The Kynix Blog

I IntroductionSummary: A photoresistor, or light-dependent resistor (LDR), is a passive electronic component that decreases in resistance as light intensity increases. Driven by the expansion of IoT and smart home automation, the global photoresistor market is projected to reach $553.75 million by 2025. This guide covers LDR working principles, circuit diagrams, types, and step-by-step Arduino integration.Photoresistor or light-dependent resistor (abbreviated as LDR) or photoconductor is a special resistor made of semiconductor materials such as cadmium sulfide or cadmium selenide. Its working principle is based on the internal photoelectric effect. The stronger the light, the lower the resistance value. With the increase of the light intensity, the resistance value decreases rapidly, and the bright resistance value can be as small as 1KΩ or less. The photoresistor is very sensitive to light, and it shows a high resistance state when there is no light, and the dark resistance can generally reach 1.5MΩ.This article includes an overview of the basic information of the photoresistor and two Arduino tutorials for the photoresistor. The content is very comprehensive and detailed. You can choose the part you want to read or read the full text. We hope this article is helpful to you!II What is a Photoresistor?2.1 What is the Definition of a Photoresistor?A photoresistor (also known as a light-dependent resistor, LDR, or photo-conductive cell) is a passive electronic component that decreases its electrical resistance as the luminosity on its sensitive surface increases.2.2 What is the Symbol for a Photoresistor?The standard schematic symbols for a photoresistor are generally represented by the designators "RL", "RG", or "R", often accompanied by a resistor icon enclosed in a circle with incoming arrows indicating light. The following figure shows the schematic symbols of the photoresistor.Figure1. Photoresistor SymbolRecommended Reading: To learn more about Resistor Symbol.2.3 What is the Composition of a Photoresistor?(1) The structure of the photoresistorA photoresistor is primarily composed of a photosensitive semiconductor layer, a glass substrate or moisture-proof film, and comb-shaped ohmic electrodes.Figure2. The Structure of PhotoresistorMaterials for manufacturing photoresistorsThe materials used for manufacturing photoresistors are primarily semiconductors such as metal sulfides, selenides, and tellurides. Usually, coating, spraying, sintering and other methods are used to make a very thin photoresistor and comb-shaped ohmic electrode on the insulating substrate, and then the lead is taken out and encapsulated in a sealed housing with a light-transmitting mirror to prevent moisture from affecting its sensitivity.III How Does the Photoresistor Work?3.1 What is the Working Principle of Photoresistors?How does a photoresistor workThe working principle of a photoresistor is based entirely on the internal photoelectric effect, where incident light energy excites electrons into the conduction band, thereby lowering the component's electrical resistance.A voltage is applied to the metal electrodes at both ends of the photoresistor, and a current flows through it. When irradiated with light of a certain wavelength, the current will increase with the increase of light intensity, thereby achieving photoelectric conversion. After the incident light disappears, the electron-hole pairs generated by the photon excitation will recombine, and the resistance of the photoresistor will return to its original value.The photoresistor has no polarity and is purely a resistive device. It can be used with either DC voltage or AC voltage. The conductivity of a semiconductor depends on the number of carriers in the semiconductor conduction band. Why is the value of the photoresistor related to the wavelength of the incident light?Simply put, it is the effect of transitions between energy levels. Photons at different wavelengths have different energies, and an electron can only absorb one photon. After an electron absorbs a photon, whether it can be converted from non-conductive to conductive electrons depends on the photon’s Energy, and the number of electrons that can conduct electricity determines the resistance of the photoresistor. Therefore, the light wavelength also affects the resistance of the photoresistor.Recommended Reading: See more about light sensor, wavelength, spectrum and photometric physical quantity.3.2 What is the Internal Photoelectric Effect?The internal photoelectric effect is a phenomenon where the absorption of photons causes a change in the electrical conductivity of a semiconductor material. This differs from the external photoelectric effect, which involves the complete escape of electrons from the material's surface.The internal photoelectric effect can be divided into two main categories:Photoconductive effect: The change in electrical resistance due to light exposure.Photovoltaic effect: The generation of a photo-induced electromotive force (voltage) across a P-N junction. PhotoconductivityThe photoconductive effect is one of two internal photoelectric effects. The internal photoelectric effect refers to the phenomenon that the electrical conductivity of a semiconductor exposed to light changes or a photo-induced electromotive force is generated. Among them, the phenomenon that the conductivity of the semiconductor changes due to light is called the photoconductivity effect.Figure3. Energy Level of AtomPhotovoltaic EffectThe photovoltaic effect occurs when a P-type and N-type semiconductor are combined, creating a P-N junction. The process unfolds as follows:Electrons in the N-type semiconductor and holes in the P-type semiconductor diffuse, forming a depletion region near the interface.When light irradiates the P-N junction, photons with sufficient energy generate minority carriers (electron-hole pairs).Under the action of the internal electric field, excited electrons flow to the N-type region, and holes flow to the P-type region.This accumulation generates an additional electromotive force (voltage) at both ends of the P-N junction.If connected to an external circuit, current flows from the P region to the N region, producing usable electrical power.Figure4. Photovoltaic EffectIV How Do You Wire a Photoresistor Application Circuit?Schematic circuit for conventional applicationsFigure5. Schematic CircuitModule parameters:Working voltage: DC3.3-5VPhotoresistor Model: 5516Module pins: 3-pin or 4-pin (an additional analog output AO for 4-pin)Common circuit diagram （3）Photoresistor application circuit diagramThe following figure is a schematic diagram of the application of the photoresistor in the light control switch. The photoresistor is connected in series with the resistor R1. When there is no light, that is, the voltage across R1 does not reach the turn-on voltage of the Q1 transistor. Once exposed to light, the resistance of the photoresistor drops rapidly. The voltage across R1 rises and the transistor turns on, which causes the transistor Q2 in the subsequent stage to turn on, and finally, the switch K opens and the bulb works.Figure6. Common Photoresistor Application Circuit Diagram(4) Photoresistor dimming circuitThe following figure is a typical light-controlled dimming circuit. Its working principle is: when the surrounding light becomes weak, the resistance of the photoresistor RG increases, which increases the partial voltage added to the capacitor C, which in turn makes the thyristor's conduction angle is increased to achieve the purpose of increasing the voltage across the lamp. Conversely, if the surrounding light becomes brighter, the resistance of RG decreases, resulting in a smaller conduction angle of the thyristor, and the voltage across the lamp decreases at the same time, dimming the light, thereby controlling the illuminance of the lamp.Figure7. Photoresistor Dimming CircuitNote: The rectifier bridge in the above circuit must be a DC pulsating voltage, and it cannot be converted into a smooth DC voltage by capacitor filtering, otherwise the circuit will not work properly. The reason is that the DC pulsating voltage can not only provide the basic conditions for the zero-crossing shutdown of the thyristor, but also enable the charging of the capacitor C to start from zero every half cycle, and accurately complete the synchronous phase-shift triggering of the thyristor.V What Are the Types of Photoresistors?5.1 Classification by MaterialsBased on material composition, photoresistors are classified into intrinsic (pure semiconductor) and extrinsic (doped semiconductor) types. Polycrystalline and single crystal photoresistors can also be divided into cadmium sulfide (CdS), cadmium selenide (CdSe), lead sulfide (PbS), lead selenide (PbSe), indium antimonide (InSb) photoresistors, etc. 5.2 Classification by Spectral CharacteristicsSpectral TypeCommon MaterialsPrimary Applications (2026)Ultraviolet (UV)Cadmium sulfide, Cadmium selenideUV detection, environmental monitoringInfrared (IR)Lead sulfide, Lead telluride, Indium antimonideAstronomical detection, non-contact measurement, IR communicationVisible LightSelenium, Silicon, Germanium, Zinc sulfideIoT smart lighting, automatic street lights, exposure devices(1) Ultraviolet photoresistor: sensitive to ultraviolet rays, including cadmium sulfide, cadmium selenide photoresistors, etc., used to detect ultraviolet rays.(2) Infrared photoresistors: mainly lead sulfide, lead telluride, and lead selenide. Photoresistors such as indium antimonide are widely used in missile guidance, astronomical detection, non-contact measurement, human disease detection, infrared spectroscopy, infrared communication and other national defense, scientific research, and industrial and agricultural production.(3) Visible light photoresistors: including selenium, cadmium sulfide, cadmium selenide, cadmium telluride, gallium arsenide, silicon, germanium, zinc sulfide photoresistors, etc. Mainly used in various photoelectric control systems, which account for a significant portion of the projected $553.75 million global photoresistor market in 2025. Applications include IoT smart lighting, automatic turning on and off of navigation lights, street lights and other lighting systems, automatic water supply and automatic water stop devices, automatic protection devices on machinery and "position detectors" Thickness detectors for thin parts, automatic exposure devices for cameras, photoelectric counters, smoke alarms, photoelectric tracking systems, etc.Figure8. Light Dependent ResistorVI The Main Parameters and Basic Characteristics of the Photoresistor6.1 What Are the Main Parameters of a Photoresistor?The main parameters of a photoresistor define its operational limits, sensitivity, and response time in various lighting conditions.1) Bright resistance (kΩ): refers to the resistance value of the photoresistor when exposed to light.2) Dark resistance (MΩ): refers to the resistance value of the photoresistor when there is no light exposure (dark environment).3) Maximum working voltage (V): refers to the highest voltage the photoresistor is allowed to withstand under the rated power.4) Bright current: refers to the current that the photoresistor passes when it is irradiated by light under the specified applied voltage.5) Dark current (mA): refers to the current that the photoresistor passes under the specified applied voltage when there is no light.6) Time constant (s): refers to the time required for the photoresistor to start from the light jump to stabilize 63% of the bright current.7) Resistance temperature coefficient: refers to the relative change of the resistance value of the photoresistor when the ambient temperature changes by 1°C.8) Sensitivity: refers to the relative change of the resistance value of the photoresistor with and without light irradiation.Figure9. LDR6.2 Basic Characteristics(1) Dark resistance and bright resistanceThe stable resistance value measured by the photoresistor under room temperature and total darkness is called dark resistance. The current flowing at this time is called dark current. For example, MG41-21 type photoresistor dark resistance is greater than or equal to 0.1M.The stable resistance value measured by the photoresistor at room temperature and under certain lighting conditions is called bright resistance. The current flowing at this time is called the bright current. The bright resistance of MG41-21 type photoresistor is less than or equal to 1k.    The difference between bright current and dark current is called photocurrent.    Obviously, the larger the dark resistance of the photoresistor, the better, and the smaller the bright resistance, the better, that is, the dark current should be small and the bright current should be large, so the sensitivity of the photoresistor is high.Figure10. Bright Current and Dark Current(2) Volt-ampere characteristicsUnder a certain illuminance, the relationship between the voltage applied across the photoresistor and the current flowing through the photoresistor is called the volt-ampere characteristic. The volt-ampere characteristic of the photoresistor is approximately a straight line, and there is no saturation phenomenon. Due to the limitation of power dissipation, the voltage across the photoresistor cannot exceed the maximum operating voltage during use. The dotted line in the figure is the allowable power consumption curve, from which the normal operating voltage of the photoresistor can be determined. (3) Photoelectric characteristics    The relationship between the photocurrent of the photoresistor and the illuminance is called the photoelectric characteristic. The photoelectric characteristics of the photoresistor are nonlinear. Therefore, it is not suitable as a detection element, which is one of the shortcomings of the photoresistor. In automatic control, it is often used as a switching photoelectric sensor.Figure11. Characteristics of the Photoelectric Effect(4) Spectral characteristicsFor incident light of different wavelengths, the relative sensitivity of the photoresistor is different. The spectral characteristics of various materials are shown in Figure 2.6.4. It can be seen from the figure that the peak value of cadmium sulfide is in the visible light region, and the peak value of lead sulfide is in the infrared region. Therefore, when selecting the photoresistor, the types of components and light sources should be considered in order to obtain satisfactory results. (5) Frequency characteristicsWhen the photoresistor is exposed to pulsed light, the photocurrent will reach a steady-state value after a period of time. When the light suddenly disappears, the photocurrent will not be zero immediately. This shows that the photoresistor has time-delay characteristics. Because different materials have different time delay characteristics of photoresistors, their frequency characteristics are also different. Figure 2.6.5 shows the relationship between the relative sensitivity Kr and the light intensity change frequency f. It can be seen that the use frequency of lead sulfide is much higher than that of thallium sulfide. However, most photoresistors have large time delays, so they cannot be used in situations where fast response is required. This is a defect of photoresistors. (6) Temperature characteristicsLike other semiconductor devices, the photoresistor is greatly affected by temperature. When the temperature increases, its dark resistance will decrease. Changes in temperature also have a great influence on spectral characteristics. Figure 2.6.6 is the spectral temperature characteristic curve of the lead sulfide photoresistor. It can be seen from the figure that its peak value moves to the short wavelength direction as the temperature rises. Therefore, in order to improve the sensitivity, or in order to receive far-infrared light, cooling measures are taken.Figure12. Temperature CharacteristicsSpectral Temperature Characteristics of Lead Sulfide Photoresistor A commonly used photoresistor is a cadmium sulfide photoresistor, which is made of semiconductor material. The resistance of the photoresistor changes with the intensity of the incident light (visible light). Under dark conditions, its resistance (dark resistance) can reach 1~10MΩ; under strong light conditions (100LX), its resistance (Bright resistance) Only a few hundred to thousands of ohms. The sensitivity of the photoresistor to light (the spectral characteristics) is very close to the human eye's response to visible light (0.4~0.76) μm. As long as the human eye can sense the light, it will cause its resistance to change. Therefore, when designing the light control circuit, the incandescent bulb (small electric bead) light or natural light is used as the control light source, which greatly simplifies the design.Figure13. Photoresistor Characteristic CurveThe corresponding resistance change of the photoresistor with the intensity of the incident light is not linear, so it cannot be used for the linear conversion of the photoelectricity. This is where the user should pay attention. Beginners can purchase a photoresistor (MG45 type), at night a 60~100W incandescent lamp, use a multimeter to directly measure the resistance of the photoresistor. When measuring, the photoresistor should be aimed at the light of the incandescent lamp, and then gradually distance from the lamp (from near to far), observe the change of the resistance value indicated by the multimeter, and the special characteristics of the photoresistor can be visually verified.Commonly used photoresistor models are sealed MG41, MG42, MG43 and unsealed MG45 (cheap price). Their rated power is below 200mW.VII How to Use a Photoresistor with Arduino?7.1 LED Control with Photoresistor and ArduinoLED Control with LDR (Photoresistor) and Arduino7.2 How to Measure Light Intensity Using a Photoresistor (Arduino)In the data collection of modern smart home systems, the measurement of light intensity is highly necessary. For example, indoor IoT lighting can be automatically adjusted according to the intensity of the light to provide users with the most comfortable environment. The tutorial here will use a photoresistor to cooperate with Arduino to complete the light data collection.(1) MaterialsArduino UNO development boardBreadboardPhotoresistor1K-10K resistance(2)Wiring method Figure14. Wiring MethodThe resistance of photosensitive resistors is very high in the condition of no light. The stronger the light, the smaller the resistance. By measuring the voltage variation on both sides of the photosensitive resistance, the variation of the photosensitive resistance can be known and the light intensity can be obtained. In the connection diagram, we find that a partial voltage resistor is connected in series for the photosensitive resistor.Figure15. CircuitIn the above figure, RL is a photoresistor, R1 is a series resistor, Vout=RLR1+RL∗Vin, in the dark, the resistance of RL will be very large, so Vout is also very large, close to 5V. Once the light is irradiated, the value of RL will decrease rapidly, so Vout will decrease accordingly. It can be seen from the above formula that R1 should not be too small, preferably around 1k~10k, otherwise the ratio will not change significantly. (3) CodeThe code part is very simple, just read the analog value of the interface connected to the photoresistor.1 light = analogRead(0);Open the serial monitor of Arduino, illuminate the photoresistor with the flashlight of the mobile phone, and observe the result:2 Serial.println("lignt :");3 Serial.println(light);7.3 Use Experiment of Arduino Photoresistor(1) MaterialsArduino UNO x1Photoresistor x1resistance 10K, 4.7K, 1K x several (or need one, but you can test the difference between different resistance values and data)(2)Wiring method Figure16. Wiring Method(3)Program#define AD5 A5 //Define analog port A5#define LED 13 //Define digital port 13 int Intensity = 0;//Illuminance value void setup() //Program initialization{   pinMode(LED, OUTPUT);//Set LED to output mode   Serial.begin(9600);//Set baud rate 9600} void loop() // Program body loop{   Intensity = analogRead(AD5); //Read the value of analog port AD5 and save it in the Intensity variable   Serial.print("Intensity = "); //Serial output "Intensity = "   Serial.println(Intensity); //The serial port outputs the value of the Intensity variable and wraps   delay(500); //Delay 500ms}(4) Power on, view serial dataTest Results:Figure17. Test ResultsThe above data is the change of the value with the flashlight and no light.(5) SummaryThe positive and negative poles are reversed and the values are reversed. The larger the resistance value, the larger the change range. Using 5V, the range is larger than 3.3V.Recommended Reading: Arduino&mBlock light sensorVIII How to Use Multimeter to Detect the Quality of Photoresistor?Measure the dark resistance: Use a black piece of paper to cover the light-transmitting window of the photoresistor. At this time, the pointer of the multimeter remains basically unchanged, and the resistance value is close to infinity. The larger the value, the better the performance of the photoresistor. If this value is very small or close to zero, it means that the photoresistor has been burnt through and damaged and can no longer be used.Measure the bright resistance value: Point a light source to the light-transmitting window of the photoresistor. At this time, the pointer of the multimeter should have a large amplitude swing, and the resistance value is significantly reduced. The smaller the value, the better the photoresistor performance. If this value is large or even infinite, it indicates that the internal open circuit of the photoresistor is damaged and can no longer be used.Test intermittent light response: Align the light-transmitting window of the photoresistor with the incident light, and use a small piece of black paper to shake the upper part of the light-shielding window of the photoresistor to make it receive light intermittently. At this time, the pointer of the multimeter should swing left and right with the black paper. If the pointer of the multimeter always stops at a certain position and does not swing with the shaking of the paper, it means that the photosensitive material of the photoresistor has been damaged.IX A Quiz about the PhotoresistorPhotoresistors, potentiometers, and thermistors are all ________.A. OutputsB. Digital inputsC. Analog inputsD. ThroughputsAnswer: CFrequently Asked QuestionsWhat is the difference between a photoresistor and a photodiode?A photoresistor is a passive component that changes resistance based on light intensity, making it slower but easier to use. A photodiode is an active semiconductor with a P-N junction that converts light into current, offering much faster response times for high-speed applications.Is a photoresistor an analog or digital component?A photoresistor is fundamentally an analog component. Its resistance changes continuously in response to varying light levels. However, when paired with a microcontroller like an Arduino and a voltage divider, its analog signal can be easily converted into digital data.What are the main types of photoresistors?Photoresistors are primarily categorized into intrinsic and extrinsic types. Intrinsic photoresistors use pure semiconductors like silicon, while extrinsic types use doped materials to detect longer wavelengths, such as infrared light, making them ideal for specialized sensors.How is a photoresistor used in smart home circuits?In modern IoT and smart home systems, photoresistors act as ambient light sensors. They automatically trigger actions like turning on outdoor security lights, adjusting indoor smart bulb brightness, or activating motorized blinds when sunlight reaches a specific threshold.{ "@context": "https://schema.org", "@graph":[ { "@type": "Article", "headline": "Photoresistor Basics: Working Principle, Types, and Arduino Tutorial", "datePublished": "2020-06-19T00:00:00Z", "dateModified": "2026-03-14T15:57:00+08:00", "author": { "@type": "Organization", "name": "ApogeeWeb" }, "publisher": { "@type": "Organization", "name": "ApogeeWeb" } }, { "@type": "FAQPage", "mainEntity":[ { "@type": "Question", "name": "What is the difference between a photoresistor and a photodiode?", "acceptedAnswer": { "@type": "Answer", "text": "A photoresistor is a passive component that changes resistance based on light intensity, making it slower but easier to use. A photodiode is an active semiconductor with a P-N junction that converts light into current, offering much faster response times for high-speed applications." } }, { "@type": "Question", "name": "Is a photoresistor an analog or digital component?", "acceptedAnswer": { "@type": "Answer", "text": "A photoresistor is fundamentally an analog component. Its resistance changes continuously in response to varying light levels. However, when paired with a microcontroller like an Arduino and a voltage divider, its analog signal can be easily converted into digital data." } }, { "@type": "Question", "name": "What are the main types of photoresistors?", "acceptedAnswer": { "@type": "Answer", "text": "Photoresistors are primarily categorized into intrinsic and extrinsic types. Intrinsic photoresistors use pure semiconductors like silicon, while extrinsic types use doped materials to detect longer wavelengths, such as infrared light, making them ideal for specialized sensors." } }, { "@type": "Question", "name": "How is a photoresistor used in smart home circuits?", "acceptedAnswer": { "@type": "Answer", "text": "In modern IoT and smart home systems, photoresistors act as ambient light sensors. They automatically trigger actions like turning on outdoor security lights, adjusting indoor smart bulb brightness, or activating motorized blinds when sunlight reaches a specific threshold." } } ] }, { "@type": "HowTo", "name": "How to Use Multimeter to Detect the Quality of Photoresistor", "step":[ { "@type": "HowToStep", "name": "Measure the dark resistance", "text": "Use a black piece of paper to cover the light-transmitting window of the photoresistor. At this time, the pointer of the multimeter remains basically unchanged, and the resistance value is close to infinity. The larger the value, the better the performance of the photoresistor. If this value is very small or close to zero, it means that the photoresistor has been burnt through and damaged and can no longer be used." }, { "@type": "HowToStep", "name": "Measure the bright resistance value", "text": "Point a light source to the light-transmitting window of the photoresistor. At this time, the pointer of the multimeter should have a large amplitude swing, and the resistance value is significantly reduced. The smaller the value, the better the photoresistor performance. If this value is large or even infinite, it indicates that the internal open circuit of the photoresistor is damaged and can no longer be used." }, { "@type": "HowToStep", "name": "Test intermittent light response", "text": "Align the light-transmitting window of the photoresistor with the incident light, and use a small piece of black paper to shake the upper part of the light-shielding window of the photoresistor to make it receive light intermittently. At this time, the pointer of the multimeter should swing left and right with the black paper. If the pointer of the multimeter always stops at a certain position and does not swing with the shaking of the paper, it means that the photosensitive material of the photoresistor has been damaged." } ] } ]}

Executive Summary: Potentiometers in 2026A potentiometer (or "pot") is a three-terminal variable resistor used to control voltage, current, and signal processing in electronic circuits. While traditional mechanical pots remain vital for audio and industrial controls, 2026 trends favor high-precision Digital Potentiometers (DigiPots) and MEMS-based sensors for IoT and robotics applications. This guide covers the latest classification standards, modern applications, and essential maintenance tips for optimal circuit performance.Ⅰ. What is a Potentiometer? (2026 Overview)A potentiometer is a critical three-terminal passive electronic component that functions as an adjustable voltage divider. Ideally suited for applications requiring user-generated input or position sensing, it consists of a resistive element (track) and a sliding wiper. If only two terminals are configured (one end and the wiper), it functions as a variable resistor or rheostat. While the core mechanical construction of potentiometers remains consistent, modern 2026 manufacturing has introduced durable conductive plastics and cermet materials to extend lifecycle and precision.Figure 1: Potentiometer Basics and Modern ClassificationsⅡ. How are Potentiometers Classified?Potentiometers are primarily classified by their movement mechanism (Linear vs. Rotary) and their control method (Analog Mechanical vs. Digital). Understanding these distinctions is crucial for selecting components for 2026-era PCB designs.Table 1. Industry Standard Potentiometer Classifications (2026)Potentiometer TypeClassification Criteria & Modern StandardsBy Resistor MaterialElectrical performance relies on the track material. Common types include wire wound (high power), synthetic carbon film (consumer audio), metal glass glaze, and conductive plastic (high durability >1M cycles). Specialized types use metal foil or metal oxide film for precision aerospace applications.By Working Environment Selected based on IP ratings and stress factors: High-precision, high-resolution, high-power, or high-temperature variants. Modern sealed potentiometers are essential for automotive and outdoor IoT sensors.By Adjustable ResistanceIncludes fully adjustable (user interface), semi-adjustable (trimpots for calibration), and fine-adjustment types. Non-contact options (Hall Effect, Photo-electric) are gaining market share in 2026 to eliminate mechanical wear and "wiper noise."By Construction MechanicsRotary: Standard rotation is 270°–300°. Multi-turn: Uses a worm gear for 10-20 turns, vital for precision calibration.Linear Slider: Standard in audio mixing consoles for visual feedback of levels (faders). By Gang Number Single Gang: Controls one circuit.Dual/Ganged: Two pots on a single shaft, standard for stereo audio volume control to maintain channel balance.By Resistance Taper (Law)Linear (Type B): Resistance changes proportionally to angle. Used for voltage division.Logarithmic (Type A/Audio): Resistance changes logarithmically to match human hearing. Essential for volume controls.By Actuation MethodManual: Hand-turned knobs or sliders.Motorized: Equipped with a servo motor for remote control and "flying fader" automation in studio consoles. Ⅲ. Detailed Guide: Common Types & ApplicationsSelecting the right potentiometer requires understanding the trade-offs between mechanical endurance, noise levels, and precision.3.1 Breakdown of Key Potentiometer VarietiesRheostat (Variable Resistor)A rheostat functions strictly as a two-terminal variable resistor used to control current. While historically significant, in 2026, the term "rheostat" is considered legacy. Modern efficiency standards prefer PWM (Pulse Width Modulation) for current control over resistive rheostats, which dissipate excess energy as heat. However, they remain useful in simple educational circuits or rugged high-power calibration scenarios. Rotary PotentiometersThe rotary potentiometer is the most ubiquitous interface component. It features a resistive track (Carbon or Cermet) and a wiper connected to a rotating shaft. Key Specs: Typical tolerance is 10%-20%. Rotation is usually 270°. 2026 Applications: Smart home dial interfaces, car audio amplifiers, light dimmers (triac control), and older telecommunication equipment. Logarithmic (Audio) PotentiometersAlso known as "Audio Taper" pots. The resistance changes logarithmically to mirror the Weber-Fechner law of human hearing. At the start of rotation, resistance changes slowly; as the angle increases, the resistance shifts rapidly. This ensures that volume adjustments sound natural and linear to the human ear. Linear Potentiometers (Faders)In linear potentiometers (slide pots), the resistance varies directly with the physical distance the slider moves. They are indispensable in audio mixing consoles (EQ, Faders) because they provide immediate visual feedback of the setting. They are also used for precise voltage division in test equipment and battery internal resistance measurements. Digital Potentiometers (DigiPots)The 2026 Standard: Digital potentiometers are CMOS integrated circuits that replace mechanical wipers with digital switching networks. Controlled via protocols like I2C or SPI, they offer vibration immunity, zero mechanical wear, and programmable precision. Use Cases: Programmable gain amplifiers (PGAs), sensor calibration, LCD contrast control, and smart IoT devices where physical knobs are unnecessary. Membrane (Soft) PotentiometersConstructed by printing carbon/graphite onto a flexible substrate. When pressed, the top layer contacts the bottom resistive track. These are ultra-low profile and widely used in modern wearables, medical devices, and robotics tactile sensors. While they have lower accuracy than wirewound types, their form factor is unmatched for compact designs. Wirewound PotentiometersKnown for high power handling and thermal stability. A resistance wire is wrapped around an insulating core. Pros: High precision, high temperature tolerance. Cons: "Zipper noise" (resolution steps) and inductance issues at high frequencies. 3.2 Critical Application: Potentiometric Position SensorsPotentiometers remain one of the most cost-effective methods for measuring displacement in industrial machinery.3.2.1 Resistive Position SensorsThese function as passive transducers. By applying a stable reference voltage across the fixed terminals, the voltage at the wiper becomes directly proportional to the shaft's angle or linear position. They are widely used in joystick controls, valve positioning, and robotics joint feedback.Figure 2. Simple Position Sensor Circuit 3.2.2 Capacitive Position Sensors (Non-Contact Alternative)For environments where mechanical wear is a concern, capacitive sensors are the superior 2026 choice. They measure position by detecting changes in capacitance between a sensor plate and the target object. These are dominant in high-precision semiconductor manufacturing, touchscreens, and fluid level sensing where physical contact is impossible.Ⅳ. Best Practices: How to Use Potentiometers SafelyTo ensure longevity and signal integrity in your circuits, adhere to these maintenance and installation guidelines:Chemical Safety: Avoid exposing polycarbonate synthetic resin pots to ammonia, ketones, or high-acid chemicals, which degrade the housing.Flux Management: Do not use water-compatible fluxes. Poor quality soldering can lead to oxidation, causing "scratchy" audio or open circuits.Soldering Temp: Prevent heat damage. Pin terminals: 235°C ±5°C. Wire terminals: 350°C ±10°C. Keep solder >1.5mm from the body.Internal Contamination: Ensure no flux enters the internal mechanism during soldering to prevent contact noise.Voltage vs. Current: Potentiometers are designed for Voltage Division. Avoid using them as Rheostats (current limiters) for high loads, as the wiper contact resistance cannot handle high current.Moisture Control: Prevent condensation. In humid environments (like marine audio), use sealed or IP67-rated potentiometers.Mechanical Installation: Do not overtighten mounting nuts. For slide pots, ensure screw length doesn't penetrate the casing and jam the fader.Knob Assembly: Support the back of the shaft when pushing on knobs to prevent internal wiper collapse.Temperature Effects: Lubricant viscosity changes with temperature. For sub-zero applications, specify low-temperature grease to maintain smooth rotation.Signal Interference: Keep shafts/sliders short to minimize acting as an antenna for EMI (Electromagnetic Interference).Thermal Derating: Carbon film power ratings drop above 70°C. Ensure adequate ventilation. Ⅴ. Advanced FAQs and Industry Trends5.1 What are the primary potentiometer types?The industry divides them into Linear (Slide) and Rotary types. A third category, Digital Potentiometers (DigiPots), is now standard for automated systems, while Membrane "Soft Pots" serve ultra-thin form factors.5.2 Quick-Fire FAQsFrequently Asked Questions (2026 Updated)1. What is the main function of a potentiometer?It acts as a variable voltage divider to measure EMF, control volume/gain, or sense position. In 2026, it is also a key component in Human-Machine Interfaces (HMI). 2. What are the top 3 modern applications?User Interface: Volume and tone control in audio gear.Robotics: Position feedback servos (servo motors).Industrial: Linear displacement sensors in injection molding machines. 3. How does a potentiometer differ from a rotary encoder?Potentiometers are absolute position sensors (they know where they are on power-up) but have limited rotation. Encoders are digital, have infinite rotation, but typically require homing (calibration) on startup. 4. Why do audio pots use a logarithmic taper?Because human hearing is non-linear. A logarithmic taper matches the ear's sensitivity, creating a smooth perceived increase in volume.{ "@context": "https://schema.org", "@type": "TechArticle", "headline": "Potentiometer Ultimate Guide 2026: Types, Applications, and Selection", "datePublished": "2020-06-08", "dateModified": "2026-01-09", "description": "A comprehensive engineering guide to Potentiometers in 2026. Covers Linear vs Rotary, Digital Potentiometers, wiring diagrams, and maintenance tips for modern electronics.", "articleBody": "A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider...", "mainEntity": { "@type": "FAQPage", "mainEntity": [ { "@type": "Question", "name": "What are the main types of potentiometers?", "acceptedAnswer": { "@type": "Answer", "text": "The three main categories are Rotary Potentiometers (knobs), Linear Potentiometers (sliders/faders), and Digital Potentiometers (DigiPots) which use ICs for control." } }, { "@type": "Question", "name": "What is the difference between a potentiometer and a rheostat?", "acceptedAnswer": { "@type": "Answer", "text": "A potentiometer uses three terminals to divide voltage. A rheostat uses only two terminals (one fixed, one wiper) to restrict current. Modern circuits prefer potentiometers or PWM over rheostats for efficiency." } }, { "@type": "Question", "name": "Where are potentiometers used in 2026?", "acceptedAnswer": { "@type": "Answer", "text": "They are used in audio volume controls, robotic arm position sensing, industrial joystick controls, and as digital calibration trimmers in IoT devices." } } ] }}

I IntroductionA capacitor is an electronic component composed of an insulator between two conductors, like a sandwich. We can understand it as a container that holds the electric charge. In actual capacitors, two conductors are filled with an insulating dielectric. There are numerous types of dielectrics, so the types of capacitors formed are also different. For example, according to dielectric materials, capacitors can be divided into gas dielectric capacitors, liquid dielectric capacitors, inorganic solid dielectric capacitors, and organic solid dielectric capacitors; according to polarity, they can be divided into polarized capacitors and non-polarized capacitors. This article will introduce the various types of capacitors in detail and some additional basic knowledge of them, mainly explaining from the perspective of the manufacturing process and structure.Capacitors: types, use and testing. CatalogI IntroductionII The Basic Principle of CapacitorsIII Film Capacitor  3.1 Metal Foil Film Capacitor  3.2 Metallized Film CapacitorIV Electrolytic Capacitor  4.1 Aluminum Electrolytic Capacitors  4.2 Tantalum Electrolytic Capacitors  4.3 Niobium Electrolytic CapacitorsV Ceramic Capacitor  5.1 Ceramic Disc Capacitor  5.2 Multi-layer Ceramic Capacitor  5.3 Monolithic Capacitors  5.4 Classification of Ceramic MediaVI SupercapacitorVII Fixed, Trimmer and Variable Capacitors  7.1 Mica Capacitor  7.2 Paper Capacitor  7.3 Trimmer Capacitor  7.4 Variable CapacitorVIII Comparison of Polarized Capacitors and Non-polarized Capacitors  8.1 Medium  8.2 Performance  8.3 Capacity  8.4 Structure  8.5 Application Environments and UseIX Axial and Radial Leaded CapacitorsX A Quiz About Capacitor TypesⅪ FAQII The Basic Principle of CapacitorsCapacitors, along with inductors and resistors, are the three basic passive devices in electronics. The function of the capacitor is to store electrical energy in the form of electric field energy.Taking the parallel plate capacitor as an example, we briefly introduce the basic principle of capacitance.Figure1. Parallel Plate CapacitorAs shown in the figure above, a DC voltage is applied to two metal plates that are close to each other and are parallel to each other (the dielectric between the plates). After stabilization, the metal plate connected to the positive electrode of the voltage will exhibit a certain amount of positive charge, while the metal plate connected to the negative electrode of the voltage will exhibit an equal amount of negative charge. In this way, an electrostatic field is formed between the two metal plates, so the capacitor stores electrical energy in the form of electric field energy, and the stored charge is Q. The amount of charge stored in the capacitor Q is related to the voltage U and its own property (that is, the capacitance value C), that is, Q=U*C. According to the theoretical derivation, the capacitance formula of the parallel plate capacitor is as follows:In this formula:C is the capacitance value, the unit is F (Farad)ε is the dielectric constant of the medium, F/mS is the area of the metal flat plate, m²d is the distance between metal plates, mThe ideal capacitor contains a dielectric, and there is no free charge, so it is impossible to produce charge movement, which is the current.  How does the ideal capacitor pass AC power? AC PowerVoltage can form an electric field inside the capacitor, and alternating voltage will produce an alternating electric field. According to the law of full current in Maxwell's equations:This means that either a current or a changing electric field can generate a magnetic field. Maxwell defines ε(∂E/∂t) as a displacement current, which is an equivalent current and represents the change of the electric field. (The current here represents the current density, or J)Let the AC voltage change sinusoidally, ie:The actual displacement current is equal to the current density times the area:Therefore, the capacitive reactance of the capacitor is 1/ωC. When the frequency is high, the capacitive reactance will be very small, which means passing the high frequency. DC BlockingThe DC voltage does not change with time, the displacement current ε(∂E/∂t) is 0, and the DC component cannot pass through.The characteristics of actual capacitors are non-ideal and have some parasitic effects; therefore, a more complicated model is needed to represent the actual capacitors. The commonly used equivalent model is as follow:Figure2. Equivalent ModelSince the medium is not absolutely insulated, there is a certain conductivity; therefore, any capacitor has a leakage current, expressed by the equivalent resistance Rleak;The conductors and electrodes of the capacitor have a certain resistivity, and there is a certain dielectric loss of the dielectric; these losses are uniformly expressed as the equivalent series resistance ESR;There is a certain inductance in the conductor of the capacitor, which has a greater impact at high frequencies, expressed as the equivalent series inductance ESL;In addition, there is a certain hysteresis in any medium, that is, after the capacitor is quickly discharged, the voltage is suddenly disconnected, and the capacitor will recover part of the charge, which is represented by a series RC circuit（Related post: LC circuit）.Most of the time, the main concern is the ESR and ESL of the capacitor. Quality FactorAs with inductors, the quality factor of the capacitor can be defined, which is the Q value, which is the ratio of the stored power of the capacitor to the power loss:Qc=(1/ωC)/ESRThe Q value is a relatively important parameter for high-frequency capacitance. Self-Resonance FrequencyBecause of the existence of ESL, a resonant circuit is formed together with C, and its resonant frequency is the self-resonant frequency of the capacitor. Before the self-resonant frequency, the impedance of the capacitor becomes smaller as the frequency increases; after the self-resonant frequency, the impedance of the capacitor becomes smaller as the frequency increases, which is inductive. As shown in the following figure:Figure3. Self-Resonance FrequencyAccording to the capacitance formula, in addition to the size of the capacitor, the size of the capacitance is related to the Permittivity of the dielectric. The performance of the dielectric affects that of the capacitor, and different media are suitable for different manufacturing processes.Capacitors can be divided into three main categories according to the manufacturing process: Film Capacitor Electrolytic Capacitor Ceramic CapacitorIII Film CapacitorFilm capacitors are made by winding two plastic films with metal electrodes into a cylindrical shape, and finally encapsulated; because its medium is usually plastic material, also known as plastic film capacitors. Its internal structure is rough as shown in the following figure:Figure4. The Structure of Film CapacitorFilm capacitors can be divided into two categories according to the manufacturing process of their electrodes:3.1 Metal Foil Film Capacitor For metal foil film capacitors, a thin metal foil, usually aluminum foil, is directly added to the plastic film as an electrode. This process is relatively simple, the electrode is easy to lead out, and can be applied to large current occasions.3.2 Metallized Film CapacitorMetalized film capacitors form a thin metal surface directly on the surface of the plastic film by vacuum deposition process as an electrode. Because the thickness of the electrode is very thin, it can be wound into a capacitor with a larger capacity. However, due to the thickness of the electrode, it is only suitable for small current applications.Figure5. Metallized Film ConstructionThe metalized film capacitor has the function of self-repair, that is, if there is a breakdown point inside the capacitor, an avalanche effect will occur at the damaged place, and the vaporized metal will form a vaporized assembly surface at the damaged place, the short circuit disappears, and the damaged point is repaired. Therefore, the reliability of the metalized thin film capacitor is very high, and will not fail due to a short circuit. There are two winding methods for film capacitors:Inductive winding method Before winding, the lead has been connected with the internal electrode.After the non-inductive winding method, gold plating and other processes are used to connect the internal electrodes of the two end surfaces into one surface, so that a smaller ESL can be obtained, and the high frequency performance should be higher.In addition, there is a laminated type non-inductive capacitor, the structure is similar to MLCC, the performance is better, and it is easy to make SMD package.Figure6. Winding MethodsThe characteristic of the film capacitor is that it can achieve large capacity and high withstand voltage. However, due to process reasons, its size is difficult to be small, and it is usually used in strong electric circuits, such as the power electronics industry.Figure7. Winding MethodsIV Electrolytic CapacitorElectrolytic capacitors use metal as an anode, and form a metal oxide film on the surface as a medium, and then wet or solid electrolyte and metal as a cathode. Electrolytic capacitors are mostly polarized. If the metal on the cathode side also has an oxide film, it is a non-polarized electrolytic capacitor.Depending on the metal used, there are three types of electrolytic capacitors:4.1 Aluminum Electrolytic CapacitorsAluminum electrolytic capacitors should be the most widely used electrolytic capacitors and the cheapest. Its basic structure is shown in the following figure:Figure8. The Structure of Aluminum Electrolytic CapacitorThe manufacturing process of aluminum electrolytic capacitors is roughly as follows:First, the aluminum foil will form a very rough surface by electroetching process, which increases the surface area of the electrode and can increase the capacitance;The anode is oxidized by a chemical method to form an oxide layer as a medium;Then, a layer of electrolytic paper is added between the anode aluminum foil and the cathode aluminum foil as a separator, and is pressed and wound;Finally, fill the electrolyte, the electrolytic paper will absorb the electrolyte, and the package is molded.Wet aluminum electrolytic capacitors using electrolyte are the most widely used, with the advantages of large capacitance, high rated voltage, and low cost. The disadvantages are also obvious, that is, shorter life, poor temperature characteristics, and larger ESR and ESL. For hardware development, it is necessary to avoid over-design. In the case of meeting performance requirements, cheap is the biggest advantage.Recommendation: How to Test Aluminum Electrolytic Capacitors4.2 Tantalum Electrolytic CapacitorsThe most widely used tantalum electrolytic capacitor should use manganese dioxide as a solid electrolyte. The internal structure of the solid tantalum electrolytic capacitor is rough as shown in the figure below:Figure9. The Internal Structure of the Solid Tantalum Electrolytic CapacitorCompared with aluminum electrolytic capacitors, the dielectric constant of tantalum oxide (tantalum pentoxide) is much higher than that of aluminum oxide (aluminum oxide). With the same volume, the capacity of tantalum capacitors is larger than that of aluminum electrolytic capacitors. Tantalum capacitors have a longer life and more stable electrical performance.Figure10. The Internal Structure of the Solid Tantalum Electrolytic CapacitorTantalum capacitors also use conductive polymer as electrolyte, the structure is similar to the manganese dioxide tantalum capacitor in the above figure, which is to replace manganese dioxide with a conductive polymer. Conductive polymers have higher conductivity than manganese dioxide, so ESR will be lower. In addition, there are wet tantalum capacitors, which are characterized by super large capacity, high withstand voltage, and low DC leakage current, which is mainly used in military and aerospace fields.Figure11. Wet Tantalum Capacitors4.3 Niobium Electrolytic CapacitorsNiobium electrolytic capacitors are similar to tantalum electrolytic capacitors, in that niobium and its oxides replace tantalum. The dielectric constant of niobium oxide (niobium pentoxide) is higher than that of tantalum oxide (tantalum pentoxide). The performance of niobium capacitors is more stable and more reliable.V Ceramic CapacitorCeramic capacitors use ceramic materials as dielectric materials. There are many types of ceramic materials with different dielectric constants and stability, which are suitable for different occasions.Ceramic capacitors mainly include the following:5.1 Ceramic Disc CapacitorThe main advantage of the ceramic capacitor is that it can withstand high voltage, and it is usually used as a safety capacitor, which can withstand 250V AC voltage. Its appearance and structure are shown below:Figure12. The Structure of Ceramic Disc Capacitor5.2 Multi-layer Ceramic CapacitorMulti-layer ceramic capacitors, that is, MLCCs, chip multi-layer ceramic capacitors are currently the most widely used capacitor types in the world. Their standardized packaging and small size are suitable for automated high-density chip production.The internal structure of the multilayer ceramic capacitor is shown below:Figure13. Internal Structure of Chip Multilayer Ceramic Capacitor5.3 Monolithic CapacitorsBecause multilayer ceramics need to be sintered and porcelainized to form an integrated structure, the multilayer ceramic capacitors in lead packages are also called monolithic capacitors.The structure of monolithic capacitors is that several ceramic film blanks are covered with electrode paddle material, and after being laminated, they are wound into an inseparable whole at a time, and the outside is encapsulated with resin.Monolithic capacitors are a new type of capacitors with small volume, large capacity, high reliability and high-temperature resistance. Low-frequency monolithic capacitors with high dielectric constant also have stable performance and are actively small.5.4 Classification of Ceramic MediaAccording to EIA-198-1F-2002, ceramic media are mainly divided into four categories:Class I: Ceramic medium with temperature compensation characteristics, the dielectric constant is mostly low, not more than 200. It is usually a paraelectric medium. Under temperature, frequency and bias voltage, the dielectric constant is relatively stable and the change is small. The loss is also very low, the dissipation factor is less than 0.01.Figure14. Coding of Class 1 Capacitors According to EIA SpecificationThe most stable and most used is the C0G capacitor, or NP0. NP0 is the code name for the IEC/EN 60384-1 standard as Negative Positive Zero, using N and P for Positive and Negative deviations.Due to the low dielectric constant, the capacitance value of C0G capacitor is small and can be up to 0.1uF. The 0402 package usually has a maximum of 1000pF. Class II, III: Among them, the temperature characteristic A-S belongs to Class II, and the dielectric constant is about several thousand. The temperature characteristic T-V belongs to Class III, and the dielectric constant can be as high as 20000. It can be seen that the performance of Class III is more unstable. According to the classification of IEC, both Class II and III belong to the second category, high dielectric constant media. For example, X5R and X7R are Class II capacitors, which are widely used in power supply decoupling, while Y5V belongs to Class III capacitors, and their performance is not stable.Figure15. EIA Coding of Class 2 and 3 CapacitorsThe capacitance value of Class II and III capacitors can be up to several hundred uF, but due to the high dielectric constant medium, most of them are ferroelectric medium (Ferroelectric), and the temperature stability is poor. In addition, the dielectric constant of ferroelectric media will decrease under DC bias voltage. Class IV: The manufacturing process is different from the usual ceramic materials. The internal ceramic particles are all a thin oxide layer on the outside, and the core is a conductor. This type of capacitor has a large capacity but a small breakdown voltage. Due to the unstable performance and high loss of these capacitors, they have been basically eliminated.VI SupercapacitorSupercapacitor refers to a new type of energy storage device between a traditional capacitor and a rechargeable battery. There are two ways to store charge: EDLC and pseudocapacitance. It not only has the characteristics of rapid charge and discharge of the capacitor but also has the energy storage characteristics of the battery. The capacity of the supercapacitor is particularly large. It can replace the battery as a power supply device, and can also be used in conjunction with the battery. Supercapacitors charge fast, can be fully charged and discharged, and can be charged to any desired voltage, as long as the rated voltage is not exceeded. There are many applications of supercapacitors, for example, many cities in China have supercapacitor electric buses. There are also applications in some electronic products, such as some driving recorders, which can continue to supply power for several days.Figure16. SupercapacitorsVII Fixed, Trimmer and Variable CapacitorsA capacitor with a fixed capacitance is called a fixed capacitor. According to the different media can be divided into ceramics, mica, paper, film, electrolysis. Having described film capacitors, electrolytic capacitors, and ceramic capacitors, let's look at the other two types of fixed capacitors.  7.1 Mica CapacitorMica capacitors can be divided into foil type and silver type. Silver electroplating is very direct on mica sheets by vacuum evaporation or sintering method. Due to the elimination of the air gap, the temperature coefficient is greatly reduced and the capacitance stability is higher than foil type. Mica capacitors are widely used in high-frequency electrical appliances and can be used as standard capacitors. The glaze capacitor is made of a special mixture with a concentration suitable for spraying into a film. The medium is then sintered with a silver layer electrode to form a "monolithic" structure. Glass glaze capacitor is comparable to a mica capacitor in performance and can withstand various climates. It can generally work at 200℃ or higher, with rated working voltage up to 500 V and loss tan = 0.0005 ~ 0.008.Figure17. Silver Mica Capacitors7.2 Paper CapacitorPaper capacitors are widely used in radio and electronic equipment. Generally, two aluminum foils are used as electrodes, which are separated by overlapping winding of capacitor paper with a thickness of 0.008 ~ 0.012 mm. Simple manufacturing process, low price, can obtain a large capacitance, generally below 0.25 F, but the capacity error is large and difficult to control, good quality is ±10%, loss (tan ≤ 0.015), temperature and frequency characteristic stability is poor. The paper capacitors commonly used in the past are non-sealed, impregnated only with ground wax, paraffin wax and chlorinated diphenyl, etc., which are prone to aging and poor stability. They are easily affected by humidity, insulation resistance decreases after being affected by moisture, and atmospheric pressure also affects them. The paper capacitor whose core is sealed inside the metal or ceramic tube is of good quality and has little influence on the external climatic conditions. It can be normally used in the situation with the relative humidity up to 95 ~ 98 %. The electrode of metalized paper capacitor uses vacuum evaporation to directly attach the metal to the capacitor paper, which is only about 1/4 of the volume of the ordinary paper capacitor. Its main feature is its "self-recovery" function, that is, it can be "self-healing" after a breakdown. It is an improved type of paper capacitor. Oil-immersed capacitors have a higher voltage than ordinary paper capacitors, good stability, suitable for high-voltage circuits.Paper capacitors are intermediate frequency capacitors, which are generally used in low-frequency circuits and usually cannot be used in frequencies higher than 3 ~ 4 MHz.Figure18. Paper Capacitor7.3 Trimmer CapacitorTrimmer capacitors, also called semi-variable capacitors, have a capacitance that can be adjusted within a small range and fixed to a certain capacitance value after adjustment.Ceramic trimmer capacitors are of high quality and small size, and can usually be divided into two types: round tube type and round chip type.Trimmer capacitors for mica and polystyrene media are usually of spring-loaded structure, which is simple in structure but less stable.The wire-wound porcelain trimmer capacitor is used to change the capacitance by removing the copper wire (external electrode), so the capacitance can only be reduced and is not suitable for repeated debugging.7.4 Variable CapacitorAs the name implies, a variable capacitor means that the capacitance value can vary over a large range and can be determined to a certain value. Variable capacitors are divided into two forms: film medium and air medium. It is commonly used in coupling and tuning circuits, such as double capacitors, ceramic capacitors and so on.VIII Comparison of Polarized Capacitors and Non-polarized Capacitors8.1 MediumWhat is the medium? To put it bluntly, is the substance between the two plates of the capacitor. Most polarized capacitors use an electrolyte as the dielectric material. Generally, capacitors of the same volume have large polar capacitance. In addition, different electrolytic materials and processes produce polarized capacitors of the same volume. Furthermore, pressure resistance is also closely related to the use of dielectric materials. There are likewise many non-polarized capacitor dielectric materials, most of which use metal oxide film and polyester. Because the reversible or irreversible performance of the medium determines the use environment of polarized and non-polarized capacitors.8.2 PerformancePerformance is the requirement for use, and maximum demand is the requirement for use. If the metal oxide film capacitor is used for filtering in the power supply part of the TV, the capacitor capacity and withstand voltage required by the filtering must be achieved. Maybe only a power supply can be installed in this case. Therefore, only polarized capacitors can be utilized for filtering, and these capacitors are irreversible. In other words, the positive electrode must be connected to the high potential end, and the negative electrode must be connected to the low potential end. Generally, the electrolytic capacitor is above 1 microfarad for coupling, decoupling, power supply filtering, etc. Non-polarized capacitors are mostly below 1 microfarad, participating in resonance, coupling, frequency selection, current limiting, etc. Of course, there are also large-capacity and high-pressure-resistant ones, which are mostly used for reactive power compensation of electric power, phase shifting of motors, and frequency shifting power supply. There are many types of non-polarized capacitors, so this article won’t go into detail.Figure19. Classification of Capacitors8.3 CapacityAs mentioned earlier, the electrical media of the same volume are different, so the capacity is not equal.8.4 StructureIn principle, any shape capacitors can be used in the environment without considering the tip discharge. The electrolytic capacitors (polarized capacitors) that are usually used are round, and the square ones are rarely utilized. The shape of non-polarized capacitors varies. Like tube shape, deformed rectangle, sheet shape, square shape,combined square shape and round shape, etc., see where it is used. Of course, there are invisible. Intangible here refers to distributed capacitance. The distributed capacitance must not be ignored in high-neck and intermediate-frequency devices.8.5 Application Environments and UseIn the repair of home appliances, all of the above may be found. If you want to understand in a simple way, you have to find out by yourself.Because of the relationship between its internal materials and construction, the capacity of polarized capacitors (such as aluminum electrolysis) can be very large, but its high-frequency characteristics are not good, so it is suitable for power supply filtering and other occasions, but there are also good high-frequency characteristics. Polarized capacitor-tantalum electrolysis, its price is relatively high; Non-polarized capacitors are small in size, low in price, and satisfactory in high-frequency characteristics, but they are not suitable for large capacity. Like ceramic capacitors, monolithic capacitors, and polyethylene (CBB) capacitors, ceramic capacitors are generally used in high-frequency filtering and oscillation circuits.Figure20. Axial and Radial Type ConstructionIX Axial and Radial Leaded CapacitorsOne method of packaging capacitors is the lead structure. 　　Axial capacitance refers to the capacitance of the two pole leads on the same axis. Generally, it is a non-inductive structure. It is made of metalized polyester film as the dielectric/electrode. The wire is tinned copper clad steel wire (or flexible wire), the outer layer is wrapped with polyester tape, and both ends are sealed with epoxy resin.Figure21. Axial Lead StructureAxial leads (the leads are on the same plane as the capacitor axis) are radial leads. The figure below shows an example of a radial lead. The lead is in the radial position of the capacitor. Critical dimensions are lead spacing "S", height "H", length "L" and thickness "P'. Because they are inserted on the printed circuit board rather than on the surface of the circuit board like surface mount components, axial And radial elements are collectively referred to as "plug-in elements".Figure22. Radial Lead StructureX A Quiz About Capacitor TypesQuestion:The capacitors which use chemical reactions to store charge are calledA.ceramic capacitorsB.fixed capacitorsC.parallel plate capacitorsD.electrolytic capacitorsAnswer:D Ⅺ FAQ1. How do you identify a capacitor?Ceramic types of capacitors generally have a 3-digit code printed onto their body to identify their capacitance value in pico-farads. Generally, the first two digits indicate the value of the capacitor and the third digit indicates the number of zero's to be added. 2. What are the 2 types of capacitors?Capacitors are divided into two mechanical groups: Fixed capacitors with fixed capacitance values and variable capacitors with variable (trimmer) or adjustable (tunable) capacitance values. The most important group is the fixed capacitors. Many got their names from the dielectric. 3. Can a 440v capacitor be used for a 230v application?The 440 volts listed on the cap is the maximum allowable voltage the capacitor can handle. You could actually use a 370-volt cap on 230 volts. ... Capacitor is connected in series with the auxiliary winding of the motor. Since winding is inductive, the voltage across the capacitor is much higher than the supply voltage. 4. What side of the capacitor is positive?Electrolytic capacitors have positive and negative sides. To tell which side is which, look for a large stripe or a minus sign (or both) on one side of the capacitor. The lead closest to that stripe or minus sign is the negative lead, and the other lead (which is unlabeled) is the positive lead. 5. What does 50 uF mean on a capacitor?It's a symbol that means micro so 50 μF means 50 microfarads or 000050 Farads. The farad is such a large unit that the microfarad is the practical unit for capacitance. 6. What are capacitors in parallel called?When capacitors are connected in parallel, the total capacitance is the sum of the individual capacitors' capacitances. If two or more capacitors are connected in parallel, the overall effect is that of a single equivalent capacitor having the sum total of the plate areas of the individual capacitors. 7. Are AC and DC capacitors interchangeable?You can use AC caps on DC. AC caps have a much higher DC rating. All capacitors have microscopic air bubbles between the foil layers. DC is just a special case where the polarity of the voltage does not change, so you can use AC capacitors - as is - in a DC application. 8. Which type of capacitor is polarized?The only type of capacitor that is polarized (works differently depending on which way the current is flowing) is the electrolytic capacitor. Electrolytic capacitors have higher capacitance, but for most purposes, the non-polarized capacitor is preferred. 9. What is the main function of the capacitor?A capacitor is an electronic component that stores and releases electricity in a circuit. It also passes alternating current without passing direct current. A capacitor is an indispensable part of electronic equipment and is thus almost invariably used in an electronic circuit. 10. What happens if you use the wrong size capacitor?If the wrong run capacitor is installed, the motor will not have an even magnetic field. This will cause the rotor to hesitate at those spots that are uneven. This hesitation will cause the motor to become noisy, increase energy consumption, cause performance to drop, and cause the motor to overheat. 

I IntroductionThe light-emitting diode is a commonly used light-emitting device, which emits energy through the recombination of electrons and holes. It is widely used in the field of lighting. Light-emitting diodes can efficiently convert electrical energy into light energy. Light-emitting diodes have a wide range of uses in modern society, such as lighting, flat panel displays, and medical devices.Light Emitting Diode (LED) Working PrincipleThis kind of electronic component appeared as early as 1962. In the early days, it could only emit low brightness red light. Later, other versions of monochromatic light were developed. The light that can be emitted today has spread to visible light, infrared light, and ultraviolet light. Initially,  the light-emitting diodes were used as indicator lights, display panels, etc. With the continuous progress of technology, light-emitting diodes have been widely used in displays and lighting.CatalogI IntroductionII Parameters of Light-emitting Diode2.1 Significance of Limit Parameters2.2 Significance of Electrical ParametersIII Working Principle of Light-emitting DiodeIV Types of Light-emitting DiodeV Materials of a Light-emitting Diode5.1 Wafer5.2 Bracket5.3 Silver glue 5.4 Gold wire 5.5 Epoxy resinVI Applications of Light-emitting Diode6.1 Display Screen and Communication Signal Display6.2 Automotive Industry6.3 LCD Backlight6.4 LED Lighting6.5 Other ApplicationsVII Trends of LED Lighting TechnologyII Parameters of Light-emitting Diode2.1 Significance of Limit Parameters(1) Allowable power consumption Pm: the maximum value of the product of the forward DC voltage applied to both ends of the LED and the current flowing through it. If this value is exceeded, the LED becomes hot and damaged.(2) Maximum forward DC current IFm: the maximum forward DC current allowed to be added. Exceeding this value can damage the diode.(3) Maximum reverse voltage VRm: the maximum reverse voltage allowed to be applied. Above this value, the light-emitting diode may be damaged by the breakdown.(4) Working environment topm: the ambient temperature range where the LED can work normally. Below or above this temperature range, the light-emitting diode will not work properly and the efficiency is greatly reduced.2.2 Significance of Electrical Parameters(1) Spectral distribution and peak wavelength: the light emitted by a certain light-emitting diode is not a single wavelength, and its wavelength is generally shown in Figure.Figure 1. Spectral Distribution and Peak WavelengthIt can be seen from the figure that the light intensity of a certain wavelength λ0 in the light emitted by the light-emitting tube is the largest, and this wavelength is the peak wavelength.(2) Luminous intensity IV: The luminous intensity of the light-emitting diode usually refers to the luminous intensity in the direction of the normal. When the radiation intensity in this direction is (1/683) W / sr, it emits 1 candela (symbol cd). Since the general LED has a low luminous intensity, the luminous intensity is usually measured in candela (mcd).(3) Spectral half-width Δλ: It represents the spectral purity of the light-emitting tube. It refers to the interval between the two wavelengths corresponding to the 1/2 peak light intensity in Figure 3.(4) Half value angle θ1 / 2 and viewing angle: θ1 / 2 refers to the angle between the direction in which the luminous intensity value is half of the axial intensity value and the luminous axis (normal direction).Two times the half-value angle is the viewing angle (or half-power angle).Figure 2. Angle Distribution of Luminous Intensity of the LEDFigure above shows the angular distribution of the luminous intensity of two different types of LEDs. The coordinates of the perpendicular (normal) AO are the relative luminous intensity (ie, the ratio of the luminous intensity to the maximum luminous intensity). Obviously, the relative luminous intensity in the normal direction is 1. The larger the angle away from the normal direction, the smaller the relative luminous intensity. From this graph, the half-value angle or viewing angle value can be obtained.(5) Forward working current If: It refers to the forward current value when the light-emitting diode is normally emitting light. In actual use, the IF should be selected below 0.6·IFm.(6) Forward working voltage VF: The working voltage given in the parameter table is obtained under a given forward current. Generally measured at IF = 20mA. The forward working voltage VF of the light-emitting diode is 1.4 ~ 3V. When the outside temperature increases, VF will decrease.(7) V-I characteristics: The relationship between the voltage and current of the light-emitting diode can be represented in the figure below.Figure 3. The Relationship between the Voltage and Current of the LEDWhen the forward voltage is less than a certain value (called a threshold), the current is extremely small and does not emit light. When the voltage exceeds a certain value, the forward current increases rapidly with the voltage and emits light. From the V-I curve, parameters such as the forward voltage, reverse current, and reverse voltage of the light-emitting tube can be obtained. The forward leakage current IR of the LED tube is less than 10μA.III Working Principle of Light-emitting DiodeThe core part of the light-emitting diode is a wafer composed of a P-type semiconductor and an N-type semiconductor. There is a transition layer between the P-type semiconductor and the N-type semiconductor, called a PN junction. In the PN junction of some semiconductor materials, the injected minority carriers and majority carriers will release excess energy. The energy is in the form of light, thereby directly converting electrical energy into light energy. The reverse voltage is added to the PN junction. Minority carriers are difficult to inject, so they do not emit light. This kind of diode is called a light-emitting diode, commonly known as LED. When it is in the forward working state (that is, the forward voltage is applied to both ends), and when the current flows from the anode to the cathode of the LED, the semiconductor crystal emits light of different colors from ultraviolet to infrared. The intensity of the light is related to the current.The principle of light-emitting diode needs to be analyzed from the following three situations:When no voltage is applied across the diode, the electrons in the N-type material will move along the PN junction between the layers. The electrons fill the holes in the P-type material and form a depletion region. In the depletion region, the semiconductor material returns to its original insulation state. That is, all holes are filled, so there is neither free electrons nor space for electrons to move in the depletion region, and the charge cannot flow.Figure 4. No Voltage is Applied Across the DiodeWhen a forward voltage is applied to the light-emitting diode, the holes injected from the P region to the N region. And the electrons injected from the N region into the P region within a few microns near the PN junction. They recombine with electrons in the N region and holes in the P region respectively. Therefore, they produce spontaneously emitted fluorescence. Different semiconductor materials have different energy states for electrons and holes. The more energy released, the shorter the wavelength of the emitted light. Diodes that emit red, green, or yellow light are commonly used.Figure 5. Apply a Forward Voltage to the LEDWhen a reverse voltage is applied to the light-emitting diode, the P-type terminal is connected to the negative electrode of the circuit, and the N-type terminal is connected to the positive electrode. And the current will not flow. Negatively charged electrons in N-type materials will be attracted to the positive electrode. Positively charged holes in P-type materials will be attracted to the negative electrode. Since holes and electrons move in the wrong direction. No current will flow through the PN junction, and the depletion region will also expand.Figure 6. Apply a Reverse Voltage to the LED LED materialColorAlGaAs GaAsP AlGaInP GaP:ZnOred and infrared InGaN/GaN GaP AlGaInP AlGaPgreenGaAsPAlGaInP AlGaInP GaPhigh brightness orange red, orange, yellow, greenGaAsPred, orange, yellowGaP ZnSe InGaN SiCred, yellow, greenGaNgreen, emerald green, blueInGaNnear ultraviolet, blue green, blueSiCblueSiblueAl2O3blueZnSeblueCultravioletAlN AlGaNUV with wavelengths far to nearTable: Inorganic Semiconductor Materials Used in Light-emitting Diodes and the Colors They EmitIV Types of Light-emitting DiodeThere are various types of light-emitting diodes according to different aspects. According to the materials used, there are gallium phosphide (GaP) light-emitting diodes, phosphorous gallium arsenide (GaAsP) light-emitting diodes, gallium arsenide (GaAs) light-emitting diodes, phosphorous indium gallium arsenide (GaAsInP) light-emitting diodes and gallium arsenide aluminide (GaAlAs) light-emitting diodes.According to its packaging structure and packaging form, there are metal packaging, ceramic packaging, plastic packaging, resin packaging, and leadless surface packaging. It can also be divided into additive color scattering package (D), colorless scattering package (W), colored transparent packaging (C), and colorless transparent packaging (T).Figure 7. Kinds of Light-emitting DiodeAccording to its package shape, it can be divided into circular, square, rectangular, triangular, and combined shapes. The figure shows the shape of several light-emitting diodes.Plastic light-emitting diodes are divided into red, amber, yellow, orange, light blue, green, black, white, transparent, and colorless according to the color of the tube body. The outer diameter of the round light-emitting diode is from ￠ 2 to ￠ 20mm. According to the light-emitting color of the light-emitting diodes, it can also be colored light and infrared light. Colored lights include red light, yellow light, orange light, green light, and so on. In addition, light-emitting diodes can be divided into ordinary monochrome light-emitting diodes, high-brightness light-emitting diodes, ultra-high-brightness light-emitting diodes, color-changing light-emitting diodes, flashing light-emitting diodes, voltage-controlled light-emitting diodes, infrared light-emitting diodes, and negative resistance light-emitting diodes.V Materials of a Light-emitting DiodeWafer, bracket, silver glue, gold wire, and epoxy resin are the five LED raw materials of light-emitting diode5.1 WaferThe structure of the wafer: it consists of a gold pad, P-pole, N-pole, PN junction, and a back gold layer (the double-pad wafer has no back gold layer). The wafer is composed of P-layer semiconductor elements and N-layer semiconductor elements. They are rearranged and combined by electron movement. It is this change that enables the wafer to be in a relatively stable state. When the positive electrode is applied to the wafer with a certain voltage, the holes in the positive P region will continue to swim toward the N region. And the electrons in the N region will move to the P region relative to the holes. While the electrons and holes move relatively, the electron holes pair with each other, exciting photons and generating light energy.The main classification of wafer: surface-emitting type: most of the light is emitted from the surface of the wafer. Five-sided light-emitting type: there is more light emitted on the surface and side.5.2 BracketThe structure of the bracket is 1 layer of iron, 1 layer of copper (good conductivity, fast heat dissipation), 1 layer of nickel (anti-oxidation), 1 layer of silver (good reflectivity, easy to solder wire)5.3 Silver glue Take H20E as an example. Silver glue is also called white glue, milky white. The role of silver glue is to conduct and bond materials (baking temperature: 100°C / 1.5H). Storage conditions: Silver glue manufacturers generally store silver glue at -40°C, and application units generally at -5°C. Single-agent is 25°C / 1 year (dry, ventilated place), mixed agent 25°C / 72 hours. Baking conditions: 150°C / 1.5H. Stirring conditions: Mix for 15 minutes in one direction.5.4 Gold wire Take φ1.0mil as an example. The gold wires used for LEDs are φ1.0mil and φ1.2mil. The material of the gold wire is generally 99.9% of the gold content of the gold wire for LED. The purpose of the gold wire: with its characteristics such as high gold content, soft, easy to deform, good conductivity and good heat dissipation, a closed circuit is formed between the wafer and the bracket. (Conversion relationship: 1 mil = 0.0254mm, 1 in = 25.4mm)5.5 Epoxy Resin Ttake EP400 as an example. Composition: A and B two parts: Glue A: it is the main agent, which consists of epoxy resin + defoamer + heat resistance agent + thinner. Agent B: it is a curing agent, consisting of acid, mold release agent, and accelerator.VI Applications of Light-emitting Diode6.1 Display Screen and Communication Signal DisplayLED lamp has the characteristics of shock resistance, fast light response, power-saving, and long life, etc. It is widely used in various indoor and outdoor displays. It is divided into full-color, three-color, and monochrome displays that are developed and produced by more than 100 units nationwide. Traffic lights mainly use ultra-high-brightness red, green, and yellow LEDs. Because LED lights are energy-saving and reliable, the traffic lights are gradually being replaced throughout the country and the speed of promotion is fast.Figure 8. Traffic Lights6.2 Automotive IndustryAutomotive lamps include dashboards, audio indicators, backlights for switches, reading lights and external brake lights, tail lights, sidelights, and headlights. Incandescent lamps for automobiles are not resistant to shock that require frequent replacement. Due to the fast response speed of the LED, the driver can be reminded of the brakes early to reduce the rear-end accident. In developed countries, the central rear high-position brake light made of LED has become a standard part of the car. The LED car tail light model launched by the American HP company in 1996 Groups can be combined into various car taillights at will. In addition, the light sources in the car dashboard and other various lighting parts can be used as ultra-high brightness light-emitting lamps. In recent years, an annual output value of 1 billion yuan will be formed, and within 5 years, an annual output value of 3 billion yuan will be formed.Figure 9. Automotive Headlight6.3 LCD BacklightLED backlights are most noticeable with high-efficiency side-emitting backlights. As an LCD backlight application, LEDs have the characteristics of long life, high luminous efficiency, no interference, and high-cost performance. They have been widely used in electronic watches, mobile phones, BP, computers, electronic calculators, and credit card machines. With the increasing miniaturization of portable electronic products, the LED backlight has more advantages.  The backlights manufacturing technology will be developed to thinner, low power consumption, and uniformity. LED is the key device of a mobile phone. An ordinary mobile phone needs about 10 LED devices, while a color screen and a mobile phone with camera function need to use about 20 LED devices. At present, the amount of mobile phone backlight is very large. 3.5 billion LED chips are used a year.6.4 LED Lighting  Early lighting products have low luminous efficiency. The light intensity can only reach a few to dozens of mcd, which is suitable for indoor occasions, such as home appliances, instrumentation, communication equipment, microcomputers, and toys. At present, the direct goal is to replace incandescent lamps and fluorescent lamps with LED light sources. This substitution trend has started to develop from local application fields. To save energy, Japan is planning to replace the incandescent light-emitting diode project (called "illuminate Japan"). The budget for the first five years is 5 billion yen. If LED replaces half of the incandescent and fluorescent lamps, the annual savings can be equivalent to the energy of 6 billion liters of crude oil. That is equivalent to the power generation of five 1.35 × 106kW nuclear power plants. It can reduce the production of carbon dioxide and other greenhouse gases and improve the living environment.6.5 Other ApplicationsFigure 10. LED Christmas LightsOther applications such as a kind of flash shoes popular with children, the built-in LED will flash when walking; the power indicator of electric toothbrushes; the popular LED Christmas lights. Due to the novel shape, rich colors, unbreakable and low-voltage safety Sexuality, LED Christmas light is generally welcomed by people. It is threatening and replacing the existing Christmas market of electric bulbs.VII Trends of LED Lighting Technology1. The mainstream light source of lighting will be converted to LED. At present, the luminous efficiency of high-power led commercial products has reached more than 150lm / W. The life span has reached more than 30,000 hours. The comprehensive performance of LEDs has exceeded other light sources. At the same time, in addition to large power, the price of LED lamps is close to lamps composed of other light sources. Therefore, LED already has certain advantages. At the same time, the light efficiency of LED laboratory products has reached more than 300lm / W. Through a reasonable heat dissipation design, the life span of more than 50,000 hours can be fully achieved. In principle, there is not much room for other light sources to improve light efficiency and life. Therefore, it can be expected that LED becoming the mainstream light source in the lighting market.2. The research of LED device technology will mainly focus on the improvement of green LED efficiency. The core device of semiconductor technology-LED, currently the red LED and the blue LED has high photoelectric efficiency, but the photoelectric efficiency of the green LED is very low. This limits the substantial application of LED spectral flexibility. Therefore, improving the light efficiency of green LEDs is the most important research topic of LED devices.3. Another study of LED technology will be the study of narrow-spectrum LED devices. The narrow spectral width of a single LED will help to truly achieve unlimited flexibility in assembling the LED spectrum. At the same time, one of the main applications of LEDs at present-LED displays, if the spectral width of monochromatic LEDs can be reduced, a larger color gamut space can be achieved.4. White LEDs for general lighting will gradually shift to RGB mode. The light sources used for general lighting are presented in the form of white light or near-white light. At present, the most comprehensive and cost-effective white LEDs on the market are also implemented by blue LEDs and YAG phosphors. However, the RGB method has higher light efficiency. It will enable the lamp to be dimmed, toned, and even adjusted the color rendering index. Therefore, with the improvement of green LED light efficiency, it is believed that the RGB method (further extended to 3 or more monochromatic LED mixed colors) will become the mainstream white LED mode.5. The characterization of the color rendering of the light source will be a long-term debate. The characterization in the form of the spectrum may be the ultimate result. The current parameter that characterizes the color rendering of the light source is the color rendering index. However, this is based on the limited spectral form of traditional light sources. The infinite flexibility of the LED spectrum will make this characterization problematic. It can be predicted that if the LED achieves true spectrum unlimited flexibility. Any single-parameter color rendering will actually be flawed, and the ultimate characterization method should be the spectrum itself.6. The application of light sources will include two basic aspects of visual applications and non-visual applications. The flexibility of LEDs in spectral assembly makes it possible to achieve various visual and non-visual optimized applications through spectral assemblies, such as agricultural lighting, medical lighting, LED Visible light communication, etc. But relatively speaking,  in the non-visual field, there are still many problems to be solved, including what kind of lighting conditions are optimized, the price of LED needs to be further reduced. The former is a scientific problem, while the latter is an industrialization problem.7. Lighting technology will be deeply integrated with information technology to create smart lighting. As a semiconductor device, LED is a good physical carrier of information technology because LED is easy to control plus the relevance of lamps and human life. Therefore, LED can be deeply integrated with information technology, and smart lighting will be born. This will be an important development direction for future LED lighting technology.8. The appearance of the lamps and lanterns will have great innovation potential. At present, most LED lamps and lanterns include LED bulbs, LED downlights, LED tubes, etc., all of which are designed to cater to people's consumption habits. Whether this is the best mechanical form of the lamp or not remains to be studied. At least, there is a lot of room for innovation in the future mechanical form of LED lamps.9. OLED will occupy an important position in the display field. Relative to LEDs that emit light similar to point light sources, OLEDs emit light in the form of surface light sources. Therefore, after LED occupies the vast majority of lighting applications in the future, OLED still has certain advantages in the display field.10. Natural lighting will be valued. In recent years, energy-saving lighting, health lighting, and ecological lighting have received great attention. The use of sunlight to achieve lighting naturally becomes the best choice. Therefore, with the advancement of technology, natural light lighting will receive more and more attention.Due to the great flexibility of LEDs in the three dimensions of scale, spectrum, and time, many innovative applications and concepts may be born in the future of LED development. This is the development trend of lighting based on artificial light sources. At the same time, as people continue to deepen the concept of green environmental protection, natural lighting will also get greater development. Frequently Asked Questions about Light-emitting Diode Tutorial1. What does light emitting diode mean?In the simplest terms, a light-emitting diode (LED) is a semiconductor device that emits light when an electric current is passed through it. Light is produced when the particles that carry the current (known as electrons and holes) combine together within the semiconductor material. 2. What is a light emitting diode used for?Light emitting diodes, commonly called LEDs, are real unsung heroes in the electronics world. They do many different jobs in all kinds of devices. They form numbers on digital clocks, transmit information from remote controls, light up watches and tell you when your appliances are turned on. 3. What type of light does LED emit?LED lighting differs from incandescent and fluorescent in several ways. When designed well, LED lighting is more efficient, versatile, and lasts longer. LEDs are “directional” light sources, which means they emit light in a specific direction, unlike incandescent and CFL, which emit light and heat in all directions. 4. Why are LED lights so bright?LED lights are so bright because they have a high lumen/watt score. ... This is an enormous difference between the levels of light you are getting from each bulb and because the LED bulb is so much higher there is no way that you would need to replace a 40W incandescent bulb with the equivalent Watt in a LED. 5. What is the difference between diode and LED?The most significant difference between the LED and diode is that the LED emits the light while the diode allows the current to flow only in one direction and opposes the flow in the opposite direction. 6. What is the basic principle of LED?Working Principle: A light-emitting diode is a two-lead semiconductor light source. It is a p–n junction diode that emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. 7. Do LED lights give off UVB?Some in the lighting business have stated that LEDs do not produce UV radiation. However studies have shown that standard LEDs do create a small amount of UV. That said, the amount of UV they actually emit is even less. This is due to the phosphors within an LED lamp that convert the Ultraviolet light to white light. 8. What are the two basic types of LEDs?The two basic types of LEDs are indicator-type LEDs and illuminator-type LEDs. Indicator-type LEDs are usually inexpensive, low-power LEDs suitable for use only as indicator lights in panel displays and electronic devices, or instrument illumination in cars and computers. 9. What is LED and its advantages?Safety is perhaps the most often overlooked advantage when it comes to LED lighting. The number one hazard when it comes to lighting is the emission of heat. LEDs emit almost no forward heat while traditional bulbs like incandescents convert more than 90% of the total energy used to power them directly into heat. 10. What is the O in OLED?Organic contrastOLED stands for organic light-emitting diode. Each pixel in an OLED display is made of a material that glows when you jab it with electricity.

I IntroductionSolid-state relays(SSRs) have unparalleled advantages over other relays, because it can make and break the circuit without contact or spark. In addition, with the progress of technology, the maturity of manufacturing and the decline in price, solid-state relay has become widely used day by day. At the same time, its position in the global market is becoming more and more important.This article will introduce what is a solid-state relays, its structure and working principle, solid-state relay wiring, advantages and disadvantages, and the difference between soild-state relay and conventional relay.Figure 1. Solid-State RelayCatalogI IntroductionII What is a Solid-State Relay(SSR)?III Structure and Working Principle of SSRs  3.1. Structure  3.2. Working PrincipleIV SSR Wiring, Advantages and Disadvantages of SSR  4.1. SSR Wiring  4.2. Advantages of SSRs  4.3. Disadvantages of SSRsV Difference between SSRs and Conventional Relays  5.1. A Brief Introduction to Conventional Relays  5.2. Differences between SSRs and Conventional Relays  5.3. Reasons for Choosing SSRsVI Questions Related to SSR WorkII What is a Solid-State Relay(SSR)?Solid-state relay (hereinafter abbreviated as "SSR") is a new type of contactless switching device composed entirely of solid-state electronic components, which makes use of the switching characteristics of electronic components (such as switching transistor, bi-directional thyristor and other semiconductor devices) to achieve the purpose of turning on and off the circuit without physical contact and spark, so it is also called "contactless switch". SSR is a four-terminal active device, in which two terminals are input terminals and the others are output terminals. It not only has the function of amplifying and driving, but also has the function of isolation, so it is very suitable for driving high-power switching actuators. Compared with electromagnetic relays, SSRs are more reliable, have a longer life, faster speed, and has less interference with the outside world, so this is the reason why it has been largely used.What is a Solid-state Relay?III Structure and Working Principle of SSRs3.1. StructureA solid-state relay consists of three parts: input circuit, isolation (coupling) and output circuit.3.1.1 Input circuitAccording to the type of input circuit, the input circuit can be divided into the DC input circuit, AC input circuit and AC/DC input circuit. Some input circuits also support TTL/CMOS and have the function of positive and negative logic control and inversion, which makes it easier to connect with TTL/CMOS circuits. For control signals with a fixed control voltage, a resistive input circuit is used. The control current is guaranteed to be greater than 5mA, for the large range of changes in the control signal (such as 3~32V) is the use of a constant-current circuit, to ensure that the current in the whole range of voltage changes in more than 5mA reliable operation. 3.1.2 Isolation (coupling)For solid-state relays, there are two ways to isolate and couple the input and output circuits: photoelectric coupling and transformer coupling. Photoelectric coupling usually uses photodiode-phototransistor, photodiode-bi-directional light-controlled thyristor, photovoltaic cell to realize the isolation control between the control side and the load side; High-frequency transformer coupling is the use of input control signals generated by a self-excited high-frequency signal coupled to the secondary, after detection and rectification, logic circuit processing to form a driving signal. 3.1.3 Output circuitThe power switch of SSR is directly connected to the power supply and the load terminal to realize the on-off switching of the load power supply. The main use of high-power crystal transistor (switch-Transistor), unidirectional thyristor (Thyristor or SCR), bidirectional thyristor (Triac), power field-effect transistor (MOSFET), insulated gate bipolar transistor (IGBT). The output circuit of the solid-state relay can also be divided into DC output circuit, AC output circuit and AC / DC output circuit. According to the type of load, it can be divided into DC solid-state relay and AC solid-state relay. For DC output, bipolar devices or power field-effect transistors can be used. For AC output, two thyristors or one triac are usually used. AC solid-state relay can be separated into single-phase AC solid-state relay and three-phase AC solid-state relay. Ac solid-state relays can be divided into random AC solid-state relays and zero-crossing AC solid-state relays according to the timing of turn-on and turn-off. 3.2. Working PrincipleSSR can be divided into two types of AC type and DC type according to the occasion of use. They are used as load switches on AC or DC power sources, and cannot be mixed. The following uses the AC SSR as an example to illustrate its working principle. Figure 1 is a block diagram of its working principle. The components ①～④ in Figure 1 form the main body of the AC SSR. From an overall perspective, the SSR has only two input terminals (A and B) and two output terminals (C and D).Figure 2. Working Principle of SSRWhen working, as long as a certain control signal is added to A and B, you can control the "on" and "off" between C and D, so as to realize the function of "switch". The function of the coupling circuit is to provide a channel between the input and output terminals for the control signals input at the A and B terminals, but electrically disconnect the (electrical) connection between the input terminal and the output terminal in the SSR, to prevent the output from affecting the input. The element used in the coupling circuit is the "optical coupler", which has high sensitivity, high return speed, and high tolerance between the input and output terminals. Because the input terminal is a light-emitting diode, it makes it easy for the input end of the SSR to match the input signal level. When in use, it can be directly connected with the computer output interface, that is, it is controlled by "1" and "0". The function of generating power lines is to generate signals that meet the requirements and to turn on the work of circuit 4, but because the off-line lines do not add special control circuits, they produce dry radiation and use pollution generators such as high-order waves or spikes, so a "zero-crossing control circuit" is specially built for this purpose. The "zero-crossing" means that when the control signal is added and the AC is over zero, the SSR is in the state; and after opening the control signal, the SSR has to wait for the junction point (zero potential) between the positive half-cycle and the half-cycle of the AC cycle before the SSR becomes stable. This design can prevent the interference of high-frequency waves and the pollution of electricity.The absorption circuit is designed to prevent the spike and surge (surge) from the power source from turning on the switching devices to the switching and operation of the controllable silicon tube (or even the operation). It is generally used to use an "R-C" series absorption circuit or non-destructive resistor (thermistor resistor).  IV SSR Wiring, Advantages and Disadvantages of SSR4.1. SSR WiringWhen the output of the relay is electrified to the coil and the output voltage is wired according to the load voltage, the contacts will close and the lamp will light up after energizing, as shown in the figure below.Figure 3. SSR WiringLooking at the physical wiring diagram for the solid-state relay below, you can see that the equipment has parameters 1, 2, 3, 4, and 60A. 60A of which represents the indicator light in action (there are two states, on and off). The INPUT word in the middle of 3 and 4 indicates the incoming terminals, and the OUTPUT word in the center of 1 and 2 indicates the outgoing terminals. Therefore, be careful not to mistakenly connect when wiring. 3 and 4 are used as trigger signals to control the on and off actions of 1 and 2. The SSR in this physical wiring diagram cannot be regulated, and some can adjust the DC voltage to adjust the voltage of the 3 and 4 outlets.Figure 4. SSR Physical Wiring DiagramThe physical wiring diagram of the solid-state relay used for electromechanical equipment is as follows, but it is generally widely used in the chemical industry, coal mine, and other fields, and requires explosion-proof and corrosion resistance.Figure 5. SSR Wiring DiagramSSRs are non-contact switching devices with relay characteristics that use semiconductor devices as switching devices instead of conventional electrical contacts. The single-phase SSR is a 4-terminal active device that includes two input terminals and two output terminals. Opto-isolated, after connecting the input terminal to a specific current value with a DC or pulse signal, you can change the output terminal from the off state to the on state.Figure 6. SSR Physical Wiring Diagram4.2. Advantages of SSRsLong Life Expectancy and High ReliabilityThe solid-state relay has no mechanical parts, solid-state device completes the contact function. It has no moving parts and can operate in high shock and vibration environments. The components of solid-state relays, due to their unique characteristics, determine the longevity and high reliability of solid-state relays. High Sensitivity, Low Control Power, Good Electromagnetic Compatibilitysolid-state relay has a wide input voltage range, low driving power, compatible with most logic integrated circuits without additional buffers or drivers. Fast TransitionsSolid-state relays use solid-state devices, which allow switching speed from milliseconds to microseconds. Low electromagnetic Interferencesolid-state relays have no input "coil" and no ignition arc and rebound, which reduces electromagnetic interference. Most AC output solid-state relays are zero voltage switches that turn on at zero voltage and turn off at zero current, reducing sudden interruptions in the current waveform and thereby reducing switching transient effects.4.3. Disadvantages of SSRsAfter conduction, The tube voltage drop is large, the forward voltage drop of SCR or bi-directional silicon can reach 1-2V, and the saturation voltage drop of the high power transistor is also between 1-2V. The on-resistance is higher than the contact resistance of mechanical contacts.Even after the semiconductor device is turned off, there can still be several microamperes to several milliamperes of leakage current, so ideal electrical insulation cannot be achieved.Because of the large tube voltage drop, large power consumption and calorific value after conduction, the volume of a high-power solid-state relay is much larger than that of the electromagnetic relay with the same capacity, and the cost is also high.The temperature characteristics of electronic components and the interference resistance of electronic circuits are poor, and the radiation resistance is also poor. If no effective measures are taken, the operating reliability will be low.Solid-state relays are more sensitive to overload and must be protected from overload by fast fuses or RC damping circuits. A load of a solid-state relay is clearly related to ambient temperature: as the temperature increases, the load capacity will decrease rapidly.The main drawbacks are the presence of voltage drops in the on-state(need corresponding heat dissipation measures), leakage currents in the off-state, AC and DC not universally usable, a small number of contact groups. In addition, indicators such as overcurrent, overvoltage, voltage rise rate, and current rise rate are poor.Figure 7. SSRV Difference between SSRs and Conventional Relays5.1. A Brief Introduction to Conventional RelaysIt generally consists of a relay coil and dynamic and static contacts. The movable contact acts through the electromagnetic attraction of the relay coil, thus realizing the connection and disconnection of the circuit. That means, there is a mechanical movement. When the current reaches a certain level, the contacts will spark. Its low price and simple structure can be attractive, but sparks and mechanical movements during the operation have a certain impact on its life span. The advantages of traditional relays are simple to drive, good insulation, and good resistance to short-term overload.The disadvantages of conventional relays are large size (cumbersome),  slow response (max ms level), and high power consumption to drive them.5.2. Differences between SSRs and Conventional RelaysAll-solid-state relays use electronic components, so they have many advantages compared with traditional relays, but they also have some limitations to some extent. The following table shows the advantages and disadvantages of solid-state relays and traditional relays.Conventional RelaysAdvantagesDisadvantages*Low residual output voltage*No heat sink required*Cheap*Can provide multiple sets of contacts and normally open normally closed contacts*No leakage current*AC and DC compatible*Compact size*Maximum switching frequency is limited (5-10Hz)*Noise*Electromagnetic interference*Limited contact life*The switching action cannot be fully synchronized*Contact bounce*Poor operating performance of high current, resulting in arc.*Interface is required to connect with digital circuit*High control power, usually higher than 200mWSSRsAdvantagesDisadvantages*Low control power, usually 10-50mW*Synchronous switch*low electromagnetic interference in synchronous switch mode *longer life, 50-100 times than that of traditional relays.*Fast response time*No mechanical moving parts*No mechanical strain*Compatible with digital circuits*Anti-vibration, anti-impact*Anti-corrosion and moisture-proof*No noise*There is residual output voltage 1-1.6V*The output can only be AC or DC, not compatible*Usually requires heat sink*Not suitable for small output signals*There is leakage current*Only single contactThese two tables show that in conventional switching applications, solid-state relays have no significant disadvantages over traditional relays. By comparison, we have to understand some of the limitations of solid-state relay applications, which will affect our final choice of the type of relay. Finally, we have to accept the idea that no relay can be used in all applications. The application of relays depends largely on the mechanical and electrical environment, so it is impossible to define a set of accurate selection parameters to guide users to make the best choice of relays. Therefore, the final choice of relays can only be made according to each specific application.Difference between Solid-state RELAY AND MAGNETIC RELAY5.3. Reasons for Choosing SSRs5.3.1. Life Expectancy of RelayWhen used correctly, the most important features of solid-state relays are long life expectancy and high reliability. In practical application, the contacts of solid-state relays can be used permanently, while the contacts of traditional relays will be affected by strain, corrosion, bonding and so on. Traditional relays will fail due to the damage of moving parts (springs, electromagnets). The life of solid-state relays is usually 50-100 times longer than that of traditional relays.5.3.2. Cheap PriceThe price is an important factor to consider in the selection of relays. Under the same technical requirements, the initial purchase cost of traditional relays is usually lower than that of solid-state relays. However, this does not take into account the service life of traditional relays and the costs incurred in the future due to monitoring, maintenance and replacement of traditional relays.5.3.3. Power ControlThe sensitivity of traditional relays to control signals is only one-twentieth of that of solid-state relays, that is, in the case of obtaining the same output power, the power required by traditional relays is usually 10-20 times that of solid-state relays. The power required for solid-state relay control is only 200-500mW, and the low power consumption can be directly compatible with digital circuit systems.5.3.4. Environmental ResistanceEnvironmental resistance is a very complex concept, but solid-state relays always have an advantage in this respect. A solid-state relay has good mechanical properties because it has no moving parts. The resin packaging shell of the solid-state relay makes it have good shock resistance, impact resistance and corrosion resistance. In addition, humidity has almost no effect on solid-state relays, only slightly reducing their insulation performance. However, traditional relays are very sensitive to humidity, and long-term high humidity will cause corrosion of traditional relays.5.3.5. Switching RateSwitching speed is also usually an important factor in choosing solid-state relays or traditional relays. Controlling the response rate is very important, even crucial, in some process control cargo machinery automation applications. In some applications where the special power factor is very low, the traditional relay can not be used. In addition, in some situations where the switch is stable and no jumping is allowed, traditional relays cannot be used.5.3.6. Electromagnetic RadiationSolid-state relays can switch the load when the circuit voltage crosses zero, thus limiting the transient phenomenon to a considerable extent and avoiding current surge and electromagnetic radiation. In some situations where the power factor is very low, the switch must be stable and the vibration is not allowed, so solid-state relays must be selected.VI Questions Related to SSR Work1. How do solid state relays work?A solid state relay (SSR) is an electronic switching device that switches on or off when an external voltage (AC or DC) is applied across its control terminals. ... Packaged solid-state relays use power semiconductor devices such as thyristors and transistors, to switch currents up to around a hundred amperes. 2. What is the difference between a relay and a solid state relay?The main difference between solid state relays and general relays is that there is no movable contacts in solid state relay (SSR). In general, solid state relays are quite similar to the mechanical relays that have movable contacts. ... SSR provide high-speed, high-frequency switching operations. 3. Where are solid state relays used?The most common application of solid state relays is in the switching of an AC load, whether that is to control the AC power for ON/OFF switching, light dimming, motor speed control or other such applications where power control is needed, these AC loads can be easily controlled with a low current DC voltage. 4. How does solid state relay works in temperature controller?The SSRL Series solid state relays are used to control large resistance heaters in conjunction with temperature controllers. ... By applying a control signal, an SSR switches “on” the AC load current, just as the moving contacts do on a mechanical contactor. Three-phase loads can be controlled using 2 or 3 SSR's. 5. How do you make a solid-state relay circuit?DIY Solid State RelayStep 1: THINGS WE NEED.Step 2: OPTOCOUPLER.Step 3: Add positive pin of led to pin 1 of optocoupler.Step 4: Add 220 Ohm resistor to -ve pin of LED.Step 5: Add jumper to pin 2 of optocoupler which will go to +ve power supply.Step 6: Join source of triac to 4th pin of optocoupler. 6. What is a solid-state relay used for?AC output solid-state relays are used to control the flow of electrical energy in alternating current power systems. The control (equivalent to electro-mechanical relay coil) voltages can be either AC or DC. 7. How fast is a solid-state relay?The SSR output is activated immediately after applying the control voltage. Consequently, this relay can turn on anywhere along the AC sinusoidal voltage curve. Response times can typically be as low as 1 ms. The SSR is particularly suitable in applications where a fast response time is desired, such as solenoids or coils. 8. How do I know if my solid state relay is bad?Solid-state relays should be checked with an ohmmeter across the normally open (N.O.) terminals when control power is off. The relays should be open, switched to OL, and closed (0.2, the internal resistance of the ohmmeter) when control power is applied. 9. What causes solid-state relay failure?If an ambient temperature exceeds the rated value, the SSR output elements may be damaged. ... If the SSR is used with loose screws of its output terminals or imperfect solder, abnormal heat generation while current flowing causes the SSR to burn out. Perform the proper wiring and soldering. 10. Do solid-state relays leak voltage?Solid-State relays have leakage. If you want to repeatedly switch something on / off, use them. But when you want the SSR to be fully off, say after pressing an off switch, a mechanical relay should be across the load to take it off the SSR. If you aren't switching repeatedly, then use a mechanical relay.  

I Introduction What is a blown fuse? A fuse is an electrical safety device that operates to provide over-current protection of an electrical circuit. Its essential component is a galvanized wire with antimony tin alloy that blows (melts) when too much current flows through it, thereby interrupting the current. This process of self-protection is called a blown fuse. This passage introduces blown fuse in the household circuit and car, mainly including its working principle, causes of a blown fuse, and how to repair it.  CatalogI IntroductionII Blown Fuse in Household Circuit2.1 Blown fuse in Household Circuit2.2 Slow Blow Fuse VS. Fast Blow FuseIII Help3.1 Six Reasons Why Fuses Blow3.2 Causes of Circuit fault From the Perspective of Blown fuse3.3 How to Change Household Fuse?IV Blown Fuse In Car4.1 What Is A Blown Fuse In Car?4.2 Why does a Car Fuse Blow?4.3 What are the Symptoms of a Blown Car Fuse?4.4 How to Replace a Fuse in a CarV One Question Related to Resistor Classification5.1 Question5.2 AnswerVI FAQII Blown Fuse in Household Circuit2.1 Blown Fuse in Household CircuitWith the increase of fire and electricity consumption in modern households, the frequency of household fires is getting higher and higher, which has become a focus of public attention. And a considerable part of the fire is caused by the blown fuse. In the state of high voltage and large current, the fluctuation and surge of the grid voltage will cause the current in the power supply to increase instantaneously and cause the fuse to blow.Figure 1. Fuse Figure 2. Blown Fuse2.2 Slow Blow Fuse VS. Fast Blow FuseLiterally, the difference between a slow blow fuse and a fast blow fuse is reaction speed. One reaction is faster and one reaction is slower. From a technical perspective, slow blow fuses are more resistant to surges than fast-blow fuses. In other words, slow-blow fuses have a higher ability to withstand instantaneous pulse currents than fast-blow wires. They can resist the surge of the surge current brought by the switch and do not act, thus ensuring the normal operation of the device. Therefore, a slow blow fuse is also called a surge resistance fuse. To explain from a deeper level, a slow blow fuse has a relatively large melting heat value I2t, and the energy required when the fuse blows are relatively large. So for fuses of the same rated current, slow blow fuses are much more pulse-resistant than fast-blow fuses. Because the I2t of the slow blow fuse is larger than that of the fast blow fuse of the same specification when the total current of the circuit is too large and the fuse blows, the slow blow will be slower than the fast blow fuse. But it doesn’t mean slow blow fuse is worse than fast blow fuse. Because if there is a fault in the circuit, the over-current will not disappear automatically, and the energy of the continuous over-current will greatly exceed the I2t of the fuse. No matter what kind of fuse, it still will be blown. Therefore, the time difference between fast-blow fuses and slow blow fuses is not so important for the device requirements they protect. Only in the case of sensitive devices in the protected circuit that require special protection, the performance of the slow blow fuse will be affected. Therefore，two kinds of blow fuse will be used in different circuits. For example, a purely resistive circuit, or a circuit that needs to protect some more sensitive and expensive components, the fast-blow fuse is necessary. On the contrary, it is best to use slow blow fuses in the power input/output parts of some circuits. In addition to protecting IC circuits, slow blow fuses can be used in most cases where fast-blow fuses are used to improve pulse resistance; on the contrary, if fast-blow fuses are used in places where slow blow fuses are used, it will often cause the power to be turned off immediately. The fuse cannot work normally.III Help3.1 Six Reasons Why Fuses Blow(1) Overloaded CircuitToo many appliances are operating at the same time,  resulting in household electricity overload, so that the fuse is blown. This situation is especially likely to occur when using air conditioners, electric heaters or adding other larger power appliances. Solution: Cut back on all that power that’s tapping a single circuit. Find outlets on other circuits to plug into or unplug what you aren’t using. (2) Connection ProblemsIn some families, although the fuse selection is reasonable and the load is not too large, it still occurs blown fuse as soon as it uses larger power appliances such as air conditioners, electric heaters, and rice cookers. The reason may be that when the fuse is installed or replaced, the fuse and the screw are in poor contact, causing fire and heating, and the screws fixing the fuse are oxidized and burned out. (3) Short CircuitIf the fuse is replaced but still blows as soon as you closed the switch, there may be a short circuit. May be short circuit or load short-circuit. Electric kettles, rice cookers and other commonly used high-power electrical appliances and inferior electrical appliances are prone to short-circuit failure. Solution: Make sure the faulty device is unplugged and there is no damage to the outlet. First, test the circuit. Then check for any damage on or around the electrical panel. If you see any damage, call an electrician before doing anything else with it. If there is none, flip the breaker switch back to its operating position. If it trips again, though, call an electrician. (4) Ground FaultA particular type of short circuit, a "ground-fault," occurs if a hot wire comes in contact with a ground wire or a metal wall box or touches wood framing members. Ground faults can be especially dangerous when they occur in areas with high levels of moisture, such as kitchens or bathrooms, or outdoor locations. (5) PulseWhen the circuit is started or the power supply is unstable, an instantaneous large current causes the fuse to be disconnected. Also, the screw is not tightened when the fuse is installed, or the fuse is damaged, all will cause the fuse blown. (6) The Wrong Type of Fuse Was InstalledFuses come in many shapes, sizes, and configurations. Many look similar but actually have very different functions. A suitable fuse must be selected and used. The fusing current of the fuse is usually 1.5-2.0 times the rated current. For example, when the total power of all appliances in the household is more than 1100W, choose a 5 amp fuse, and use a number 20 fuse with a diameter of 0.98MM. When the current exceeds 7.5 amps to 10 amps, the fuse will automatically blow to achieve the purpose of protection. 3.2 Causes of Circuit fault From the Perspective of Blown FuseThe blown fuse is one of the common faults of the circuit. If not handled properly, it will cause a new fault. Therefore, we should learn to judge the cause of circuit failure from the fuse blown condition. (1)Situation: The fuse blows fast, often with a "snap" sound. Most fuses are turned into small round beads. The gap between the fuses is large, and sometimes the entire fuse is almost completely melted.Analysis: This situation indicates that the blown fuse is caused by a short circuit in the line. Therefore, the circuit can work normally only after finding the short-circuit place, eliminating the short-circuit fault, and then connecting the fuse. (2)Situation: The fuse is disconnected from the middle, the gap between the disconnection is small, and a very thin residual part is left at both ends.Analysis: This is caused by the fuse being too thin, or the passing current is too large. It should be installed with a slightly thicker fuse. (3)Situation: The connection between fuse and screw joints is blown out, and the disconnection gap is small.Analysis: This is because the fastening screw that fixes the fuse is not tightened, the fuse is not in good contact with the screw, the resistance is too large when the current passes, and the generated heat is also increased. Heat doesn't dissipate as fast as it produces, so the fuse blows. In this case, connect the fuse directly and tighten the fastening screws. (4)Situation: The fuse blowing position is uncertain and the gap is small.Analysis: This situation is generally caused by the longitudinal tension of the fuse or a gap in the radial position, and the local diameter of the fuse becomes thinner. Just replace it with a new one. 3.3 How to Change Household Fuse?• Guide(1) The fuse of Knife Switch① Find the main knife switch of the circuit and check the power supply to make sure that the fuse in the knife switch has blown.② Put on rubber shoes and rubber gloves. Bring the prepared pliers and spare fuse in advance.③ After power off, disassemble the upper and lower body shells of the knife switch and use the pliers to remove the old fuse that has melted. Be careful not to touch the electrical circuit.④ Replace with a new fuse and then check if there is a short circuit. If not, you can install the case and close it. (2) Household fuse① Open the fuse box with a screwdriver and then check to see if the fuse is blown.② Install a fuse of similar length to the previous fuse. After installation, check whether it is done. How to Replace Fuse Wire of a Blown Fuse• AttentionWhen replacing the fuse, please pay attention: remove the cover of the insulation box, and do not directly connect the fuse in the insulation box. When installing the fuse, the two ends of the fuse should be wound clockwise around the screw. It should not be over-tightened or loosened, so as not to damage the fuse or cause poor contact, otherwise, it will be easy to blow.IV Blown Fuse In Car4.1 What Is A Blown Fuse In Car?Just like many other appliances, the purpose of fuses in cars is to protect the electrical system within. The basic components of a fuse are one fuse element and two terminals. And the fuse itself works as a bridge between the vehicle and the particular system. If the system is overheated, the fuse element will heat up and melt, and, eventually, the circuit will stop working.4.2 Why does a Car Fuse Blow?The circuit of a general vehicle has gone through a very detailed experiment before leaving the factory, even at the beginning of the design. It should be fine, but why does the vehicle fuse still break? Normally, there are two main reasons for the breakdown of a car fuse, one is that the load of the electrical appliance is too large, and the other is the short circuit in the car circuit. The electrical appliance is overloaded. This is also the reason why most fuses blow.  After buying a car, some people randomly modify electrical equipment, changing headlights, car audio equipment, using inferior cigarette lighters, adapters, and high-power electrical appliances. The operating power of some electrical equipment may be higher than the factory-set value. Once used, it may cause the fuse of the lamp to blow and short circuit in the automobile circuit. After the car has been used for a long time, some of the wire rubber has deteriorated, which has exposed the metal wire and caused a short circuit. Some car owners will directly flush the engine compartment with water pipes, which may cause water in the fuse box and short circuit.4.3 What are the Symptoms of a Blown Car Fuse?After the car fuse is blown, the most intuitive performance is that the car's related functions are disabled and the car cannot drive normally. The battery has power but the vehicle cannot start. In this case, it is likely that the fuse responsible for starting the motor has burned out. When you find that the vehicle can not start, remember not to start continuously, which will cause the battery to discharge continuously and lead to complete power failure. While the vehicle is running, the tachometer display is normal, but the speedometer display is zero, and the ABS warning light is on, indicating that the fuse corresponding to the ABS is burned out.4.4 How to Replace a Fuse in a Car(1) Turn off the start switch and all electrical equipment(2) Disconnect the negative battery cable(3) Figure out the blown fuse.(4) Using needle-nose pliers or some small tweezers, remove the broken fuse.(5) Replace the blown fuse with another new fuse of the same amperage.If the replacement fuse is damaged, you should immediately go to the relevant car service station for inspection. How To Safely Change A Blown FuseV One Question Related to Blown Fuse5.1 QuestionHow does blown fuse work?A. By having pieces of metal wire that melt when current gets too highB. By having an electromagnet that will break a circuit if the current gets too highC. By having pieces of metal wire that melt when current gets too lowD. By having an electromagnet that will break a circuit if the current gets too low5.2 AnswerA  VI FAQ1. How do I know if a fuse has blown?Remove the fuse from its holder. In some cases, you may need a small screwdriver to unscrew the fuse holder cap. Look at the fuse wire. If there is a visible gap in the wire or a dark or metallic smear inside the glass then the fuse is blown and needs to be replaced. 2. What happens when a fuse blows?When a fuse blows, a metal filament inside the fuse has burned through, meaning that you'll need to replace the fuse with a new one. 3. How long do fuses last?Fuses never need to be replaced unless they are tripped/activated by a failing component or any other even with the circuits of the car. They are encapsulated in plastic and are in a vacuum inside the piece. As long as the current limit isn't reached, that wire will not burn out. 4. Can a blown fuse stop a car from starting?A blown fuse in the starter circuit could be the cause of a no-start problem. Broken or corroded wiring-Damaged or dirty wires to the battery or to the starter solenoid (or wires that are loose) can prevent sufficient power from reaching the starter. 5. Can a blown fuse cause a fire?Absolutely, an outlet that has blown a fuse can start a fire. If the problem was whatever was plugged into it, and that item is no longer there, there should be no problem, but if the problem was within the outlet itself it should be repaired immediately. The time to a fire could be from 2 minutes to 2 years. 6. Do fuses go bad with age?Yes indeed, fuses do expire from old age. Yes, fuses can get tired, but it's equally possible you have an intermittent problem with the switch or perhaps the starting capacitor (assuming it's not 3ph). First, replace the fuse and see if you get lucky, then diagnose further if needed. 7. What causes a fuse to burn?First, and most commonly, when too many lights or plug-in appliances draw power from the circuit, it can overload the capacity of the fuse and cause the metal ribbon inside the fuse to melt through. ... A mis-wired lamp, for example, can cause a short circuit and blown fuse if it is plugged into an outlet. 8. How do you fix a blown fuse in a plug?Lift it with your screwdriver to dislodge it. Replace the fuse with a fuse of the same amperage (check the appliance's instructions if unsure) Reassemble the plug, plug it into the wall and switch the device back on. If a blown fuse was the problem, your appliance should now be working again as normal. 9. How does a fuse in a plug work?A plug fuse is a safety device that is connected to an electrical circuit to prevent excessive current flow during fault conditions. Upon overload, the wire fuse element heats up and melts, or blows with a resounding bang, interrupting and cutting off the current flow. 10. Can a fuse look good and still be bad?Due to the way fuses are engineered, the likelihood that a fuse would become faulty without blowing is pretty slim, but there are rare instances in which a fuse might appear completely fine, even though no current runs through it.