The Kynix Blog

IntroductionWith the improvement of living standards, all kinds of electrical equipment have gradually entered thousands of households. In many electrical appliances, air conditioning is also essential. However, many consumers are ignorant of the working principles of air conditioners and the principles of cooling and heating. In fact, for the operation of the air conditioner, the key to its operation is the air conditioner capacitor. Without this part, the air conditioner cannot operate normally. So what exactly is an air conditioner capacitor? What are the structural characteristics of this part?CatalogⅠ What is Air Conditioner CapacitorⅡ Types of Air Conditioner Capacitor  2.1 Electrolytic Capacitor    2.2 Safety Capacitor   2.3 Ceramic Capacitor   2.4 Capacitors for Starting and Running Air ConditionerⅢ Structure Characteristic of Air Conditioner CapacitorⅣ Working Principle of Air Conditioner CapacitorⅤ Main Reasons for the Failure of Air Conditioner Capacitor  5.1 Heat Exposure    5.2 Voltage Capacity    5.3 Shorter LifespanⅥ The Detection of Air Conditioner CapacitorⅦ Methods to Repair And Replace Air Conditioner CapacitorⅧ Frequently Asked Questions about Air Conditioner CapacitorⅠ What is Air Conditioner CapacitorThe so-called air conditioner capacitors are also called aluminum electrolytic capacitors. It is a capacitor made of an aluminum cylinder as the negative electrode, which is filled with liquid electrolyte, and inserted into a curved aluminum strip as the positive electrode. The core of the air conditioner capacitor is made by overlapping and winding anode aluminum foil, liner paper impregnated with electrolyte, cathode aluminum foil, and natural oxide film. After the core is immersed in the electrolyte, it is sealed with an aluminum shell and a plastic cover to form an air conditioner capacitor. Generally, there is a plastic sleeve outside the aluminum shell of the air conditioner capacitor.So-called air conditioner capacitiorsAlso, it's a little cylindrical container within your air conditioner that stores and distributes energy. When you turn on your air conditioner, it demands more power than your home's electrical system can provide—this is where the capacitor comes in. Moreover, the AC capacitor is a component within the outdoor condensing unit of an air conditioner or heat pump. It delivers power to the motor driving the air conditioning system. The capacitor delivers initial energy burst to turn the system on when it's time for a cooling cycle.) Ⅱ Types of Air Conditioner Capacitor2.1 Electrolytic Capacitor This capacitor for air conditioner has polarity and leads labeled with + or - marks. It is typically used to smoothen the DC voltage after it has been rectified by diodes. They aided in reducing the ripples in the DC supply. The smaller the ripple, the larger the capacitance of the capacitor employed. This use can be seen in a simple linear power supply with a step-down transformer.2.2 Safety CapacitorSafety capacitors are commonly used in the inverter control circuit of an air conditioner. They can be classified into X or Y types and used in the circuit's live parts always be careful when dealing with these capacitors as some charge on them may cause shock even when the power supply has been cut off.Safety Capacitor PictureGood design should have bleeding resistors to remove the charge from the device after the air conditioner has been switched off. Ensure proper certification marks such as VDE, UL and CE markings are present on the bodies of the capacitors before using them. Together with inductor coils, these capacitors are used to reduce the harmonics generated from the rapid switching of the AC power supply by the insulated gate bipolar transistors (IGBT).2.3 Ceramic Capacitor Ceramic capacitors are used as bypass capacitors to bypass the high-frequency content of a circuit. They could be placed parallel to the DC power intake of integrated circuits to bypass certain high frequencies noise in the circuit that may have an adverse effect on the sensitive circuitry. As the more transformerless power supply is becoming common today due to its better efficiency and smaller space, you will see many surface mount capacitors being used in multilayer printed circuit boards. These capacitors and inductor coils are used to reduce the harmonics, which are generated from the rapid switching of the AC power supply by the insulated gate bipolar transistors (IGBT).2.4 Capacitors for Starting and Running Air ConditionerThese capacitors are commonly used in single-phase electric motors. START capacitor is used to alter the phase difference between a capacitor-start motor's START and RUN windings. This difference resulted in the generation of a starting torque capable of starting the motor with a full load connected to it. Start and Running CapacitorThe RUN cap. is used to further adjust the phase difference between the two windings, resulting in even more beginning torque. The connections in the motor are identified by marks on the single-phase compressor. The designations are R (connected to the RUN winding), S (connected to the START winding), and C (connected to the CUT winding) (common of the two windings).Ⅲ Structure Characteristic of Air Conditioner Capacitor1) The working medium of the air conditioner capacitor is to form a very thin layer of aluminum oxide (Al2O3) on the surface of the aluminum foil through anodization. This oxide dielectric layer and the anode of the capacitor are combined into a complete system, and the two are interdependent. The electrodes and dielectrics of what we usually call capacitors are independent of each other. 2) The anode aluminum foil and cathode aluminum foil of air conditioner capacitors are usually corroded aluminum foil, and the actual surface area is much larger than its apparent surface area. It is one reason why air conditioner capacitors usually have large capacitance. Due to the use of aluminum foil with many fine etched holes, the liquid electrolyte is usually needed to more effectively use its actual electrode area.The Structure of  Airconditioner Capacitors  3) The negative foil acts as an electrical lead in the air conditioner capacitor. Because the electrolyte as the cathode of the air conditioner capacitor cannot be directly connected to the external circuit, an electrical path must be formed through another metal electrode and other parts of the circuit. 4) Since the dielectric oxide film of the air conditioner capacitor is obtained by anodic oxidation, and its thickness is proportional to the voltage applied by the anodic oxidation, in principle, the thickness of the dielectric layer of the air conditioner capacitor can be artificially and accurately controlled. It is precisely because of the structure characteristics and functions of the air conditioner capacitor that the air conditioner can operate normally. It should be noted that the capacitor should be checked for short circuit, open circuit and leakage before it is installed in the circuit, and its capacitance value should be checked. When installing, make it easy to see the capacitor type, capacity, withstand voltage and other symbols for verification. The above points are related introductions to the structure characteristics of air conditioner capacitors. In fact, for air conditioner capacitors, it is not just used in air-conditioning. But there are many applications, such as air conditioning inverters, color TVs, displays, LED lights, energy-saving lamps and so on. Relatively speaking, the scope of application of air conditioner capacitors is usually in the field of household appliances.Ⅳ Working Principle of Air Conditioner CapacitorThe capacitor is a key component to start the air conditioner motor. Most air conditioners on the market now use capacitors to start the air conditioner and take into account the operation. The damage of the capacitor will cause the compressor start current to rise too quickly, automatically turn on the protection mode to stop or fail to start the compressor, which will cause the air conditioner to fail to operate normally or automatically power off during the startup process. When the air conditioner is powered on, the capacitor acts as conduction to help the compressor start normally. The capacitor gathers and stores energy while your air conditioner is running; in other words, it functions similarly to a rechargeable battery. That way, when your air conditioner requires a large burst of energy, the capacitor can supply it and keep everything working smoothly. The compressor (or compressors, depending on your air conditioner) powers the air conditioner's compressor, blower motor, and fan motor, which all rely on the compressor to stay operating and cold air flowing through your home.Ⅴ Main Reasons for the Failure of Air Conditioner CapacitorA capacitor experiences significant strain over its lifetime and using an air conditioner more frequently than typical increases this strain. Most capacitors are designed to last approximately twenty years under ideal conditions, although ideal conditions are not usually met. There are three major causes of failure for most capacitors:This vedio shows that how to tell a AC Capacitor is bad !5.1 Heat ExposureHeat exposure is a term used to describe the condition of being exposed to heat.While air conditioners are designed to keep you cool in hot weather, the hotter the environment, the more likely your capacitor will fail. Overheating the machine might cause harm and limit its lifespan. Keeping your air conditioner covered and well ventilated is an important aspect of reducing the risks of high temperatures in Houston.5.2 Voltage CapacityThere are several air conditioner capacitors for various AC models, each with its voltage rating. The higher the voltage of a capacitor, the more expensive the part, so it may be tempting to replace it with a lower level capacitor. This, however, places a significantly greater demand on the capacitor, reducing its lifespan.5.3 Shorter Lifespan Again, most capacitors have a lifespan of roughly twenty years, but that also means they are only useful in certain situations. Older capacitors will be less capable, and higher-than-average AC consumption, as well as having a capacitor with malfunctioning parts, will limit its lifespan. One of the most serious issues with an AC capacitor failure is that it might cause harm to other components that it powers. Fans can wear out, and electric connections can be damaged—if you spot a problem with the capacitor, replace it as soon as possible to avoid extra maintenance needs and expenditures. Ⅵ The Detection of Air Conditioner CapacitorMethod 1: Use 220V alternating current to connect directly, you can connect one pole first, and touch the other capacitor pin with another power cord. If there is an obvious small spark when touched, you can be sure that the capacitor is charged, which means that the capacitor is not broken. Method 2: Pointer multimeter, you can also use the digital meter to measure capacitance. If you use a pointer multimeter, generally use the R × 1K gear, and connect the test leads to the two poles of the capacitor respectively. At this time, the pointer of the multimeter will swing and then slowly return to or near the zero position. Such a capacitor is good. The larger the capacity of the capacitor, the longer the charging time, and the slower the pointer swings in the 00 direction. If it is connected, the resistance value displayed by the pointer does not move, it is bad.The methods of dectecting a airconditioner capacitorMethod 3: Check with a digital multimeter. Set the digital multimeter to an appropriate resistance range. The red and black test leads respectively touch the two poles of the capacitor under test. At this time, the display value will gradually increase from 0 until the overflow symbol "1" is displayed. If 0 is always displayed, it means that the capacitor is short-circuited. If it always shows overflow, it may be an open circuit between the capacitors, or the selected resistance file is not suitable. The principle of selecting the resistance gear is: when the capacitor is large, the low resistance gear should be used; when the capacitor has a small capacity, the high resistance gear should be selected. Ⅶ Methods to Repair And Replace Air Conditioner CapacitorWhen you've established that your capacitor needs to be replaced, you have a few options. Because it is similar to a battery, the method is as simple as swapping it out for a new one. However, it is a bit more involved than simply removing the old capacitor and replacing it, so don't try it yourself if you aren't comfortable handling the parts.There are various tips on how to replace a capacitor on your own, however here are some fundamentals to remember:  Find the right replacement capacitor. The capacitor should have a voltage and capacitance level on it, and you need to match that in your replacement. Writing down that and the make and model of your air conditioner can help the type of capacitor you need. Power down your air conditioner before starting any fixes. It may sound like common sense, but it’s still vital. Working with high-electricity machinery can be dangerous without proper safety. Discharge the capacitor. Even with your air conditioner turned off, the capacitor still has a significant amount of energy stored inside (that’s it is a job, after all). You need to discharge that energy so as not to cause damage to yourself during handling or after disposal. Make sure to wear proper safety equipment as well.Take notes. Either draw a diagram of how your capacitor is connected or take several pictures to aid in the reconnection process.Be aware of capacitor differences.·B If you’ve selected the same type of capacitor as your old one, this won’t be as much of an issue. However, some capacitors have different labels for the connections you need, so be aware of where these need to reattach so that you don’t have additional troubles.Ⅷ Frequently Asked Questions about Air Conditioner Capacitor1. What does a capacitor do for an air conditioner?The main job of capacitors is to store electrons to provide start-up energy for your air conditioner, they build up a charge when electricity runs through them by swapping electrons between the two conductive plates inside. 2. How much does it cost to replace a capacitor on an air conditioner?The average HVAC capacitor cost is around $170. Prices generally range between $120 and $250, including professional installation. Branded units are more expensive, costing upwards of $400 or more. The price you pay depends on the brand, model, voltage and the labor required for installation. 3. How long does an AC capacitor last?The life expectancy of the air conditioner capacitor lies between 10-20 years. However, various factors, such as heat exposure, may tamper with their lifespan. If your capacitor is tiny or was built with the wrong parts, it may not live long. 4. Why is AC running but not cooling?Condenser Unit is BlockedIf your air conditioner is running, but not lowering temperatures inside, one issue could be a blocked or clogged condenser coil. When operating correctly, the condenser fan draws air into the outdoor unit through the condenser coil to pull heat energy out of your home. 5. Can I replace the AC capacitor myself?Yes, you can. It could be a capacitor, or it could be a compressor. Since capacitors are cheap, it may be worth a try to see for yourself if that's it, if not you will need a technician. There is really no “DIY” fix when it comes to repairing or replacing a capacitor. 6. How do I know what capacitor to get for my AC?Multiply the full load amps by 2,650. Divide this number by the supply voltage. The full load amps and the supply voltage can be found in the owner's manual. The resulting number is the MicroFarad of the capacitor you need. 7. Do air conditioner capacitors get weak?Power surges can cause a capacitor to fail, too.Obviously, a lightning strike from a summer thunderstorm can overload and burn out your HVAC's electrical system., Also weaker power surges can cause damage to capacitors over time. Those weaker surges can be caused by fluctuations in the electrical grid. 8. Should I turn off AC if it's not cooling?If your ac is still not cooling, there is one more thing you need to do. This is very important. TURN IT OFF and call your HVAC service provider to assist you. We always tell our customers to turn off an ac that is not cooling properly. 9. What does a bad capacitor look like?Well, bad caps typically have a domed or swollen top. Sometimes really bad caps can leak their electrolyte out of themselves too. Then you may see this brown crust around the capacitor, or perhaps on it. It often looks somewhat like a dried coffee stain.

IntroductionNowadays, more and more mobile phones support NFC function. Of course, many people don’t know what NFC really is. Near-Field Communication (NFC) is a short-range wireless technology. NFC has functions of mobile payment, data transmission, information browsing and access control. It provides a simple, touch-sensitive solution to exchange information, access content and services simply and intuitively. At the same time, NFC has the characteristics of low cost, easy to use and more intuitive, which makes it more potential in certain fields.What is NFC? How NFC Works? Applications of NFCCatalogIntroductionⅠ What is NFC On Phone?Ⅱ NFC Application ModeⅢ NFC Operational ModeⅣ NFC Uses On PhoneⅤ Which Phones Have NFC?Ⅰ What is NFC On Phone?In theory, NFC is a set of protocols for communication between two electronic devices about four inches at the most. So you device have to be very close to another NFC enabled device to transfer the data or do payment, in other words, long distance or non NFC devices will not be able to operate normally. NFC evolved from the integration of radio-frequency identification (RFID) and interconnection technology. It combines inductive card readers, inductive cards and point-to-point functions on a chip, which can identify and exchange data with compatible devices within a short distance exchange. NFC was originally a simple merger of RFID technology and network technology in the pass, and now has evolved into a short-range wireless communication technology. With the popularity of smart phones, it develops rapidly.Like RFID, NFC information is also transmitted through electromagnetic induction coupling in the wireless frequency part of the spectrum, but there is still a big difference between the two. First of all, NFC is a wireless connection technology that provides easy, safe, and rapid communication experience. Its transmission range is smaller than that of RFID, because RFID can support several meters or even tens of meters. What’s more, due to the unique signal attenuation technology adopted by NFC, NFC has the characteristics of short distance, high bandwidth, and low energy consumption.With NFC mobile phones, people can get the services and transactions at any place in any time. In short, through NFC-supported devices, people can complete payment or transfer data.Ⅱ NFC Application ModeNFC devices can be used as contactless smart cards, write/read terminals, and device-to-device data transmission paths. It has a wide range of applications, which can be divided into three basic types:Close→Finish. For applications such as access control or traffic/event ticket checking, users only need to bring the device storing the ticket or access code close to the reader. It can also be used for simple data capture applications, such as reading URLs from smart tags on posters.Close→Confirm. In applications such as mobile payment, the user must enter a password to confirm the transaction, or only accept the transaction.Close→Connect. By linking two NFC-enabled devices, you can perform point-to-point network data transmission, such as downloading music, exchanging images, or synchronizing address books.NFC devices may provide more than one function. Consumers can explore and understand the functions of the device and find out the potential functions and services of the NFC device. Ⅲ NFC Operational ModeNFC uses two-way recognition and connection. Its working modes include card emulation, P2P mode and reader/writer mode. Both NFC and Bluetooth are short-range communication technologies, and are integrated into mobile phones. NFC does not require complicated setup procedures, and it can also simplify Bluetooth connections. The advantage of NFC is that its setup procedure is shorter, but it cannot reach the low power compared with Bluetooth. The maximum data transfer capacity of NFC is 424 kbit/s, which is much smaller than Bluetooth V2.1 (2.1 Mbit/s). Although NFC is inferior to Bluetooth in transmission speed and distance, it does not require a power source. For mobile phones or portable electronic products, NFC is more convenient to use.NFC is superior to infrared(IR) transmission and Bluetooth. As a consumer-oriented transaction mechanism, NFC is faster, more reliable and much simpler than IR, which requires strict alignment to transmit data. Compared with Bluetooth, NFC is not suitable for long-distance data communication and. So NFC and Bluetooth complement each other and coexist. In fact, NFC protocol can be used to improve the Bluetooth pairing process between two devices.Ⅳ NFC Uses On PhoneAs a bus and subway card. we all know that most of our bills can be paid by mobile phones, but we often face a problem, that is, forgetting to bring the card or change. Now we have an NFC-enabled mobile phone to reduce embarrassing situations. Turn on the local subway and bus functions on the mobile phone, so that we can use the mobile phone to pay. To put it simply, the NFC function can turn your mobile phone into a bus card, you can also recharge the bus card online, and you can read the card data to check the balance, etc. At present, the most widely used field of NFC is also in bus/subway card.As a door-access card. It’s really troublesome to forget to bring the access card, but now we don’t have to worry, because the NFC function of the mobile phone can also be used directly as the access card to enter the door. We only need to click the virtual key in the mobile phone, and then place access card on the back of the mobile phone for data reading. After reading the relevant information, we can directly use the mobile phone’s NFC to act as the access card.Read the bank card information directly. For example, we usually need to check the consumption records of our bank card. We need to download the bank’s official software to be able to check or go to the bank. If the mobile phone has the NFC function, we can get the bank card information according to the relevant operation, like the bank card’s consumption records and balances, which is very convenient for us.Bluetooth speakers connected to NFC, there are many Bluetooth speakers on the market that are also equipped with NFC function. When we connect, we only need to use a mobile phone that supports NFC function to turn on the Bluetooth speaker, which is more than we need to set up Bluetooth before. Pairing connection is much more convenient.File transfer, although we can use the network to transfer files now, the speed is very fast, but if the mobile phone does not have a network, the NFC function is more important, only need to use the NFC function of the two mobile phones Open and paste together, we can transfer music, pictures or files, which is still very useful. Of course, now the same brand of mobile phones also have their own fast data transmission function, and no network is required.The above are some practical small functions that NFC can bring in mobile phones, which is still very practical for our lives. Of course, there are more other similar functions, we can stack them according to the actual situation.Ⅴ Which Phones Have NFC?The following smartphone models are all from the official website data, but there will be gaps in different regions, and all local models shall prevail.HuaweiSamsungMate X2, Mate XS, Mate X, Mate 40 RS, Mate 40 Pro+, Mate 40 Pro, Mate 40, Mate 40E, Mate 30, Mate 30 RS, Mate 30 Pro, Mate 30 Pro 5G, Mate 30 5G, Mate 20, Mate 20 RS, Mate 20 X 5G, Mate 20 X, Mate 20 Pro, Mate 10, Mate 10 Pro, Mate 9, Mate 9 Pro, Mate 8, Mate 7, Mate SW21, W20Z Fold2, Z FlipJ7 Pro, J7+, J7(2016), J5, J4, J3C9 Pro, C7 Pro, C7, C5 Pro, C5GRAND Prime, MEGA2, ALPHA G8508S, CORE Lite 4G, CORE AdvanceP40 Pro+, P40 Pro, P40, P30 Pro, P30, P20 Pro, P20, P10 Plus, P10Note20 Ultra, Note20, Note10+ 5G, Note10+, Note10, Note10 Lite, Note9, Note8, Note7, Note5, Note4, Note3nova 8 Pro, nova 8, nova 7 Pro, nova 7, nova 6, nova 5 Pro, nova 2sA90, A80, A71 5G, A71, A70, A60, A51, A50s, A31, A21s, A20, A9 Star Lite, A9, A8S, A8+, A8S21 Ultra, S21+, S21, S20 Ultra, S20+, S20, S10 5G, S10+, S9+, S9, S8+, S8 OnePlusMicrosoft LumiaOnePlus 8 Pro, OnePlus 7 Pro, OnePlus 7, OnePlus 6, OnePlus 5, OnePlus 3, OnePlus 1,OnePlus 8T, OnePlus 7T Pro, OnePlus 7T, OnePlus 6T, OnePlus 5T, OnePlus 3TLumia 950 XL, Lumia 950, Lumia 930, Lumia 925, Lumia 920, Lumia 650, Lumia 640 XL, Lumia 640 Apple IphoneSony Xperiaiphone 12 Pro, iphone 12, iphone 12 mini, iphone 11 Pro Max, iphone 11 Pro, iphone 11iphone XS Max, iphone XS, iphone XR, iphone Xiphone 8 Plus, iphone 8, iphone 7 Plus, iphone 7, iphone 6s Plus, iphone 6s, iphone 6 Plus, iphone 6iphone SE 2, iphone SEXperia 1, Xperia XZs, Xperia XZ2 Compact, Xperia XZ2 Premium, Xperia XZ2, Xperia XZ Premium, Xperia XZXperia XA2 Ultra, Xperia XA1 Ultra, Xperia XA1 Plus, Xperia XA1, Xperia X CompactLT29i, LT26i, MT27i, Xperia L1, Xperia E5 HTCLGHTC U UltraHTC Desire 21 Pro, HTC Desire 20+, HTC Desire 20 Pro, HTC Desire 19S, HTC Desire 19+, HTC Desire 12S, HTC Desire 626HTC U20 5G, HTC U12 Life, HTC U12+, HTC U11+, HTC U11, HTC U11 EYEsHTC 10 lifestyle, HTC 10New HTC One, HTC One E9+, HTC One M9, HTC One M8LG G7fitLG G7+ ThinQ, LG G7 ThinQ, LG G5, LG G4, LG G3, LG G2LG Q Stylus+, Q6+, Q6LG V40 ThinQ, LG V35 ThinQ, LG V30+, LG V30, LG V20, LG V10LG Stylus 3, LG Stylus 2+LG AKA RealmeZTERealme GT, Realme X50m, Realme X50 Pro, Realme X50, Realme X2 Pro, Realme X2ZTE Axon 7s, Axon 20 5G, Axon 11 5G, Axon 10 Pro 5G, Axon 10 Pro, ZTE T900, ZTE A602NubiaBlackBerryZ17 S, Z17, Z11, Z9 Max, Z9, Z7 Max, Z17 mini, Z5 mini, Z5S(LET)keyone, 9900, 9810(4G) Frequently Asked Questions about NFC Technology1. What is NFC technology?Near-Field Communication (NFC) is a set of communication protocols for communication between two electronic devices over a distance of 4 cm (11⁄2 in) or less. NFC offers a low-speed connection with simple setup that can be used to bootstrap more-capable wireless connections. It is a contact-less communication technology based on a radio frequency (RF) field. 2. How does near field communication NFC work?Near-field communication transmits data through electromagnetic radio fields to enable two devices to communicate with each other. To work, both devices must contain NFC chips, as transactions take place within a very short distance. 3. Do all mobile phones have NFC?All the latest Android smartphones can scan NFC without an app but there are a few older models that do not support NFC. 4. Is RFID same as NFC?The short answer: RFID stands for Radio Frequency Identification, a one-way communication method at varying distances. NFC, or Near Field Communication, is a version that allows for two-way communication. NFC is not totally contactless, typically requiring devices to be within a few inches of each other. 5. What is NFC vs Bluetooth?NFC is great for transferring small amounts of data over a very short distance and is used mostly for wireless payments and access cards. Bluetooth allows for a more extended range of connectivity and devices such as cellphones, speakers, and headphones commonly use it.

IntroductionLC circuit, also called passive filtering circuit, is commonly used for harmonic compensation, which does not require additional power supply. It is generally composed of capacitors, inductors and resistors. This kind of filtering circuit is easy to design, but its pass-band magnification and cut-off frequency vary with the load, which is not suitable for occasions with high signal processing requirements. Passive filtering circuits are usually used in power circuits, like DC power rectification, or large current loads.LC (Inductor-Capacitor) CircuitsCatalogIntroductionⅠ LC Circuit TypesⅡ LC Circuit CharacteristicsⅢ LC Circuit Working FeaturesⅣ LC Circuit FunctionsⅤ LC Circuit CalculationⅠ LC Circuit TypesCommonly used filter circuits include passive filter and active filter. If the circuit are only composed of passive components (resistors, capacitors, inductors), it is called a passive filter circuit. The main forms of passive filtering are capacitive filtering, inductive filtering and compound filtering (including inverted L-type, LC-type , LC-π type and RC-π type, etc.). The filter circuit is not only composed of passive components, but also composed of active components (bipolar tubes, unipolar tubes, integrated operational amplifiers), which is called an active filter circuit, and its main form is active RC(resistor-capacitor) circuit.The LC circuit has advantages of simple structure, high reliability, and wide range of applications. Its main feature is that the resistance of the inductor is small, and the DC loss is small. What’s more, the inductance in LC circuit to alternating current is large, so that the filtering effect is good.LC circuits are divided into LC low-pass filters, LC band-pass filters, high-pass filters, LC all-pass filters, and LC band-stop filters according to their functions. According to tuning, they are further divided into single-tuned filters, double-tuned filters and three-tuned filters and so on. The LC filter design process mainly considers its resonant frequency, capacitor withstand voltage, and inductor withstand current. In addition, it is necessary to pay attention to that passive LC circuits are not easy to integrate.  Ⅱ LC Circuit CharacteristicsThe LC circuit is generally formed by a proper combination of inductors, capacitors and resistors, and parallel with the harmonic source. It not only for filtering, but also takes into account the role of compensation.Figure 1. LC Circuit TypesThe following are the characteristics of several LC circuits:1) The load impedance of the L-type filter is high, and the source impedance is low.2) The load impedance of the inverted L filter is low, and the source impedance is high.3) The load impedance of the T-type filter is low, and the source impedance is low.4) The load impedance of the Π filter is high, and the source impedance is high.In actual use, these features are generally followed. In practice, impedance is difficult to estimate, especially in high frequency bands. Due to parasitic parameters, the circuit impedance changes greatly, and the circuit impedance is also related to the working state of the circuit, so the debugging shall prevail in practice. Ⅲ LC Circuit Working FeaturesAccording to the different impedance of reactive components to AC and DC, the basic form of the LC circuit composed of capacitor C and inductance L is shown in the figure. Because the capacitor C is open to DC and has a small impedance to AC, C is connected in parallel at both ends of the load, while the inductor L has a small impedance to DC and a large impedance to AC, so L should be connected in series with the load.In electronic circuits, the inductor coil acts on the finite current of the alternating current. From the inductance formula XL=2πfL, it can be known that the larger the inductance L, the higher the frequency f, and the larger the inductive reactance. We already know that capacitors have the ability to "block DC and pass AC", while inductors have the function of "pass DC, block AC, pass low frequencies, and block high frequencies". If the direct current accompanied by many interference signals is passed through the LC filter circuit, most of the AC interference signals will be prevented by the inductance from being absorbed and turned into magnetic induction and thermal energy, and most of the rest will be bypassed to the ground by the capacitor, which can suppress the interference. So a relatively pure DC current at the output is getting.The inductance of the power supply on PCB is generally made of a very thick enameled wire wrapped around a round magnetic core coated with various colors. In addition, there are usually several tall filter aluminum electrolytic capacitors nearby, which is a classic LC filter circuit. In addition, PCB also uses a large number of snake-type lines and chip tantalum capacitors to form an LC circuit. Few people notice, when design LC circuit, the snake line folds back and forth on the circuit board, which can also be regarded as a small inductance.In short, the principle of the LC filter circuit is actually a combination of the basic characteristics of the L and C components. Because the capacitive reactance of the capacitor xc=2nfc will decrease as the signal frequency increases, and the inductance of the inductor xl=2f will increase as the signal frequency increases. If the capacitors and inductors are connected in series, parallel or mixed together, the impedance of their combination will also vary greatly depending on the frequency of the signal. This shows that different filter circuits will present a small or large reactance to a certain frequency signal, so that it can pass or block the frequency signal. Thereby filter circuit plays a role in selecting a certain frequency signal and filtering out a certain frequency signal.Figure 2. LC Resonating CircuitsⅣ LC Circuit Functions1) LC circuit can be used as a filter circuit used in some power supplies. If the DC power with many interference signals is passed through the LC filter circuit, most of the AC interference signals will be blocked by the inductance and become magnetic induction and thermal energy. Most of them are bypassed to ground by capacitors, which can suppress the effect of interference signals and obtain relatively pure DC current output.2) Have oscillation effect, or sometimes generate a clock signal for the single-chip microcomputer (some have an external clock signal). 3) It can also be used as a frequency selection circuit, or a transmitting oscillation circuit (but it must be a circuit that can send and receive signals), and it also serves for the generation of input signals from other circuits.4) Since the output voltage of the rectifier circuit is not all pure DC, the output of the rectifier circuit observed from an oscilloscope is very different from the DC, and the waveform contains a large pulsating component, which is called ripple. In order to obtain the ideal DC voltage, it is necessary to use an LC circuit composed of reactive components (such as capacitors and inductors) with energy storage function to filter out the pulsating elements of output voltage.Ⅴ LC Circuit Calculation1) The voltage of the RC tank capacitor is:Voltage=U*exp(-t/rc)U represents the initial value of the voltage, rc represents the resistance and capacitance, t is the elapsed time, and exp (-t/rc) represents the -t/rc power of e.Time constant τ=rcNamely the product of capacitance and resistance, voltage = U*exp(-t/τ) after introducing the time constantTherefore, the voltage change with zero input response is an exponential decay process, theoretically infinite time, but generally it is considered that the decay is over after 3 to 5 time constants.Therefore, the discharge time depends on the time constant τ=rc2) For the LC oscillating circuit, it is related to the product of the LC circuit.Specifically, for the general LRC loop,R>2*sqr (L/R)R=2*sqr(L/R)R>2*sqr (L/R)sqr (X) represents the root sign (X)Divided into three situations, roughly speaking, the discharge time depends on the value of R, L, C in the circuit, U is not equal to 0 and I = 0, the capacitor discharges through L, RTwo eigenvalues can be obtained by solving second-order partial differential equations such as:p1=-(R/2L)+spr[(R/2L)*(R/2L)-1/LC]p1=-(R/2L)-spr[(R/2L)*(R/2L)-1/LC]Capacitor voltage=[U/(p2-p1)]*[p2exp(p1*t)-p1exp(p2*t)]Based on this, the relationship between capacitor discharge time and LRC can be analyzed. Frequently Asked Questions about LC Circuit1. What is meant by LC circuit?An LC circuit is a circuit that uses the elements inductor (L) and capacitor ( C). This circuit is also referred as resonating circuit, tank circuit, or tuned circuit. 2. What does an LC circuit do?LC circuits are used either for generating signals at a particular frequency, or picking out a signal at a particular frequency from a more complex signal; this function is called a bandpass filter. 3. Where are LC circuits used?The LC circuit is used to select or generate a specific frequency signal. The application of LC circuits is reflected in many electronic devices, especially radio devices, such as transmitters, radio receivers and television receivers, amplifiers, oscillators, filters, tuners and frequency mixers. 4. What are the properties of LC circuit?An LC circuit is a closed loop with just two elements: a capacitor and an inductor. It has a resonance property like mechanical systems such as a pendulum or a mass on a spring: there is a special frequency that it likes to oscillate at, and therefore responds strongly to. 5. What is LC in LC oscillation?LC oscillations- The electric current and the charge on the capacitor in the circuit undergo electrical LC oscillations when a charged capacitor is connected to an inductor. The electrical energy stored in the capacitor is its initial charge which is named as q_m.

IntroductionInductor is a passive component that used extensively with capacitors and resistors to create filters for analog circuits and in signal processing. Also it is an energy storage device in many switched-mode power supplies. As a major value of inductor, inductance is the ratio of wire current and the magnetic flux which is created by the flow of electrical current in the magnetic field. When a DC current passes through the inductor, there are only fixed magnetic lines around it, which do not change with time. However, when an alternating current is passed through the coil, the magnetic lines around inductor that will change with time.Inductors and Inductance DefinitionCatalogIntroductionⅠ Inductor Working PrincipleⅡ What Does Inductor Do?Ⅲ Inductor Main ParametersⅣ Inductor ClassificationⅤ Chip Inductor5.1 Purpose of a Chip Inductor5.2 Chip Inductor Classification5.3 Three Methods for Reading Chip InductorsⅠ Inductor Working PrincipleWhen ac current is applied to an inductor coil, its own current changes, making its own magnetic flux to change, and then causing induced electromotive force. This phenomenon is called self-inductance. The direction of self-induced current always be affected. When the alternating current increases, the direction of self-inductance current is opposite to that of AC current. When the AC current is weaken, the direction of self-inductance current is the same as that of alternating current, which has blocking effect.1) Self-inductionWhen current flows through the coil, a magnetic field is generated around the coil. When the current in the coil changes, the surrounding magnetic field also changes accordingly. This changing magnetic field can cause the coil itself to generate induced electromotive force (EMF is used to represent the terminal voltage of the ideal power supply for active components).2) Mutual InductanceWhen two inductor coils are close to each other, the change of the magnetic field of one coil will affect the other one, and this effect is mutual inductance. The magnitude of the it depends on the degree of coupling between the self-inductance and the two coils. The components made by this principle are called mutual inductors.Ⅱ What Does Inductor Do?The inductor mainly plays the role of filtering, oscillating, delaying, tuning and frequency selection in the circuit, as well as filtering signal, filtering noise, stabilizing current and suppressing electromagnetic wave interference. The most common role of inductance in a circuit is to form an LC filter circuit together with a capacitor. Capacitors have the characteristic of "block DC and pass AC", while inductors have the function of "pass DC and block AC". It can be made into low-frequency and high-frequency choke coils by making use of its properties. Common filter inductors are for this purpose.➡️Pass DC: It means that in a direct current circuit, the inductor acts as a wire and has no effect.➡️Block AC: In an AC circuit, the inductor will have impedance, that is, XL. The current in the entire circuit will become smaller, which has a certain blocking effect on AC. The self-induced electromotive force is always opposed to the current change in the coil. Mainly can be divided into high-frequency choke coil and low-frequency choke coil.➡️Inductor has the function of generating self-induced EMF, which is also called energy storage function. Like a capacitor, it is also an important energy storage component, which is widely used in switching power supplies. In addition, the phase relationship between the voltage across the inductor and the current: the voltage leads the current by 90 degrees, which is just the opposite of the capacitor. Using this characteristic, inductors and capacitors form LC series and parallel circuits, which can be used for frequency selection. In reality, they have been widely used in circuits, especially in radio circuits.If the direct current accompanied by many interference signals is passed through the LC filter circuit, then the AC interference signal will be consumed by the inductance into heat. When the pure DC current passes through the inductor, the AC interference signal in it will also become magnetic induction and heat energy, the higher frequency is most likely to be blocked by the inductor, which used to suppress the higher frequency interference signal.➡️Tuning and Frequency SelectionThe inductance coil and the capacitor are connected in parallel to form an LC tuning circuit. That is, the natural oscillation frequency f0 of the circuit is equal to the frequency f of the non-AC signal, and the inductance and capacitive reactance of the loop are also equal, so the electromagnetic energy oscillates between the inductor and the capacitor. This is the resonance phenomenon of the LC loop. During resonance, since the inductance and capacitive reactance of the circuit are equal and opposite, the inductance of the total current of the loop is the smallest and the current is the largest (referring to the AC signal of f=f0), so the LC resonance circuit has the function of selecting the frequency, therefore an AC signal of a certain frequency is selected.➡️ChokeIt is used to block low-frequency alternating current, and pulsating direct current flows to pure direct-current in circuits. Go further, it is commonly used in the middle of two filter capacitors at the output of a rectifier circuit. The choke and capacitor form a filter circuit. In the high-frequency circuit: to prevent the high-frequency current from flowing to the low-frequency end, which is commonly as the high-frequency choke of old regenerative radio.➡️FilterIt also prevents the rectified pulsating DC current from flowing to the pure DC circuit. The choke (to simplify the circuit and reduce the cost, replace the choke with a pure resistance) and two capacitors (electrolytic capacitors) form a filter circuit. The use of capacitor charging and discharging and AC choke coil to block the alternating current to smooth direct current and obtain the pure direct current.➡️OscillationWe often say that rectification is to transform AC into DC, so oscillation is the reverse process of it. We call the circuit that completes this process an "oscillator." Oscillator waveform: there are sine wave, sawtooth wave, trapezoidal wave, square wave, rectangular wave, spike wave. The frequency ranges from a few Hz to tens of GHz. It is widely used in the field of wired power and radio.Ⅲ Inductor Main ParametersThe main parameters of inductor include inductance, allowable deviation, quality factor, distributed capacitance and rated current.1) InductanceInductance is also called self-inductance, which is a physical quantity that represents the self-inductance of an inductor. The size of the inductance mainly depends on the number of turns  of the coil, the winding method, the core and its material, etc. Generally, the more coil turns and the denser the coils, the greater the inductance. A coil with a magnetic core has a larger inductance than a coil without a magnetic core. What’s more, a coil with a larger magnetic core has a larger inductance.The basic unit of inductance is Henry, represented by the letter "H". Commonly used units are millihenry (mH) and microhenry (μH). The relationship between them is:1H=1000mH1mH=1000μH2) Allowable DeviationThe allowable deviation refers to the allowable error value between the nominal inductance and the actual inductance.Generally, inductors used in circuits such as oscillation or filtering require high accuracy, with an allowable deviation of ±0.2%~±0.5%; while the accuracy requirements of coils used for coupling and high-frequency blocking are not high; the allowable deviation is ±10 %~15%.3) Quality FactorQuality factor, also called Q value, is the main parameter to measure the quality of an inductor. It refers to the ratio of the inductance presented by the inductor to its equivalent loss resistance when it works under a certain frequency of AC voltage. The higher the Q value of an inductor, the smaller its loss and the higher its efficiency.The Q factor is related to the DC resistance of the coil wire, the dielectric loss of the coil frame, and the loss caused by the core and shield.4) Distributed CapacitanceDistributed capacitance refers to the capacitance that exists between the turns of the coil, the coil and the magnetic core, the coil and the ground, and the coil and the metal. The smaller the distributed capacitance of the inductor, the better its stability. Distributed capacitance can make the equivalent energy dissipation resistance larger. To reduce it, silk-covered wire or multi-strand enameled wire is commonly used, and sometimes honeycomb winding method is also used.5) Rated Current The rated current refers to the maximum current value that the inductor can withstand under the allowable working environment. If the operating current exceeds the rated current, the inductor will change its performance parameters due to heat, and even burn out due to overcurrent.Ⅳ Inductor ClassificationAccording to the form of inductor: fixed inductance, variable inductance.According to the nature of the magnetic conductor: air core coil, ferrite coil, iron core coil, copper core coil.According to work nature: antenna coil, oscillating coil, choke coil, trap coil, deflection coil.According to winding structure: single-layer coil, multi-layer coil, honeycomb coil.According to working frequency: high frequency coil, low frequency coil.According to structural characteristics: magnetic core coil, variable inductance coil, color code inductor coil, non-magnetic core coil, etc. Ⅴ Chip Inductor5.1 Purpose of a Chip InductorChip inductors are electromagnetic induction components wound with insulated wires. It is a commonly used electronic component. The function of the chip inductor: it is simple to say that it can isolate and filter the AC signal or form a resonant circuit with capacitors, resistors, etc. The inductor coil and capacitor in parallel can form an LC tuning circuit. Any current flowing through the chip inductor will generate a magnetic field, and its magnetic flux will act on the circuit.When the current passing through the chip inductor changes, the DC voltage potential generated in the chip inductor will prevent the current from changing. When the current passing through the inductor coil increases, and the current passing through the inductor coil decreases, the self-induced electromotive force is in the same direction as the current, which prevent the current from decreasing and release the stored energy at the same time. The direction of flow is opposite to prevent the increase of current, and at the same time, part of the electric energy is converted into magnetic field and stored in the inductor. Therefore, with inductor filtering, not only the pulsation of load current and voltage is reduced, the waveform becomes smooth, and the rectifier diode is turned on.The role of shielded chip inductors is different from that of the general one. The general chip inductors are not shielded in the circuit to achieve the desired effect. The shielded current instability of this kind inductor in some circuits plays a good blocking role. A metal shield surrounds the positively charged conductor, and the inside of the shield will induce the same amount of negative charge as the charged conductor. A positive charge equal to that of a charged conductor appears on the outside. If the metal shield is grounded, the positive charge on the outside will flow into the ground, and there will be no electric field on the outside, that is, the electric field of the positive conductor is shielded.The shielding inductance also plays a role of coupling in the circuit. In order to reduce the coupling interference voltage of the alternating electric field to the sensitive circuit, the inductance can be set with a metal shield with good conductivity between the interference source and the sensitive circuit, in addition, the metal shield is grounded. The coupling interference voltage to the sensitive circuit depends on the product of the alternating electric field voltage, the coupling capacitance and the ground resistance of the metal shield. As long as the metal shield is well grounded, the coupling interference voltage can be reduced. The electric field shielding is mainly based on reflection, so the thickness of the shielding body does not need to be too large, and the structural strength is the main consideration.5.2 Chip Inductor Classification1) Winding TypeIt is characterized by a wide range of inductance (mH～H), high inductance accuracy, low loss (that is, large Q), large allowable current, strong manufacturing process inheritance, simplicity, and low cost, and the shortcoming is size. For example, the ceramic core winding type chip inductor can maintain a stable inductance and a fairly high Q value at such a high frequency, so it occupies a place in the high-frequency circuit.NL series inductors are wire-wound type, 0.01~100uH, accuracy 5%, high Q value, which can meet general needs. NLC type is suitable for power circuit, rated current up to 300mA.NLV type is high Q value, environmentally friendly (reconstituted plastic), and can be interchanged with NL.NLFC has a magnetic screen and is suitable for power cords.2) Layer TypeIt has good magnetic shielding, high sintering density and good mechanical strength. The disadvantages of it are low pass rate, high cost, small inductance, and low Q value.Compared with wire wound chip inductors, it has many advantages: Small size is helpful to the miniaturization of the circuit.Closed magnetic circuit will not interfere with surrounding components, and will not be interfered by neighboring components, which is beneficial to high-density installation.Integrated structure, high reliability; good heat resistance and solderability.Regular shape is suitable for automatic surface mounting production.MLK type inductor has the characteristics of small size, good solderability, magnetic screen, high-density design, monolithic structure, and high reliability.MLG type has a small inductance and uses high-frequency ceramics, which is suitable for high-frequency circuits.MLK type working frequency is 12GHz, with high Q and low inductance (1n~22nH).3) Film TypeIt has the characteristics of maintaining high Q, high precision, high stability and small size in the microwave frequency band. The internal electrodes are concentrated on the same layer, and the magnetic field distribution is concentrated, which can ensure that the device parameters after mounting do not change much, and show good frequency characteristics above 100MHz.4) Weaving TypeIts characteristic is that the inductance per unit volume at 1MHz is larger than other chip inductors, small in size, and easy to install on the substrate. It is usually used as a miniature magnetic component for power processing.In actual applications, the inductor should be selected according to the situation, circuit requirement, and the material cost.5.3 Three Methods for Reading Chip Inductors1) Digital Position Identification (generally rectangular chip resistors use this nominal method)This method is to use three digits on the resistor to indicate its resistance. Its first and second digits are significant digits, and the third digit represents the number of "0"s added after the significant digits, no letters will appear in this place.For example: "472'" means "4720Ω"; "151" means "1510Ω". If it is a decimal, use "R" to mean "decimal point". It occupies one significant digit, and the remaining two are significant digits.For example: "2R4" means "2.4Ω"; "R15" means "0.15Ω".2) Resistor Color Code (generally cylindrical fixed resistors use this nominal method)Chip resistors are the same as general resistors. Most of them use four rings (sometimes three rings) to indicate their resistance. The first ring and the second ring are significant numbers, and the third ring is the magnification. For example: "brown, green and black" means "15Ω"; "blue, gray, orange and silver" means "68kΩ", the error is ±10%.3) E96 Number Mixes with LetterThis method also uses three digits to indicate the resistance value, that is, "two digits plus one letter". Two digits represent the E96 series resistance. Its third digit is the magnification expressed by the letter code. For example: "51D" means "332×103; 332kΩ"; "249Y" means "249×10-2; 2.49". Frequently Asked Questions about Inductor Uses1. What is inductor and its function?An inductor is arguably the simplest of all electronic components. It's a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. Typically, an inductor will consist of an insulated wire that's wound into a coil, much like a resistor. 2. What is the basic principle of inductor?An inductor is a passive electronic component which is capable of storing electrical energy in the form of magnetic energy. Basically, it uses a conductor that is wound into a coil, and when electricity flows into the coil from the left to the right, this will generate a magnetic field in the clockwise direction. 3. What is the function of inductor in AC circuit?Inductors store their energy in the form of a magnetic field that is created when a voltage is applied across the terminals of an inductor. The growth of the current flowing through the inductor is not instant but is determined by the inductors own self-induced or back emf value. 4. Does an inductor block AC?We know that inductor has inductive reactance property by which it opposes the flow of current through it. The equation of inductive reactance is, ... For this reason, an inductor can totally block the very high-frequency AC. 5. Why AC is blocked by inductor?Since inductor behaves like a resistor, DC flows through an inductor. The AC flowing through L produces timevarying magnetic field which in turn induces self- induced emf (back emf). ... For an ideal inductor of zero ohmic resistance, the back emf is equal and opposite to the applied emf.

IntroductionIn the lighting industry, people often have a misunderstanding about dimming LED lights. And the reality is that the application of LED light source dimming technology in engineering is often unsatisfactory. Why is this the case? Is the LED light source dimming technology immature, or the technology is difficult to master? So this article analyzes the LED dimmer to help readers to fully understand and master it.Dimming all kinds of LEDs?CatalogIntroductionⅠ Dimming LED Lights1.1 What is Dimming?1.2 LED Dimming Circuit Example1.3 LED Dimming Using SCRⅡ Dimming LED Using PWM2.1 LED Dimming Current2.2 LED PWM Dimmer2.3 LED PWM Dimming Advantages2.4 LED PWM Dimming Problems2.5 DALI PWM Dimmer IntroductionⅢ Main LED Dimmers ComparisonsⅠ Dimming LED Lights1.1 What is Dimming?LED dimmer switch is an electrical device that changes the luminous flux of the light source in the lighting device and adjusts the illuminance level. The purpose of the dimmer is to adjust the different brightness of the light. By reducing or increasing the rms voltage, the light output of different intensities produced by the average power lamp is promoted. Although variable voltage devices can be used for various purposes, this regulation is aimed at controlling lighting. Regarding the LED dimmer switch, we must first understand the volt-ampere characteristics of the LED. That is, the characteristics of the current flowing through the LED PN junction with voltage. Generally, the reverse characteristic curve changes steeply. When the voltage exceeds a certain threshold, the current will rise exponentially, thereby breaking down the LED PN junction. The forward voltage of the LED is also determined by its forward current. It can be seen from the figure that the change of the forward current will cause the corresponding change of the forward voltage, to be precise, the decrease of the forward current will also cause the decrease of the forward voltage. Therefore, when the current is lowered, the voltage of the LED will also decrease, which will change the relationship between the power supply voltage and the load voltage.Figure 1. Diode Volt-Ampere Characteristics CurveTherefore, from the volt-ampere characteristics of the LED, we can know that the dimming of the light source cannot be achieved simply by reducing the input voltage or input current of the LED. In addition, the waveform of the sine wave of the LED is different from the waveform of the incandescent lamp, so it cannot simply change its conduction angle to achieve the purpose of dimming.LED dimming methods can be divided into analog dimming and digital dimming. Analog dimming is to achieve dimming by changing the current in the LED loop. The power supply voltage remains unchanged, and the current in the loop is changed by changing the resistance value to achieve the effect of changing the brightness of the LED. Many analog dimming is an extension of this method. Its advantage is that the current can be continuous, but the range of adjustable current is often limited by hardware, and there are few adjustment gears. This method is not ideal for high-precision lighting equipment.Digital dimming, also known as PWM (Pulse Width Modulation) dimming, uses PWM waves to turn on and off the LED to change the on-time of the forward current to achieve the effect of brightness adjustment. This method is based on the fact that the human eye is not sensitive enough to the brightness flicker. If the frequency of brightness and darkness exceeds 100Hz, the average brightness is seen by the human eye, not the LED flickering. PWM adjusts the brightness by adjusting the ratio of light and dark time. In a PWM cycle, because the perceived brightness of human eyes to flicker is a cumulative process, that is, the brighter time accounts for the greater the proportion of the entire cycle. The longer the time, the brighter the human eye feels.1.2 LED Dimming Circuit ExampleFor example, in an LED lamp with an input of 24V, 8 1W high-power LEDs are connected in series. When the forward current is 350mA, the forward voltage of each LED is 3.3V, then 8 pieces in series is 26.4V, so a constant current source greater than 24V should be used. However, in order to dimming, the current is reduced to 100mA. At this time, the forward voltage is only 2.8V, and 8 pieces are connected in series to 22.4V. The load voltage becomes lower than the input voltage, so that a constant current source larger than 24V cannot work, and finally the LED will flicker.In this case, you may choose a step-down (wide voltage) constant current source, such as a 10V-30V constant current source for dimming. However, if this type is adjusted to a low forward voltage, the LED load current will also become very low. So the step-down ratio is very large, beyond the normal working range of constant current source, which will make LED unable to work and cause flicker. In addition, LED works at low brightness for a long time, which will reduce its efficiency and increase the temperature rise. Because the efficiency of the step-down constant current source is related to the voltage ratio, the larger the voltage drop ratio, the lower the efficiency. And greater power loss on the chip will damage the life of the constant current source and the LED light source.1.3 LED Dimming Using SCROrdinary incandescent lamps and halogen lamps usually use thyristors for dimming. Because they are pure resistance devices, and do not require the input voltage to be a sine wave. Their current waveform is always the same as the voltage waveform, no matter how the voltage waveform deviates from the sine wave, changing the effective value of the input voltage will dim the LED light .However, the adjustment of LED light source by thyristor dimming will cause unexpected problems, that is, the LC filter at the input will cause the thyristor to oscillate. This oscillation is indifferent to the incandescent lamp, human eyes can't see it at all because of thermal inertia. However, this dimming method will cause the driving power of LED produce audio noise and flicker. It will also destroy the waveform of the sine wave, thereby reducing its power factor value (usually lower than 0.5), which greatly reduces the system efficiency of the LED. Moreover, the thyristor dimming waveform increases the harmonic coefficient, and the non-sinusoidal waveform will cause serious electromagnetic interference on the line to pollute the power grid.Ⅱ Dimming LED Using PWM2.1 LED Dimming CurrentHere, you may ask: Lower voltage or current or thyristor dimming methods are not suitable for LED light source dimming, so what is the most suitable method?Is it an analog (0-10V) dimming method? May be not. Analog dimming faces a severe challenge, which is the output current accuracy. Almost every LED driver needs some kind of series resistance to distinguish the current, and the tolerance, offset and delay in the analog (0-10V) dimming drive cause a relatively fixed error, which will reduce the accuracy of the output current, and the final output current cannot be specified, controlled or guaranteed. Therefore, to ensure the dimming effect of the LED light source, one of the important rules is to reduce the output current error and improve the current accuracy in a closed loop system.2.2 LED PWM DimmerThe PWM dimming method can solve the above problems very well. Because diode characteristics, LED can realize fast switching, and its allowable switching speed can be as high as microseconds or more. Therefore, as long as the power supply is changed to a pulse constant current source, the brightness can be changed by PWM. This PWM dimming. This method is like a sluice that opens and closes in microseconds or more. The switching frequency of it is so fast that humans can’t recognize the state of its opening with the naked eye. As a result, people can only identify the speed of its switching frequency by the amount of water downstream. In addition, because the sluice changes the duty cycle of the output water flow (effective water flow), it does not change the instantaneous water pressure and flow rate, so the opening and closing action of the sluice gate will not affect the hydropower generation. The amount of water flowing down and power generation are just changed. Therefore, the PWM dimming method does not change the instantaneous voltage and current of the input LED PN junction, but changes the duty cycle of the output current to change LED brightness.2.3 LED PWM Dimming Advantages1) There will not be any LED chromatogram shift, because the LED always works between the full amplitude current and 0.2) It has a very high dimming accuracy, because the pulse waveform can be controlled to a high precision.3) Even if the light is dimmed in a wide range, there will be no flicker. Because it will not change the working conditions of the constant current source (boost ratio or step-down ratio), problems such as overheating are less to occur.4) It can be combined with digital (DALI/DSI/DMX 512) control technology for control, because the digital control signal can easily be transformed into a PWM signal.2.4 LED PWM Dimming Problems1) Because the LED is in a fast switching state, if the working frequency is very low, the human eye will feel flicker. In order to make full use of the residual visual phenomenon of the human eyes, its operating frequency should be higher than 100Hz, preferably 200Hz.2) Eliminate the howling caused by dimming. Although the human eye can't detect it above 200Hz, it is within the range of human hearing until 20kHz. At this time, it is possible to hear the slightest voice. There are two ways to solve this problem: One is to increase the switching frequency above 20kHz, out of the range of human hearing, another is to find out the sound-producing device and deal with it.At present, some manufacturers have solved the above problems well. A good LED light source dimming technology needs a good LED control signal technology to match and cooperate in order to become an effective, stable and reliable system. For example, the LED PWM dimming method has the advantage that the digital control signal can easily be converted into a PWM signal. At the same time, in the digital control signal of lighting, DALI (Digital Addressable Lighting Interface) has the unparalleled superiority of other lighting digital control methods, and it is also the mainstream of the current digital control application in the lighting industry. Therefore, the matching of PWM dimming mode and DALI takes into account their respective advantages, where PWM dimming technology solves the final dimming problem of LED light sources, and DALI solves the control, feedback and networking of each LED light.Figure 2. LED PWM Dimming Circuit2.5 DALI PWM Dimmer IntroductionThe biggest feature of DALI technology is that each lamp has an independent address. Through the DALI system software, a single lamp or any lamp set can be accurately dimmed and switched, regardless of whether the lamps are on strong current loop or not. That is to say, the lighting control has nothing to do with the strong current circuit. The DALI system software can independently address single or multiple lamps on the same strong current circuit or different circuits, to achieve individual control and arbitrary grouping set. This concept brings great flexibility to lighting control, which can meet different LED lighting requirements. Even after installation, they can still modify the control requirements at will, without having to do anything to the wiring.The following are the application advantages of PWM dimming method combined with DALI.1) The design is simple and easy to implement.In the design, as long as they are connected to each other through the digital signal interface, they are connected in parallel to the 2-core control line. All design process can be programmed by computer software during installation and debugging, which not only saves design costs, but also improve working efficiency.2) Simple and economical installationThe DALI control line has no special requirements for the wire and no polarity requirements during installation. It only requires the main power line to be separated from the control line. The control line does not need to be shielded. When the current on the control line is 250mA and the line is 300 meters long, the drop does not exceed 2V. The control line and the power line can be parallel, no need to bury the line separately. The compact design of the control components does not require a special control cabinet, so installation is simple and economical.3) Simple and convenient operationThe PWM LED driver with DALI control can automatically handle filament preheating, ignition, dimming, switching, fault detection and other functions. The user interface is very friendly. Users can operate and control without deep understanding, such as sending a change. According to the command of the scene, each relevant LED driver calculates the dimming rate according to the difference between the current brightness and the required installation brightness to achieve that all the LED light sources are synchronized to the required scene brightness.4) Accurate and reliable controlDALI is a digital signal, which is different from an analog signal. The signal of 1010 can realize disturbance-free control, and will not distort the control signal due to long-distance voltage drop. Therefore, even if the DALI digital signal control line and the strong wire are in the same line and tube, it will not be disturbed. The DALI signal is two-way transmission, which not only transmits control commands forward, but also feeds back the information of the LED driver's status, fault information, switch, and actual brightness value to the system.5) Wide range of applicationsNowadays, DALI interface is not only used for fluorescent lamp ballast dimming, various electronic transformers for halogen lamps, electronic ballasts for gas discharge lamps. DALI technology also employed in wide range of LED light control makes it more and more widely. Ⅲ Main LED Dimmers Comparisons1) SCR DimmingFigure 3. SCR Dimming Circuit Diagram✅Advantages: It has the advantages of high adjustment accuracy, small size, light weight, easy remote control, etc., which occupies a leading position in the market.❎Disadvantages: The front-cut LED dimmer is prone to generate noise, so it is not recommended for high-demand occasions. The minimum load will vary depending on the LED dimmer and light source. It is necessary to consider derating to adapt to the spike caused by the driver. The typical derating percentage should be 25%-30% of the maximum rated load of the dimmer circuit. 2) CMOS DimmingFigure 4. CMOS Dimming Circuit Diagram✅Advantages: There is no minimum load requirement, so that better performance can be achieved on a single LED lighting device or a very small load.❎Disadvantages: High cost, complicated dimming circuits, lack of high-power products, and poor stability. 3) 0-10V DimmingFigure 5. 0-10V Dimming Circuit Diagram✅Advantages: Simple application, good compatibility, high precision, better dimming effect than phase-cut dimming.❎Disadvantages: Need to add additional control lines and controllers. The dimming effect is related to the wire diameter, cable material, power current, and power supply quantity of 0-10V dimming. 4) DALI DimmingFigure 6. DALI Dimming Circuit Diagram✅Advantages: Accurate and smooth dimming, two-way communication, and strong anti-interference ability, mainly used in single lamp control.❎Disadvantages: Like 0-10V products, additional control circuits and controllers need to be added. 5) DMX512 DimmingFigure 7. DMX512 Dimming Circuit Diagram✅Advantages: Powerful control functions bring rich lighting effects to architectural lighting, night lighting, studios and variety shows.❎Disadvantages: Special wiring layout and types are required, and certain programming is required to set the basic colors and scenes, which is more costly for later maintenance. The ideal transmission distance of DMX signal is less than 200 meters. And meanwhile, in actual use, the signal is greatly interfered by the outside world. 6) SLC and Ready2mains DimmingFigure 8. LED Dimming via Ready2mains✅Advantages: The digital dimming signal is transmitted through the AC wire, without additional signal wires and wiring. Digital signal transmission has good anti-interference performance and excellent dimming effect.❎Disadvantages: At present, there are relatively few products using this type of digital dimming technology, so there are relatively few compatible products. Frequently Asked Questions about LED Dimmer1. What are LED dimmers?An LED dimmer is the term for a device that performs a dimming control operation within such an LED lighting device. LEDs react instantaneously to alterations in power input, making solid state lighting especially suitable for dimming scenarios. 2. Why do my LED dimmer lights flicker?LED bulb flickering can be traced in almost every instance to a non-compatible dimmer switch in the lighting circuit. ... LED bulbs don't have glowing filaments. When the dimmer switch goes off and on many times per second, the LED bulb becomes a flickering strobe light. 3. Do you need a special dimmer for LED lights?Use an LED Dimmer switchA standard dimmer switch cannot be used with an LED light as you will never be able to dim the LED light either completely or not very well. LED lights need their own special electronic dimmer switch to have a fully functioning and dimming light. 4. How do LED dimmer switches work?In the case of PWM, dimmable LEDs work by creating a dimming effect. Unlike traditional lighting such as incandescent, dimmable LED bulbs don't rely on voltage to dictate their level of brightness. Instead, they essentially rely on a cycle of being on and off. 5. What is the best dimmer switch for LED lights?Best Overall: Lutron Toggler Single-Pole/3-Way Light Dimmer.Best Budget: GE Slide Dimmer Rocker Wall Switch, Single Pole.Best Smart: Kasa Smart Dimmer Switch HS220.Best for Bedrooms: Lutron Maestro LED+ Dimmer Switch, Single-Pole or Multi-Location.Best for LED: Lutron Diva LED+ Dimmer Switch, Single-Pole or 3-Way.

IntroductionDo you know buffer amplifier or isolation amplifier? The operational amplifier is an extremely efficient and versatile device. As we all known, the op amp is a component that amplifies the weak signal, which can be made into different forms according to the circuit requirements, and the voltage follower is one of them. Most voltage follower circuit will use an Op-amp. A follower is specifically an op amp wired to have a gain of +1. IE, the output is the same polarity and voltage as the input. That is, the output signal is exactly the same as the input signal. Here op amp voltage follower is used to isolate the signal and enhance load capacity. Op-amp as Voltage FollowerIntroductionⅠ Voltage Follower OP AmplifierⅡ Voltage Follower Characteristics2.1 Op Amp Impedance Matching2.2 Buffer Amplifier & Isolation AmplifierⅢ Op Amp Follower Circuit Analysis3.1 Op Amp Voltage and Load3.2 Op Amp Voltage Follower Stability3.3 Op Amp Phase Difference Problem3.4 Adding Feedback ResistanceⅣ Op Amp Voltage Follower ApplicationⅠ Voltage Follower OP AmplifierThe op amp follower sacrifices the voltage amplification factor in exchange for the performance of increasing the input impedance and reducing the output impedance. Because the gain of the op amp is extremely high, the input impedance of the op amp follower tends to be infinite, and the output impedance tends to zero. Within the rated output current range, the feedback voltage is equal to the output voltage, the output voltage is in phase with the input voltage, and the output voltage is slightly smaller than the input voltage. It should be noted that voltage follower is a special case of negative feedback amplifier (voltage series).Op amp voltage follower is actually a simple circuit structure which play a role in impedance matching. When a weaker signal is used to drive a relatively high current, voltage follower is often added in the middle, so that it can make weak signal stronger. It improves the load capacity to a considerable extent, while ensuring that the waveform and amplitude of the signal remain unchanged.For example, a single-chip microcomputer outputs a PWM signal to control LED lights. One LED does not require much current, so there is generally no big problem, however, when multiple LEDs need to light, current may definitely not large enough. If the current output is not enough, which may affect the signal output by the single-chip microcomputer, in this way, the voltage follower comes in handy.Ⅱ Voltage Follower Characteristics2.1 Op Amp Impedance MatchingWhen the op amp gain is approximately 1, that is, the magnification is approximately 1. The "follow" in the follower means that the voltage remains unchanged before and after, and the output waveform is almost not lost. It can be composed of transistors or operational amplifiers (best). Because the op amp input impedance is large and the output impedance is small, voltage follower can reduce the impact on the signal and improve the load capacity.2.2 Buffer Amplifier & Isolation AmplifierHere is a question, how to understand the buffering effect? Is the voltage of the former having a small impact on the back circuit? No, it is equivalent to a constant voltage source. Within the design requirement, no matter how the circuit connected to the subsequent stage changes, the output voltage is constant and does not change. In this way, the magnification or other performance of the previous stage can be kept unchanged. Otherwise, if the previous-stage input impedance is large, and the latter stage is small, the signal will definitely be distorted. For example, if a sinusoidal voltage waveform with a peak value of 10V, the sinusoidal peak value loaded to the latter stage may only be 8V. After adding a voltage follower, the waveform loaded on the input of the voltage follower will basically not change, and the input-output stage voltage ratio is very close to unity. So there will be no distortion.Since the output impedance of the voltage amplifier is generally relatively high, usually in the range of several kiloohms to tens of kiloohms. If the input impedance of the subsequent stage is relatively small, part of the signal will be lost in the output resistance of the previous stage. At this time, a voltage follower is needed to buffer from it. Another advantage of applying a voltage follower is that the op amp input impedance is increased, so that the capacity of the input capacitance can be greatly reduced, which provides a prerequisite guarantee for the application of high-quality capacitors.Another question, what about isolation? Because the op amp input impedance of the voltage follower is very large, it can be approximated as an open circuit. Of course, this open circuit is for the previous circuit. In this case, the previous circuit will not affect the subsequent circuit. However, "open circuit" means what, is it really open? No, the previous voltage is transmitted, but the corresponding current is not transmitted. This is the isolation effect.For example, if the MCU outputs a PWM waveform, you want to use it to control the brightness of a small light bulb. However, the output capacity of the IO port of the general MCU is limited. You can directly use the PWM output from the IO port to drive one light bulb. More than one doesn't work. In this case, you can add a voltage follower, so that the voltage is still the original voltage, but the driving ability has improved. Of course, the output capacity is not increased out of thin air, but comes from the input power of the op amp. In electronics, the diode has current amplification capability, and its source of amplification capability also comes from the power supply.In Hi-Fi circuits, the controversy about negative feedback has been around for a long time. In fact, if there is no negative feedback, most amplifying circuits will not work well. However, due to the introduction of a large loop negative feedback circuit, the back EMF of the speaker will pass through the feedback circuit and be superimposed with the input signal. The sound quality is blurred and the clarity is reduced. Therefore, some of the final stages of the power amplifier adopt a circuit without large loop negative feedback, trying to eliminate the disadvantages by disconnecting the negative feedback loop. However, since the operating current of the final stage of the amplifier varies greatly, its distortion is difficult to control. Here, the function of the voltage follower is just for the application. Putting the circuit between the front stage and the power amplifier can cut off the interference effect of the back electromotive force of the speaker on the front stage, so that the clarity of the sound quality is greatly improved. Ⅲ Op Amp Follower Circuit Analysis3.1 Op Amp Voltage and LoadFigure 1. Op Amp Voltage Follower SchematicThe output and the inverting input terminal are connected in series with a 10k resistor to ensure excellent characteristics. An ac signal is input at the non-inverting input terminal. Of course, dc and ac are all okay, so you will get a very high voltage at the output terminal. AC voltage that is similar and has excellent load capacity, with buffering and isolation effects.3.2 Op Amp Voltage Follower StabilityThe problem of using a voltage follower to keep the operational amplifier stable, that is, how to reduce the oscillation in the amplifier circuit using negative feedback to maintain stability, there is still no final conclusion. The ideal operating state of the op amp is that the output voltage and the input voltage are in phase, that is, when the applied voltage at the negative input causes the output to increase, the op amp can reduce the increased voltage accordingly. However, there is always a difference in phase between the input and output in reality. When the phase difference between the output and the output is 180°, the negative input and the positive input are exactly the same, but the output that should have been reduced is enhanced. It becomes a state of positive and negative collapse. If it falls into this state in a specific frequency band and still maintains the original amplitude, then the output frequency and oscillation state will continue.Figure 2. Feedback Loop3.3 Op Amp Phase Difference ProblemThe main reason for the phase difference between the input and the output:1) Due to the inherent characteristics of op amps.2) Due to the characteristics of the other feedback loop in circuit.Figure 3. Gain-frequency, Phase-frequency CurveFig 3(a), Fig 3(b)and Fig 3(c) respectively represent the voltage gain-frequency characteristic and phase-frequency characteristic of the operational amplifier. As shown in the figure, the voltage gain and phase vary with frequency. The difference between the op amp gain and the gain after feedback (0dB when using a voltage follower) is the gain (feedback gain) of the feedback loop. If the feedback gain is less than 1 time (0dB), then, the phase changes by 180° and returns to the positive feedback state, the negative gain will gradually attenuate in the circuit and theoretically will not cause oscillation.On the contrary, when the phase changes by 180°, if the loop gain corresponding to the frequency is 1 time, the original amplitude will be maintained. If the loop gain corresponding to the frequency is greater than 1, the amplitude will gradually diverge. In most cases, in the process of amplitude divergence, the amplitude is limited due to the influence of nonlinear elements such as the maximum output voltage, and the oscillation state will be maintained.Therefore, the difference between the phase corresponding to the frequency when the loop gain is 0dB, 180° is an important factor for judging the stability of the negative feedback loop, and this parameter is called the phase margin. Unless otherwise specified, when a single amplifier is used as a voltage follower, sufficient phase margin must be maintained (Fig 3b.).3.4 Adding Feedback ResistanceWhen the operational amplifier is used as a follower, when the internal resistance of the signal source is large, adding a feedback resistor with the same resistance as the internal resistance of the signal source can reduce the output offset voltage and improve the follow accuracy. The follower with feedback resistance has a certain current limiting protection effect on the circuit when the circuit is "blocked", which is its advantage.The voltage follower is originally a non-inverting operational amplifier. One of the common features of it is that a common-mode voltage is added to the non-inverting terminal and the inverting terminal.Once this common-mode voltage exceeds the allowable common-mode input voltage range, for example, if the inverting terminal signal is too large, it will cause the input stage transistor to saturate. The inverting terminal signal will be directly added to the second stage of the op amp, making the inverting input becomes non-inverting input, that is, negative feedback becomes positive feedback, and the output signal passes through the feedback loop to further saturate the input stage transistor. As a result of this, the amplifier is of course no longer in normal working condition. Even if the input signal is canceled, it will not immediately return to the normal state. This phenomenon is called blocking.When it occurs, if the feedback loop resistance is not large enough, the current in the feedback loop may burn the input stage transistors and even harm the second stage. In order to avoid blocking, in addition to choosing an op amp with a large common-mode input voltage range, a clamp circuit is often added to the input of the amplifier to ensure that the common-mode voltage at the input does not exceed the allowable range.Of course, in a small-signal inverting operational amplifier, especially in circuits with capacitive elements such as integrating operational amplifiers, blocking may also occur. The processing method is the same as that of the non-inverting amplifier. Ⅳ Op Amp Voltage Follower ApplicationIn many typical circuit designs, there will be an op amp follower before the AD converter. Whether this follower is necessary or not depends on the requirements of the circuit based on the understanding of the function of the follower. First analyze the role of the voltage follower here:The function of the voltage follower here is impedance transformation.Impact 1: The input impedance becomes very high, so that the impact on the input signal can be small.Impact 2: The output impedance becomes very low, and the impact of AD input impedance on the input signal can be very small.It can be seen that the follower is very meaningful. Secondly, analyze your own circuit and the signal under test to make a decision whether to use a follower. Here are some rules to confirm:1) If the output impedance of the signal is very small, then the Impact 1 can be ignored.2) If the input impedance of AD converter is very large, then two impacts can be ignored.3) If both impacts can be ignored, no voltage follower is necessary.4) If there is an impact, a voltage follower is needed. Frequently Asked Questions about Op Amp Voltage Follower1. Which amplifier is called as voltage follower Why?This means that the op amp does not provide any amplification to the signal. The reason it is called a voltage follower is because the output voltage directly follows the input voltage, meaning the output voltage is the same as the input voltage. 2. What is the use of voltage follower?A voltage follower can be used as a buffer because it draws very little current due to the high input impedance of the amplifier, thus eliminating loading effects while still maintaining the same voltage at the output. 3. What do you mean by voltage follower circuit?A voltage follower is also known as a unity gain amplifier, a voltage buffer, or an isolation amplifier. In a voltage follower circuit, the output voltage is equal to the input voltage; thus, it has a gain of one (unity) and does not amplify the incoming signal. 4. What is an op amp buffer?An op-amp voltage buffer mirrors a voltage from a high-impedance input to a low-impedance output. 8 min read. A voltage buffer, also known as a voltage follower, or a unity gain amplifier, is an amplifier with a gain of 1. It's one of the simplest possible op-amp circuits with closed-loop feedback. 5. What is an op amp buffer circuit used for?A buffer is a unity gain amplifier packaged in an integrated circuit. Its function is to provide sufficient drive capability to pass signals or data bits along to a succeeding stage. Voltage buffers increase available current for low impedance inputs while retaining the voltage level.