The Kynix Blog

ⅠIntroduction Channel MOSFETs are a type of Metal Oxide Semiconductor Device. It consists of the n-substrate in the center with a high concentration of light doping. This is a list of the three-terminal devices. It has unipolar characteristics because the majority of the charge carriers are essential for its operation. Because of the two p materials used in the circuitry, the majority of the carriers are holes. It is further subdivided based on the presence of channels.   Catalog ⅠIntroduction Ⅱ What is P-Channel  MOSFET? Ⅲ P Channel MOSFET Characteristics Ⅳ How P-Channel MOSFETs Are Constructed Internally? Ⅴ Types of P-Channel MOSFET 5.1 P Channel with Enhancement MOSFET 5.1.1  How a P-Channel Enhancement-type MOSFET Works? 5.1.2 How to Turn on a P-Channel Enhancement Type MOSFET? 5.1.3 How to Turn Off a P-Channel Enhancement Type MOSFET? 5.2 P Channel Depletion MOSFET 5.2.1 How a P-Channel Depletion-type MOSFET Works? 5.2.2 How to Turn on a P-Channel Depletion Type MOSFET? 5.2.3 How to Turn Off a P-Channel Depletion Type MOSFET? Ⅵ How to use only positive voltage in this p-channel MOSFET tutorial? 6.1 VGS Threshold 6.2 P-Channel MOSFET Tutorial and Explanation Ⅶ FAQ     Ⅱ What is P-Channel  MOSFET?   A MOSFET is formed when a lightly doped N-type substrate is connected to two highly doped P-type materials. Doping refers to the concentration of impurities added to the atom. The p-channel formed between the two P-type substrates could be the consequence of induced voltages or it could have existed previously.    MOSFET Symbol    Ⅲ P Channel MOSFET Characteristics   The voltage controlled devices are represented by MOSFETs.These devices have high input impedance values.The conductivity of the channel in a P-channel is caused by the application of negative polarity at the gate terminal.     Ⅳ How P-Channel MOSFETs Are Constructed Internally?    P-Channel MOSFET   A P-Channel MOSFET is consists of a P channel, which is a channel that is mostly made up of hole current carriers. N-type material is used for the gate terminals.  How the transistor operates and whether it turns on or off  is determined by the amount and type of voltage (negative or positive)     P-Channel MOSFET as a Switch. Turn ON a 12V Motor with Arduino. (Step-By-Step Guide)     Ⅴ Types of P-Channel MOSFET   The p-channel MOSFET’s are classified as:   (1)P-channel with the Enhancement MOSFET (2) P-channel with the Depletion MOSFET     5.1 P Channel with Enhancement MOSFET   This MOSFET is constructed with a lightly doped n-substrate. The length separates the two heavily doped p-type materials (L). This L is referred to as the channel length.   Above the substrate, a thin layer of type silicon dioxide is deposited. This layer is commonly referred to as the dielectric layer. The source and drain are formed by the two P types. The gate terminal is formed by the aluminum plating used above the dielectric. The ground is connected to the source and the body of the MOSFET.   The gate terminal has been subjected to a negative voltage. Because of the effect of capacitance, the positive concentration of charges settles below at the dielectric layer. Because of repulsive forces, the electrons present at the n substrate are shifted, and the uncovered value of the positive ions layer can be found there. In an n-type substrate, the holes, which are minority carriers, combine with a few electrons to form a bond.   However, further application of the negative voltage cracks the covalent bonds, thereby breaking the pairs formed between electrons and holes. It results in the formation of holes and an increase in the carrier concentration of holes in the channel. When a negative voltage is applied to the drain terminal, the channel becomes conductive, allowing current to flow through the transistor.     5.1.1  How a P-Channel Enhancement-type MOSFET Works? circuit example     5.1.2 How to Turn on a P-Channel Enhancement Type MOSFET?     To turn on a P-Channel Enhancement-type MOSFET, apply a positive voltage VS to the MOSFET's source and a negative voltage to the MOSFET's gate terminal (the gate must be sufficiently more negative than the threshold voltage across the drain-source region) (VGDS). A current will be allowed to flow through the source-drain channel as a result of this.   With a sufficient positive voltage, VS, applied to the source and load, and a sufficient negative voltage applied to the gate, the P-Channel Enhancement-type MOSFET is fully functional and operating in the active 'ON' mode.     5.1.3 How to Turn Off a P-Channel Enhancement Type MOSFET?   There are two ways to turn off a P-channel enhancement type MOSFET. You can either disconnect the bias positive voltage, VS, which powers the source. Alternatively, you can disable the negative voltage applied to the transistor's gate.     5.2 P Channel Depletion MOSFET When compared to n channel depletion MOSFETs, the formation of p channel depletion is simply in reverse. Because of the presence of p-type impurities in the channel, it is pre-built. When a negative voltage is applied to the terminal gate, the free holes that represent the minority carriers at the n-type are attracted to the channel of the positive type impurity ions. When a drain terminal is reverse biased in this condition, the device begins to conduct, but as the negative voltage in the drain terminal increases, the depletion layer forms.   This region is affected by the concentration of the layer formed by positive ions. The width of the depletion region influences the conductivity of the channel. The current at the terminal is controlled by varying the voltage value of the region. Finally, the gate and drain retain their negative polarity, while the source maintains its zero value.     5.2.1 How a P-Channel Depletion-type MOSFET Works?   circuit  P-Channel Depletion-type MOSFET   5.2.2 How to Turn on a P-Channel Depletion Type MOSFET? The gate voltage feeding the gate terminal should be 0V for maximum operation if you switch on a P-Channel Depletion-Type MOSFET. The drain current is at its maximum when the gate voltage is 0V, and the transistor is in the active 'ON' region of conduction.     5.2.3 How to Turn Off a P-Channel Depletion Type MOSFET?   There are two methods for turning off a P-channel MOSFET. You can either switch off the bias positive voltage, VDD, which powers the drain, or you can turn it back on. Alternatively, you can apply a negative voltage to the gate. The current is cut down when a negative voltage is used to the gate. As the gate voltage, VG, becomes more negative, the current decreases until it reaches cutoff, at which point the MOSFET is in the 'OFF' state. It prevents a great source-drain current from flowing.   MOSFET transistors are applied for switching as well as amplifying. MOSFETs are among the most widely used transistors today. Because of their high input impedance, they draw very little input current, which is simple to manufacture, can be made very small, and consume very little power.       Ⅵ How to use only positive voltage in this p-channel MOSFET tutorial?   6.1 VGS Threshold   VGSth: an abbreviation for Voltage Threshold from Gate to Source is one of their critical properties we need to know about using MOSFETs. The resistance between the DRAIN and SOURCE pins changes as the voltage difference between those two pins changes. This is the threshold at which a MOSFET turns on and off.   The resistance changes depending on whether the MOSFET is N-Channel or P-Channel.     6.2 P-Channel MOSFET Tutorial and Explanation   For a P-Channel MOSFET, look at the VGSth. VGSth is a negative value, as you may have noticed. As an example, consider the datasheet for an IRF5305.     specification   The specification of VGSth is -2.0V to -4.0V. So, how could this MOSFET work with an Arduino, LaunchPad, Raspberry Pi, or any other microcontroller? Is it really necessary to generate negative voltages?     It’s about the difference:   This is where the "negative voltage" myth comes into play: Because the datasheet says negative, you need negative voltage to work. Datasheets, on the other hand, never lie (except when they do...).   Let's take a literal look at what the specification says. "A negative four-volt voltage from gate to source." You could read it as "GATE voltage value minus SOURCE voltage value" in other words.   Consider the following voltages in this "high-side switch" configuration:     negative voltage     The GATE now has a voltage of 5 volts. The SOURCE is 5 volts as well. It means that the Vgs is 5V – 5V = 0V. In this case, the Vgs is 0 volts. This voltage indicates that the MOSFET is off, or that it is open.   This is the same circuit as before, but the GATE is now connected to ground rather than 5 volts.       circuit  example in 5 volts     Let's take another look at the SOURCE and GATE. The SOURCE remains at 5 volts. However, the GATE is now at the ground, indicating that it is 0V. If you subtract the GATE voltage from the SOURCE voltage, you get 0V – 5V = -5V. This will activate the MOSFET.   Have you noticed what just happened? Using only positive voltage supplies, we obtained a "negative" voltage...     Why use N-Channel over P-Channel?   A tutorial on when to use an n-channel and p-channel MOSFET would be required. A great application for P-Channel is in a circuit where the voltage levels of your load and logic are the same. For example, suppose you're attempting to activate a 5-volt relay with an Arduino. The current required by the relay coil is too high for an I/O pin, but the coil requires 5V to function. Use a P-Channel MOSFET to turn on the relay from the Arduino's I/O pin in this case.   If your load voltage is higher, such as 12 or 24V, you should consider using an N-Channel MOSFET in a "low side" configuration.   Ⅶ FAQ   1. How do you test P MOSFET? Hold the MosFet by the case or the tab but don't touch the metal parts of the test probes with any of the other MosFet's terminals until needed. 2) First, touch the meter positive lead onto the MosFet's 'Gate'. 3) Now move the positive probe to the 'Drain'. You should get a 'low' reading.   2. When would you use a MOSFET? Power MOSFETs are commonly used in automotive electronics, particularly as switching devices in electronic control units, and as power converters in modern electric vehicles. The insulated-gate bipolar transistor (IGBT), a hybrid MOS-bipolar transistor, is also used for a wide variety of applications.   3. What is MOSFET? MOSFET stands for metal-oxide-semiconductor field-effect transistor. It is a field-effect transistor with a MOS structure. Typically, the MOSFET is a three-terminal device with gate (G), drain (D) and source (S) terminals.   4. What are the types of MOSFET? Different Types of MOSFET Transistors PMOS Logic. As previously mentioned, the integration of a MOSFET allows for high levels of circuit efficiency when compared with BJTs. ... NMOS Logic. ... CMOS Logic. ... Depletion Mode MOSFET Devices. ... MISFETs. ... Floating-Gate MOSFETs (FGMOS) ... Power MOSFETs. ... DMOS.                  

Ⅰ IntroductionIn an analog world surrounded by digital devices, we exist in a fascinating intersection of two domains. In nature, everything we observe, feel, or measure is analog—such as light, temperature, speed, pressure, and sound. However, most electronic devices around us are digital, ranging from basic digital watches to sophisticated supercomputers and AI systems. Therefore, for microcontrollers, microprocessors, and modern computing systems to understand and process real-world phenomena, we need devices that can convert these analog parameters into digital values. This conversion is performed by an ADC (Analog-to-Digital Converter), and in this comprehensive guide, we will explore their functionality, types, and applications in modern electronics.Ⅱ Definition of ADC (Analog-to-Digital Converter)An Analog-to-Digital Converter (ADC) is a circuit that converts continuous voltage values (analog signals) into binary values (digital data) that can be interpreted and processed by digital computers and microcontrollers. These ADC circuits can be found as standalone integrated circuits (ICs) or embedded within microcontrollers, system-on-chip (SoC) designs, and digital signal processors (DSPs). The conversion process involves sampling the analog signal at discrete time intervals and quantizing the amplitude into digital codes.Modern ADCs are fundamental components in virtually all electronic systems that interface with the physical world, from smartphones and IoT devices to medical equipment and automotive sensors.Ⅲ The Reasons for Using ADCsToday's electronics ecosystem is predominantly digital; the era of analog computers has long passed. However, the physical world we inhabit remains inherently analog and continuous. Digital systems can only process discrete values—essentially ones and zeros—which creates a fundamental incompatibility with analog signals.For example, a temperature sensor such as the LM35 outputs a temperature-dependent voltage—specifically, 10 mV per degree Celsius. If we connect this directly to a digital input pin, the microcontroller will only register it as either HIGH or LOW based on threshold voltages (typically around 0.8V for LOW and 2V for HIGH in 5V systems), which provides no useful temperature information. Instead, we use an ADC to convert the analog voltage input into a multi-bit digital value that can be directly processed by the microprocessor's data bus, enabling precise calculations, data logging, and control decisions.Key reasons for using ADCs include:Enabling digital processing of real-world analog signalsFacilitating data storage and transmission in digital formatAllowing complex mathematical operations on sensor dataEnabling machine learning and AI applications with sensor inputsProviding noise immunity through digital signal processingⅣ Working Principles of ADCUnderstanding ADC operation is best approached by viewing it as a mathematical mapping function. The ADC maps continuous analog voltage values to discrete binary numbers within a defined range. This process involves three fundamental steps: sampling, quantization, and encoding.The ADC needs to bridge the gap between the analog voltage domain and the digital logic domain. Since digital registers can only accept discrete logic levels (HIGH/LOW), directly connecting an analog signal would produce unreliable results. The ADC acts as an intelligent interface that periodically samples the analog input and converts each sample into a binary representation.Figure 1: Analog to Digital Conversion ProcessHere are the essential characteristics of ADCs that determine their performance and suitability for different applications:4.1 Reference VoltageNo ADC operates in absolute terms; instead, it requires a reference voltage that defines the full-scale range. The reference voltage represents the maximum analog input that corresponds to the highest possible digital output value. For example, in a 10-bit converter with a 5V reference voltage, the binary value 1111111111 (1023 in decimal—the highest possible 10-bit number) corresponds to 5V, while 0000000000 (0 in decimal) corresponds to 0V.Since 10 bits provide 210 = 1024 possible values (0-1023), each binary step represents approximately 5V / 1024 ≈ 4.88 mV. This measure is called the resolution or LSB (Least Significant Bit) voltage of the ADC. The formula is:Resolution (V) = VREF / 2nwhere VREF is the reference voltage and n is the number of bitsIf the analog voltage changes by less than one LSB (4.88mV in this example), the ADC cannot detect the change—this creates a quantization error. To minimize this error and improve measurement precision, you can either use an ADC with higher resolution (more bits) or reduce the reference voltage to match your signal range more closely.Modern ADCs are available with resolutions ranging from 8 bits (256 levels) for simple applications to 32 bits (over 4 billion levels) for precision scientific instruments, though 12-bit and 16-bit converters are most common in embedded systems.4.2 Sample Rate (Sampling Speed)The sample rate, also called sampling frequency, refers to the number of analog-to-digital conversions the ADC performs per second, measured in samples per second (S/s or SPS). High-performance ADCs can achieve sample rates exceeding 1 GS/s (giga-samples per second, or one billion samples per second), while precision ADCs might operate at just a few samples per second.According to the Nyquist-Shannon sampling theorem, to accurately reconstruct a signal, the sampling rate must be at least twice the highest frequency component in the signal. For example, to digitize audio signals with frequencies up to 20 kHz, you need a sampling rate of at least 40 kHz (which is why CD audio uses 44.1 kHz).The sampling speed depends on the ADC architecture and the required accuracy. Generally, there's a trade-off between speed and resolution: high-speed ADCs (like flash ADCs) typically have lower resolution (8-10 bits), while high-resolution ADCs (like sigma-delta ADCs) operate at lower speeds. This is because achieving higher precision requires more time to accurately measure and convert the analog signal.4.3 Additional Key SpecificationsSignal-to-Noise Ratio (SNR): Measures the ratio of the desired signal power to background noise, typically expressed in decibels (dB). Higher SNR indicates better performance.Effective Number of Bits (ENOB): Accounts for real-world imperfections and indicates the actual resolution achieved in practice, which is typically less than the nominal bit count.Input Impedance: The electrical resistance presented by the ADC input, which affects how it loads the source circuit. High input impedance is generally desirable to minimize signal distortion.Ⅴ Types of ADCsVarious ADC architectures have been developed to optimize for different combinations of speed, resolution, power consumption, and cost. Here are the most common types:5.1 Flash ADCs (Parallel ADCs)Flash ADCs are the fastest type of analog-to-digital converter, capable of conversion rates exceeding 1 GS/s. They consist of a resistor ladder voltage divider and an array of comparators—one for each quantization level. For an n-bit flash ADC, 2n - 1 comparators are required.Figure 2: Flash ADC ArchitectureAll comparators operate simultaneously (in parallel), comparing the input voltage against their respective reference levels. The comparator outputs are then fed through a priority encoder that converts the thermometer code into binary format. The conversion speed is limited only by the propagation delays of the comparators and encoder, making flash ADCs ideal for high-speed applications like video processing and radar systems.Advantages: Extremely fast, simple operationDisadvantages: High power consumption, large chip area, limited resolution (typically 8-10 bits due to exponential growth in component count), expensive for high-resolution designs5.2 Successive Approximation Register (SAR) ADCsSAR ADCs are among the most popular and widely used converters, offering an excellent balance between speed, resolution, and power consumption. They consist of a sample-and-hold circuit, a comparator, a Digital-to-Analog Converter (DAC), and successive approximation logic.The conversion process uses a binary search algorithm. Starting with the most significant bit (MSB), the SAR sets each bit to '1' and compares the DAC output with the input voltage. If the DAC output exceeds the input, the bit is cleared to '0'; otherwise, it remains '1'. This process repeats for each bit from MSB to LSB, requiring n clock cycles for an n-bit conversion.SAR ADCs are ubiquitous in microcontrollers (including Arduino, STM32, ESP32, and most ARM Cortex-M devices) and can achieve resolutions from 8 to 18 bits with sampling rates from 100 kS/s to several MS/s.Advantages: Good resolution, moderate speed, low power consumption, cost-effectiveDisadvantages: Slower than flash ADCs, requires n clock cycles for n-bit conversion5.3 Sigma-Delta (ΣΔ) ADCsSigma-delta ADCs achieve very high resolution (16 to 32 bits) by using oversampling and noise-shaping techniques. They sample the input at a rate much higher than the Nyquist rate and use digital filtering to achieve high effective resolution at lower output data rates.These converters are ideal for precision measurement applications such as digital scales, industrial sensors, audio recording equipment, and medical instrumentation where accuracy is paramount and speed is less critical.Advantages: Excellent resolution and linearity, good noise rejection, simple analog circuitryDisadvantages: Slow conversion rate, complex digital filtering required, higher latency5.4 Dual-Slope (Integrating) ADCsDual-slope ADCs integrate the input signal for a fixed period, then integrate a reference voltage of opposite polarity until the integrator returns to zero. The time required for the second integration is proportional to the input voltage. A counter measures this time, providing the digital output.While slow, dual-slope ADCs offer excellent noise rejection (especially for 50/60 Hz line frequency noise) and are commonly used in digital multimeters and panel meters.Advantages: High accuracy, excellent noise rejection, low costDisadvantages: Very slow conversion speed, typically limited to a few conversions per second5.5 Pipeline ADCsPipeline ADCs divide the conversion into multiple stages, with each stage resolving a few bits. The residue from each stage is amplified and passed to the next stage. This architecture allows for high sampling rates (10-100 MS/s) with moderate resolution (8-16 bits), making them popular in video processing, communications, and imaging applications.Ⅵ Applications of ADCs6.1 Digital Oscilloscopes and MultimetersWhile analog oscilloscopes provide real-time display with minimal processing delay, they cannot store waveforms, perform automated measurements, or conduct advanced signal analysis. Digital oscilloscopes solve these limitations by employing high-speed, high-resolution ADCs (typically 8-12 bits at sampling rates up to several GS/s).Modern digital oscilloscopes can capture transient events, perform FFT analysis, decode serial protocols, and store thousands of waveforms for later analysis. Similarly, digital multimeters use precision ADCs (often dual-slope or sigma-delta types) to provide accurate voltage, current, and resistance measurements with 3½ to 8½ digit resolution.6.2 Microcontrollers and Embedded SystemsNearly all modern microcontrollers include integrated ADCs, making them essential for IoT devices, sensor interfaces, and embedded control systems. Common examples include:Arduino (ATmega328P): 10-bit SAR ADC, 6 channels, up to 15 kS/sSTM32 series: 12-bit SAR ADC, multiple channels, up to 5 MS/s (varies by model)ESP32: 12-bit SAR ADC, 18 channels, up to 2 MS/sRaspberry Pi Pico (RP2040): 12-bit SAR ADC, 4 channels, 500 kS/sNordic nRF52 series: 12-bit SAR ADC for low-power wireless applicationsThe Arduino IDE provides a convenient analogRead() function that reads an analog voltage on any analog input pin and returns a 10-bit integer value (0-1023), making ADC usage accessible even for beginners.6.3 Digital Power Supplies and Battery ManagementModern programmable power supplies and battery management systems rely heavily on ADCs to monitor output voltage, current, and temperature. These measurements enable precise regulation, protection features, and user interfaces displaying real-time parameters. High-resolution ADCs (16-24 bits) are often used in precision laboratory power supplies to achieve millivolt-level accuracy.6.4 Audio Recording and ProcessingProfessional audio equipment uses high-quality sigma-delta ADCs with 24-bit resolution and sampling rates of 44.1 kHz, 48 kHz, 96 kHz, or even 192 kHz. These converters enable digital recording, processing, and storage of audio signals with exceptional fidelity. Consumer devices like smartphones and laptops also incorporate audio ADCs for voice recording and communication.6.5 Medical InstrumentationMedical devices such as ECG monitors, pulse oximeters, blood glucose meters, and patient monitoring systems all depend on precision ADCs to convert physiological signals into digital data for analysis, display, and storage. These applications demand high accuracy, low noise, and often require specialized ADCs designed for biomedical signals.6.6 Automotive and Industrial SensorsModern vehicles contain hundreds of sensors monitoring engine parameters, emissions, tire pressure, temperature, acceleration, and more—all requiring ADCs for digital processing. Industrial automation similarly relies on ADCs for process control, quality monitoring, and predictive maintenance applications.Ⅶ How to Use External ADC ICsWhen the built-in ADC of a microcontroller doesn't meet your requirements—whether due to insufficient resolution, speed, or channel count—external ADC ICs provide a solution. Popular external ADC modules include the ADS1115, MCP3008, AD7606, and ADS1256, which can be interfaced with microcontrollers, Raspberry Pi, and other digital systems.Let's examine the Texas Instruments ADS1115, a popular 16-bit ADC with advanced features and excellent performance:Figure 3: ADS1115 16-bit ADC Module7.1 Key Features of Modern ADC ICsI²C/SPI Interface: The ADS1115 uses the I²C bus for communication, making it easy to interface with Arduino, Raspberry Pi, ESP32, and other platforms. Extensive libraries are available in multiple programming languages, simplifying implementation. The I²C interface also allows multiple ADCs to share the same bus using different addresses.Low Power Consumption: Modern ADC ICs are designed for efficiency, with the ADS1115 consuming only 150 µA in continuous conversion mode and less than 1 µA in power-down mode. The operating voltage range of 2.0V to 5.5V makes it compatible with both 3.3V and 5V systems.Programmable Gain Amplifier (PGA): The ADS1115 includes a built-in PGA with selectable gain settings (±6.144V, ±4.096V, ±2.048V, ±1.024V, ±0.512V, ±0.256V), allowing you to optimize the measurement range for your signal amplitude and maximize resolution.Flexible Input Configuration: The four analog inputs can be configured as four single-ended inputs or two differential pairs, providing versatility for different measurement scenarios. Differential inputs are particularly useful for rejecting common-mode noise.Programmable Comparator: An integrated comparator with programmable thresholds can generate interrupts when the input exceeds specified limits, enabling efficient event-driven programming without continuous polling.High Resolution: With 16-bit resolution, the ADS1115 provides 65,536 discrete levels, offering significantly better precision than typical 10-bit or 12-bit microcontroller ADCs. At the ±4.096V range, this translates to approximately 125 µV per step.Ⅷ Limitations and Considerations of ADCsWhile ADCs are essential components, they do have inherent limitations that designers must consider:Conversion Time: ADCs require finite time to perform conversions, ranging from nanoseconds (flash ADCs) to milliseconds (high-resolution sigma-delta ADCs). This introduces latency that may be problematic in real-time control systems.Quantization Error: The discrete nature of digital representation means that analog values between quantization levels cannot be precisely represented, introducing an inherent error of up to ±½ LSB.Aliasing: If the input signal contains frequency components above half the sampling rate (Nyquist frequency), aliasing occurs, causing high-frequency signals to appear as lower frequencies in the digital output. Anti-aliasing filters are required to prevent this.Noise and Interference: ADCs are sensitive to electrical noise, which can degrade measurement accuracy. Proper PCB layout, grounding, filtering, and shielding are essential for optimal performance.Input Impedance Effects: The ADC input impedance can load the source circuit, potentially affecting the signal being measured. Buffer amplifiers may be necessary for high-impedance sources.Cost and Complexity: High-performance ADCs (high resolution and high speed) are expensive and may require complex supporting circuitry, including precision voltage references, low-noise power supplies, and sophisticated digital signal processing.Power Consumption: High-speed ADCs can consume significant power, which may be problematic in battery-powered or energy-constrained applications.Ⅸ Frequently Asked Questions (FAQ)1. Why do we need an ADC converter?The physical world is inherently analog—sound waves, light, temperature, pressure, and other phenomena exist as continuous values. However, digital computers and microcontrollers can only process discrete binary numbers (ones and zeros). ADCs bridge this gap by sampling analog signals and converting them into digital representations that computers can store, process, and analyze. This enables applications ranging from digital audio recording and sensor data logging to medical diagnostics and industrial automation. Without ADCs, modern digital systems would be unable to interact with or measure real-world phenomena.2. What is the slowest type of ADC?Dual-slope (integrating) ADCs are among the slowest, typically performing only a few conversions per second. However, this slow speed is often intentional—these ADCs integrate the signal over a long period, which provides excellent noise rejection, particularly for 50/60 Hz power line interference. They're commonly used in digital multimeters where accuracy is more important than speed. Sigma-delta ADCs can also be quite slow when configured for maximum resolution, though they offer superior performance compared to dual-slope designs.3. What is the difference between 8-bit, 10-bit, and 12-bit ADCs?The bit count determines the resolution—how finely the ADC can divide the voltage range. An 8-bit ADC provides 256 discrete levels (2⁸), a 10-bit ADC provides 1,024 levels (2¹⁰), and a 12-bit ADC provides 4,096 levels (2¹²). With a 5V reference: an 8-bit ADC has ~19.5 mV per step, a 10-bit ADC has ~4.9 mV per step, and a 12-bit ADC has ~1.2 mV per step. Higher resolution allows detection of smaller voltage changes, making the measurement more precise. However, higher resolution often comes with trade-offs in speed, cost, and complexity. Choose the resolution based on your application's accuracy requirements.4. What is the difference between ADC and DAC?An ADC (Analog-to-Digital Converter) is an input device that converts continuous analog signals into discrete digital values for processing by digital systems. A DAC (Digital-to-Analog Converter) performs the opposite function—it's an output device that converts digital values into continuous analog signals. For example, when recording audio, an ADC converts sound waves (analog) into digital data; when playing back that audio, a DAC converts the digital data back into analog signals that drive speakers. Both are essential for digital systems to interact with the analog world.5. How does the ADC inside a microcontroller work?Most microcontrollers use SAR (Successive Approximation Register) ADCs due to their good balance of speed, resolution, and power efficiency. The process involves: (1) A sample-and-hold circuit captures and holds the input voltage stable during conversion; (2) The SAR logic performs a binary search, testing each bit from MSB to LSB by comparing the input against a DAC output; (3) After n clock cycles (for n bits), the final binary value is stored in a register where the CPU can read it. The entire process typically takes a few microseconds, and many microcontrollers can perform conversions automatically in the background using DMA (Direct Memory Access).6. How do you convert analog to digital?The conversion process involves three main steps: (1) Sampling: The continuous analog signal is measured at discrete time intervals determined by the sampling rate; (2) Quantization: Each sampled voltage value is mapped to the nearest discrete level based on the ADC's resolution; (3) Encoding: The quantized level is represented as a binary number. The sampling rate must be at least twice the highest frequency in the signal (Nyquist theorem) to avoid aliasing, and the resolution must be sufficient to capture the required detail in the amplitude.7. Why do we need to convert analog to digital?Digital representation offers numerous advantages: (1) Processing: Digital signals can be easily manipulated using algorithms, filters, and mathematical operations; (2) Storage: Digital data can be stored indefinitely without degradation; (3) Transmission: Digital signals are less susceptible to noise and interference during transmission; (4) Accuracy: Digital systems can perform precise calculations and measurements; (5) Integration: Digital data can be easily shared between different systems and processed by computers; (6) Advanced Features: Digital signals enable machine learning, pattern recognition, and sophisticated analysis impossible with analog systems.8. What are common applications of ADCs?ADCs are used in countless applications: digital oscilloscopes and multimeters for test equipment; microcontrollers and embedded systems for sensor interfaces; audio recording and playback equipment; medical devices (ECG, pulse oximeters, blood pressure monitors); automotive sensors (engine management, safety systems); industrial process control; telecommunications equipment; digital cameras and imaging systems; touchscreen interfaces; battery management systems; smart home devices and IoT sensors; scientific instrumentation; and data acquisition systems. Essentially, any application requiring a digital system to measure or respond to analog phenomena requires an ADC.9. What's the difference between analog and digital signals?Analog signals are continuous in both time and amplitude—they can take any value within a range and change smoothly over time. Examples include sound waves, temperature variations, and light intensity. Digital signals are discrete in both time and amplitude—they exist only at specific time intervals (samples) and can only take specific values (quantization levels). Digital signals are typically represented as binary numbers (sequences of 1s and 0s). While analog signals directly represent physical phenomena, digital signals are representations that approximate the analog world in a form that computers can process.10. What factors should I consider when choosing an ADC?Key selection criteria include: (1) Resolution: How many bits are needed for your accuracy requirements? (2) Sampling Rate: How fast must you sample to capture your signal's frequency content? (3) Input Range: Does it match your signal amplitude? (4) Number of Channels: How many signals need to be measured? (5) Interface: SPI, I²C, parallel, or integrated? (6) Power Consumption: Critical for battery-powered applications; (7) Cost: Balance performance with budget; (8) Package Size: PCB space constraints; (9) Input Type: Single-ended or differential? (10) Additional Features: Built-in PGA, reference, comparator, etc. Consider your application's priorities—speed, accuracy, power, or cost—and choose accordingly.Ⅹ ConclusionAnalog-to-Digital Converters are fundamental building blocks of modern electronics, serving as the essential bridge between our analog physical world and the digital systems that process information. From the simplest temperature sensor in a home thermostat to the sophisticated signal processing in medical imaging equipment, ADCs enable digital systems to perceive, measure, and respond to real-world phenomena.Understanding ADC specifications—resolution, sampling rate, input range, and architecture—is crucial for selecting the right converter for your application. Whether you're using the built-in ADC in a microcontroller for a hobby project or designing a precision measurement system with external high-resolution ADCs, the principles remain the same: sample the analog world accurately and convert it to digital form for processing.As technology advances, ADCs continue to improve in resolution, speed, and power efficiency while decreasing in cost and size. This ongoing evolution enables new applications in IoT, wearable devices, autonomous vehicles, and countless other fields where the digital and analog worlds intersect.Last Updated: November 2025

IntroductionFlash memory card, as a high-quality choice for small storage at this stage, has always been favored by consumers due to its many advantages such as good portability, large optional capacity, and plug-and-play. This article will introduce the definition, product type, function, service life and other aspects in detail. CatalogIntroductionRelated Video IntroductionⅠ What is a flash memory card?Ⅱ The Evolution of Flash Memory CardⅢ Types of Flash Memory CardsⅣ Reference Value of the Amount of Data Stored in the Flash Memory CardⅤ What is the Life Expectancy of Flash Memory? (Take the SD CARD as an Example)Ⅵ FAQ about Flash Memory Card Related Video IntroductionVideo: How Does Flash Memory Work?Video Description: In this video, I am going to explain how Flash Memory and Solid-state drives (SSD) work! Have fun, get some popcorn and enjoy! Everybody stores pictures, music, and videos on their devices nowadays. The encoded information is even stored when the device shuts down due to low energy. After powering it on again, we find the same media and are glad that it did not disappear. Flash memory was invented in 1984 by Japanese engineer Fujio Masuoka at the Toshiba Corporation. An electrical storage medium that does not require any energy to retain data. The name "Flash" was suggested by a coworker of Masuoka, Shoji Ariizumi because the erasure process of the newly invented device reminded him of a camera's flash. Later, the invention of flash memory allowed the wide use of solid-state-drives (SSD) that most of us have in their computers today. Ⅰ What is a flash memory card?A flash memory card (also known as a storage card) is a small storage device that stores data on portable or remote computing devices using nonvolatile semiconductor memory. Text, images, audio, and video are examples of such data. The majority of current products use flash memory, but other memory technologies, such as devices that combine dynamic random access memory (DRAM) and flash memory, are being developed. Figure:flash memory card Ⅱ The Evolution of Flash Memory CardAn unknown Toshiba engineer applied for a patent for simultaneous erasable EEPROM in 1980.Perhaps even Dr. Fujio Kaoka didn't realize the value of this patent, let alone the senior Toshiba company, so this cross-epoch patent went unnoticed for four years.Dr. Gang Gang's invention was not made public until 1984, when he presented it at the IEEE International Electron Devices Meeting (IEDM) in San Francisco, California.Intel recognized the enormous potential of this invention at the conference and released the first commercial NOR Flash chip in 1988. (the original CompactFlash was originally based on NOR Flash, although it later switched to a lower-cost NAND Flash.) The story does not end there. Dr. Fujio Kaoka discovered that NOR Flash has a long erasure time and thus invented NAND Flash in 1986. NAND Flash has a faster erasing time and a smaller area for each memory cell than NOR Flash, giving it a higher storage density and lower cost per bit. Since then, flash memory (both NOR and NAND) has been created. The irony is that despite his significant contribution, he only received a few hundred dollars in Toshiba rewards and a high-ranking but laid-back position. He couldn't take this kind of treatment as an engineer and had to resign and enroll in university to continue his scientific research. Memory cards based on NAND Flash were later developed. SmartMedia was the first application of NAND Flash. Since then, NAND Flash has been adopted by a wide range of storage media. Ⅲ Types of Flash Memory CardsMultimedia Card,A Multimedia Card is a type of flash memory card. Its size is 32mm 24mm 1.4mm and weight is 1.5 grams, making it ideal for digital imaging, music, mobile phones, PDAs, e-books, toys, and other products. However, due to a lack of support from consumer digital manufacturers, there aren't many products in the digital product market that can use MMC memory cards.Figure:Multimedia Card Panasonic, Toshiba, and SanDisk of Japan collaborated to develop the SD card (Secure Digital). It is 32mm24mm2.1mm in size and weighs only 2 grams, but it has a large capacity, a high data transmission rate, and good flexibility. The SD card's structure ensures the security of digital file transfer, and it is simple to reformat, so it has a wide range of applications. SD cards are widely used as storage media in digital cameras. As a result, the SD card is the most widely used memory card.Figure:SD Card Mini SD cards are derived from SD cards, and their performance is comparable to that of standard SD cards. Mini SD cards, like SD cards, have a hardware data write protection switch to prevent accidental deletion of stored content. The Mini SD card, on the other hand, is 40 percent smaller than the SD card, measuring only 21.5 mm20 mm1.4mm. It is fully compatible with standard SD card slots and can be used with a dedicated adapter card.Figure:Mini SD Card The most important difference, however, is that the Mini SD card uses a low-power design, making it more suitable for mobile communication equipment than the SD card. It is currently used primarily in information terminal equipment such as mobile phones, PDAs, and handheld computers. T-Flash card, full name: TransFLash (also: Micro SD), is a very small flash memory card developed and launched jointly by Motorola and SANDISK. It has the advantage of being small and is primarily used in mobile phones, but as capacity increased, it gradually began to be used in a broader range of fields. At the same time, it has a large capacity and can be connected to the SD card slot via an adapter.Figure:T-Flash Card Memory Stick is the full name of a mobile storage medium developed by Sony Corporation of Japan. This type of storage device resembles chewing gum and has a high level of compatibility. Later, Sony reduced the volume based on the memory stick to about one-third and designed and manufactured the memory stick Duo. This type of memory stick Duo is ideal for use in small mobile phones and digital cameras, as well as various mp3 players and other electronic devices.Figure:Memory Stick The latest bus and interface standard is PCI-e flash memory card (PCI-Express). It was originally known as "3GIO." PCIe is a serial point-to-point dual-channel high-bandwidth transmission standard. Exclusive channel bandwidth is assigned to the connected devices. Shared resources, primarily supporting functions such as active power management, error reporting, end-to-end reliability transmission, hot plug, and service quality (QOS). The concept is based on NAND flash memory.Figure:PCI-e Flash Memory Card CF cards (Compact Flash) were originally used in portable electronic devices as a data storage device. It revolutionized the use of flash memory as a storage device, which was first produced by SanDisk in 1994 and formulated relevant specifications. Many devices are currently using its physical format. However, the CF card's capacity is limited, and increasing its capacity cannot keep up with the development of digital camera pixels. The size is relatively large when compared to other types of memory cards, and the operating temperature is generally 0-40 degrees Celsius, which limits its performance.Figure:CF Card Sony's XQD memory card is a type of memory card. It is much smaller than a standard CF card, only about half the size. The XQD memory card, on the other hand, retains the CF card's fast and stable reading. Furthermore, the XQD memory card employs an upgradeable high-performance interface. It had a read and write speed of 125 megabits per second.Figure:XQD Memory Card Olympus and Fuji jointly launched the XD-Picture Card (xD) memory card. It has an extremely small external size of 20mm25mm1.7mm and a weight of only 2 grams. Its read and write speeds can reach 5MB/S and 3MB/S, respectively. Initially, the XD card was primarily used in Olympus and Fuji digital camera products. Despite the fact that its performance can meet the requirement of writing large amounts of data and its power consumption is lower, the relatively high price has severely limited the development of XD cards. Olympus and Fuji digital cameras no longer exclusively use XD cards as storage media.Figure:XD Card The M2 card is a new Memory Stick Micro (M2) memory card jointly released by Sony and SanDisk. It debuted in March 2006. This type of M2 card uses an ultra-small circuit design, specifically for large-capacity, small-volume mobile storage needs; it weighs only 16 grams, has dimensions of only 15 12.5 1.2mm, and has a volume roughly one-fourth that of a memory stick Pro Duo.Figure:M2 Card  Ⅳ Reference Value of the Amount of Data Stored in the Flash Memory Card PhotosVideosMusice-books                          FormatStorage JPEG(10MP)MP4(minutes)MP3PDF(10MB)16GB320810883040163832GB641621766080327664GB128324352121606553128GB2566487042432013107256GB51328174084864026214  Ⅴ What is the Life Expectancy of Flash Memory? (Take the SD CARD as an Example)An SD card is a solid-state device, which means it has no moving parts. This is a significant advancement over older portable storage devices, such as floppy disks, which had thin, flimsy disks spinning at high speeds. The components of an SD card are part of its circuitry, which is why they are so small and compact. Data is stored on flash memory chips found on circuitry. Flash memory is a type of EEPROM chip (Electrically Erasable Programmable Read Only Memory). There are two types of memory cells used in solid-state devices such as SD cards. Lots of SD cards employ single-level memory cells that are either turned on or off. Because these cells can only store a single value, they are fast and dependable. The disadvantage is that you need a large number of them in a large memory card. Most low-cost SD cards use multi-level cell chips. Each cell stores a voltage, and the level of the voltage represents a range of values. Memory cells are insulated to prevent charge leakage. This insulation, however, is eroded each time a write action is performed. This can cause the voltage in a cell to fluctuate slightly over time, causing the data on the SD card to become corrupted. Most modern SD cards are designed to detect and avoid these problem cells, but if there are too many, the card may not have enough memory to map them over time. The exact lifespan of an SD card is determined by a number of factors. If you use your card on a regular basis, it should last a long time assuming it doesn't physically break first. For example, if you use it more than once a week, it's a good idea to replace it once a year.Due to the various pressures people put on SD cards, determining when to replace them is difficult. Most likely, your SD card will physically stop working due to damage before it begins corrupting your data. SD cards are made with low-cost components to keep costs low, and as a result, they are prone to breaking. SD cards are definitely not suitable for long-term storage due to the charge in the cells leaking over time. Although there are special SD cards designed to be written to only once and used for archival purposes, commercially available SD cards such as those found in cameras should not be used in this manner. Most SD cards will not keep data for more than five years. The best way to keep your data safe is to copy it as soon as possible from your SD card to your computer. Ⅵ FAQ about Flash Memory Card1. What are the benefits of flash memory?Increased Durability. Unlike traditional hard-disk drives, flash drives lack moving parts, maximum Portability, plenty of Storage Capacity,Fast Transfer Speeds, compatibility with Many Devices, use Flash Drives as Promotional Materials. 2. Why do smartphones use flash memory?Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed. It's used as primary storage memory on various portable devices due to its low cost, compact size, great physical endurance and low power consumption. 3. Is Flash Memory expensive?Traditional storage drives cost about 7 or 8 cents per usable gigabyte, while flash storage drives cost about 40 cents per usable gigabyte. The price of solid-state drives (SSDs) is falling, but the price of flash storage is declining even faster. 4. What is the difference between flash and EEPROM memory?Flash memory is a distinct type of EEPROM, which is programmed and erased in large blocks. Flash uses NAND-type memory, while EEPROM uses NOR type. Flash is block-wise erasable, while EEPROM is byte-wise erasable. Flash is constantly rewritten, while other EEPROMs are seldom rewritten. 5. How reliable is a flash memory card?Today most commercially available flash memory is guaranteed to withstand 100 000 or more programme-erase cycles with some manufacturers guaranteeing a life of over 1 000 000 cycles. 

A Relay is an electrically operated switch. It allows a low-power signal (like one from a microcontroller or dashboard switch) to control a high-power circuit (like an electric motor, headlights, or industrial machinery). In essence, it provides complete electrical isolation between the control system (input loop) and the controlled system (output loop).Used extensively in automotive systems, industrial automation, and modern Smart Home setups, the relay acts as an "automatic switch." It uses a small current to control a much larger one, offering crucial benefits like automatic adjustment, safety protection, and circuit conversion.As of 2025, while Solid State Relays (SSRs) are gaining popularity for their silence and longevity, the traditional electromechanical relay remains the industry standard for high-current and cost-effective switching. This guide covers how to wire these essential components effectively.Ⅰ Electrical Relay Structure & BasicsFigure 1. Electrical Relay StructureTo understand how to wire a relay, you must first understand its internal architecture:Core Components: A relay consists of four primary parts: the coil, the magnetic circuit (core/yoke), the spring, and the contacts.The Coil: When energized, the coil generates an electromagnetic field. This attraction pulls the armature, changing the state of the contacts.Magnetic Circuit: Comprising an iron core, choke, and armature, this establishes the path for magnetic flux.Air Gap: This is the critical distance between the armature and the core. When the coil is off, the gap is at its maximum (contacts in initial state). When on, the gap closes (contacts switched).The Spring: Provides the resetting force. When the coil is de-energized, the spring pushes the armature back to its original position.Contacts: These execute the control. They are divided into Normally Closed (NC) and Normally Open (NO).Energized: NC opens, NO closes.De-energized: Contacts reset to initial state.Common Types of Relays:Voltage Relays: High coil turns, thin wire. Connected in parallel with the load. (Most common).Current Relays: Few turns, thick wire. Connected in series with the load.Intermediate Relays: Used for signal transmission and controlling multiple secondary circuits.Ⅱ How Do Relays Work?An electromechanical relay is a switch operated by an electromagnet. When the coil receives current, the magnetic force pulls the "Common" (COM) contact arm from the "Normally Closed" (NC) position to the "Normally Open" (NO) position. When power is cut, a spring snaps it back.In short: When a specific input (voltage, current, temperature) hits a set value, the relay changes the state of the output circuit to control or protect the system.Example Analysis: Controlling a LightFigure 2. 8 Pin Relay Wiring ConnectionFigure 3. Relay Controls One LightWiring Logic:To control a lamp using a relay, the power circuit is wired through the relay's contacts. The Neutral wire connects directly to the lamp. The Live (Hot) wire connects to the relay's Normally Open (NO) contact. When the relay is triggered, the circuit closes, and the light turns on.Figure 4. Relay Controls Two Lights (Toggle)Dual Light Setup: By using both NC and NO contacts, you can toggle between two loads. When the coil is OFF, the NC light is ON. When the coil is ON, the NC light turns OFF and the NO light turns ON.Ⅲ Relay Wiring with Different Pins3.1 3-Pin RelayWhat is a 3-Pin Relay?These are commonly found in automotive applications as Flasher Units (for turn signals) or simplified horn relays. They work on electromechanical or thermal principles to cycle power on and off.How to Wire a 3-Pin Relay:Figure 5. 3-Pin Relay Wiring DiagramStandard configuration for a horn or load:Pin 1 (Load): Connected to the device (e.g., horn).Pin 2 (Battery/Power): Connected to the 12V power source (Common).Pin 3 (Switch/Coil): Connected to the button (e.g., steering wheel button).3.2 4-Pin Relay (SPST)What is a 4-Pin Relay?The 4-pin relay is the most common Single Pole Single Throw (SPST) relay used in automotive and general electronics to switch a single circuit on or off.How to Wire a 4-Pin Relay:Figure 6. 4-Pin Relay Wiring DiagramPins 85 & 86 (Coil): These control the magnet. Connect one to ground and the other to your switch (+12V).Pin 30 (Common): Connected to the high-power source (Battery +).Pin 87 (Normally Open): Connected to the load (Fan, Light, Motor).When the coil (85/86) is energized, Pin 30 connects to Pin 87.Figure 7. Standard 12V 40A 4-Pin RelayFigure 8. Coil Pins (85 & 86)Figure 9. Contact Pins (30 & 87)3.3 5-Pin Relay (SPDT)What is a 5-Pin Relay?This is a Single Pole Double Throw (SPDT) relay. It allows you to switch power between two circuits (e.g., High Beam vs. Low Beam) or simply use the "Normally Closed" feature.How to Wire a 5-Pin Relay:Figure 10. 5-Pin Relay Wiring DiagramPins 85 & 86: Coil (Control).Pin 30: Common (Power In).Pin 87a: Normally Closed (Power flows here when relay is OFF).Pin 87: Normally Open (Power flows here when relay is ON).3.4 6-Pin RelayWhat is a 6-Pin Relay?A 6-pin relay often functions similarly to a 5-pin but includes an extra terminal for internal bridging or specific DPDT signal configurations. In some automotive wiper relays, the extra pin handles parking logic.Wiring Overview:Figure 11. 6-Pin Relay Wiring DiagramTypically, two pins act as the coil, and the remaining four form two pairs of switching contacts (or one complex changeover). Always check the specific datasheet, as 6-pin configurations vary more than standard 4/5-pin types.3.5 8-Pin Relay (DPDT)What is an 8-Pin Relay?This is usually a Double Pole Double Throw (DPDT) relay. It effectively houses two 5-pin relays inside one shell, controlled by a single coil. It is ideal for reversing polarity on motors.How to Wire an 8-Pin Relay:Figure 12. 8-Pin Relay Wiring DiagramPins 2 & 7: Coil terminals (Power these to activate).Pins 1 & 8: Common terminals (COM).Pins 3 & 6: Normally Open (NO).Pins 4 & 5: Normally Closed (NC).3.6 Intermediate (Auxiliary) RelayWhat is an Intermediate Relay?Often used in industrial control panels (DIN Rail mounted), these relays transmit signals to control multiple larger contactors or actuators simultaneously. They are the backbone of classical automation logic.Wiring and Safety (Flyback Diodes):Figure 13. Intermediate Relay Wiring DiagramStandard industrial numbering (IEC):13 & 14: Coil (A1/A2).Contacts: Arranged in groups (e.g., 5-6-7-8 as NC, 9-10-11-12 as NO).⚠️ 2025 Safety Tip: When using intermediate relays with DC currents, always install a Freewheeling (Flyback) Diode across the coil (Reverse biased: Cathode to Positive). When the coil turns off, the collapsing magnetic field creates a high-voltage spike (back EMF) that can destroy sensitive control electronics (like PLCs or Arduino boards).Ⅳ FAQ: Relay Wiring in 20251. What is the difference between a Solid State Relay (SSR) and a Mechanical Relay?Mechanical relays use moving parts (magnets/contacts) and make a "click" sound. They are cheaper and handle high surge currents well. SSRs use semiconductors (light/optical isolation), have no moving parts, are silent, and last much longer, but they generate heat and are generally more expensive.2. What do the numbers on a standard automotive relay mean?These are DIN standard numbers: 30: Common (Main Power Input) 85: Coil Ground 86: Coil Positive (Trigger) 87: Normally Open (Output when ON) 87a: Normally Closed (Output when OFF)3. Does a Smart Home relay switch require a Neutral wire?Yes. Unlike older mechanical switches that just cut the Live line, most modern 2025 Smart Relays (WiFi/Zigbee) need a Neutral wire to power their internal WiFi chip so they can stay connected even when the light is off.4. What happens if I wire Pins 85 and 86 backwards?On a standard mechanical relay without a diode, nothing happens—it will still work because the coil is not polarized. However, if the relay has a built-in suppression diode (common in modern cars), wiring it backwards will cause a dead short and blow your fuse.5. What is an SPDT Relay?SPDT stands for Single Pole Double Throw. It has one input (Common) and two outputs (NC and NO). It can route power to Circuit A when off, and switch to Circuit B when on.6. Can I use a 12V relay on a 24V circuit?No. You must match the Coil Voltage to your control system (e.g., 12V car vs. 24V truck). However, the contacts (switch part) can often handle higher voltages than the coil. Always check the rating printed on the case.

In this article, we will provide you the basic information of relay: what is a relay? What types of relays are there? What are their characteristics? How to maintain the common faults of the relay? With these questions, let us find the answers in the article together.     Catalog     I. What is a Relay?     1.1 Electrical Symbol     1.2 Contact Form     1.3 Functions of Relay II. Relay Classification III. Main Types of Relay IV. How to Test a Relay V. Influencing Factors of Relay Reliability VI. Maintenance of Common Faults of Relay VII. Example Explanation: Delay Relays FAQ   I. What is a Relay? This video will explain what is a relay, and how does a relay works with basic information about construction and different types of relay.   Relay is a kind of electric control device. When the change of input quantity (excitation quantity) reaches the prescribed requirement, the controlled quantity will be changed step by step in the electric output circuit. It has an interactive relationship between the control system (also known as the input loop) and the controlled system (also known as the output loop). Usually used in an automatic control circuit, it is a kind of automatic switch which uses a small current to control the operation of a large current. Therefore, it can play the role of automatic regulation, safety protection, conversion circuit, and so on.   1.1 Electrical Symbol A relay is composed of two parts: coil and contact group, the graphic symbol of the relay in a circuit diagram also includes two parts: a box for coil and a set of contact symbols for contact combination. When the contact circuit is relatively simple, the contact group is often drawn directly on one side of the circle frame, which is called centralized representation.   Relay coils are represented by a rectangular symbol in the circuit, and if the relay has two coils, draw two side-by-side boxes. The contacts of relays are represented in two ways: one is to draw them directly on the side of the box, which is more intuitive. The other is to draw each contact point into its own control circuit according to the need for circuit connection. Usually, the contact of the same relay is marked with the same text symbol, and the contact group is numbered to show the difference.   1.2 Contact Form There are three basic forms of contact for relays: 1. The two contacts are disconnected when power off, and the two contacts are closed when power on.   2. The two contacts are closed when power off and the two contacts are disconnected when the power on.    3. The contact group has three contact points, that is, a moving contact in the middle and a static contact in the upper and lower parts of the contact group, respectively. When the coil is power-off, the dynamic contact is disconnected from one of the static contacts and connected with the other. After the coil is power-on, the dynamic contact moves, the connecting contacts state is opposite to the power-off state to achieve the purpose of conversion. Such contact groups are called switching contacts.      1.3 Functions of Relay Relay is an automatic switching element with an isolation function. It is widely used in remote control, telemetry, communication, automatic control, electromechanical integration, and power electronic equipment. It is one of the most important control components.   The relay generally has induction parts (input section) that can reflect a certain input variable (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light, etc.); an executing part (output section) capable of realizing power-on and power-off state of the controlled circuit. Between the input port and the output port of the relay, there is also an intermediate mechanism (driving section) for coupling the input, the function processing, and the driving of the output.   As a control element, relays generally have the following functions:   1) Expand the control range: for example, when the control signal of the multi-contact relay reaches a certain value, the multi-circuit can be switched on and off at the same time according to the different connecting forms of the contact group.   2) Amplification: a very small volume can control a large power circuit, such as sensitive relays, intermediate relays, etc.   3) Synthesis signal: when a plurality of control signals input multiple winding relays in the prescribed form, a predetermined control effect can be achieved by comparing and synthesizing.   4) Automatic, remote control, monitoring: relays on the automatic device, together with other electrical appliances, can form a program control circuit to achieve automatic operation.   II. Relay Classification   1. According to the working principle or structural characteristics of relays: 1) Electromagnetic relay: an electrical relay that is driven by the suction of an input circuit between an electromagnet core and an armature. 2) Solid relay: a relay in which electronic components perform their functions without mechanical movement, and the input and output are isolated. 3) Temperature relay: a relay that operates when the external temperature reaches a certain value. 4) Reed relay: a relay operates by a reed that is sealed in a tube and has a dual action caused by the electricity action on the reed and the armature. 5) Time relay: When the input signal is added or removed, the output part needs to be delayed or limited to a specified time to close off. 6) High-frequency relay: a relay used for switching a high frequency, a radio frequency circuit which had a minimum loss. 7) Polarization relay: a relay driven by magnetic field synthesis caused by a polarized magnetic field and a controlled current acting through the magnetic field generated by the control coil. The direction of the operating relay depends on the direction of the current flowing through the control coil. 8) Other types of relay: optical relay, sound relay, thermal relay, instrument relay, Hall effect relay, differential relay, etc.   2. According to shape size of relays: 1)miniature relay  2)subminiature relay 3)small miniature relay Note: for sealed or enclosed relays, the size is the maximum of the three vertical dimensions of the relay body, excluding the dimensions of mounting, leading end, rib pressing, edge pressing, flanging, and sealing solder joint.   3. According to the load of the relays: 1) micro power relay 2) small power relay 3) medium power relay 4) high power relay    4. According to the protective characteristics of relays: 1) sealed relay  2) enclosed relay 3) unenclosed/ open relay   5. According to the principle of action: 1) electromagnetic type 2) induction type 3) rectifier type 4) electronic type 5) dig type   6. According to the physical quantity of the reaction: 1) current relay 2) voltage relay 3) power relay 4) impedance relay  5) frequency relay 6) gas relay   7. According to the role of relays in the protection circuit: 1) starting relay  2) measuring relay  3) time relay 4) auxiliary/intermediate relay 5) signal relay 6) exit relay    III. Main Types of Relay   1) electromagnetic relay As long as a certain voltage is added at both ends of the coil, a certain current will flow through the coil, producing an electromagnetic effect, and the armature will contact the iron core under the action of electromagnetic force attraction, thus driving the armature dynamic contact and static contact (normally open contact) suction. When the coil is powered off, the electromagnetic suction also disappears, and the armature will return to its original position in the reaction force of the spring and release the dynamic contact from the original static contact (normally closed contact). In this way to achieve the purpose of switching on and off. In addition, it can be distinguished the "normal open and closed contacts of the relay.   Note: The static contact in the broken state when the coil is powered off is known as the "normal open-contact"; the static contact in the on-state is called the "normal closed-contact". Relays generally have two circuits, a low-voltage control circuit, and a high-voltage working circuit.   2) solid-state relay  A solid-state relay is a kind of four-terminal device with two connection terminals as input and the other two as output. In the middle, an isolation device is used to realize the electrical isolation of the input and output.   Solid-state relays can be divided into AC type and DC type according to the type of load power supply. According to the switch, type can be divided into normal open type and normally closed type. According to the isolation type, it can be divided into hybrid type, transformer isolation type, and photoelectric isolation type, and the photoelectric isolation type is the most.   3) thermal reed relay A thermal reed relay is a new type of thermosensitive switch which uses thermosensitive magnetic material to detect and control temperature. It consists of a temperature-sensitive magnetic ring, constant magnetic ring, reed tube, heat conduction mounting sheet, a plastic substrate, and other accessories. Thermal reed relays do not use coil excitation but are driven by magnetic forces generated by constant magnetic rings. In addition, whether the constant magnetic ring can provide magnetic force to drive the reed tube is determined by the temperature control characteristic of the temperature sensing magnetic ring.     4) reed relay Reed relay is a kind of coil sensing device, which uses a coil to produce a magnetic field to drive a magnetic reed tube. In addition, the characteristics of reed relays include small size, lightweight, fast reaction speed, short jump time, and so on.   When a whole piece of ferromagnetic metal or other conductive material is close to it, turn on or turn off the circuit. Reed relay consists of a permanent magnet and a reed tube. Both of them fixed to a bracket without magnetism or magnetic conduction. Take the line of the permanent magnet's north-south pole as the axis, which should be coincident or basically coincident with the axis of the reed. From far to near, adjust the distance between the permanent magnet and the reed tube, and fix the position of the magnet when it happens to move (turning off for normally open reed tube and turning on for normally closed reed tube). At this point, when there's a whole piece of magnetic material, and when the iron plate is close to the magnet and the reed tube at the same time, the reed tube will move again and return to the state without magnetic field action; when the iron plate leaves, the spring tube will move in the opposite direction. The reed relay has a strong structure, sealed contact, and high durability. It can be used as a position limiting switch for mechanical equipment, and can also be used to detect whether iron doors, windows, etc.    5) optical relay An optical relay is a semiconductor relay used in AC/ DC, refers to the integration of light-emitting and light-receiving devices. The input side and the output side are electrically insulated, but the signal can be transmitted through the optical. Its characteristics are semi-permanent, micro-current, high impedance, insulating, voltage-resistance, ultra-small, optical-transmission, contact-free, and so on.   It is mainly used in measuring equipment, communication equipment, security equipment, medical equipment, and so on. 6) time relay Time relay is a kind of control apparatus that uses electromagnetic principle or mechanical principle to realize time delay control. There are many kinds of it, such as air damping type, power-driven type, and electronic type.   Air damping time relay is often used in AC circuit, which uses the principle of air throttling through orifice compensation to obtain delay action. It consists of an electromagnetic system, delay mechanism, and contact. Time relay can be divided into two types: power-on delay type and power-off delay type.   The time delay range of the air-damping time relay is large (0.4~60s and 0.4~180s). Its structure is simple, and its accuracy is low. When the coil is electrified (voltage specification is ac380v, ac220v or dc220v, dc24v, etc.), the armature and bracket are attracted by the iron core and moved down instantly, so that the instantaneous action contact is turned on or off, and meanwhile, the piston rod and lever cannot fall with the armature at the same time, because the upper end of the rod is attached to the rubber film in the air chamber, and when the rod begins to move downward under the action of the released spring, the rubber film falls downward. Air becomes thin in the upper air chamber and the damping piston rod drops slowly. After a certain period of time, the piston rod drops to a certain position, then pushes the delay contact action through the lever, causing the dynamic break contact to break and the dynamic close contact turned off. From the coil to the delay contact to complete the action, this time is the delay time of the relay. The delay time can be changed by adjusting the size of the air chamber inlet hole. After the suction coil is powered off, the relay is restored by the action of the recovery spring, and the air was ejected quickly through the vent hole. 7) auxiliary relay a. characteristics of auxiliary relay:   The relay is composed of several high-quality sealed small relays with low coil voltage, which is damp-proof, dust-proof, non-breaking, high reliability, and overcomes the shortcomings of the electromagnetic auxiliary relay wire which is too thin and easy to break. Low power consumption, low-temperature rise, no need to attach high-power resistance, easy installation and connection, large capacity of a relay contact, long working life, easy to observe on the spot, and so on. The delay only needs to be adjusted by the dial switch on the panel, the delay precision is high, and the delay range can be set freely in 0.02S~ 5.00S.   Purpose of intermediate relay: auxiliary relay is used in various protection and automatic control lines to increase the number of contacts and the capacity of contacts in the protection and control loop.   b. classification of auxiliary relays:   static auxiliary relay   delay auxiliary relay   electromagnetic auxiliary relay   elevator auxiliary relay   rail auxiliary relay   c. auxiliary relay principle   When the coil is electrified, the moving iron core is absorbed under the action of the electromagnetic force, and the moving contact action is driven so that the normally closed contact is separated and the normally open contact is closed. When the coil is powered off and the moving iron core drives the dynamic contact to reset under the action of the spring. The working principle of the relay is that when a certain input (such as voltage, current, temperature, velocity, pressure, etc.) reaches a predetermined value, it operates. In order to change the working state of the control circuit, so as to achieve the established purpose of control or protection. In this process, the relay mainly plays a role in the transmission of the signal.   d. function of the auxiliary relay   The general circuit is often divided into two parts of the main circuit and a control circuit. The relay is mainly used for a control circuit, and the contactor is mainly used for the main circuit. Through the relay, using one control signal can control the other one or several signals, and the control of starting, stopping, linkage, and so on. The main control object is a contactor, the contact of the contactor is relatively large, and the carrying capacity is strong, but the control of weak current too strong electricity can be realized through the contactor, and a control object is an electric appliance.   1. Replace small contactor   The contact of the auxiliary relay has a certain load capacity. When the load capacity is small, it can be used instead of the small contractor, such as the electric shutter and the control of some small appliances. This advantage is that not only can play the purpose of control, but also can save space so that the electrical control part of the more refined.   2. Increase the number of contacts   This is the most common use of auxiliary relays, for example, in a circuit control system where a contact needs to control multiple contactors or other components, adding an auxiliary relay to the line.   3. Increase contact capacity   We know that although the contact capacity of the auxiliary relay is not very large, it also has a certain capacity with load, and the current required for its drive is very small. Therefore, the auxiliary relay can be used to expand the contact capacity. For example, it is not possible to use induction switches directly and the output of the transistor to control the heavy load of electrical components. In fact, the auxiliary relay is used in the control line, and the other load is controlled by the auxiliary relay to enlarge the control capacity.   4. Convert pin type   In the industrial control circuit, it is often necessary to use the normally closed contact of the contactor to achieve the control purpose. However, the normally closed contacts carried by the contractor are not enough to achieve the control task. At this time, an auxiliary relay can be parallel to the original contactor coil, and the corresponding components can be controlled by the normally closed contact of the auxiliary relay, and the contact type can be transformed to achieve the desired control purpose.   5. As a switch In some control circuits, intermediate relays are often used to turn on and off some electrical components, such as automatic demagnetization circuits common in color televisions or displays, and transistor controls the on and off of intermediate relays, which are controlled by the opening and closing of their contacts, such as color televisions or displays. So as to control the demagnetization coil on-off action.   6. Switching voltage   7. Eliminating interference in the circuit   8. Power direction relay   An electrical appliance that causes the controlled output circuit to be switched on or off when the input (such as voltage, current, temperature, etc.) reaches a specified value. It can be divided into two categories of electrical volume (such as current, voltage, frequency, power, etc.) relay and non-electrical volume (such as temperature, pressure, speed, etc.) relay. It has the advantages of fast movement, stable work, long service life, small volume, and so on. Widely used in power protection, automation, motion, remote control, measurement, and communication devices.       Common Types   1. overcurrent relay The overcurrent relay is a relay that operates from the current beyond its set value and can be used as a system line and overload protection. The most commonly used is an induction type overcurrent relay, which is opposite to the rotating disk of aluminum or copper by an electromagnet. The rotating disc is rotated by means of the electromagnetic induction principle so as to achieve the protective effect.   action principles:   The inductive overcurrent relay uses the secondary current of the current transformer to generate a magnetic field in the relay to cause the disk to rotate, but the current flowing through the relay must be greater than the current value of a certain current to rotate.   2. overvoltage relay  Overvoltage relay, its main purpose is that when the abnormal voltage of the system rises to more than 120% rating, the overvoltage relay operates so that the circuit breaker can jump off and protect the electric equipment from damage. The construction and operation principle of induction overvoltage relay are similar to those of overcurrent relay, except the main loop.   3. under voltage relay The under voltage relay is constructed in the same way as the overvoltage relay, except that the inner contact and the turntable turn immediately when the voltage is applied.   4. ground overvoltage relay The grounding overvoltage relay has the same structure as the overvoltage relay, and uses a three-phase three-wire non-grounding system, and is connected to the earthing transformer with an open triangle earthing to detect zero-phase voltage.   5. grounding overcurrent relay Grounding overcurrent relay, abbreviated as GCR, is a kind of high-voltage line earthing protection relay.   Main uses:   1) grounding overcurrent protection of high resistance grounding system.   2) grounding protection of generator stator winding.   3) layer short circuit protection of phase-separated generator.   4) overheat protection of grounding transformer.   6. selective grounding relay Selective grounding relay, also called directional grounding relay, is used in non-grounding systems to protect distribution lines. In addition, it can also be used in overhead lines and cable systems.   Selective grounding relay: if a zero-phase sequence current is detected by a grounding voltage transformer when a line is grounded, the selective grounding relay can accurately detect the fault line and alert it and disconnect it according to the requirement. And then continue to send electricity to the normal operating line.   7. free-phase relay In the three-phase line, phase-failure relay or phase-failure protection relay will burn out the single-phase operation of the motor if it does not cut off the line immediately when there is a one-wire break in the power supply end and causes the single-phase.   8. percentage differential relay A percentage differential relay is used as the AC motor of the transformer. Alternator with differential protection and over-current protection relay used as the protection devices, and when abnormal current generated by external fault flows over protection equipment, if current on the transformer is unbalanced or inconsistent with the characteristics of the current transformer, in these cases, this phenomenon will extend several times and cause failure operation to the relay.     IV. How to Test a Relay Relay is the key device in the intelligent prepaid electric energy meter, the life of the relay determines the life of the meter to a certain extent, thus the performance of the relay is very important to the operation of the intelligent prepaid electric energy meter. There are many manufacturers of relays around the world. Their production scale is quite different, the technical level and performance parameters are very different. Therefore, the manufacturers of electric energy meters must have a set of perfect testing devices when detecting and selecting relays. To ensure the quality of the meter. At the same time, the national power grid has also strengthened the sampling detection of the relay performance parameters in the intelligent electric energy meter, which also needs the corresponding testing equipment to check the quality of the meter produced by different manufacturers. However, at present, relay testing equipment is not only a single test item, but detection process also can not be automated completely, the detection data needs manual processing and analysis, the detection results are random, artificial, and the detection efficiency is low, in addition, there is no guarantee of safety.   According to the test requirements of relay performance parameters, the test items can be divided into two categories: one is the test items without load current, such as operating value, contact resistance, service life; the other, test items with load current, such as contact voltage, electrical life, overload capacity.   1.Measuring coil resistance: the multimeter R×10Ω barrier can be used to measure the resistance value of the relay coil, so as to judge whether there is an open circuit phenomenon in the coil. The resistance value of the relay coil is closely related to its working voltage and current. And the service voltage and working current can be calculated by the resistance value of the coil.   2. Contact resistance measurement: using the resistance barrier of the multimeter, the resistance value of the normally closed contact and the moving point resistance should be 0, and the resistance value of the normally open contact and the moving point shall be infinitely large. From this, you can distinguish between the normally closed contact and the normally open contact.   3. Measure the pull-in voltage and current: using an adjustable voltage stabilizing power supply and ammeter, input a set of voltages to the relay, and connect the ammeter in the power supply circuit to monitor. Slowly raise the power supply voltage and note down the pull-in voltage and current when the relay absorbs sound. To be accurate, you can try a few more times and get the average value. Measurement of release voltage and discharge current: it is also like the above-mentioned connection test, when the relay suction, then gradually reduce the power supply voltage, when heard the relay again release sound, note the voltage and current at this time, in addition, you can also try more than a few times to get an average release voltage and current. Generally, the release voltage of the relay is about 10% of the pull-in voltage, and it will not work properly if the release voltage is too small (less than 1/ 10 of the pull-in voltage), which will affect the stability of the circuit and the device operation.   1. Understand the necessary conditions firstly.   1) The power supply voltage of the control circuit can provide the maximum current.  2) Voltage and current in the controlled circuit. 3) The requiring contacts on the controlled circuit. When the relay is selected, the power supply voltage of the general control circuit can be used as the basic factor for selection. The control circuit should provide sufficient working currently for the relay, otherwise, the relay absorption is unstable.   2. After consulting the relevant information to determine the applying conditions, you can find out the type and specification number of the relays required. If you already have a relay on hand, you can check whether it can be used against the data. Finally, consider whether the size is appropriate.   3. Pay attention to the volume of the apparatus. For general electrical appliances, consider the volume of the chassis and the layout of the circuit board installation. For small electrical appliances, such as toys, remote control devices should select ultra-small relay products.     The main test items are briefly described as follows:    (1) Operating value: The voltage required for relay action.    (2) Contact resistance: When electric contact closes, the resistance value between two contacts.   (3) Mechanical life: In the case of the mechanical part without damage, the relay switching times.   (4) Contact voltage: When the electric shock is closed, a certain load current is applied in the electric shock circuit, at this time, the voltage value between the contacts.    (5) Electric life: When the rated voltage is applied on both ends of the relay drive coil and the rated resistive load is applied in the contact circuit, the reliable operation times of the relay under the condition of duty cycle 1:4 less than 300 cycles per hour.    (6) Overload capacity: When the rated voltage is applied on both ends of the relay drive coil and 1.5 times rated load is applied in the contact circuit, the reliable operation times of the relay under the condition of (10 ±1) times/ minute (operation frequency). V. Influencing Factors of Relay Reliability   1.The influence of environment on relay reliability: the average fault interval time of relay working in GB and SF is the highest, reaching 820000h, while in the NU environment, it is only 60000h.   2.The effect of quality grade on relay reliability: the average failure interval of the A1 relay is 3660000h, while that of the C class relay is 110000, the difference between them is 33 times. It can be seen that the quality level of the relay has a great impact on its reliable performance.   3.The effect of the contact form on the reliability of relay: the contact form of the relay will also affect its reliability. The reliability of the single-throw relay is higher than that of the double-throw relay with the same number of tools, and the reliability decreases gradually with the increase of tool number, in addition, the reliability of a single-throw relay is higher than that of the double-throw relay with the same number of cutters. The average failure interval of a single-pole, single-throw relay is 5.5 times that of a four-pole double-throw relay.   4.The influence of structures on relay reliability: there are 24 types of relay structures, and all of them have an influence on the reliability of the relay.   5.Effect of temperature on the reliability of relay: the operating temperature range of the relay is between -25℃ and 70℃. With the increase of temperature, the average time between failures of the relay gradually decreases.   6.The effect of operating rate on relay reliability: with the increase of relay operating rate, the average fault interval time decreases exponentially. Therefore, if the designed circuit requires the relay to operate at a very high speed, it is necessary to carefully detect the relay in order to replace it in time for circuit maintenance.   7.The effect of the current ratio on the reliability of the relay: the so-called current ratio is the ratio of the operating load current of the relay to the rated load current. The current ratio has a great influence on the reliability of the relay, especially when the current ratio is greater than 0.1, the average fault interval time is rapidly reduced, and the current ratio is less than 0.1, the average fault interval time is basically unchanged, therefore, the load with a larger current rating is selected to reduce the current ratio when the circuit is designed because this ensures that the relay and even the entire circuit are not reduced in reliability due to the fluctuation of the operating current. VI. Maintenance of Common Faults of Relay   a. Maintenance of the sensing mechanism For electromagnetic (voltage, current, intermediate) relay, its sensing mechanism is the electromagnetic system. The fault of the electromagnetic system is mainly focused on the coil and the moving and static iron core.   1) coil fault Coil faults are usually caused by coil insulation damage; mechanical injuries form a turn-to-turn short circuit or grounding. Because the power supply voltage is too low, and dynamic, static core contact does not connect tightly, resulting in the current through the coil is too large, the coil heated to burn. The coil should be rewound during the repair. If the armature is not sucked after the coil is electrified, it may be that the wire connection of the coil is removed, so that the coil is short-circuited, therefore, the joint should be re-welded.   2) iron core fault The main fault of the iron core is that the armature can not be absorbed after the power on, which may be caused by the broken coil, having impurities between the moving and static iron core, and the low voltage of the power supply, thus repair should be differentiated. After the power on, the armature noise is big, this may be due to moving or static core contact surface is not smooth, or there is oil on the surface. During repair, the coil should be removed, filing or flattening the contact surface, and oil should be cleaned. Noise may be due to short-circuit or ring fracture, replacing new short-circuit ring to repair. After power loss, if the armature cannot be released immediately, possibly because the moving armature is stuck, the air gap of the iron core is too small, and the spring strain and the contact surface of the iron core have been polluted by oil. Taking maintenance should be differentiated according to the cause of the fault, or adjust the size of the air gap, or replace the springs, or use gasoline cleaning oil.   For the thermal relay, the sensing mechanism is the thermal component, and the common fault is that the thermal component burns out, or operation failures of the thermal element and does not operate.   (1) Thermal component burnout. This may be due to a short circuit on the load side or the high frequency of action of the thermal element. The thermal components should be replaced during maintenance and the setting value should be adjusted again. (2) Operation failure of thermal component. This may be due to the setting value is too small, the operation without overload, or the strong impact and vibration influence, make its action mechanism loosening and tripping. (3) No operation of thermal component. This may be due to the setting value is too small to lose the thermal element overload protection function. During maintenance, the setting current should be adjusted according to the overload working current.   b. Inspection and repair of executing parts Most relay actuators are contact systems. Through its "power on" and "power off" to complete a certain control function. Contact system faults generally caused by contact overheating, wear, melting soldering, and so on. The main reasons for contact overheating are insufficient capacity, insufficient contact pressure, surface oxidation or uncleanliness, etc. The main cause of wear is that the contact capacity is too small, the arc temperature is too high to cause contact metal oxidation, and so on. The main cause of contact melting soldering is that the arc temperature is too high, or the contact is seriously moved, and so on.   The order of maintenance of the contacts is as follows:   1) Open the outer cover and check the contact surface. 2) If the contact surface is oxidized, it is not necessary for the silver contact to be processed, and the oxide layer on the surface of the Cu contact may be lightly scraped with a file or a knife with a knife. 3) If the contact surface is not clean, clean it with gasoline or carbon tetrachloride. 4) If there is a burning trace on the surface of the contact, it is not necessary to repair the silver contact, and the copper contact should be repaired by a file or with a knife. Sand cloth or sandpaper is not allowed to be used for refurbishment, to avoid poor contact due to the residual stand. 5) Contact should be replaced if it welded. If the contact capacity is too small, replace the relay with a larger capacity. 6) If the contact pressure is insufficient, adjust the spring or replace the spring to increase the pressure, if the pressure is insufficient, the contact should be replaced.   c. Maintenance of intermediate part   1) In that air-type time relay, the intermediate part is mainly an airbag. The common faults are time delays. This may be because the airbag is not tight or air-leak, the action delay is shortened, and even the delay is not delayed; it is also possible that the air passage of the airbag is blocked so that the action delay is prolonged. In terms of repair, the former shall reassemble or replace the new airbag, and the latter should open the air chamber and remove the blockage. 2) For the speed relay, its rubberwood pendulum belongs to the intermediate part. If the motor can not stop braking during reverse braking, it is possible that the tilting rod of rubberwood is broken, and it should be replaced when overhauled.     VII. Example Explanation: Delay Relays RF Cafe has said "Relays are a topic that never goes out of date even with the advent of fully solid state relays that use semiconductors in the conduction path,there are still many applications that only mechanical contacts can satisfy." in April 1967 electornics world. It is true that there are switching diode arrays that can handle very high powers,but they are typically expensive compare with relays. Today, let's talk about something about time-delay relays.     What is time delay relays? Time delay relays are simply control relays with a time delay built in. Their purpose is to control an event based on time. The difference between relays and time delay relays is when the output contacts open & close: on a control relay, it happens when voltage is applied and removed from the coil; on time delay relays, the contacts can open or close before or after some time delay. Time delay relays have an important influence in industrial contor logic circuits. There are some examples following:   Flashing light control (time on, time off): two time-delay relays are used in conjunction with one another to provide a constant-frequency on/off pulsing of contacts for sending intermittent power to a lamp. Motor soft-start delay control: Instead of starting large electric motors by switching full power from a dead stop condition, reduced voltage can be switched for a “softer” start and less inrush current. After a prescribed time delay (provided by a time-delay relay), full power is applied. Furnace safety purge control: Before a combustion-type furnace can be safely lit, the air fan must be run for a specified amount of time to “purge” the furnace chamber of any potentially flammable or explosive vapors. A time-delay relay provides the furnace control logic with this necessary time element.   How does time delay relay work? Time delay relays can provide simple, reliable, and economical control. Adjusting the delay time is often as simple as turning a knob. Providing time-delayed switching to start a motor, control a load, or affect a process, TDRs are typically used in industrial applications and OEM equipment. Additionally, they play an important role for targeted logic needs, such as in a small panel or in sub-panels. They have a variety of features and operating characteristics, such as compactness, economy, simplicity, and ease-of-use.Time delay relays not only can be available as plug-in devices but aslo as single-function,single-time-range devices traditionally.   All in all, with an on-delay timer, timing begins when voltage is applied. When the time has expired, the contacts close — and remain closed until voltage is removed from the coil.   Time delay relays circuit and working     See the above circuit diagram, time delay relay circuit contains an electromechanical relay and driver circuit, this circuit decides the time delay to give power supply to the electromechanical relay coil by the way to the load connected to the relay.   This circuit is divided into two sections. The first section is time delay elements such as voltage divider resistor series and two electrolytic capacitors. The second section is a relay with an indicator LED. Resistor R1, potentiometer, and R2 connected in series and across to the DC input supply, the output of the variable resistor (potentiometer) is connected to the C1 capacitor and reverse-biased Zener diode then C2 capacitor finally to the base of transistor SL100. 12V Relay is connected with the collector terminal of SL100 transistor and Bicolor LED terminal green is connected with the emitter of Q1 and terminal Red is connected across collector.   When the supply given to this circuit depends on the value of the Potentiometer small level voltage passed to C1 and it gets charged when its completed and above the cutoff limit of the Zener diode, Voltage passed to the C2 capacitor and it gets charge, finally the base-emitter voltage limit of Q1 transistor reached by the C2 then Q1 gets turn ON and Relay coil gets complete DC supply then Relay energized for to complete the above process it takes some time delay depends on Potentiometer value, C1-C2 charge time and Zener diode breakdown voltage hence we can achieve few seconds to few minutes time delay.   By changing the Potentiometer value or C1-C2 value we can achieve different time delay levels. We can use this circuit to turn ON or turn OFF some sensitive time delay required electrical applications.     How to select a delay relay? Selecting a relay, there are many factors that need to consider including data on thermal,motor-driven, pneumatic, RC, slugged, hydraulic, escapement, and solid-state types.   The fantastic growth of the field of automatic industrial control has increased the demand for new and more versatile devices to perform the basic electrical switching functions required. The use of time-delay relays has grown rapidly to keep pace with the demand for the basic function which they can perform: that of obtaining a predetermined delay from one switch operation to another.     (A) Delay on energization. (B) Delay on de-energization. Time-delay relays perform in a manner quite similar to a standard relay in that they have contacts that open and close when power is applied and removed from the input terminals. The basic difference is that a delay is incorporated into the contact opening or dosing. Time-delay relays are used in a wide range of applications: from determining how full your coffee cup will be when you put a dime in a vending machine, to shutting off the cutting oil on a milling machine. The most popular time-delay relay is the delay on operation, or de-energization, in which the normally open load switching contacts transfer at a predetermined time after power is applied to the input. The contacts drop out immediately upon the removal of the input power   Often a time delay on release, or de-energization, is required. In this case, the normally open load switching contacts operate immediately when the input power is applied and remain in this position as long as the input power remains "on". Upon removal of this power the timing begins, and after a predetermined delay, the contacts drop out. Several variations on these two basic timing modes are used, such as interval "on", automatic recycle, combined "on" and "off" timers, and sequence timers. Many of these can be made by simple connections of the two basic types.   FAQ   1. What is Relay and its uses? Relays are switches that open and close circuits electromechanically or electronically. Relays control one electrical circuit by opening and closing contacts in another circuit. ... In addition, relays are also widely used to switch starting coils, heating elements, pilot lights and audible alarms.   2. What is the relay device? Relay is an asynchronous, screen-free walkie talkie system that allows parents to stay in touch with their kids at the push of a button. Relay is a Republic Wireless product, and makes use of the carrier's cell phone network (via T-Mobile and Sprint).    3. What is Relay and its types? Relays are electrically operated switches. They are used to control a circuit by a separate low-power signal or to control several circuits with one signal. ... The three main types of relays are electromechanical, solid-state, and reed. This overload protection relay reacts to overheating.   4. What is the working principle of relay? Relay works on the principle of electromagnetic induction. When the electromagnet is applied with some current it induces a magnetic field around it. Above image shows working of the relay . A switch is used to apply DC current to the load.   5. Does relay important? Converting a small electrical input into a high-current output is no easy feat, but this task is necessary to efficiently operate a wide range of standard appliances and vehicles. Many circuits achieve these conversions through the use of relays, which are indispensable in all kinds of electronic equipment.   6. What are the 5 applications of relay? Applications of Relays in Electronic Circuits: Relay Drive by Means of a Transistor. Relay Drive by Means of SCR. Relay Drive from External Contacts. LED Series and Parallel Connections. Electronic Circuit Drive by Means of a Relay. Power Source Circuit. PC Board Design Considerations. 7. What is difference between relay and circuit breaker? The Relay is a switching and sensing device, but the Circuit breaker is an isolating or disconnecting device. Relays operate on low power input voltage. ... The Relay is used to control or select one among many circuits, whereas Circuit Breaker is one per circuit. Relay acts an electrical amplifier for discrete signal.   8. How fast can a relay switch? 5 to 15 ms. While the mechanical construction of electromechanical relays allows for much flexibility in switching capability, they have one important limitation: speed. When compared to other relays, electromechanical relays are relatively slow devices -- typical models can switch and settle in 5 to 15 ms.   9. Why do I need a relay for LED lights? Relays can be used to switch a low-current trigger to high current, switch a circuit on or off, reverse polarity, and much more. When adding LED lights, such as off-road light bars, driving/work lights, or other auxiliary lights to a vehicle, you must add a circuit to power the light adequately.   10. What is the major application of relays in our daily lives? The typical applications of electromechanical relays include motor control, automotive applications such as an electrical fuel pump, industrial applications where control of high voltages and currents is intended, controlling large power loads, and so on.   You May Also Like: Making a Arduino Variable Timer Relay How to Drive Thermostat by Using Solid State Relay Product Recommendation: CMRD6055 CB-1001B-70 G6K-2F-Y-TR DC24

IntroductionFor people who have been in touch with digital circuits or analog circuits, the 555 IC is definitely classic work. With its low cost and reliable performance, it is widely used in various electrical appliances, including instruments and meters, household appliances, electric toys, and automatic control. The 555 timer only needs a few external resistors and capacitors to realize pulse generation and conversion circuits, such as multiple oscillators, monostable triggers and schmitt triggers. So how does it work in the circuit? What the role of its circuit? Here gives several typical 555 circuit examples for specific analysis.555 Timers Circuit LearningCatalogIntroductionⅠ Basic 555 Timer Circuit AnalysisⅡ 555 Multivibrator Circuit AnalysisⅢ 555 Timer Monostable Flip Flop Circuit AnalysisⅣ Classic 555 Timer Circuits DiagramsⅤ 555 Timer IC ModesⅠ Basic 555 Timer Circuit Analysis555 Means What?555 timer is a convenient and powerful IC, which is widely used in signal generation, conversion, control and detection. The origin of this name, because it is divided by three 5KΩ resistors. The 555 timer is a simple integrated circuit that can be used to make many different electronic circuits. With the following circuits analysis you will know how 555 IC works.Figure 1. Basic 555 Timer Circuit✔️ Circuit AnalysisR is not the reset terminal, when set to 0, Q is 0,  is 1, Uo outputs 0, and is 1 added to the base of the transistor T, the transistor is in the conducting state.① When R=0, Q=1, uo=0, T is saturated and turned on.② When R=1 (there is no reset function at this time):UTH>2VCC/3, UTR>VCC/3, C1=0, C2=1, Q=1 or =0, uo=0, T is saturated and turned on. (Analysis: C1's positive input terminal is 2VCC/3, C1's negative input UTH terminal is greater than the positive input terminal, working in saturation, and output 0. C2's negative input terminal is 1VCC/3, which is smaller than the positive input Terminal UTH, and outputs 1. There is a horizontal line above RD and SD, which means low level, meaning is Reset. C1 outputs 0, RD is valid, then Q is 0, not 1, Uo outputs 0, and is not acting on the base of the triode.)③ When R=1, UTH<2VCC/3, UTR>VCC/3, C1=1, C2=1, Q and remain unchanged, uo and T remain unchanged. (Analysis is the same as above)④ When R=1, UTH＜2VCC/3, UTR＜VCC/3, C1=1, C2=0, Q=0, =1, uo=1, T is cut off. (Analysis is the same as above) Learn how the inputs interact with the supply voltage to trigger and reset the output high and low. Find out which pins can be used to adjust the threshold at which that change happens.Ⅱ 555 Multivibrator Circuit AnalysisFigure 2. 555 Multivibrator Circuit Analysis Figure 3. 555 Multivibrator Circuit Example✔️ Circuit Analysis First, the power supply VCC charges the capacitor C through R1 and R2, and the voltage of the capacitor must be relatively small, less than 1VCC/3. Similarly, the positive terminal of C1 is 2VCC/3, the negative terminal of C2 is 1VCC/3, and the TH and TR terminals are connected At the same time, it is less than 1VCC/3 at the beginning. At this time, C1 outputs 1, C2 outputs 0, and the set terminal is valid (with detailed confirmation): Q is 1, is not 0, and uo is 1, the transistor is cut off, and outputs high level. At this time, the power supply is still charging the capacitor. When the TH and TR terminals are connected together, the voltage is less than 2VCC/3 and greater than 1VCC/3; C1 outputs 1, C2 outputs 1, the transistor is cut off, and uo is 1. When the capacitor is greater than 2VCC/3, C1 outputs 0 and C2 outputs 1. At this time, Q is 0, is not 1, uo is 0, the output is low, and the transistor is turned on. The capacitor will be discharged through pin 7. After this, the voltage at the point where TH and TR connected will gradually decrease, less than 2VCC/3 and greater than 1VCC/3, and then it will be less than 1VCC/3, to form a harmonic oscillator.The pulse width tp1 of the first transient state, that is, the time required for uc to rise from VCC/3 charging to 2VCC/3 (charged through two resistors):The second transient state pulse width tp2, that is, the time required for uc to discharge from 2VCC/3 to VCC/3:Duty cycle: the time that the high level occupies the entire cycle., it can be seen that its duty cycle is always greater than 50%.Examples 1Circuit with Adjustable Duty Cycle (add an adjustable resistor)Figure 4. Circuit with Adjustable Duty Cycle (add an adjustable resistor)It can be calculated:Where T1=0.7R1C (T1 is charging time), T2=0.7R2C (T2 is discharging time)Total time T=T1+T2=0.7(R1+R2)CSo R1, R2, and C are determined, and the period T is also determined.Duty Cycle Calculation Example 2Circuit with Adjustable Duty Cycle (1KHz)Figure 5. Circuit with Adjustable Duty Cycle (1KHz)✔️ Circuit AnalysisT = 0.7(R1+R2)C, f = 1/T, the duty cycle circuit only needs to adjust the resistance value. Ⅲ 555 Timer Monostable Flip Flop Circuit AnalysisWorking Characteristics① It has two different working states: steady state and transient state.② Under the action of an external trigger pulse, it can switch from the steady state to the transient state. After the transient state is maintained for a period of time, the circuit can automatically return to the steady state.③ The transient state cannot be maintained for a long time, and the duration of its sustaining time depends on the parameters of the circuit itself and has nothing to do with the trigger pulse. So what is the principle of a monostable circuit?Figure 6. 555 Timer Monostable Circuit Analysis Figure 7. 555 Timer Monostable Circuit Example✔️ Circuit AnalysisFirst, the TR terminal is at a high level ui, which must be greater than 1VCC/3. At this time, C2 outputs 1, and the power supply charges capacitor C through R. The charging voltage is less than 1VCC/3 (TH), CO voltage is equal to 2VCC/3, C1 outputs 1, and it is in the holding state at this time. Assuming that the non-reset terminal of R is reset before power on, the output of uo is 0, and then the previous state is still maintained and the output is 0 at this time. is 1, the transistor is turned on, the capacitor is discharged through pin 7, and uc is zero level. At a certain moment, ui is low, C1 still outputs 1, C2 outputs 0, Q is 1, is 0, uo outputs 1 (high level), and the transistor has been in the cut-off state. At this time, VCC can charge the capacitor (uc is getting larger). When uc is between 1VCC/3~2VCC/3, assuming that the TR terminal returns to the original state (high level), C1 outputs 1 , C2 outputs 1, at this time uo keeps in original state, it is still 1, and the transistor is in the cut-off state. When uc is greater than 2VCC/3, C2 is still 1, C1 output is 0, Q is 0, is 1, and uo is 0, the transistor is turned on and in a discharging state, at this time, uc is getting smaller and smaller.Summery:1. As long as a low-level trigger signal is given, the temporary stable stay time is the charging time of voltage 0V~ 2Ucc/3 (the time represented by tp).2. Charging time Tp=1.1RC3. It can be used as a timing circuit, and the time can be determined by RC.Example: Timing Circuit Design (1s delay time)Figure 8. 555 Timer Delay Circuit ExampleⅣ Classic 555 Timer Circuits DiagramsThere are A LOT of projects out there using the 555 in various ways and it’s easy to find schematics to make a project that has already been proven. Here lists some typical projects using 555 timer in circuits. Let’s have a look. 🔺 Car Tachometer🔺 SIREN🔺 Flashing Lights🔺 Knight Rider Circuit🔺 Laser Ray🔺 Latch🔺 LED Dimmer🔺 555 Amplifier🔺 Light Detector🔺 Machine Gun🔺 Metal Detector🔺 Motor PWM🔺 Music Box🔺 Zener Diode Tester Ⅴ 555 Timer IC Modes555 timer will use different models in different circuits to meet circuit requirements. Therefore, it has many derivative models produced by different companies with different pin functions, and uses CMOS design. What;s more, some chips include several integrated 555 timers. Some common models of the 555 chip family are as follows:ManufacturerModelRemarksCustom Silicon SolutionsCSS555/CSS555CCMOS chip, minimum working voltage 1.2V, IDD < 5µACEMIULY7855*ECG SemiconductorsECG955MTimer Single Rc-type OscillatorExarXR-555Highly stable controllerFairchildNE555/KA555Time-delay or mono-stableHarrisHA555*IK SemiconILC555CMOS chip, minimum working voltage 2VTexas InstrumentsSE555/NE555*RenesasICM7555CMOS RC timersLithic SystemsLC555Available in Industry's Smallest 8-Bump DSBGAMaximICM7555CMOS RC timers, minimum working voltage 2VMotorolaMC1455/MC1555Monolithic timerNational SemiconductorLM1455/LM555/LM555C*National SemiconductorLMC555CMOS chip, minimum working voltage 1.5VNTE SylvaniaNTE955MAccurate time delaysRaytheonRM555/RC555*RCACA555/CA555C*STMicroelectronicsNE555N/ K3T647*Texas InstrumentsSN52555/SN72555*Texas InstrumentsTLC555CMOS chip, minimum working voltage 2VZetexZSCT1555Precision single cell timerNXPICM7555CMOSHitachi SemiconductorHA17555Accurate time delays or oscillations Frequently Asked Questions about 555 Timer Circuit1. What does a 555 timer do in a circuit?The 555 timer IC is a very cheap, popular and useful precision timing device which can act as either a simple timer to generate single pulses or long time delays, or as a relaxation oscillator producing a string of stabilised waveforms of varying duty cycles from 50 to 100%. 2. How much voltage can a 555 timer take?The standard TTL 555 can operate from a supply voltage between 4.5 volts and 18 volts, with its output voltage approximately 2 volts lower than its supply voltage VCC. The 555 can source or sink a maximum output current of 200mA, (but it may get hot at this level), so the circuit variations are unlimited. 3. What are the modes of operation of a timer?The timer registers can be used in two modes. These modes areTimer mode and the Counter mode. The only difference between these two modes is the source for incrementing the timer registers. 4. What are the basic operation modes of the 555 timer?The operating modes of a 555 timer are astable, bistable and monostable. Each mode of operation signifies with a circuit diagram and its output. 5. What is the maximum frequency of a 555 timer?2MHzaccording to the website, the 555 timer has a maximum frequency of 2MHz.