cool.Use cooling fans: Fans improve airflow and reduce the risk of heat buildup.Optimize load conditions: Operate the converter within its rated capacity to minimize thermal stress.Choose high-quality components: Reliable components are less likely to fail under heat stress.Note: Regular maintenance, such as cleaning dust from heat sinks and fans, ensures effective cooling.Repairing Overheated ConvertersIf your converter overheats, you can take steps to repair it:Inspect for damage: Check for burnt components or melted solder joints.Replace faulty parts: Swap out damaged capacitors, inductors, or MOSFETs with new ones.Reapply thermal paste: Thermal paste improves heat transfer between components and heat sinks.Warning: If overheating persists after repairs, consult a professional to avoid further damage.By addressing overheating concerns early, you can extend the life of your DC-to-DC converter and ensure consistent performance.Troubleshooting DC-DC ConvertersDiagnostic methods for identifying issuesIdentifying the root cause of a problem in your DC-to-DC converter requires a systematic approach. Start by observing the symptoms, such as irregular output voltage or overheating. These signs often point to underlying faults in the circuit. A step-by-step diagnostic process can help you pinpoint the issue efficiently.Proven Technique:A robust fault diagnosis system for DC–DC Boost converters uses advanced methods like a linear switch fault detection observer and fault recognition observers. These tools compare actual and estimated outputs to detect discrepancies, enabling accurate fault identification. This approach has been validated through theoretical analysis, simulations, and experiments.You can also rely on field-tested methods to enhance your diagnostics:The inversion-based fault detection method uses an inverse model of a switched linear system to estimate faults in real-time.A fuzzy logic scheme isolates faults related to switches, voltage and current sensors, and capacitors.Health condition monitoring employs feature values and semi-supervised learning to classify faults with high accuracy.By combining these techniques, you can identify faults quickly and reduce downtime.Tools required for troubleshootingHaving the right tools is essential for effective troubleshooting. Without them, diagnosing and repairing your converter becomes a guessing game. Equip yourself with the following tools to streamline the process:Multimeter: Measures voltage, current, and resistance to identify irregularities in the circuit.Oscilloscope: Visualizes waveforms to detect anomalies in the output voltage or current.Soldering Kit: Repairs damaged connections and replaces faulty components.Thermal Imaging Camera: Identifies overheating components by detecting temperature variations.LCR Meter: Tests inductors, capacitors, and resistors for proper functionality.Each tool plays a specific role in diagnosing issues. For example, a multimeter helps you verify the connection integrity, while an oscilloscope provides a detailed view of the converter's performance. Investing in these tools ensures accurate troubleshooting and saves time.Testing individual componentsOnce you identify the general area of the fault, test individual components to confirm the issue. Start with the most failure-prone parts, such as capacitors, inductors, and MOSFETs.Capacitors: Check for bulging, leakage, or discoloration. Use an LCR meter to measure capacitance and ensure it matches the specifications.Inductors: Inspect for physical damage or overheating. Test the inductance value to confirm it falls within the acceptable range.MOSFETs: Verify the gate, drain, and source connections using a multimeter. Look for short circuits or open circuits that indicate failure.Tip: Always disconnect the component from the circuit before testing to avoid inaccurate readings.If a component fails the test, replace it with a new one that meets the manufacturer's specifications. This step ensures the converter operates reliably after the repair.By systematically testing each component, you can isolate the fault and restore your DC-to-DC converter to optimal performance.Common mistakes to avoidWhen troubleshooting DC-to-DC converters, avoiding common mistakes can save you time and prevent further damage. These errors often stem from oversight or lack of understanding, but recognizing them early can help you maintain your converter's performance.Choosing the wrong inductorSelecting an inductor with incorrect specifications can disrupt the converter's efficiency and stability. Low inductance values often lead to overheating, which damages components and reduces the lifespan of your device. Always verify the inductor's specifications against the converter's requirements before installation.Setting an improper soft start timeA fast soft start may cause the converter to fail during startup. This issue can trigger overcurrent protection mechanisms, preventing the converter from functioning properly. Adjust the soft start time to ensure a smooth and stable startup process.Misplacing components on the PCBIncorrect placement of components on the printed circuit board (PCB) increases power loss and risks damaging the circuitry. For example, placing capacitors too far from the load can result in unstable output voltage. Follow the manufacturer's layout guidelines to optimize component placement and maintain reliable operation.Tip: Double-check your PCB layout and component specifications before powering up the converter. This simple step can prevent costly mistakes.Neglecting connection integrityLoose or poorly soldered connections often lead to intermittent faults. These faults can cause irregular output voltage or current delivery problems. Inspect all connections carefully and re-solder any weak joints to ensure a stable circuit.Skipping component testingFailing to test individual components during troubleshooting can result in missed faults. For instance, a damaged capacitor may not visibly show signs of failure but can still affect the converter's performance. Use tools like multimeters and LCR meters to test components thoroughly.Ignoring thermal managementOverheating remains a critical problem in DC-to-DC converters. Skipping preventive measures like installing heat sinks or cooling fans can lead to thermal stress and component failure. Regularly clean heat sinks and ensure proper airflow to keep your converter cool.By avoiding these mistakes, you can troubleshoot your DC-to-DC converter effectively and restore its optimal performance.Practical Repair SolutionsTechniques for repairing damaged partsRepairing damaged parts in a DC-to-DC converter requires precision and attention to detail. Start by addressing thermal management issues. Poor heat dissipation often leads to component failure. You can improve this by adding heat sinks, thermal vias, or increasing airflow around the converter. These steps help maintain optimal operating temperatures and prevent overheating.When dealing with damaged components, inspect solder joints for cracks or weak connections. Re-soldering these joints can restore electrical continuity. For burnt or melted parts, carefully desolder and replace them with new components. Always match the replacement parts to the converter's specifications to ensure compatibility.Tip: Use a magnifying glass to inspect small components and solder joints for damage. This helps you identify issues that are not visible to the naked eye.Replacement options for failed componentsReplacing failed components is often more practical than repairing them. Modern technologies like the Digital Twin (DT) controller provide innovative solutions. When a physical controller fails, the DT controller activates immediately, ensuring the system continues to function. Experimental results show that this approach maintains stable output voltage and system performance.For traditional repairs, focus on replacing high-failure-rate components like capacitors, inductors, and MOSFETs. Use high-quality parts that meet the circuit's electrical requirements, including nominal ratings and derating factors. This ensures long-term reliability and prevents future failures.Note: Always test the converter after replacing components to verify proper functionality.Optimizing converter performanceOptimizing your DC-to-DC converter enhances its efficiency and reliability. Advanced techniques like ANN-based Maximum Power Point Tracking (MPPT) improve conversion efficiency, especially in solar power applications. This method addresses issues with fixed step sizes, ensuring smoother operation.You can also optimize performance by maintaining proper charging voltage and charging current levels. Regularly monitor these parameters to prevent overcharging or undercharging your battery. Additionally, ensure the converter operates within its rated capacity to avoid thermal stress.Tip: Install a cooling fan to improve airflow and keep the converter cool during high-load operations.By implementing these strategies, you can extend the lifespan of your converter and maintain consistent performance.Preventive measures for long-term reliabilityEnsuring the long-term reliability of your DC-to-DC converter requires consistent care and attention. By following preventive measures, you can reduce the risk of failures and extend the lifespan of your device.1. Regular MaintenanceRoutine maintenance is essential for keeping your converter in top condition. Dust and debris can accumulate on components, leading to overheating or poor performance. Clean the converter regularly using compressed air or a soft brush. Inspect solder joints and connections for signs of wear or damage.Tip: Schedule maintenance checks every three to six months to catch potential issues early.2. Monitor Operating ConditionsOperating your converter within its specified limits prevents unnecessary stress on components. Check the input voltage, output voltage, and current levels to ensure they stay within the recommended range. Avoid exposing the converter to high ambient temperatures or excessive humidity.Key parameters to monitor:Input voltage rangeOutput current capacityAmbient temperature3. Use High-Quality ComponentsInvesting in high-quality components reduces the likelihood of failures. Cheap or substandard parts may save money initially but can lead to costly repairs later. Choose components that meet or exceed the manufacturer's specifications.Note: Always verify the ratings of capacitors, inductors, and MOSFETs before installation.4. Implement Thermal ManagementHeat is one of the leading causes of component failure. Install heat sinks or cooling fans to improve heat dissipation. Ensure proper airflow around the converter by placing it in a well-ventilated area.Warning: Never operate the converter without adequate cooling, as this can lead to permanent damage.5. Perform Periodic TestingTesting your converter periodically helps identify potential problems before they escalate. Use tools like multimeters and oscilloscopes to check for irregularities in voltage or current. Replace any components that show signs of wear or degradation.By adopting these preventive measures, you can ensure your DC-to-DC converter operates reliably for years to come. Consistent care not only improves performance but also saves you time and money in the long run.When to Seek Professional HelpSigns of irreparable damageSome issues in DC-to-DC converters signal irreparable damage. You should look for these signs to determine if professional help is necessary:Electrolytic capacitors often degrade over time. This degradation causes voltage ripple, reducing the converter's efficiency.Continuous operation with degraded capacitors can lead to permanent damage.Capacitors account for nearly 30% of failures in power converters, highlighting their critical role in reliability.If you notice persistent voltage ripple or damaged capacitors, stop using the converter immediately. Attempting to operate it further may worsen the damage.Benefits of expert consultationProfessional repair services offer several advantages. Experts have the tools and knowledge to diagnose complex issues accurately. They can identify problems that may not be visible during basic troubleshooting.Consulting a professional ensures your converter is repaired using high-quality components. This reduces the risk of future failures. Experts also optimize the converter's performance, improving its efficiency and reliability.Tip: Professionals can help you maintain proper charging voltage and charging current levels, ensuring your battery charges safely and efficiently.Finding reliable repair servicesFinding a trustworthy repair service is essential for restoring your DC-to-DC converter. Start by researching local repair shops with positive reviews. Look for technicians who specialize in power electronics and have experience with DC-to-DC converters.Ask about their repair process and the components they use. Reliable services use high-quality parts that meet the manufacturer's specifications. You can also check if they offer warranties for their repairs.Note: A good repair service will test your converter thoroughly after repairs to ensure it operates correctly.By recognizing signs of irreparable damage and seeking professional help, you can save time and prevent further issues. Reliable repair services ensure your converter performs optimally and charges your battery efficiently.Proper troubleshooting and repair of your DC-to-DC converter can significantly enhance its performance. You can achieve improvements like reducing output noise to less than 30μV and ripple to below 100μV, while boosting efficiency from 68% to over 71%. Regular maintenance, such as monitoring charging voltage and charging current, ensures your battery charges safely and efficiently. Preventive measures like cleaning and thermal management extend the converter’s lifespan. If issues persist, consulting a professional guarantees reliable repairs and optimal performance. Addressing problems early saves time and protects your equipment.FAQWhat should you do if your DC-to-DC converter fails to charge the battery?First, check the input voltage and ensure it matches the converter's specifications. Inspect the connections for loose wires or damage. Test the output voltage to confirm it aligns with the battery's charging requirements. Replace faulty components if necessary.How can you prevent overcharging your battery with a DC-to-DC converter?Use a converter with built-in overcharge protection. Monitor the charging voltage and current to ensure they stay within safe limits. Disconnect the converter once the battery reaches full charge. Regularly inspect the converter for signs of malfunction.Why does your battery fail to hold a charge after using a DC-to-DC converter?A failing battery may result from improper charging conditions. Check if the converter provides the correct voltage and current. Overcharging or undercharging can damage the battery over time. Replace the battery if it no longer holds a charge.Can a DC-to-DC converter charge multiple batteries simultaneously?Yes, but only if the converter supports multiple outputs or the batteries are connected in parallel. Ensure the converter's output voltage matches the charging requirements of all batteries. Monitor the charging process to avoid overloading the converter.How do you optimize the charging efficiency of your DC-to-DC converter?Keep the converter clean and well-ventilated to prevent overheating. Use high-quality components to maintain stable performance. Monitor the charging voltage and current to ensure they align with the battery's specifications. Regular maintenance improves charging efficiency and extends the converter's lifespan.

    This article shows how to use the buck converter for inverting or non-inverting voltage rails, and use it as an inverting buck-boost converter.     Catalog I. Brief Introduction II. Buck Converter III. Three DC/DC Converter Topologies 3.1 Isolated Buck Topology 3.2 Inverting Buck-boost (step-up and step-down)   Topology4 3.3 Isolated   Buck-boost Topology: +/- output5 FAQ   I. Brief Introduction   As we all known,power supply circuits come in the form of voltage step-up or step-down DC/DC converter. Nowadays,more and more applications require multiple voltage rails to drive ICs.The rails may be inverting,or non-inverting,with or without isolation.   While designers typically use multiple buck converters with single filter inductors, they add cost, footprint, and height. A simpler alternative is to use a single buck converter with coupled inductors or transformers configured in isolated converter topologies. Designers can use the buck converter for inverting or non-inverting voltage rails, and they can configure it for use as an inverting buck-boost converter.   Coupled inductors or transformers can also be used with a buck-boost converter to generate multiple inverting or non-inverting outputs with voltage step-up/down function. However, do you know what is isolated non-isolate DC/DC converter topologies? How they can be implemented using a single synchronous buck converter?   II. Buck Converter   A step-down transformer is a transformer that converts the higher voltage of the input end to the ideal voltage with relatively low output to achieve the purpose of reducing the pressure. A step-down transformer is a very important piece of equipment in the power transmission and transformation system.   Its normal operation is related to not only its own safety, but also the reliable power supply of users, and directly affects the stability of the power system. The protection configuration of the step-down transformer should satisfy in any case, the transformer can not be burned, the accident is enlarged, and the stability of the power system is affected. The principle of its work, the principle of relay protection, operation conditions, operation and requirements, and the abnormal operation and processing methods are introduced in detail. III. Three DC/DC Converter Topologies   The beauty of generating various converter topologies based on a single buck converter is that an optocoupler and its related circuitry are not required. This provides the benefit of a smaller footprint, lower component count, reduced complexity, and cost savings. Besides generating multiple outputs, the buck converter is configurable to operate as an inverting buck-boost converter, essentially providing a voltage step-up function. In addition, designers can create an isolated buck-boost converter using a similar concept.   3.1 Isolated Buck Topology A. +/- Step-down output: circuit operation1 An inverting and non-inverting step-down output can be generated with an isolated buck topology. Fig1 shows how it delivers a +/- output rail to any application that requires a positive and a negative supply. Fig1 Synchronous buck regulator uses isolated buck topology to generate ± Vout rail1   With reference to Fig1, the primary and secondary outputs are given by the following equations, assuming the leakage inductance of the coupled inductor or transformer and the DC resistance of the windings is negligible: where VIN is the input voltage, VO1 and VO2 are the primary and secondary outputs, respectively, D is the duty cycle, N is the turns ratio of the transformer, and Vdiode is the forward voltage drop across the diode.   During the cycle when the high side switch is on (current flow indicated by the green arrow in Fig1), the primary current ramps up and stores the energy in the magnetizing inductance of the transformer and the primary output capacitor. The diode on the secondary side is reverse biased and the load current on the secondary side is supplied by the output capacitor.   During the cycle when the low side switch is on (current flow indicated by the red arrow in Fig1), the primary current ramps down and releases the stored energy in the magnetizing inductance of the transformer, and the load current on the primary side is supplied by the output capacitor.   The diode on the secondary side is forward biased and the current flows from the transformer to supply current to the load, and charges up the secondary output capacitor. At steady state, the voltage at the secondary output is proportionally inverted compared to the voltage at the primary output, assuming the diode voltage drop, transformer winding resistance, and leakage inductances are negligible. Fig2 shows the operating waveforms for this architecture.   Fig2 Operating waveforms for a +/- step-down design1   B. +/+ step-down output2 Employing the same concept of generating secondary outputs using a coupled inductor or transformer, the secondary side can be configured differently to generate positive or negative secondary voltages. To generate a positive secondary output, the polarities of the transformer/coupled inductor as well as the secondary side diode are reversed. Fig3 shows an isolated buck topology to generate a dual +VOUT rail. Fig3 Isolated buck topology to generate a dual + VOUT rail2 C. +/+/- step-down output3 Fig4 shows an isolated buck topology to generate three outputs (dual +VOUT and single –VOUT rail). For a multiple output configuration, the total current of the various outputs reflected to the primary side must accounted for to make sure the IC is able to handle the resultant current. Fig4 Isolated buck topology to generate three outputs, dual +VOUT and single –VOUT rail3 The equations for the above circuit are as given below: Where VO1 is the primary output and VO2 and VO3 are the positive and negative secondary outputs, respectively, D is the duty cycle, N1 and N2 are the turns ratio of the transformer for VO2 and VO3, respectively. Vdiode is the forward voltage drop across the diode. IOUT1, IOUT2, and IOUT3 are the output current drawn from VO1, VO2, and VO3, respectively, IDS_pk is the peak current through the top switch and Δi is the triangular portion of the primary inductor ripple current.   3.2 Inverting Buck-boost (step-up and step-down) Topology4 An inverting buck-boost converter can be derived from the synchronous buck converter by connecting its GND terminal as the negative output of the buck-boost converter and the VOUT terminal of the buck converter as the GND of the buck-boost converter. Fig5 shows the circuit diagram of configuring the ISL85415 buck switcher as an inverting buck-boost converter. FigConfiguring a buck converter into an inverting buck-boost converter4 The equation for output voltage and output current are as follows: where VIN is the input voltage, VO1 is the output voltage, D is the duty cycle, IOUT is the output current, and IL is the inductor current.   During the cycle when the high side switch is on (current flow indicated by the green arrow in Fig5), the inductor current ramps up and stores energy in the inductor, and the output capacitor provides current to the load.    During the cycle when the low side switch is on (current flow indicated by the red arrow in Fig5), the inductor current ramps down and provides current to the load as well as charges the output capacitor. Operating waveforms for the inverting buck-boost design are shown in Fig6.     Fig6 Operating waveforms for an inverting buck-boost design4   3.3 Isolated Buck-boost Topology: +/- output5 A ± step-up/down output voltage can be realized using the isolated buck-boost topology. The filter inductor can be replaced with a transformer (or coupled inductor) to obtain a positive secondary output. Fig7 shows an isolated buck-boost topology to generate a ± step-up/down VOUT rail. Fig8 shows the operating waveforms for the isolated buck-boost design.   Fig7 Isolated buck-boost topology to generate a ± VOUT rail5 The voltage and current equations for the above circuit are given below: where VIN is the input voltage, VO2 is the secondary output voltage, Vdiode is the forward voltage drop across the diode, D is the duty cycle, N is the turns ratio of the transformer, IDS_pk is the peak current through the top switch, Δi is the triangular portion of the primary inductor ripple current, and IOUT1 and IOUT2 are the output current drawn from VO1 and VO2, respectively. Fig8 Operating waveforms for an Isolated buck-boost Topology: +/- output5 FAQ   1. What does a buck converter do? The buck converter is a very simple type of DC-DC converter that produces an output voltage that is less than its input. The buck converter is so named because the inductor always “bucks” or acts against the input voltage. The output voltage of an ideal buck converter is equal to the product of the switching duty cycle and the supply voltage. Like many power supply topologies, the buck converter operates on the principal of storing energy in an inductor. The voltage drop across an inductor is proportional to changes in electric current flowing through the device. 2. What is principle of Buck-boost converter? A Buck-Boost converter transforms a positive DC voltage at the input to a negative DC voltage at the output. The circuit operation depends on the conduction state of the MOSFET: On-state: The current through the inductor increases and the diode is in blocking state. 3. Are buck converters safe? A buck converter is probably no less reliable than most other topologies. It usually comes down to the reliability of the solder joints. The thing to remember about buck regulators is; if the series switch transistor fails SC - it dumps the full unregulated voltage into the load. 4. Are buck converters efficient? Buck converters can be highly efficient (often higher than 90%), making them useful for tasks such as converting a computer's main (bulk) supply voltage (often 12 V) down to lower voltages needed by USB, DRAM and the CPU (5V, 3.3V or 1.8V, see PSU). 5. How do buck converters work? The buck Converter circuit consists of the switching transistor, together with the flywheel circuit (Dl, L1 and C1). While the transistor is on, current is flowing through the load via the inductor L1. The action of any inductor opposes changes in current flow and also acts as a store of energy. 6. Do buck converters waste power? In a buck or boost converter, some energy is transferred directly from the source to the load as well, but the same principle applies. You can also look at a buck converter as an L-C filter on a square wave from the source. Again, all components are lossless, so there's no waste. 7. Does a buck converter limit current? The buck converter must operate at a very small duty cycle to keep the inductor current below the peak current limit threshold. ... Valley Current Limiting: Provides an additional level of protection. You can implement valley current limiting by sensing the inductor current when the low-side switch is on. 8. How do you adjust the current in a buck converter? You don't "adjust" output current. Loads draw whatever amount of current they need, provided the power supply can deliver it. If your total load exceeds the buck converter's rating of 3A, then you will be overloading it. If your total load is less than 3A, then you need not adjust anything. 9. How do you control a buck converter? A Buck converter consists of a transistor and diode that applies the supply voltage on an inductor capacitor, LC, circuit. The output voltage is the voltage across the capacitor. The input voltage u on the LC circuit is controlled by pulse width modulation, PWM. 10. What is the difference between buck and boost converter? In PV applications, generally, a Buck converter is used to charge the battery (since the output from a Buck converter is supposed to be less than its input), while a Boost converter is used to "match the load voltage" from the (supposedly) low voltage PV input.  

  This article will be divided into three parts--individual transformer , parallel transformer and redundancy requirements for bulk power transformers.     Catalog   I. Individual Transformer II. Parallel Transformer III. Redundancy Requirements for Bulk Power Transformers FAQ   I. Individual Transformer   Just see the following picture, it includes the protection for banks where fuses are used on the primary. Overall differential protection may be applied by using CTs in the transformer primary bushings for larger or important banks. The common connection is shown with delta on the source (primary) side and wye-grounded on the secondary side. Other possible connections: delta–delta, wye–wye, or primary-wye– secondary-delta. Figure 1 – Transformer protection without primary-side circuit breaker   About the analysis of power circuit, you can see the article: Analysis of Switching Power Supply Principle   Note: Secondary circuits should have 51 and 51N relays. Therefore, transformer secondary breaker and relays may be omitted unless another source connects to the secondary bus. 51N relay can be omitted with 51G available.   For transformer banks with primary breakers, the protection is summarized in Figure 2.   Relay 51G provides backup protection for secondary bus and feeder faults and must be time-coordinated, with other ground relays protecting the various feeder circuits on the secondary bus. Similarly, phase relays 51 must be coordinated with the phase relays on the feeders. The common connection is shown with delta on the source (primary) side and wye-grounded on the secondary side. Other possible connections: delta–delta, wye–wye, primary-wye– secondary-delta, three-winding, or autotransformer.   Figure 2 – Transformer protection with primary-side circuit breaker   "52S may be omitted in some applications requiring 151G to coordinate with and trip the secondary circuit devices if used." II. Parallel Transformer   The protection for transformer banks where the secondaries are connected together by a bus tie breaker is summarized in the following picture(a,b,c).   The arrangement shown is typical for large- or critical-load substations, especially for industrial plants. The loads are supplied from separate buses that are connected together by a bus tiebreaker (52T) that may be operated either normally closed (NC) or normally open (NO).   Figure 3a – Single line diagram of transformer and secondary bus protection for a typical double-source supply with secondary tie and breaker   If you operated NO, the protection of the first picture and second is applicable. If operated with 52T NC, the protection of the first picture and second is applicable with the secondary side modified. Figure 3b – Secondary protection with high-side fuses With the bus tiebreaker closed, there is a possibility for the interchange of power between the two sources. Here, current flows from one source through its transformer, the secondary buses, and back through the other transformer to the second source. Generally, this is neither desirable nor permitted.   "To prevent this operation, directional time–overcurrent relays (67, 67N) are applied to each transformer."   Figure 3c – Secondary protection with high-side breaker The single-line connections are shown in Figure 3b and Figure 3c, with complete three-line connections in the following figure.   Note: They operate only for fault current that flows into the transformer and trip the secondary breaker (52–1 or 52–2). This is also important in removing a secondary fault source for faults in the transformer bank. The phase relays (67) can be set on a low of the minimum tap.   Load current certainly flows through the relay, but normally not in the operating direction. The low tap continuous rating must not be exceeded by increasing the maximum load current. The 67-time setting must coordinate with the protection on the transformer primary. When used, the ground relay can be set on minimum setting and time, because coordination is not necessary.   Figure 4 – Three-line connections for reverse-phase and partial differential backup protection The inverse-time–overcurrent relays (51, 51N) provide bus protection and backup protection for the feeder circuits. These relays trip both 52–1 (or 52–2) and 52T. This is a partial differential connection and these units must be time-coordinated with the protection on the several feeders that are connected to the bus.   "Only two-phase relays are required, but the third relay (shown optionally in Figure 4) provides additional redundancy. When a ground differential is used, as illustrated in Figure 3c, 67N and 51N are omitted."   Ground-fault backup is provided by 51G, 151G, and 251G inverse-time overcurrent relays (Figure 3abc). Relay 251G provides bus ground-fault protection and backup for the feeder circuit ground relays. It must be time- coordinated with these. It trips the bus tie 52T, as the fault could be either on the bus or on the associated feeders.   If the fault continues to exist with the bus tie open, relay 151G trips breaker 52–1 (or 52–2). Thus, 151G must coordinate with 251G. If the fault persists, it is between the secondary breaker, in the transformer winding, or in the grounding impedance.   Relay 51G set to coordinate with 151G is the last resort. It trips the high-side or primary breaker to remove the transformer from the service.   III. Redundancy Requirements for Bulk Power Transformers   When transformers are connected to bulk power systems, redundancy requirements for related protection need to be addressed. To provide the required redundancy, two separate differential schemes may be applied.   "Redundancy for transformer faults may also be obtained by a differential scheme and sudden pressure."   In such an application, the sudden pressure protection needs to be supplied with additional protection for faults on the transformer bushings and leads, as sudden pressure devices will not respond to faults in these areas. Redundant schemes for disconnecting the transformer from the system when a high-side breaker is not applied can be obtained by using various combinations of the methods. Take an example, two separate transfer trip systems may be applied although they are expensive. A cheaper alternative is to combine a transfer trip scheme and a faulty switch. It may be possible to delay closing the fault switch for a few cycles to allow time for the transfer trip scheme, provided it is operational, to de-energize the failed transformer before the closing of the fault switch. This would spare the power system from being subject to a solid fault when the fault switch closes, whenever the transfer trip scheme works properly.   When a high-side breaker is applied and it fails to operate, breaker failure protection is required to enable isolation of a faulted transformer. The breaker failure scheme may require the application of a fault switch, transfer trip scheme, or a second interrupting device if other local breakers are not available to isolate the transformer.   FAQ     1. What is the use of transformer? Transformers are employed for widely varying purposes; e.g., to reduce the voltage of conventional power circuits to operate low-voltage devices, such as doorbells and toy electric trains, and to raise the voltage from electric generators so that electric power can be transmitted over long distances.   2. What are the 3 types of transformers? There are three primary types of voltage transformers (VT): electromagnetic, capacitor, and optical.   3. What is the basic principle of transformer? A transformer consists of two electrically isolated coils and operates on Faraday's principal of “mutual induction”, in which an EMF is induced in the transformers secondary coil by the magnetic flux generated by the voltages and currents flowing in the primary coil winding.   4. Does a transformer convert AC to DC? A transformer is built to transfer the energy from one circuit into another circuit by way of magnetic coupling. ... An alternating current creates a magnetic flux in the core on its way through the first winding, inducing the voltage in the others. It can convert high and low voltages, it cannot convert AC to DC.   5. What are the main parts of transformer? There are three basic parts of a transformer: a. an iron core which serves as a magnetic conductor, b. a primary winding or coil of wire and. c. a secondary winding or coil of wire.   6. What are the classification of transformer? Depending upon the type of construction used, the transformers are classified into two categories viz.: (i) Core type, and (ii) Shell type. Depending upon the type of service, in the field of power system, they are classified as: (i) Power transformers, and (ii) Distribution transformers.   7. Can a transformer work on DC? As mentioned before, transformers do not allow DC input to flow through. This is known as DC isolation. This is because a change in current cannot be generated by DC; meaning that there is no changing magnetic field to induce a voltage across the secondary component.   8. How do you convert a transformer? This conversion is made by winding two separate conductors around a common iron core. Applying an alternating voltage to the primary conductor produces current which sets up a magnetic field around itself. This is known as mutual inductance.   9. What are two components of no load current in transformer? The no-load current of a transformer consists of two components: The Magnetization Current iM is the current required to produce the flux in the transformer core. The Core-loss Current ih+e is the current required to make up for hysteresis and eddy current losses.   10. Which type of transformer core is most efficient? SHELL CORE. The most popular and efficient transformer core is the SHELL CORE, as illustrated in figure (4). As shown, each layer of the core consists of E- and I-shaped sections of metal. These sections are butted together to form the laminations.   11. What is the power factor of transformer? The power factor of a distribution transformer is between (0.75 to 0.80) when secondary is connected to u.p.f loads.   12. Why do we need Transformers? Transformers help improve safety and efficiency of power systems by raising and lowering voltage levels as and when needed. They are used in a wide range of residential and industrial applications, primarily and perhaps most importantly in the distribution and regulation of power across long distances.   13. What is the difference between a step up transformer and a step down transformer? A transformer that increases the voltage from primary to secondary (more secondary winding turns than primary winding turns) is called a step-up transformer. Conversely, a transformer designed to do just the opposite is called a step-down transformer.   14. Are transformers dangerous? There is no established evidence that the exposure to magnetic fields from powerlines, substations, transformers or other electrical sources, regardless of the proximity, causes any health effects.   15. Why transformer rating is in kVA not in kW? Copper losses (I²R) depends on current which passing through transformer winding while Iron losses or core losses or Insulation losses depends on Voltage. ... That's why the transformer rating may be expressed in VA or kVA, not in W or kW.    

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