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Comprehensive understanding of TVS diode operating principles, types, selection and applications1 Introduction: What is a TVS DiodeIn today's era of increasingly miniaturized and complex electronic devices, Transient Voltage Suppression (TVS) diodes have become indispensable components in the protection of electronic systems. Transient voltage threats—such as Electrostatic Discharge (ESD), Electrical Fast Transients (EFT), and induced lightning strikes—can cause catastrophic damage to sensitive electronic components within microseconds, leading to equipment failure or even safety hazards.TVS diodes are semiconductor devices specifically designed to protect electronic circuits from these transient voltage threats. As the name suggests, they effectively suppress transient voltages by diverting excess energy and limiting the voltage across the protected device. According to the latest market data, the global TVS diode market is projected to grow from $2.44 billion in 2025 to $3.45 billion by 2033, with a compound annual growth rate of 4.37%."The annual loss in electronic equipment due to electrostatic discharge (ESD) and voltage transients is estimated to be approximately $5 billion. Proper transient protection measures can reduce this loss by more than 80%." — Electronic Manufacturers AssociationThis article will comprehensively introduce the working principles, types, parameter selection, application scenarios, and comparisons with other protection devices of TVS diodes, helping electronic engineers and enthusiasts correctly understand and apply this important circuit protection component. Whether you are an experienced designer or a beginner, this guide will provide you with in-depth insights and practical knowledge about TVS diodes.2 Working Principle of TVS Diodes2.1 Basic ConceptsTVS diodes are essentially specially designed avalanche breakdown diodes, specifically used for handling transient overvoltage events. Their working principle is based on the avalanche breakdown characteristics of semiconductor PN junctions. Under normal operating conditions, TVS diodes present a high impedance state, barely affecting the normal operation of the protected circuit. When the applied voltage exceeds its preset breakdown voltage (VBR), the diode rapidly enters a conduction state, diverting excess current while maintaining its terminal voltage at a safe level (known as the clamping voltage VC).TVS diodes need to satisfy three key characteristics to work effectively:Fast response time: TVS diodes typically respond at the sub-nanosecond level (<1ns), which is crucial for capturing extremely brief voltage spikes.High surge current capability: Ability to withstand large currents (typically from a few amperes to hundreds of amperes) for short periods without degradation or damage.Precise clamping characteristics: Maintaining a relatively fixed voltage in the conducting state to ensure the protected circuit is not damaged.2.2 Internal StructureStructurally, TVS diodes differ fundamentally from standard PN junction diodes. They typically employ larger chip areas and thicker epitaxial layers to withstand higher transient power. The typical structure of TVS diodes includes:Unidirectional TVS: Basically a large-area PN structure, optimized for single-direction overvoltage protectionBidirectional TVS: Usually consisting of two back-to-back unidirectional TVS structures, providing bidirectional protectionThe electrical characteristics of TVS diodes are controlled by their semiconductor doping concentration and junction area, thereby achieving the desired breakdown voltage and clamping voltage.2.3 Protection MechanismThe protection mechanism of TVS diodes can be broken down into the following stages:Normal Operating State: When the circuit operates within its nominal voltage range, the TVS diode is in a high impedance state with minimal leakage current (typically in the microampere range or even lower).Transient Event Occurrence: When a transient voltage appears and reaches the reverse breakdown voltage (VBR) of the TVS diode, the diode quickly enters the avalanche breakdown state.Current Diversion: In the conduction state, the TVS diode diverts excess transient current while maintaining its terminal voltage at the clamping voltage (VC) level.Energy Absorption: The TVS diode absorbs the energy from the transient event and dissipates it as heat.Return to Normal: After the transient event ends, the TVS diode automatically returns to its high impedance state without requiring reset or replacement.Professional TipThe response speed of TVS diodes (typically <1ns) is much faster than traditional protection devices like fuses or varistors (typically at the microsecond level). This makes them particularly suitable for protecting modern semiconductor devices that are extremely sensitive to transient events, such as MOSFETs, microcontrollers, and communication interfaces.3 Types of TVS Diodes3.1 Unidirectional TVS DiodesUnidirectional TVS diodes are primarily used in direct current (DC) circuits to protect against transient voltages in either the positive or negative direction (depending on the installation direction). They provide standard diode forward conduction characteristics (typically around 0.7V forward voltage drop) in one direction and avalanche breakdown protection in the opposite direction.Key characteristics include:Suitable for unipolar signal lines and DC power linesLower clamping voltage compared to equivalent bidirectional TVSTypical applications include DC power lines, MOSFET gate protection, etc."When selecting a unidirectional TVS diode, ensure its reverse working voltage is slightly higher than the maximum operating voltage of the system, which ensures it won't conduct under normal operating conditions." — Circuit Protection Design Manual3.2 Bidirectional TVS DiodesBidirectional TVS diodes are essentially two unidirectional TVS connected back-to-back in series, providing similar protection characteristics in both directions. They are particularly suitable for alternating current (AC) signal lines and data lines that require protection in both positive and negative directions.The main applications of bidirectional TVS diodes include:AC signal and power linesBipolar signals (such as audio signals)Data communication lines (such as RS-232, RS-485, CAN bus, etc.)I/O port protectionCompared to unidirectional TVS, bidirectional TVS typically have symmetrical breakdown voltages in both directions, making them particularly suitable for protecting AC signals and bipolar data lines.3.3 TVS Diode ArraysTVS diode arrays are devices that integrate multiple TVS diodes in a single package, designed specifically for protecting multi-line interfaces (such as USB, HDMI, Ethernet, etc.). They typically come in small packages suitable for space-constrained applications.The main advantages of TVS arrays:Multi-channel protection, reducing PCB space usageSimplified design and layoutMore consistent protection characteristicsReduced overall wiring complexity and parasitic effectsCommon TVS array packages include SOT-23-6/8, SOIC-8, QFN, and ultra-small DFN/CSP packages designed for portable electronic devices and high-density PCB designs.Important NoteWhen selecting TVS arrays, consider the coupling effects between channels. High-quality TVS array designs should ensure that a transient event on one channel does not affect other channels through parasitic coupling.4 TVS Diode Selection Parameters4.1 Key ParametersSelecting suitable TVS diodes requires consideration of multiple key parameters, which collectively determine the device's protection capability and application range:ParameterSymbolDefinitionSelection ConsiderationReverse Working VoltageVRWMMaximum reverse voltage that the device can continuously withstandShould be greater than the system's maximum operating voltageReverse Breakdown VoltageVBRVoltage at which the device begins to enter avalanche stateTypically 1.1~1.5 times VRWMClamping VoltageVCMaximum voltage at specific test currentShould be lower than the voltage tolerance of the protected componentPeak Pulse CurrentIPPMaximum transient current the device can withstandShould be greater than the current of expected transient eventsPeak Pulse PowerPPPMaximum transient power the device can absorbDepends on application scenario and expected threat levelReverse Leakage CurrentIRLeakage current at VRWMShould be low enough to not affect normal operationJunction CapacitanceCJParasitic capacitance of TVS diodeLow capacitance types should be selected for high-speed signal linesProfessional TipFor high-speed data lines (such as USB 3.0, HDMI, PCIe, etc.), selecting low-capacitance TVS diodes is crucial. Higher parasitic capacitance can lead to signal integrity issues and data transmission errors. Modern low-capacitance TVS diodes typically have capacitance values as low as 0.5pF.4.2 Selection GuideSelecting appropriate TVS diodes is key to ensuring effective protection. Here is a systematic selection process:Determine the system's maximum operating voltage: Analyze the normal voltage range of the protected circuit, including possible fluctuations.Select reverse working voltage (VRWM): Should be slightly higher than the system's maximum operating voltage, ensuring the TVS doesn't conduct during normal operation.Determine the voltage tolerance of the protected device: This will determine the required upper limit of clamping voltage (VC).Evaluate transient threat types and levels: Determine the required protection level based on application environment (industrial, automotive, consumer electronics, etc.) and applicable standards (IEC 61000-4-2/4/5, etc.).Determine peak pulse current/power requirements: Should be based on worst-case transient event analysis.Consider signal bandwidth requirements: High-speed signals require low-capacitance TVS devices.Evaluate space limitations and heat dissipation conditions: Select appropriate packaging.Reference selection criteria for different applications:Power line protection: Select VRWM slightly higher than maximum power supply voltage, consider higher power handling capabilityData line protection: Prioritize low-capacitance models, ensure signal integrityAutomotive electronics: Select TVS diodes that comply with AEC-Q101 certification, wide operating temperature range, and high energy handling capabilityPortable devices: Consider small package size and low leakage current characteristics4.3 Package TypesTVS diode packages are diverse, ranging from power devices to miniature surface-mount packages. Selecting the appropriate package is crucial for meeting space, power, and heat dissipation requirements:Package TypeSize CharacteristicsPower Handling CapabilityTypical ApplicationsDO-214 (SMA, SMB, SMC)Medium-sized SMD package400W - 5000WPower lines, industrial interface protectionSOD-123/SOD-323Small SMD package150W - 500WMedium to low power applications, space-constrained scenariosSOT-23/SOT-363Small multi-pin package100W - 300WMulti-channel protection, data linesDFN/CSPUltra-small package50W - 200WMobile devices, wearable devicesQFN/SOICMulti-channel array packageVaries by number of channelsMulti-line interface protection (USB, HDMI, etc.)Important NoteWhen selecting a package, consider power dissipation capability simultaneously. For high-power applications, ensure the PCB design provides sufficient heat dissipation paths, such as increasing copper foil area, adding thermal vias, etc. Improper heat dissipation can significantly reduce the actual protection capability of TVS diodes.5 TVS Diode Application Areas5.1 Industrial ApplicationsIndustrial environments typically face harsh electrical conditions, including induced lightning, motor switching transients, power surges, etc. TVS diodes play a crucial role in these applications:Industrial automation systems: Protecting PLC inputs/outputs, sensor interfaces, and communication busesFactory equipment: Protecting motor drivers, frequency converters, and control circuitsMeasuring instruments: Ensuring stability and accuracy of precision measurement circuitsFieldbus systems: Protecting industrial communication interfaces such as RS-485, PROFIBUS, DeviceNet, etc.Industrial applications typically require TVS diodes with high power handling capability and wide operating temperature range. In these applications, reliability and durability are primary considerations.5.2 Automotive ElectronicsAutomotive electronic systems are exposed to harsh electrical and environmental conditions, requiring special protection measures. Automotive-grade TVS diodes typically need to meet AEC-Q101 standards and withstand a wide range of temperatures and electrical transients.Major automotive applications include:Engine Control Units (ECUs): Protecting sensor inputs and actuator control linesIn-vehicle networks: CAN bus, LIN bus, and FlexRay communication line protectionPower management systems: Protecting power conversion and distribution circuitsSafety systems: Airbag controllers, ABS, and ADAS systemsInfotainment systems: Protecting audio/video interfaces and USB connections"As the level of automotive electronics continues to increase, especially with the popularization of 48V systems and electric vehicles, TVS protection in automotive environments has become more important than ever before." — Automotive Electronics Design Magazine5.3 Consumer ElectronicsIn consumer electronic products, TVS diodes are mainly used to protect interface circuits and sensitive components from ESD and power transients. These applications typically have strict requirements for size, cost, and performance.Mobile devices: Protection for charging interfaces, audio interfaces, and data ports in smartphones and tabletsPersonal computers: Protection for USB, HDMI, Ethernet, and other I/O interfacesHome appliances: Protection for control circuits and power inputsWearable devices: Protection for battery management and communication interfacesIn consumer electronics applications, small size, low capacitance, and low cost are important selection factors. As interface speeds continue to increase, low-capacitance TVS diodes are becoming increasingly important.5.4 Telecommunications EquipmentCommunications equipment is frequently exposed to harsh outdoor environments and is susceptible to lightning strikes and power transients. These applications require robust protection solutions:Base station equipment: Protection for RF paths, power inputs, and control linesNetwork switching equipment: Protection for Ethernet ports and backplane connectionsLine interface protection: DSL, T1/E1 line interface circuitsPower line protection: AC/DC converter input protectionCommunication applications typically require compliance with specific standards such as IEC 61000-4-5 (surge), GR-1089-CORE, and ITU K.20/K.21 standards, which influence the selection of TVS diodes.TVS Diode AdvantagesNanosecond-level response timeLow clamping voltageNo degradation design (can withstand thousands of overvoltage events)Bidirectional protection capability (bidirectional type)No follow current (auto-recovery)TVS Diode LimitationsLimited power handling capability (compared to large varistors)Higher cost (especially high-power models)Parasitic capacitance may affect high-speed signalsDifficulty handling extremely high-energy eventsInstallation direction sensitive (unidirectional type)6 TVS Diode Market TrendsThe TVS diode market is experiencing significant growth and technological evolution, driven by multiple factors:According to market research data, the global TVS diode market is expected to grow from $2.45 billion in 2025 to $3.45 billion by 2033, with a compound annual growth rate of 4.37%. The following are the main trends affecting the market:Miniaturization and Low Capacitance: As electronic devices continue to miniaturize, demand for ultra-small package TVS diodes is rapidly growing. Simultaneously, high-speed interfaces (such as USB 3.2, HDMI 2.1, PCIe 5.0, etc.) are driving a surge in demand for low-capacitance TVS diodes.Automotive Electronics Growth: The rise of electric vehicles, autonomous driving features, and advanced driver assistance systems (ADAS) has greatly promoted the demand for high-performance automotive-grade TVS diodes. According to forecasts, automotive electronics will be the fastest-growing segment in the TVS diode market, with an expected growth rate of 13% between 2025-2033.Proliferation of IoT Devices: With over 75 billion IoT devices expected to be deployed globally by 2026, there is a massive demand for low-power, small-form-factor TVS protection solutions.Integrated Protection Solutions: There is an increasing trend toward multifunctional protection components that integrate TVS diodes with other protective elements (such as PTCs, fuses, common mode chokes, etc.) into a single package, providing comprehensive protection.New Material Technologies: Wide bandgap semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN) are emerging in high-performance TVS diodes, offering higher temperature tolerance and greater energy handling capabilities.In terms of regional market distribution, the Asia-Pacific region (especially China, South Korea, and Taiwan) is expected to account for the largest market share, primarily due to the region's strong electronics manufacturing industry and rapidly developing automotive industry. North American and European markets will be driven by high-end applications and stringent regulatory environments."As electronic devices become smaller and more complex, there is growing demand for 'one-stop' integrated protection solutions. This is driving the development of multifunctional TVS devices that not only provide overvoltage protection but also integrate EMI filtering and surge limiting functions." — Semiconductor Industry AnalystTechnological development directions include TVS diodes with higher energy density, lower clamping ratio (ratio of clamping voltage to reverse working voltage), and specialized protection solutions for fast charging applications. The industry is also focused on manufacturing process innovations to reduce production costs and improve reliability.7 Comparison of TVS Diodes with Other Protection Devices7.1 TVS Diodes vs VaristorsTVS diodes and varistors (MOVs) are two commonly used overvoltage protection devices, each with their own advantages and disadvantages:TVS Diode AdvantagesFaster response time (<1ns vs. MOV's ~25ns)More precise and stable clamping voltageNo performance degradation (can withstand thousands of overvoltage events)Lower leakage currentSmaller size (especially modern SMD packages)Varistor AdvantagesCan handle higher transient energy (under comparable volume conditions)Generally lower costHigher voltage ratings available (up to several kilovolts)Inherently bidirectional operationBetter suited for AC line protectionApplication scenario comparison:TVS diodes are suitable for: Protecting sensitive electronic equipment, high-speed data lines, applications requiring precise clamping voltageVaristors are suitable for: AC power line protection, high-energy surge protection, cost-sensitive applications, primary/secondary surge protection7.2 TVS Diodes vs Zener DiodesAlthough TVS diodes and Zener diodes operate based on similar physical principles, they have fundamental design differences and application scenarios:CharacteristicTVS DiodeZener DiodePrimary FunctionTransient overvoltage protectionVoltage regulation and referenceChip DesignLarge area PN junction to handle transient powerSmall area structure optimized for stabilityPower HandlingHigh peak power, low continuous powerLow peak power, moderate continuous powerResponse TimeExtremely fast (sub-nanosecond)Fast (nanosecond level)Temperature CoefficientTypically higherCan be very low (temperature compensated types)While Zener diodes can serve as simple protection elements in some low-power applications, TVS diodes are optimized specifically for handling high-energy transient events, providing more reliable protection capabilities.Important NoteDo not use Zener diodes for protection scenarios requiring high energy handling capability. Transient events exceeding their power handling capacity, even for short durations, will cause permanent damage to the Zener diode, leaving the protected circuit exposed to danger.7.3 Protection Device Comparison TableThe following table summarizes the key characteristics comparison of common overvoltage protection devices:CharacteristicTVS DiodeVaristorGas Discharge TubeMultilayer Varistor CeramicResponse Time< 1ns (extremely fast)~25ns (fast)>100ns (slow)~1ns (extremely fast)Clamping PrecisionHighMediumLowMedium-highPower CapacityMediumHighVery highLowLeakage CurrentVery lowHigherExtremely lowRelatively lowLifespan/DurabilityVery longSignificant degradationLimited number of operationsRelatively longCapacitanceMedium to low (special models)MediumVery lowHigherMain ApplicationsData lines, DC power, secondary protectionAC power, primary protectionCommunication lines, primary protectionLow-power signal linesIn practical applications, multi-layer protection strategies are often adopted, combining different types of protection devices to achieve optimal performance. For example, using gas discharge tubes or varistors as primary protection, followed by TVS diodes as secondary protection, to achieve the best protection effect.8 PCB Design Practical TipsProper use of TVS diodes in PCB design is critical for effective protection. Here are some key design considerations:Placement: TVS diodes should be placed as close as possible to the interface or device being protected. Ideally, the TVS should be the first component "seen" by signals or power lines coming from external connections.Layout Best Practices:Keep TVS connections to ground as short and direct as possible to reduce parasitic inductanceUse wider PCB traces to reduce impedanceAvoid connecting TVS to ground planes through narrow viasUse multiple parallel vias when necessary to lower impedanceGrounding Strategy: For high-speed signal protection, TVS diodes should be connected to a low-impedance ground plane, avoiding shared current return paths with sensitive analog or digital grounds.Thermal Management: High-power TVS diodes may require additional thermal management measures. Design sufficient copper area for heat dissipation, and when necessary, use thermal vias to connect to inner or bottom layer copper.Pro TipWhen protecting high-speed differential pairs (such as USB 3.0, HDMI, PCIe, etc.), select differential pair TVS diodes specifically designed for these applications, and ensure that the layout maintains symmetry to preserve signal integrity.For particularly sensitive circuits or applications in harsh environments, consider multi-stage protection schemes:Use high-power TVS or varistors as the first stage of protection to handle most of the energyUse precision TVS diodes as the second stage of protection to precisely control residual voltageAdd RC filters if necessary to further attenuate high-frequency components9 Frequently Asked QuestionsQ: What's the difference between TVS diodes and regular diodes?A: While both are semiconductor devices based on PN junctions, TVS diodes are specifically designed to handle high-energy transient events, featuring larger junction areas, higher power handling capabilities, and precise breakdown voltage characteristics. Regular diodes are primarily used for rectification or signal processing and are not suitable as protection devices.Q: How do I determine the power requirements for a TVS diode?A: Power requirements depend on the characteristics of the expected transient events. Consider the peak voltage of the transient, its duration, and possible energy levels. Typically, you should refer to industry standards applicable to your specific application (such as IEC 61000-4-5 surge standard or IEC 61000-4-2 ESD standard) to determine worst-case energy levels, then select a TVS diode with sufficient safety margin.Q: Do TVS diodes affect high-speed signal integrity?A: Yes, the parasitic capacitance of TVS diodes can affect high-speed signal integrity. For high-speed interfaces such as USB 3.0, HDMI 2.0, PCIe, etc., specialized low-capacitance TVS diodes (typically <1pF) should be selected. Additionally, PCB layout is critical for minimizing signal integrity issues.Q: How do I choose between unidirectional and bidirectional TVS diodes?A: For unipolar signal lines and DC power lines, unidirectional TVS diodes are typically used, offering lower clamping voltage in one direction. For signal lines that may experience voltage in both directions (such as AC signals, data lines, audio lines, etc.), bidirectional TVS diodes should be used. If uncertain, bidirectional models are generally the safer choice, although unidirectional types can provide lower clamping voltage.Q: Do TVS diodes have a "service life"? Do they degrade over time?A: Unlike varistors, TVS diodes do not significantly degrade when used within their rated parameters. They can withstand thousands of transient events within their rated range without performance deterioration. However, transient events exceeding their ratings may cause damage or performance degradation to the TVS diode.10. Conclusion and Future OutlookTVS diodes, as key components in the protection of modern electronic devices, provide effective defense against transient voltage threats. Their fast response time, excellent clamping performance, and reliability make them ideal for protecting increasingly sensitive and complex electronic systems.As electronic devices continue to evolve toward higher speeds, smaller sizes, and lower power consumption, TVS protection technology continues to evolve as well. Future trends in TVS diode technology include:Lower clamping ratio: Allowing protection of low-voltage circuits with smaller voltage marginsUltra-low capacitance designs: Supporting next-generation ultra-high-speed interfaces (such as USB4, PCIe 6.0, etc.)Higher power density: Providing more protection in smaller packagesMultifunctional integrated protection: Combining EMI filtering, common mode suppression, and ESD protection functionsWide bandgap semiconductor materials: Using SiC and GaN to provide better temperature performance and reliabilityWhen selecting and applying TVS diodes, a comprehensive understanding of key parameters, awareness of the specific application requirements and constraints, and adherence to good design practices are crucial for achieving effective circuit protection. As electronic systems become more complex and sensitive, professional circuit protection design will continue to be a key factor in ensuring product reliability and durability."In electronic design, neglecting transient protection is often a major source of system reliability issues. Proper selection and application of TVS diodes is not just a technical consideration but a critical investment in ensuring product quality and customer satisfaction." — Electronic System Reliability HandbookThrough this comprehensive introduction to TVS diodes, we hope to provide electronic engineers and designers with the necessary knowledge for selecting and using these critical protection devices to create more reliable and durable electronic systems.About the AuthorElectronics engineer with over 10 years of experience in circuit design and electronic protection. Specializing in power management, signal integrity and circuit protection, he has assisted many companies in designing reliable electronic systems.Extended ReadingDiodes Understanding Switching Diodes: Principles, Advantages, and Applications5 Items You Need to Know About DiodesDiode Rectifier Basics and Circuit Types OverviewLast Updated: 2025-04-28 body { font-family: 'Arial', sans-serif !important;; line-height: 1.6 !important; color: #333; background-color: #f9fafb; } .container { max-width: 1200px; margin: 0 auto; padding: 20px; } h2, h3, h4 { font-weight: 700; margin-top: 1.5em; margin-bottom: 0.5em; color: #1a56db; } } h2 { font-size: 2rem; border-bottom: 2px solid #e5e7eb; padding-bottom: 0.5rem; } h3 { font-size: 1.5rem; color: #2563eb; } h4 { font-size: 1.25rem; color: #3b82f6; } p { margin-bottom: 1.5rem; } .quote { background-color: #e0f2fe; border-left: 4px solid #3b82f6; padding: 1rem; margin: 1.5rem 0; border-radius: 0 6px 6px 0; } table { width: 100%; border-collapse: collapse; margin: 1.5rem 0; } table, th, td { border: 1px solid #e5e7eb; } th, td { padding: 0.75rem 1rem; text-align: left; } th { background-color: #f3f4f6; font-weight: 600; } tr:nth-child(even) { background-color: #f9fafb; } ul, ol { margin-bottom: 1.5rem !important;; padding-left: 2rem !important;; } ul li, ol li { margin-bottom: 0.5rem !important;; } .pro-tip { background-color: #d1fae5; border-radius: 6px; padding: 1rem; margin: 1.5rem 0; border-left: 4px solid #10b981; } .important-note { background-color: #fee2e2; border-radius: 6px; padding: 1rem; margin: 1.5rem 0; border-left: 4px solid #ef4444; } .toc { background-color: #f3f4f6; padding: 1.5rem; border-radius: 6px; margin-bottom: 2rem; } .toc ul { list-style-type: none; padding-left: 0; } .toc ul ul { padding-left: 1.5rem !important;; } .toc li { margin-bottom: 0.5rem !important;; } .toc a { text-decoration: none; color: #2563eb; } .toc a:hover { text-decoration: underline; } .author-section { background-color: #f3f4f6; border-radius: 6px; padding: 1.5rem; margin-top: 3rem; display: flex; align-items: center; } .author-section img { width: 80px; height: 80px; border-radius: 50%; margin-right: 1.5rem; margin-top: 0; margin-bottom: 0; } .pros-cons { display: flex; gap: 20px; margin: 1.5rem 0; } .pros, .cons { flex: 1; padding: 1rem; border-radius: 6px; } .pros { background-color: #d1fae5; } .cons { background-color: #fee2e2; } .faq-item { margin-bottom: 1.5rem; } .faq-question { font-weight: bold; color: #1e3a8a; margin-bottom: 0.5rem; }

Executive Summary: What is a Phototransistor?A phototransistor is a light-sensitive semiconductor device that converts incident light into electric current while providing internal gain amplification. Unlike simple photodiodes, phototransistors utilize a bipolar junction structure (NPN or PNP) to amplify the signal, making them highly effective for optical switching, object detection, and encoding systems in modern 2026 electronics.Ⅰ Introduction to PhototransistorsThe phototransistor is a specialized semiconductor device engineered to detect light levels and modulate the current flowing between the emitter and collector based on the photon intensity it receives.While both phototransistors and photodiodes serve as optical sensors, the phototransistor distinguishes itself through high sensitivity attributed to the internal gain of its bipolar transistor architecture. As of 2026, this intrinsic amplification makes phototransistors the preferred choice for applications requiring robust signal detection without complex external amplification circuitry.Ⅱ Video Tutorial: How Phototransistors WorkVisual learners can understand the practical operation of light detection in the following tutorial.Phototransistor Tutorial Phototransistor Video Description:A comprehensive tutorial demonstrating how to utilize phototransistors for precise light detection in circuit design.  Ⅲ What Is a Phototransistor?A phototransistor is an electronic switching and current amplification component that operates by converting photon energy into electrical signals. When light strikes the exposed base-collector junction, a reverse current flows proportional to the luminance intensity.Widely used to convert light pulses into digital electrical signals, these components are powered by light interactions rather than solely electrical bias at the base. They offer high gain and low cost, making them ubiquitous in 2026 consumer electronics. Figure 1: Phototransistor SymbolFunctionally, phototransistors share similarities with photoresistors (LDRs), but with a key distinction: phototransistors generate current and voltage through the photovoltaic effect and amplification, whereas LDRs only change resistance.Transistors with the base terminal exposed are chemically doped to maximize light sensitivity. Photons striking the depletion layer generate electron-hole pairs, activating the transistor just as a base current would in a standard BJT. Silicon-based photosensors typically respond to visible and near-infrared radiation (approx. 400nm to 1100nm). Ⅳ How are Phototransistors Constructed?The phototransistor's structure is specifically optimized for photo-applications by maximizing the area of the base-collector junction. While ordinary bipolar transistors exhibit some photosensitivity, phototransistors feature significantly larger base and collector areas to capture maximum light flux.Figure 2: Construction of a PhototransistorⅤ Semiconductor Material EvolutionHistorical phototransistors utilized a homo-junction structure, fabricated entirely from germanium or silicon. In contrast, modern 2026 phototransistors often employ type III-V semiconductor materials, such as gallium arsenide (GaAs), to target specific wavelengths and increase efficiency.Key structural variations include:NPN Topology: The most popular configuration due to the higher mobility of electrons compared to holes.Heterostructures: Utilizing different materials on either side of the PN junction to enhance conversion efficiency.Mesa Structure: A common physical layout for optimized light absorption.Schottky Junctions: Occasionally used for the collector to improve switching speeds.To ensure optimal sensitivity, the emitter contact is frequently offset, preventing it from blocking light from reaching the active region. Ⅵ How Does a Phototransistor Work?A phototransistor operates by using light to control the flow of current, effectively replacing the base current of a standard transistor with photon energy.Biasing: The collector is biased positively relative to the emitter (in NPN), creating a reverse-biased Base-Collector (B-C) junction.Injection: Light strikes the B-C junction, generating electron-hole pairs.Amplification: The movement of these carriers constitutes a base current, which the transistor amplifies by its gain factor (hFE).Typically, the physical base terminal is left unconnected (floating), as the device is controlled entirely by incident light. Ⅶ Key Electrical CharacteristicsSince phototransistors are essentially Bipolar NPN Transistors with an exposed junction, their V-I characteristics resemble a standard BJT family of curves, but with Light Intensity (mW/cm²) replacing Base Current (IB).Dark Current: When no light is present, a minuscule leakage current flows from collector to emitter. In high-precision applications, minimizing this Dark Current is crucial.Light Current: As light intensity increases, the base current rises, triggering the amplification process. Figure 3: Reverse Bias Configuration The collector current characteristics curve below demonstrates the linear relationship between light intensity and output current in the active region.Figure 4: Collector Current vs. Irradiance Ⅷ Selection Criteria & PropertiesWhen selecting a component for 2026 designs, engineers must evaluate specific properties to ensure the device matches the optical environment.Critical Datasheet Properties:Peak Wavelength: The specific color of light (e.g., 850nm IR vs. 560nm Visible) the device is most sensitive to.Linearity: How accurately the output follows the input light intensity.Sensitivity: The ratio of output current to incident light power.Response Time: The rise and fall time, which determines the maximum data rate (typically slower than photodiodes).Acceptance Angle: The field of view from which the sensor can detect light. Ⅸ Common Types: BJT vs. FETPhototransistors are primarily categorized by their internal transistor architecture:BJT Phototransistor: The standard type. In darkness, it leaks only ~100 nA. Under illumination, it can conduct up to 50mA. This high current handling capability distinguishes it from photodiodes.Photo-FET (Field Effect Transistor): Utilizes light to generate a gate voltage that controls the drain-source current. Photo-FETs offer extremely high input impedance and are more sensitive to weak light signals, though they are less common in general switching applications. Ⅹ Practical Circuit Examples (2026 Applications)The primary goal of phototransistor circuits is to generate a usable output voltage from light-induced current. Unlike photodiodes which often require Transimpedance Amplifiers (TIA), phototransistors have built-in gain, allowing for simpler circuit designs.Common Configurations:Common-Emitter (Inverting): Output voltage drops as light increases.Common-Collector (Non-Inverting): Output voltage rises as light increases.Figure 5: Basic Amplifier Configurations 10.1 Step-by-Step Circuit Implementations 1. Light Operated Relay (Automatic Day Switch)Mechanism: When light strikes phototransistor Q1, it conducts, supplying base current to the driver transistor Q2. Q2 then activates the mechanical relay, turning on the connected load. 2. Darkness Operated Relay (Night Light)Mechanism: By inverting the logic, the relay activates only when light is absent. In darkness, the phototransistor turns off (high resistance), allowing the bias resistor to trigger Q2. 3. Light Interruption Alarm (Security System)Mechanism: This circuit functions as a tripwire. Under normal conditions (laser/light hitting sensor), the phototransistor pulls the SCR gate LOW (off). When the beam is broken by an intruder, the gate voltage rises, latching the SCR and sounding the alarm until manually reset. Ⅺ Datasheet Specifications to WatchTo ensure system reliability, consult the following parameters in manufacturer datasheets:Collector Current (IC): Maximum current the device can handle (typically 1mA - 50mA).Dark Current (ID): Leakage current in total darkness (lower is better for precision).Peak Wavelength (λp): The wavelength of maximum sensitivity.VCE(sat): Collector-Emitter saturation voltage.Rise/Fall Time (tr/tf): Critical for optical data transmission applications.Power Dissipation (Ptot): Thermal limits of the package. ⅻ Pros and Cons AnalysisSelecting the right optical sensor requires balancing sensitivity, speed, and cost.AdvantagesDisadvantagesHigh Gain: Produces higher current output than photodiodes, reducing the need for external amplifiers.Limited Voltage: Cannot withstand high voltages compared to Thyristors or Triacs.Cost-Effective: Inexpensive to manufacture and integrate into ICs.Slower Speed: Slower response time (lower bandwidth) compared to PIN photodiodes.Simplicity: Can drive small relays or logic gates directly in simple circuits.Temperature Sensitivity: Dark current increases significantly with temperature fluctuations. XIII Modern Applications in 2026Due to their versatility, phototransistors are integral to many modern technologies:Optocouplers (Optoisolators): Protecting low-voltage logic circuits from high-voltage spikes in power supplies.Optical Encoders: Used in robotics and motors to detect position and speed.Object Detection: Proximity sensors in smartphones and automated manufacturing lines.Safety Systems: Smoke detectors and light curtain barriers for industrial machinery.Remote Control Receivers: IR detection for consumer electronics (though often integrated with demodulators). XIV Comparison: Photodiode vs. PhototransistorWhile both detect light, their use cases differ based on speed and sensitivity needs.FeaturePhotodiodePhototransistorOutputLow Current (µA)High Current (mA) - AmplifiedResponse SpeedVery Fast (Nanoseconds)Moderate (Microseconds)ApplicationsFiber Optics, High-Speed DataRemote Controls, Light Switches, EncodersNoiseLow NoiseHigher Noise levels XV Frequently Asked Questions1. What type of device is a phototransistor?A phototransistor is a bipolar semiconductor device. It functions as a transistor where the base current is generated by incident photons striking the exposed semiconductor junction, rather than an electrical connection.2. What is the main difference between a standard transistor and a phototransistor?Physically, the primary difference is the packaging. A phototransistor has a transparent lens or window to allow light to reach the junction, and it often lacks an external base pin. Electrically, it is controlled by light intensity rather than input current.3. Is a phototransistor considered a sensor?Yes, it is a discrete photosensor. It detects the presence and intensity of light and converts it into a measurable electrical signal.4. How do you test if a phototransistor is working?You can test it using a multimeter or a simple circuit:Connect the phototransistor in series with a resistor and LED to a power source (checking polarity).Expose the sensor to light; the LED should brighten.Cover the sensor; the LED should dim or turn off.5. Which is better: Photodiode or Phototransistor?Neither is universally "better"; it depends on the application. For high-speed data (like fiber optics), a photodiode is superior. For switching and sensing without extra amplifiers, a phototransistor is more efficient due to its internal gain.{ "@context": "https://schema.org", "@graph": [ { "@type": "Article", "headline": "Phototransistors: The Ultimate 2026 Guide", "datePublished": "2021-12-02", "dateModified": "2026-01-07", "description": "A comprehensive guide to phototransistors, covering construction, working principles, circuit diagrams, and 2026 applications.", "image": "https://www.kynix.com/editor_u/image/20211202/2021120216390176.jpg", "author": { "@type": "Organization", "name": "Kynix Electronics" } }, { "@type": "FAQPage", "mainEntity": [ { "@type": "Question", "name": "What type of device is a phototransistor?", "acceptedAnswer": { "@type": "Answer", "text": "A phototransistor is a bipolar semiconductor device where the base current is generated by incident photons striking the exposed junction." } }, { "@type": "Question", "name": "What is the difference between a transistor and a phototransistor?", "acceptedAnswer": { "@type": "Answer", "text": "The main difference is that a phototransistor has an exposed optical window and is controlled by light intensity, whereas a standard transistor is controlled by electrical current at the base pin." } }, { "@type": "Question", "name": "Is a phototransistor a sensor?", "acceptedAnswer": { "@type": "Answer", "text": "Yes, a phototransistor is a discrete photosensor that converts light intensity into an electrical signal." } }, { "@type": "Question", "name": "Which is better: Photodiode or Phototransistor?", "acceptedAnswer": { "@type": "Answer", "text": "Photodiodes are better for high-speed data applications, while phototransistors are better for switching and sensing applications requiring higher sensitivity and gain." } } ] }, { "@type": "HowTo", "name": "How to Build a Simple Light Interruption Alarm", "step": [ { "@type": "HowToStep", "name": "Setup the Phototransistor", "text": "Connect the phototransistor to a pull-down resistor to create a voltage divider." }, { "@type": "HowToStep", "name": "Connect the SCR", "text": "Connect the output of the phototransistor junction to the Gate of an SCR (Silicon Controlled Rectifier)." }, { "@type": "HowToStep", "name": "Align the Light Source", "text": "Point a laser or light beam directly at the phototransistor. This keeps the SCR gate low (Off)." }, { "@type": "HowToStep", "name": "Trigger the Alarm", "text": "Interrupt the light beam. The phototransistor turns off, voltage spikes at the SCR gate, latching the alarm on." } ] } ]}

Introduction   If you've heard much about furnaces and their components, you've almost certainly heard the term "blower." Because the blower is an important component of the furnace, we'll explain what it is, how it works, and what to expect if it develops problems.   The blower is one of your furnace's most aptly named components: its sole purpose is to blow hot air through the ducts and into your home.   There is an important distinction to be made between a blower motor and a blower fan. Although they are frequently referred to as the "blower," the majority of problems you will encounter will be with the blower motor itself. After all, the blower fan is merely an accessory to the motor.   Figure1: Blower motors are able to move large volumes of air since they use fan cages in enclosed spaces.   Catolog Introduction Ⅰ What Is a Blower Motor? Ⅱ How does a Blower Motor Works? Ⅲ Why Blower Motor need Maintenance? Ⅳ Types of Blower Motors Ⅴ What is the Components of a Blower Motor? Ⅵ Where is a Blower Motor Located? Ⅶ How to test the blower motor? Ⅷ What are Some Of The Symptoms of a Failing Blower Motor? Ⅸ Can I Change Out The Blower Motor Myself? Ⅹ What Steps DO I need to take for this DIY Blower Motor Replacement? Ⅺ FAQ     Ⅰ What Is a Blower Motor?   A blower motor is a motor that drives the fan in a car's heating and air conditioning system.   A blower motor is a part of a home's HVAC system. When the heating system is operated, the motor blows heated air through vents. When the air conditioning system is on, some blower motors blow cold air. Blower motors are classified into two types: single-speed motors and variable-speed motors. Single-speed blower motors only produce one speed of airflow. Variable-speed motors change their speed to blow air at different levels. A properly functioning blower motor is still a significant part of your home's HVAC system. The blower motor is critical in keeping your home at a comfortable temperature.       Understand Blower Motor Circuits to Better Diagnose Problems (Season 5/E12)       Ⅱ How does a Blower Motor Works?     ostats cooperated with the home's heating and cooling systems to monitor the temperature. When the temperature falls below the thermostat setting, the furnace activates. The furnace generates hot (or cold) air, which must then circulate throughout your home. This is when the blower motor kicks in.   A blower motor circulates the heated or cooled air produced by the furnace throughout the home to ensure the temperature meets the temperature set on the thermostat. It accomplishes this by spinning a fan, which blows air through your home's ventilation system. Even a small blower motor can move a significant amount of air.       Figure2: motor circuit   When in use, single-speed motors operate at one speed and full energy capacity. The thermostat controls the operation of your blower motor by telling it when to turn on and off. Single-speed motors can cause cold spots because they only run when the thermostat signals them to. Variable-speed motors, on the other hand, blow air at higher and lower speeds as needed. As a result, this motor contributes to a more evenly distributed temperature throughout your home. Furthermore, variable-speed motors are typically more energy-efficient than single-speed motors, allowing you to save money on your monthly energy bills.       Ⅲ Why Blower Motor need Maintenance?   One of the most obvious signs that your blower motor has failed is that your furnace is persistently working while the house remains cool. You can ensure your family's year-round comfort by properly maintaining your furnace's blower motor. When each heating season is coming, clean the fan blades, inspect the motor belt for wear and tear, and lubricate the motor adequately.   Even with proper maintenance, some problems can cause your blower motor to stop working. Common problems, for example, involve the resistor, fan relay, and climate control switches. An experienced HVAC professional, on the other hand, evaluates and repairs any problems with these components.     Figure3: blower motor in HVAC     Blower motor failure can also be caused by a worn-out bearing, a broken or worn-out motor, or an obstructed fan cage. However, routine maintenance, such as regular cleaning, keeps the motor clean. Furnaces are frequently found in basements and laundry rooms. As a result, dirt and even small lint particles frequently find their way into the engine, causing burnouts. In addition, dirt or debris falling down the ventilation system frequently obstructs the blower motor fan cage.       Ⅳ Types of Blower Motors   There are two types of blower motors. The first option is a single-speed transmission. When the thermostat indicates that the temperature in your home has dropped or increased beyond the desired setting, single-speed blower motors will activate.   The variable-speed blower motor is the second type of blower motor. Variable-speed blower motors are distinguished from single-speed blower motors by their ability to move at different speeds, allowing them to better command the flow of air in your home. Variable-speed blower motors use less energy. They consume 2-4 amps, whereas older-style motors consume 12 amps. The amount of electricity consumed by the motor is measured in amps. The slower speed also contributes to efficiency.   Variable motors also circulate the air in your home more frequently, preventing cold spots. Finally, variable speed blower motors are quieter than single-speed blower motors.       Ⅴ What is the Components of a Blower Motor?   The components of a blower motor can vary depending on the application, but they typically include:   a direct current motora fan housing that can be bolted down (also known as a wheel or cage)Some blower motors are wired differently than others, but the majority of systems use a few other components to control their operation, such as:a fan relay and a blower motor resistor   Figure4: components of a blower motor         Ⅵ Where is a Blower Motor Located?     A blower motor is typically found in the heater box, though each vehicle is slightly different. Some blower motors are easily accessible, while others are hidden beneath the dash. Blower motors are commonly found inside the passenger compartment for most passenger cars and trucks, but in some cases, the heater box, blower motor, or both are located in and accessed from, the engine compartment.       Figure5: Mazada3     Large vehicles, such as large SUVs and vans, may have multiple blower motors. In those cases, one blower motor is typically located in the front heater box and another somewhere in the rear of the vehicle. These vehicles may also have an additional heater core located in the passenger compartment's back end.       Ⅶ How to test the blower motor?   If the blower motor does not function properly, the blower motor has to be diagnosed preferentially. When the blower motor is on, the voltage at the blower motor connector is typically measured. If there is a voltage at the motor (at least 4-6 Volts at low speed and 12 Volts at high speed), but the motor does not run, the motor is defective or jammed. Voltage testing of the blower motor The voltage at the blower motor is being tested. If there is a voltage at the motor (at least 4-6 Volts at low speed and 12 Volts at high speed), but the motor does not run, the motor is defective. Leaves, twigs, nuts, and pieces of a ripped cabin filter can all jam the blower motor's blade. This is a common occurrence in many automobiles.   If there is no voltage at the motor, the entire blower motor circuit, beginning with a fuse, has to be tested. See also: how to test a fuse in a car.     Figure6 : Testing the voltage at the blower motor. If there is a voltage at the motor (at least 4-6 Volt at low speed and 12 Volt at high speed), but the motor doesn't run, the motor is bad.       Ⅷ What are Some Of The Symptoms of a Failing Blower Motor? When the blower motor is faulty , it will come out some of the symptoms of a bad or a failing blower motor.   Low Or Inadequate Airflow From the Vents Low or shaky airflow from the vents is one of the most noticeable signs of a faulty blower motor. When you turn on the A/C or heat, the vents will blow out air, but it will be much lower or fainter than you're used to. This is a good indication that your blower motor is either broken or starting to wear out. A faulty blower motor will not properly cool or heat a vehicle. The temperature in the car's cabin will also be uncontrollable.     The Fan Will Only Blow At Specific Speeds Another sign of a faulty blower motor is a motor that only operates at certain speeds. Many blower motors are designed and built to operate at different speeds. Their design allows for the control of various cabin temperatures. You have a faulty blower motor if it does not push air at any of its specific settings.     There is No Air Coming From The Vents When there is no air flow from your vehicle's vents when the A/C or heat is turned on, this indicates that you have a faulty blower motor. If your blower motor fails or short circuits, there will be no airflow produced for the system. This type of situation necessitates a complete replacement of the blower motor in order to restore proper system operation.   Figure67: No Air Coming From The Vents     Smoke Is Being Blown At You Have you noticed a burning odor while driving your car? Then you should pull over as soon as possible. You could have a blown-out blower motor. Your blower motor may also have bad wiring or a short circuit. That burned or short-circuited blower motor could be emitting burning odors and smoke that you should not inhale or endure. If you inspect your blower motor and discover a blown fuse in the blower motor circuit, you have proof that the circuit was overloaded.       Ⅸ Can I Change Out The Blower Motor Myself?   You certainly can. You can successfully replace the blower motor if you have the patience, the right tools, and the energy.   What tools are required for a blow motor replacement? The following tools are required for a successful blow motor change out:   Set of Rachet and SocketService manual for a small flat heat screwdriverNew cabin air filter and blower motorCleaning cloths and flashlights       Ⅹ What Steps DO I need to take for this DIY Blower Motor Replacement?   Check that you're parked on a level surface and that your parking brake is engaged. Remove your car's hood and disconnect the battery.     Step1: Find the blower-motor service manual. Important Note: If your vehicle was built prior to the mid-late 1990s, your blower motor may be located inside the engine bay, on the firewall on the passenger side. It should be easy to find.     Step2: Remove the lower trim from your glove box. This may necessitate the removal of a few bolts.Examine your supplies for clips and plastic connectors. Please be gentle and mild with them if you do. You want them to fit back together properly.     Step3:  Take a look in your glove box. Then take it out. This usually only necessitates a push of the retaining clips to the side, allowing you to unlatch the glovebox from its housing. With your flashlight, enter the footwell.   Step4: Then, raise your eyes to the ceiling until you see the blower motor. Look for three or six bolts that keep it together.   Step5: Use your sockets and ratchet kit to remove the bolts. These bolts are almost certainly metric-sized bolts.The motor assembly for your blower should easily slide out. This should also allow you to disconnect the HVAC vent connections. It is now time to disconnect the electrical power connector. You can dislodge the clips by hand or by using a small flathead screwdriver.   Step6: Use your old blower as a template for installing the new blower. Allow plenty of time to install the new blower. You may also need to replace a gasket.You can now connect the vehicle's power supply. After that, it's time to reinstall the HVAC vents. Then, carefully slide the blower motor into the bracket. You can now secure your new blower.     Step7:  The next step is to replace your glovebox and lower trim panel. After that, you can reconnect the battery in your vehicle. You are now ready to start your engine and test the blower motor's operation. You can accomplish this by selecting a few different levels of A/C and heat.   Step8: Check to see if there is a strong blow coming from the vents and if there are any unusual noises.     Ⅺ FAQ   1. How Does A Blower Motor Work in a Vehicle? Once you turn on the vehicle’s heater, the blower motor will blow that heat across the core. Then it will send that heat through the vents, so that you stay warm as you drive your vehicle. The same is true once you turn on your vehicle’s air conditioning. The same process will happen, except the cold air will blow through the vents, to keep you cool as you drive your vehicle.     2. What is The Average Blower Motor Replacement Cost? The average cost of a blower motor replacement can fall between $340 and $400. Labor alone for a blower motor replacement can cost up to $300. Of course, these figures are approximate. You will have to visit a mechanic so that he or she can look at your vehicle and give you an exact value.   3. What causes blower motor failure? Like other components in your HVAC system, the blower motor can wear down over time. Some of the reasons a blower motor might fail are overheating, and excessive moisture. ... Blower motors that are clogged with debris, or that become saturated with moisture can fail due to overworking or electrical shorts.     4. What does a bad blower motor sound like? A defective blower motor will make a continuous sound noticeable by the passengers in the vehicle. It can manifest as a knocking, whirring, clunking, vibrating, squealing, or whining noise that persists until the blower motor is replaced.       5. How long do blower motors last? 10 to 20 years The blower motor in your home or office should last anywhere from 10 to 20 years. Modern sealed bearings and sealed bushings can push the lifespan to its maximum of 20 years.     6. How long does it take to replace a blower motor? DIY or Pro Installation: It's going to take a furnace repair technician between 45 minutes and 90 minutes to replace the motor, clean the fan, adjust the motor, test it and put the furnace back together. The biggest factor is how easy it is to get the assembly out.     7. Can you drive a car with a bad blower motor? A bad heater blower motor will not affect the safety of your car, with the possible exception of you not being able to clear the windshield of snow, ice, or condensation if the defrosters don't work. But you won't be comfortable inside your car, especially during the cold of winter and the heat of summer.          

Catalog Introduction Design Flow of Chip Design Specification Development Design Details of the Chip Draw a Blueprint for the Plane About Wafer What Is a Wafer How to Make Single Crystal Wafer Metallurgical Purification Pulling the Crystal Design Flow of Chip Manufacture What Is an IC Chip Metal Sputtering Coating Photoresistance Etching Technology Photoresist Removal Nano-Process What Is the Nano-Process How Tiny Is the Nanometer Purpose of Reducing the Process Physical Limitations of Downsizing About Encapsulation Two Common Packages DIP Package BGA Package Two Ways to Reduce Size SoC SiP Introduction A chip is a silicon chip that contains an integrated circuit, so the chip is also called an integrated circuit. It may be only 2.5 centimeters in square size, but it contains tens of millions of transistors. Simpler processors, on the other hand, may have thousands of transistors engraved on chips which are a few millimeters in size. Chip is the most important part of electronic equipment, which undertakes the function of operation and storage. Design Flow of Chip The birth of a chip can be divided into two parts: design and manufacture. First, let's take a look at the complex and tedious chip design process. Fig 1. The process of making a chip is like building a house with Lego. First, the wafer is used as the foundation and the necessary IC chips can be produced after layers are stacked on top of each other. However, there is no use in having no amount of manufacturing capacity without a design drawing. Therefore, the role of an architect is very important. But who is the architect in IC's design? The next step is to introduce the IC design. In the IC production process, IC is mostly planned and designed by professional IC design companies, such as MediaTek, Qualcomm, Intel and other well-known large factories, all of which design their own IC chips to provide different specifications and efficiency chips for downstream manufacturers to choose from. Because IC is designed by the factories themselves, so IC design depends very much on the technology of engineers and the quality of engineers affects the value of an enterprise. But what are the steps engineers take to design an IC chip? The design process can be simply divided into the following steps. Design Specification Development In IC design, the most important step is specification development. This step is like deciding how many rooms, bathrooms, what building codes to comply with, and designing after all the features have been identified so that no additional time is spent on subsequent modifications. The IC design needs to go through similar steps to ensure that the chip is designed without any errors. The first step in specification development is to determine the purpose and effectiveness of IC and to set the general direction. The next step is to see what protocols to comply with, such as the wireless card chip needs to comply with IEEE 802.11 and other specifications. Otherwise, the chip will not be compatible with the products on the market, so that it will not be able to connect to other devices. Finally, the implementation method of this IC is established, different functions are allocated into different units, and the method of connecting different units is established, so that the specification can be completed. Design Details of the Chip After designing the specifications, it is followed by the details of the design chip. This step is like making a preliminary note of the planning of the building and depicting the overall outline for subsequent drawing. In IC chip, the hardware description language (HDL) is used to describe the circuit. The commonly used HDLs are Verilog, VHDL, and so on, which can easily express the function of a IC by code. This is followed by checking the correctness of the program's functionality and continuously modifying it until it meets the desired functionality. Fig 2. Verilog Example of 32 Bits Adder Draw a Blueprint for the Plane With a complete plan, the next step is to draw a blueprint for the plane. In IC design, the step of logic synthesis is to put the unmistakable HDL code into the electronic design automation tool (EDA tool), to let the computer convert HDL code into logic circuit, resulting in the following circuit diagram. After that, it is repeatedly determined whether the logic gate design conforms to the specification and is modified until the function is correct. Fig 3. The Result of the Synthesis of the Control Unit Finally, the synthesized code is put into another set of EDA tool for circuit layout and winding (Place And Route). After continuous detection, the following circuit diagram will be formed. You can see blue, red, green, yellow and other different colors, each of which represents a mask. As for the use of the mask, how should it be used? Fig 4. The Commonly Used Calculus Chip-FFT Chip, Which Completes the Circuit Layout and the Winding Result ——The chip is stacked by layers of masks. First of all, it is now known that an IC will produce multiple masks. These masks have the difference between the upper and lower layers and each layer has its own task. The following figure is a simple mask example. Taking the most basic element CMOS in the integrated circuit as an example, the full name of CMOS is complementary metal oxide semiconductor. That is, the combination of NMOS and PMOS to form CMOS. As for what is a metal oxide semiconductor (MOS)? This kind of component which is widely used in the chip is more difficult to explain, and it is more difficult for the general reader to figure it out, so there is no more detailed study here. In the following figure, on the left is the circuit diagram formed after the circuit layout and winding, and you have already known that each color represents a mask. On the right is the way each mask is spread out. Production is to start from the bottom, in accordance with the method proposed in the manufacture of the IC chip, layer by layer, and finally the desired chip will be produced. Fig 5.  At this point, you should have a preliminary understanding of the IC design. The overall view is very clear that IC design is a very complex major, but also thanks to the maturity of computer-aided software, so that IC design can be accelerated. The IC design relies heavily on the wisdom of engineers, and each of the steps described here has its own expertise and can be separated into multiple professional courses. For example, writing a hardware description language does not simply require familiarity with the programming language. You also need to understand how logic circuits work, how to convert the required algorithms into programs, and how synthetic software converts programs into logic gates. What Is a Wafer? In semiconductor news, it is always mentioned in the size of the wafer, such as 8-inch or 12-inch wafer. But what is the so-called wafer? What part of it is 8 inches? What is the difficulty of producing large wafers? Here is a step-by-step introduction to the most important foundation of semiconductors-what is a "wafer". Wafer is the basis for making all kinds of computer chips. We can compare chip manufacturing to building a house with Lego blocks and building the shape we want (that is, all kinds of chips) by stacking one layer after another. However, if there is no good foundation, the built house will be tilted back and forth, contrary to our wishes. In order to make the perfect house, we need a smooth substrate. For chip manufacturing, this substrate is the wafer that will be described next. First of all, think back to when you were a child playing with Lego blocks, there would be a small round bulge on the surface of the building blocks. With this structure, we can stack the two blocks firmly together without using glue. Chip manufacturing, also in a way like this, binds subsequent atoms to the substrate. Therefore, we need to find a substrate with a neat surface in order to meet the conditions needed for subsequent manufacturing. Fig 6. In solid materials, there is a special crystal structure. That is, single crystal (Monocrystalline). It has the characteristics of atoms one after another closely arranged together, which can form a flat atomic surface. Therefore, using single crystal to make wafer can meet the above needs. However, how to produce such a material? There are two main steps, respectively, purification and crystal pulling. After this, such a material can be completed. How to Make Single Crystal Wafer? Metallurgical Purification The purification is divided into two stages. The first step is metallurgical purification. During this process, we add carbon and convert silicon oxide into silicon with a purity of more than 98% in a redox manner. Most metals, such as iron or copper, are refined in this way to obtain sufficient purity of metal. However, 98% is still not enough for chip manufacturing and still needs to be further improved. Therefore, Siemens process will be used for purification, so that the high purity polysilicon needed for semiconductor process will be obtained. Fig 7. Silicon Column Manufacturing Process Pulling the Crystal Then there is the step of pulling the crystal. First, the high purity polysilicon obtained earlier is melted to form liquid silicon. After that, the single crystal silicon seed is in contact with the liquid surface and slowly pulls up as it rotates. As for why single crystal silicon is needed, that is because silicon atoms are arranged in the same way as people queue up. They will need to arrange the head so that later people can arrange it correctly. And silicon seed is an important row head, so that the later atoms know how to queue up. Finally, after the silicon atoms leaving the liquid surface solidify, the neatly arranged single crystal silicon columns are completed. Fig 8. Single Crystal Silicon Column But what do 8 inches and 12 inches stand for? It refers to the diameter of thin wafers being treated and sliced into，which is from the surface of the part of a crystal column that looks like a pencil rod. What is the difficulty of making large wafers? As mentioned earlier, the crystal column is made as if it were making marshmallows, rotating and forming at the same time. If you have made marshmallows, you should know that it is very difficult to make large and solid marshmallows, and the same is true of the crystal pulling process. The speed of rotation and the control of temperature will affect the quality of the crystal column. As a result, the larger the size, the higher the speed and temperature requirements are, so it is more difficult to make high-quality 12-inch wafers than 8-inch wafers. However, a whole silicon column cannot be made into a chip-making substrate. In order to produce a silicon wafer, the silicon column needs to be cut transversely into a wafer with a diamond knife, and the wafer can be polished to form the silicon wafer needed for chip manufacturing. After so many steps, the fabrication of the chip substrate is complete, and the next step is to stack the house, that is, chip manufacturing. So, how to make a chip? Manufacture ——Stacked chips After introducing what silicon wafers are, you also know that making IC chips is like building a house with Lego blocks, creating the shape you want by stacking layer after layer. However, there are quite a few steps to build a house, and so is IC manufacturing. What are the steps to make IC? Next, the process of IC chip manufacturing will be introduced. What Is an IC Chip? Before we begin, we need to know what an IC chip is. IC, which means integrated circuit (Integrated Circuit), is the design of the circuit that is in the form of stacking together. In this way, we can reduce the area required to connect the circuit. The following figure is a 3D diagram of the IC circuit, from which you can see that its structure is like the beams and columns of a house. It is done layer by layer and this is the reason why IC manufacturing is compared to building a house. Fig 9. 3D Profile of IC Chip From the 3D profile of the IC chip in the image above, the dark blue part at the bottom is the wafer introduced in the previous step. From this picture, we can see more clearly how important the wafer substrate plays in the chip. As for the red and khaki parts, they are the places to be completed when IC is made. First of all, the red part can be compared to the hall on the first floor of the building. The hall on the first floor is the door of a house because everyone and everything come in and out of here. It has more functionality under the control of traffic. Therefore, compared with other floors, the construction will be more complex and requires more steps. In IC circuit, this hall is the logic gate layer; it is the most important part of the whole IC by combining a variety of logic gates together and completes the fully functional IC chip. The yellow part is like a normal floor. Compared with the first floor, there will not be much complex structure, and each floor will not change much when it is built. The purpose of this layer is to connect the logic gates of the red part. The reason why so many layers are needed is that there are so many lines to be connected that a single layer cannot hold all the lines. So it is necessary to stack a few more layers to achieve this goal. Among them, the lines of different layers will be connected up and down to meet the needs of the wiring. ——Layered construction, layer by layer architecture Once you know the construction of IC, let's show you how to make it. Imagine that if we want to make a fine drawing with a paint spray tank, we need to cut out the cover plate of the figure and cover it on paper. Then spray the paint evenly on the paper and remove the mask when the paint is dry. After repeating this step over and over again, you can complete neat and complex graphics. IC is made in a similar way, by covering up a layer of stacking. Fig 10.  When making IC, you can simply divide into the above four steps. Although the actual manufacturing steps will be different and the materials used will be different, but generally using a similar principle. This process is slightly different from painting: IC manufacturing is to paint first and then cover while painting is to cover and then paint. And the processes are described below. Metal sputtering:  Sprinkle the metal material which is to be used evenly on the wafer to form a thin film. Coating photoresistance:  First put the photoresist material on the wafer, and then hit the beam on the desired part through the mask to destroy the structure of the photoresist material. Next, use chemicals to wash away the damaged material. Etching technology:  The silicon wafer without photoresistance protection will be etched by ion beam. Photoresist removal:  Use the photoresist solution to dissolve the remaining photoresist, so that a process can be completed. Finally, a lot of IC chips will be completed on a whole wafer, and then as long as the completed square IC chips are cut off, they can be sent to the packaging factory for packaging. What is the packaging factory? We'll have to explain it later. Nano-Process What is the nano-process? Samsung and TSMC compete fiercely in advanced semiconductor processes because both of them want to take the lead in wafer contract manufacturing to win orders, which has almost become a battle between 14 nanometers and 16 nanometers. But what is the meaning of 14 nm and 16 nm, and where do they refer? What are the benefits and problems that will be brought about by the reduction of the process? Next we will give a brief description of the nano-process. How tiny is the nanometer? Before you start, you need to understand what nanometer really means. Mathematically, nanometers are 0.000000001 meters, but this is a pretty bad example. After all, we can only see a lot of zeros after the decimal point, but we don't actually feel it. If you compare it with the thickness of nail, it may be more obvious. If you actually measure it with a ruler, you can tell that the thickness of the nail is about 0.0001 meters (0.1mm), that is to say, try to cut the side of a nail into 100000 lines, each of which is about one nanometer. From this, we can slightly imagine how tiny a nanometer is. Purpose of Reducing the Process After knowing how small the nanometer is, it is necessary to understand the purpose of reducing the process. The main purpose of reducing the transistor is to insert more transistors into smaller chips so that the chip will not become larger as a result of technological advances; second, it can increase the computational efficiency of the processor; moreover, reducing the volume can also reduce the power consumption. Finally, after the chip size is reduced, it is easier to plug into the mobile device to meet the needs of thinness and lightness in the future. Come back to explore what the nano-process is and we will take 14 nm as an example. The process refers to the minimum size of 14 nm in the chip. The following figure shows the appearance of a traditional transistor, as an example. The main purpose of reducing transistor is to reduce power consumption, but which part needs to be reduced to achieve this goal? The L in the figure on the left is what we expect to shrink. By reducing the gate length, the current can be routed from the Drain side to the Source end in a shorter path (if you are interested, you can use Google to search for MOSFET, which will be explained in more detail). Fig 11. In addition, computers operate on 0 and 1. How can we use transistors to meet this purpose? The way to do this is to determine whether the transistor has current flow. When a voltage supply is made at the Gate (green square), the current will flow from the Drain to the Source, and if there is no supply voltage, the current will not flow, so that it can represent 1 and 0. (As to why 0 and 1 are used to judge, if you are interested, you can go to the Brin algebra. That is the way we use this method to make a computer.) Physical Limitations of Downsizing However, the process cannot be reduced indefinitely. When we narrow the transistor to about 20 nanometers, we will encounter problems in quantum physics, so that the transistor has a leakage phenomenon, offsetting the benefits of L. As a way to improve, the concept of FinFET (Tri-Gate) was imported, as shown in the figure above. The leakage caused by physical phenomena can be reduced by importing this technology. Fig 12. More importantly, this method can increase the contact area between the Gate end and the lower layer. In traditional practice (top left), the contact surface has only one plane, but with FinFET (Tri-Gate), the contact surface will become three-dimensional, and the contact area can be easily increased. This allows the Source-Drain side to be smaller while maintaining the same contact area, which is of considerable help in reducing the size. Finally, why would anyone say that it would be a pretty serious challenge for factories to enter the 10-nanometer process? It is mainly because the size of an atom is about 0.1 nanometers, and in the case of 10 nanometers, there are fewer than 100 atoms in a line. It is very difficult to make, and as long as there is an atomic defect, such as atoms falling out or impurities in the production process, there will be unknown phenomena, affecting the yield of the product. If you can't imagine the difficulty, you can do a small experiment. Line up a 10 × 10 square with 100 small beads on the table, cut a piece of paper to cover the beads, then brush off the beads next to it with a small brush, and finally make it form a 10 × 5 rectangle. In this way, we can know the difficulties faced by the major factories and how difficult it is to achieve this goal. Encapsulation After a long process, from design to manufacture, finally we got an IC chip. However, a chip is so small and thin that it can be easily scratched and damaged if it is not protected from the outside. In addition, because of the small size of the chip, if you do not use a larger size of the shell, it will not be easy to manually place on the circuit board. Therefore, the next step is to describe the encapsulation: Two Common Packages At present, there are two common packages; one is the DIP package, which is common in electric toys and looks like a centipede, the other is the BGA package, which is common when buying boxed CPU. As for other packaging methods, there are PGA (Pin Grid Array) used in the early CPU or an improved version of QFP (plastic square flat package) of DIP. Because there are so many packaging methods, only DIP and BGA encapsulation are described below: ——Enduring Traditional Packaging DIP Package The first thing to introduce is the Dual Inline Package (DIP), we can see from the following figure that the IC chip with this package will look like a black centipede at the foot of the dual inline connection and this is the earliest IC packaging technology. It has the advantage of low cost and is suitable for small chips without too many wires. However, because most of them are plastic, the heat dissipation effect is poor, which cannot meet the requirements of the current high-speed chips. Therefore, most of the chips using this package are durable chips, such as OP741 shown in the following figure or smaller IC chips with less speed requirements and fewer holes. Fig 13.  The IC chip shown on the left is a common voltage amplifier named OP741. On the right is its section. The package connects the chip to the leadframe with a gold wire. BGA Package As for spherical array (Ball Grid Array,BGA) packaging, compared with DIP, it is smaller and can be easily placed in smaller devices. In addition, because the pin is located under the chip, it can hold more metal pins than the DIP so it is Ideal for chips that require more contacts. However, the cost of this packaging method is high and the connection method is more complex, so it is mostly used in high unit price products. Fig 14.  On the left is a chip encapsulated in BGA. On the right is a schematic diagram of BGA using a cladding packaging. ——The rise of mobile devices and the emergence of new technologies on the stage Two Ways to Reduce Size However, the use of these packaging methods will cost a considerable amount of volume. For example, today's mobile devices, wearing devices, and so on, require quite a variety of components. If each component is packaged independently, it will cost a lot of space. Therefore, there are two ways to meet the requirements of reducing size. They are SoC (System On Chip) and SiP (System In Packet). SoC At the beginning of the rise of smart phones, the term SoC can be found in major financial magazines, but what is SoC? To put it simply, ICs with different functions are integrated into one chip. By this method, not only the volume can be reduced, but also the distance between different IC can be reduced, and the calculation speed of the chip can be improved. As for the manufacturing method, during the IC design phase, different ICs are put together and then a mask is made through the design process described earlier. However, SoC is not the only advantage; to design a SoC requires considerable technical cooperation. When IC chips are encapsulated, they have their own external protection, and the distance between IC and IC is long, so there is no interactive interference. But when all the ICs are wrapped together, it is the beginning of a nightmare. The IC design factory has to change from the original simple design IC, to the IC which requires them to understand and integrate the various functions. Therefore, it increase the workload of engineers. In addition, there will also be a lot of situations, such as the high-frequency signal of the communication chip may affect the IC of other functions and so on. In addition, SoC also needs to obtain IP (intellectual property) authorization from other vendors in order to put components designed by others into SoC. Because making SoC needs to obtain the design details of the whole IC in order to make a complete mask, which also increases the design cost of SoC. Some people may question why not just design one by yourself. That is because designing all kinds of IC requires a lot of knowledge related to the IC, only a rich enterprise like Apple can have a budget to poach top engineers from well-known enterprises. It's still a lot cheaper to design a whole new IC through collaborative licensing than to develop it by yourself. SiP As an alternative, SiP has leapt onto the stage of integrating chips. Unlike SoC, it buys IC from different enterprises and finishes the last step, which is to encapsulate the IC. In this way, the IP licensing step is eliminated and the design cost is significantly reduced. In addition, because they are independent ICs, the degree of interference with each other is greatly reduced. Fig 15. Apple Watch uses SiP technology to package the entire computer architecture into a chip, not only to meet the desired performance but also to reduce the size, so that the watch has more space for battery release. The most famous product using SiP technology is Apple Watch. Because the internal space of Watch is too small, it cannot use the traditional technology, the design cost of SoC is too high, SiP has become the first choice. With SiP technology, not only the volume can be reduced, but also the distance between each IC can be shortened, so SiP can be a feasible compromise. The following figure shows the structure of the Apple Watch chip, and you can see that quite a few IC are included in it. Fig 16. Internal configuration Diagram of S1 Chip encapsulated by SiP in Apple Watch After the packaging is completed, we will enter the testing stage. At this stage, it is necessary to confirm whether the encapsulated IC is functioning properly and that it can be shipped to the assembly plant after it is correct, so that the electronic products we can see can be made. So far, the semiconductor industry has completed the task of the whole production.

This article would introduce MCU in details, including analysis its internal structure, and elaborate some important concepts, especially would put emphasis on the concept of memory decoding.   Catalog I. What is MCU? II. Some Basic Concepts 2.1 The Meaning of Rom 2.2 The Meaning of Bit 2.3 The Meaning of Bytes III. The Working Principle of Memory IV. MCU Circuit v. Memory Decoding FAQ   I. What is MCU?   MCU(microcomputer) is an integrated circuit chip. It integrates the microprocessor(CPU), which has data-handling technology such as arithmetic, logic and data transfer, etc, random access data memory(RAM), read-only program memory(ROM), input and output circuit (I/O port) that using the very large scale processing-data technology and may also include a timing counter, serial communication port (SCI), display drive circuit (LCD or LED drive circuit), pulse width modulation circuit (PWM), analog multiplexer and A/D converter, which form a minimum but perfect computer system.   Under the control of software, these circuits can complete the tasks specified by the program designer accurately, quickly, and efficiently. From this point of view, the single-chip microcomputer has the function which the microprocessor does not have, it has intelligent control functions which the modern industry control request separately. And this is the single-chip microcomputer's biggest characteristic.       II. Some Basic Concepts   2.1 The Meaning of Rom Let's think about a problem: when we write instruction in a programmer into an MCU and then take off it, the MCU can execute the instruction, so the instruction must be stored somewhere in the MCU. And this place can still maintain this instruction not to be lost after it power-off. What place is this? This place is the internal ROM of MCU, which is the read-only program memory. Why do you call it read-only memory? We use the programmer, external equipment, to write to the ROM operation under special conditions. In the MCU normal working conditions,  the data can only read but can’t write in, so we call it ROM.   2.2 The Meaning of Bit From the experiment above, we already know that the level of a lamp or a line can represent two states: 0 and 1. In fact, this is a binary bit, thus we call a line a bit, expressed in BIT.   2.3 The Meaning of Bytes A line can represent 0 and 1, two lines can express 00, 01, 10, 11 four states, that is, it can express 0 to 3, and three can express 0 to 7. The computer usually put with eight lines together, counting at the same time, can represent 0 to 255, for a count of 256 states. These eight lines or 8-bit is called a byte (BYTE).   III. The Working Principle of Memory   Structure All the instructions that a single-chip microcomputer can execute are the instructional systems of it. Different kinds of single-chip computers have different instructional systems. In order for a single-chip microcomputer to automatically complete a specific task, the problems to be solved must be programmed into a series of instructions (these instructions must be recognized and executed by the selected single-chip microcomputer). These instructions integrated into the program, and the program needs to be stored in memory—a storage unit.    The memory consists of many storage units (the smallest unit of storage), just as a building has many rooms, each room in a large building is assigned a unique room number. Each storage unit must also be assigned a unique address number, which is known as the address of the storage unit so that the address of the storage cell is known. The instructions are stored in these units. The storage unit can be found, where the stored instructions can be taken out and then executed.   Memory is the place where data is stored. It uses the electricity level to store the data, that is, it actually stores the electrical level, not the number of 1234 that we are used to thinking of. A memory is like a small drawer. If there are eight small drawers in a small drawer, each one is used to store the "charge," and the charge is passed in or released through the wire attached to it. You can think of a wire as a pipe, and the charge in the grid is like water, so it's easy to understand it. Each small drawer in memory is a place for data, which we call a ''bit''.   With this structure, we can start storing data. If we want to put in a data 12, that is 00001100, and we just have to fill the second and third squares with the charge, and the other cells are free of the charges. But the problem is that memory has a lot of cells, and the lines are parallel, and when you put the charge in it, you put the charge in all the cells, and when you release the charge, you release the charge from each cell. In the case of it, no matter how many cells the memory has, it can only be put in the same number, which is certainly not what we want.    A little bit to change structurally,  there's a control line on each unit, and if you want to put the data in the unit, give a signal to the control line of the unit. Therefore, the control line turns on the switch so that the charge can flow freely. And there is no signal on the other unit control lines, so the switch turns off and will not be affected, so that if you handle the control lines of different units, you can write different data to each unit. Similarly, if you want to take data from one unit, just turn on the corresponding control switch.     IV. MCU Circuit   A circuit is always made up of components connected by wires. In analog circuits, wiring is not a problem, because there is usually a serial relationship between the devices, and there are not many connections between the devices, but the computer circuits are different. The microprocessor is the core for it, each device must be connected to the microprocessor, the work of each device must be coordinated, so it needs a lot of connections.   If still like analog circuits, there will be an amazing number of lines between microprocessors and devices, so the concept of a bus has been introduced into the microprocessor, and each device has shared the connection. All 8 data lines are connected to eight common lines, that is, the equivalent of each device is in parallel, but this is not enough. If there are two devices delivering data at the same time, one is 0 and the other is 1, what exactly does the receiver get? This situation is not allowed, so control through the control line to make the device working time-sharing, at any time there can be only one device to send data ( multiple devices can receive at the same time).      V. Memory Decoding   So how do we control the control lines of each unit? It is not that simple to lead the control lines of each unit out of the integrated circuit. There are 65,536 units in a model 27512 memory, and if each line is drawn out, the integrated circuit must have more than 60,000 feet, so it is necessary to find a way to reduce the number of lines. We have a way called decoding, briefly introduce: one line can represent two states and two lines can represent four states and three lines can represent eight kinds, and so on, thus we only need 16 lines to represent 65536 states.   Since the decoding problem solved, let's focus on another problem. Where did the eight lines in each unit come from? Actually, it is connected to the computer, in general, the eight wires not only for memory but also connected to other devices. The problem arises in this way. Because these eight wires are not dedicated to the memory and the computer, it is not good if a unit is always connected to the eight wires. For example, if the value in this memory cell is 0FFH but there one unit is OOH, then what the line set at a high level or a low level?   Thus we have to separate them. The solution is: when the outside wire is connected to the pin of the integrated circuit, it does not directly attach to the units, but a set of switches is added to the middle. Normally we leave the switch off, and if we really want to write data to this memory, or read the data out of the memory, just turn the switch on. This set of switches is selected by three leads: read control, write control, and chip selector.    To write data into the chip, select the chip first, then send a write signal, the switch turns on, and the incoming data (charge) is written into the film chip. If you want to read, select the film chip first, and then send out the read signal, the switch turns on, and the data is sent out. The read and write signals are also connected to another memory at the same time, but the chip selector ends are different.   Although there is a read or write signal, there is no chip selection signal, so the other memory will not "misunderstand" and result in a conflict. What will happen if you pick two chips at the same time? Actually, this can’t be happening because the system is designed and controlled by computer, not by the human. If any, there’s something wrong with the circuit.     From the introduction above, we have seen that the eight lines used to transmit data are not dedicated, but shared by many devices, so we call it data bus. The data line of the device is called the data bus, and all the control lines of the device are called the control bus. There are memory cells in the internal or external memory and other devices of a single chip. Units must be assigned addresses before they can be used. Of course, the assigned addresses are also given in the form of electrical signals. Because there are too many memory cells, there are many lines for address allocation, which are called address buses. Sixteen address lines are also connected, called address buses.   FAQ   1. What are the characteristics of microcomputer? a. Small size and low cost. b. One user. c. Easy to use. d. Low computing power. e. Commonly used for personal application.   2. What are the advantages of microcomputer? a. This computer is widely used today. b. The microcomputer is small in size. c. The microcomputer is used to design different software and app. d. This type of computer is a low cost, so all the users can easily buy. e. No need for highly trained staff for operating microcomputer to office work.   3. Why microcontrollers are often called single chip computers? Single-chip computers are mainly of the form known as Microcontroller chips (the most commonly known are the PIC range by Microchip inc) and used in embedded devices. They provide much more basic functionality but are far simpler to work with as they don't require any external chips in order to function.   4. What is single chip microcomputer that has everything inbuilt? This is a microcomputer built using separate components (CPU, Memory, etc.). ... For some specific applications, we also have single chip computers in a VLSI chip. This single chip microcomputer will have a CPU, memory and I/O interfaces, timers, ADC/DACs etc. on a single chip itself.   5. What is difference between microprocessor and microcomputer? The main difference between Microprocessor and Microcomputer is that the Microprocessor is a computer processor contained on an integrated-circuit chip and Microcomputer is a small, relatively inexpensive computer. ... Microprocessors contain both combinational logic and sequential digital logic.   6. Is Raspberry Pi a microcomputer? The Raspberry PI is a microcomputer that's often used by hobbyists to create projects like animated LED displays or bird watchers.   7. Which is a feature of a single chip microcomputer? A single-chip microcomputer is a major branch of a microcomputer. The biggest feature of the structure is that the CPU, memory, timer and various input/output interface circuits are integrated on a very large-scale integrated circuit chip. In terms of its composition and function, a single chip is a computer.   8. What are the components of microcomputer? The main components are: (1) the central processing unit (CPU), (2) input devices, (3) output devices, and (4) memory. The CPU of a microcomputer performs all the arithmetic, logic, and data handling functions of the microcomputer.   9. Is microcontroller a microcomputer? A Microcontroller is a small and low-cost microcomputer, which is designed to perform the specific tasks of embedded systems like displaying microwave information, receiving remote signals etc.   10. What is the definition of microcomputer? Microcomputer, an electronic device with a microprocessor as its central processing unit (CPU). Microcomputer was formerly a commonly used term for personal computers, particularly any of a class of small digital computers whose CPU is contained on a single integrated semiconductor chip.   You May Also Like Transformers Basics: Construction, Types, Materials and Design Switched Mode Power Supply Tutorial: Principles & Functions of SMPS Circuits List of Basic Electronic Components Switching Power Supply Tutorial: 4V～16V

This paper introduces a switching power supply with the half-bridge circuit. Its input voltage is AC 220V ±20V, the output voltage is DC 4V ~16V, the maximum current is 40A, and the working frequency is 50kHz. And its design idea, working principle, and characteristics of the power supply are introduced emphatically. 12V 10A switching power supply (with schematic and explanation)   Catalog   I. Introduction II. Main Technical Indicators III. Main Functions Description 3.1 AC EMI Filter and Rectifier Filter Circuit 3.2 Half-bridge Power Converter 3.3 Design of Power Transformer 3.4 Design of Auxiliary Power Supply 3.5 Drive Circuit 3.6 Fan Wind Speed Control Circuit 3.7 PWM Control Circuit 3.8 Current Fold back Circuit FAQ       I. Introduction Power supplies with the voltage of 5~15V and current at 5~40A are most commonly used in scientific research, production, experiments and other applications. The maximum current of the general experimental power supply is only 5A or 10A, For this purpose, a switching power supply with continuously adjustable voltage at 4V~16V and maximum output current of 40A has been developed. It adopts half-bridge circuit, with power MOS transistor as switching device and the switching frequency is 50kHz. Light weight, small volume and low cost are advantages of it.   II. Main Technical Indicators   1) Output Voltage: AC 220V±20％  2) Input Voltage: DC 4～16V(adjustable) 3) Output Current: 0~40A 4) Output Voltage Adjustment Rate: ≤1％ 5) Ripple Voltage Up: p≤50mV 6) Current / Voltage Display Function and Fault Alarm Indication   Basic Working Principles and Schematic Diagrams The schematic block diagram of the power supply is shown in Fig.1. After 220V AC voltage is filtered by EMI and rectifier, about 300V DC voltage is added to the half-bridge converter to drive the power MOS tube with the dual pulse signal generated by the pulse width modulation(PWM) circuit. The quasi-square-wave voltage is gained by coupling and isolating the power transformer, and a stable DC output voltage can be obtained by rectifying filter feedback control. Fig. 1 Working Block Diagram of Integral Power Supply   III. Main Functions Description   3.1 AC EMI Filter and Rectifier Filter Circuit Fig.2 AC EMI Filter and Input Rectifier Filter Circuit The power line of the electronic equipment is an important way of electromagnetic interference (EMI) to get into or out of the electronic equipment, but installing the power line filter at the entrance of the power line of the equipment can effectively cut off the transmission path of EMI. And it composed of IEC plug power filter and PCB power filter.   The main purpose of the IEC plug power filter is to prevent the interference from the power grid from entering the power supply box, and for PCB power filter the purpose is to suppress the high frequency noise generated when the power switch is switched. Bridge rectifier circuit is used when AC input voltage is 220V, if JTI jumper is short-connected, then 110V is suitable.   Because the input voltage is high and the capacitor capacity is large, the surge impulse current will be produced at the moment when the power network is switched on, and the general surge current value is tens of times that of the steady current.   This may result in the damage of rectifier bridge and input fuse, or the saturation damage to power devices of high frequency transformer cores, and the reduction of the service life of high voltage electrolytic capacitors, etc. So the input soft start circuit composed of resistance R1 and relay K1 is added in front of rectifier bridge to avoid those damages.   3.2 Half-bridge Power Converter The power supply uses half-bridge converter circuit, as shown in Fig.3, its operating frequency is 50kHz, the main parts on the primary side are power transistors: Q4 and Q5, and capacitors: C34 and C35. Q4 and Q5 alternately conduct and cutoff, A positive and negative square wave pulse voltage of U1/2 is generated through the primary winding N1 of a high frequency transformer. The energy is transferred from transformer to the output, and Q4 and Q5 use IRFP460 power MOS transistor. Fig.3 Switching Power Supply Schematic   3.3  Design of Power Transformer   1) Setting of the Working Frequency The working frequency has a great influence on the volume, weight and circuit characteristics of the power supply. The output filter inductance and capacitance volume decrease with high working frequency, but the switching loss increases, the heat quantity increases and the radiator volume increases. Therefore, according to the factors such as components and cost performance, optimizing the operating frequency of power supply, the formula is fs=50kHz, T=1/fs=1/50kHz=20μs.   2)Core Selection ①Selecting the EE type ferrite core made of R2KB ferrite material, has many advantages, such as versatility, large lead space, convenient wiring operation, economics, and so on. ②Determination of Working Magnetic Induction Intensity: Bm The saturation magnetic induction intensity of R2KB soft magnetic ferrite material is Bs=0.47T, considering that Bs will decrease at high temperature, and in order to prevent the saturation of high-frequency transformer at the moment of closing,  selecting Bm=1 / 3Bs= 0.15T ③Calculation and Determination of Core Type The geometric cross-sectional area S and the window area Q of the magnetic core have a certain functional relationship with the output power Po. For half-bridge converters, when the pulse waveform is an approximately square wave, having SQ= (1) η—Efficiency j—Current density, generally 300~500A/cm2 kc—Fill factor of magnetic core, ferrite core kc=1 Ku—Filling coefficient of copper, related to the wire diameter, winding process, winding number, and so on, is generally about 0.1~0.5. The units of each parameter: Po—W，S—cm2, Q—cm2, Bm—T, fs—Hz, j—A/cm2. The values each parameter:  Po=640W，Ku=0.3,j=300A/cm2,η=0.8,Bm=0.15T, plugging these into formula(1) to get SQ=4.558cm4. From the manufacturer manual of EE55 magnetic core: S=3.54cm2, Q=3.1042cm2, calculating SQ=10.9cm4, the SQ value of EE55 magnetic core is larger than the calculated value. EE55 magnetic core is the option.   3) Calculating Turns of Primary and Secondary Side Windings Calculate the primary number turns of windings according to the lowest input voltage and the full load(the duty ratio is maximum). It is known that the DC input voltage of Umin=176V after rectifying and filtering is Udmin=1.2 × 176 = 211.2V. For the half-bridge circuit, the voltage applied on the primary winding of the power transformer is equal to half of the input voltage, that is Upmin=Udmin/2=105.6V, assuming Dmax=0.9(the maximum duty ratio), getting tonmax= T × Dmax= 20 × 0.9 μs.   Design of an Output Voltage 4~16V Switching Power Supply   Fig.4 Schematic Diagram of Auxiliary Power Supply Upmin×tonmax×104=105.6×9.0×10－6×104, plugging into formula N1=8.9 turns,  the maximum output voltage is Uomax=16V when calculating secondary turns; the secondary circuit uses full wave rectifier, Us as the inductive voltage on the secondary winding and Uo as the output voltage and Uf as the rectifier diode voltage drop, taking 1 V as the voltage drop, Uz is filter inductor equal circuit voltage drop taking 0.3V, getting Us=19.22V×N2=N1×8.9=1.8 turns; For the convenience of winding the transformer, if the secondary winding is 2 turns, then the primary winding will be corrected to N1=N2=10 turns.   4) Selected Wire Diameter When selecting the wire diameter of the winding, the skin effect of the wire should be considered. It is generally required that the wire diameter be less than two times the penetration depth, and the penetration depth Δ is determined by formula (2), Δ= (2), and the unit of penetration depth Δ is m. In formula ω is the angular frequency: ω=2πfs; μ is magnetic conductivity, for the relative permeability of copper wire: μr=1 , 则μ=μ0×μr=4π×10－7H/m; γ is the conductivity of copper, γ = 58 × 10 —6Ωm. The operating frequency of the transformer is 50kHz, and the penetration depth of the copper conductor is Δ=0.2956mm at this frequency, thus the diameter of the winding wire must be copper wire whose diameter is less than 0.59mm. In addition, the current density of copper wire is generally 3 ~ 6 A / mm2, the 0.56mm enamelled wire with 8 strands in parallel for the primary is 10 turns, and the thick 0.15mm flat copper strip with 2 turns in the secondary.   3.4 Design of Auxiliary Power Supply The auxiliary power supply using RCC converter (Ringing Choke Converter), is shown in Fig.4. The input voltage is AC 220 V, as rectifier filter voltage, and the output DC voltage is 12.5 V, the output DC current is 0.5 A. In the circuit, Q8 and transformer primary winding N1 and feedback winding N3 constitute self-excited oscillation. R72 is starting resistance. Q9, R77 constitutes primary overcurrent protection of auxiliary power supply. D20, C81, ZD1, Q11, R75, N76 constitutes voltage detection and voltage stabilizing circuit. The DC component of the base current of Q 8 keeps the output voltage constant, and the transformer is made of EE19 material and LP3 material. The primary is 180 turns, the feedback winding is 5.5 turns, the secondary is 11 turns, the primary inductance is 2.6 MHz, the core gap is 0.4mm.   3.5 Drive Circuit The drive circuit is shown in Fig.5. TL494 outputs the pulse signal of 50kHz and drives the power MOS transistor through the coupling of a high-frequency pulse transformer. The secondary pulse voltage is a timing MOS switch, during which Q7 ends, and the drain circuit formed by it does not work. Q7 conducts when the second pulse voltage is 0, rapidly releasing the gate charge of MOS, and accelerating MOS cutoff. R70 is the spike to suppress the driving pulse, R68, D15, R67 used to speed up driving and suppress the oscillation caused by driving pulse, D17, and the connected pulse transformer windings form a demagnetization circuit.  Fig.5 Driving Circuit Schematic Diagram 3.6 Fan Wind Speed Control Circuit Fan wind speed control circuit is shown in Fig.6. Based on the decreasing trend of diode forward tube pressure drop with increasing temperature, D9 and D10 are used as radiator temperature samplers close to the radiator. When the temperature of the radiator rises with the increase of output power, the level of the positive phase input of the operational amplifier N2A decreases, the output low level causes the transistor Q3 to start conducting, and the voltage on the fan rises.   The rotational speed rises and finally reaches the maximum speed. When the load is lighter and the radiator temperature is lower than 50 ℃, the output of N2A is high level, Q3 is not conductive, and auxiliary electricity 12.5V stepped down by resistance R57 supplying to fan, thus the fan is running at low speed and low noise. The circuit can improve the working life of the fan, increase the reliability of the circuit and reduce the noise caused by the fan in the case of a small load.   Fig.6 Fan Wind Speed Control Circuit 3.7 PWM Control Circuit The general pulse width modulator (TL494,) used in the control circuit has the advantages of generality and low cost, as shown in Fig.7. The output voltage is sampled by R40, RV2, RV1, R41 and then sent to the TL494 pin 1 after the R5 impedance matching. RV1 installed in power front panel to realize the output voltage adjustment. R103 and C14 sample the output inductor L1 front signal which delivering through R5 to TL494 pin 1 to improve power supply stability and eliminate the influence of L1 on loop stability.   3.8 Current Foldback Circuit In order to enhance the reliability of the power supply, this power supply adopts two-stage over-current protection: primary and secondary. Current transformer CT1 is initially used to detect the primary transformer current. The detected current signal is converted from R60 to voltage signal, then filtered by D2~D4 and C9, and then the voltage is divided by potentiometer RV3, and inverted by N3, finally added to the Q 1 tube base. When the primary current is abnormal, the inverter reverses the Q1 switch and adds a high level of VREF=5V to the TL494 pin 4 (the TL494 dead-zone control pin, which is turned off at a high level), TL494 is off. Overcurrent protection on the main output DC line uses R45-R56 resistance as the sampling resistance. When the output current increases, the level of pin15 becomes lower. When the output current is greater than 105% of 40A, the internal operational amplifier of TL494 acts. The pin3 level rises, limiting the increase of the output pulse width, and the power supply is in the limiting state. FAQ   1. How does a switching power supply work? The “switch” in a switching power supply is actually a semiconductor – a MOSFET that is either off or on – driven into its saturation range to transfer power across nearly zero resistance. It does this many thousands of times per second, creating the high-frequency AC intermediary.   2. What is difference between linear and switching power supply? Linear power supplies deliver DC by passing the primary AC voltage through a transformer and then filtering it to remove the AC component. Switching power supplies feature higher efficiencies, lighter weight, longer hold up times, and the ability to handle wider input voltage ranges.   3. What is a switching power supply 12v? Switching regulated 12VDC power supplies, sometimes referred to as SMPS power supplies, switchers, or switched mode power supplies, regulate the 12VDC output voltage using a complex high frequency switching technique that employs pulse width modulation and feedback. Acopian switching regulated power supplies also employ extensive EMI filtering and shielding to attenuate both common and differential mode noise conducted to the line and load. Galvanic isolation is standard in our 12VDC switchers, affording our users input to output and output to ground isolation for maximum versatility. Acopian switching regulated power supplies are highly efficient, small and lightweight, and are available in both AC-DC single and wide-adjust output and DC-DC configurations.   4. What is a DC switching power supply? A Switching DC power supply (also known as switch mode power supply) regulates the output voltage through a process called pulse width modulation (PWM). The PWM process generates some high frequency noise, but enables the switching power supplies to be built with very high power efficiency and small form factor.   5. When should you use a switching power supply? Switching power supplies are primarily used in digital systems such as telecommunication devices, computing equipment, audio equipment, mobile phone chargers, medical test devices, arc welding equipment and automotive chargers.   6. Is a switching power supply regulated? A switch mode power supply regulates an output voltage with pulse width modulation (PWM). This process creates high-frequency noise but it provides a high-efficiency rating in a small form factor. ... The low DC voltage is finally converted into a steady DC output with another set of diodes, capacitors, and inductors.   7. Is a switching power supply DC? A switching power supply takes an AC input, but rectifies and filters into DC first, is converted back into AC at some high switching frequency, steps down the voltage with a transformer, then is rectified and filtered into a DC output.   8. How do I know if my power supply is regulated? You can generally stick one probe into the middle of the connector, and hold the other against the outside. With a few exceptions, the middle is positive, so use the red lead there, and use the black lead on the outside shell. Regulated supplies, without any load, should measure very close to the target voltage of 12v.   9. Can I use a switching power supply to drive a DC motor? A simple unregulated analog power supply may be easier and be able to supply the large starting under load current more that the switching one. DC motors are not too fussy about the supply, and will usually run quite well on unfiltered DC.   10. What are the 3 types of power supply? There are three subsets of regulated power supplies: linear, switched, and battery-based. Of the three basic regulated power supply designs, linear is the least complicated system, but switched and battery power have their advantages.   You May Also Like Learn Some Basic Knowledge about Capacitor Voltage Transformer The Latest Development of Electric Vehicle Power Management Technology Design a Momentary Pushbutton in the Circuit of Laching Power Switch