The Kynix Blog

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. 

I IntroductionThis article introduces the basics of low voltage transformer, including the definition of low voltage transformer, the principle of low voltage transformer, its installation method, malfunction, and how to repair a household low voltage transformer. A transformer is an electronic instrument that we can use everywhere in our lives. For example, we are inseparable from the mobile phone chargers. The internal components also have transformers. For example, the power supply in our computers is also composed of transformers. Therefore, all electronic products are indispensable for transformers. The transformers used in electronic components are all power transformers (included low voltage transformers). The power transformer is mainly used in electronic products to convert the power supply to the voltage required by the electronic circuit.CatalogⅠIntroductionⅡ Basics of low voltage transformer2.1 Definition of low voltage transformer2.2 Types of low voltage transformers2.3 How does low voltage transformer work?2.4 Design requirements of low voltage transformer2.5 Application environmentⅢ Differences between low&high voltage transformerⅣ How to Estimate the Loss of Low Voltage TransformerV Guide to What You May be Interested in5.1 How to Install Low Voltage Transformer for Household?5.2 How to Troubleshoot a Low-Voltage Transformer5.3 Repairing a household transformer5.4 Malfunction of factory low voltage transformerVI One Question Related to Low Voltage Transformer6.1 Question (Multiple choice questions)6.2 AnswerVII FAQII Basics of Low Voltage Transformer2.1 Definition of Low Voltage Transformer Transformers are important power equipment in our life, especially low-voltage transformer. Whether it is for large-scale power plants or home circuits, it is inseparable from the transformer. There are two kinds of transformers used in our life, one is the high-voltage transformer which used in the high-voltage or ultra-high-voltage circuit, the other is the low-voltage transformer which used in the family lighting circuit or small power circuit.The so-called low-voltage transformer refers to the transformer with low load voltage. As long as the load is lower than 600V, it can be called a low-voltage transformer. The low-voltage transformer is mainly composed of primary coil, secondary coil, and a magnet iron circuit. Low voltage transformers are commonly used for low voltage lighting, which typically only uses 12 or 24 volts. 2.2 Types of Low Voltage TransformersThere are two main types of low voltage transformers: electronic and magnetic.（1）Electronic Low Voltage TransformersElectronic transformers are much smaller, lighter, and less expensive than magnetic counterparts. But they only have about a 5-6 year lifespan. Also, electronic low voltage transformers are known for being noisy.Electronic Low Voltage TransformersAdvantagesDisadvantages▪ Smaller and lighter, easier to hide▪ Less expensive▪ Shorter life span▪ Noisy▪ Heat-sensitive（2）Magnetic Low Voltage TransformersThere are two types of magnetic transformers: stack laminated and toroidal.  Stack laminated transformers have a longer lifespan, about 15 to 20 years. But they only operate at about 80 to 85 percent efficiency, also are known for being noisy.Toroidal transformers are very quiet and more energy efficient. They can operate at about 90 to 95 percent efficiency. And they are long-lived, lasting 20 to 25 years.Magnetic Low Voltage TransformersAdvantagesDisadvantages▪ Long life span of over 15 years▪ Energy efficient▪ Quiet▪ Heavy, big, and difficult to hide▪ Expensive2.3 How Does Low Voltage Transformer Work?Electricity and magnetism are two kinds of energy that can mutually transform. Electricity can generate magnetism, and magnetism can also generate electricity. The low-voltage transformer uses this principle to adjust the voltage through the mutual conversion of electricity and magnetism.A low voltage transformer consists of two electrical coils of wire, one of which is called primary winding and the other is called secondary winding. The primary side of the transformer collects power and the secondary side provides power.Figure 1. Low Voltage Transformer StructureThe two coils intertwine together on a magnet iron circuit core, but without electrically in contact with each other. The magnetic core is made of soft magnetic material, which consists of laminations connected together to help reduce core loss. The core allows power to be transferred from one coil to another. When the primary winding is connected to the power supply, the generated magnetic field transfers the voltage to the secondary winding.Figure 2.  How Does Low Voltage Transformer Work?In summary, the primary winding transforms the electrical power into magnet field when connected to the input voltage supply while secondary winding transforms alternating magnetic field into electrical power of required output.2.4 Design Requirements of Low Voltage TransformerThe low-voltage transformer should be vacuum cast, molded resin encapsulated, 60Hz, Class F insulation, comply with the requirements of IEC726, and meet the requirements of capacity, voltage, phase number, and wiring shown. Each low-voltage transformer has separate primary and secondary windings, and there are two 2.5% normal voltage full-capacity taps above and below the rated voltage on the primary side. The low-voltage transformer should be installed on a base that can isolate, reduce vibration and noise, and the iron core and coil should be properly fixed to withstand the mechanical stress generated in the event of line failure and can withstand 16460 Lite 16460-6 V2. 0 2002/ 11/ 25 Vibration and impact during shipment. Unless otherwise specified, the impedance of low-voltage transformers shall be in accordance with IEC 726. The average noise level of the low-voltage transformer should not exceed the value specified in IEC 726. Each dry-type low-voltage transformer should have appropriate terminals to accommodate the required primary and secondary wiring connections. Low-voltage transformers can be reserved for cable entry from either side or bottom.2.5 Application Environment(1) Ambient air temperature - 5 ℃ to + 40 ℃, 24-houraverage value not more than + 35 ℃(2) The altitude of the installation site shall not exceed 2000m(3) The relative humidity of the atmosphere shall not exceed50% when the ambient air temperature is + 40 ℃(4) A place without violent shaking and impact vibrationIII Differences Between Low&High Voltage Transformer Low Voltage TransformerHigh Voltage Transformerwindingcontinuous windingInterleaved WindingscoolingOil-immersed cooling or air coolingOil-immersed coolingstructureoil tank structurebell jar type oil tankⅣ How to Estimate the Loss of Low Voltage TransformerTransformer loss include copper loss and iron loss. The loss of iron loss is also called no-load loss, and the loss of copper loss is also called load loss. The open circuit of the secondary winding of the transformer applies the no-load current of rated frequency and rated voltage to the primary side, and the active loss caused by the transformer core is called the no-load loss of the transformer. The loss figure can be obtained by the unit loss of the iron core silicon steel sheet multiply the quality of the silicon steel sheet. In general, its loss is very small. For example, the S9-100/10 distribution transformer has a no-load loss of 290W. The larger the transformer capacity, the smaller the no-load loss, generally between 0.3-0.15% of the rated capacity. However, the transformer works continuously for 24 hours, and this loss cannot be ignored. The load loss: The short-circuit of the coil on the secondary side apply the rated current at the rated frequency on the primary side. The transformer loss at this time is the loss of the transformer coil and the iron core. Let's take the S9 series transformer as an example and see its load loss value:The load loss of S9-100/10000 transformer is 1500W.The load loss of S9-1000/10000 transformer is 10300W.The load loss of a transformer is generally between 0.9-1.8%. The larger the transformer, the smaller the load loss.V Guide to What You Maybe Interested in 5.1 How to Install Low Voltage Transformer for Household? First, make sure you have an outlet available. Most family homes will have several outdoor power outlets installed. Second, think about the layout of the lighting. It is important to plan ahead when installing low voltage lighting so that you can avoid any potential problems, especially with the setup.Third, choose a transformer.①Magnetic or Electronic.②Make sure to buy a transformer that can handle the lighting load you need it to.Fourth, install the transformer. Transformers are installed simply by plugging them into your outdoor outlet.5.2 How to Troubleshoot a Low-Voltage Transformer(1) First, check whether there are obvious abnormalities by observing the appearance of the transformer: such as whether the coil lead is broken, whether the insulating material has scorch marks, whether the fastening screw of the iron core is loose, whether the silicon steel sheet is rusted, and whether the winding coil is exposed Wait. (2) Test a transformer with a digital multimeter, open all secondary windings, put the multimeter in the AC block (500mA, in series into the primary winding). When the plug of the primary winding is inserted into the 220V AC mains supply, the multimeter indicates the no-load current value. This value shall not be greater than 10% - 20% of the full load current of the transformer. Generally, the normal no-load current of the power transformer of common electronic equipment should be about 100mA. If too much is exceeded, the transformer has a short-circuit fault. Low Voltage Electronic Transformer Troubleshooting Guide5.3 Repairing a Transformer(1) Understand the reasons for the problem. Generally, a transformer has failed due to some fault in the electrical circuit.(2) Check the replacement transformer. If the short circuit is caused by component failure, the new transformer may still burn out. If you replace the transformer, examine it to make sure that the incident will not occur again.(3) Check the condition of the external fuse. If the transformer has an internal fuse, there may not be a fuse on the power line. On the contrary, the device must be protected by a fuse mounted on the power circuit. Check whether the fuse is intact and replace the faulty fuse.(4) Check the secondary power consumption. Sometimes, this kind of consumption is very high, which leads to equipment failure. If the transformer has multiple ratings and the multimeter shows the value "OL" during the measurement, it may be a short circuit in the secondary winding.5.4 Malfunction of Factory Low Voltage Transformer(1) Abnormal sound in transformerThe abnormal sound inside the transformer may be caused by the following reasons:①Heavy overload causes buzzing sound inside the transformer; ② Due to poor internal contact or breakdown point, the transformer occurs crackle sound③ Some parts of the connection shaft and the core of the transformer are loose, which causes the silicon steel sheet to vibrate④ When there is a grounding or short-circuit fault in the power grid, a large current flows through the winding, which will produce strong noise⑤ The iron core, the winding discharges to the shell, or the core ground wire is disconnected. All these can make the transformer discharge sound. (2) The oil level of the transformer is too high or too lowUnder normal circumstances, the changes in oil temperature can cause a change in oil level. As the oil temperature changes, the oil level also changes accordingly. However, under abnormal conditions, abnormal oil levels can also be caused by faults such as oil seepage and water seepage and other accidents. Second, the change in oil temperature is related to load conditions, ambient temperature and other conditions. When the change of oil level is inconsistent with these elements, it may be a false oil level. (3) Transformer oil quality has deteriorated or oil temperature has suddenly increasedIn working condition, the main function of transformer oil is cooling and insulation. When running overheated for a long time or if water enters the casing and absorbs moisture, the oil quality will deteriorate. Through the oil mark, we can found  that the oil color is abnormally deepened or blackened. Through sampling and analysis, it can be detected that the oil contains carbon particles and moisture, the acid value increases, the flashpoint decreases, and the insulation strength decreases. This situation can easily lead to serious accidents. A sudden rise in oil temperature when the transformer is operating normally is often related to the overheating inside the transformer. The iron core catches fire, the internal screws are loose, the cooling device is faulty, the transformer is heavily overloaded, all may cause the oil temperature to rise suddenly. (4) Transformer on fireWhen the transformer is out of order and it is not handled in time, it may catch fire. When the transformer is on fire, the insulating oil burns and turns into gas, which makes the oil tank burst. The burning insulating oil sprays out of the transformer, which will cause equipment damage and property loss. The short circuit inside or outside the transformer wire, severe overload, a lightning strike may cause the transformer to catch fire.VI One Question Related to Low Voltage Transformer6.1 Question (Multiple choice questions)The winding of wire around a core which is connected to a source of energy is called the ______ coil.primarysecondarytertiary6.2 AnswerA、B  VII FAQ1. What are low voltage transformers?A low voltage transformer is at the heart of every landscape lighting system. It converts 120-volt current to a low voltage current (between 12-15 VAC). ... Magnetic transformers use two coils to reduce the voltage from 120 volts down to 12 volts. 2. What low voltage transformer do I need?Transformers generally range from 150- to 900-watt capacity. Matching the size of the transformer to the lighting design is important for the efficient operation and function of the system. House current, 120 volts, is reduced by a transformer to 12 to 20 volts, the current needed to operate low-voltage landscaping lights. 3. What are low voltage transformers used for?Low Voltage Transformers Low voltage transformers are power transformers that are used to change the voltage capacity of a low-voltage electrical transmission line. Typically, electronic low voltage transformers convert 120 volts into 12 volts or 24 volts. 4. How do you test a low voltage transformer?• Identify the transformer's terminals, using its label as a guide. • Turn a multimeter to its VAC function. • Test the transformer's input voltage with the multimeter, using the transformer's label as a terminal guide. • Test the transformer's output voltage with the multimeter. 5. How long do low voltage transformers last?20 to 25 years.They operate at about 90 to 95 percent efficiency and can run for a very long time, anywhere from 20 to 25 years. They also are much quieter, so you can place them close to the fixtures, rather than having to run wires a long way from the transformer to the fixture itself. 6. Can I plug a low voltage transformer into an extension cord?One warning though to be observed is to never use an extension cord between the transformer and the electrical outlet. Always plug the transformer directly into the power outlet. As you can see, low voltage outdoor lighting is not all that hard to install or maintain. 7. Can you hardwire a low voltage transformer?To hardwire a low voltage transformer, the main power should be turned off at the breaker panel before making any electrical connections. ... The polarity of these wires is not important; either wire on the output side of the transformer may be connected to either wire of the low voltage circuit. 8. Do you need a transformer for low voltage lighting?When operating low voltage lights, you need a transformer to convert your standard line voltage (120V or 277V) into low voltage (12V or 24V). This allows your lights to function properly. If you connect low voltage lights directly to line power, the higher voltage would cause them to burn out immediately. 9. How do you tell if a transformer is going bad?Symptoms of power quality issues include vibration, excessive buzzing or humming and overheating. Technicians should occasionally check the power of transformers that supply nonlinear loads, such as variable frequency drives (VFDs) or switching power supplies. 10. Can you replace a transformer with a light fitting?They will have a transformer either in the ceiling or light fitting. Some LED bulbs, like the Philips Master LED range, have in-built circuitry that can deal with most (but not all) transformers, so you don't have to change them. In other cases, you need to replace the transformer with an LED driver. 

I IntroductionThe ballast has become an important additional device in the gas discharge light source circuit. Because most gas discharge lamps are made using arc discharge characteristics and have negative characteristics (also known as negative resistance characteristics) where the voltage decreases with increasing current, it is impossible to establish a stable operating point. In order to stabilize the discharge and limit the working current of the lamp, ballast must be installed in the gas discharge light source circuit. This article will introduce what is a ballast, how does the ballast work, its function, type, fault symptoms, and how to replace a broken ballast.What is a ballast?CatalogI IntroductionII What is a Ballast?III Types of Ballasts 3.1 Inductive Ballast(Magnetic Ballast) 3.2 Electrical Ballast 3.3 Resistance Ballast 3.4 Magnetic Leakage Ballast 3.5 Capacitive Ballast 3.6 LC BallastIV The Function of the BallastV How to Replace a Ballast? 5.1 How to Tell If the Lamp is Broken or the Ballast is Broken 5.2 Symptoms of Ballast Failure 5.3 Replacement ProcedureVI Several Common Terms for Ballasts 6.1 Ballast Loss 6.2 Ballast Factor 6.3 Ballast Efficacy Factor 6.4 Crest Factor 6.5 Power FactorVII One Quiz about the BallastVIII FAQII What is a Ballast?The ballast is a device that acts as a current limiter and generates an instantaneous high voltage on the fluorescent lamp. It is made by wrapping the enameled wire around an iron core made of silicon steel. Such a coil with an iron core, when instantaneously turned on / off and powered on, will generate a high voltage by self-induction, which is added to the electrodes (filament) at both ends of the fluorescent tube. This action is carried out alternately. When the starter (bubble jump) is closed, the filament of the lamp tube conducts heat through the current limit of the ballast; when the starter is open, the ballast will generate a high voltage on the filament at both ends of the lamp tube. The filament emits electrons to hit the fluorescent powder of the tube wall, and the starter repeatedly turns on and off a few times, thereby turning on the lamp. When the lamp emits light normally, the internal resistance becomes smaller, and the starter will always maintain an open-circuit state so that the current will work stably through the lamp and the ballast to make the lamp emit light normally.Figure1. BallastIII Types of Ballasts3.1 Inductive Ballast(Magnetic Ballast)3.1.1 DefinitionInductive ballast, also known as magnetic ballast, is an iron core inductance coil. The nature of the inductance is that when the current in the coil changes, the magnetic flux will change in the coil, which will generate an induced electromotive force. Thus hindering the current changes. 3.1.2 How Does the Inductive Ballast Work?When the switch is a closed circuit of 220V, 50Hz AC power, the electric current flows through the ballast to the starter, lamp filament, the filament heating (at the beginning of the starter is broken, due to a greater than 180V AC voltage, the starter has jumped the gas inside the bubble glow discharge, jump bimetallic strip is heated inside the bubble expansion deformation, two electrodes together, forming pathways to the filament heating).Figure2. The Circuit of Inductive Ballast When the two electrodes of the starter are close together because there is no arc discharge, the bimetallic sheet cools, and the two electrodes are disconnected. Due to the inductance of the inductive ballast, when the two electrodes are disconnected, the current in the circuit suddenly disappears. Therefore, the ballast generates a high pulse voltage, which is superimposed with the power supply voltage and is added to both ends of the lamp tube to ionize the inert gas in the lamp tube and cause arc discharge. (High pulse voltage-time is about 1ms 600V ~ 1500V, the exact voltage value depends on the type of lamp). During the normal lighting process, the self-inductance of the ballast serves to stabilize the current in the circuit. 3.2 Electrical Ballast3.2.1 DefinitionAn electrical ballast is a type of ballast, which refers to an electronic device that uses electronic technology to drive an electric light source to produce the required lighting. The electronic components convert the energy of the power grid to meet the voltage and current required by the matching lamps with AC or DC power.Figure3. Electrical Ballast 3.2.2 How Does the Electrical Ballast Work?The power frequency power supply becomes a DC power supply after passing through a radio frequency interference (RFI) filter, full-wave rectification, and passive (or active) power factor corrector (PPFC or APFC). Through the DC / AC converter, output high-frequency AC power of 20K-100KHZ, which is added to the LC series resonant circuit connected to the lamp to heat the filament, and at the same time, a resonant high voltage is generated on the capacitor and added to both ends of the lamp tube. However, the "discharge" of the lamp tube is turned into the "on" state and then enters the light-emitting state. At this time, the high-frequency inductance plays a role in limiting the increase of the current and ensuring that the lamp tube obtains the lamp voltage and lamp current required for normal operation.Figure4. How an Electrical Ballast Work 3.3 Resistance BallastIt regulates the lamp current by the voltage on the resistor proportional to the current. In the gas discharge light source circuit equipped with DC power supply, the application of resistance ballast is relatively simple in design and processing, but the power consumption is large and the efficiency is low. Resistance gas ballasts are also used in gas discharge light source circuits equipped with AC power sources. For example, in self-ballasted high-pressure mercury lamp circuits, tungsten wires are used as resistance ballasts. But generally speaking, the application of a resistor ballast in an AC circuit will affect the lamp current waveform, and make the luminous efficiency of the lamp decrease and the stability deteriorate, but it can improve the circuit power factor. 3.4 Magnetic Leakage BallastThe magnetic leakage ballast is a type of LC leading peak type circuit. The fundamental wave is mutated by auto-coupling boost and local magnetic saturation, and then it resonates with the working capacitor to obtain a higher open-circuit voltage and longer-lasting lamp operating current. It is a kind of high power factor lighting circuit, the line power factor reaches 0.90 ~ 0.97, which has its unique advantages for point HID light sources.Figure5. Magnetic Leakage Ballast 3.5 Capacitive BallastA capacitor is used as a ballast in a gas discharge light source circuit equipped with an AC power source. It cannot limit the instantaneous current of the lamp, only the total amount of charge that passes through the circuit in each half-cycle. In the low-frequency AC circuit, the lamp current waveform will be seriously distorted, forming a high pulse peak current (effective value is not large), which has a very harmful effect on the lamp electrode, resulting in a significant reduction in lamp life. Therefore, capacitors are rarely used as ballasts in low-frequency AC circuits. In higher frequency (20 ～ 100kHz) AC circuits, capacitors can be used as ballasts to obtain satisfactory results. The power consumption is small, the current waveform distortion is small, the volume is small, the weight is light, and there is no noise.Figure6. Circuit for Ballast-Ignitor-Capacitor-Lamp 3.6 LC BallastThere are the following two forms. (1) Ballast composed of inductor and capacitor connected in series. The designed capacitive reactance is usually about twice the inductive reactance, and the total impedance is capacitive. It belongs to the advanced ballast, that is, the phase of the lamp current leads to the phase of the power supply voltage. Compared with resistive ballast and inductive ballast, the power consumption is small, especially with good steady current characteristics, and the short-circuit characteristics when the lamp is started are also good. Combined with the use of hysteretic inductance ballast, it can greatly improve the power factor of the circuit. However, the repetitive ionization voltage provided every half cycle when the power supply voltage is commutated is low, and the repetitive ignition ability is poor.Figure7. Circuit of the LC Ballast for T5 28W Lamps (2) Ballast composed of magnetic leakage transformer and capacitor. Generally, it belongs to the advanced ballast. If the parameters are selected properly, the circuit power factor can be better improved. Its main performance is the same as the previous form of LC ballast. If a special leakage magnetic transformer structure is selected in the design to form an LC leading peak ballast, in addition to the above advantages, it can also greatly improve repeated ignition ability. This is an ideal ballast. The disadvantage is that the design and processing are more complicated. To better understand this part, you can see more details about LC circuit. IV The Function of the BallastLimit the Starting Current of the Lamp to A Suitable RangeStarting current refers to the current through the lamp within 30 seconds after the lamp is powered on or during the lamp preheating process. In general (especially in the state of lowest temperature), the starting current is much larger than the operating current of the lamp, so each lamp has a maximum starting current. If the starting current is too large, the service life of the lamp will be shortened; if the current is too small, the lamp cannot be preheated to the normal starting state or the process from glow discharge to arc discharge cannot be completed. The starting current provided by the ballast should not only start the lamp in a short time but also not affect the normal service life of the lamp. The Open Circuit Voltage Provided Is Sufficient for the Lamp to Start SmoothlyWhen the open-circuit peak voltage of the ballast is used as the starting voltage of the lamp, it must be sufficient to ionize the gas in the gas discharge lamp, that is, to generate a peak current that causes a glow-to-arc transition discharge between the electrodes, so that the lamp can start to work. High-pressure mercury lamps and metal halide lamps are more difficult to start at low temperatures, and the open-circuit peak voltage provided by the ballast must be sufficiently high.Figure8. How Electronic Ballast Functions Prevent the Lamp Power from Changing GreatlyAlthough the lamp has a certain range of voltage values during the design and delivery of the lamp, the voltage value of the lamp changes during actual use and throughout its life. This requires the matching ballast to adjust it within a certain range so that the lamp power does not change significantly. The ideal ballast should be such that the lamp power of the newly used lamp and the lamp near the end of its life are not too different. Working Current of Automatic Control LampStable impedance within a certain voltage range is the basic condition that the impedance ballast can control the working current of the lamp. The ballast uses the time change rate of the voltage proportional to the current to adjust the working current of the lamp. When the open-circuit voltage in a certain period causes the lamp operating current to increase, the inductive effect of the ballast will limit the rate of current increase; when the current starts to decrease, the inductive effect will prevent the rate of current decrease. V How to Replace a Ballast?5.1 How to Tell If the Lamp is Broken or the Ballast is Broken(1) The fluorescent lamp requires a ballast to meet the voltage required for the fluorescent lamp to start and work. If the lamp is broken, you can try another lamp to trouble the lamp cover. If it can be lit, the lamp is broken, if it is still not lit, the ballast is broken; (2) Using a universal meter to measure the disconnection of the lamp filament can also be judged: use a universal meter to measure the two ends of the fluorescent lamp separately. If the resistance is not zero, it means that the fluorescent lamp is broken, and the light can be shorted According to the method, if the inspection of the two components of the lamp tube and the light emitter is good, the ballast is broken.Fluorescent Light Troubleshooting and Repair: starter, bulb or ballast?5.2 Symptoms of Ballast Failure(1) The shell of the lamp or ballast appears black.(2) Use an electric pen to detect the ballast. There is no electricity at the incoming and outgoing ends.(3) Use an electric pen to detect that there is electricity at the incoming end, but no electricity at the outgoing end, which means that there is a disconnection inside the ballast.(4) If the shell of the ballast is charged with an electric pen, it means that the ballast has a leakage problem.(5) Use an electric pen to detect that there is electricity at the incoming and outgoing ends. The housing is not live, but the light is off. The light is still off when the trigger is replaced.(6) Use a multimeter with a resistance level of 200 to measure the resistance of the coil. The resistance is infinite.Figure9. Flurescent Ballast Tear Down5.3 Replacement Procedure(1) Open the lampshade: There are three clips around the lampshade that can be rotated. Use a screwdriver to turn the clip away to remove the lamp cover. Place the removed clip in a fixed place so that it can be reinstalled.(2) Observe the position of each component(3) Check whether the old lamp is broken. In general, a section with a longer ring lamp will appear gray. In this case, we should know that it is caused by the sublimation of a substance inside the lamp tube under a high-temperature environment.(4) Remove the lamp: After the lamp cover is opened, remove it, you can see there is a wire slot on the ring lamp. A wire extending from the lamp holder in the center is inserted into this slot. This wire is plug-in type, just pull it out! The ring tube inside is clamped and fixed by three bent metal pieces. This piece of metal is elastic and breaks apart with a screwdriver. You can remove the ring lamp. Pay attention to the wiring inside.(5) Replace the ballast: the ballast of the ring lamp, the two white wires are 220V power cords, there is no difference between positive and negative. The four small round holes on the box are the sockets for the lamp feet. Remove the chassis, disconnect the power cord, put the ballast down, and replace it with a new one.(6) Ring lamp installation: The steps are exactly the reverse when they are removed. Fix the new lamp, and fix the lamp with the three bent metal cards. Use a screwdriver to tighten. Then connect the wires. Stick it with tape and fix it. At the same time, clamp the wire slot on the ring lamp.(7) Install the lampshade: put back the three clips that were just removed. Fix the lampshade. Turn on the power. You can test whether the light is on. If it's on, it's a good replacement lamp. Precautions:(1) Be sure to cut off the main power switch before operation;(2) When removing the lamp cover, small parts such as cards and screws must be placed. In order to reinstall it finally.Figure10. Ballast KitsVI Several Common Terms for Ballasts6.1 Ballast LossThis value represents that the energy consumed by the electronic ballast itself is converted into heat energy instead of light energy. This value can be calculated by subtracting the power consumed by all lamp tubes from the total output power. Generally speaking, the traditional 40W dual-lamp ballast consumes about 22W, while the electronic ballast consumes about 7W. 6.2 Ballast FactorThis value can show the relative effect of the light output of the electronic ballast. The value is the percentage obtained by dividing the measured light output of the electronic ballast by the light output of the standard ballast light. Generally speaking, the higher the value, the better the light output effect. For electronic ballasts, it must not be less than 0.9, but there are also electronic ballasts designed to emphasize high output values and its light output ratio can be up to 1.18 to 1.28. 6.3 Ballast Efficacy FactorThis value can be obtained by dividing the light output ratio (Ballast Factor) by the ballast input power value (Input Power). In the US market, sellers usually use this value to measure and compare the pros and cons of the efficiency of various electronic ballasts. The higher the value, the better the efficiency of the electronic ballast.Figure11. Impedance Ballast6.4 Crest FactorIt is also called wave height rate. This value has a direct and critical impact on the life of the lamp tube. Most lamp tube manufacturers recommend that this value is preferably less than 1.7. Excessively high values can easily cause blackening of the lamp tube and shorten the service life of the lamp tube. The definition of the crest factor refers to the peak current divided by the average current when an electronic ballast is used to light a fluorescent tube. 6.5 Power FactorThis value can represent the efficiency value of the electronic ballast to convert the external input voltage and current into available power. The higher the power factor value, the better the company that supplies the power system (referred to as the power company). In order to encourage consumers to use electronic ballasts with high power factors, foreign power companies have adopted a subsidy policy, but consumers generally think that the higher the PF value, the more power they save. This is a wrong concept because the amount of power saved is not related to the PF value.Figure12. Inductive BallastVII One Quiz about the BallastQuestion: Which of the following ballasts are required to have thermal protection?A. The ballast of a fluorescent luminaire installed indoors, including a replacement ballast for this type of luminaireB. A simple reactance ballast in a fluorescent luminaire with straight tubular lampsC. A ballast in a fluorescent exit luminaireD. A ballast in a fluorescent luminaire used for egress lighting and energized only during a failure of the normal supplyE. All of the aboveAnswer: A  VIII FAQ1. What does a ballast do?In a fluorescent lighting system, the ballast regulates the current to the lamps and provides sufficient voltage to start the lamps. Without a ballast to limit its current, a fluorescent lamp connected directly to a high voltage power source would rapidly and uncontrollably increase its current draw. 2. Do you need a ballast with LED lights?LED technology does not require a ballast to regulate the amount of energy flowing to the lights. LEDs require less energy and can be sensitive to excess energy. A ballast bypass is a common procedure to remove the ballast from the existing fixture. 3. What is ballast and why is it important?Ballast is defined as any solid or liquid that is brought on board a ship to increase stability. Ballasting is essential if a ship is carrying a heavy load in one hold and a lighter load in another, or when the ship is empty or facing rough seas. 4. What happens when a ballast goes bad?If the ballast is bad, then the needle won't move. If you're using a digital multimeter, often the digital readout will possibly list a ‘1’ when it doesn't find a measurable resistance. 5. Is ballast and choke the same?A choke is an inductor designed to have a high reactance to a particular frequency when used in a signal-carrying circuit. An electrical ballast (sometimes called control gear) is a device intended to limit the amount of current flowing in an electric circuit. 6. How long should a ballast last?According to the Certified Ballast Manufacturers Association, the average magnetic ballast lasts about 75,000 hours or 12 to 15 years with normal use. The optimum economic life of a fluorescent lighting system with magnetic ballasts is usually about 15 years. 7. How do I know if my ballast is T8 or T12?If no markings are available, the size in diameter of the tube is the easiest way to determine the type you have installed. T8 tubes are 1-inch in diameter and T12 tubes are 1 1/2 -inch. 8. How often does a ballast need to be replaced?A typical ballast will generally last about 20 years, but cold environments and bad bulbs can decrease this lifespan significantly. You can get a new ballast at a hardware store or home center and install it in about 10 minutes. 9. Can you bypass a ballast on a fluorescent light?If the existing fluorescent tube fixture you want to replace has a non-shunted tombstone, you can proceed with the ballast bypass procedure. Nonetheless, if the existing fixture offers a shunted tombstone, you should replace it with a non-shunted variant. 10. What's in a light ballast?They're usually rectangular black boxes with wires coming out of one or both ends. Lighting ballasts for fluorescent light bulbs and HID lamps made before 1980 may contain polychlorinated biphenyls (PCBs). When the manufacture of PCBs was banned, existing equipment containing PCBs was allowed to remain in use. 

Ⅰ IntroductionA high-pass filter (HPF), also called a low-cut filter or bass-cut filter, passes signals with a frequency higher than a certain cutoff frequency and attenuates signals with frequencies lower than the cutoff frequency. That is, unnecessary low-frequency components or low-frequency signal interference are removed. High-pass filters use the same two topologies as the low-pass filters: Sallen-Key and MFB. The only difference is that the positions of the resistors and the capacitors have changed. In other words, High-pass filters are complementary to low-pass filters.Figure 1. High Pass RC Filter CircuitCatalogⅠ IntroductionⅡ High-pass Filter Basic2.1 Terminology2.2 High-pass Filter Circuit2.2 Cutoff FrequencyⅢ High-pass Filter Types3.1 Passive High-pass Filter and Active High-pass Filter3.2 First-order High-pass Filter and Second-order High-pass FilterⅣ High-pass Filter Transfer FunctionⅤ High-pass Filter OrderⅥ Difference between High-pass Filter and Low-pass FilterⅦ High-pass Filter Application7.1 Question7.2 AnswerⅡ High-pass Filter Basic2.1 TerminologyA high-pass filter is a combination device of capacitors, inductors, and resistors that allows signal components above a certain frequency to pass through and greatly suppress signal components below that frequency. Its characteristics can be described in time domain and frequency domain by impulse response and frequency response respectively. The latter is represented by a function whose frequency is an independent variable. The latter is a function representation of frequency as an independent variable, which is generally a complex variable function with complex variable jω as an independent variable, expressed as H (jω). The H(ω) and amplitude φ(ω) are functions of angular frequency ω, which are called the "amplitude-frequency response" and "phase-frequency response" of the system, respectively. They show the signal components of different frequencies in the excitation source through the amplitude and phase changes encountered in this system. It can be proved that the "frequency response" of the system is the of the "impulse response" of the system, based on the Fourier Transform. When a linear passive system can be represented by an N-order linear differential equation, the frequency response H (jω) is a rational fraction, and its numerator and denominator correspond to the right and left sides of the differential equation, respectively.RC High Pass Filter Explained 2.2 High-pass Filter CircuitBasic high-pass filters are constructed using resistors with capacitors or inductors. The high-pass filter composed of resistors and capacitors is called a high-pass RC filter, and the high-pass filter with resistors and inductors is called a high-pass RL filter.Figure 2. Simple Passive High Pass RC Filter Circuit2.2 Cutoff FrequencyGenerally, the cutoff frequency of the filter refers to the right frequency point of the low-pass filter passband and the left frequency point of the high-pass filter passband, that is, the frequency response point of the filter. Usually defined by 1dB or 3dB relative loss point. For a high-pass filter, its cutoff frequency is that frequency at which the output (load) voltage equals 70.7% of the input voltage (source). The high-pass filter is based on the insertion loss at a sufficiently high -passband frequency without parasitic stopband. Figure 3. High Pass Filter Cutoff Frequency Ⅲ High-pass Filter TypesThe following two classification methods are independent of each other. Active high-pass filters are more common, such as first-order active high-pass filters and second-order active high-pass filters.3.1 Passive High-pass Filter and Active High-pass FilterAccording to the different part devices, it can be divided into passive high-pass filter and active high-pass filter. Passive high-pass filterA kind of filters composed of passive components (resistor R, inductor L, and capacitor C), which is constructed using the principle that the reactance of capacitors and inductive components changes with frequency. The advantages of this type of filter are: the circuit is relatively simple, no DC power supply is required, and the reliability is high. The disadvantages are: the signal in the passband has energy loss, the load effect is more obvious, and electromagnetic induction is easily caused when using inductive components. When L is large, the volume and weight of the filter are relatively large, and it is not suitable in the low frequency domain. Active high-pass filterA filter consists of passive components (usually R and C) and active devices (such as integrated operational amplifiers). The advantage of this type of filter is that the signal in the passband has no energy loss, but also can be amplified, the load effect is not obvious, and the mutual influence is small when the multi-stage cascade is connected. It is easy to form a high-order filter using the simple method of cascade, and the filter is small, light, and does not require magnetic shielding (because no inductive components are used). The disadvantage is that the passband range is limited by the bandwidth of active devices (such as integrated op amps) and requires a DC power supply, and reliability is not as high as the passive filters, thus it is not suitable for high voltage, high frequency and high power.Figure 4. LM741 Active High-pass Filter Circuit 3.2 First-order High-pass Filter and Second-order High-pass FilterAccording to the mathematical characteristics, it is divided into a first-order high-pass filter and a second-order high-pass filter, third-order high-pass filterand so on.Figure 5. Circuit Diagrams of High-pass Filter First Order High Pass FilterThe first order high-pass filter requires a capacitor with a very high capacity, which causes very high fundamental losses, and therefore, it is rarely used.Figure 6. First-order High-pass FilterThe derivation process is as follows: CV = Q (C represents capacitance, V voltage, Q electric quantity)Loop current，whereLaplace transform: Differential form:,  Second-order High Pass FilterThe second-order high-pass filter has the best performance, but causes higher fundamental losses compared with the other type. The second-order filter means that the filter contains the second-order differential in the time domain expression, or the highest order of s of the transfer function denominator is 2, and the gain of the filter to DC component is 1.Second-order High Pass filter Circuit (voltage controlled)Figure 5. Second-order High Pass filter CircuitPassband gain:Transfer function:Frequency response:where, the expressing formula can be foundConclusion: When f is less than f0, the slope of the amplitude-frequency characteristic curve is + 40dB / dec; when Avp is greater than or equal to 3, the circuit self-excited. Multichannel feedback high-pass filterFigure 6. Multichannel Feedback High-pass FilterVoltage transfer function of this circuit:Relationship between circuit parameters and components:This circuit is designed with equal capacitance, that is, let C2 = C3 = C, C1 = | K | C, there is Ⅳ High-pass Filter Transfer FunctionHow to determine the transfer function of each high-pass filterThe high-order filter consists of a cascade of second-order filter sections and first-order filter sections, and each filter section has a specific transfer function. In addition, the cutoff frequency and quality factor Q should be determined for the second-order filter sections, and for the first order sections, only the cutoff frequency is to be determined. The general form of voltage transfer function of second-order high-pass filter:Wc is the cut-off frequency, and the amplitude-frequency characteristic around the cut-off frequency is closely related to Q. K is the passband gain, which is the amplification factor when the frequency tends to infinity in the high-pass filter. The general form of voltage transfer function of first-order high-pass filter:The meaning of Wc and K is the same as that of the second-order high-pass filter, but there has no Q value.When designing and calculating, to determine these parameters, it is necessary to check the normalized pole table of the filter to complete it through a certain conversion. (Whether a low-pass, high-pass, band-pass, or band-reject filter, its frequency characteristics can be obtained by frequency coordinate transformation of the low-pass filter, so the low-pass filter also called a original filter.)Figure 7. High-pass Filter Block Diagram A common voltage-controlled voltage source high-pass filter circuit is used as an example. Its circuit diagram and voltage transfer function are as follows:Figure 8. Voltage-controlled High-pass Filter CircuitComparing this formula with the general expression of the transfer function of the second-order high-pass filter, we can know the cutoff frequency in the voltage-controlled voltage source high-pass filter circuit: Ⅴ High-pass Filter OrderHow to determine the order of the high-pass filterThe order of Butterworth high pass filter isWhere n represents the order of filter, FC is the cut-off frequency of - 3dB, F2 is the frequency of a specified attenuation within the transition band, and A2 is the attenuation at F2. The order of Chebyshev high pass filter is:Where n is the filter order, fc is the equal ripple cutoff frequency, a1 is the gain fluctuation (dB) in the passband, f2 is the frequency of a specified attenuation in the transition band, and a2 is the attenuation at f2 Volume (dB).The fc in the above formula represents the equal-ripple cut-off frequency, that is, the frequency of attenuation in the transition zone at a1. If the -3dB cutoff frequency is used in the design, it must be converted to an equal ripple cutoff frequency to get the above formula. The following table shows the proportional relationship between the cut-off frequency such as the Chebyshev high-pass filter and the -3dB cut-off frequency.Table 1: Ratio FC / f-3db of equal ripple bandwidth to - 3dB bandwidth of Chebyshev high pass filtern23456a1=0.1dB1.94321.36901.21311.13471.0929a1=0.2dB1.67431.28351.15641.09921.0685a1=0.5dB1.38971.16751.09311.05931.0410a1=1dB1.21761.09491.05301.03381.0234 The high-order active high-pass filter is formed by cascading several second-order high-pass filters (first-order high-pass filters should be added for odd-order ones). Each filter is called a filter section, and each has its own independent and Q value. The filter formed after the cascade can constitute different types of filters, such as Butterworth filter and Chebyshev filter. Calculation of first-order high-pass filter section: Calculation of second-order high-pass filter section:  Ⅵ Difference between High-pass Filter and Low-pass FilterThe difference between a high-pass filter and a low-pass filter is that a high-pass filter allows high-frequency or AC component signals to pass and suppresses low-frequency or DC components. A low-pass filter is a filter that allows low-frequency or DC components in a signal to pass through and suppress high-frequency components or interference and noise. In general, the low-pass filter retains signals that are smaller than the cutoff frequency, while the high-pass filter retains signals that are larger than the cutoff frequency. Ⅶ High-pass Filter Application1) In the power system, a high-pass filter is used to filter out harmonics of a certain order and above during harmonic compensation.2) In audio systemThe most overlooked and most useful EQ tool is the high-pass filter, which can remove unwanted low-frequency noise from the audio source. The high-pass filter can be a part on the EQ equalizer, or it can be an independent plug-in or device. Usually our speakers, mixers or microphones are equipped with high-pass filters, because the low-cutting of the recorded human voice can make it easy to distinguish the noise, although this type of noise is very low and difficult to detect. For example, in most musical instruments, the high-pass filter is used to cut off the sound lower 100Hz. You will find that the sound work is miraculously clean, but this does not apply to low-frequency instruments such as kick drums and bass. Ⅷ Question Related to High-pass Filter and Going Further7.1 QuestionWhat is the bandwidth of high pass filter?7.2 AnswerThe bandwidth of the filter denotes the value of frequency from which signals are allowed to pass. For example, if the bandwidth of the high pass filter is given as 50 kHz it means that only frequencies from 50 kHz to infinity are allowed to pass. Frequently Asked Questions about High Pass Filter1. What is a high pass filter used for?A high-pass filter effectively cuts out the frequency response of a mic below a certain set point, allowing only the frequencies above this point to “pass” through as the audio signal. High-pass filters remove unwanted and excess low-end energy that otherwise degrades the audio signal. 2. How is the high pass filters formed?A high pass filter can be formed by placing a capacitor in series with an inverting gain stage. 3. What are the types of high pass filter?The various types of High Pass Filters include:High Pass R-C Filter CircuitHigh Pass R-L Filter CircuitInverted L type High-Pass-Filter CircuitT- Type High-Pass-Filterπ Type High-Pass-FilterHigh-Pass-Filter using Op-AmpButterworth High-Pass-Filter 4. When should I use high pass filter?A high-pass filter is a simple, but effective EQ curve that scoops out unwanted low frequencies from an audio source. Like most engineers, I use them at many points in my mixes to clean up woofy signals and tighten up arrangements. 5. What is the cutoff frequency of a high pass filter?The cutoff frequency for a high-pass filter is that frequency at which the output (load) voltage equals 70.7% of the input (source) voltage. Above the cutoff frequency, the output voltage is greater than 70.7% of the input, and vice versa.