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CatalogⅠ IntroductionⅡ The Layout of the Car MarketⅢ The Layout in the Industrial FieldⅣ The Layout on the Internet of ThingsⅤ ConclusionⅠ IntroductionON Semiconductor: In 2021, it will focus on the automotive, industrial and cloud power, and the Internet of Things marketThe end of the year and the beginning of the year is often a time for companies to make summaries and outlook, and the semiconductor industry is no exception. Not long ago, ON Semiconductor also made a year-end review of 2020 and revealed to the media what ON Semiconductor plans to do in 2021. "The year 2020 is a year of surprises for everyone. People around the world are experiencing the worst epidemic in a century. The good news is that the epidemic has eased in some parts of the world. Looking forward to 2021, we hope to get out of the epidemic as soon as possible and have a more favorable business environment." DavidSomo, senior vice president of strategy, marketing and solution engineering at ON Semiconductor, said in his opening remarks at the press conference.Due to the epidemic, the global economic situation in 2020 is not optimistic. According to Bloomberg data, GDP growth in 2020 is expected to drop from 2.8 percent in 2019 to minus 3.7 percent. China will be the only major economy in the world with positive growth by 2020, while all other economies are expected to suffer single-digit declines. Fortunately, in the second half of 2020, the global economy began to recover. As indicated by the PMI (Purchasing Managers' Index), manufacturing activity in all major economies resumed growth in the second half of the year, with the only exception being Japan, which also showed a positive trend. DavidSomo expressed an optimistic outlook for the global economy in 2021. "We expect that the economic outlook for next year will be positive, significantly better than this year, and there is a consensus for overall GDP growth of around 5% in 2021," he said. He also stressed that, for its part, ON Semiconductor wants to be a reliable supplier of power, analog, sensor and connection solutions, enabling innovation in energy-efficient electronics. It will focus on providing comprehensive solutions to global customers in the automotive, industrial and cloud power markets, as well as the Internet of Things market. Ⅱ The Layout of the Car MarketIn the automotive sector, ON Semiconductor implements a comprehensive sensor product and solution layout, including image sensors, radar, lidar, ultrasonic sensors and other products and solutions. In additon to sensors, R&D resources continue to be invested in silicon and silicon carbide power semiconductors, as well as LED lighting and automotive power management products. Those investments have also paid off handsomely, accounting for 33% of ON Semiconductor's $5.5 billion in 2019 revenue. DavidSomo pointed out that in the future, ON Semiconductor will continue to develop new products in the automotive market and increase investment in research and development. "On the automotive side, we will push forward research and development around sensors, autonomous driving-related applications, new energy vehicles, and the electrification of vehicles." He revealed. ON Semiconductor is one of the top 10 semiconductor suppliers in the automotive industry. DavidSomo proudly states, "Since entering the automotive market in 2010, ON Semiconductor has shipped 130 billion chips to automotive customers by 2019. In 2019, there were more than 230 ON Semiconductor devices used in every vehicle produced worldwide."The company has set the industry standard for automotive image sensors, with more than 120 million of them shipped to Advanced Driver Assistance System (ADAS) applications. Over the past 13 years, more than 400 million ON Semiconductor automotive image sensors have been used in vehicles on the road. ON Semiconductor has developed a complete portfolio of product solutions and sensor modes to support L4 and L5 autonomous vehicles, including ultrasonic sensor interfaces, image sensors, solid-state LIDAR and millimeter-wave radar technologies. DavidSomo said that ON Semiconductor's MMW technology, acquired from IBM Research Group in Sea Law (IBM), has been used in communications and fiber optics, and plans to use the technology in the automotive sector. It is currently being tested with customers for prototypes but has not yet been used in commercial automotive production. In the case of LiDAR, the technology came from the acquisition of sensL to acquire technology on solid-state LiDAR. According to DavidSomo, sensL was originally designed for use in the medical market but is now being developed for use in the automotive market. "Multiple customers have incorporated our Silicon Photomultiplier (SiPM) and Single-Photon Avalanche Diode (SPAD) technologies into solid-state lidar systems, enabling commercial lidar applications in the automotive industry for L2+ and L3 level autonomous driving safety applications." He went on to point it out. On the cost side, DavidSomo says that because ON Semiconductor's lidar solution is a solid-state solution, it has been able to bring the cost of lidar down from more than $1,000 for mechanical rotation in the past to the current $500 range for solid-state solutions. In terms of image sensors, over the years, ON Semiconductor has made three acquisitions, including Aptina, Cypress's image sensor technology and TrueSense, to enrich its image sensor portfolio.Ⅲ The Layout in the Industrial FieldDavidSomo said that ON Semiconductor offers a wide range of power and automation solutions in the industrial and cloud power markets that support different application scenarios. In terms of power semiconductors, in 2018, ON Semiconductor ranked second behind Infineon with a market share of about 9 percent, according to IHS. As an example, he pointed out that powering the cloud requires several processes, including generation, power supply and power demand management. "In these processes, we have a complete silicon and silicon carbide technology portfolio that supports power generation, transmission and distribution, as well as power and demand management for data centers and 5G base stations." He points it out. In terms of energy efficiency improvement, the use of ON Semiconductor's cloud power solution increased energy efficiency by about 0.5%. In a typical VL data center, the savings over the life of the system are estimated at approximately $38 million. The energy efficiency improvement is only 0.5%, which may not sound like much, but when measured at the system-wide level of deployment, the savings over the lifetime of the system are significant. The development of energy infrastructure is also unstoppable, as a society and the government further promote the development of new energy sources and shift more from coal-fired power generation to renewable energy sources such as wind and solar power. In order to save energy and reduce emissions, reduce air pollution, from fuel vehicles to new energy vehicles, which has generated the demand for electric vehicle charging pile, and ON Semiconductor silicon and silicon carbide power discrete devices and modules, can support the construction of electric vehicle charging pile. Similarly, its power technologies, such as solar inverters used in solar panels, enable clean energy generation, and "ON Semiconductor is fortunate to partner with customers in China to develop applications in these areas." DavidSomo said. Manufacturing is also one of the biggest users of energy. In the United States, our power solutions are used in plant motor drive systems, resulting in savings of more than $350 million per year. If applied globally, the potential savings could reach approximately $5.8 billion per year, resulting in energy efficiency improvements in manufacturing motor drive systems.Ⅳ The Layout on the Internet of ThingsIn the Internet of Things (IoT) area, ON Semiconductor has a complete set of key components and modules that enable devices to be connected, intelligent, aware and actuated in their operating environment."Of course, we recognize that our semiconductor components are not sufficient to build the end-to-end connected Internet of Things (IoT) systems that our customers need, so we are investing more to accelerate development and provide our customers with a number of development tools to enable faster application development and market deployment." DavidSomo admits. While ON Semiconductor can provide many of the key building blocks, DavidSomo believes it is important to work with partners in the Internet of Things (IoT) ecosystem to build IoT solutions for secure end-to-end connectivity. As shown in the figure below, ON Semiconductor works with a number of technology partners to enhance the performance of IoT devices developed by clients, as well as with infrastructure providers such as cloud service providers to enable edge devices to connect securely and stably to the cloud. He also revealed that the company is focusing on three vertical areas in the Internet of Things, namely asset tracking and monitoring, connected lighting, and smart homes and building automation.Ⅴ ConclusionIn conclusion, DavidSomo said that in the process of semiconductor device manufacturing, ON Semiconductor also recognizes the growing need to provide its customers with complete system solutions that add value. As a result, ON Semiconductor offers modular products for power components and built-in controls, as well as reference design kits to speed up customer product development. ON Semiconductor also provides software and design tools to help customers complete designs faster and get their equipment to market faster. He also stressed that ON Semiconductor will focus on research and development, and is committed to developing innovative products and solutions including power, simulation, sensors and connectivity solutions. "Through both endogenous growth and exogenous acquistions, we are further enhancing our capabilities to support the applications our customers are developing, while also building our professional application capabilities to help them develop products better and faster to market."

IntroductionSeries Circuits and Parallel Circuits are main circuit connections, also a third type of circuit involves the dual use of series and parallel connections in a circuit. Circuit connection is a kind of principle for layout diagram that shows the relationship between components drawn by physical and electrical standardized symbols for research and engineering planning. As we all know, there are two types of circuit we can make, called series and parallel. They provide solutions for analyzing performance, installing electronic and electrical products.CatalogIntroductionⅠ Series Circuits and Parallel CircuitsⅡ Series Circuits and Parallel Circuits Calculation2.1 Resistors2.2 Capacitors2.3 Inductor2.4 Switch2.5 Power Supply2.6 Series and Parallel Circuits RulesⅢ Six Circuit Design Software Tools Introduction3.1 Protel PCB Design Platform3.2 Altium Designer3.3 Quartus II3.4 Electronics Workbench (EWB)3.5 NI Multisim3.6 Allegro PCBⅣ Frequently Asked Questions about Series and Parallel CircuitsⅠ Series Circuits and Parallel CircuitsWhat is the difference between series and parallel circuits? Just have a look of the following video and words description about series circuits and parallel circuits to get the basics and differences of them.Series vs Parallel CircuitsSeries connection is one of the basic ways to connect circuit elements. The circuit formed by connecting various electrical parts in series. In the series circuit, the current through each part is equal.Parallel connection is another connection method between electrical components. Components connected in parallel are connected in multiple paths so that the current can split up, and the same voltage is applied to each component.Ⅱ Series Circuits and Parallel Circuits Calculation👉 Resistors in Series and Parallel Circuits2.1 ResistorsResistors in SeriesAs shown in the figure, n resistors connect in series. Now connect the power supply to both ends of this series circuit. According to Kirchhoff’s current law, the current given from the power supply is equal to the current through each resistor, so .According to Ohm’s law, the voltage across the k-th resistor is equal to the current through multiplied by its resistance .According to Kirchhoff’s voltage law, the voltage across the power supply is equal to the algebraic sum of the voltage across all resistors.Therefore, the equivalent resistance Req of n resistors in series is .According to Ohm’s law, the voltage across the power source is equal to the given current times the equivalent resistance .Pay attention to the voltage shared by the resistors of the series circuit is proportional.Conductance G is the reciprocal of resistance R, so the equivalent conductance of n resistors in series is Among them, Gn is the conductance of the n-th resistor.For the simple case of two resistors in series, the equivalent conductance is .Resistors in ParallelWhen linear resistors connect in parallel, the conductance (the reciprocal of resistance) is equal to the sum of the conductances of the parallel resistors, which is called the equivalent conductance, and the reciprocal is called the equivalent resistance. For example, the resistances of R1, R2, and R3, their conductances are G1, G2, and G3, respectively. The total resistance R and total conductance G of the parallel circuit are calculated according to the formula .Note: Calculate the total series and parallel resistance of a circuit using Apogeeweb's Parallel and Series Resistor Calculator. 👉 Capacitors in Series and Parallel Circuits2.2 CapacitorsCapacitors in SeriesAs shown in the figure, n capacitors are connected in series. From the definition of capacitor, it can be obtained that the current passing through the k-th capacitor is equal to its capacitance multiplied by the voltage change rate across it:According to Kirchhoff’s current law, the current i given from the power source (ac or dc) is equal to the current passing through each capacitor, so According to Kirchhoff’s voltage law, the voltage across the power supply is equal to the algebraic sum of the voltage across all capacitors:The voltage change rate of the power supply end is .Therefore, the equivalent capacitance Ceq of n capacitors in series is Each capacitor has a “voltage rating” set by its manufacturer. Assuming that the working voltage exceeds the voltage rating of the capacitor, it may cause capacitor failure. In order to avoid it, several similar capacitors can be connected in series to make the algebraic sum of the voltage rating greater than the operating voltage. However, this will also reduce the equivalent capacitance of the circuit.Capacitors in ParallelAs shown in the figure, n capacitors are connected in parallel. From the definition of capacitor, it can be obtained that the current ik through the k-th capacitor is equal to its capacitance Ck multiplied by the voltage change rate across it:According to Kirchhoff’s voltage law, the voltage across the power supply is equal to the voltage across each capacitor:According to Kirchhoff’s current law, the current given from the power source (dc or ac) is equal to the algebraic sum of the current through each capacitor: Therefore, the equivalent capacitance Ceq of n capacitors in parallel is .Note: Calculate the total series and parallel capacitance of a circuit using Apogeeweb's Series and Parallel Capacitance Calculator. 👉 Inductors in Series and Parallel Circuits2.3 InductorInductor in SeriesAs shown in the figure, n inductors are connected in series. According to the method described above, the equivalent inductance can be calculated as .Among them, Ln is the inductance of the n-th inductor.The magnetic field generated by the inductor will be coupled with the winding coil of the adjacent inductor. So it is difficult to avoid the mutual influence of the adjacent inductors. The mutual inductance M of physical quantities can give a measure of this influence.A series circuit composed of two inductors L1 and L2, and the mutual inductance Ms.1) Assuming that the magnetic fields or fluxes generated by two inductors are in the same direction, the equivalent mutual inductance Leq is expressed by the equation: 2) Assuming that the magnetic fields or fluxes generated by two inductors are in opposite directions, Leq is expressed by the equation:For a parallel circuit with three or more inductors, it is necessary to consider the self-inductance of each inductor and the mutual inductance among the inductors, which makes the calculation more complicated. The equivalent inductance is the algebraic sum of all self-inductance and mutual inductance.For example, a series circuit composed of three inductors will involve three self-inductances and six mutual inductances. The self-inductances of the three inductors are M11, M22, and M33, and the mutual inductances are M12, M13, M21, M23, M31, and M32.Equivalent inductance is .Since the mutual inductance between any two inductors is equal to each other, the latter two sets of mutual inductance can be combined:Inductors in ParallelN ideal inductors without mutual inductance are connected in parallel. Similar to the method described above, the equivalent inductance Leq can be calculated as .Among them, Li is the inductance of the i-th inductor.The above equation describes an ideal case where n inductors are connected in parallel without mutual inductance.A parallel circuit composed of two inductors with inductances L1 and L2 and mutual inductance M:1) Assuming that the magnetic fields or fluxes generated by two inductors are in the same direction, the equivalent mutual inductance Leq is expressed by the equation: 2) Assuming that the magnetic fields or fluxes generated by two inductors are in opposite directions, Leq is expressed by the equation:For a parallel circuit with three or more inductors, it is necessary to consider the self-inductance of each inductor and the mutual inductance among the inductors, which makes the calculation more complicated. 👉 Switch in Series and Parallel Circuits2.4 SwitchSwitch in SeriesTwo or more switches are connected in series to form an or gate circuit. Assuming a power supply is connected to both ends of the circuit, current will only flow when all switches are closed.Switch in ParallelTwo or more switches are connected in parallel to form an or gate circuit. Assuming that a power supply is connected to both ends of this circuit, even though any one of the switches is closed, current will flow. 👉 Power Supply in Series and Parallel Circuits2.5 Power SupplyPower Supply in SeriesFor example, assuming that several cells in the battery pack are connected in series to form a power source, the voltage across the power source is the algebraic sum of the voltages across all cells.Power Supply in ParallelFor example, assuming that a battery pack uses several single batteries with the same voltage connected in parallel as a power source, the voltage across the power source is equal to the voltage across the single battery.Note: Get more info from Switching Power Supply Circuit Diagram with Explanation. 2.6 Series and Parallel Circuits RulesHow to judge whether the electrical circuits are connected in series or in parallel? Series and parallel are the two most basic forms of circuit connection, and there are certain differences between them. So get to know their basic characteristics well according to the following specific methods.(1) Visual CheckLook at the connection form of electrical parts in the circuit. The one by one in sequence is series; the one paralleled between two points of the circuit is parallel.(2) Current FlowWhen the current flowing from the positive pole of the power supply to each element in turn shows that the circuit is in series; when the current flows to two branches and get together at a certain place finally, it indicates that the circuit is in parallel.(3) Removing ComponentsRemove one electrical part at will to see whether other electrical components are working normally. If the circuit can continue to work, then the connection relationship of this circuit is in parallel, otherwise, it is in series. Ⅲ Six Circuit Design Software Tools Introduction3.1 Protel PCB Design PlatformProtel PCB is a CAD software for the circuit industry launched by Protel Systems Pty Ltd in 1985, and has rebranded to Altium Designer. It has many advantages compared with many EDA software for circuit designers. Almost all circuit companies use it. The early Protel PCB was mainly used as a printed board automatic wiring tool. It ran in DOS and had fewer hardware requirements. It can run under the 1M memory of a 286 machine without a hard disk. However, it’s less functional, only electrical schematic drawing and printed board design functions, and the PCB layout rate of automatic wiring is also low.It is a professional circuit board drawing tool. It includes electrical schematic drawing, analog circuit and digital circuit mixed signal simulation, multilayer PCB design, programmable logic device design, chart generation, circuit table generation, and supports macro operations, etc. And it has a client/server architecture. PROTEL is also compatible with some other design software file formats, such as ORCAD, PSPICE, EXCEL, etc. Using automatic routing of multi-layer can achieve 100% layout rate of high-density PCBs.3.2 Altium DesignerAltium Designer is one of the most popular of the high end PCB design software packages on the market today. It provides a single, unified application that incorporates all the technologies and capabilities necessary for complete electronic products, which mainly runs on the Windows operating system. This software provides designers with brand-new design solutions through the perfect integration of schematic design, circuit simulation, PCB drawing editing, topology logic automatic routing, signal integrity analysis and design output, etc. When using this software, the quality and efficiency of circuit design can be greatly improved.Fully inheriting the functions and advantages of the previous series of versions of Protel 99SE and Protel DXP, Altium Designer has many improvements and many high-end features. The platform broadens the traditional interface of board-level design and fully integrates FPGA design functions and SOPC design implementation functions, allowing engineers to integrate FPGA in system design with PCB design and embedded design. With these advantages, Altium Designer requires higher computer system performance than the previous version. 3.3 Quartus IIThe Altera Quartus II design software is a multiplatform design environment that easily adapts to your specific needs in all phases of FPGA and CPLD design. In other words, Quartus II software delivers the highest productivity and performance for Altera FPGAs, CPLDs, and HardCopy ASICs. It is a comprehensive CPLD/FPGA development software, and supports schematics, VHDL, VerilogHDL and AHDL (Altera Hardware supports Description Language) and other design input forms. Quartus II embedded with its own synthesizer and simulator, can complete the process of design input to the hardware configuration. It can run in Windows, Linux and Unix. Use Tcl scripts to complete the design process, and it also provides a complete user graphical interface design method. Quartus II has the characteristics of fast running speed, unified interface, centralized function, easy to learn and easy to use.Quartus II provides a fully integrated development which independent of circuit structure, with all the features of digital logic design, including:1. You can use the schematic diagram, structural block diagram, VerilogHDL, AHDL and VHDL to complete the circuit description, and save it as a design entity file.2. Chip (circuit) plane layout wiring editing3. With LogicLock region, users can build and optimize the system, and add subsequent modules that have little or no impact on the performance of the original system.4. Powerful logic synthesis tool5. Complete circuit function simulation and sequential logic simulation6. Timing analysis and critical path delay analysis7. Signaltap ii logic analyzer can be used for embedded logic analysis.8. Support the addition and creation of software source files, and link them to generate programming files.9. Use the combined compilation method to complete the overall design process at one time.10. Automatically locate compilation errors.11. Efficient period programming and verification12. Read into standard EDIF, VHDL and Verilog netlist files.13. It can generate VHDL and Verilog netlist files used by third-party EDA software.3.4 Electronics Workbench (EWB)EWB is is a mixed-mode SPICE-based electronics design and simulation tool, launched by Interactive Image Technology Co., Ltd. in the early 1990s. It is used for mixed simulation of analog circuits and digital circuits. With this powerful software, you can directly see the output of various circuits on the screen.Compared with other EDA software, EWB is a smaller software, and its function is relatively single. However. its simulation function is very powerful, almost 100% simulation results of real circuits. It provides parts such as multimeters, oscilloscopes, signal generators, frequency sweepers, logic analyzers, digital signal generators, logic converters, etc., and its device library contains many transistor components, integrated circuits and digital gate circuit chips from large companies.  In addition, components that are not in the device library can also be imported externally. Among many circuit simulation software, EWB is the easiest to use. Its working interface is very intuitive. The schematic diagram and various tools are in the same window. People who have never touched it can use the software proficiently with a short-time learning. For electronic designers, it is an excellent EDA tool. For many circuits, you can know its results without using a soldering iron. If you want to change components or change parameters, you only need to click the mouse. It can also be used as an auxiliary teaching software for electrical knowledge.3.5 NI MultisimMultisim is a Windows-based simulation tool launched by National Instruments (NI) Co., Ltd.. It is industry standard SPICE simulation and circuit design software for analog, digital, and power electronics in education and research. It includes graphical input of circuit schematics, circuit hardware description language input, and has rich simulation analysis capabilities. Engineers can use it to interactively build circuit schematics and simulate the circuit.With SPICE simulation, designers can quickly capture, simulate and analyze new designs without knowing SPICE deeply, which also makes it more suitable for electronics education. Through Multisim and virtual instrument technology, PCB designers and electronics educators can complete a complete integrated design process from theory to schematic capture and simulation to prototype design and testing.NI Multisim software is an EDA tool software specially used for electronic circuit simulation and design. As a personal desktop electronic design tool running in Windows, NI Multisim is a complete integrated design environment. Its computer simulation and virtual instrument technology can solve the problem of disconnection between theoretical teaching and actual reality experiment. Students can easily reproduce the theoretical knowledge they have learned through computer simulation, and can use virtual instrument technology to create their own instruments. It has an intuitive graphical interface, abundant components, powerful simulation capabilities, abundant testing instruments and complete analysis methods. NI Multisim software is a not bad teaching tool.3.6 Allegro PCBAllegro PCB is an advanced PCB design routing tool introduced by Cadence. It provides a good and interactive working interface, and powerful and complete functions. Provide the most perfect solution for the current high-speed, high-density, multi-layer complex PCB design and wiring, with the combination of its front-end products Cadence, OrCAD, and Capture. Allegro has a complete constraint setting. Users only need to set the wiring rules as required. The wiring design requirements can be met without violating DRC, thus saving tedious manual inspection time and improving work efficiency. It can also define parameters such as minimum line width or line length to meet the various requirements of today's high-speed circuit board wiring. Allegro PCB enables you to do high-speed design, RF antenna, flex-circuitry, and design for manufacturing (DFM) technology.For the drawing and modification functions of copper foil that the industry attaches great importance to, Allegro provides a simple and convenient inner layer division function, as well as the ability to review the inner layer of the positive and negative film. For copper paving, it can also be divided into dynamic copper or static copper, which can be used for different applications. Dynamic copper parameters can be divided into different levels of settings for all copper, single copper or single object, so as to meet the requirements of different connection effects or spacing values to match the special settings due to design requirements. Ⅳ Frequently Asked Questions about Series and Parallel Circuits1. What is the difference between parallel and series circuits?In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents flowing through each component. ... In a series circuit, every device must function for the circuit to be complete. If one bulb burns out in a series circuit, the entire circuit is broken. 2. What are the rules for series and parallel circuits?Rules regarding Series and Parallel CircuitsVoltage drops add to equal total voltage.All components share the same (equal) current.Resistances add to equal total resistance. 3. What are the similarities and differences between series and parallel circuits?Series circuits are designed so that the current through each component is the same, whereas parallel circuits are designed so that the voltage through each component is the same. 4. Why is resistance different in series and parallel?In a series circuit, the output current of the first resistor flows into the input of the second resistor; therefore, the current is the same in each resistor. In a parallel circuit, all of the resistor leads on one side of the resistors are connected together and all the leads on the other side are connected together. 5. Which software is best for circuit design?Based on Proto-Electronics client preferences, we have drawn up the top 10 best electronics CAD software programmes.EagleAltiumProteusKiCadCadence OrCAD PCB DesignerDesignSparkProtelCadstar

CatalogⅠ Isolation Transformer DefinitionⅡ Isolation Transformer ConstructionⅢ How Isolation Transformers Work?Ⅳ What's the Main Function of an Isolation Transformer?Ⅴ Special Purpose Isolation Transformers 5.1 Pulse Transformers 5.2 Austin Transformers 5.3 Instrument TransformersⅥ What are the Benefits of Isolation Transformers?Ⅶ Isolation Transformers VS AutotransformersⅧ FAQⅠ Isolation Transformer DefinitionTwo copper coils that are wrapped around each other and are each supplied by their own power source make up an isolation transformer. While the term "isolation transformer" applies technically to any transformer, it is specifically a transformer that isolates an alternating current from a circuit. By separating two circuits with an induction loop or lowering the voltage of the alternating current until it enters the circuit itself, an isolation transformer does this. Transformers isolated from each other with main (input) and secondary (output) windings are known as isolation transformers. Under this configuration, a dielectric insulation barrier electrically separates the input power and output power.Ⅱ Isolation Transformer ConstructionTransformers can be described as two coils surrounding a core of ferromagnetic material, as shown in Figure 4.The main and secondary coils are shown in the schematic representation; the electric source is connected to the primary, and the isolated output is taken from the secondary. Physically, the coils are distinct from each other and the heart. An early transformer was first used by Michael Faraday during his studies studying electromagnetism. Faraday found that a current-carrying wire generates a magnetic field surrounding the wire and that a current in one generated a magnetic field when two different wires were coiled around a toroid of soft iron, and the changing flux, in turn, induced a voltage in the other. Now known as mutual induction, Faraday is credited with finding that a shifting magnetic flux is caused in a circuit by an electromotive force according to the formula:Sometimes this is shown using the absolute value of E:  The negative indicating the electromotive force opposes the current.Although isolation is provided by any transformer consisting of two separate coils and no grounding shields, the term isolation transformer applies to transformers specifically designed for electrical insulation, the primary purpose of which is to isolate the AC source from circuits, devices and primary and secondary windings. They also have special insulation between the primary and secondary coils and are built between windings to withstand high voltages. Since the capacitance and resistive paths of the coils can be connected to power line/transient voltage noise, isolation transformers have additional features to minimize common-mode noise (which occurs on both hot and neutral ground-referenced wires), transverse mode noise (which occurs between hot and neutral wires) and electromagnetic noise. DC signals and interference caused by ground loops are blocked by the transformer. To reduce any capacitance between the windings, electrostatic shields are used for sensitive equipment (computers or measuring instruments). The insulation transformers used for protection generally have a 1:1 turn ratio, with the number equal to the turns in the primary and secondary windings, but when the voltage still needs to be changed, step-up and step-down isolation transformers are used. Check the specifications for the included features, the scores, and how they are designed when selecting an isolation transformer.Ⅲ How Isolation Transformers Work?Isolation transformers act in the same manner as other transformer types. To allow the primary coil to induce a current in the secondary coil, the isolation transformer is made of two electromagnets that are wrapped around each other. If more than the secondary coil is wound in the primary coil, the voltage is diminished. If more than the primary coil is wound into the secondary coil, the voltage is increased. In order to maintain the same voltage but to distinguish two circuits, an isolation transformer could have primary and secondary coils that are wound the same by causing a current from one coil to the other rather than providing a direct link.Ⅳ What's the Main Function of an Isolation Transformer?Its main role is to include certain circuits that are not capable of directly handling an alternating current safely. Not only does this ensure the full protection of your system, but it also helps to prevent short-circuits or fire accidents. It is included in most of the equipment to reduce the voltage until it hits the application for safety purposes. Another essential feature of using this transformer is that it helps to manage any required amount of voltage.Ⅴ Special Purpose Isolation TransformersIsolation transformers have been developed for specialized applications. Some examples are:5.1 Pulse Transformers: Optimized for the propagation of rectangular electrical pulses and to provide digital signal electrical isolation. These are used in the networking of computers.5.2 Austin Transformers: These power the air-traffic obstacle lamps you see on antenna structures, invented by Arthur O. Austin. The lighting circuitry on the antenna mast would conduct radio-frequency energy to the earth, if not isolated. The AC building mains are also completely separated from the tower by these transformers.5.3 Instrument Transformers: They are used to provide reliable voltage for meters and to securely isolate control circuits from high voltages/current. The transformer's primary winding is linked to the high voltage/current circuit and the meter, much like the connections shown in Figure 3, is linked to the secondary circuit.Note: Some transformers are manufactured with only one winding that is tapped on the winding at various locations to split it into main and secondary portions. Known as auto-transformers, as the single winding is shared, these devices do not provide isolation. Separate coils have isolation transformers, with no physical connection between the coils, no ground on earth.Ⅵ What are the Benefits of Isolation Transformers?Because of their diverse uses and advantages, different industries and companies use isolation transformers. Some of its most significant advantages are listed here.• Isolation can be replaced by isolation transformers in various circuits. With a 1:1 ratio, the main and secondary windings can be separated by insulation transformers.• Transformers of isolation allow direct current power isolation simpler. In the case of telephone lines, where amplifiers are needed at different intervals, the separation of direct current components from the signal is performed by isolation transformers to control every amplifier on the line.• By uniting a vessel with the electric power source, isolation transformers eliminate the possibility of electric shock. They allow the isolation of the person from the resource in such a way that the electrical wires do not directly contact the power line.• Without isolation in electronics testing and servicing, it can prove dangerous to contact a live portion of the circuit. For isolation, 1:1 ratio transformers are therefore used to provide protection. For gadgets that use electricity, isolation transformers have therefore proven to be an excellent choice.• With the aid of isolation transformers, all kinds of noise and sound produced by connecting the signal from the audio amplifier to the speaker output circuit are minimized.• The amount created by a radio frequency on wide circuit devices is separated from the transmitter line by isolation transformers. They facilitate the relation to the transmitted signals of the amount generated by the radio frequency amplifier and direct it toward the antenna.Ⅶ Isolation Transformer VS AutotransformerAn isolation transformer is a main and secondary coil winding electrical transformer. By insulation, these windings are isolated. This insulation reduces the possibility of electrocution by simultaneously contacting the active components and the ground.An autotransformer is a single-winding electrical transformer. The term "auto" applies not to any kind of automatic system but single-coil working alone. Portions of the same winding serve as both the main and secondary sides of the transformer in an autotransformer.• Operation of an Isolation TransformerAn isolation transformer's primary function is to separate circuits. These transformers are designed and produced between the two windings with attention to capacitive coupling. Alternating current (AC) current from the primary to the secondary will also be coupled by the capacitance between primary and secondary windings.• Operation of an AutotransformerAn autotransformer's primary function is to control the transmission line voltage and can be used to convert voltages. An autotransformer automatically changes the voltage according to the load, with only one winding. Such transformers require the correct operation of AC currents and will not operate on direct current.• Common Applications for an AutotransformerBoost at end of the long transmission line to compensate for line lossesReduced starter voltage for an induction motorTo enable rectifier output control, multi-tap feeding the primaryFluorescent light fixture start-up• Common Applications for an Isolation TransformerComputers and peripheralsMedical EquipmentRemote control equipmentTelecommunication equipment Ⅷ FAQ1. What is an isolation transformer?Isolation transformer is basically a transformer with winding ratio of 1:1, i.e., it has same number of primary as well as secondary windings.Isolation transformer provides electrical isolation between two circuits by transfering energy in magnetic form from one circuit to another.First circuit is connected in primary of transformer. Electric supply on this circuit is converted to magnetic field on primary winding and magnetic field magnetises secondary winding which is converted into electrical energy again in secondary circuit. Since it has 1:1 winding ratio voltage and current level of secondary circuit are same as that of primary circuit. So both circuits are electrically isolated yet energy is being transferred between them. 2. Where and why are isolation transformers used?As the name suggests, they are used to isolate the two circuits electrically by providing a galvanic isolation between them. There are many reasons to use an isolation transformer.Isolation transformers block transmission of the DC component in signals from one circuit to the other, but allow AC components in signals to pass.Isolation transformers are used for impedance matching to get the most efficient power transfer between stages and to keep different stages electrically isolated to prevent ground loops.Isolation transformers prevents harmonics from transferring from one side to other side. 3. How does an isolation transformer protect against an electric shock?It doesn’t always protect against an electric shock but it will protect against an electric shock to earth for a single fault in a Multiply Earthed Neutral (MEN) system. Current needs a return path to the source and if teh secondary windings of the isolating transformer are not earthed then there is no return path for current flowing through the person back to the other terminal of the secondary winding. All that happens is that the contacted winding assumes the earth potential.You will still get shocked if you contact both terminals or if you have multiple devices with earth faults that provide a return path for the current.The benefit is that the isolating transformer continues to supply current even in the event of a short to earth on one of its secondary windings. 4. What are the disadvantages of isolation transformer?The Isolation Transformer is a specially designed transformer which is used to isolate two different electrical circuits. The Isolation Transformer is mainly used to isolate the load or powered device from the power supply.Some Disadvantages of Isolation Transformer are given below.• When the Isolation Transformer operating as Pulse Transformer and it operate at low frequency there is distortion produces in secondary or output waveform.• When isolation transformer operating at DC pulse signal, the saturation property of the core reduces.• Isolation Transformer specially designed, that is why it is costlier than a normal transformer. 5. What's the difference between an isolation transformer and a regular transformer?• The transformers having primary and secondary winding which are separated from each other known as Isolation transformer where as Regular Transformer are used for sending and receiving electricity .• Isolation transformers are not used to increase or decrease voltage and Regular Transformer is used to increase or decrease the voltage and current in an electrical circuit.• There are used to breaking the circuit into primary and secondary, so direct current noise can’t get through. Regular Transformers are designed to modify an alternating current voltage that runs from one electric circuit to another through electromagnetic induction. 6. What is the difference between isolation transformer and step up transformer?Main purpose of isolation transformer is to electrically isolate two sides or circuits. This is done mostly for safety reasons. You may make the second side shock proof, or it may have its own DC supply.Usually the turns ratio of isolation transformer is one, meaning input and output will be same in magnitude, though occasionally it could be different.While primary of transformer may be connected to live wire, secondary becomes safe from electric shock. Two different circuits can be connected this way.Step up transformer is used for increasing the voltage from one level to a higher one. Main purpose is to have higher voltage level for the circuit on secondary side. The two sides may or may not be isolated, and turns ratio is greater than one. 7. What is the working principle of an isolating transformer?Isolation transformer is just similar to our normal transformer but the difference is in the transformation ratio. It is 1:1 in isolation transformer. So it also works on the Faraday's law of mutual induction. It says that the emf induced in the secondary coil due to te production of magnetic flux by the voltages and currents of the primary coil. 8. What are the applications of isolating transformers?• The main application of Isolation Transformer is, to make the isolation between a power supply and a powered circuit or powered device for the safety purpose.• Isolation Transformer is used to transform electrical power between two circuits which are not connected electrically to each other. Those two circuits are may have the same voltage level or different voltage level.• Isolation transformers are can be used as Pulse Transformer.• Isolation transformers are used for computer network design. Here isolation transformer act as Pulse Transformer.• Sometimes the Isolation Transformer used in electrical circuits as well as an electronic circuit to provide protection against Electrical shock. 9. Why do we need an isolation transformer to connect an oscilloscope?The scope input shield is connected to the power outlet ground via the scope chassis for safety. It should never be connected to any point not at the same potential as that ground.Either the device under test should also be grounded, or completely isolated from ground. The isolation transformer is the preferred method in most cases.When testing circuits solely using DC power, a lab type DC supply may have outputs isolated from ground. This is also acceptable.It is important to think of all possible paths that arise through connections to other equipment, or parts of a system. The isolation transformer is safe in the most situations.  10. What is the working process of an isolation transformer?Isolation transformers are very important for providing isolation in medical instruments powered by the mains grid (220 V or 110 V AC), which is connected to the primary of an isolation transformer, but where the electronic network connected to the patient is connected to the secondary of the transformer. Since the secondary network is isolated from the primary, there is no path for an AC current from the mains to go to the ground through the patient. 

IntroductionAlarm Circuits and Control Circuits are pretty common in daily life. A control circuit is a special type of circuit used to control the operation of a completely separate power circuit. Alarm circuit is a security circuit to reduce life loss and poverty under the excepted prevailing conditions. Both are quite famous and you probably could have seen plenty of different versions of them. Here, we will introduce several available home/office hobby circuits for smoking alarm, temperature controlling and timing, with their design principles, and component selection. They will provide more convenience for your daily life.A Simple Guide to Electronic Components in CircuitsCatalogIntroductionⅠ Indoor Monitoring Circuit DesignⅡ Smoke Alarm Circuit DesignⅢ Temperature Controlled Circuit Using NE555Ⅳ Temperature Sensor Circuit for Temp MeasuringⅤ Water Tank Temperature Controlled ProjectⅥ Cyclic Timing Circuit DiagramⅦ Indoor Overvoltage Protection Circuit DesignⅧ Temperature Fan Controller DiagramⅨ Water Boiling Alarm Circuit DesignⅩ FAQEvery alarm circuit and control circuit is composed of a number of basic components connected together to achieve the desired performance. The following lists some common and simple alarm and control circuits diagrams to share different ideas for protecting your home/office and making your life more easier.Ⅰ Indoor Monitoring Circuit DesignThe monitor can detect infrared rays emitted by the human body, and when a person enters the monitoring area, it can sound for alarm. It is suitable for homes, offices, warehouses, laboratories and other important occasions.👍 Circuit Working ModelFigure 1. Infrared Detection Alarm CircuitThe device consists of an infrared sensor, a signal amplifier circuit, a voltage comparator, a delay circuit and an audio alarm circuit. When the sensor IC1 detects the infrared signal radiated by the human body in front, it outputs a weak electrical signal from the pin②. It is amplified by the first-stage amplifying circuit formed by the transistor VT1, and then input to the operational amplifier IC2 through C2 with high gain and low-noise amplification. IC3 acts as a voltage comparator. Its pin⑤ reference voltage is provided by R10 and VD1. When the signal voltage output by IC2 pin① pass to the IC3 pin⑥, the voltages of the two input terminals are compared. At this time, IC3 pin⑦ changes from the high level to the low level. IC4 is an alarm delay circuit, formed by R14 and C6. Its continuous time is about 1 minute.When IC3 pin⑦ becomes low level, C6 discharges through VD2, IC4 pin② becomes low level,  which is compared with IC4 pin③ reference voltage. When it is lower than its reference voltage, IC4 pin① changes to high level, VT2 is turned on, and the buzzer BL is powered on and emits an alarm sound. After the infrared signal of the humans disappears, IC3 pin⑦ outputs to high level, and VD2 is cut off at this time. Since the voltage at both ends of C6 cannot change suddenly, charge C6 slowly through R14. When the voltage at both ends of C6 is higher than its reference voltages, IC4 pin① becomes low level for about 1 minute. That is, the alarm time lasts for 1 minute.The power-on delay circuit is composed of VT3, R20, and C8. It is mainly to prevent alarming immediately when powering on, so that the user has enough time to leave the monitoring site, and at the same time can prevent a false alarm occurred during a power cut. The device uses 9-12V DC power supply, with T step-down, full-bridge rectification, and C10 filtering. The detection circuit uses IC5 for power supply, and automatic non-stop conversion with AC and DC. 👉 Components SelectionIC1 adopts imported device Q74, the wavelength is 9~10um. IC2 uses op-amp LM358, which has high gain and low power consumption. IC3 and IC4 are dual voltage comparators LM393 with low power consumption and low offset voltage. Among them, C2 and C5 must use tantalum capacitors with small drain electrodes, otherwise the debugging will be affected. R12 is the key element to adjust sensitivity, and linear high-precision sealed type should be selected. Other components can be selected as shown in the circuit diagram. 👉 DIY and AdjustmentWhen making, a Fresnel lens is installed in front of the IC1 sensor. Since the frequency range of the human body is 0.1~10Hz, it is necessary to use the Fresnel lens to multiply the frequency of the human body. After installation finished, connect the power supply for debugging. Let a person walk about 7-10m in front of the detector, adjust R12 in the circuit, and make the buzzer alarm. As long as the other parts are of good quality and welded correctly, they can work normally without debugging. The static working current of this machine is about 10mA. It will enter the waiting state about 1 minute after the power is turned on. As long as someone enters the monitoring area, it will alarm, and stops in 1 minute. In addition, if the buzzer is changed to a relay to drive other devices, it will be used for other controls. Ⅱ Smoke Alarm Circuit DesignThis smoke alarmer can be used in family rooms or various places where smoking is forbidden (such as hospitals, conference rooms, etc.). When someone smokes, the no-smoking warning device will emit a warning sound of "No Smoking!" to remind the smoker to stop smoking consciously.👍 Circuit Working ModelFigure 2. Smoke Alarm CircuitThe no-smoking warning circuit is composed of a smoke detector, a monostable trigger, a voice generator and a power amplifier circuit. The smoke detector consists of potentiometer RP1, resistor R1 and gas sensor. The monostable trigger has time-base integrated circuit IC1, resistor R2, capacitor C1, and potentiometer RP2. The voice generator circuit is composed of voice integrated circuit IC2, resistors R3-R5, capacitor C2 and Zener diode VS. The audio power amplifier circuit includes transistor V, boost power amplifier module IC3, resistors R6 and R7, capacitors C3 and C4, and speaker BL.When the gas sensor doesn’t detect smoke, the resistance value between A and B is relatively large. IC1 pin2 is high level (higher than 2VCC/3), pin3 outputs low level, while voice generator circuit and the audio power amplifier circuit does not work. When someone smokes and the gas sensor detects the smoke, the resistance value between the A and B becomes smaller, causing the voltage of IC1 pin2 to drop. When the voltage of this pin drops to VCC/3, IC1 pin3 changes from low level to high level. Pass through current limiter R3, filter C2 and Zener diode VS, the high level will generate 4.2V DC voltage, which is supplied to voice IC2 and crystal arm. After IC2 energizes and works, it outputs a voice electrical signal. After the signal is amplified by V and IC3, it makes BL to emit a voice warning sound of "No Smoking!" 👉 Components SelectionRl~R7 selects 1/4W carbon film resistor or metal film resistor for use. RP1 and RP2 can choose small linear potentiometer or variable resistor. C1, C2 and C4 all use aluminum electrolytic capacitors with a withstand voltage of 16V; C3 uses monolithic capacitors. VS selects the silicon Zener diode of 1/2W, 4.2V for use. V uses S9013 or C8050 silicon NPN transistors. IC1 uses the NE555 timer IC; IC2 uses the voice integrated circuit; lC3 uses the WVH68 boost power amplifier thick-mode IC. BL selects 8Ω, 1~3W electrodynamic speakers. The gas sensor is MQK-2 type sensor. 👉 DIY and AdjustmentThis no-smoking warning device can be used as a smoke alarm to detect fires or harmful gases, and combustible gases. Adjusting the RP1 resistance can change the heating current of the gas sensor (usually about 130mA). And adjusting the RP2 resistance can change the sensitivity of the monostable trigger circuit. Ⅲ Temperature Controlled Circuit Using NE555This circuit is an automatic temperature controller composed of a 555 timer IC and a few peripheral components. Because the voltage at each point in the circuit comes from the same DC power supply, it does not need a high-performance regulated one. Using the capacitor step-down method can work reliably. The circuit components are low in price, small in size, and easy to self-made under amateur conditions. The automatic temperature controller made by this circuit can be used for electric heating control in industrial production and household use, with good effect.👍 Circuit Working ModelFigure 3. 555 Timer Based Circuit for Temperature ControlWhen the temperature is low, the resistance of the thermistor Rt with a negative temperature coefficient is large, the potential of pin2 of the 555 timer IC is lower than 1/3 of the voltage of Ec (about 4V), and its pin3 output high level. At this time, V conducts, the heater RL is heating, and the timing cycle starts. When the temperature of the thermistor Rt is higher than the set value and the timing cycle has not been completed, the heater RL will cut off after the timing cycle stops. When the Rt temperature drops below the set value, V will conduct again and turn on the heater RL for heating. In this way, automatic temperature control can be achieved. 👉 Components SelectionIn this circuit, the thermistor Rt can be a negative temperature coefficient type MF12 or MF53, or other types of negative temperature coefficient thermistors with different resistance values, as long as Rt＋VR1= 2R4 is satisfied under the temperature condition to be controlled. A larger potentiometer VR1 can have a larger adjustment range, but its sensitivity will decrease. The bidirectional thyristor V can also be selected according to the size of the load current. There are no special requirements for other components. Choose according to the parameters given in the circuit diagram. 👉 DIY and AdjustmentThe whole circuit can be installed on PCB. Generally, debugging is not required. The time interval is 1... .1R2×C3, which should be smaller than the thermal time constant of the heating system, but not too small, otherwise it will cause excessive radio frequency interference due to the thyristor V turns on or off rapidly. After installation and debugging, it can be put into a small plastic box, and the thermistor Rt can be led to the required place. Ⅳ Temperature Sensor Circuit for Temp MeasuringThis circuit is a thermometer made by AD590 special integrated temperature sensor, which has the characteristics of simple structure, reliable use and high precision.👍 Circuit Working ModelFigure 4. Digital Thermometer CircuitAfter the 100V AC voltage passes through the transformer T1, the rectifier bridge stack UR and the capacitor C1, the DC voltage is obtained, and then the adjustable voltage regulator circuit μA723C provides a stable working voltage for the temperature sensor AD590. AD590 is a new type of current output temperature sensor, composed of multiple transistors and resistors with the same parameters. When a specific DC working voltage is applied to both ends of the sensor, if the sensor temperature is 1 degree Celsius, the output current of the sensor changes by 1 μA. The changing current of the sensor is converted into a voltage signal through the resistor R5 and the variable resistor RP2, and then output to the digital meter, which displays the temperature change. 👉 Components SelectionThe IC selects AD590-series temperature sensor. There are no special requirements for other components of this circuit, and can be selected according to the parameters given in the circuit diagram. 👉 DIY and AdjustmentBy adjusting the value of resistor R5 and variable resistor RP2, the sensitivity of the circuit output can be improved. Ⅴ Water Tank Temperature Controlled ProjectAn automatic fish tank water temperature controller uses a negative temperature coefficient thermistor as a temperature sensor to automatically heat the fish tank through heating gas. The transient time of this circuit is small, which is beneficial to the accuracy of temperature control. And it is suitable for various sizes of fish tanks.👍 Circuit Working ModelFigure 5. Automatic Control of Fishbowl Water TemperatureAfter being rectified by diodes VD2~VD5 and filtered by capacitor C2, a voltage of about 12V is provided to the control part of the circuit. 555 timer is connected as a monostable flip-flop, the transient state is 11s. Set the control temperature to 25ºC, adjust the potentiometer RP, to get RP + Rt = 2R1 ( Rt is the thermistor with negative temperature coefficient). When the temperature is lower than 25ºC, the Rt resistance value increases, and the pin2 of the 555 timer is low level, then the pin3 output changes from low level to high level. The relay K is turned on, and its contact is closed. The heating tube starts to heat until the temperature returns to 25ºC, the Rt resistance value becomes smaller, the pin2 of the 555 timer is at high level, and the pin3 outputs low level. The relay K loses power, its contact is open, and the heating stops. 👉 Components SelectionIC uses NE555, NA555, SL555 and other 555 timer ICs; VD1 uses IN4148 silicon switching diodes; LED uses common light-emitting diodes; VD2~VD5 uses IN4001 silicon rectifier diodes; Rt uses 470Ω MF51-type negative temperature coefficient thermistors at room temperature; RP uses WSW organic solid trimming potentiometer; R1and R2 uses RXT-1/8W carbon film resistors; C1 and C3 uses CD11-16V electrolytic capacitors; C2 uses CT1 ceramic dielectric capacitors; K uses 12V JZC-22F electromagnetic relay. 👉 DIY and AdjustmentThe temperature sensor probe connects the thermistor Rt with wires, and then seals the solder joint with epoxy glue, to avoid water erosion. As long as the circuit is correct in the DIY process, this circuit is easy to operate. If the component performance is good, it can be used without debugging after installation. Ⅵ Cyclic Timing Circuit DiagramThe circuit can set the cycle time of the equipment and each time it works, allowing the equipment to work continuously according to the set time. This circuit can be applied to control occasions such as timing pumping, timing ventilation, and timing cut off.👍 Circuit Working ModelFgiure 6. Cycle Timing CircuitAfter the circuit is stepped down through the capacitor C2 and the bleeder resistor R3, and then rectified by the bridge stack IC2, and stabilized by VD2, a DC voltage of about 12V is obtained to supply power to IC1 and other circuits. IC1 is a 14-bit binary counter/frequency divider integrated circuit. A clock oscillator with a certain frequency is formed by the internal circuits of R1, R2, C1 and IC1 to provide clock pulses for timing IC1. When the circuit is powered on, it first enters the working gap waiting time of the device. IC1 internally realizes the delay by counting and dividing the clock pulse.  When the timing is up (according to the parameters in the figure, about 3 hours), the Q14 terminal of IC1 outputs high level, making the transistor V conducts. The relay KA gets to work, and drives the controlled equipment to start working. At this time, IC1 starts to count the working time of the device again. When the timing expires (according to the parameters in the figure, about 20 minutes), the Q14 terminal outputs low level. So that V is cut off and the device stops working. And meanwhile, IC1 automatically resets and starts the next timing. So that the device can perform timing cycle according to requirements. In the figure, VL is a working indicator. 👉 Components SelectionIntegrated circuit IC1 chooses 14-bit binary counter/frequency divider CD4066, or CC4066 or other digital circuit integrated blocks with the same function. IC2 selects a 1A, 50V bridge stack, or can be connected with four 1N4007 diodes. Transistor V uses NPN-type transistor 8050, and other transistors such as 9013 or 3DG12 can also be used. VD1 selects rectifier diode 1N4007; VD1 selects 1W, 12V silicon regulator tube, such as 1N4742; VD3 ~VD5 use switching diodes 1N4148; VL selects ordinary light-emitting diodes. Resistors R1, R2, R4, R6 and R7 use 1/4W metal film resistors; R3 and R5 use 1/2W carbon film resistors. C1 selects polyester or monolithic capacitors; C2 selects polypropylene capacitors with a withstand voltage of 450V and above; C3 selects aluminum electrolytic capacitors with a withstand voltage of 16V. Relay KA chooses a miniature relay with a coil voltage of 12V, and the contacts capacity is determined according to the power of the controlled device. 👉 DIY and AdjustmentAfter the circuit is installed, it can work normally without debugging. When you need to adjust the control time, you can adjust the parameters of R1, and C1. Also you can change the position of the IC1 output control terminal (Q4 ~Q14). Ⅶ Indoor Overvoltage Protection Circuit DesignBecause the instability of the mains, the household appliances often affected, their service life may reduce. In serious cases, it is easy to burn out due to voltage surge. The circuit described in this example can solve this problem well.👍 Circuit Working ModelFigure 7. Overvoltage Protection Circuit for AppliancesThe mains supply provides a stable 12V working voltage for the switch integrated circuit via C1, VD1, and DW1. VD3, R2 and RP1 form a voltage divider sampling circuit. When the mains voltage is normal, DW2 cannot be turned on, the working voltage of TWH8778 pin⑤ is lower than 1.6V. The relay J does not pull in, and the mains supplies the CZ socket through the J-1 normally closed contact. When the mains voltage is high than the normal setting, DW2 breaks down, the potential of TWH8778 pin⑤ rises to 1.6V, causing the IC to flip, pin ③ outputs high level. At this time, the relay is pulled in, and the electrical power supply is immediately cut off, avoiding the overvoltage affects electrical appliances. 👉 Components SelectionC1 uses 0.47µ/400V electrolytic capacitor, relay J uses 6V DC contactor; RP uses ordinary trimming potentiometer, chip IC can be TWH8778-type electronic switch or TWH8752-type electronic switch. 👉 DIY and AdjustmentAfter the device is welded correctly, connect the mains power to the input end of the voltage regulator, cooperate with the voltage regulator and carefully adjust RP1, so that the relay J is closed when the voltage is 250V, and then the circuit is connected to the mains power grid. Ⅷ Temperature Fan Controller DiagramThis is an automatic fan temperature controlled governor, which can automatically adjust the speed according to the temperature change. The circuit can be adjusted, so it can be used for the control of other electrical equipment.👍 Circuit Working ModelFigure 8. Automatic Temperature Control and Speed Regulation in Fan CircuitThe IC in the picture is a 555 timer IC, which forms a multivibrator with components of R2, R3 and C2. It can send out a rectangular wave signal with an adjustable duty cycle. When the temperature changes, the resistance value of the thermistor changes, so the duty cycle of the square wave output by the multivibrator changes. Adjusting the conduction angle of the bidirectional thyristor VT changes the voltage across the fan electrodes, which automatically adjusts the speed of the electric fan. 👉 Components SelectionThe integrated circuit IC selects NE555 timer, and models such as LM555 and TLC555 can also be used. VT is a bidirectional thyristor, its withstand voltage should be above 400V, and the rated current should be reasonably selected according to the capacity of the electric fan to be controlled. Resistor R1～R5 can choose ordinary 1/8 or 1/4W carbon film resistors; Rt is a negative temperature coefficient thermistor, and can choose a thermistor with a resistance of about 10KΩ at room temperature. Capacitor C1 uses ordinary aluminum electrolytic capacitors; Capacitors C2 and C3 are polyester capacitors. VD is a Zener diode with a steady voltage of 9.1V. 👉 DIY and AdjustmentYou can make your own PCB, or use a universal one. After the circuit is installed, the temperature of the thermistor Rt can be artificially changed to observe the speed of the fan motor. If the temperature control effect is not ideal, the resistance value or temperature change range of the thermistor can be adjusted appropriately. Ⅸ Water Boiling Alarm Circuit DesignOnce the water boils in the kitchen, if it is not turned gas off in time, the boiling water will overflow and extinguish the flame. The gas may spill, which is very unsafe. This problem can be solved by using the water alarm.👍 Circuit Working ModelFigure 9. Boiling Water Alarm CircuitThis circuit uses thermistor as the temperature sensing element. When the water temperature rises, the resistance of the thermistor decreases and the potential at point A increases. When the potential at point A is higher than the conversion voltage of the IC-1 inverter, the IC -1 will output low level, IC-2 will output high level. Making the audio oscillator composed of IC-3 and IC-4 work, and the piezoelectric ceramic sheet makes sound. When IC-2 outputs low level, the audio oscillator doesn’t work, and the piezoelectric ceramic chip is silent. 👉 Components SelectionIC uses C066 two input terminal four NAND gate, working voltage 3V~18V, power supply is 3V~6V; RT thermistor selection resistance value is about 1kΩ; piezoelectric ceramic chip diameter is 27mm; resistor selection is ordinary 1/8 or 1/4W metal film resistors. 👉 DIY and AdjustmentFind two starter shells of waste fluorescent lamps, use iron sheet as a clip, close the tops of the two starters, and fasten them with screws. One of the starters can be set on the mouth of the kettle to obtain the temperature of the water. The two pins of the thermistor are welded on the cover of the other starter and put into the shell. Note that the thermistor must be close to the inner shell wall to facilitate heat transfer. Solder the outer lead of the thermistor and the temperature sensor. After all the components are welded and checked, you can turn on the power for debugging. Put the temperature sensor on the mouth of the kettle, and adjust the RP when the water boils to make the piezoelectric ceramic sheet sound. Repeat it several times before this circuit can be used normally. If you want to change the sound frequency, you can change the C2 capacity. If you feel that the sound is light, you can connect an external transistor to the IC-4 output terminal to amplify the sound.  Ⅹ FAQ1. How do you make a security alarm circuit?The cathode of the photodiode is connected to the supply while the anode is connected to a 10KΩ resistor. Another end of the resistor is connected to the ground. The anode terminal of the photodiode is also connected to pin 5 of the LM358 op-amp, which is the non-inverting terminal. 2. What is the technique of alarm circuits?In a closed-circuit system, the electric circuit is closed when the door is shut. This means that as long as the door is closed, electricity can flow from one end of the circuit to the other. But if somebody opens the door, the circuit is opened, and electricity can't flow. This triggers an alarm. 3. What is a security alarm circuit?This circuit will help you to guard your precious documents as well as jewelry from intruders or theft. All you need is just to place this circuit in front of the locker or below the mat so when any unknown person comes and walks over the switch, the circuit will trigger and the sound of an alarm comes. 4. What type of circuits are security alarms made of?The simplest type of contact-operated security circuit consists of an alarm bell (or a buzzer or electronic 'siren sound' generator, etc.), wired in series with a normally-open (n.o.) close-to-operate switch; the combination being wired across a suitable battery supply, as shown in the basic 'door-bell' alarm circuit ... 5. What are the three basic parts of an alarm system?The main components of an alarm system would be a sensor, a camera, a motion detector, a buzzer a flash light and batteries. It is a component that is usually used to detect noise or movement. Sensors are usually connected to the circuit. 

CatalogCatalogⅠ Oscillation DefinitionⅡ Definition of Voltage Controlled OscillatorⅢ Types of Voltage Controlled Oscillator  3.1 Harmonic Oscillators  3.2 Relaxation OscillatorsⅣ Working Principle of Voltage Controlled OscillatorⅤ Voltage Controlled Oscillator Requirements  5.1 VCO tuning range  5.2 VCO tuning gain  5.3 VCO V/f slopeⅥ Voltage Controlled Oscillator FeedbackⅦ Colpitts & Clapp Voltage Controlled Oscillator CircuitsⅧ Voltage Controlled Oscillator Varactor Issues  8.1 Abrupt  8.2 Hyper-abruptⅨ FAQⅠ Oscillation DefinitionAn oscillator is a circuit that, without any input, generates a continuous, repeated, alternating waveform. Basically, oscillators transform unidirectional current flow from a DC source into an alternating waveform that, as determined by its circuit components, is of the desired frequency. By observing the behavior of the LC tank circuit shown in Figure 1 below, which uses an inductor L and a completely pre-charged capacitor C as its components, the basic theory behind the operation of oscillators can be understood. In this case, the capacitor initially begins discharging through the inductor, which results in the conversion of its electrical energy into an electromagnetic field that can be stored in the inductor. There will be no current flow in the circuit until the capacitor discharges fully.The stored electromagnetic field, however, would have created a back-emf by then, which results in the flow of current through the circuit in the same direction as before. This flow of current through the circuit continues until the electromagnetic field collapses, resulting in the electromagnetic energy back-conversion into electrical form, allowing the cycle to repeat. Now, however, the capacitor would have been charged with the opposite polarity, because of which an oscillating waveform is obtained as the output. However, because of the resistance of the circuit, the oscillations that occur due to the inter-conversion between the two energy-forms will not continue indefinitely as they will be subject to the impact of energy loss. The amplitude of these oscillations gradually decreases to zero as a result, making them damp. This means that the energy loss needs to be balanced to achieve continuous oscillations and constant amplitude. However, in order to achieve oscillations of constant amplitude, it should be noted that the energy supplied should be precisely regulated and must be equal to that of the energy lost.Ⅱ Definition of Voltage Controlled OscillatorA voltage-controlled oscillator (VCO) is an output signal oscillator whose output can be varied over a particular frequency range that is controlled by the DC voltage input. It is an oscillator whose output frequency is directly connected by its input to the voltage applied (FM control).A main parameter of the VCO is the sweeping time: this is the minimum time required to turn or sweep from minimum frequency to maximum frequency or reverse. From an external analog signal, the VCO can be modulated by amplitude (AM). To produce the requested RF power level, an external power amplifier may be required.Ⅲ Types of Voltage Controlled OscillatorThe VCOs can be categorized based on the output waveform:• Harmonic Oscillators• Relaxation Oscillators3.1 Harmonic OscillatorsThe output waveform that harmonic oscillators generate is sinusoidal. This can also apply to the oscillator that regulates the linear voltage. The LC and Crystal oscillators are examples. Here, the capacitance of the diode varies according to the voltage around the diode. This in turn alters the LC circuit's capacitance. Hence, the frequency of the output will change. The advantages are frequency stability in terms of power supply, noise and temperature, and frequency control precision. The only downside is that this form of the oscillator on monolithic ICs can not be implemented effortlessly.3.2 Relaxation OscillatorsThe waveform output produced by harmonic oscillators is a screwed tooth. Using the decreased amount of components, this type may provide a wide range of frequency. It can primarily be used in ICs that are monolithic. The oscillators for relaxation may have the following topologies: • Delay-based ring VCOs • Grounded capacitor VCOs • Emitter-coupled VCOs Here: In delay-based ring VCOs, in a ring shape, the gain stages are connected. As the name implies, in every single point, the frequency is connected to the delay. The VCOs of the second and third types act almost equally. The time taken in each stage is directly linked to the capacitor's charging and discharging time.Ⅳ Working Principle of Voltage Controlled Oscillator Using several voltage regulation electronic components such as varactor diodes, transistors, Op-amps, etc., VCO circuits can be built Here, using Op-amps, we are going to address the function of a VCO. Below, the circuit diagram is shown.A square wave is going to be the output waveform of this VCO. The output frequency is, as we know, connected to the control voltage. The first Op-amp will act as an integrator inside this circuit. The arrangement of the voltage divider is applied here. Because of this, half of the control voltage given as input is supplied to the Op-amp 1 positive terminal. At the negative terminal, the same voltage level is retained. This is to maintain the voltage drop, R1 as half of the control voltage, across the resistor. The current flowing from the R1 resistor passes through the MOSFET when the MOSFET is in good condition. The R2 has half of the resistance, the same drop in voltage and twice the current as of the R1's. So, the attached capacitor is charged by the extra current. To supply this current, the Op-amp 1 should have a gradually increasing output voltage. The current flowing from the R1 resistor passes through the capacitor and gets discharged when the MOSFET is out of order. The output voltage obtained at this time from the Op-amp 1 will decrease. A triangular waveform is therefore produced as the output of Op-amp 1. The Op-amp 2 will act as a catalyst for Schmitt. A triangular wave that is the output of the Op-amp 1 is the input to this Op-amp. If the input voltage is greater than the threshold level, VCC will be the output from the Op-amp 2. If the input voltage is lower than the threshold level, the Op-amp 2 output is zero. The output of the Op-amp 2 is therefore going to be square waves. LM566 IC or IC 566 is an instance of VCO. In fact, it is an integrated 8-pin circuit that can generate double-square wave and triangular wave outputs. Below, the internal circuit is depicted.Ⅴ Voltage Controlled Oscillator RequirementsThere are several parameters that must be considered before the design begins when designing a voltage-regulated oscillator, VCO. These describe the parameters of key performance required for the VCO. 5.1 VCO tuning rangeIt is clear that the oscillator that is powered by voltage must be able to tune over the range that the loop is supposed to work over. This requirement is not always simple to satisfy and, in certain extreme situations, can require the VCO or resonant circuit to be switched. 5.2 VCO tuning gainThe gain of the oscillator regulated by voltage is important. It is calculated per Hz (or V/MHz, etc) in terms of volts. It is the tuning shift for a given change in voltage, as indicated by the units. Any of the overall loop design factors and measurements are influenced by the voltage-controlled oscillator gain.At lower frequencies, the VCO response curves can be shown to be relatively straight. They typically flatten out at higher voltages, however, where the capacitance changes from the variable diodes decrease. 5.3 VCO V/f slopeFor any voltage-driven oscillator used in a phase-locked loop, it is a crucial requirement that the voltage to frequency curve is monotonic, i.e. it always shifts in the same context, usually increasing voltage frequency. If ti alters, as can generally occur in some instances due to spurious resonances, etc., this can cause the loop to become unstable. This must therefore be avoided if the phase-locked loop is to work satisfactorily. This curve shows a slight dip which will result in an unstable phase-locked loop.Phase noise efficiency: In some PLL applications, the phase noise performance of the voltage regulated oscillator is of particular importance - particularly where it is used in frequency synthesizers. Outside of the PLL loop bandwidth, the phase noise output of the voltage-regulated oscillator is the dominant factor in phase noise. While the operation of the PLL reduces close-in noise, there is no reduction in VCO phase noise outside the loop bandwidth. These are some of the main specifications that must be understood from the outset of the VCO design. Careful optimization of the tuned circuit Q, especially the use of variable diodes with as high a Q as possible, selection of the active system, optimization of the oscillator feedback.Ⅵ Voltage Controlled Oscillator FeedbackA VCO can be considered, like any oscillator, as an amplifier and a feedback loop. It is possible to denote the amplifier's gain as A and the feedback as B. For the circuit to oscillate, 360 ° must be the complete phase shift around the loop and unity must be the gain. Signals are fed back around the loop in this manner so that they are addictive and, as a result, any slight disturbance in the loop is fed back and builds up. Because the feedback network is frequency-dependent, the signal is based on one frequency, the feedback network is resonant, and a single frequency signal is produced. A typical emitter circuit is used by many oscillators and thus by VCOs. This in itself generates a 180° phase shift, leaving a further 180° to be given by the feedback network. A typical base circuit where there is no phase shift between the emitter and collector signals (assuming a bipolar transistor is used) can be used by other oscillator or VCO circuits and the phase shift network must provide either 0 ° or 360 °. The device requires a resonant circuit for the oscillator to oscillate on a given frequency to ensure that the oscillation happens on a given frequency. The resonant circuit may be one of a variety of LC resonant circuit configurations, depending on the circuit, or a quartz crystal, etc., in either series or parallel resonance.Ⅶ Colpitts & Clapp Voltage Controlled Oscillator CircuitsThe Colpitts and Clapp oscillator circuits are two commonly used formats for the VCO. Of the two, the most commonly used is the Colpitts circuit, but both are somewhat similar in their configuration. These circuits serve as oscillators because an active device such as a bipolar transistor with capacitors positioned between the base and the emitter (C1) and the emitter and the ground (C2) has been found to fulfill the requirements needed to provide adequate feedback for the output of the oscillator in the correct step. The C1:C2 ratio must be greater than one for the oscillation to take place. The resonant circuit is rendered between the base and ground by adding an inductive function. This consists of only an inductor in the Colpitts circuit, while an inductor and capacitor in series are used in the Clapp circuit.The resonance conditions are that:The capacitance for the overall resonant circuit consists of a series of combinations of the two C1 and C2 series capacitors. The capacitor in the series with the inductor is also used in the series with C1 and C2 in the case of the Clapp oscillator.The capacitance of the series is thus:It is important to change the resonant point of the circuit to make the oscillator tune. This is better accomplished in the case of the Colpitts oscillator, by inserting a capacitor across the indicator. Alternatively, the capacitor may be in series with the inductor for the Clapp oscillator. A circuit where the inductive reactance is located between the base and ground is often favored for high-frequency applications because it is less vulnerable to spurious oscillations and other anomalies.Ⅷ Voltage Controlled Oscillator Varactor IssuesIn order to ensure that the drive frequency in the tuned circuit is not too high, caution must be taken in the design of the circuit when varactor diodes are used inside a voltage-driven oscillator. If this is the case, then the varactor diodes, reducing the Q and increasing the number of spurious signals, can be forced into forwarding conduction. Within a VCO, there are two main types of varactor diode that can be used-the name refers to the diode junction and this impacts their output.8.1 Abrupt: Abrupt diodes have a relatively sharp transition between the areas of the diode, as the name implies. They are able to give a higher Q than their hyper-abrupt relatives, while abrupt varactor diodes do not offer such a high tuning range or linear transfer characteristic. This results in a better oscillator phase noise output regulated by voltage. The other point to note is that in order to have the appropriate tuning range, abrupt varactor diodes may need a high tuning voltage, as certain diodes may need a tuning voltage for the VCO to differ up to 50 volts or slightly more. This can cause problems with supplying the drive circuits with a voltage supply with a sufficiently high voltage.8.2 Hyper-abrupt: There is a relatively linear voltage for hyper-abrupt diodes: the capacitance curve. As a consequence, in some applications, they give a very linear tuning characteristic that may be needed. They can also tune over a wide range, and can normally tune over an octave range with less than a 20-volt tuning voltage shift. They do not give an especially high Q standard, however. Since this will deduct from the tuned circuit's overall Q, this will mean that the output of the phase noise is as good as that which can be obtained using an abrupt varactor diode. Despite the apparent simplicity of the circuit, the voltage-controlled oscillator design is far from trivial. A design would also involve careful optimization of the levels of input coupled with the system and layout. The VCO's design will need to carefully balance the requirements of sometimes conflicting requirements, such as a large tuning range and low noise phase. The standards of efficiency that can be achieved are surprisingly good once the design has been completely configured and the design has been completed.Ⅸ FAQ1. What is a Voltage Controlled Oscillator?A voltage-controlled oscillator (VCO) is an electronic oscillator whose oscillation frequency is controlled by a voltage input. The applied input voltage determines the instantaneous oscillation frequency. 2. What is the use of VCO in PLL?VCO stands for Voltage Controlled Oscillator. PLL operation is simple. VCO creates a high-frequency clock that is divided by some factor. This divided frequency is compared against a stable, reference, frequency using a phase comparator and difference (in-phase or frequency) is converted into voltage and fed back into VCO.Depending on voltage difference VCO frequency will be higher or lower.For example, let’s suppose we have VCO generating 10000 at 5V and divide by 100 dividers. The reference frequency is 90. The phase comparator will subtract two frequencies, 100 - 90 = 10 and will produce some voltage proportional to the frequency difference. This voltage is fed back into VCO and will increase 5V to 6V. Voltage increase will result in frequency drop. The process will continue as long as VCO generated frequency is equal to reference, in our case 9000.From above we see PLL output frequency is: Out = Ref * DividerVCO in RF is produced using varicap diodes - diodes which capacity depends on reverse voltage. Varicap diodes are available with capacities ranging from 1pF up to 500pF and capacity change 2 - 20. How PLL is stable depends on the reference clock and a phase comparator. In the simplest case phase comparator are the XOR gate and RC filter. 3. Why is VCO better than DCO?Of course, the real answer depends on the application. But one important application for a VCO is to implement a so-called phase-lock-loop. In that application, the smoothly continuous frequency vs voltage characteristic of a VCO would allow the VCO to track some variable reference frequency much more precisely. A 'typical' DCO in the same application could only achieve a step-wise approximation to tight tracking. Another, historically more important, application of a VCO is as the primary component of an FM broadcast transmitter. Using a conventional DCO in this application would typically produce an unacceptable amount of weird, noisy distortion in the demodulated audio as the DCO control input attempted to track the audio signal. But yes, it is possible to conceptualize, and even practical to design, a DCO whose frequency control steps are so fine and rapid that, used in an FM broadcast transmitter, the listener would not notice the step-wise tuning of the carrier. 4. What is the function of a VCO voltage-controlled oscillator?A voltage-controlled oscillator (VCO) is an electronic oscillator whose oscillation frequency is controlled by a voltage input. The applied input voltage determines the instantaneous oscillation frequency. 5. How does voltage control oscillator work?A voltage-controlled oscillator is an oscillator with an output signal whose output can be varied over a range, which is controlled by the input DC voltage. It is an oscillator whose output frequency is directly related to the voltage at its input. The oscillation frequency varies from few hertz to hundreds of GHz. 6. How do you make a voltage-controlled oscillator?To make a VCO, the oscillator needs to be tuned by a voltage. This can be achieved by making the variable capacitor from varactor diodes. The tuning voltage for the VCO can then be applied to the varactors. 7. What is the output of VCO?The VCO has an output power level of -3 dBm into 50 Ω with phase noise of -101 dBc/Hz typical at 100 kHz offset. The control voltage range is 0.4 to 2.4 volts, and load pulling is typically 0.75 MHz, pk-pk. Power supply pushing is 280 kHz/volt (typical). 8. What is the VCO tuning range?The VCO is linearly tunable from 806 to 1,113 MHz with a 34% tuning range controlled linearly by the tuning voltage. The phase noise of the VCO is -100.4 dBc/Hz at 100-kHz offset frequency from a 903 MHz carrier. 9. What is VCO phase noise?Characterizing Phase Noise. The term phase noise is widely used for describing short-term random frequency fluctuations of a. signal. Frequency stability is a measure of the degree to which an oscillator maintains the same value. 10. Which is the input terminal in a VCO?It generates the square wave at the output whose frequency is determined by a control voltage. The first op-amp works as an integrator. The control voltage is applied at the input terminal and due to the voltage divider arrangement, half the control voltage is applied at the positive terminal of the first op-amp. 

Introduction: A Comprehensive Guide to Using a Multimeter in 2025When it comes to measuring instruments, the question often arises: how do you use a multimeter effectively? A Multimeter, also known as a VOM (volt-ohm-milliammeter) or DMM (Digital Multimeter), is the indispensable "Swiss Army Knife" for electronics. It is used to measure two or more electrical values—principally voltage (volts), current (amps), and resistance (ohms) in electronic and electrical circuits.In 2025, modern multimeters have evolved significantly. Beyond basic measurements, many now include features like capacitance testing, transistor checks, temperature sensing, and even Bluetooth connectivity for smartphone data logging. Whether you are troubleshooting a smart home device, checking automotive wiring, or testing a battery, the multimeter is your primary diagnostic tool.Multimeters are generally divided into two types: analog multimeters and digital multimeters (DMM). While analog meters use a moving needle, digital versions are now the industry standard, offering high accuracy, auto-ranging capabilities, and easy-to-read LCD or OLED displays. This guide is designed for beginners and will cover the basic parts, working principles, functions, and safety tips for using a multimeter in the modern era.Ⅰ What are the Parts of a Multimeter?The anatomy of a multitester generally includes a display (scale or screen), a selection knob, ports (jacks), and test probes. However, the interface differs between the older analog style and modern digital tools.Analog Multimeters: Use a microammeter with a moving pointer (needle) to display readings against a printed scale. They require the user to interpret the scale based on the selected range.Digital Multimeters (DMM): The current mainstream choice. They feature a numeric digital display, often with a backlight for dark environments. Modern DMMs may also include "True RMS" for accurate AC readings and auto-ranging features that automatically select the correct measurement scale for you.A common digital multimeter is composed of three main interface parts:1.1 The Display (Meter Head)On a digital multimeter, this is the LCD or LED screen where measurement values are shown. It often displays icons for battery life, high voltage warnings, and the unit of measurement (e.g., V, A, Ω). High-end models in 2025 may feature high-resolution color screens or bar graphs that mimic analog needles to show fluctuating signals.1.2 Measuring Circuit (Internal)Hidden inside the case, the measuring circuit converts incoming analog signals (voltage, current, resistance) into digital data. It is composed of precision resistors, an Analog-to-Digital (A/D) converter, and protective fuses to ensure safety during overload.1.3 Rotary SwitchThe central dial allows you to select the function (Volts, Amps, Ohms) and the range. In Auto-ranging multimeters, you simply select the function (e.g., DC Voltage), and the meter automatically adjusts to the scale of the signal. In Manual-ranging meters, you must select the specific range (e.g., 20V, 200V) yourself.Ⅱ Working Principle of MultimeterA Digital Multimeter (DMM) works by converting an analog input signal into a digital value using an A/D converter. The core logic involves comparing the input voltage against a reference voltage.To measure current and resistance, the multimeter actually uses voltage as the base reference:Current: The meter measures the voltage drop across a known internal shunt resistor.Resistance: The meter outputs a small, known current through the component being tested and measures the resulting voltage to calculate resistance (Ohm's Law).Modern DMMs use complex logic control circuits to manage the display, auto-ranging, and safety checks, ensuring that the reading on the screen is stable and accurate. Ⅲ Multimeter Operating ProceduresTo ensure accuracy and safety—especially with modern high-energy circuits—follow these steps:Safety Check: Inspect your test leads for damaged insulation. Ensure the multimeter is rated for the voltage you are testing (e.g., CAT III or CAT IV ratings for household mains).Select Function: Turn the rotary dial to the correct setting (Voltage, Current, or Resistance) before connecting the probes.Select Range: If using a manual-ranging meter and the value is unknown, always start at the maximum range and switch down to lower ranges to get a precise reading. Auto-ranging meters handle this automatically.Zero Calibration: For resistance measurements on analog meters, touch the probes together and zero the needle. Digital meters usually auto-zero, but you can check the "Rel" (Relative) mode on advanced models to null out lead resistance.Power Off for Resistance: Never measure resistance or continuity on a live circuit. Turn off the power to the device before testing.Probe Handling: Keep your fingers behind the finger guards on the test probes to avoid electric shock.Ⅳ Common Multimeter FunctionsMeasure Resistance (Ohms - Ω)Ensure the circuit power is OFF. Connect the test leads across the component (resistor, coil, etc.). Note: Measuring a component while it is soldered to a PCB may give inaccurate results due to parallel paths from other components.Measure Current (Amps - A/mA)Critical Step: You must physically move the red probe to the specific "Amps" or "mA" jack on the multimeter. The meter must be connected in series with the circuit (you must break the circuit and let current flow through the meter). Warning: Connecting a meter in current mode across a voltage source (parallel) will blow the meter's fuse.Measure Voltage (Volts - V)Connect the meter in parallel (across the component or power source). Ensure you select AC (V~) for wall outlets or DC (V=) for batteries.Detect Short Circuit (Continuity)Set the dial to the continuity mode (often marked with a sound wave symbol). Touch probes to two points. If resistance is near zero (a short), the multimeter will beep. This is excellent for checking broken wires or fuses.Non-Contact Voltage (NCV)Many modern multimeters (2020s era and later) include an NCV sensor at the tip. This allows you to detect the presence of live AC voltage in a wire or outlet without touching the metal contacts.Test ICs and ComponentsWhile multimeters can check supply voltage (VCC) and ground pins on Integrated Circuits (ICs), troubleshooting internal IC logic is often better done with an oscilloscope or logic analyzer. However, a multimeter is perfect for finding shorted pins. Ⅴ Multimeter Usage Tips1. Probe Safety: Never touch the metal tips of the probes during a test. Always hold the insulated handles behind the finger guards.2. Switching Gears: Never rotate the selection dial while the probes are connected to a live high-voltage circuit. This can cause internal arcing. Disconnect probes, switch modes, then reconnect.3. Battery Maintenance: If the multimeter will not be used for a long period, remove the internal battery to prevent leakage and corrosion.4. High Voltage Awareness: Be aware of the "CAT" rating of your meter. Do not use a CAT II meter for main service panels (which require CAT III or CAT IV ratings).Video: How to Use a Multimeter?Ⅵ How to Find Circuit Faults with Multimeter6.1 General Troubleshooting Strategy1. Visual InspectionBefore measuring, look for charred components, swollen capacitors, or loose wires. Touching components (cautiously) to check for overheating can also identify shorts.2. Voltage TracingMeasure the voltage at various points in the circuit starting from the power source. If voltage is present at point A but missing at point B, the fault lies between them (e.g., a broken trace or failed component).3. Hidden TroubleshootingIntermittent failures are often caused by "cold" solder joints or loose connectors. Continuity mode is vital here. Wiggle wires while testing continuity; if the beep stops, you have found a loose connection. 6.2 Measuring Techniques6.2.1 Voltage Measuring PointsTesting voltage against a "Ground" reference is the standard method. Connect the black probe to the circuit Ground (GND) and use the red probe to touch various test points (VCC, output pins). Deviations from the expected voltage (e.g., getting 2V on a 5V line) usually indicate a problem.6.2.2 Measuring Parameters Selection① Always check if you are measuring AC or DC. Measuring AC voltage while in DC mode (or vice versa) will give false readings.② For signal circuits, remember that standard multimeters measure "Average" or "RMS" voltage. They may not accurately show fast data pulses—an oscilloscope is required for that.③ Polarity: In DC mode, if you reverse the probes (Red on negative, Black on positive), the screen will simply show a negative sign (e.g., -12V). This is normal and safe for digital meters. Ⅶ How to Measure Current with Digital MultimeterMeasuring DC Current1. Insert the Red test lead into the jack marked "mA" (for low current) or "10A/20A" (for high current). Insert the Black lead into "COM".2. Turn the dial to the DC Current setting (A=).3. Break the circuit: You must physically interrupt the wire and place the multimeter probes in line with the circuit so current flows through the meter.4. Power on the circuit and read the value.Figure 1. Measuring Operating Current of a DC Relay If the reading is negative, your probes are reversed (current is entering the black probe). This does not damage a digital meter.Figure 2. Measuring DC Current in Series Measuring Current with an Analog MultimeterWith analog meters, polarity matters. If you connect probes backward, the needle will deflect to the left (below zero), potentially damaging the mechanism. Always ensure Red connects to the more positive side and Black to the negative side.Figure 3. Series connection with Analog Multimeter Figure 4. Reading the Scale on an Analog Multimeter Measuring AC CurrentThe process is similar to DC, but you must select the AC Current setting (A~). For high currents (e.g., household mains), it is highly recommended to use a Clamp Meter instead of a standard multimeter for safety. A clamp meter measures current via magnetic fields without breaking the circuit.Figure 5. AC Measurement Diagram Ⅷ Which is Better: Analog or Digital Multimeter?For 99% of users in 2025, the Digital Multimeter (DMM) is superior. It offers higher accuracy, higher input impedance (which means it doesn't affect the circuit you are testing), and easier readability. Analog meters are now a niche tool, primarily used by technicians who need to see real-time trends or rapid fluctuations that a digital digital might miss (though modern DMMs with "bar graphs" solve this).Analog MultimeterDigital MultimeterVisualizes trends/fluctuations easily via needle movement.Easy to read exact numbers; no parallax errors.Lower input impedance (can load down sensitive circuits).High input impedance (better for delicate electronics).Susceptible to damage from physical shock (drops).generally more rugged and durable.Often requires manual zeroing and range selection.Includes Auto-ranging, Auto-polarity, and specialized functions.Both meters have their place, but if you can only afford one, buy a Digital Multimeter. They are now available at very affordable price points without sacrificing essential accuracy. Ⅸ Best Multimeter Brands in 2025When selecting a multimeter, reliability and safety are paramount. Brands differ by their target audience: Professionals (industrial use) vs. Hobbyists (home use). Below are reputable brands recognized in the industry today.*Etekcity (Budget/Home)Mastech GroupInnova (Automotive)Klein ToolsKeysight Technologies (formerly Agilent)BrymenKaiweets / AstroAI (Budget)Fluke (Professional Gold Standard)ExtechAmprobeHioki Ⅹ Frequently Asked Questions1. What is a multimeter primarily used for?A digital multimeter is a diagnostic tool used to measure electrical values—principally voltage (Volts), current (Amps), and resistance (Ohms). It is standard equipment for electricians, automotive mechanics, and HVAC technicians. 2. What is "Auto-Ranging"?Auto-ranging is a feature on digital multimeters where the meter automatically selects the correct measurement range for the signal it detects. You simply select "Voltage," and the meter decides if it's millivolts or hundreds of volts. This saves time and prevents setup errors. 3. Why is "True RMS" important?True RMS (Root Mean Square) allows a multimeter to accurately measure AC voltage even when the sine wave is distorted (common in motor drives, HVAC systems, and computers). Non-True RMS meters are only accurate on perfect sine waves. 4. Can I use a multimeter to test a battery?Yes. Set the multimeter to DC Voltage (V=). Connect the red probe to the positive (+) terminal and black to negative (-). A fully charged 1.5V AA battery should read greater than 1.5V (usually 1.6V). If it reads below 1.2V, it is dead. 5. What are CAT ratings?CAT ratings (Category I, II, III, IV) define the safety level of the meter. CAT III or CAT IV is recommended for testing household wiring and mains power to protect against dangerous transient voltage spikes.