The Kynix Blog

IntroductionThe hard disk interface is the connecting part between the hard disk and the host computer system, and its function is to transmit data between the hard disk cache and the host memory. Different hard disk interfaces determine the data transmission speed between the hard disk and the computer. In the entire system, the quality of the hard disk interface directly affects the speed of the program and the performance of the system. From this article, you can understand the connector concepts of IDE, SATA, SCSI, Fibre Channel (FC) and SAS and their development process, and finally two important interface protocols: AHCI and NVMe.SAS, SATA, SCSI, FC, and IDE ExplainedCatalogIntroductionⅠ Bus Interface TypesⅡ What is IDE?2.1 Integrated Drive Electronics Definition2.2 IDE Mode2.3 IDE Advantages and DisadvantagesⅢ What is SCSI?3.1 SCSI Basics3.2 SCSI VersionⅣ What is Fiber Channel (FC)?4.1 Overview of Fibre Channel4.2 Fibre Channel ProtocolⅤ What is SATA?5.1 Serial ATA Definition5.2 SATA Interface5.3 IDE vs SATA InterfaceⅥ What is M.2?Ⅶ What is SAS?Ⅷ Tech Guide: AHCI and NVMe Protocol8.1 AHCI Protocol8.2 NVMe Protocol8.3 Tech NoteⅠ Bus Interface TypesFrom an overall point of view, hard disk interfaces are divided into five types: parallel ATA (PATA, also called IDE or EIDE), SATA, SCSI, Fibre Channel, and SAS. IDE is mostly used in household products. And some of it are used in website servers. SCSI is mainly used in the server market. While Fibre Channel is only used in high-end servers and is expensive. SATA is now the mainstream hard disk. Most notebook computers and desktop computers use it, and solid state hard drives also use it. SAS is generally used in servers. It has fast transmission speed and strong reliability. Under the broad categories of IDE and SCSI, there has a variety of specific interface types that can be divided according to different technical specification and transmission speed. Ⅱ What is IDE?2.1 Integrated Drive Electronics DefinitionThe full name of IDE is "Integrated Drive Electronics", and its original meaning refers to the hard disk drive that integrates the "hard disk controller" and the "disk body". This approach reduces the number and length of cables for the hard disk interface, enhances the reliability of data transmission, and makes hard disk manufacturing easier. Many hard disks used to have IDE interfaces, but now almost all hard disk interfaces are standard with SATA.IDE represents a type of hard disk interfaces, but in actual applications, people are also used to call it the first IDE-type hard disk ATA-1. This type of interface has been eliminated with the development of technology. With the time passes, more types of hard disk interfaces are developed, such as ATA, Ultra ATA, DMA, Ultra DMA and other interfaces are all IDE hard disk interfaces.2.2 IDE ModeThere are three transmission modes for IDE: PIO (Programmed I/O), DMA (Driect Memory Access), and Ultra DMA (UDMA).The biggest drawback of PIO mode is that it consumes a lot of CPU resources. The IDE interface running in PIO mode has a data transfer rate ranging from 3.3MB/s (PIO mode 0) to 16.6MB/s (PIO mode 4). There are two types of DMA modes: Single-Word DMA and Multi-Word DMA. The highest transfer rate of Single-Word DMA mode is 8.33MB/s, and Multi-Word DMA (Double Word) can reach 16.66MB/s. The biggest difference between the DMA and the PIO is that the DMA mode does not rely too much on CPU instructions to run, which can save the processor's operating code.Due to the emergence and rapid popularity of the UDMA mode, PIO and DMA are immediately replaced by UDMA. UDMA is a standard protocol under the Ultra ATA system, which is based on the 16-bit Multi-Word DMA mode. One of the advantages of UDMA is that in addition to the advantages of DMA mode, it also applies CRC (Cyclic Redundancy Check) technology to enhance the performance of error detection and debugging during data transmission. Since the introduction of the Ultra ATA standard, its interface has applied DDR (Double Data Rate) technology to double the transmission speed, with a transmission speed of up to 100MB/s. 2.3 IDE Advantages and DisadvantagesAdvantages: Compatible and cost-effective.Disadvantages: slow data transmission speed, short cable length, fewer connected devices, no support for hot swap, poor upgrading ability of interface speed. Ⅲ What is SCSI?3.1 SCSI BasicsThe full name of SCSI is "Small Computer System Interface", which is a completely different interface from IDE. SCSI is not specifically designed for hard disks, but a high-speed data transmission technology widely used in minicomputers. It has the advantages of wide application range, multitask, large bandwidth, low CPU occupancy rate, and hot swap. So SCSI is mainly used in medium and high-end servers and high-end workstations. But the higher price makes it difficult to popularize like IDE. SCSI also has some potential problems. It has limited system BIOS support, and it has to be set for each computer. There's also no common SCSI software interface.Figure 1. SCSI Interface3.2 SCSI VersionSCSI VersionDescriptionsSCSI-1developed in 1986(obsolete)Introduced in 1979, supported synchronous and asynchronous SCSI peripherals.SCSI-2adopted in 1994Introduced in 1992, also known as fast SCSI, supported any SCSI device.SCSI-3debuted in 1995It is the standard currently in use. Ⅳ What is Fiber Channel (FC)?4.1 Overview of Fibre ChannelFibre Channel is the same as SCSI. It is not originally an interface technology developed for hard disk design and development, but specifically designed for network systems. However, as storage systems develop, they are gradually applied to hard disk systems. Fibre Channel is developed to improve the speed and flexibility of multi-disk storage systems. And it greatly improves the communication speed of multi-disk systems. The main characteristics of Fibre Channel are: hot swap, high-speed bandwidth, remote connection, large number of connected devices, etc. It can meet the high data transmission rate requirements of high-end workstations, servers, mass storage sub-networks, and peripherals for bidirectional and serial data communication through hubs, switches and point-to-point connection.4.2 Fibre Channel ProtocolFiber Channel ProtocolDescriptionsFC-0Physical layer, customizes different media, set transmission distance and signal mechanism standards, defines optical fiber, copper interfaces, and cable indicatorsFC-1Encode/DecodeFC-2Framing protocol /flow controlFC-3common services such as data encryption and compressionFC-4Protocol mapping layer, which defines the interface between fibre channel and upper-layer protocol. Upper-layer applications such as SCSI protocol, HBA FC-4 interface functions. FC-4 supports multiple protocols, such as FCP-SCSI, FC-IP, and FC-VI. Ⅴ What is SATA?5.1 Serial ATA DefinitionSATA stands for "Serial Advanced Technology Attachment" or "Serial ATA". It is an interface used to connect ATA hard drives to a computer's motherboard. SATA adopts serial connection mode. Serial ATA bus uses embedded clock signal, which has stronger error correction ability. Compared with the past, its biggest difference is that it can check transmission instructions (not just data). Errors are automatically corrected, which greatly improves the reliability of data transmission.Now the general interface is SATA interfaces. The reason why it can replace IDE is because the performance of the SATA is much better than that of the IDE. SATA speed is also much higher than IDE, and it also supports hot swap/hot-plugging.5.2 SATA InterfaceMost of the computers we use are also SATA interfaces. The current SATA interface has three versions 1.0, 2.0, and 3.0. The larger the version number, the later it appears, the better the performance, which mainly due to the faster data transfer rate. SATA 3.0 is the most common interface used today, though there have been four revisions since its introduction, namely 3.1 through 3.4. The SATA interface version is backward compatible, and the higher version is compatible with the lower. Some SATA hard disks provide jumpers. Due to the jumper settings are different, the version number of the SATA interface of the same hard disk is different. In addition, the actual transfer rate of the interface requires the support of the SATA motherboard.SSD has better performance, smaller size, and higher interface requirements. High-performance SSDs have basically switched to M.2, U.2 and PCIe, but SATA interfaces will not be eliminated in a short time. It is still in mainstream market, especially the HDD market. The SATA 3.3 specification upgraded by SATA-IO also brings some new features, optimizing the support of SMR, and can be powered off remotely. SMR shingled magnetic recording technology can increase the storage density of HDD by 25%.The SATA interface entered the 6Gbps era from the 3.0 standard in 2009. In 2011, SATA 3.1 was updated, SATA 3.2 was updated in 2013, and then SATA 3.3 was updated in 2016. These subversion upgraded have not brought many new functions. After all, the bottleneck of HDDs is not the speed, and it is difficult to make big improvements from the interface. 5.3 IDE vs SATA InterfaceSATA hard disk has a new design structure, fast data transmission, save space, and many other advantages over IDE hard disk:1) SATA hard disk has a higher transmission speed than IDE hard disk. SATA can provide a peak transfer rate of 150MB/s. It will reach 300 MB/s and 600 MB/s with the development. At that time, we will get a transfer rate nearly 10 times faster than IDE hard drives.2) Compared with the PATA40-pin data cable of IDE hard disks, the SATA cable is small and thin. And the transmission distance is long, which can be extended to 1 meter, making it easier to install equipment and wiring in the machine. Because the size of the connector is small, this kind of cable effectively improves the air flow inside the computer and also speedsthe heat dissipation in the case.3) Thepower consumption has been reduced. SATA hard drives can work with 500 mA of current.4) SATA can be backward compatible with PATA devices by using multi-purpose chipsets or serial-parallel converters. Since SATA and PATA can use the same drive, there is no need to upgrade or change the operating system.5) SATA does not need to set the master and slave disk jumpers. The BIOS will number it in the order of 1, 2, 3. Whilethe IDE hard disk needs to set the master and slave disks through jumpers.6) SATA also supports hot plugging and can be used like a U disk. IDE hard disks do not support hot swap. Ⅵ What is M.2?The M.2 interface is a new interface specification. It is a new standard tailored for Ultrabooks to replace the original mSATA interface. Whether it is a smaller size or higher transmission performance, M.2 is far better than mSATA.M.2 interfaces are generally divided into two types. When buying M.2 SSDs, you need to pay attention to internal agreements. One is to use the traditional SATA AHCI protocol, which has no difference in performance with ordinary SATA solid hard drives; another is to use the brand-new NVMe protocol, which can provide SSD performance up to 3000MB/s or more. Ⅶ What is SAS?SAS (Serial Attached SCSI) is a new generation of SCS technology, which is the same as the current popular SATA technology. It uses serial technology to obtain higher transmission speed and improves internal space by shortening the cable. SAS is a new interface developed after the parallel SCSI. This interface is designed to improve the performance, availability, and expandability of the storage system, and to provide compatibility with the SATA.SAS technology can be backward compatible with SATA. Specifically, the compatibility of the two is mainly reflected in the compatibility of the physical part and the protocol. At the physical layer, the SAS interface and the SATA interface are fully compatible, and the SATA hard disk can be directly used in the SAS environment. In terms of interface standards, SATA is a sub-standard of SAS, so the SAS controller can directly control SATA hard drives, but SAS cannot be directly used in the SATA environment. Because the SATA controller cannot control the SAS hard disk. As for the protocol, SAS is composed of three types of protocols, which use corresponding protocols for data transmission according to different devices. Among them, the serial SCSI protocol (SSP) is used to transmit SCSI commands, the SCSI management protocol (SMP) is used to maintain and manage connected devices, and the SATA channel protocol (STP) is used to transfer data between SAS and SATA. Therefore, under the cooperation of three protocols, SAS can seamlessly work with SATA and some SCSI devices.The backplane of the SAS system can be connected to dual-port, high-performance SAS drives and high-capacity, low-cost SATA drives. So SAS drives and SATA drives can exist in a storage system at the same time. But it should be noted that the SATA system is not compatible with SAS, so SAS drives cannot be connected to the SATA backplane. Due to the compatibility of the SAS system, users can use hard drives with different interfaces to meet the capacity or performance requirements of various applications. So they have more flexibility when expanding the storage system, allowing storage devices to maximize application benefits.In the system, each SAS port can connect up to 16256 external devices, and SAS adopts a point-to-point serial transmission directly with a transmission rate of up to 3Gbps. It is estimated that there will be 6Gbps or even 12Gbps high-speed interfaces in the future. The SAS interface performance has also been greatly improved. It also provides 3.5-inch and 2.5-inch interfaces, so it can meet the requirements of different server environments. SAS relies on SAS expanders to connect more devices. Most expanders have 12 ports.Compare with the traditional parallel SCSI, SAS has a significant increase in interface speed. With the use of serial cables, it not only can achieve a longer connection distance, but also improve the anti-interference ability. In addition, this cable can also significantly improve the heat dissipation inside the chassis. Ⅷ Tech Guide: AHCI and NVMe ProtocolHere we will focus on the AHCI protocol and NVMe protocol of the solid state drive (SSD).There are two mainstream transmission protocols for SSD (Solid State Drive): One is the AHCI protocol, and the other is the NVMe protocol.8.1 AHCI ProtocolAdvanced Host Controller Interface (AHCI), sets the operation of Serial ATA (SATA) host controllers in a non-implementation-specific manner in its motherboard chipsets. That is, AHCI allows storage drivers to connect advanced SATA functions. When we use SATA SSD, we must enable AHCI mode in the motherboard settings. This is because when the AHCI mode is turned on, the number of useless seeks of the SSD can be greatly shortened and the data search time can be reduced. So that the SSD under multi-tasking can exert all the performance and effects. According to related performance tests, after the AHCI mode is turned on, the SSD read and write performance is increased by about 30%. However, with the gradual enhancement of SSD performance, these standards have also become a major bottleneck restricting solid state drives. Because the AHCI standard designed for hard disk drives is not suitable for low-latency solid state drives.8.2 NVMe ProtocolAnother transmission protocol is the NVMe protocol that represents the future performance trend. The so-called NVMe protocol is to make full use of the low latency and parallelism of PCI-E channels, greatly improve the read and write performance of SSDs under controllable storage costs. It reduces the high latency caused by the AHCI, and completely liberates ultimate performance of SATA SSD.NVMe Specification1.0 (March 2011)1.1 (October 2012)1.2 (November 2014)Fabric's NVMe (2014)NVM-MI (November 2015)1.3 (April 2017)1.4 (July 2019)Due to the flash memory particles and the main control, the SSD(solid state drives) price with M.2 NVMe protocol is very high, which is about twice the price of SATA SSD. So buy the corresponding level of solid state hard drive based on the configuration and requirements of the computer. Otherwise it will cause performance waste.In terms of software layer, the delay of NVMe standard is less than half of AHCI. NVMe streamlines the calling method and does not need to read registers when executing commands. Each command of AHCI needs to read registers 4 times, which consumes 8000 CPU times in total loop, causing a delay of about 2.5 ms. NVMe can support receiving commands and prioritizing requests from multi-core processors at the same time.NVMe has automatic power state switching and dynamic power management functions. The device can switch to Power State 1 after being idle for 50ms from Power State 0. If it continues to be idle, it will enter Power State 2 with lower power consumption after 500ms. There will be a short delay when switching. The SSD can be controlled at a very low level when it is idle. In terms of power management, the NVMe SSD will have a greater advantage than the AHCI SSD. This is important for mobile devices, which can significantly increase the power endurance of notebooks. Moreover, NVMe SSD can be easily matched to different platforms and systems, and can work normally without the corresponding driver provided by the manufacturer. At present, Windows, Linux, Solaris, Unix, VMware, UEFI, etc, support the NVMe SSD.PCIe SSDs based on the NVMe protocol far exceed the traditional AHCI-based SATA SSDs in terms of performance and practicability. It can be said to be the future of the development of the SSD industry. But the traditional SATA interface will become the first choice for ordinary machine installations under the background of reduced manufacturing costs.8.3 Tech Note8.3.1 PCI-E BasicPCI-E (peripheral component interconnect express) is a high-speed serial computer expansion bus standard. Its original name is "3GIO". It was proposed by Intel in 2001 to replace the old PCI, PCI-X, and AGP bus standard. It belongs to high-speed serial point-to-point high-bandwidth dual-channel transmission. The connected devices allocate exclusive channel bandwidth and do not share bus bandwidth. It mainly supports active power management, error reporting, end-to-end reliable transmission, hot plugging, quality of service ( QOS), and other functions. PCI-E also has a variety of specifications, from PCI-E x1 to PCI-E x32, which can meet the needs of low-speed devices and high-speed devices in a certain period of time in the future.The PCI-E bus protocol can be directly connected to the CPU with almost no delay, making it an excellent companion to the NVMe standard. In the era of the AHCI standard, the actual performance of PCIe can hardly be exerted due to the agreement limit.Table: PCle VersionVersionYearDescriptionPCIe 1.0a2003The data rate per channel is 250 MB/s, and the transmission rate is 2.5 GT/s.PCIe 1.12005The data rate has not changed and it is fully compatible with PCIe 1.0a.PCIe 2.02007It doubles the transfer rate from PCIe 1.0 to 5 GT/s, and the throughput per channel rises from 250 MB/s to 500 MB/s.PCIe 2.12009Its speed is the same as PCIe 2.0, supporting troubleshooting system.PCIe 3.02010Transmitter and receiver equalization, PLL improvements, clock data recovery, and channels are all improved.PCIe 3.12014Various improvements based on the PCIe 3.0 specifications.PCIe 4.02016Double the bandwidth provided by PCIe 3.0, maintain software support, and have backward compatibility for the used mechanical interfaces.PCI-E SD 7.02018A new generation of SD 7.0 standard specifications 8.3.2 Interface Size IntroductionThe size and application of the hard disk can be divided into:0.85 inches, mostly used in portable devices such as mobile phones.1 inch, mostly used in digital cameras (CF type II interface).1.8 inches, used in some notebook computers and external hard disk enclosures.2.5 inches, commonly used in notebook computers and external hard disk enclosures.3.5 inches, mostly used in desktop computers. External hard drive enclosures with 3.5-inch requires an external power supply. Frequently Asked Questions about Hard Disk Drive Interface1. Which is a hard disk interface?Today's hard drives use SATA or SAS interfaces, which are the serial versions of their PATA and SCSI predecessors. SATA drives are found in every personal computer, and SAS drives, which are enterprise class, are found in servers and high-end workstations. 2. What are the three most common types of hard drive interfaces?There are three different kinds of hard drives: SATA, SSD and NVMe. 3. What is the fastest hard drive interface?PCIe provides a faster interface speed than SATA. An SSD connected via a PCIe 3.0 x16 interface can have a link speed of 16 Gb/s. In contrast the SATA 3.0 standard only provides 6.0 Gb/s. Solid State Drives (SSDs) come in a number of different form factors and are available with different interface connects. 4. What are the types of drive interfaces?Hard disk drives are accessed over one of a number of bus types, including parallel ATA (PATA, also called IDE or EIDE; described before the introduction of SATA as ATA), Serial ATA (SATA), SCSI, Serial Attached SCSI (SAS), and Fibre Channel. 5. What is PATA hard disk?Parallel ATA (Parallel Advanced Technology Attachment or PATA) is a standard for connecting hard drives into computer systems. As its name implies, PATA is based on parallel signaling technology, unlike serial ATA (SATA) devices that use serial signaling technology. 6. Can I connect a SATA hard drive to an IDE motherboard?Yes now you can connect the SATA hard drive to an IDE motherboard very easy. Just visit your near computer hardware shop or amazon to search “SATA bilateral IDE” card. This card will covert the SATA hard desk to IDE. After this your hard desk can be connected IDE motherboard. 7. Why is SCSI still used?It's a fast bus that can connect lots of devices to a computer at the same time, including hard drives, scanners, CD-ROM/RW drives, printers and tape drives. Other technologies, like serial-ATA (SATA), have largely replaced it in new systems, but SCSI is still in use. 8. Can I replace an ATA drive with a SATA drive?Replacing the ATA drive with a SATA drive you will need the SATA drivers for your system unless the bios is set to IDE emulation. Windows won't recognize the drive without the drivers installed or IDE emulation turned on. 9. Is NVMe and M 2 the same?NVMe stands for Non-Volatile Memory Express, and it refers to the way in which data is moved, rather than the shape of the drive itself. ... There are some NVMe drives that are designed to fit into a standard PCIe motherboard slot much like a graphics card, but most NVMe drives use the M. 2 form factor. 10. What is a m2 SATA drive?M. 2 is a form factor for SSDs (solid-state drives) that's shaped like a stick of gum. These SSDs are generally faster but more expensive than traditional, 2.5-inch SSDs. Thin laptops are increasingly using M. 2 SSDs because they take up less room than 2.5-inch SSDs or hard drives.

IntroductionResistors are usually connected in a circuit in various ways, and the two most basic ways are series and parallel. This article will mainly introduce these two connection methods, including their definitions, formulas, circuit diagrams, examples and identification methods. In addition, the article also introduces Ohm's law and Kirchhoff's law, which are very important in understanding the series and parallel connections of resistors.You may need these two calculators in reading this arrticle:① Ohm's Law Calculator② Parallel and Series Resistance CalculatorThe following video explains the basics of resistors in series and parallel, which can promote your understanding of this article. But it does not matter so much if you skip this video since the article explains in detail and is comprehensive.Resistors in series and parallel - deriving the formulaCatalogIntroductionCatalogI Series Connection of ResistorsII Parallel Connection of ResistorsIII Resistor Combination(Mixed Resistor Circuit)IV Ohm's Law  4.1 What is Ohm's Law?  4.2 What is Closed Circuit Ohm's Law?  4.3 The Key Points of Studying Ohm's LawV Kirchhoff's Law  5.1 Concepts  5.2 Kirchhoff's First Law (Nodal Current Law)  5.3 Kirchhoff's Second Law (Law of Loop Voltage)  5.4 Application Note of Kirchhoff's LawVI Series and Parallel Circuit Identification MethodsVII QuizⅧ FAQI Series Connection of Resistors(1) Circuit characteristicsFigure1. Resistors in seriesThe figure shows the series connection of n resistors, and the voltage and current reference directions are related. The circuit characteristics are derived from Kirchhoff’s law:(A) The resistors are connected in sequence. According to KCL, the current flowing through the resistors is the same;(B) According to KVL, the total voltage of the circuit is equal to the sum of the voltages of the series resistors, namely:(2) Equivalent resistanceFigure2. Equivalent resistance circuitSubstituting Ohm's law into the voltage expression, we get:The above formula illustrates that the series circuit of multiple resistors in Figure (a) and the circuit of single resistor in Figure (b) have the same VCR, which is equivalent to each other.The equivalent resistance is:In conclusion:The resistors are connected in series, and the equivalent resistance is equal to the sum of the sub-resistances;The equivalent resistance is greater than any one of the series resistance.The partial pressure of series resistanceIf the total voltage across the series resistor is known, what is the divided voltage on each resistor? From figure (a) and figure (b) we know:MeetIn conclusion:Resistors are connected in series, and the voltage on each sub-resistor is proportional to the resistance value. The higher the resistance value, the higher the voltage. Therefore, the series circuit can be used as a voltage divider circuit.Example 1: Calculate the voltage across the two series resistors as shown in the figure.Figure3. Circuit of Example1Solution: From the partial pressure formula of series resistance:(Note the direction of U2)(3) PowerThe power of each resistor is:SoTotal power:Draw conclusions from the above formulas:When resistors are connected in series, the power consumed by each resistor is proportional to the size of the resistor, that is, the larger the resistance, the larger the power consumed;The power consumed by the equivalent resistance is equal to the sum of the power consumed by each series resistor.II Parallel Connection of Resistors(1) Circuit characteristicsFigure4. Parallel circuit characteristics The figure shows the parallel connection of n resistors, and the voltage and current reference directions are related. The circuit characteristics are derived from Kirchhoff's law:(a) The two ends of each resistor are connected together. According to KVL, the two ends of each resistor are at the same voltage;(b) According to KCL, the total current of the circuit is equal to the sum of the currents flowing through the parallel resistors, namely:(2) Equivalent resistanceFigure5. Equivalent resistance in parallel connectionSubstituting Ohm's law into the current expression, we get:G =1/R is the conductanceThe above formula illustrates that the parallel circuit of multiple resistors in Figure (a) and the circuit of single resistor in Figure (b) have the same VCR, which is equivalent to each other.The equivalent conductance is:Therefore,Namely,The most commonly used formula to find the equivalent resistance when two resistors are connected in parallel:In conclusion:The resistors are connected in parallel, and the equivalent conductance is equal to the sum of the conductances and greater than the partial conductance;The reciprocal of the equivalent resistance is equal to the sum of the reciprocals of the sub-resistances, and the equivalent resistance is less than any parallel sub-resistance.Current distribution of parallel resistanceIf the total current of the parallel resistance circuit is known, find the current on each sub-resistance and call it a shunt. From figure (a) and figure (b) we know:Namely,MeetFor two resistors in parallel, there are:Conclusion: When the resistors are connected in parallel, the current on each sub-resistor is inversely proportional to the resistance value, and the current divided by the larger resistance value is smaller. Therefore, the parallel resistor circuit can be used as a shunt circuit.(3) PowerThe power of each resistor is:SoTotal power:Draw conclusions from the above formulas:When resistors are connected in parallel, the power consumed by each resistor is inversely proportional to the size of the resistor, that is, the larger the resistance, the smaller the power consumed;The power consumed by the equivalent resistor is equal to the sum of the power consumed by each parallel connected resistor.consumed by each series resistor.III Resistor Combination(Mixed Resistor Circuit)A circuit with resistors connected in series and connected in parallel is called a resistor combination or mixed resistor circuit. The part where the resistors are connected in series has the characteristics of a resistor series circuit, and the part where the resistors are connected in parallel has the characteristics of a resistor parallel circuit.Example 2: The circuit is shown in the figure, please calculate the voltage and current of each branch.Figure6. Example circuit 2Solution: This is a resistor series and parallel circuit. First find the equivalent resistance Reg = 11W, and the current and voltage of each branch are:The general steps for solving series and parallel circuits can be obtained from the above examples:⚫ Find the equivalent resistance or equivalent conductance;⚫ Apply Ohm's law to find the total voltage or total current;⚫ Apply Ohm's law or voltage division and shunt formula to find the current and voltage on each resistor.Therefore, the key issue in analyzing series-parallel circuits is to distinguish the relationship between series and parallel circuits.To determine the series-parallel relationship of the circuit, the following 4 points should be mastered:⚫ Look at the structural characteristics of the circuit. If two resistors are connected end-to-end, they are connected in series;⚫ Look at the relationship between voltage and current. If the current flowing through the two resistors is the same current, it is connected in series; if the two electrical groups bear the same voltage, it is connected in parallel.⚫ Equivalent to deformation of the circuit. For example, the left branch can be twisted to the right, the upper branch can be turned down, the curved branch can be straightened, etc.; the short circuit in the circuit can be compressed and extended at will; the multi-point grounding can be connected by a short circuit . Generally, if it is really a problem with a resistor series circuit, it can be distinguished.⚫ Find the equipotential point. For circuits with symmetrical characteristics, if two points can be judged to be equipotential points, according to the concept of circuit equivalence, one is to use short wires to connect the equipotential points; the other is to break the branch that connects the equipotential points. Open (because there is no current in the branch), thus obtain the series-parallel relationship of the resistance.IV Ohm's Law4.1 What is Ohm's Law?(1) The content of Ohm's lawWhen there is a potential difference between the two ends of the conductor, an electric field appears inside the conductor, and the charge moves in a directional motion under the force of the electric field to generate current. German physicist Ohm summed up Ohm's law in 1826 through a large number of experiments: Under steady conditions, the intensity of the current passing through a section of conductor is proportional to the voltage across the conductor.(2) Mathematical expression of Ohm's law Note: The unit of the physical quantity in the formula: the unit of I is ampere (A), the unit of U is volt (V), and the unit of R is ohm (Ω).The proportional coefficient R in the formula is determined by the properties of the conductor and is called the resistance of the conductor. Unit: Ohm (Ω). The reciprocal of resistance is called conductance and is represented by G, that isUnit: Siemens (S).(3) Understanding and explanation of Ohm's law● Applicable conditions of Ohm's law: applicable to pure resistance circuits (that is, when working with electrical appliances, the consumed electrical energy is completely converted into internal energy.)● I, U and R in the formula must correspond to the same conductor or the same circuit. If it is in different time, different conductor or different section of circuit, I, U, and R can not be mixed, therefore, the three physical quantities should be marked with angles in order to distinguish under normal circumstances.● For the same conductor (that is, R does not change), I and U are proportional; for the same power source (that is, U does not change), I and R are inversely proportional.● R=ρL/S is the definition of resistance, which means that the resistance of a conductor is determined by the material, length and cross-sectional area of ​​the conductor itself. In addition, resistance is also related to factors such as temperature.● The formula transformed from Ohm's law is a measure of resistance. It indicates that the resistance of a conductor can be given by U/I, that is, the ratio of R to U and I is related, but the magnitude of R itself is related to the applied voltage U and the passing current Factors such as the size of I are irrelevant.● Knowing any two quantities among I, U and R, you can find another quantity.● Issues that need special attention and re-emphasis: I, U and R in the formula must be in the same circuit; when using the formula to calculate, the unit of each physical quantity must be unified.The above explanations are all part of Ohm’s law, which only applies to pure resistance circuits.(4) Pure resistance circuitA pure resistance circuit is a circuit with only resistance elements in addition to the power supply, or inductance and capacitance elements, but their influence on the circuit is negligible. The voltage and current have the same frequency and phase.The resistance converts all the energy obtained from the power supply into internal energy. This kind of circuit is called a pure resistance circuit. Here is a brief explanation from the energy point of view.Basically, as long as there is no conversion of electric energy other than internal energy, this circuit is a pure resistance circuit.4.2 What is Closed Circuit Ohm's Law?In an AC circuit, Ohm's law also holds, but the resistance R should be changed to impedance Z, that is, I = U/Z. If the circuit is closed and contains a power supply, it is called a full circuit, as shown in the figure below. The dotted line in the figure is the power supply, which is called an internal circuit. The circuit outside the power supply is called an external circuit. Since the power supply has internal resistance, the current not only has a voltage drop when passing through an external circuit, but also has an internal voltage drop when passing through an internal circuit. In the whole circuit, the current intensity is proportional to the electromotive force E of the power supply, and inversely proportional to the resistance (R+r) of the whole circuit (including the inner circuit and the outer circuit). This is the Ohm's law of the whole circuit, expressed by the formula:Where I- the current in the circuit, A; E- the electromotive force of the power supply, V; R- the resistance of the external circuit, Ω; r- the resistance of the internal circuit, Ω.From the above formula, in the circuit shown in the figure below, E=IR+Ir=Uouter+Uinner.Figure7. The simplest closed circuitIn the formula, U external = IR-external circuit voltage; U internal = Ir-internal circuit voltage.It should be noted that, since the internal resistance of the power supply itself and the internal resistance of the connecting wires are generally not large, the calculation results that are ignored in the calculation are basically correct. But sometimes it is necessary to calculate the internal voltage drop of the power supply, and to accurately calculate the current of the whole circuit, it is necessary to use the whole circuit Ohm's law. For example, in the figure below, if E=10V, r=0.1Ω, R=1kΩ, then:Figure8. An application example of Ohm's law of closed circuit① When S is connected to the 1 position, the circuit is in the open state,Ammeter readingThe reading of the voltmeter is U=IR=0.01×1000=10 (V), or U=E-Ir=10-0.01×0.1≈10 (V).②When S is connected to the 2 position, the circuit is in an open state, so the reading of the ammeter is 0; the reading of the voltmeter is U=E=10(V).③When S is connected to the 3 position, the circuit is in a short-circuit state, the reading of the ammeter is I=E/r=10/0.1=100(A)A; the reading of the voltmeter U=0(V).4.3 The Key Points of Studying Ohm's LawOhm's law is an important basic law in electricity. It is a law that is summarized and summarized through experiments. To master this law, we must pay attention to the following points:(1) Ohm's law applies to the entire circuit or a part of the circuit from the positive pole to the negative pole of the power supply, and it is a pure resistance circuit.(2) The current I "passing through" in Ohm's law, the voltage U at "both ends" and the resistance R of the "conductor" are all corresponding physical quantities on the same conductor or the same circuit. The above relationship does not exist between the current, voltage, and resistance of different conductors. Therefore, when using the formula I=U/R, the current, voltage, and resistance of the same conductor or the same circuit must be substituted into the calculation, and the three correspond one to one.(3) There is simultaneity among the three physical quantities in Ohm’s law. Even on the same part of the circuit, the closing or opening of the switch and the movement of the sliding position of the sliding varistor will cause the change of the circuit, which will lead to the current in the circuit. , Voltage, resistance changes, so the three quantities in the formula I=U/R are the same time value.(4) The difference between I=U/R and R=U/I:Ohm's law expression I=U/R means that the current in the conductor is related to the voltage across the conductor and the resistance in the conductor. When the resistance R is constant, the current I in the conductor is proportional to the voltage U across the conductor; when the voltage U across the conductor is constant, the current I in the conductor is inversely proportional to the resistance R of the conductor.R=U/I is derived from Ohm’s law expression. It means that the resistance value of a certain section of conductor is equal to the ratio of the voltage across the section of the conductor to the current passing through it. This ratio R is the property of the conductor itself and cannot be understood as R is directly proportional to U and inversely proportional to I. This is also the difference between physics and mathematics.(5) Ohm's law reflects the causal relationship between current intensity and voltage, and the restrictive relationship between current intensity and resistance under certain conditions. That is, when the resistance is constant, the current intensity is proportional to the voltage across the conductor; when the voltage is constant, the current intensity is inversely proportional to the resistance of the conductor. When establishing a proportional relationship, we must pay attention to its conditions. Ohm's law states that the current intensity through a conductor is determined by two factors, the voltage across the conductor and the resistance of the conductor.V Kirchhoff's LawKirchhoff's law includes the first law and the second law. They are the basic laws that are indispensable for the analysis and calculation of complex circuits.5.1 Concepts • BranchA two-terminal element connected in a circuit is a branch. Usually a certain current flows through the branch. (This definition is not universal. For example, if two components are connected in series and then connected in a circuit, it can only be regarded as a branch.)• NodeThe connection point between the branch and the branch is called a node. Usually the current diverges at the junction.• Loop loopA closed path formed by branches is called a loop.Figure9. 6 elements, 6 branches, 4 nodes, 3 independent circuits5.2 Kirchhoff's First Law (Nodal Current Law)The textual expression of KCL: For any node, the algebraic sum of the current flowing into (or out of) the node is equal to zero.Its mathematical expression:The regulation of current positive and negative: Generally, the current flowing into the node is positive, and the current flowing out of the node is negative.The physical meaning of KCL: conservation of chargeNote: KCL is not only applicable to a node, but also to a part of the circuit, as shown in the shaded part of the above figure:i3＝i65.3 Kirchhoff's Second Law (Law of Loop Voltage)KVL’s literal expression: In any closed loop of the circuit, go around a circle in a certain direction, and the algebraic sum of the voltage of each segment is zero.That is: or. When applying the law of loop voltage, the electromotive force is often written on the left side of the equation, and the voltage is written on the right side of the equation.The method for determining the sign of each electromotive force and voltage in the second expression is as follows:① First select the current direction of each branch.② Any choice of the detour direction along the loop (clockwise or counterclockwise).③ If the direction of the current flowing through the resistor is the same as the detour direction, the voltage drop on the resistor is positive, otherwise, it is negative.④ If the direction of the electromotive force is the same as the direction of the orbit, the electromotive force is positive, otherwise, it is negative.The physical meaning of KVL: energy conservation.5.4 Application Note of Kirchhoff's Law• Kirchhoff’s law is a general law that the circuit should satisfy, and has nothing to do with the specific properties of the components;• Kirchhoff’s law applies to any lumped circuit, that is, nonlinear, time-varying circuits, etc.;• Application steps:A. Divide the branch roads and number them;B. Specify the branch current and voltage reference direction, and generally need to be associated;C. Select the appropriate node according to the meaning of the question, and apply KCL;D. Or choose the appropriate circuit according to the meaning of the question, apply KVL, and pay attention to independence.Example: Use KVL to derive the relationship between the total resistance and the sub-resistance and the voltage division formula in the series resistance circuit.Apply KVL according to the current and voltage reference direction and the detour direction of the loop calibrated in the figure:-u+u1+u2+…+un = 0 or u=u1+u2+…+un Because the voltage and current of each resistor obey Ohm's law: uk=iRk, there are:u = i × R1 + i× R2 +...... +i× Rn = i× ( R1+R2+…+Rn)= i Re among them: Re=R1+R2+…+Rn, which is the total resistance or equivalent resistance.uk = iRk=( u/Re ) Rk, which is the voltage division formula of the series circuitVI Series and Parallel Circuit Identification MethodsMethod 1: Current flow method(1) Starting from the positive pole of the power supply, use arrows to mark the path of the current along the connected wires, and finally return to the negative pole of the power supply;(2) Observe whether the current has a shunt and confluence point:If there is only one path for the current in the circuit, the components are connected in series (as shown in Figure a below);If there is a shunt point and a confluence point in the circuit, that is, the direction of the current is greater than one path, the components between the shunt point and the confluence point are connected in parallel (as shown in Figure b below)Figure10. Current flow methodMethod 2: Demolition methodRemove any electrical appliances:If the other electrical appliance cannot work, the two electrical appliances are connected in series (as shown in Figure a below)If the other consumer still works without being affected, the two consumers are connected in parallel (as shown in Figure b below)Figure11. Demolition methodMethod 3: Node MethodFor other non-intuitive non-series circuits, the situation is more complicated and needs to be judged according to several steps:The first step is to mark nodes. That is, use different letters (or symbols) to mark all nodes of the circuit. As shown in the following figure (a), the four points A, B, C, and D are all nodes in the circuit.The second step is to merge the nodes. According to the characteristics of the nodes, some of the nodes you have marked may be equivalent to the same node. The letters (or symbols) belonging to the same node must be changed to the same letter (or symbol), as shown in the circuit shown in Figure (a) Point A and point C are the same node, C should be changed to A, point B and point D should be the same node, D should be rewritten as B, that is to say, the circuit shown in Figure (a) essentially has two nodes A and B .Figure12. Node MethodThe third step is to determine the connection mode of the circuit. There are usually two ways to judge:Method one:Direct judgment: as shown in the figure (a) above, both ends of the resistors R1, R2 and R3 are independently connected to nodes A and B, so R1, R2 and R3 are connected in parallel.Method Two:Drawing judgment: that is, draw the intuitive equivalent circuit diagram of the original diagram. The specific drawing method of the intuitive equivalent circuit diagram of the circuit diagram in Figure (a) is: first determine the two points A and B on the paper, and then combine the original diagrams A and B. The components between the two points B are independently connected to the newly determined points A and B, as shown in the above figure (b), that is, the equivalent circuit diagram of figure (a) is figure (b).Warm reminder: The "node method" is generally used to identify irregular and more complex circuits, which has certain difficulties. There are many ways to identify series and parallel circuits, but you can choose the most suitable method according to your own understanding of the method when using it.VII QuizThe voltage dropped across the 300 ohm resistor isA. 6V B.9V C.2V D.30VAnswer: AⅧ FAQ1. What is the difference between two resistors connected in series, and two resistors connected in parallel?When resistors are in series then net resistance is the sum of individual resistances whereas in parallel it is the sum of the reciprocal of individual resistances.When a resistor is in series the current is the same through all resistors but the voltage is different. The sum of the voltage drop across each resistor is equal to the voltage across a resistor connected in series.When the resistor is in parallel the voltage across each resistor is the same while the current through each resistor is different.In series, the net resistance is higher (sum of each resistance) while in parallel net resistance is lower (net resistance is lower than smallest resistance connected in parallel). 2. Why are resistors connected in series and parallel?Connecting resistors in series increase their total resistance and the power they can handle by distributing the applied voltage. The current flow is the same for each resistor regardless of its resistance.Connecting resistors in parallel reduce their total resistance while at the same time increasing their power they can handle by sharing the current flow in the circuit. The voltage drop across each resistor is the same regardless of its resistance. 3. What is the difference between resistors in parallel and resistors in a series?For resistors in parallel, the voltage across them is the same while the current is the sum let take a case of two resistors connected in parallel the formula 1/Req=1/R1+1/R2 further simplify Req=R1*R2/(R1+R2)While for resistors in series their current is the same but the voltage is the sum and let still take the case of two resistors connected in series to obtain their equivalent Req= R1+R2. 4. How are resistors added in series and parallel?When resistors are connected one after each other this is called connecting in series. This is shown below. To calculate the total overall resistance of a number of resistors connected in this way you add up the individual resistances. This is done using the following formula: Rtotal = R1 + R2 +R3 and so on. 5. Why is resistance different in series and parallel?When resistors are connected in parallel, more current flows from the source than would flow for any of them individually, so the total resistance is lower. Each resistor in parallel has the same full voltage of the source applied to it, but divide the total current amongst them. 6. How do you calculate resistors in parallel?Parallel Resistor EquationIf the two resistances or impedances in parallel are equal and of the same value, then the total or equivalent resistance, RT is equal to half the value of one resistor. That is equal to R/2 and for three equal resistors in parallel, R/3, etc. 7. Why is resistance less in parallel?When resistors are connected in parallel, more current flows from the source than would flow for any of them individually, so the total resistance is lower. 8. How do you sum resistors in parallel?The sum of the currents through each path is equal to the total current that flows from the source. You can find total resistance in a Parallel circuit with the following formula: 1/Rt = 1/R1 + 1/R2 + 1/R3 +... If one of the parallel paths is broken, the current will continue to flow in all the other paths. 9. What happens when you add a resistor in series?When resistors are connected in series, the total voltage (or potential difference) across all the resistors is equal to the sum of the voltages across each resistor. ... In other words, the voltages around the circuit add up to the voltage of the supply. 10. What is the difference between series connection and parallel connection?A parallel circuit refers to a circuit with two or more two paths for the current to flow. ... In a series circuit, all the components are arranged in a single line. In a parallel circuit, all the components are arranged parallel to each other. 

IntroductionIn electronics, operational amplifiers are generally dual/quadruple configurations. So users can consider using the extra amplifier as a comparator. Electrical symbols of the comparator and the operational amplifier are very similar. They are devices with one input inverting terminal and one non-inverting terminal, and one output terminal. In addition, the output voltage range of the output terminal is generally between the rail-to-rail power supply. Meanwhile, they have same features of low bias voltage, high gain and high common-mode rejection ratio. When an op amp is used as a comparator, its own gain bandwidth product, group delay, slew rate and other parameters are likely to be changed due to internal frequency compensation and saturation effects. For an optimized single device, this change can be seen as an economical solution. This article discusses the specifications and characteristics to consider when using op-amps as comparators and provides design advice. How operational amplifier be a comparator and what the difference between them.Op Amp vs ComparatorCatalogIntroductionⅠ Operational Amplifier and Comparator1.1 Electronic Op Amp1.2 Electrical ComparatorⅡ Circuit Structure Comparison2.1 Op Amp2.2 ComparatorⅢ Difference between Amplifier and Comparator3.1 Total Difference Summary3.2 Distinctions between Op-amp and ComparatorⅣ Basic Use of Comparators and Op AmpsⅤ Op-amp Comparator5.1 Technique5.2 Op Amp Comparators DisadvantagesⅥ Using Op Amps as Comparators NotesⅦ ConclusionⅠ Operational Amplifier and Comparator1.1 Electronic Op AmpThe operational amplifier is a kind of differential amplifiers with high input resistance, low output resistance, high open gain (open-loop gain), and has the function of amplifying the voltage difference between the active input pin and the negative input pin. Operational amplifiers and voltage comparators are indeed the same in principle and diagram symbol. That said, they have 5 pins: two of which are power supply (+) and supply power (-), another two pins are non-inverting input (+) and non-inverting input terminal (-), and the last pin is the output terminal.Figure 1. Op Amp Symbol1.2 Electrical ComparatorComparing two or more data items to determine whether they are equal, or determining the  relationship and arrangement order between them is called comparison. A circuit or device that can realize this is called a comparator. Specifically, it is a circuit that compares an analog voltage signal with a reference voltage. The two inputs of the comparator are analog signals, and the output is a binary signal 0 or 1. When the difference of the input voltage increases or decreases and the sign of the positive and negative remains unchanged, the output remains constant. Comparing the voltages of the two input terminals, if the voltage at the positive input terminal is a and the voltage at the negative input terminal is b, when a>b, the output is high level(logic 1); when a<b, the output is low level(logic 0). The schematic diagram is shown below (the voltage at the input terminals of the comparator is IN1 and IN2, the power supply is VCC/GND, the pull-up resistor is 1K, and the pull-up voltage is VCC.).Figure 2. Volatge ComparatorWhen output voltage IN1＞IN2, positive input is in high level with high voltage.When output voltage IN2＞IN1, negative input is in low level with high voltage.A reference voltage is usually applied to an input terminal. Then the output will indicate the  signal applied to the other input. Comparators are often used to determine whether a signal is above or below the reference level. And meawhile, the comparator can form a non-sinusoidal waveform conversion circuit and be used in fields such as analog and digital signal conversion.When the reference voltage is zero, the comparator is called a zero-crossing detector. It uses to convert a sine wave into a square wave. Two comparators can form a "window" circuit, which is used to determine whether a signal is between two limited values. In an output state of the comparator changes as quickly as possible, and sometimes the output of the comparator is required to have a certain logical relationship with the input, a dedicated strobe pulse is required. At this time, the op amp comparator only has an output during operation. In general, a dedicated comparator IC has better performance. And it replaces the operational amplifier in some applications. The most common advantage is that the comparator IC operates with a single power supply.The comparator has a wide range of uses, and can be used for discrete control of voltage signals such as thermistors and photosensitive sensors. For example, the voltage value of the photoresistor is collected by a comparator to determine whether it is day or night. What’s more, the comparator can also be used for voltage adjustment in an analog negative feedback circuit.Figure 3. TLC311 ComparatorIt can be seen from the diagram that the difference between the operational amplifier and the comparator lies in the output circuit. The operational amplifier uses a dual-transistor push-pull output. While the comparator uses only one transistor, the collector is connected to the output terminal, and the emitter is grounded. In addition, the comparator requires an external pull-up resistor from the positive power supply terminal to the output terminal, which is equivalent to the collector resistance of the transistor. Op amp can be used for linear amplifying circuit (negative feedback), as well as the non-linear signal voltage comparison (open-loop or positive feedback). The comparator can only be used for signal voltage comparison, not for linear amplifier circuits (because it has no frequency compensation). Both can be used for signal voltage comparison, but the comparator is designed as a high-speed switch, which has a faster conversion rate and a shorter delay than an operational amplifier. Ⅱ Circuit Structure Comparison2.1 Op AmpFigure 4. Op Amp CircuitOp amp circuit generally consists of input segment, gain segment, and output segment. The input  is composed of a differential amplifier section for amplifying the voltage difference between two pins. In addition, the in-phase signal component (the state where there is no potential difference between the pins and the input voltage is some) is not amplified to take a cancellation effect. If only relying on the differential amplifier circuit, the gain is insufficient, so the gain section is used to further increase the open gain of the operational amplifier.The anti-vibration phase compensation capacitor is connected between the gain section of the ordinary operational amplifier. In order to avoid changes in the characteristics of the operational amplifier due to loads such as resistors connected to the output pins, a compensation capacitor is connected with the output as a buffer.The change (distortion, voltage drop, etc.) in output characteristics caused by the load is mainly determined by the circuit structure and current capability of the output section.Generally, types of output circuit stages are A, B, C, and AB type, which are classified according to the amount of drive current flowing in the output (the difference in bias voltage). Depending on the amount of drive current, the level of distortion coefficient in the output section will change. The order of general circuit distortion from small to large is type A, type AB, type B, and type C. 2.2 ComparatorFigure 5. Comparator CircuitThe comparator circuit structure is basically the same as that of an operational amplifier. Because a negative feedback circuit is not used, there is no built-in phase compensation capacitor for vibration isolation. Owing to it can limit the operating speed between the input and output, the response time is significantly improved compared with the operational amplifier.The output circuit form of the comparator is mainly divided into open collector (open drain) type and push-pull output type. The figure shows the internal equivalent circuit of BA10393, it is also an open collector output circuit. Ⅲ Difference between Amplifier and Comparator3.1 Total Difference Summary(1) The main difference between amplifier and comparator is the closed-loop characteristic. Most of the amplifiers work in a closed loop state, so it is required that they cannot be self-excited after the closed loop. Most of the comparators work in an open loop state and pursue speed. For the case of relatively low frequencies, the amplifier can completely replace the comparator (the output level should be considered), but in most cases, the comparator cannot be used as an amplifier.In order to increase the speed, the comparator optimization will reduce the range of closed-loop stability. While the op amp is optimized for the closed-loop stable range, so the speed is reduced. If an amplifier used as a comparator, as for performance, you may pay more than an amplifier price for its closed-loop stability.In other words, whether an op amp is used as a comparator or not is to see the negative feedback depth of the circuit. Therefore, a shallow closed-loop comparator may work in the amplifier state and will not have self-excited state. However, a lot of experiments must be done to ensure that the op amp is stable under all working conditions.(2) In general speaking, the comparator is an open-loop application of the op amp, but the comparator is designed for voltage threshold comparison. The required comparison threshold must be accurate, and the rise or fall time of output edge after comparison should be short. It conforms to TTL/CMOS level/or OC, etc., does not require the accuracy of the intermediate links, in addition, the driving capability is also different. In short, using op amps as comparators cannot achieve full-scale output in most cases, or the edge time after comparison is too long. So it is better to use special comparators in the design.Figure 6. Op Amp and Comparator Symbol3.2 Distinctions between Op-amp and ComparatorAlthough the electrical symbols of the comparator and the op amp are the same on the circuit diagram, the two devices have big differences and are generally not interchangeable. The differences are as following:1. The flipping speed of the comparator is fast, on the level of ns, while the flipping speed of the op amp is generally us level(except for special high-speed op amps).2. The op amp can be connected to the negative feedback circuit, but the comparator cannot use negative feedback. Although the comparator also has two input terminals of the inverting and non-inverting phase, when connecting negative feedback, the circuit cannot work stably without phase compensation circuit inside. But it is the main reason why the comparator is much faster than the op amp.3. The output stage of the operational amplifier generally adopts a push-pull circuit and a bipolar output. The output stage of most comparators is an open collector structure, so pull-up resistors and unipolar output are needed, which are easy to connect to digital circuits.4. Based on input, many operational amplifiers have built-in protection circuits to prevent large voltages from damaging the chip. When a large differential voltage is input, the input work will become abnormal, because the differential input voltage range of the op amp is usually limited. In addition, the common-mode input voltage range of non-rail-to-rail op amps cannot reach the positive power rail, but the comparator supports the positive power rail. Op amps and comparators have many similar parameters. It is more convenient to choose op amps instead of comparators in applications that require low offset voltage, low offset current, and high common mode rejection. Ⅳ Basic Use of Comparators and Op AmpsFigure 7. Operational Amplifier and ComparatorThe comparator is an open-loop circuit. Its function is to compare the voltage of the output terminal. When the voltage at the positive input terminal is large (IN2>IN1), the output is in high level (note: The comparator is an OC output, and the output terminal needs a pull-up resistor. A few volts will be pulled up to output a few volts, otherwise, the output will be an open circuit). When the negative input terminal voltage is large (IN1>IN2), the output will be in low level (GND). The voltage comparator input signal is an analog voltage, and the output signal generally only has two steady-state voltages of high level and low level. The voltage comparator can convert various periodic signals into rectangular waves.Operational amplifier can be used in linear amplifying circuit, and can also be used in non-linear circuit (used as comparator). It is widely used in electrical circuits, such as non-inverting amplification, inverse proportional amplification, difference, addition circuit, subtraction circuit, integral and differential circuit.  Ⅴ Op-amp Comparator5.1 TechniqueThe functions of the operational amplifier are more complicated, but the comparator is relatively simple. When the frequency requirement is not high, the operational amplifier can also be used as a low-performance comparator in practical applications.In theory, an operational amplifier with an open-loop configuration (no negative feedback) can function as a low-end comparator. When the voltage of the non-inverting input terminal (V+) is higher than the inverting input terminal (V-), due to the higher open-loop gain, a positive saturation voltage +U is output. When the voltage of the inverting input terminal (V-) is higher than the positive input terminal (V+), a reverse saturation voltage -U is output. For an op amp that works in a linear negative feedback configuration and is powered by a separate voltage (±V), is different from a non-linear comparator without negative feedback. 5.2 Op Amp Comparators DisadvantagesIn practice, the use of op amp comparators has the following disadvantages compared with the use of dedicated comparators:1) The op amp is designed to work in a linear segment with negative feedback, so saturated op amps generally have a slower flip speed. Most op amps have a compensation capacitor used to limit the slew rate of high-frequency signals. This makes the op amp comparator generally have a propagation delay on the level of microseconds, but a dedicated comparator is on the level of nanoseconds.2) The op amp does not have a built-in hysteresis circuit and requires a special external network to delay the input signal. 3) The static operating current of the op amp is stable only under negative feedback conditions. When the input voltage is not equal, there will be a DC offset.   4) The function of the comparator is to generate the input signal for the digital circuit. When using the op amp comparator, it is necessary to consider the compatibility with the digital circuit interface.5) Interference may occur between different frequencies of multiple op amps.6) Many op amps have diodes connected in reverse series at the input. The input of the two poles of the op amp is generally the same, which will not cause operational problems. But the two poles of the comparator need to be connected to different voltages, which may cause unexpected breakdown of the diode.7) Integrated circuits of dedicated comparator, which better combine the characteristics of analog and digital. It provides an output representing the logic state related to two analog voltages, one of which is a fixed reference quantity. When another voltage exceeds the reference value, is less than the reference value, or is in a specified range, the comparator can send a signal. It has an optimized combination of high gain, wide bandwidth and large flip rate to quickly change the output state. And the conversion time of digital signals is usually very fast. Ⅵ Using Op Amps as Comparators NotesThere are many points should remember when using op amps as comparators in circuits. You must consider five main op-amp characteristics to ensure expected performance:1) Power SupplyIf the logic and operational amplifier share the same power supply, the rail-to-rail operational amplifier can drive CMOS and TTL logic. but if they do not share the same power supply, an additional interface circuit is required.2) Input impedance and Bias CurrentWhen the operational amplifier is used as a comparator, it must meet the high input impedance condition. The input impedance of the CMOS voltage feedback operational amplifier is in the megohm level, which meets the requirement. As for current feedback (transconductance) operational amplifiers, the inverting input terminal has extremely low impedance, which cannot be used as a comparator.3) Differential Input CharacteristicsThe original intention of operational amplifier design is to cooperate with negative feedback to reduce the differential input as much as possible. In specific applications, the actual differential input voltage and the maximum differential input voltage that the op amp can actually provide should be considered.4) Common-mode Input CharacteristicsFor the old FET-type input operational amplifier, when the input exceeds the common-mode voltage range allowed by the device, a phase reversal will occur. At present, the op amps produced by various manufacturers use various methods to prevent the op amps from phase inversion. If the actual common-mode voltage range exceeds the allowable input common-mode voltage range of the op amp, you need to actually verify whether it is working properly.5) StabilityBecause there is no negative feedback externally, the open loop gain of the op amp used as a comparator is very high. Therefore, parasitic capacitance of the PCB and ground impedance of the non-inverting input terminal may cause the output to oscillate.Figure 8. Window Comparator CircuitⅦ ConclusionAlthough op amps are not designed to be used as comparators, nevertheless, many applications where the use of an op amp as a comparator is an economical engineering decision. It is important to make an reasonable decision to ensure that the op amp chosen performs as expected.That said, it is necessary to read the data sheets carefully and to consider the effects of op amp parameters on the application. Because the op amp is being used in a nonstandard manner, it may not reflect actual behavior, and some circuit experiment is advisable. Furthermore, because not all devices are typical in their behavior, some pessimism is warranted when interpreting the experimental results. Frequently Asked Questions about Operational Amplifier as Comparator1. Can an op amp be used as a comparator?However, op amps can also be used as comparators, which causes them to operate non-linearly. The inputs are driven hard and the output voltage slams to the power supply rail. 2. How does a comparator op amp work?A comparator circuit compares two voltages and outputs either a 1 (the voltage at the plus side; VDD in the illustration) or a 0 (the voltage at the negative side) to indicate which is larger. Comparators are often used, for example, to check whether an input has reached some predetermined value. 3. How op amp can be used as comparator in open loop configuration?Thus, an op-amp operating in open loop configuration will have an output that goes to positive saturation or negative saturation level or switch between positive and negative saturation levels and thus clips the output above these levels. This principle is used in a comparator circuit with two inputs and an output. 4. What is the difference between a comparator and an amplifier?Unlike operational amplifiers that usually operate with the input voltages at the same level, comparators typically see large differential voltage swings at their inputs. But some comparators without rail-to-rail inputs are specified to have a limited common mode input voltage range. 5. What is the difference between op amp and comparator?The difference between an op-amp comparator and a voltage comparator is in the output stage as a standard op-amp has an output stage that is optimized for linear operation, while the output stage of a voltage comparator is optimized for continuous saturated operation as it is always intended to be close to one supply.

IntroductionThe relay is an electrical device regarded as a switch in the circuit. That is, the current in the control circuit depends on the "open" and "close" of relay contacts. Therefore, the reliability and service life of the relay depend on the quality and performance of the contacts greatly. The performance of the contact is affected by factors such as contact material, contact voltage, load type, operating frequency, atmospheric environment, contact configuration and bounce.  If any of these factors cannot meet the predetermined value, contact problems such as electrochemical corrosion of the metal between the contacts, contact welding, contact wear, and contact resistance may occur. The volume of the load determines the size of the voltage and current that the relay can control (The rated load of the contact refers to the voltage and current that the electromagnetic relay allows to break.). If you not pay attention to it when use, it is easy to damage the relay contacts.Relay ContactCatalogIntroductionⅠ Relay Contact Form ConfigurationⅡ Relay Contact SymbolⅢ Relay Contact Fault Analysis3.1 Terminology3.2 Contact Bonding and Fusion Welding3.3 Contact Erosion3.4 Contact Metal Migration3.5 Contact Loose and Crack3.6 Contact DustⅣ Contact Protection MethodsⅤ Frequently Asked Questions about Relay ContactⅠ Relay Contact Form Configurationa. Normally Opened ContactIt would mean the contacts are normally open when the coil of the relay is not energized or there is no magnetic field nearby in a reed switch. b. Normally Closed ContactIt would mean the contacts are normally closed when the coil of the relay is not energized or there is no magnetic field nearby in a reed switch. c. Common ContactIt would have 3 leads and would have one normally open and one normally closed circuit. This is also called a “changeover” because the common contact changes from the normally closed position to the normally open position when the coil is energized in a relay or a magnetic field is nearby in a reed switch. Ⅱ Relay Contact Symbol Ⅲ Relay Contact Fault Analysis3.1 TerminologyThere is something in which the relay contact seems to be closed, but the circuit works abnormally sometimes. This is due to the existence of the contact resistance of the relay contacts. When the current passes through the closed contact, the contact resistance will consume a certain amount of power, which will increase the temperature of the contact. If the current is large, the contact material will soften and deform, resulting in greater contact resistance, and even having welding failure in severe cases, making the closed contact unable to be disconnected. Another form of contact resistance is "membrane resistance". Because the contacts of the relay are exposed to the air for a long time, there will always be compounds produced by dust, water vapor, and chemical gas, which will adhere to the contacts to form a thin film. Because of it, the conductivity of the contacts will become worse, and even become non-conductive in severe cases. 3.2 Contact Bonding and Fusion WeldingContact bonding usually occurs when the contacts are in a static connection. Contact resistance making the temperature of the conductive spots and nearby materials increase, which leads to a great increase in the diffusion rate and a large expansion of the contact area. The molecular force formed by the mutual extrusion and penetration of metal molecules at the contact point is the internal factor leading to the contact bonding, in addition, the sliding friction between the contacts is a necessary condition for accelerating the molecular extrusion penetration and accumulating bonding force. The size of the bonding force depends on the rigidity of the contact material and the physical conditions that cause molecular extrusion and penetration. Whether the contacts are bonded depends on the bonding force is greater than the return force of the reed. Fusion welding refers to the phenomenon that the contact areas of two electrodes are united together by metal welding. According to the reasons for formation, welding can be divided into static welding and dynamic welding. The Joule heat generated by the contact resistor melts the contacts part, and the phenomenon that they are combined and cannot be disconnected is called static welding. In the process of the contacts controlling the external circuit, the contact pressure of the contacts is near zero or above, and meanwhile, the liquid metal bridge between the contacts made. The welding phenomenon that occurs owing to the arc heat flow melting the contacts is called dynamic welding. 3.3 Contact ErosionA load of contact switching is mostly inductive. When the inductive load is disconnected, its accumulated magnetic energy will generate a high back electromotive force at both ends of the contact, which will break up the air gap between the contacts to form sparks and cause electrical corrosion. Cause the contact surface to dent or stick and cannot be separated, all of them belong to poor contact, which will result in a short circuit. The main factors that affect arc erosion include the characteristics of the arc and its effect on the heat flow and force of the electrode and the response of the contact material to the heat and force of the arc. In general, there are two main forms of arc erosion: 1) Vaporization and evaporation: Under the action of arc energy, the surface material of the contact changes from solid to liquid, and then into a gaseous state to leave the contact. Except that, in certain conditions, the contact material also has a sublimation process from a solid-state to a gas state. 2) Liquid splashing: Under the action of arc energy, a certain area of the surface of the contact melts. The liquid metal splashes out in the form of tiny droplets under the action of various forces, resulting in a larger material loss. These forces include spot pressure, electrostatic field force, electromagnetic force, force and reaction force of material movement, contact surface tension, etc. The form of arc erosion varies with the contact material and load current conditions. When the load current is small, the erosion of the contact material is dominated by vaporization and evaporation. When the current is increased, not only the vaporization and evaporation of the contact material but also the splashing phenomenon of liquid metal will occur. When the current is further increased, the metal liquid splashing becomes the main form of contact erosion. Preventing electrical corrosion between the contacts can be obtained by setting up a resistance spark extinguishing circuit and a resistance-capacitance spark extinguishing circuit. Therefore, when choosing a relay, you should consider the voltage applied to the contact and the load capacity of the contact. For example a relay with a contact load of 28V(DC)×10A means that the relay’s contact can only work at a DC voltage of 28V, and the contact current is 10A. If these two ratings are exceeded, the service life of the relay will be affected, and even the contacts will be burnt and damaged. In addition, the number of circuits that the relay needs to control should be determined according to actual requirements. In the same model series of relays, there are generally a variety of contact forms for selection, and each group of contacts should be fully utilized when using. 3.4 Contact Metal MigrationDuring the working process, there is usually a mutual transfer of materials between two contacts. If this mutual transfer cannot be offset, a net transfer of materials occurs. The significant contact metal migration is a big net transfer. The asymmetry of various factors in the contact operation is the main reason for the metal migration of the contact. These factors include arc, contact material characteristics and various external forces. Details are as following: 1) The arc has various forms of energy input to the contacts. For the contact at the cathode, the kinetic energy of the ion current colliding with the cathode after being accelerated by decompression, the potential energy released by the ion current on the cathode surface and the electrons, the arc column radiation or the energy conducted to the cathode surface, and the cathode Joule heat generated by the current in the body. All of these energies will increase the temperature of the contact material, resulting in contact material melting and evaporation. 2) The contact has various forces in the working process, including electronic force, electrostatic force, electromagnetic force, the reaction force of material movement, plasma flow force, these forces may cause the metal in the molten pool on the surface of the contact Liquid splashing occurs. 3) The material properties that affect the migration of the contact metal include electrical conductivity, specific heat capacity, latent heat of melting and vaporization, melting point and boiling point, metallurgical dynamics, and so on. In addition, the size, shape, and connection form of the contacts will also affect the metal migration. 3.5 Contact Loose and CrackContacts are electrical contact parts for relays to switch loads. Some products have contacts that are press-fitted by riveting. The main drawbacks of this installing method are loose contacts, cracks in the contacts, or excessive size and so on. They will affect the contact reliability of the relay. The loosening of contacts is caused by the improper size of the mating part of the reed and the contact or the improper adjustment force by the operator. Contact cracking is caused by too high material hardness or too much pressure. Different crafts should be used for contacts of different materials, and some contact materials with higher hardness should be annealed before contact manufacturing, riveting, or welding. 3.6 Contact DustSometime after use, dust and dirt will deposit on the contacts of the relay, which will cause a black oxide film on the surface, resulting in poor contact. Therefore, the contacts need to be cleaned regularly. For example, carbon tetrachloride liquid can be used to ensure good contact performance.  Ⅳ Contact Protection MethodsFigure 1. Contact Oscillogram (contact action time, release time, rebound time and stabilization time)We know that the relay contact protection needs to be more careful than MOSFET. Generally, the load of the relay is much larger than MOSFET. Common DC motors, DC clutches and DC solenoid valves with large DC loads, these inductive load switches are often closed, because surges caused by hundreds of or even thousands of back electromotive force will shorten the life of the contacts or even completely damage them. On the contrary, if the current is small, such as around 1A, the back electromotive force will cause arc discharge, which will cause metal oxides to contaminate the contacts, leading to failure of the contacts and increasing contact resistance. Protect contacts mainly to extend the use time of the relay, because the contacts will always accumulate carbon and age, and the surface is not as clean as it was originally. What’s more, when the relay life is approaching the end, its contact resistance will increase rapidly. Generally, under normal temperature and pressure, the breakdown voltage of the key dielectric in the air is 200~300V. Therefore, our goal is generally to control the voltage below 200V or less.Figure 2. Breakdown VoltageThere generally have the following methods to do it:MethodCircuitCharacteristicComponent SelectionResistor and CapacitorIf the load is related to time, the initial leakage current may cause the load to malfunction.R: The contact voltage is 1VC: The contact current is 1A, and the value of RC varies with the relay and load.The function of the capacitor C is to suppress the excessive voltage when the inductor is discharged.The value of resistance R is determined by the test needs.The breakdown voltage of the capacitor C is 200~300V.If the load is a relay or solenoid valve, the release time will be extended. When the contact power supply voltage range is 24V~ 48V, the voltage across the load is 100 ~ 200V.DiodeThe diode (regarded as a freewheeling diode) acts as a channel for the coil to release energy and a way to dissipate heat. Compared with the RC circuit, it significantly changes the release time of the relay (2~5 times).The reverse breakdown voltage is at least 10 times the power supply voltage, and the forward current is equivalent to the load.Zener DiodeThis circuit effectively prevents the diode from affecting the release time of the relay.The breakdown voltage of the Zener diode must be consistent with the power supply voltage of the relay.VaristorBased on the characteristics of the varistor to stabilize the voltage, this circuit can prevent the contact voltage from being too high, and also slightly delay the relay release time. When the load contact power supply voltage is 24V or 48V, and the voltage across the load is 100 to 200V, the varistor is very effective. * Standard diodes can significantly extend the rebound time. Connecting conventional diodes in series with Zener diodes will affect it lightly. If it is an inductive load, when the contacts are separated, a longer rebound time prolongs the arc generation time and shortens the life of the contacts. For example, a relay with a diode connected to the coil needs 9.8ms to release the contact. Combining the Zener diode with the small signal diode can shorten the time to 1.9ms. In addition, the return time of the relay without a diode connected to the coil is 1.5ms. Although the inductive load is not easy to handle than the resistive load, the use of effective protection will make the performance better. There are two methods that can’t be used.Figure 3. Capacitor and Relay CircuitIn the actual circuit, the protection device (diode, resistor, capacitor, varistor, etc.) and the load should have a certain distance. If the two are too far apart, the effect of the protective device may be weakened. Generally, the distance between the two should be within 50cm. DC loads at higher frequencies will cause abnormal switch corrosion (electric spark generation). When the DC solenoid valve or clutch is controlled at a higher frequency, the contacts may have corrosion. The reason for this is that when an electric spark (arc discharge) is generated, the reaction between nitrogen and oxygen causes contact corrosion. Ⅴ Frequently Asked Questions about Relay Contact1. How do relay contacts work?A relay is an electrically operated switch. They commonly use an electromagnet (coil) to operate their internal mechanical switching mechanism (contacts). When a relay contact is open, this will switch power ON for a circuit when the coil is activated. 2. What is a relay contact output?A relay contact output works basically like an on/off switch. To simplify, if the output is "off" the circuit will be broken (open). If the output is "on" the contact will be made, completing the circuit. Therefore, the controller does not supply any current or voltage itself. 3. Why do relay contacts weld?Consequently, when the contacts are ON again, short-circuited current from the capacitance may cause contact weld. This circuit effectively suppresses arcs when the contacts are OFF. When the contacts are ON again, however, charge current flows to the capacitor, which may result in contact weld. 4. How do I protect my relay contacts?Various ways to protect relay contacts from the effects of switching an inductive load – from left to right: a diode, a spark quench capacitor, Zener diodes or a transil, a varistor. 5. What is a contact form relay?Contact Form: The arrangement of the contacts in the relay. This determines how many circuits the relay can operate. Form 1A (or “1 Form A): One circuit is opened and closed with the contacts in a Normally Open position. 6. What is a relay contact?Relays control one electrical circuit by opening and closing contacts in another circuit. ... When a relay contact is Normally Closed (NC), there is a closed contact when the relay is not energized. In either case, applying electrical current to the contacts will change their state. 7. How many contacts does a relay have?Two. A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core, an iron yoke that provides a low reluctance path for magnetic flux, a movable iron armature, and one or more sets of contacts. 8. What is the difference between relay and contactor?A contactor joins 2 poles together, without a common circuit between them, while a relay has a common contact that connects to a neutral position. Additionally, contactors are commonly rated for up to 1000V, while relays are usually rated to the only 250V. 9. What is the purpose of contactor or relay?A contactor is a large relay, usually used to switch current to an electric motor or another high-power load. Large electric motors can be protected from overcurrent damage through the use of overload heaters and overload contacts. 10. What are the three major parts of a contactor or relay?There are three major parts of a contactor or relay: the coil, mechanical linkage and contacts. The coil is used to create a magnetic field and is rated based on voltage (24 V, 120 V, 208/204 V, 480 V). The mechanical linkage connects the armature to the contacts when the coil is energized, completing the circuit. Recommended ReadingBasic Knowledge of Relay Electronics Tutorial with VideoThe Role of the Relay and Its Working PrincipleHow Relays Work? Relay Functions and Applications

IntroductionCapacitors are components that store electricity and electrical energy (potential energy) and play an important role in circuits such as tuning, bypassing coupling, and filtering. Capacitors are connected in parallel to increase capacity, and capacitors are connected in series to decrease capacity. When the capacitor is connected in series in the circuit, it can prevent the sudden change of voltage and absorb the overvoltage in the peak state. The series resistance plays a damping role, and the resistance consumes the energy of the overvoltage, thereby suppressing the oscillation of the circuit. When the capacitor is connected in parallel, the parallel resistor can absorb the electric energy of the capacitor, prevent the discharge current of the capacitor from being too large, and avoid damaging the devices (such as thyristors) connected in parallel with it. This is a very comprehensive article including the calculation formulas, circuits, and related common problems of series capacitors and parallel capacitors.Capacitors in Series & Parallel - Electronics BasicsCatalogIntroductionCatalogI What are the Capacitors in Series and Parallel?II Calculation Methods of Capacitance of a Series/Parallel Network  2.1 The Series and Parallel Combination  2.2 Voltage Division  2.3 How to Divide the Voltage When Capacitors are Connected in Series?  2.4 What is the Voltage Division Formula When Connecting 2 Capacitors in Series?III The Equivalent Method of Series or Parallel Connection of Capacitors with Different Rated Voltages and CapacitiesIV Comparison Table of Capacitors in Series and Parallel  4.1 Calculation Comparison of Capacitors in Series and Parallel  4.2 Correspondence Between Magnetic Circuit and Electric Circuit  4.3 Basic Physical Quantities of Magnetic Field and Magnetic CircuitV Frequently Asked Questions about Capacitors in Series and ParallelVI Electrolytic Capacitors in Series  6.1 Function and Purpose of 2 Electrolytic Capacitors in Anti-phase Series  6.2 Is the Electrolytic Capacitor in Series a Non-polarised Capacitor?VII QuizVIII FAQI What are the Capacitors in Series and Parallel?1.1 Parallel Connection of CapacitorsWe can describe the capacitors in parallel as a "water tank", but the water tank stores water, and the capacitor stores electric charges. If multiple capacitors are connected in parallel, they can naturally store more charge.(1) The equivalent capacitance after parallel connection is equal to the sum of the capacitance of each capacitance;(2) The voltage at both ends of each capacitor after parallel connection is equal;The withstand voltage after parallel connection is equal to the smallest capacitor voltage, and the equivalent capacitance is C1+C2, as shown in the figure below.Figure1. Parallel Connection of Capacitors1.2 Series Connection of Capacitors(1) The equivalent capacitance capacity after series connection is equal to the sum of the reciprocal of each capacitance;(2) The capacitance of each capacitor after series connection is equal;(3) The withstand voltage after series connection is equal to the sum of each capacitor voltage.After the capacitor is connected in series, it is equivalent to increase the distance between the two poles. The more the number in series, the smaller the capacitance, but the higher the withstand voltage. In actual circuit design, we generally rarely use capacitors in series, but capacitors in parallel are often used. Sometimes the capacity of a single capacitor is not enough, and one more is added.Figure2. Series Connection of CapacitorsII Calculation Methods of Capacitance of a Series/Parallel Network2.1 The Series and Parallel Combination(1) How to calculate the series capacitance of a capacitor?Suppose there are n capacitors connected in series. The series combination of these n capacitors is connected across a voltage source of V volts. Let us consider that the voltages across capacitors 1, 2, 3...n are V 1, V 2, V 3... Vn, respectively. The capacitances of capacitors 1, 2, 3 ... n are C 1, V 2, V 3 ... C n farad. Since all capacitors are connected in series, each of them will get the same charge, ie it is Q Coulomb. Now we know that the charge at both ends of the capacitor is only the product of the potential difference between the two ends of the capacitor and its capacitance value.Since the series combination of these capacitors is connected across the source of the voltage V volts, replacing the series combination n of multiple capacitors.If we consider a single equivalent capacitor of C,Now we get from equations 1 and 2,Therefore, when multiple capacitors are connected in series, the reciprocal of the equivalent capacitance of the system is given by the arithmetic sum of the reciprocal of their respective capacitances. (2) How to calculate the capacitance in parallel circuits?Suppose there are n capacitors connected in parallel. The parallel combination of these n capacitors is connected across the V volt voltage source. Since the capacitors are connected in parallel to the same voltage source, the charge of each capacitor is different and depends on their respective capacitance values. Let us consider that the charges of capacitors 1, 2, 3...n are Q 1, Q 2, Q 3,..., Q n coulombs, respectively. The capacitances of capacitors 1, 2, 3,..., n are C_1, C_2, C_3,... C_n coulombs respectively. It is now known that a charging capacitor is just the product of the voltage across the capacitor and its capacitance value. therefore,Now instead of connecting multiple capacitors in parallel, if we connect a single equivalent capacitor with capacitance C across the voltage source, then the total charge at both ends of the equivalent capacitor,Since all capacitors are connected in parallelWe can get from equations 1 and 2,Therefore, when multiple capacitors are connected in parallel, the capacitance of the system is given by the arithmetic sum of their respective capacitances.Figure3. (a) Three capacitors are connected in parallel. Each capacitor is connected directly to the battery.              (b) The charge on the equivalent capacitor is the sum of the charges on the individual capacitors. (3) Other related calculation formulasWhen the capacitor is connected in parallel, the area of the electrode is increased, and the capacitance is increased. The total capacity when connected in parallel is the sum of each capacity. When the capacitors are connected in series, the resistance value of the capacitor should be smaller than the insulation resistance of the capacitor in parallel to make the voltage distribution on each capacitor even, so as not to damage the capacitor due to uneven voltage distribution. The series and parallel calculations of capacitors are just the opposite of the series and parallel calculations of resistors.Voltage is the voltage during charging. The relationship between capacity and current, voltage is similar to power and is related to load.When voltage and capacity are quantitative, the smaller the load resistance, the larger the current and the shorter the time.When the voltage and load are quantitative, the larger the capacity, the longer the current and the longer the time.But in the actual discharge circuit, the general load is unchanged, the voltage of the capacitor is gradually reduced, and the current is gradually reduced. (1) Electric capacity (uf) = current (mA)/15Current limiting resistance (Ω)=310/maximum allowable surge currentDischarge resistance (KΩ)=500/capacitance (uf) (2) Calculation method C=15×IC is the capacitance of the capacitor, the unit is microfarad; the i device is the working current, the unit is ampere.For example, if the resistance of a bulb is 0.6 amps, the capacitance should be 15×0.6=9 microfarads, and a 9 microfarad capacitor in series is sufficient. (3) Empirical formula, 1uF output 50mA (if it is linear, a 10000F super capacitor can reach a surge current of 500 megaamps) (4) The calculation of the half-wave rectification method should provide about 30mA current per uF capacitance, which is a reference on the 50Hz220V line in China.The current is doubled in full-wave rectification, that is, 60mA current can be provided per uF.Formula: R*C≥(3～5)*T/2, you need to know the frequency of the lowest signal in the ripple component (that is, the maximum T), and then determine the value of C. ● Capacitor capacityCapacitor capacity indicates the size of electric energy that can be stored. The obstructive effect of capacitors on AC signals is called capacitive reactance. The capacitive reactance is related to the frequency and capacitance of the AC signal. The capacitive reactance XC=1/2πf c (f represents the frequency of the AC signal, and C represents the capacitance of the capacitor). ● The capacity unit and withstand voltage of the capacitor.The basic unit of capacitance is F (farad), and other units include: millifarad (mF), microfarad (uF), nanofarad (nF), picofarad (pF). Since the capacity of the unit F is too large, we generally see units of μF, nF, and pF. Conversion relationship: 1F=1000000μF, 1μF=1000nF=1000000pF. Each capacitor has its withstand voltage value, denoted by V. Generally, the nominal withstand voltage of the electrodeless capacitor is relatively high: 63V, 100V, 160V, 250V, 400V, 600V, 1000V, etc. The withstand voltage of polar capacitors is relatively low. Generally, the nominal withstand voltage values ​​are: 4V, 6.3V, 10V, 16V, 25V, 35V, 50V, 63V, 80V, 100V, 220V, 400V, etc. Power capacitor calculation: such as a three-phase capacitor bank with a nominal voltage of 690v and a capacity of 15kvar. Used in 600v circuit, delta connection, the actual effective capacity is: s=15kvar*600*600/(690*690)=11.34kvar. That is: the capacity and voltage are proportional to the square.2.2 Voltage DivisionDue to the large capacity of large capacitors, the volume is generally large, and they are usually made by multi-layer winding, which leads to a relatively large distributed inductance of large capacitors (also called equivalent series inductance, or ESL for short). The impedance of the inductor to the high frequency signal is very large, so the high frequency performance of the large capacitor is not good. Some small-capacity capacitors are just the opposite. Because of their small capacity, the volume can be made small (shortening the lead wire reduces the ESL, because a piece of wire can also be regarded as an inductance), and flat capacitors are often used Structure, such a small capacity capacitor has a small ESL so that it has a good high frequency performance, but due to the small capacity, the impedance to low frequency signals is large. So, if we want to pass the low frequency and high frequency signals well, we use a large capacitor and then a small capacitor.The commonly used small capacitor is 0.1uF CBB capacitor is better (ceramic capacitor is also OK), when the frequency is higher, you can also connect smaller capacitors in parallel, such as a few pF, hundreds of pF. In digital circuits, a 0.1uF capacitor is generally connected to the ground in parallel to the power pin of each chip (this capacitor is called a decoupling capacitor, of course, it can also be understood as a power filter capacitor, the closer the chip is, the better), because The signal in these places is mainly high-frequency signal, and it is enough to use a smaller capacitor to filter. The impedance of an ideal capacitor decreases as the frequency increases (R = 1/jwc), but an ideal capacitor does not exist. Due to the distributed inductance effect of the capacitor pins, the capacitor is no longer a simple capacitor in the high frequency range. , It should be regarded as a series high-frequency equivalent circuit of capacitance and inductance. When the frequency is higher than its resonance frequency, the impedance shows the characteristic of increasing with the increase of frequency, which is the inductance characteristic. At this time, the capacitance is like An inductance. On the contrary, inductors have the same characteristics. Large capacitors in parallel with small capacitors are widely used in power supply filtering. The fundamental reason is the self-resonance characteristics of the capacitor. The combination of large and small capacitors can well suppress low-frequency to high-frequency power interference signals. Small capacitors filter high frequencies (high self-resonant frequency), and large capacitors filter low frequencies (low self-resonant frequency). The two complement each other. ● Series voltage divider ratio: V1 = C2/(C1 + C2)*V...the larger the capacitance, the smaller the voltage divided, which is the same under AC and DC conditions● Parallel shunt ratio: I1 = C1/(C1 + C2)*I...The larger the capacitance, the larger the current that passes. Of course, this is under AC conditions.Explanation: When two or more capacitors are connected in series, it is equivalent to lengthening the insulation distance, because only the two polar plates on the two sides work, and because the capacitance is inversely proportional to the distance, the distance increases and the capacitance decreases; two or two When the above capacitors are connected in parallel, the area equivalent to the plate increases, and because the capacitance is proportional to the area, the area increases and the capacitance increases. ● Capacitors in series: After the capacitors are connected in series, the capacity decreases and the withstand voltage increases. Formula: 1\C1+1\C2=1\C If two 50uf are connected in series, it becomes 25uf.● Withstand voltage = add the withstand voltage values ​​of two capacitors. If two 100V withstand voltages are connected in series, it becomes 200V.● The formula for calculating the capacity of the series circuit of the capacitor C: 1/C=1/C+1/C2+1/C3+.+1/CnC is the total capacitance value of the capacitor series circuit, C1, C2, C3, Cn are the capacitance values of each capacitor in the capacitor parallel circuit, that is, the reciprocal of the total capacitance of the series circuit is equal to the sum of the reciprocal of the capacitance of each capacitor in the series circuit.Figure4. Capacitors in Series and Parallel2.3 How to Divide the Voltage When Capacitors are Connected in Series?For example 4V voltage source, two capacitors of 0.5F and 1F in series. If it is a DC voltage source, according to the characteristics of capacitor series voltage division introduced in middle school physics:(1) The total voltage across the capacitor series circuit is equal to the sum of the divided voltages across the capacitors. That is, U= U1+ U2+ U3+…+Un.(2) When capacitors are connected in series, the voltage distributed on each capacitor is inversely proportional to its capacitance. That is, Un = Q / Cn (because in the capacitor series circuit, the amount of charge carried on each capacitor is equal, so the larger the capacitor, the lower the voltage, and the smaller the capacitor, the higher the voltage. .)Then the voltage source of 4V, the voltage on the two capacitors of 0.5F and 1F are 8/3V and 4/3V respectively 2. If it is an AC voltage source, from the impedance of the capacitor Xc=1/jωC, we can see |Xc| and C In inverse proportion, the same result can be obtained by using |Xc| as a resistor to calculate the voltage divider.2.4 What is the Voltage Division Formula When Connecting 2 Capacitors in Series?This is a theoretical calculation problem. It is necessary to assume that the withstand voltage value of the capacitor has no margin, that is, a capacitor of 200pF is breakdown when it exceeds 500V; a capacitor of 300pF is breakdown when it exceeds 900V.After adding 1000V voltage, the 200pF capacitor will withstand 600V voltage. Regardless of the capacitor's withstand voltage margin, the 200pF capacitor will break down; at this time, 1000V will all be added to the 300pF capacitor, which exceeds its withstand voltage, so it will breakdown. Calculation formula:If there are M capacitors connected in series, the actual voltage value Un of any capacitor Cn is:Un=U*C/Cn Among them: U is the total voltage; C is the total capacity of M capacitors in series.For two capacitors in series, the formula evolves into:Assuming that the total voltage is U, the voltages on C1 and C2 are U1 and U2 respectively, thenU1=C2*U/(C1+C2)U2=C1*U/(C1+C2)III The Equivalent Method of Series or Parallel Connection of Capacitors with Different Rated Voltages and CapacitiesThe equivalent method of using capacitors with the same rated voltage in series or in parallel is relatively simple and commonly used.Several capacitors with different rated voltages and different capacities are connected in series or in parallel, and the equivalent methods are different. Now give examples to illustrate. There are three capacitors C1: 220µF /10V C2: 100µF/25V C3: 10µF/100VCalculate their parallel and series equivalent values ​​respectively. (1) Parallel equivalent method1) Equivalent capacitanceC and = C1 + C2 + C3= 220µF + 100µF + 10µF/= 330µF2) Equivalent withstand voltageU parallel = U1 = 10V (take the minimum withstand voltage value U1) (2) Series equivalent method1) Equivalent capacitance1/C string ==1/C1 + 1/C2 + 1/C3= 1/220 + 1/100 + 1/10= 252/2200C string == 2200/252≈ 8 (µF)2) Equivalent withstand voltage ● Compare the Q value of each capacitorQ1= C1 X U1 Q2=C2 X U2 Q3=C3 X U3= 220 X 10 =100 X 25 =10 X 100=2200 (C) =2500 (C) =1000 (C)Q = Q3 =1000 (C) (take the minimum power value Q3) ● Find the actual allowable withstand voltage value of each capacitorU1 (actual) = Q/C1 U2 (actual) = Q/C2 U3 (actual) = Q/C3= 1000/220 = 1000/100 = 1000/10≈4.5(V) = 10 (V) =100 (V)3) U string = U1 (actual) + U2 (actual) + U3 (actual)≈4.5 + 10 + 100≈114.5(V)Figure5. Equivalent CapacitanceIV Comparison Table of Capacitors in Series and Parallel4.1 Calculation Comparison of Capacitors in Series and Parallel4.2 Correspondence Between Magnetic Circuit and Electric Circuit4.3 Basic Physical Quantities of Magnetic Field and Magnetic CircuitV Frequently Asked Questions about Capacitors in Series and Parallel(1) Do capacitors charge faster in parallel or series?If two capacitors with the same capacity are connected in parallel or in series in the same circuit, the capacitor in series will charge faster, because the capacity of the capacitor is reduced by half after the capacitor is connected in series, and the charging time becomes shorter. The capacity of the capacitor after parallel connection is doubled, and the charging time will be longer for the same charging circuit. (2) The electric charge of each capacitor in the series circuit is equal. Why is the electric charge of each capacitor equal to the electric charge of the equivalent capacitor?Capacitor voltage: U=Q/CQ=I*tSo U=(I*t)/CWhen the capacitors connected in series are connected to the power supply, the capacitors start to charge. The current flowing through each capacitor is the same. As time goes by, the voltage of each capacitor increases. However, due to the different voltage rise rates of C, the sum of the voltage of each capacitor is equal to the power supply. When the voltage is applied, charging stops and the current is zero. Analyze this process: the current flowing through each capacitor during the entire charging process is the same, and the elapsed time is the same, so the current of each capacitor is the same over time, so the amount of charge is the same and equal to the capacity of the capacitor.Figure6. A Charging State of Three Capacitors in Parallel(3) Are the filter capacitors in the power amplifier power supply connected in parallel?The filter capacitor of the power amplifier power supply is set to eliminate some of the AC components contained in the rectification from AC to DC (the purpose is to improve the audio quality), so all capacitors with larger capacity are selected, generally using electrolysis above tens of microfarads Capacitor. The parallel connection of capacitors is the addition of the capacity of each capacitor, usually forming a standard type 1 filter circuit: "capacitor-resistor (or inductance)-capacitor". If the capacitors are connected in series, the capacity will decrease, it will only increase the cost and occupy more space, meaningless. The power supply line filter capacitor of the amplifier circuit of the power amplifier is generally grouped in parallel. Depending on the design of the power supply, the single power supply circuit may also be directly connected in parallel, or divided into two groups. The two groups are separated by power inductors or resistors into two filter circuits to form a pie-type filter circuit; if it is a dual power supply circuit, , It is generally divided into two groups as for the two groups of power lines. The easiest way to increase the filter capacitor of the power amplifier is to see the positive and negative poles and the rated withstand voltage. Connecting them in parallel can improve the stability of the DC voltage and improve the low-frequency characteristics of the amplifier, making the low frequency of the speaker sound more full and round. Capacitors are generally used in parallel, and capacitors of different capacities filter noise at different frequencies. Large-capacity capacitors can only be realized by electrolytic capacitors. Electrolytic capacitors have positive and negative polarity and are very loud when connected reversely.VI Electrolytic Capacitors in Series6.1 Function and Purpose of 2 Electrolytic Capacitors in Anti-phase SeriesIn some circuit designs, it is seen that two electrolytic capacitors are connected in series in the reverse phase. The capacity of the two components should be equal and the withstand voltage is the same. In AC circuits, the leakage current can be reduced. Just use a non-polar capacitor to get a large-capacity non-polar capacitor. . Large-capacity non-polar capacitors are more expensive. The electrolytic capacitor has a large capacity and is cheap, but it has a polarity, and the two are connected in reverse series. It is non-polar. It can only be used in very low voltage applications (up to 1-2V). The voltage is slightly higher. When the capacitor is used in the opposite direction, the leakage will be large. The accumulated effect will cause the electrolytic capacitor to heat up and eventually cause the capacitor to explode. Electrolytic capacitors are used in DC circuits. So its series connection should be the negative pole of the first one and the positive pole of the second (just like dry batteries in series). But in the circuit, there is indeed a case where the negative poles of two electrolytic capacitors are connected to the negative pole (inverted series), and the two positive poles are used. This is because it is used in an AC circuit (in a circuit where DC and AC coexist), There is no guarantee that the potential of one pole is always higher than the other pole), so that when the capacitor is under reverse voltage, serious leakage current will be generated. At this time, non-polar capacitors should be used, but non-polar capacitors are expensive and expensive. The volume is large, so some people use two electrolytic capacitors to "reverse series".  Its working state is that when there is alternating current, one of them is in the reverse state. Due to its serious leakage, the voltage drop across it is very small. Almost all of the voltage falls on the positive capacitor, and when the other half cycle of the alternating current, the state of the two capacitors will be exchanged, so these two capacitors are used as one, and the total capacitance is equal to any one of them. The total withstands voltage value is equal to 2 times of any capacitor.6.2 Is the Electrolytic Capacitor in Series a Non-polarised Capacitor?Of course, two electrolytic capacitors in parallel will not work. If two electrolytic capacitors are connected in series, it will still not work without applying a proper bias voltage. Applying a bias voltage is quite complicated, especially when both ends of the capacitor (two in series) are not grounded (the bias voltage must be floating). Considering the complexity of applying the bias voltage, it is better not to use this method: connect the negative poles of the two capacitors, and connect the two capacitors in parallel with a high-current diode. The positive of the diode is connected to the negative of the capacitor, and the negative is connected to the positive of the capacitor. Parallel connection of course still has polarity. If reverse parallel connection, it is non-polar, but it is non-polar. Reverse series connection is also not advisable. If you do a test, you will find that there must be a capacitor that withstands the backpressure. If the voltage is large, it will blow up. Unless special measures are taken, the voltage is always applied to the capacitor with the positive voltage. on. Two electrolytic capacitors of the same capacity can be connected in series, but a diode must be connected in anti-parallel to prevent the reverse breakdown of the electrolytic capacitor. After adding a diode, it is okay if it is used for filtering, but it is definitely not good for blocking DC. Because the electrolytic capacitor is only charged and not discharged. Two identical electrolytic capacitors connected in reverse series can replace non-polar capacitors with the same capacity. The dielectric loss of the electrolytic capacitor is very large, and it must be connected to the AC circuit after the voltage is greatly reduced. Otherwise, it is either burned or fried.VII Quiz● QuestionA network of five capacitors of C is connected to a 100 V supply, as shown below figure. Determine(a) the equivalent capacitance of the network(b) the charge on each capacitor. ● SolutionIn the given network, the top three Capacitance is in series, So equivalent capacitance of the top part1C1=1C+1C+1CC1=C3Similarly, the lower two Capacitance is in series, So equivalent capacitance of lower part1C2=1C+1CC2=C2 Now both C1 and C2 are in parallel, so equivalent Capacitance of the NetworkCeq=C1+C2=C3+C2=5C3Now Charge on top part will beQ1=C1V=CV3Now Charge on lower part will beQ2=C2V=CV2  VIII FAQ1. How do you solve capacitors in series and parallel?To calculate the total overall capacitance of a number of capacitors connected in this way you add up the individual capacitances using the following formula: CTotal = C1 + C2 + C3 and so on Example: To calculate the total capacitance for these three capacitors in parallel. 2. How do you know if a capacitor is in series or parallel?In your circuit current, all of the current going to one capacitor must also go to the other. Therefore they are in series. Hope this helps. If two (two-terminal) circuit elements are series-connected, they have identical (not just equal) currents through. 3. What is a capacitor in parallel?Capacitors are connected together in parallel when both of their terminals are connected to each terminal of another capacitor. The voltage ( Vc ) connected across all the capacitors that are connected in parallel is the same. 4. Can you put two capacitors in series?If two or more capacitors are connected in series, the overall effect is that of a single (equivalent) capacitor having the sum total of the plate spacings of the individual capacitors. With resistors, series connections result in additive values while parallel connections result in diminished values. 5. How are capacitors connected in series?Here are the rules for calculating capacitances in series: If the capacitors are of equal value, you're in luck. All you must do is divide the value of one of the individual capacitors by the number of capacitors. For example, the total capacitance of two, 100 μF capacitors is 50 μF. 6. Why capacitor is connected in parallel?Capacitors are devices used to store electrical energy in the form of electrical charges. By connecting several capacitors in parallel, the resulting circuit is able to store more energy since the equivalent capacitance is the sum of individual capacitances of all capacitors involved. 7. Do capacitors in series increase voltage?Capacitors connected in series will have lower total capacitance than any single one in the circuit. This series circuit offers a higher total voltage rating. The voltage drop across each capacitor adds up to the total applied voltage. This is why series capacitors are generally avoided in power circuits. 8. Do capacitors in series or parallel store more energy?The energy stored in a capacitor is a function of the voltage across the capacitor. The voltage will be higher when they are in parallel, so the parallel connection stores the most energy. 9. Why voltage is different in a series combination of capacitors?In a series combination, since the charge stored is the same as the same charge flows through all the capacitors, the potential difference across each will be different. 10. When capacitors are wired in parallel what must be the same for the two capacitors?The charge in the two capacitors is different. Capacitors connected in parallel are connected to the same start and end points of the input and output that's why they have the same potential difference.  

IntroductionA relay is an electromagnetic switch operated by a relatively small electric current that can turn on or off a much larger electric current. It consists of a set of input terminals for a single or multiple control signals, and a set of operating contact terminals. Because of unique characteristics, it is widely used in many fields. How does a relay work? What the functions of relays, let’s check the following details.How Does A Relay Work?CatalogIntroductionⅠ Working Principle  1.1 Operation Example: Relay as a Switch  1.2 Working Principle of Different RelaysⅡ What is the Function of a Relay?  2.1 Summary  2.2 Types of RelayⅢ Relay Applications  3.1 Automotive Field  3.2 Household Appliance  3.3 Industrial Relays  3.4 Example Analysis: JYB-714 Liquid Level RelayⅣ Relay Selection RulesⅤ One Question Related to DC RelayⅥ Frequently Asked Questions about How Relay WorksⅠ Working PrincipleThe relay is generally composed of an iron core, coil, armature, contact reed and so on. As long as both ends of the coil having a voltage, a certain current will flow through the coil, which will produce electromagnetic effects. Under the action of the electromagnetic force, the armature will overcome the pull force of the return spring and attract to the core, thereby the movable contact and the static contact (normally opened terminal) are in the state of pull-in.Figure 1. Relay StructureWhen the coil is power-off, the electromagnetic attraction will disappear. The armature will move back to its original position under the reaction force of the spring, making the movable contact and the static contact (normally closed terminal) contract together. Under the actions of pull-in and release, achieve the purpose of conducting and cutting off in the circuit. 1.1 Operation Example: Relay as a SwitchThe following figure is the circuit diagram of the relay controlling the light. The relay has normally open contacts and normally closed contacts. The movable contact is a common terminal. This is a DC relay powered by a battery. When the coil of the relay is powered by a DC power supply, the coil with the iron core will generate the corresponding magnetic field to adsorb the armature, and the movable contact will move from the normally closed contact side to the normally open contact side, which is equal to the normally open contact being pulled in. We can see that the start/stop button, battery, and relay coil form a control loop. As long as this loop is closed, the current will flow through the coil and a magnetic field will be generated. The normally open contact, the lamp, and the control power supply (the other battery in the picture) form a loop. When the normally opened contact is closed, the loop is closed and the current will flow from the positive of control power supply to the bulb, passing through the closed normally opened contact to the negative pole, so that the light will on.Figure 2. A relay as a SwitchWhen the start/stop button disconnects, the coil has no current. So that the armature will not be attracted by the magnetic force, and will be reset by the spring. So that the other end of the moving contact will go from the normally opened contact to the normally closed contact. The circuit of the bulb is forcibly disconnected and does not turn on.Figure 3. Relay Controls a Light1.2 Working Principle of Different Relays1) Electromagnetic RelayIt works by using the suction force generated by the circuit in the input circuit between the electromagnet core and the armature.2) Solid State RelayElectronic components have their functions without mechanical moving parts, and the input and output are isolated.3) Temperature RelayIt will act when the outside temperature reaches a given value.4) Reed RelayUsing the reed action sealed in the tube, open, close, or switch the circuit with the function of the electric contact reed and the armature magnetic circuit.5) Time RelayWhen the input signal is added or removed, the output part needs to be delayed or time-limited before closing or opening its controlled circuit until the specified time.6) High-frequency Relay It is used to switch high-frequency and radiofrequency lines with minimal loss.7) Polarized RelayA polarized magnetic field and a control current are combined to act by the magnetic field generated by the control coil. Ⅱ What is the Function of a Relay?2.1 SummaryRelay is an automatic switching element with isolation function, which is widely used for remote control, telemetry, communication, automatic control, electronic equipment, etc. It is the most important control element in the circuits.Relays generally have a sensing mechanism (input part) that can reflect certain input variables (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light, etc.); there is a mechanism (input part) that can realize "switch on" and "switch off" to the controlled circuit. Between the input end and the output end of the relay, there is also an intermediate mechanism for coupling isolation of the input quantity, functional processing and driving the output part (driving part). As a control element, relays have the following functions:1) Expanding control rangeFor example, when the control signal of a multi-contact relay reaches a certain value, multiple circuits can be switched, disconnected, and connected at the same time from different forms of contact groups.2) AmplificationFor example, using a very small control quantity can control a large power circuit, such as sensitive relays, intermediate relays and so on.3) Integrated signalFor example, when multiple control signals are input to a multi-winding relay in a prescribed form, they will be relatively integrated to achieve a predetermined control effect.4) Automatic control, remote control, and monitoringFor example, the relay on the automatic device and other electrical appliances can form a program control circuit to realize automatic operation. 2.2 Types of RelayIntermediate RelayIt is the function of converting and transmitting the control signal. That is, its input signal is the power off/on the signal of the coil, and the output signal is the contact action of the intermediate relay. In essence, it belongs to one of the voltage relays and has the characteristics of multi-contacts (six pairs or even more). The contact can withstand a large current (rated current is 5A~10A), and its action is more sensitive (response time less than 0.05s). Voltage RelayIts main principle uses the voltage signal, and determines the action of the contact according to the coil voltage, in addition, the coil needs to be connected in parallel with the load during circuit design. The voltage relay can be divided into AC and DC type according to the coil voltage, and can be divided into overvoltage and Undervoltage according to the operating voltage. Therefore, their functions are also different. As for the overvoltage relay, when the coil voltage is within the rated value range, the armature will not make any pull-in action. On the contrary, the action will execute if the coil voltage is exceeded. The AC overvoltage relay plays the role of overvoltage protection in the circuit. When the coil voltage reaches or exceeds the rated value of the coil, the armature will make a pull-in action, and the coil voltage will be lower than the rated value. The Undervoltage relay mainly plays a role of Undervoltage protection in the circuit when the armature is released immediately. Current RelayIt works according to the current signal and determines the contact action according to the current of the coil. The current relay coil needs to be connected in series with the load when having the installation. According to the coil current, it can be divided into two types AC and DC. According to the action current, it can be divided into overcurrent and undercurrent types.Since the load current will pass through the coil when having overcurrent, the coil rated current (that is, the setting current) is usually chosen to be equal to the maximum load current. When the load current is not higher than the setting value, the armature will not act. On the contrary, if it exceeds, a pull-in action will occur. The main function of the overcurrent relay is to play overcurrent protection in the circuit, especially in some occasions where impulsive over-current occurs. Because it has a good protective effect.  The principle of the undercurrent relay is that when the current in the coil reaches or exceeds the operating current value, the armature will perform a pull-in action. On the contrary, the armature will be released immediately when the coil current is less than the operating current value. In a normal state, if the load current exceeds the working current of the coil, the armature will also perform pull-in. When the load current drops below the coil current, the armature will be released. Time RelayIt belongs to a relay that starts with the input signal (that is when the coil is powered on or off) and will output the signal (contact closed or disconnected) after a preset delay in advance. Time relays are generally used in relatively low voltage or current circuits to turn on and off higher voltage or current, just as an electric switch device in the circuit used for automatic control.Figure 4. Electrical Relay Symbol (SPST/SPDT/DPST/DPDT)Ⅲ Relay ApplicationsRelays are employed in a wide range of fields, and their environmental conditions and technical requirements vary greatly. What’s more, in the same application field there are different requirements. Here are some examples and a brief description.3.1 Automotive FieldThe automotive industry is increasingly using relays. The more common relays are: starting relays to start motors, horn relays, open circuit relay of motor or generator, regulating relays for charging voltage and current, flashing relays, control relays fro light brightness,control relays for air conditioning, and so on. The power supply in the car now mostly uses 12V, and the coil voltage is mostly set to be 12V. Due to the battery power supply, the voltage is unstable.  The environmental conditions are not good, for example, the suction voltage is less than 60VH (rated working voltage), and the overvoltage of the coil is required to 1.5VH. What’s more, the power consumption of the coil is relatively large, generally 1.6~2W, and the temperature rise is relatively high. Their environmental requirements are also quite harsh: the ambient temperature range is -40℃～100℃; the relay used in the engine box must be able to withstand the damage of sand, dust, water, salt, and oil; vibration and shock are undoubtedly affecting normal operation. 3.2 Household Appliance1) Air conditioning relays are mainly used to control compressor motors, fan motors and cooling pump motors to have control functions. Owing to the moment when the load starts, a large inrush current appears, which is about 6 times the full-load operating current. It takes a long time for the compressor motor to reach full speed (the power of the home appliance compressor motor is generally 1 to 3 horsepower, where the fan motor and cooling pump motor are 1/4 to 2 horsepower.), which is a serious threat to the relay contacts to eliminate as much as possible the contact bounce when the relay is sucked.  Because the relay is required to release fast, minimize contact bounce as much as possible. The safety requirements are also strict and must be recognized by a safety certification agency. For example, as for product environmental conditions, the ambient temperature requires -40 to 55℃, relative humidity up to 40%, 90RH, and have rainwater infiltration. Because weight and size are not important indicators, the relay is required to be robust and impact resistant.2) Relay used in washing machines, microwave ovens, electric heaters, etc. Relay contact load: the large load can reach 220V, 5000W heater (or 1 horsepower motor), and the small load can be as small as driving solenoids load, other relay coils load, indicator light load, etc. The expected life span of the relay is required to reach 5 to 10 years. That is to say, the electrical life of the relay is required to reach 105 times to 2×105 times. Ambient temperature: -40 to 55°C (85°C for microwave ovens and electric heaters); relative humidity 20 to 95%/RH. 3.3 Industrial RelaysIn industrial control, the main control function is completed by the universal AC relay. The relay is usually driven by a button or limit switch. It is also used in traffic signal controllers, temperature controllers, etc. The contacts of the relay can control solenoid valves, larger start motors, and indicator lights.  What’s more, the field of digital control has expanded the application of relays. Copy milling and coordinate boring are operated by data programming, and the signals are sent to the machine tool controller, memory unit and other logic elements to control 2 to 5 axes of the coordinate servo motor. With this mechanical control method, it is easy to control drilling machines, hexagonal lathes, ordinary lathes and automatic profiling machines.The digital control system requires the relay to have the ability to adapt to low-level signals, medium sensitivity, fast action and high switching reliability. The environmental conditions for the installation of industrial machinery must be considered. For instance, operating industrial machinery and surrounding equipment always transmit some shocks and vibrations to the control cabinet, and they also have the influence of splashing cutting coolant. So that these unfavorable environmental conditions must still be considered when selecting and designing relays. With strict safety requirements, high requirements are needed for electrical insulation, voltage resistance, and flame retardants. 3.4 Example Analysis: JYB-714 Liquid Level RelayLiquid level relay is a kind of relay that uses liquid level to control the circuit. To be specific, this is a relay with electronic circuits inside. Based on the conductivity of the liquid, when the liquid level reaches a certain height, the relay will act to cut off the power; when the liquid level is lower than a certain position, turn on the power to make the pump work.  To achieve the role of automated control, this control is composed of sensors and control actuators. According to the conductivity of water, but it is poor and cannot directly drive the relay. Therefore, there must be an electronic circuit to amplify the current to drive the relay to work. So the sensor of the liquid level controller is generally a wire. The line is divided into three types, high and low, and the middle line. The high is the water level overflow point to control the water level freely, in addition, the water will stop to fill in automatically. At the low water level, the low point is the automatic water filling point. Where the middle is constant contact.JYB-714 Liquid Level Relay①, ⑧ are the working power connecting terminals of the relay. ① is connected to L1, ⑧ is connected to N.②, ③, and ④ output the automatic control signal, and the working voltage of the output terminal is AC220V. ③ is the output signal common end, the level control signal of the water supply pump is output between ② and ③, and the drainage pump level control signal is output between ③ and ④.  ⑤, ⑥, ⑦ are the wiring terminals corresponding to the liquid level electrodes A, B, C in the pool.  ⑤ is connected to the high water level electrode A, ⑥ is connected to the low water level electrode B, and ⑦ connect to the lowest common electrode C. Note that in the experiment, the water inlet electrode uses a copper hard insulated wire of 1 to 1.5mm2, and the water inlet end is stripped of 5mm insulation. In addition, the safety voltage between the liquid level electrode terminals is DC24V. Tech Note1) Drainage type liquid level relay instructions"High" is the upper limit liquid level control point of the pool. When the water level rises to a high level, the water contacts the probe (electrode), and the controller automatically turns on the pump and starts to drain."Middle" is the lower limit liquid level control point of the pool. When the water level drops below the midpoint level, the water and the probe (electrode) are out of contact, and the controller automatically turns off the pump and stops draining."Low" is the ground line of the pool, the lowest point of the pool. 2) The difference between water-supply type liquid level relay and drainage-type liquid level relay:Water-supply type liquid level relay works in water shortage and stops when the water is full.The drainage-type relay works when water is full and stops in a water shortage.Figure 5. A RelayⅣ Relay Selection RulesTo use the relay well, the correct selection is very important. First of all, you must get a thorough understanding of characteristics and requirements of the controlled object, and have careful consideration. The principle, purpose, technical parameters, structural characteristics, specifications and models of the selected relays should be analyzed. On this basis, the relay should be correctly selected according to the actual situation and specific conditions of the project.1. The necessary conditions① The power supply voltage of the control circuit, the maximum current that can be provided.② Voltage and current in the controlled circuit. ③ Contact: When selecting a relay, on the one hand, you should consider whether the control circuit can provide enough working current, otherwise the pull-in of the relay is unstable. When the pull-in and release time of the relay cannot meet the requirements, the time constant of the coil loop can be changed to solve the problem. On the other hand, there is the elimination of electric sparks. Due to the small on-off current of the relay contacts, there will be no arc between the contacts, but "spark discharge" will occur. This is due to the presence of inductance in the contact circuit, and an overvoltage will appear on the inductance when it is disconnected. Together with power supply voltage on the contact gap, so that the contact gap will break down and discharge. Because of energy limitation, only spark discharge will generate. The alternating energy conversion between the capacitance and inductance existing between the contacts makes the spark looming and becoming a high-frequency signal. In addition, spark discharge will cause damage to the contacts, resulting in short service life. 2. After consulting the relevant materials to determine the conditions of use, you can find the relevant materials to find out the specific relay. If you already have a relay on hand, you can check whether it can be used according to the datasheet, and finally consider whether the size is appropriate. 3. Pay attention to the size of the appliance. If it is employed in general electrical appliances, in addition to the cabinet volume, small relays mainly consider the circuit board installation layout. For small electrical appliances, such as toys and remote control devices, ultra-small relay products should be used. 4. Rated load and service life are reference values, which will vary greatly according to different environmental factors, load properties and types. So it is better to confirm in actual or simulate actual use. 5. Try to use rectangular wave control for DC relays, and use sine wave control for AC relays. 6. In order to maintain the performance of the relay, please be careful not to drop the relay or subject it to strong shocks. 7. Do not use the relay in an environment with much dust and harmful gas. Harmful gases include gas containing sulfur, silicon, nitrogen oxides, etc. 8. As for the magnetic latching relay, it should be placed in the action or reset position as needed before use. 9. For polarized relays, please pay attention to the polarity of the coil voltage. 10. The relay is a heat-resistant component. High temperature can speed up the aging of the internal plastic and insulating materials of the relay. Contacts are oxidized and corroded, making it difficult to extinguish the arc. The technical parameters of the electrical components decay and the reliability reduces. So that good ventilation conditions should be maintained.And meanwhile, the low temperature cannot be ignored. Low temperature can aggravate the cold adhesion of the contacts and expose the contact surface. Many manufacturers’ relays indicate that the minimum temperature is -25°C, but high-voltage switches are also used in extreme cold. So it is recommended to leave the room when selecting the model to avoid the relay being unreliable due to low temperature. If circumstances permit, add heaters in the high cold area to ensure that the relay operates reliably and ensure the stability of the entire system. 11. Under the condition of low air pressure, the heat dissipation condition of the relay goes bad,  and the temperature of the coil rises, which changes the given pull-in and release parameters of the relay, affecting the normal operation of the relay. The low air pressure can also reduce the insulation resistance of the relay. It is difficult to extinguish the arc and is easy to melt the contacts and affect the reliability of the relay. It can be used normally at an altitude of fewer than 2000 meters, and it needs capacitance derated used at an altitude of more than 2000 meters. 12. Reduce the impact of mechanical stress on the relay. Mechanical force mainly refers to stress such as vibration, impact, and collision on the control system. The self-vibration of the circuit breaker in the high-voltage switch and the vibration caused by the opening and closing operations has a greater impact on the relay. An intermediate relay with a balanced armature mechanism should be selected. Electromagnetic relays have cantilevered beam structure, the natural frequency is low, oscillation and impact will cause resonance, resulting in the relay contact pressure to drop and contact instant disconnection or contact vibration, which will affect the reliability of the relay. It suggests that vibration measures should be taken to prevent resonance. Ⅴ One Question Related to DC Relay5.1 QuestionHow Does a DC relay work?5.2 AnswerA DC relay uses a single coil of wire wound around the iron core to make the electromagnet. When the DC coil is energized, the magnetism generated in the core is steady because the DC just keeps going. The steady magnetism keeps the lever attracted as long as the DC is flowing. Ⅵ Frequently Asked Questions about How Relay Works1. What is a relay and how it works?A relay is an electrically operated switch. They commonly use an electromagnet (coil) to operate their internal mechanical switching mechanism (contacts). When a relay contact is open, this will switch power ON for a circuit when the coil is activated. 2. Why relay is used?The switch may have any number of contacts in multiple contact forms, such as making contacts, break contacts or combinations thereof. Relays are used where it is necessary to control a circuit by an independent low-power signal, or where several circuits must be controlled by one signal. 3. How do you know if a relay is working?The only tool required to check a relay is a multimeter. With the relay removed from the fuse box, the multimeter set to measure DC voltage and the switch in the cab activated, first check to see if there are 12 volts at the 85 positions in the fuse box where the relay plugs in (or wherever the relay is located). 4. What is the main function of the relay?Relays are electric switches that use electromagnetism to convert small electrical stimuli into larger currents. These conversions occur when electrical inputs activate electromagnets to either form or break existing circuits. 5. What is the difference between relay and switch?The main difference between Relay and Switch is that the Relay is an electrically operated switch and Switch is an electrical component that can break an electrical circuit. ... Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. 6. Are Relays AC or DC?A Dc relay coil has a resistance that limits the dc current. An AC coil relies on its impedance for governing the current. An AC relay will remain contact closed due to mechanical inertia and a little mechanical hysteresis and, the fact that an alternating north and south pole both attract the relay armature. 7. How a relay works in a car?Although there are various relay designs, the ones most commonly found in low voltage auto and marine applications are electro-mechanical relays that work by activating an electromagnet to pull a set of contacts to make or break a circuit. These are used extensively throughout vehicle electrical systems. 8. What happens when a relay fails?If the ignition relay shorts burns out or otherwise fails while the engine is operating it will cut off power to the fuel pump and ignition system. ... In some instances of a faulty relay the vehicle will be able to restart once the relay cools off, only to stall out once again after the relay overheats. 9. Does a relay need constant power?The answer to that one is No. Relays have a finite lifetime in terms of how many times they can open and close. And limit to how much current they can handle. But keeping a relay constantly energized does not wear it out. 10. Why is a relay better than a switch?Relays are a better choice for switching large currents (> 5A). Relays can switch many contacts at once. Disadvantages of relays: • Relays are bulkier than transistors for switching small currents. Relays cannot switch rapidly (except reed relays), transistors can switch many times per second. Recommended ReadingBasic Knowledge of Relay Electronics Tutorial with VideoThe Role of the Relay and Its Working PrincipleThe Types of Common Relay and How to Choose Relay?