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Ⅰ IntroductionComputer memory is used to store programs and data. The main function of memory is to read and write. For random access memory RAM, their main functions are to read and write, and for read-only memory ROM, the main function is only to read. In general, the memory can be a card,  a floppy disk, etc., they can be active or fixed, which used to access data.This Video Introduce How Memory Store Data and How CPU Access Them.Program is the basis of computer operation, and data is the object of computer operation. Regardless of whether it is a program or data, it is expressed in binary form in the memory, and is collectively referred to as information. In a computer, the memory capacity represents by byte (abbreviated as B) as the basic unit, a byte is composed of 8 binary bits. In addition to bytes, the storage capacity is expressed in KB, MB, GB, and TB (which may be referred to as K, M, G, and T, respectively. For example, 128MB may be referred to as 128M). Among them, 1KB=1024B, 1MB=1024KB, 1GB=1024MB, 1TB=1024GB.CatalogⅠ IntroductionⅡ How to Store and Access Data?Ⅲ What Computer Memory Do?3.1 Explain Computer Memory3.2 Binary Decoder3.3 Chip Select & BusⅣ Example: 8086 MicroprocessorⅤ Technology Improvement5.1 What is Direct Memory Access (DMA)?5.2 DMA Transfer Modes5.3 DMA Transfer Process5.4 DMA Advantages and DisadvantagesⅥ Questions Related to Computer Memory WorksⅡ How to Store and Access Data?Before you know how the electronic memory works, it is necessary to get a general idea of the normal computer operation.Turn on the computer.First, the computer loads data from ROM and executes a power-on self-test (POST) to ensure that all major components are working properly. As part of this test, fast read/write operations check all memory addresses to ensure that there are no errors in the memory chip by memory controller. Read-write operation means writing data to a certain bit and then reading from it.Second, the computer loads the basic input/output system (BIOS) from the ROM. The BIOS provides the most basic information about storage devices, boot order, security, automatic identification functions, and other basic items.The computer loads the operating system from the hard drive into the system RAM. Normally, as long as the computer is turned on, the critical part of the operating system is kept in RAM. This allows the CPU to immediately access the operating system, thereby enhancing the performance and functionality of the entire system.Third, when an application is opened, it will be loaded into RAM. To save RAM space, only the basic part of the app programs are loaded, and then load other parts as needed. After the application is loaded, all files that have been opened for use in the RAM. When saving files and closing applications, files will be written to the designated storage device, and then the loading will be cleared from the RAM. It should be noted a fact that, if the changed files are not saved to the permanent storage device before being erased, they will be lost.In the above operation, every time the content is loaded or opened, it is put into RAM. This only means that it has been put into the temporary storage area of computer so that the CPU can more easily access the information. The CPU requests the required data from the RAM, processes it, and then writes the new data back to the RAM with successive cycles. In most computers, data processing reached millions of times between the CPU and RAM per second.Ⅲ What Computer Memory Do?3.1 Explain Computer MemoryThe memory is composed of a storage body, an address decoder, a read-write control circuit, an address bus, and a data bus.A semiconductor memory is like a small drawer, and there are eight small grids in it. Each small grid is used to store charge. The charge is transferred in or discharged through the wire connected to it. It is easy to understand, if you think of a wire as a water pipe, and the electric charge in the small grid is like the water. Each small drawer in the memory is a place to store data, which we call a cell.Figure 1. Computer MemoryThere are many cells in a memory, and the lines are connected in parallel. When the charge is applied, the charge will fill all the cells. When the charge is released, the charge in each cell will be discharged. This is of course not what we want. To avoid it, the memory structure should be changed slightly. There is a control line on each cell. Which unit you want to put the data, a signal is given to the control line of this unit. Be specific, this control line is like a switch, the charge can flow freely when switch on, and there is no signal on the control line of other cells to affect each other. So as long as you control the control lines of different cells, you can write different data to each unit. In the same way, if you want to get data from a unit, you only need to turn on the corresponding control line. 3.2 Binary DecoderFigure 2. DecoderFirst, how to control the control lines of each unit is not easy. For example, there are 655,36 units in a 27,512 memory chip, and each wire has to led out. This integrated circuit must have more than 60,000 pins. Obviously, this is clumsy. At this time, a way of decoding is made. Let’s briefly introduce it: a line can represent 2 states, 2 lines can represent 4 states, etc. And so on, 16 lines can be represented for 65536 states. 3.3 Chip Select & BusNext to the last question, let us focus on another problem. Where did the eight wires connect with each cell come from? In general, there are connected from the computer, and they also connect with other parts except for a memory chip. In this case, a problem arises. Since these eight lines are not dedicated between the memory and the computer, if you always connect a unit to these eight lines, this may cause confusion . For example, the value in a memory unit is 0FFH, in other memory cell is 00H, it is hard to figure out the high level or low level which these lines represent. So we have to separate them. The method is, when external wires are connected to the pins of the integrated circuit, they are not directly connected to each unit, and a group of switches is added between chip and computer. If we really want to write data to this memory or read data from the memory, then just turn on the switch. This group of switches is selected by three leads: read control end, write control end and chip select end.To write data to the chip, first is selecting chip, then send out a write signal, and the switch is turn on, therefore, the data is written to the chip. If you want to read, first is selecting chip, then send the read signal, and the switch is closed, the data is sent out. In addition, the read and write signals should be connected to another memory. Since the chip select terminals are different, there is no conflict when having read or write operation. Many people still have a question, will these two chips be selected at the same time? As long as it is a well-designed system, it will not happen, because it is controlled by mathematical calculation, not a manual control. If there is a situation where two chips are selected at the same time, it may be a circuit failure.It can be seen from the above that the eight lines used to transfer data are not dedicated, but are shared by many components, so we call them the data bus. The other 16 address lines are also connected together, called the address bus. Ⅳ Example: 8086 MicroprocessorThe CPU is connected to the storage unit and the I/O interface circuit through an address bus, a data bus, and a control bus. So how does the CPU access a certain address in the memory? Next, we will use the 8086 microprocessor architecture as an example, because its structure is simple and easy to introduce.Figure 3. 8086 MicroprocessorIf the CPU wants to read and write memory data, there must be wires to connect them together. In a computer, this kind of wire is called a bus. If you disassemble the computer case, it is easy to see that there is a collection of wires. These wires send signals at the same time, and each wire is either high or low level. The bus is divided into address bus, data bus and control bus according to different functions. Taking the above diagram as an example, the CPU needs to read the information at address 3, which is roughly divided into the following steps:The CPU outputs the physical address 3 to the address line.The control line needs to select the corresponding storage device, and then inform the device that data will be read from it.The storage device will send data 8 to the data line.Figure 4. 8086 CPUFrom here we see that there is a bus connection between the CPU and the storage device. In fact, there is a bus inside the CPU. It connects different components, such as registers, operators, and controllers. But in the computer, the bit number of different buses is not necessarily the same. For example, the internal bus of the 8086 is 16-bit, the address bus is 20-bit, and the data bus is 16-bit.Another question, since the 8086 CPU is a 16-bit structure, how can it output a 20-bit physical address? In fact, it is very simple. The address adder solves this way: segment address (16 bits) x 16 + offset address (16 bits) = physical address (20 bits), such as B800H x 16 + 1111H = B9000H. If you are not familiar with hexadecimal, then we can use decimal to describe this calculation. For example, home, school, and library are on a straight line. The distance between them is as shown in the following figure. Show the distance of the library: the library is 200m away from home, which is actually its physical address. But now there are some limits. We can only communicate with our friends through paper slips. Unfortunately, we can only write 2 digits on the papers, and the number of paper is not limited, so we agreed on the rule: paper 1x10+paper 2 = physical address, for example, write 11 on the paper 1 and 90 on the paper 2, which means that the school is 110m away from home and the library is 90m away from the school. The maximum distance that these two pieces of paper can represent is 99x10+99=1089.The above mentioned is the concept of offset address of the segment address. Let's imagine that if the internal bus of the 8086 CPU is 20-bits, it can directly represent the physical address. Therefore, the concept of segment address is not critical here. What's more, the CPU hardware design will change in the future, and it may be completely different.What we should know is how the CPU reads information from memory, and how does the CPU know whether the read information is ordinary data or a program that needs to be executed? We know that there are many registers in the CPU (that is used to store information), it specifies 2 registers, called CS, IP (CS is used to store the segment address, IP is used to store the offset address). They represent the physical address of the current machine code that needs to be executed. During the execution of the code, the CPU will maintain the values of CS and IP. For example, for each execution of the machine code, IP will increase the corresponding value to point to the next instruction. By analogy, we can use other registers to represent the physical address of the data. Therefore, the binary information in the memory has no difference to the CPU. Distinguishing the program and the data depends on the register. Ⅴ Technology ImprovementWhether it is a PC card or the high-speed read-write disk in the storage system, we can not do data operation without the support of a hardware DMA.Figure 5. 8237 DMA Controller5.1 What is Direct Memory Access (DMA)?DMA refers to the interface technology that the external device directly exchanges data with the system memory without going through the CPU. It is a high-speed data transfer method that allows direct reading and writing of data between external devices and memory, neither through the CPU nor CPU intervention.To read the data of the peripherals into the memory or transfer the data of the memory to the peripherals, it is generally done through CPU control, such as CPU program query or interrupt mode. Using interrupts for data transfer can greatly increase the CPU utilization. But it has shortcomings. For a high-speed I/O device and the case of batch exchange of data, the DMA method can be used to solve the efficiency and speed problems. DMA directly exchanges data between peripherals and memory, so the speed of data transfer depends on the working speed of the memory and peripherals.The data transfer operation is performed under a "DMA controller". In addition to the CPU doing a little processing at the beginning and end, the CPU can execute other tasks during the transfer. In this way, the CPU and I/O are in parallel operation. Therefore, the efficiency of the computer system is greatly improved.Figure 6. DMA ControllerWhen realizing DMA transmission, the bus is directly controlled by the DMA controller. Therefore, there is a problem of bus control transfer. That is, before the DMA transfer, the CPU should hand over the bus control to the DMA controller, and after the transfer is done, the DMA controller should immediately return the bus control to the CPU. 5.2 DMA Transfer ModesPeripherals can directly access the memory through the DMA controller, and at the same time, the CPU can continue to execute programs. So how does the DMA controller and CPU use memory in the same time? The following three modes are generally used:(1) Burst mode: Stop the CPU access.(2) Cycle stealing mode: DMA return the control of buses to CPU after transfer of one word at a time.(3) Transparent mode: DMA and CPU access memory alternately. Burst ModeWhen the peripheral device requests to transfer a batch of data, the DMA controller sends a stop signal to the CPU, requesting the CPU to give up to use the address bus, data bus, and related control bus. After the DMA controller obtains the bus control right, it starts the data transfer. After a batch of data has been transferred, the DMA controller informs the CPU that it can use the memory and returns the bus control to it. Figure (a) is a time chart of this transmission method. Obviously, in this DMA transfer process, the CPU is basically in a non-working state or stands by.Advantage: It is suitable for group transmission of equipment requiring high data transmission rate.Disadvantages: In the internal access stage of the DMA controller, the memory performance is not fully utilized, that is to say, a considerable part of the memory work cycle is idle. This is because the interval between two data transmitted by a peripheral device is generally always greater than the memory storage period, even for high-speed I/O devices. For example, a floppy disk requires about 32us to read an 8-bit binary number, and the storage period of semiconductor memory is less than 0.5us, so many idle storage periods cannot be used by the CPU. Cycle Stealing ModeWhen the I/O device has no DMA request, the CPU accesses the memory as required by the program. Once the I/O device executes a DMA request, one or several memory cycles will be embezzled.The time sharing of this transmission mode is as follows:　1) At this time, the CPU does not need to access RAM, for example, the CPU is executing a multiplication instruction. Due to the long execution time of this instruction, there is no conflict between the I/O access and the CPU access, that is, the I/O device stealing one or two memory cycles has no effect on the CPU execution.2) When the I/O device accesses, so does the CPU, which creates an access violation. In this case, the I/O device takes first, because it has an access time requirement, the previous I /O data must be accessed before the next request arrives. Obviously, the I/O device steals one or two memory cycles, which means that the CPU has delayed the execution of the instruction. More specifically, inserting a DMA request during the CPU's execution of the in-access instruction embezzles one or two memory cycles. Compared with the method of stopping CPU access, cycle stealing not only achieves I/O transfer, but also utilizes the efficiency of memory and CPU greatly. It is a win-win  method. However, I/O device diversion has the process of applying for bus control, establishing line control, and returning bus control. Transferring a word takes one cycle for RAM, but it is generally 2-5 memory cycles for DMA controllers (depending on the delay of the logic line). Therefore, the method is suitable for the case where the read/write cycle of the I/O device is greater than the RAM storage cycle. Transparent ModeIf the CPU's work cycle is much longer than the memory access cycle, this method can make the highest efficiency of CPU and DMA access at the same time. Assuming that the CPU work cycle is 1.2μs and the memory access cycle is less than 0.6μs, then a CPU cycle can be divided into two sub-cycles, C1 and C2, where C1 is for DMA controller access and C2 is for CPU access.The time sharing of this transmission method is as follows: The following figure is the detailed time of DMA and CPU alternate accesses. C1 is dedicated to the DMA controller and C2 is dedicated to the CPU. This method does not require the bus usage right. It is allocated through C1 and C2. The CPU and the DMA controller each have their own control registers such as internal address registers, data registers, and read/write signals. In the C1 cycle, if the DMA controller has an access request, it can send signals such as address and data to the bus. In the C2 cycle, if the CPU has an access request, it also do the same process. In fact, for the bus, this is a multiplexer controlled by C1 and C2. This transfer of bus control power takes almost no time, so the efficiency of DMA transfer is very high.It is like transparent glass to the CPU, without any influence. Working in a transparent DMA mode, the CPU neither stops the main program running nor enters the stand-by state. It is an efficient working method, and the corresponding hardware logic is more complicated. 5.3 DMA Transfer ProcessFigure 7. DMA Working ProcessRequestThe CPU initializes the DMA controller and gives an operation command to the I/O interface, then the I/O interface issues a DMA request. ResponseThe DMA controller determines the priority and shielding of the DMA request, and makes a bus request to the bus adjudication logic. When the CPU executes the current bus cycle, the bus control can be released. At this time, the bus arbitration logic outputs a bus response, indicating that the DMA has responded, and notifies the I/O interface to take the DMA transfer through controller. TransferAfter the DMA controller obtains the bus control right, the CPU immediately stops s or only performs internal operations. The DMA controller outputs read and write commands to control the RAM and I/O interface directly. Under the control of the DMA controller, the data is directly transferred between the memory and the external device. In addition, it is necessary to provide the starting position and length of the data to be transferred. Rising an InterruptWhen the specified batch of data transfer is finished, the DMA controller releases the bus control right and sends an end signal to the I/O interface. When the I/O interface receives it, on the one hand, it stops the I/O device, on the other hand, it makes an interrupt request to the CPU. The CPU is free from the state of non-intervention, and performs a section to check the correctness of the DMA transfer operation code. Finally, the CPU will show the transfer result and carry out the original program.It can be seen that the DMA transfer method does not require the CPU to directly control the transfer, nor does it have the process of retaining and restoring the scene when having the interrupt process. Through the hardware, a direct path for data transfer is opened for the RAM and I/O devices, that is DMA. 5.4 DMA Advantages and DisadvantagesA:DMA reduces the clock cycle requires to read or write a patch of data, which improve the system operation efficiency.D:As a hardware device, running DMA control will increase cost.DMA can cause cache coherence problem. Ⅵ Questions Related to Computer Memory Works1. What is the purpose of computer memory?Computer random access memory (RAM) is one of the most important components in determining your system's performance. RAM gives applications a place to store and access data on a short-term basis. It stores the information your computer is actively using so that it can be accessed quickly. 2. What is the role of memory in a computer system?Computer memory or random access memory (RAM) is your system's short-term data storage; it stores the information your computer is actively using so that it can be accessed quickly. The more programs your system is running, the more memory you'll need. 3. Where is 8086 microprocessor used for?8086 Microprocessor is an enhanced version of 8085Microprocessor that was designed by Intel in 1976. It is a 16-bit Microprocessor having 20 address lines and16 data lines that provides up to 1MB storage. It consists of powerful instruction set, which provides operations like multiplication and division easily. 4. How does direct memory access DMA work?With DMA, the CPU first initiates the transfer, then it does other operations while the transfer is in progress, and it finally receives an interrupt from the DMA controller (DMAC) when the operation is done. ... DMA can also be used for "memory to memory" copying or moving of data within memory. 5. Why is DMA faster than CPU?The direct memory access or DMA mode of data transfer is faster amongst all the mode of data transfer . ... The device request the cpu through a DMA controller to hold its data ,address and control bus so that the device may transfer data directly to or from memory.

IntroductionThyristor, commonly known as silicon controlled rectifier(SCR), its normative term is reverse blocking three-terminal thyristor. Thyristors are high-power semiconductor devices that have both switching and rectifying functions, and are used in various circuits such as controllable rectification and frequency conversion, inverters, and non-contact switches. As long as it is provided with a weak point trigger signal, it can control the strong electric output. So it is a bridge for semiconductor devices to enter the field of strong electricity from the field of weak electricity. So far, thyristors are the most widely used semiconductor devices in the electronics industry. Despite the continuous emergence of various new semiconductor materials, 98% of semiconductor materials are still silicon materials, which are still the basis of the integrated circuit industry. It is widely used due to its small size, light weight, high power and long life.Intro to Thyristors: the SCRCatalogIntroductionⅠ Thyristor Basics1.1 Brief Introduction of Thyristor1.2 Working Principle of  ThyristorⅡ The Main Characteristics of Thyristors2.1 Basic Structure of Thyristor2.2 Volt-ampere Characteristics of Thyristors2.3 Static Characteristics of Thyristors2.4 Characteristic Equation of ThyristorⅢ The Main Parameters of Thyristor3.1 Main Parameters of Unidirectional Thyristors3.2 Main Parameters of TRIACⅣ Main Function of ThyristorⅠ Thyristor Basics1.1 Brief Introduction of ThyristorThyristor, also called silicon controlled rectifier, is an abbreviation of semiconductor thyristor. It is a high-current switching semiconductor device that uses small currents to control. There are two commonly used types: ordinary thyristors (also called unidirectional thyristors) and TRIAC(triode for alternating current). Because of its small size, light weight, high efficiency, long life, vibration resistance and because it is noiseless, easy to use, it has attracted great attention from domestic, foreign, industrial and agricultural production departments in a short period of time and has been widely used in various production equipment and household appliances. According to its working principle, it can be roughly divided into four categories: f— Rectification: change AC power into adjustable DC power. — Inverter: converts DC power to AC power with a certain frequency. — DC switch: used for DC loop switch or DC voltage regulation. — AC switch: used for AC loop switch or AC voltage regulation. According to its service objects, it can be used in industries, agriculture, national defense, transportation, mining, metallurgy, light industry, chemical industry and other departments.In performance, thyristors not only have unidirectional conductivity, but also have more valuable controllability than silicon rectifier elements (commonly known as "dead silicon"). It has only two states: on and off.Thyristors can control high-power electromechanical equipment with milliamp currents. If the frequency exceeds this value, the average switching current allowed to pass will decrease due to the significant increase in the switching losses of the components. At this time, the nominal current should be degraded.Thyristors have many advantages, such as: controlling high power with low power, power amplification multiples up to several hundred thousand times; extremely fast response, turn on and off in microseconds; non-contact operation, no spark, no noise; high efficiency, low cost and so on.Disadvantages of thyristors: poor static and dynamic overload capacity; easy to be misguided due to interference.The two types of thyristors, unidirectional thyristors and three-terminal TRIAC, are briefly introduced below.1.2 Working Principle of  Thyristora. Unidirectional ThyristorThe internal structure of the unidirectional thyristor is shown in figure 1 (a). It can be seen from figure 1 (a) that the unidirectional thyristor is composed of four layers semiconductors P1N1P2N2. There are three PN junctions in the middle: the junction J1, J2, and J3. The anode A is drawn from P1, the cathode K is drawn from N2, and the control electrode (or gate) G is drawn from the middle P2. The circuit symbol of the unidirectional thyristor is shown in figure 1 (b). Figure 1. Schematic Diagram and Circuit Symbol of Unidirectional ThyristorIn order to understand the working principle of the unidirectional thyristor, the unidirectional thyristor can be equivalently regarded as a combination of a PNP transistor T1 and an NPN transistor T2. The middle layer P2 and layer N1 are shared by two transistors. The anode A is equivalent to the emitter of T1, and the cathode K is equivalent to the emitter of T2, as shown in figure 2. Figure 2. Working Principle of Unidirectional ThyristorThe key to understanding how unidirectional thyristors work is to understand the role of the control electrode.(1) No voltage or reverse voltage is applied to the control electrodeWhen the control electrode is left floating or a reverse voltage is applied between the control electrode and the cathode, that is, UGK<0, there must be IG=0. If a reverse voltage is applied between the anode and the cathode, that is, UAK＜0. Due to J, and J2, the transmitting junctions of T1, T2, are both reverse biased and T1 and T2 are in the off state, at this time, the current flowing through the unidirectional thyristor is only the reverse saturation current of the J1 and J3, IA≈0, and the unidirectional thyristor is in the blocking state; if a forward voltage is applied between the anode and the cathode, that is, UAK>0, J2 is in a reverse biased state, because IG=0, T2 must be in the off state. and the current in the unidirectional thyristor is only the reverse of J2. At this time, the current in the unidirectional thyristor is just the reverse saturation current of J2, IA≈0, and the unidirectional thyristor is still in the blocking state. Therefore, when no voltage is applied to the control pole or reverse voltage is applied, IG = 0, the unidirectional thyristor is in a blocking state, and has positive and negative blocking capabilities.(2) Apply forward voltage to the control electrodeWhen a forward voltage is applied between the control electrode and the cathode, that is, UGK> 0, the emitter junction J3 of T2 is in a forward bias, and IG≠0. If a reverse voltage is applied between the anode and the cathode, that is, UAK <0, because the emission junction J1 of T1 is reverse biased and T1 is in the off state, the unidirectional thyristor is in the blocking state, IA≈0; If a forward voltage is applied between the anode and the cathode, that is, UAK> 0, because the emission junctions J1, J3 of T1, T2 are forward biased, and the collector junction J2 is reverse biased, T1, T2 will be in an amplified state. After IG is amplified by T2, the collector current of T2 is IC2 = β2IG. The collector current of T2 is the base current of T1, after being amplified by T1, the collector current of T1 is IC1 = β1β2IG. This current flows into the base of T2 for amplification, and in this cycle, a strong positive feedback is formed, which makes T1, T2 quickly enter the saturation state, and the unidirectional thyristor is in the on state. After the unidirectional thyristor is turned on, UAK, the value of the voltage between the anode and the cathode is very small, and the external power supply voltage is almost completely dropped on the load.(3) Turn-off of the unidirectional thyristorFrom the above analysis, it can be seen that after the unidirectional thyristor is turned on, the base of T2 always has the collector current IC1 of T1 flowing, and the value of IC1 is much larger than the IG applied at the beginning. So even if the control electrode voltage disappears and IG = 0, it can still rely on the positive feedback of the tube itself to maintain conduction. Therefore, once the unidirectional thyristor is turned on, the control electrode will lose the function of controlling. After the unidirectional thyristor is turned on, if you want it to turn off again, the anode current IA must be reduced so that it cannot maintain positive feedback. To this end, the anode can be disconnected or a reverse voltage can be applied between the anode and the cathode.To sum up, under the condition that a forward voltage is applied between the anode and the cathode of the unidirectional thyristor, if a forward voltage is added between the control electrode and the cathode at a certain time, the unidirectional thyristor will change from the blocking state to the conducting state. This is triggered into conduction. After the unidirectional thyristor is turned on, the control electrode will lose the function of controlling. If you want to turn off the unidirectional thyristor again, you must make its anode current less than a certain value IH (called the holding current) or reduce the voltage UAK between anode and cathode to zero. b. TRIACA TRIAC is a three-terminal element with a five-layer structure of N1P1N2P2N3. It has three electrodes: a main electrode A1, a main electrode A2, and a control electrode (or gate) G. It is also a gate control switch. Regardless of its structure or characteristics, it can be regarded as a pair of anti-parallel ordinary thyristors. Its structure, equivalent circuit and symbols are shown in figure 3. Figure 3. Symbol, Structure and Equivalent Circuit of the TRIACThe main electrodes A2 and A1 of the triac are connected in series with the control object (load) RL, which is equivalent to a non-contact switch. The "on" or "off" of this switch is controlled by a signal uG (called a trigger signal) on the control electrode G. When there is a voltage (u ≠ 0) between the main electrodes A2 and A1, the moment the trigger signal uG appears, it will be conductive between A2 and A1 of the TRIAC, which is equivalent to the closed state of the switch. And once it is turned on, even if uG disappears, it can be kept on until u = 0 or the current in the series circuit of the main electrode and the load is reduced to a certain value, then it is turned off. After the cutoff, it is equivalent to the off state of the switch. In this way, the small current signal on the control electrode can be used to control the large current in the main electrode circuit. Figure 4. Volt-ampere Characteristic Curve of TRIACGenerally speaking, regardless of the voltage polarity between the two main electrodes A2 and A1 of TRIAC, as long as a certain amplitude of positive and negative pulses is applied to the control electrode, it can be turned on. So i represents the current in the main electrode and u represents the voltage between A2 and A1. The functional relationship between the two (called the volt-ampere characteristic curve) is shown in figure 4. It can be seen from the curve that the TRIAC has basically the same symmetrical performance in the first quadrant and the third quadrant.According to the voltage u on the main electrode and the polarity of the trigger pulse voltage uG on the control electrode, combined with the volt-ampere characteristic curve, the TRIAC can be divided into four trigger modes, which are defined as follows:(1) I+trigger: In the first quadrant of the characteristic curve (A2 is positive), the control electrode is a positive trigger relative to A1.(2) I-trigger: In the first quadrant of the characteristic curve (A2 is positive), the control electrode is a negative trigger relative to A1.(3) Ⅲ+trigger: In the third quadrant of the characteristic curve (A2 is negative), the control electrode is a positive trigger relative to A1.(4) Ⅲ-trigger: In the third quadrant of the characteristic curve (A2 is negative), the control electrode is a negative trigger relative to A1.Among these four trigger modes, I+ and III- have higher sensitivity, and are two commonly used trigger modes.In the control circuit of the new type electric heating electric appliance, the trigger signal applied to the control electrode of TRIAC is output by a single chip microcomputer or an integrated circuit. Some output a continuous positive (or negative) voltage signal, and some output a series of zero-crossing trigger pulses synchronized with a 50Hz sinusoidal AC power supply. The former is called a potential trigger, while the latter is called a pulse trigger. Their waveforms are shown in figure 5 and figure 6, respectively. Figure 5. Figure 6. Ⅱ The Main Characteristics of Thyristors2.1 Basic Structure of ThyristorA thyristor (also known as semiconductor controlled rectifier) is a high-power semiconductor device with a four-layer structure (PNPN). It has three lead-out electrodes, namely anode (A), cathode (K) and gate (G). Its symbolic representation and device cross-section are shown in figure 7. Figure 7. Symbol Representation and Device Cross-sectionOrdinary thyristors bidirectionally diffuse P-type impurities (aluminum or boron) in an N-type silicon wafer to form a P1N1P2 structure, and then diffuse N-type impurities (phosphorus or antimony) to form a cathode in most regions of P2, and at the same time lead out a gate electrode on P2 and form an ohmic contact is formed in the P1 as the anode.2.2 Volt-ampere Characteristics of ThyristorsThe on and off states of the thyristor are determined by the anode voltage, anode current and gate current. Volt-ampere characteristic curves are usually used to describe the relationship between them, as shown in figure 8. Figure 8. Volt-ampere Characteristic Curve of ThyristorWhen the thyristor VAK applies a forward voltage, J1 and J3 are forward biased, and J2 is reverse biased. The applied voltage almost falls on J2, and J2 plays a role of blocking the current. With the increase of VAK, as long as VAK <VBO, the passing anode current IA is small, so this region is called a forward blocking state. When VAK increases beyond VBO, the anode current suddenly increases, and it will be in a low voltage and high current state at the moment the characteristic curve passes the negative resistance. The on-state current IT determined by the load flows through the thyristor, the device voltage drop is about 1V, and the state corresponding to the CD section of the characteristic curve is called the on-state. VBO and its corresponding IBO are usually referred to as forward breakover voltage and breakover current. After the thyristor is turned on, it can maintain the on-state by itself. The transition from the on-state to the off-state is usually controlled by an external circuit without using a gate signal, that is, the device can be turned off only when the current is below a certain threshold value called the holding current IH.When the thyristor is in the off-state (VAK <VBO), if the gate electrode is made positive with respect to the cathode and the gate electrode is supplied with current IG, the thyristor will breakover at a lower voltage. The breakover voltage VBO and the breakover current IBO are both functions of IG. The larger the IG, the smaller the VBO. As shown in figure 3, once the thyristor is turned on, the device is turned on even if the gate signal is removed.When the anode of the thyristor is negative with respect to the cathode, as long as VAK <VBO, IA is small and has nothing to do with IG. However, when the reverse voltage is large (VAK≈VBO), the reverse leakage current through the thyristor increases sharply, showing thyristor breakdown. Therefore, VBO is called the reverse breakover voltage and breakover current.2.3 Static Characteristics of ThyristorsThe thyristor has 3 PN junctions, and the characteristic curve can be divided into (0 ~ 1) blocking area, (1 ~ 2) breakover area, (2 ~ 3) negative resistance area and (3 ~ 4) conducting area. a. Forward Working Area— Forward blocking (0 ~ 1) areaWhen a forward voltage is applied between AK, J1 and J3 bear the forward voltage, while J2 bears the reverse voltage, and the applied voltage falls almost entirely on J2. The reverse-biased J2 acts to block the current, and the thyristor is not conducting at this time.— Avalanche area (1 ~ 2 is also called breakover area)When the applied voltage rises close to the avalanche breakdown voltage VBJ2 of J2, the width of the space charge region of the reverse-biased J2 expands, and the internal electric field is greatly enhanced, which causes the multiplication effect to be strengthened. As a result, the current through J2 suddenly increases, and the current flowing through the device also increases. At this time, the current passing through J2 is transformed from the original reverse current to the current which is mainly attenuated by J1 and J3 through the base region and multiplied in the space charge region of J2. This is the avalanche area where the voltage increases and the current increases sharply. Therefore, the characteristic curve turns in the area, so it is called the breakover area.— Load area (2 ~ 3)When the applied voltage is greater than the breakover voltage, a large number of electron-hole pairs generated by the avalanche doubling of the space charge region of J2 are extracted by the reverse electric field. The electrons enter the region N1 and the holes enter the region P2. Due to the inability to recombine quickly, carrier accumulation occurs near both sides of J2: holes in region P2 and electrons in region N1, compensating for the charge of the ionized impurities and narrowing the space charge region. As a result, the potential in region P2 increases and the potential in the region N1 decreases, which acts to offset the external electric field. As the applied voltage at J2 decreases, the avalanche multiplication effect also weakens. On the other hand, the forward voltage of J1 and J3 has been enhanced, and the injection has increased, causing the current through J2 to increase, so a negative resistance phenomenon has occurred in which the current increases and the voltage decreases.— Low resistance on-state region (3 ~ 4)As mentioned above, the multiplication effect causes the accumulation of electrons and holes on both sides of J2, causing the reverse bias voltage of J2 to decrease; at the same time, the injection of J1 and J3 is enhanced, and the circuit is increased, so that charges continue to accumulate on both sides of J2, and the junction voltage continues to decrease. When the voltage drops to the point where the avalanche multiplication stops and all the junction voltages are cancelled, holes and electrons still accumulate on both sides of J2, and J2 becomes forward biased. At this time, J1, J2, and J3 are all forward biased, and large currents can pass through the device  because it is in a low-resistance on-state region. When fully conducting, its volt-ampere characteristic is similar to that of a rectifier element.b. Reverse Working Area (0 ~ 5)When the device is operating in reverse, J1 and J3 are reverse biased. Due to the very low breakdown voltage of the heavily doped J3, J1 withstands almost all of the applied voltage. The volt-ampere characteristic of the device is the volt-ampere characteristic curve of the reverse bias diode. Therefore, the PNPN thyristor has a reverse blocking region, and when the voltage increases above the J1 breakdown voltage, the current increases sharply due to the avalanche multiplication effect, at which time the thyristor is broken down. 2.4 Characteristic Equation of ThyristorA two-terminal device of a PNPN four-layer structure can be regarded as P1N1P2 and N1P2N2 transistors with current amplification coefficients of α1 and α2, respectively, where J2 is a common collector junction. When a forward voltage is applied to the device, the forward-biased J1 injects holes and passes through region N1 to reach the collector junction (J2). The hole current is α1IA; while the forward-biased J3 injects electrons and passes through region P2. The current carried to J2 is α2IK. Because J2 is in the reverse direction, the current through J2 also includes its own reverse saturation current, ICO.The current through J2 is the sum of the above three, that is,（1）Assuming the emission efficiency γ1 = γ2 = 1, according to the principle of current continuity IJ2 = IA = IK, so formula (1) becomes:（2）The formula shows that when the forward voltage is less than the avalanche breakdown voltage VB of J2, the multiplication effect is small and the injection current is also small. So α1 and α2 are also very small, thus（3）The ICO at this time was also small. Therefore, J1 and J3 are forward biased, so increasing VAK can only increase the reverse bias of J2. It cannot increase the ICO and IA a lot, so the device is always in the blocking state, and the current flowing through the device is the same order of magnitude as the ICO. Therefore, formula (3) is called a blocking condition.When the increase in VAK causes the reverse bias of J2 to increase and avalanche multiplication occurs, assuming multiplication factor Mn = Mp = M, then ICO, α1, and α2 will all increase by M times, so (2) becomes（4）At this time, the denominator becomes smaller, and IA will increase rapidly with the growth of VAK, so when（5）The avalanche steady-state limit is reached (VAK = VBO), and the current will tend to infinity, so equation (5) is called the forward breakover condition., , Using this feature, the breakover point conditions are derived from the characteristic curve equation (4). Because α1 and α2 are functions of current, M is a function of VJ2, which can be approximated with M(VJ2)=M(VAK), ICO is a constant and derive  with respect to (4). The outcome is（6）Since the breakover voltage is lower than the breakdown voltage,  must be a constant value. Because , the numerator must also be zero and obtain （7）According to the definition of transistor DC voltage amplification factor,                      （8）We can get the small signal current amplification factor                      （9）Using formula (9), formula (7) can be changed to                        （10）That is, at the breakover point, the product of the multiplication factor and the sum of the small signal is exactly 1. As long as the PNPN structure satisfies the above formula, it has switching characteristics, that is, it can be switched from an off-state to an on-state.Because α changes with the current IE, when IA increases, both α1 and α2 increase. It can be seen that, when the current is large, the value of M satisfying (6) can be reduced instead. This shows that IA increases and VAK decreases accordingly.α is both a function name of the current and a function of the collector junction voltage. When the current increases as α is constant, the corresponding reverse bias of the collector junction decreases. When the current is large,                             （11）According to equation (2), J2 provides an on-state current (ICO <0). Therefore, J2 must be forward biased, so J1, J2, and J3 are all forward biased, and the device is conducting. The off-state of the device changes to the on-state. The key is that J2 junction must be changed from reverse-biased to forward-biased. The condition for J2 to reverse to the forward direction is that holes and electrons should accumulate in regions P2 and N1, respectively. The condition for the accumulation of holes in region P2 is that the amount of holes α1IA injected by the J1 and collected by J2 into region P2 is greater than the amount of holes that disappear by recombination with (1-α2) IK, that is                           （12）Since IA=IK, α1+α2＞1 is obtained. As long as the conditions are true, the hole accumulation in region P2 is the same, and the region electron accumulation condition is（13）Thus （14）It can be seen that when the condition of α1+α2＞1 is satisfied, the potential of region P2 is positive, and the potential of region N1 is negative. J2 becomes forward-biased and the device is in a conducting state, so α1+α2＞1 is called a conducting condition.Figure 9. SCR (Silicon Controlled Rectifier) Symbol Ⅲ The Main Parameters of Thyristor3.1 Main Parameters of Unidirectional ThyristorsIn order to correctly use a unidirectional thyristor, it is necessary not only to understand its working principle, but also to master its main parameters.(1) Forward repetitive peak voltage UFRMUnder the condition that the control electrode is disconnected and the unidirectional thyristor is in the forward blocking state, when the junction temperature of the unidirectional thyristor is the rated value, it is allowed 50 times per second, and the duration should not exceed 10 ms. The forward peak voltage that can be repeatedly applied to the unidirectional thyristor is called the forward repetitive peak voltage, which is expressed by UFRM. Generally, the secondary voltage is specified as 80% of the forward breakover voltage.(2) Reverse repetitive peak voltage URRMUnder the same conditions as the forward repetitive peak voltage, the reverse peak voltage that can be repeatedly applied to the unidirectional thyristor is called the reverse repetitive peak voltage, which is expressed by URRM and is generally 80% of the reverse breakover voltage.(3) Rated voltage UNUsually, the smaller one of UFRM and URRM is used as the rated voltage of the unidirectional thyristor. This is because the voltage added to the tube in practice is generally a positive and negative symmetrical voltage, so the voltage with a smaller value shall prevail. But because the transient over-voltage will also damage the tube, when selecting the tube, for safety reasons, the rated voltage of the tube is required to be greater than 2 to 3 times the actual peak voltage.(4) Rated forward average current IFThe average value of the power frequency sinusoidal half-wave current allowed to pass through the unidirectional thyristor under the ambient temperature of 40°C and specified heat dissipation conditions is called the rated forward average current IF. How many amp of the unidirectional thyristors we generally say refers to this current value. The amount of IF is related to factors such as the ambient temperature, heat dissipation conditions, and the conduction angle of the component. The rated current of the unidirectional thyristor is calibrated by the power frequency sinusoidal half-wave average current under certain conditions. This is because the load connected to the rectifier output often requires the average current to measure its performance. However, from the perspective of the unidirectional thyristor heating, regardless of the current waveform flowing through the unidirectional thyristor and the conduction angle of the unidirectional thyristor, as long as the effective value of the designed current is equal to the effective value of the rated current IF, then the heating of the unidirectional thyristor is equivalent and allowed.(5) Holding current IHAt room temperature, under the condition of the control electrode short circuit, the minimum anode current required to maintain the unidirectional thyristor to continue conducting is called the holding current IH. If the anode current of the unidirectional thyristor is less than this value, the unidirectional thyristor will change from the conducting state to the blocking state.(6) Control electrode trigger voltage UGK and trigger current IGAt room temperature, under the condition that the voltage between the anode and cathode of the unidirectional thyristor is 6V, the minimum DC current value of the control electrode required to change the unidirectional thyristor from the blocking state to the conducting state is called the trigger current IG. The DC voltage UGK between the control electrode and the cathode corresponding to the trigger current IG is called a trigger voltage. Generally, UGK is about 1 to 5V, and IG is tens to hundreds of mA.3.2 Main Parameters of TRIACIn various control circuits, the TRIAC is a relatively easy-to-damage component. Once the TRIAC is found to be damaged, you just need to replace the TRIAC with the same parameters. There are many characteristic parameters of TRIAC, and the following are the main parameters that should be considered during maintenance.— Off-state repetitive peak voltage-rated voltage VDRMWhen the control electrode is disconnected and the component is at the rated junction temperature, the voltage corresponding to the sharp bending point of the forward and reverse volt-ampere characteristics is called the off-state non-repeating peak voltage. 80% of it is called the off-state repetitive peak voltage. It is also called rated voltage, which is expressed by VDRM.When the TRIAC works, the peak value of the applied voltage momentarily exceeds the reverse non-repetitive peak voltage, which can cause permanent damage to the TRIAC. Moreover, due to the increase in ambient temperature or poor heat dissipation, the reverse non-repetitive peak voltage value may decrease. Therefore, when a TRIAC is selected, its rated voltage value should be 2 to 3 times the possible maximum voltage in actual operation. If the power supply voltage is 220V, a TRIAC with a rated voltage above 500V should be selected so that the selected components can withstand the surge voltage.— Rated on-state average current—rated current IT(AV)Under the specified conditions, the maximum average on-state current allowed when the TRIAC is on is called the rated on-state average current. According to the standard series of TRIAC, this current is taken to the corresponding current level, which is often referred to as the rated current for short and represented by IT(AV).Because the current overload capacity of the TRIAC is much smaller than that of ordinary motors and electrical appliances, the rated current of the TRIAC should be 1.5 to 2 times the maximum current in actual operation when selected.— Gate trigger current IGT (voltage UGT)This refers to the minimum trigger signal current (voltage) value that can make the TRIAC conduct reliably and add to the control electrode. If the trigger current (voltage) obtained by the TRIAC control electrode is less than the number of times, the TRIAC may not be turned on.— On-state average voltage UT(AV)Once the TRIAC is turned on, it is equivalent to the closed switch. Because the TRIAC is connected in series with the load, the smaller the voltage between the two main electrodes, the better. After the TRIAC is turned on, the average value of the voltage between the two main electrodes is called the on-state average voltage, which is usually referred to as the tube voltage drop. If the tube pressure drop of the TRIAC is too large, the motors and solenoid valves it controls may not work properly because they cannot get the full voltage.— Holding currentWhen the control electrode is disconnected at room temperature, the TRIAC is reduced from a large on-state current to a minimum main electrode current that is just necessary to maintain conduction, which is called a holding current. The TRIAC is turned off only when the main electrode current decreases below the holding current. Ⅳ Main Function of ThyristorThe functions of thyristors are as follows: first, converter rectification; second, voltage regulation; third, frequency conversion; fourth, switch (contactless switch). The most basic use of ordinary thyristors is controlled rectification. The diode rectifier circuit we are familiar with is an uncontrollable rectifier circuit. If the diode is replaced by a thyristor, it can constitute a controllable rectifier circuit, inverter, non-contact switch, achieve motor speed control, motor excitation, automatic control and so on. In electrical technology, the half cycle of alternating current is often defined as 180°, which is called the electrical angle. In this way, in each positive half cycle of U2, the electrical angle experienced from the beginning of the zero value to the moment when the trigger pulse arrives is called the control angle α; the electrical angle at which the thyristor conducts in each positive half cycle is called the conduction angle θ. Obviously, both α and θ are used to indicate the on or off range of the thyristor during the half cycle of the forward voltage. Controllable rectification is achieved by changing the control angle α or the conduction angle θ, and changing the average value UL of the pulsed DC voltage on the load. The function of a thyristor is not only rectification, it can also be used as a non-contact switch to quickly turn on or off the circuit, to achieve the inverter that converts DC power to AC power, to change AC power of one frequency to AC power of another frequency, etc. This article mainly introduces the basic principle, characteristics and main parameters of thyristors. Frequently Asked Questions about Thyristors (SCR)1. What are the characteristics of SCR?Characteristics of Thyristor or Characteristics of SCRReverse Blocking Mode of Thyristor. Initially for the reverse blocking mode of the thyristor, the cathode is made positive with respect to anode by supplying voltage E and the gate to cathode supply voltage Es is detached initially by keeping switch S open.Forward Blocking ModeForward Conduction Mode 2. Why SCR is called as thyristor?Silicon Controlled Rectifier (SCR) is a unidirectional semiconductor device made of silicon. This device is the solid state equivalent of thyratron and hence it is also referred to as thyristor or thyroid transistor. 3. Is SCR and thyristor are same?Thyristor is a 4 layer device formed by alternate combination of p and n type semiconductor materials. It is a device used for rectification and switching purpose. SCR is the mostly used member of thyristor family and it is the name commonly used when we talk about thyristors. 4. What is a thyristor used for?Thyristors are mainly used where high currents and voltages are involved, and are often used to control alternating currents, where the change of polarity of the current causes the device to switch off automatically, referred to as "zero cross" operation. 5. How does a SCR thyristor work?So how does it work? With no current flowing into the gate, the thyristor is switched off and no current flows between the anode and the cathode. When a current flows into the gate, it effectively flows into the base (input) of the lower (n-p-n) transistor, turning it on.

I OverviewValve regulated lead acid battery (VRLA battery) is generally divided into gel battery and AGM battery. Figure 1. Classification of VRLA BatteryGel battery is a valve regulated lead acid battery made by gel technology which not only refers to whether the battery contains gel electrolyte, but also includes the battery design ideas, structural characteristics, manufacturing technology and other technical measures to ensure the corresponding performance of the battery.Figure 2. Gel BatterySimilarly, for AGM battery, it also refers to valve regulated lead acid batteries manufactured by AGM technology. To hold the sulfuric acid in the battery with AGM separator is only one of the technical features of AGM battery.Figure 3. AGM BatteryBecause the two technologies are completely different, there is a great difference in performance between gel battery and AGM battery. In order to better understand the performance difference between gel battery and AGM battery, this article deeply discusses their differences in terms of battery design.Sealed Lead Acid Battery Recovery(The man in the vedio shows how to clean, open, refill, desulfate and test a totally dead sealed lead acid battery.)CatalogI OverviewII AGM vs. Gel Batteries: Electrolyte Fixation TechnologyIII AGM vs. Gel Batteries: ElectrolyteIV AGM vs. Gel Batteries: Polar Group4.1 AGM Battery has Excellent LargeCurrent Discharge Performance4.2 Make Full Use of Active Substances4.3 Conducive to the Transmission of Oxygen4.4 Prevent the Battery from Entering the Life Decline Period RrematurelyV AGM vs. Gel Batteries: Oxygen CycleVI AGM vs. Gel Batteries: CostVII ConclusionVIII AGM vs.Gel Batteries QuizII AGM vs. Gel Batteries: Electrolyte Fixation TechnologyBecause both gel battery and AGM battery adopt cathodic absorption maintenance-free technology based on internal oxygen cycle, there is no essential difference in maintenance-free technology, only in the way of fixing electrolyte.For the AGM battery, the AGM manufacturing technology is adopted, and the electrolyte in the battery, which is dilute sulfuric acid, can be held in the glass separator. The electrolyte is fixed by making use of the porosity of the glass separator, which has a strong adsorption, allowing the electrolyte to become immobilized. Its principle is similar to the principle of water absorbing sponge.Figure 4. Water Absorbing SpongeBecause dilute sulfuric acid is made of pure sulfuric acid and water, the density of pure sulfuric acid is 1.84g/cm3, and the density of pure water is 1.0g/cm3. In the backup battery, the storage battery is kept stationary for a long time. Due to the effect of gravity, the dilute sulfuric acid electrolyte will stratify, that is, the sulfuric acid density at the bottom is high, while the sulfuric acid density at the top is low. In high-type batteries, this delamination phenomenon is particularly evident. Therefore, in conventional batteries, the height of the battery generally does not exceed 400 mm.Figure 5. Delamination of ElectrolyteThe layering of the electrolyte will make the active material on the top of the electrode plate unable to release the capacity it should have because of insufficient acid, and it will be overcharged during charging. And the bottom will be difficult to charge because the sulfuric acid concentration is too high. At the same time, due to the delamination of the acid, concentration polarization back-EMF will also be generated in the upper and lower parts of the electrode plate, which ultimately reduces the operating voltage and capacity of the battery. Furthermore, excessively high sulfuric acid at the bottom will also accelerate the corrosion of the bottom grid and the sulfation of the plates, thereby shortening the battery life.For gel battery, it adopts gel manufacturing technology, and the electrolyte in the battery is fixed in the silicon gel. The fixation of the electrolyte is due to the silicone space network structure formed by the polymerization of gel gel particles to effectively fix the sulfuric acid electrolyte. The principle is similar to the use of jelly to fix the sulfuric acid electrolyte. In the space network, the silica gel is the skeleton supporting the entire network, and the sulfate ion can move freely at a certain level, which can ensure the smooth progress of the battery chemical reaction, that is, the smooth charge and discharge of the battery.Figure 6. Gel Battery ElectrolyteBecause the spatial network structure of silica gel is rich in a large number of silicon oxidation bonds, it can form hydrogen bonds with hydrogen in the sulfuric acid molecule. Due to this weak chemical action, the silica gel easily adsorbs and releases sulfuric acid molecules. Even if the electrolyte is not moved for a long time, due to the existence of this effect, it can basically offset the effect of gravity, so that the diluted sulfuric acid electrolyte is evenly distributed up and down, and it is not easy to cause delamination. Furthermore, the average pore size of the gel itself is about 100 times smaller than the average pore size of the AGM separator, and the comparative area of the gel itself is much larger than the specific surface area of the AGM separator. The small pores or micropores can be better keep sulfuric acid electrolyte. In the gel battery, since the electrolyte is not layered, the active materials on the upper and lower parts of the inner electrode plate of the battery can be fully utilized, so the battery has a long life span and can also be manufactured as a high-type battery.Figure 7. NO Delamination of ElectrolyteIII AGM vs. Gel Batteries: ElectrolyteThe AGM battery uses an AGM separator to fix the sulfuric acid electrolyte. In order to make the oxygen generated in the positive electrode in the later stage of charging easy to pass through the separator to the negative electrode and be absorbed by the negative electrode, a lean liquid design must be adopted to ensure the smooth progress of the internal oxygen cycle. The so-called lean electrolyte design takes the sponge's liquid absorption as an example. Under normal conditions, a sponge can be 100g of water. The actual design is only to allow the sponge to absorb 80~90g of water. This design is a lean electrolyte design. Therefore, the amount of sulfuric acid electrolyte in the AGM battery is relatively small. In lead-acid batteries, the sulfuric acid electrolyte is involved in the electrochemical reaction of the battery. In order to ensure the discharge performance of the battery (the amount of sulfuric acid needs to be sufficient), it can only be achieved by increasing the sulfuric acid concentration. Therefore, AGM batteries generally use higher density/concentration sulfuric acid.Due to the small amount of electrolyte in the AGM battery, the high concentration of sulfuric acid has a series of adverse effects on the battery itself. Since the amount of electrolyte in the AGM battery is relatively small and the heat capacity of the battery is also small, the AGM battery is sensitive to temperature. For batteries with the same capacity that can be fully charged, if the same amount of electricity is charged, the temperature rise of the AGM battery is significantly greater than that of the gel battery.For AGM batteries, due to the use of higher concentration of sulfuric acid, the grid corrosion is faster, and it is easier to produce inert lead sulfate, which makes the battery's charge acceptance worse, and the battery is more difficult to charge. That is, AGM batteries are more prone to early capacity decay. With the extension of battery life, the AGM battery continuously loses water due to overcharging, and the sulfuric acid concentration in the battery rises slowly, which is more serious. In batteries, the sulfuric acid saturation of the AGM separator is usually 95% to 85%. Compared with a fully saturated separator, when the saturation is 85%, the effective internal resistance of the battery increases by 90%. When the sulfuric acid saturation of the separator in the battery is less than 85%, the battery life will quickly end due to excessive tail current, lack of acid and excessive internal resistance. Therefore, for AGM batteries, the battery loses 10% of its water, and the life of the battery is reduced by more than 50%.Figure 8. Influence of AGM Battery Lean Liquid Design on Battery PerformanceThe development of the gel battery itself is based on the improvement of the flooded battery. Because the sulfuric acid electrolyte is fixed by silicon gel, the gas transmission inside the gel battery is completed through the channel formed by the cracks generated by the gel cracking. The amount of electrolyte does not affect the gas transmission channel. Therefore, there is no strict limit on the amount of electrolyte, and the liquid-rich design is usually adopted to ensure that the battery has better performance. Therefore, the amount of electrolyte in the gel battery is relatively large. For large-density batteries, the amount of rich liquid is about 20%, and for medium-density batteries, the amount of rich liquid is about 15%. Gel batteries generally use a lower concentration of acid than AGM batteries. At a lower acid density, the corrosion rate of the grid is lower, and the battery's charge acceptance is also significantly improved, thereby extending the battery's life span. Secondly, the gel battery has more electrolyte. The more electrolyte, the greater the heat capacity of the battery, so the gel battery is not very sensitive to temperature. The high temperature has relatively little effect on the performance and life span of the gel battery. In addition, due to the high voltage or maintenance operations such as equalizing or overcharging the battery during long-term use, the battery may lose water. The gel battery has more electrolyte and a small amount of water loss, which has little effect on the life of the battery. Therefore, the life span is longer and the battery stability is better.How a lead-acid battery works(The man in this vedio explains the essential principles of a lead-acid battery. )IV AGM vs. Gel Batteries: Polar Group In AGM batteries, the assembly compression ratio of the pole group has a very important impact on the battery performance and battery life.Appropriately increasing the pole group assembly pressure of the battery has the following benefits:4.1 AGM Battery has Excellent LargeCurrent Discharge PerformanceThe AGM battery adopts a tight assembly structure, so that the distance between the positive and negative plates is smaller, and the distance of ion conduction in the battery is shorter. Thereby reducing the internal resistance of the battery. Furthermore, with the tight assembly structure, the electrode plate and the separator maintain good contact, and the contact resistance between the separator and the electrode plate is also reduced. These make AGM batteries more conducive to large current discharge.4.2 Make Full Use of Active SubstancesBecause the AGM separator not only plays the role of isolating the positive and negative plates, but also plays the role of storing and maintaining the electrolyte. Adopting a tight assembly structure, the polar plate is close to the AGM separator, which allows the electrolyte to impregnate the entire polar plate, so that the active material is fully utilized, and the use capacity of the battery is increased.4.3 Conducive to the Transmission of OxygenWith a tight assembly structure, the polar plate is in close contact with the AGM separator, which is conducive to the smooth diffusion of oxygen through the separator to the negative electrode. Because the polar plate is under a large pressure, the AGM separator is compressed, and the micropores in the AGM separator perpendicular to the direction of the separator become larger, making oxygen easily penetrate the separator from the positive electrode to the negative electrode.On the other hand, because the AGM separator is compressed, the pores parallel to the direction of the separator plate become smaller, thereby suppressing the escape of oxygen generated in the positive electrode along the plane direction of the separator.4.4 Prevent the Battery from Entering the Life Decline Period RrematurelyTo prevent the battery from entering the life decline period prematurely, AGM separator has a strong liquid absorption performance and a high porosity. It is a separator made of hydrophilic glass fibers and does not contain a binder. The separator itself has poor strength. The material of the AGM separator is shown in Figure 9 below.Figure 9. Glass Fibers Put the AGM separator in boiling water for 1 hour, the AGM separator may disintegrate into pure glass fiber. If the AGM battery is loosely assembled, the escape of oxygen generated at the end of the battery charge may change the microstructure of the AGM separator, making the battery prone to early capacity decay. The tight assembly structure can effectively suppress the softening and shedding of the positive electrode active material, thereby greatly extending the life span of the AGM battery. Therefore, the AGM battery must adopt a tight assembly design. This structure not only makes the oxygen circulation in the battery more smoothly, but also ensures that the AGM battery has excellent large current discharge performance and better life span.In a gel battery, the viscosity of the gel electrolyte is much greater than that of dilute sulfuric acid, so if the assembly is too tight, it is not conducive to the gel electrolyte entering the pole group. Therefore, the assembly of the pole group is relatively loose. The separator used is usually a microporous plastic separator containing ribs to facilitate the gel electrolyte to enter the pole group and the inside of the separator. The separator of the gel battery mainly serves to isolate the positive and negative plates. The gel battery itself is developed on the basis of the rich liquid battery, and basically maintains the characteristics of the original rich liquid battery, and there is no strict requirement for the assembly pressure of the battery pole group. In the gel battery, due to the loose requirements for the assembly of the pole group, the distance between the positive and negative plates is relatively large, and the ion conduction distance in the battery is long, so the internal resistance of the gel battery is usually large, which is more suitable for medium current and small. When the current is discharged, the large current performance of the battery is relatively poor. V AGM vs. Gel Batteries: Oxygen Cycle In VRLA batteries, oxygen is transferred from the positive electrode to the negative electrode, where it is compounded. According to the principle of oxygen circulation, the recombination of oxygen at the negative electrode mainly occurs at this three-phase interface.There are two ways of oxygen transmission: one is vertical transmission, that is, the oxygen generated by the positive electrode first moves to the periphery of the pole group, and then reaches the negative electrode plate. The second is horizontal transmission, that is, the oxygen generated by the positive plate directly penetrates the separator to reach the negative electrode.In VRLA batteries, the gas channel that generates oxygen circulation not only occurs in the separator between the positive and negative plates, but also occurs in the outer space of the pole group. In AGM sealed batteries, the gas generated from the positive electrode needs to grow from small bubbles to larger bubbles at the end of charging or during the float charging process. As the bubbles continue to grow, they expand into the AGM separator, and the sulfuric acid electrolyte in the large pores in the separator is discharged to form a gas channel, and oxygen is transferred from the positive electrode to the negative electrode.Figure 10. VRLA BatteryTherefore, only when the oxygen pressure generated by the positive electrode reaches a certain level, a number of oxygen channels will be formed in the AGM separator. After the gas is transferred to the negative electrode, it is absorbed by the negative electrode, and the discharged sulfuric acid liquid will reoccupy the gas channel in the AGM separator until the bubbles generated on the surface of the positive electrode grow again to form a gas channel. Therefore, in the AGM battery, the gas passage from the positive electrode through the separator to the negative electrode may be unstable or discontinuous.In the AGM battery, due to the fact that after the sulfuric acid electrolyte is added to the separator, the assembly pressure is greatly reduced, and the surface of the electrode plate and the separator is uneven, so that there is always a relatively large gap between the electrode plate and the separator. The direct transmission of oxygen from the positive electrode to the negative electrode is difficult, so in AGM batteries, a considerable amount of oxygen is transferred vertically. Since the pore size of the polar plate is smaller than that of the AGM separator, more electrolyte is retained in the polar plate. The lead and negative electrodes on the side plates of the battery pole group are not covered with colloids, etc., and it is easy to form a three-phase interface of gas, liquid, and solid. In the AGM battery, the reaction between lead and anode and oxygen not only occurs on the surface between the positive and negative plates, but a considerable amount of oxygen circulation also occurs on the negative plates outside the pole group. The rapid recombination of oxygen on the side panel of the pole group also makes the total pressure of the gas chamber inside the battery lower than that of the gel battery. It is reported that stiffening strips on the inner wall of the battery tank can greatly increase the efficiency of oxygen circulation.Figure 11. AGM BatteryIn the study of the gel battery, it was found that in the gel battery, with the extension of the use time and the formation of micro-cracks in the colloid, the total gas chamber pressure in the gel battery is higher than the total gas chamber pressure of the AGM battery at equilibrium, vertical oxygen transmission in the direction is suppressed. In the gel battery, with the extension of use time, the silicone gel will dry crack, forming fine cracks, thereby forming a channel for oxygen to be transferred from the positive electrode to the negative electrode. In a gel battery in normal operation, since both the positive and negative plates are covered with gel, the oxygen compound reaction rate on the negative plate on the side of the pole group is extremely low. The compound reaction of oxygen on the negative electrode mainly occurs on the negative electrode plate corresponding to the positive electrode plate. That is, horizontal transmission is mainly used. Furthermore, in the gel battery, the electrolyte saturation has an important influence on the oxygen transmission mode. When the saturation is higher than 91.5%, the transmission mode is mainly vertical transmission; when the saturation is lower than 91.5%, mainly horizontal transmission. In the oxygen cycle of the gel battery, the transmission of oxygen in the vertical direction is slower than in the AGM battery; Compared with the AGM battery, the gel battery is more conducive to the horizontal transmission of oxygen. In the gel battery, since it is a gas channel formed by dry cracking of the gel, the gas transmission channel is basically stable. VI AGM vs. Gel Batteries: CostThe cost of gel batteries is higher than that of AGM batteries in terms of equipment, separators, and materials:First, the cost of equippment. In the production of gel batteries, not only the equipment for glue distribution but also the special equipment for glue filling is needed. Due to the use of gel electrolyte, the gelation phenomenon may occur due to the high viscosity of the gel electrolyte, so the production process control requirements are completely different from the production process of the AGM battery, the process is more complicated, and the technology is difficult to master.Second, the cost of separators. The gel battery uses a microporous plastic separator, which requires high porosity, good strength, and thin thickness. The cost of a high-quality microporous separator is relatively high. For AGM batteries, the separator is made of ultra-fine glass fiber, and the manufacturing process is relatively simple and the cost is low.Third, the cost of materials. The design margin of the electrolyte of the gel battery is generally larger. Not only does it increase the silicone gel material, it also requires more sulfuric acid electrolyte. The total weight of sulfuric acid electrolyte and silica gel is heavier and the material cost is higher.Therefore, the overall cost of the gel battery is high. As for AGM battery, the production process is relatively simple, the process is better controlled, and the battery is lighter, so the cost is lower than gel battery.Figure 12. AGM vs. Gel Batteries: CostVII ConclusionFrom the foregoing comparative analysis, it can be seen that AGM batteries and gel batteries are two types of batteries manufactured using different design ideas.For AGM batteries, AGM separators are used to fix the electrolyte, which is generally designed with a lean electrolyte and a tight assembly structure, which makes the battery lighter and has better large current discharge performance. Due to the low amount of acid, high-density sulfuric acid is required. The life span of AGM batteries is relatively short, and the manufacturing cost is relatively low.For the gel battery, it adopts a rich-liquid design, the amount of sulfuric acid electrolyte used is large, the density of sulfuric acid is relatively rare, the battery performance is more stable, the life span is longer, and the manufacturing cost is higher. VIII AGM vs.Gel Batteries QuizFigure 13. Quiz1. What is a gel battery?A gel battery (often referred to as a gel cell battery) is a lead-acid battery that is valve regulated. When the electrolyte is mixed with sulphuric acid and silica, it becomes a relatively stationary gel substance. 2. What is better AGM or gel battery?AGM batteries are comparably cheaper than Gel batteries, but they present a longer life span and offer bigger bursts of amps when needed. These batteries work best in high-power usage, such as sports vehicles. 3. What are the advantages of a gel battery?These types of batteries will operate effectively between an incredible -40 degrees Fahrenheit and 140 degrees Fahrenheit. Additionally, their gel make-up makes them better able to withstand corrosion, shock, and vibration. Slower discharging for a longer lifespan. 4. Is AGM a gel battery?AGM (Absorbed Glass Mat) and gel batteries are both examples of VRLA (Valve Regulated Lead-Acid) batteries. ... In common parlance, the term gel battery is used to indicate both AGM and Gel batteries. AGM batteries may also be called “membrane”, “starved electrolyte” or “dry” batteries. 5. Is an AGM battery worth the extra money?Definitely worth the price. The biggest perk is they hold their charge. You can charge it in the fall, come spring it's still 100% charged. I know mine has lasted quite a bit longer than my old lead batteries…that said, I never spent the money on lead then I now do on AGMS.

IntroductionThe 1N4007 is a general-purpose silicon rectifier diode, typically found in a plastic DO-41 axial package. It is widely used in various AC-to-DC rectifier circuits, bridge rectifier circuits, and general-purpose power supply applications. The 1N4007 utilizes the unidirectional conductivity of the P-N junction to convert alternating current into pulsed direct current. Due to its high reverse voltage rating (1000V) and low cost, it is one of the most popular components in electronics.Ⅰ 1N4007 Diode Specifications1.1 Rectifier Diode OverviewThe 1N4007 is a standard recovery rectifier diode. In low-power/low-current scenarios, the forward voltage (Vf) is typically around 0.7V to 0.8V. However, under its full rated load (1A), the forward voltage drop can reach up to 1.1V.Note on Frequency: The reverse recovery time (Trr) of the 1N4007 is in the microsecond (μs) range (typically 2μs to 30μs depending on conditions). This classifies it as a "slow" diode, meaning it is suitable for 50Hz/60Hz mains rectification but not suitable for high-frequency switching circuits (like high-frequency DC-DC converters), where Fast Recovery (FR) or Ultra-Fast (UF) diodes are required.Rectifier diodes make full use of unidirectional conductivity. They block the negative half-cycle of an AC waveform to convert it into a pulsating DC signal. To smooth this output, they are usually used in combination with a capacitor. The diode is connected in series, and the capacitor is connected in parallel to the load.Figure 1. 1N4007 Bridge Rectifier Circuit Example1.2 Nomenclature: What does 1N4007 mean?"1": Represents the number of junctions. In JEDEC nomenclature, "1" stands for a component with one P-N junction (a diode)."N": Stands for semiconductor device, registered with the EIA (Electronic Industries Alliance) / JEDEC."4007": The specific registration number indicating the device's electrical characteristics within the 1N400x series.1.3 1N4007 Pins and SymbolPINDescription1 (Marked with Band)Cathode (-)2 (Unmarked)Anode (+)1.4 1N4007 Basic Parameters (at 25°C)Type: Standard Recovery Silicon RectifierMax Average Forward Rectified Current (Io): 1.0 APeak Forward Surge Current (Ifsm): 30 A (for 8.3ms single half-sine-wave)Max Repetitive Peak Reverse Voltage (Vrrm): 1000 VMax DC Blocking Voltage: 1000 VMax Forward Voltage Drop (Vf): 1.1 V (at 1.0A current)Max Reverse Leakage Current (Ir): 5 μA (at rated DC blocking voltage)Typical Junction Capacitance (Cj): 15 pF (measured at 4V, 1MHz)Typical Thermal Resistance: 65 °C/W (Junction to Ambient)Operating Temperature Range: -55°C to +150°CFigure 2. Forward Current Derating Curve1.5 1N4007 FeaturesLow reverse leakage currentHigh surge current capability (up to 30A non-repetitive)RoHS compliant and available in Pb-Free packagesHigh-temperature soldering guaranteed: 260°C/10 seconds.Mechanical Data:Case: DO-41 Molded PlasticTerminals: Plated axial leads, solderable per MIL-STD-202Polarity: Color band denotes cathode endⅡ 1N4001-1N4007 Series ComparisonThe 1N400x series contains diodes that are physically identical and rated for the same current (1A). The only difference is the Maximum Repetitive Reverse Voltage (Vrrm). Because the 1N4007 has the highest voltage rating (1000V), it can replace any other diode in the series (1N4001 through 1N4006).ModelCurrent (A)Max Peak Reverse Voltage (V)Max RMS Voltage (V)1N4001150351N40021100701N400312001401N400414002801N400516004201N400618005601N400711000700Ⅲ Alternative Models & EquivalentsThe 1N4007 can often be replaced by higher-spec diodes.Higher Current: 1N5399 (1.5A) and 1N5408 (3.0A). Note: The 1N5408 has thicker leads and a larger body (DO-201AD) and may not fit all PCB holes designed for the 1N4007.Fast Recovery: If high-frequency performance is required, FR107 (Fast Recovery) or UF4007 (Ultra Fast) are excellent replacements. They share the same voltage/current ratings but switch off much faster.Schottky Diodes (Caution): While Schottky diodes like 1N5819 or 1N5818 have a lower forward voltage drop (higher efficiency), they usually have much lower reverse voltage ratings (often 20V-40V). Do not replace a 1N4007 with a Schottky diode in high-voltage circuits (like 110V/220V mains) or the diode will fail instantly. However, for low voltage (e.g., 12V) DC inputs, a Schottky like the SB1100 (100V) can be a more efficient substitute.ModelMax Reverse Voltage (V)Avg Rectified Current (A)Max Surge Current (A)Max Reverse Leakage (μA)1N4007100013051N539910001.55051N5408100032005FR10710001305 (Fast Recovery)Ⅳ 1N4007 vs. M7 (SMD Versions)When moving from Through-Hole Technology (THT) to Surface Mount Technology (SMT), the electrical equivalents of the 1N4007 are identified by different package codes.1N4007: This specifically refers to the DO-41 axial lead package (through-hole).M7: This is the SMA (DO-214AC) surface mount version of the 1N4007. It is electrically identical (1A, 1000V).A7: This is the SOD-123 surface mount version. It is smaller than the SMA package but carries similar specs (usually slightly lower thermal dissipation).SM4007: This generally refers to the MELF (DO-213AB) cylindrical surface mount package, though "SM4007" is sometimes used generically for any SMD version.Figure 3. DO-41 Package (1N4007)Summary: If you see a diode marked "M7" on a circuit board, it is a surface-mount 1N4007.Ⅴ 1N4007 Application Examples5.1 Solving Auxiliary Winding OvervoltageThe slow recovery characteristics of the 1N4007 can sometimes be advantageous over faster diodes in specific power supply applications.In Flyback power supplies, multi-output transformers can suffer from poor cross-regulation. A common issue is the VCC auxiliary winding voltage rising too high, triggering the IC's Over-Voltage Protection (OVP). This often happens because a fast diode (like the HER107) rectifies the high-frequency leakage inductance spike (the "ringing") at the leading edge of the waveform, rather than just the plateau voltage.Figure 4. IC Control CircuitSolution: By replacing the fast HER107 with a standard speed 1N4007, the slower turn-on time ignores the initial high-frequency spike. This effectively filters the peak voltage, lowering the average VCC voltage seen by the IC and preventing false OVP triggering.5.2 RCD Snubber EMI SuppressionIn RCD (Resistor-Capacitor-Diode) snubber circuits used to protect MOSFETs in Flyback converters, using a slow diode like the 1N4007 can help improve Electro-Magnetic Interference (EMI).Figure 5. RCD Absorption CircuitHow it works: A "fast" diode snaps off very quickly, which can induce high-frequency ringing. The 1N4007 takes longer to recover (reverse recovery). During this brief recovery period, a small amount of reverse current flows back. This "soft recovery" acts as a dampener, absorbing some of the oscillation energy and reducing the voltage stress and EMI radiation on the MOSFET drain.Trade-off: The downside is that the 1N4007 will generate more heat due to reverse recovery losses. This technique is generally suitable for lower-power adapters (<20W) where EMI is a priority and thermal overhead is available.Ⅵ FAQ1. What is a 1N4007 diode used for?It is a general-purpose rectifier diode used to convert AC to DC, prevent reverse polarity, and protect circuits from voltage spikes (flyback protection).2. What is the difference between 1N4001 and 1N4007?The only difference is the Peak Repetitive Reverse Voltage. The 1N4001 is rated for 50V, while the 1N4007 is rated for 1000V. 1N4007 can replace a 1N4001, but a 1N4001 cannot replace a 1N4007 in high-voltage circuits.3. Can I replace 1N4148 with 1N4007?Generally, No. The 1N4148 is a high-speed signal diode (very fast switching, low current). The 1N4007 is a power rectifier (slow switching, high current). • If you put a 1N4007 in a high-speed data circuit, it will be too slow and fail to work.• If you put a 1N4148 in a power circuit, it will likely burn out due to its lower current limit (200mA vs 1A).4. How much current can a 1N4007 diode handle?It can handle 1 Ampere of continuous rectified current. It can handle a non-repetitive surge of 30 Amperes (for less than 8.3ms), which is useful for inrush current at startup.5. What is the voltage drop of 1N4007?While often cited as 0.6V or 0.7V, under a full 1A load, the voltage drop is typically 0.9V to 1.1V.6. What is M7 diode?M7 is the surface-mount (SMD) code for the 1N4007 diode in an SMA package. It has the same electrical specs: 1A, 1000V. body { font-family: Arial, sans-serif; line-height: 1.6; color: #333; } h2 { color: #2c3e50; border-bottom: 2px solid #3598db; padding-bottom: 10px; margin-top: 30px; } h3 { color: #34495e; margin-top: 20px; } table { width: 100%; border-collapse: collapse; margin: 20px 0; } table, th, td { border: 1px solid #ddd; } th, td { padding: 12px; text-align: left; } th { background-color: #f2f2f2; } img { max-width: 100%; height: auto; display: block; margin: 20px auto; } .note { background-color: #f9f9f9; border-left: 6px solid #2196F3; padding: 10px; font-style: italic; } .warning { background-color: #fff3cd; border-left: 6px solid #ffc107; padding: 10px; }

CatalogⅠ Definition of Fuel Pump RelayⅡ Function of Fuel Pump Relay Ⅲ Application of Fuel Pump Relay in Vehicles  3.1 The working principle of automobile relay  3.2 The function of automobile relayⅣ The Location of Fuel Pump RelayⅤ Symptoms of a bad Fuel Pump RelayⅥ How to Replace the Fuel Pump Relay   6.1  Part 1: Removing the fuel pump relay  Step 1:  Step 2:  Step 3:  Step 4:  Step 5:  Step 6:  Step 7:  Step 8:  Step 9:  6.2 Part 2:  Installing the new fuel pump relay  6.3 Part 3: Checking for fuel pump relay operation  6.4 Part 4: Test drive the vehicleⅦ  Frequently Asked Questions about Fuel Pump Relay Failure Analysis Ⅰ Definition of Fuel Pump Relay As most people are familiar with, the fuel pump is a component inside the fuel tank that enables the combustion engine to run by providing pressure in the fuel lines to push gasoline to the combustion engine.  The fuel pump can fail for a variety of causes, one of which is a less well-known problem with the fuel pump relay. A fuel pump relay is a compact unit with many sprockets on one side that are clipped onto the ignition system and is covered in a plastic container. A gasoline pump relay is, in some ways, similar to an automotive fuse in that it is an electrical component. It controls the flow of current to the electric fuel pump, ensuring that the component receives enough power to function properly but not so much that it is damaged. Fuel pumps consume a lot of power, which may cause the electrical system and the pump to overheat  if  it weren't for the relay.Ⅱ Function of Fuel Pump RelayIn general, the relay acts as a power monitor for the fuel pump, activating it when the ignition is turned on and turning it off when the vehicle is turned off. When the ignition switch is turned to the on position for the first time, the fuel pump can be heard humming. This provides fuel to start the vehicle, and once the vehicle is running, the vehicle's computer sends a signal, and the fuel pump relay turns off. The fuel pump in the vehicle will now be powered by another source, typically the oil pressure sending unit.The vedio shows that how a fuel pump relay worksⅢ Application of Fuel Pump Relay in VehiclesAutomobile relays are composed of a magnetic circuit system, contact system, and restoration mechanism, as indispensable circuit components, such as automobile lights, air conditioners, electric seats, electric doors and windows, ABS devices, etc. have control relays. 3.1 The working principle of automobile relayThe electromagnetic relay applies the principle of electromagnetic induction. When the coil goes through the DC, the coil generates a magnetic field, and the moving iron is attracted to drive the contact reed, which separates the static contacts and closes the moving contacts. The iron core loses its magnetism when the electromagnetic coil current is switched off, the moving iron core is reset by the spring force, the moving contract is unfolded, and the static one is closed.The contact in the off position is a typically open contact, and the contact in the on position is a normally closed contact when the relay coil is not activated.  Between a normally open contact and a normally closed contact, there is a moving contact called a changeover contact. There can exist one or more ordinarily open contacts, normally closed contacts, and conversion contacts in the same relay.  In most electromagnetic relays, there is only one coil. A text sign is commonly used to identify the relay coil and its contacts, and each group of contacts is identified with a subscript, to illustrate the relay plainly and simply on the circuit.3.2 The function of automobile relayBy controlling the current of the low-voltage line, the current of the high-voltage line is controlled, and it acts as a current switch. The main function of the car is to start the motor rotation by controlling the large current by small current, thereby driving the rotor of the magneto inside the generator to rotate, giving the ignition Input the ignition pulse signal to make the ignition  generate electric sparks, ignite the mixed gas in the cylinder and do work. Relays belong to the switch category. It takes advantage of electromagnetic and electrical  and mechanical principles to close or open contacts to drive or control related circuits. A relay is a control device that is consisted of two parts: a controlled system (input loop) and a control system (output loop) (output loop). The output quantity changes abruptly from zero to a given value (or from a certain value to zero) when the input quantity (electricity, magnetism, light, heat, and other physical qualities) reaches a certain value, allowing the circuit to be controlled, protected, regulated, and transmitted.Ⅳ The Location of Fuel Pump RelayThe majority of fuel-pump relay units are found beneath the dashboard, near the steering wheel. In certain circumstances, the unit is positioned near the engine's firewall or in the location where the steering column is attached. The fuel pump relay's end is usually at the center of the floorboard, under the carpet in the front area of the passenger or driver's side footwell. The fuel pump relays can be found in a variety of locations depending on the vehicle. If you have your owner's manual (and if you don't, you can get a new one from owner Manual), check it and look at the schematic to see where the location is. This is not an accurate list, it is only for a few models of vehicle. But it contains the most common locations where I've found this component.  If you need to find the exact placement of the fuel pump relay quickly, consult your service manual.Figure1: the general location of fuel pump replay• Driver’s Side Kicker PanelNissan prefers to hide the fuel pump relay beneath a plastic cover near the brake or gas pedal, which is held in place by a couple of bolts. To get to the part, simply remove the bolts and the cover! •  Near The Fuse BoxI've seen it in the fuse box or very close to the fuses in numerous Mazdas and Toyotas. • Passenger Side Firewall Near DipstickThe pump relay is located behind the oil dipstick near the strut/shock housing on older Mitsubishis, particularly the Evolutions.Ⅴ Symptoms of a bad Fuel Pump Relay• Engine stallsAn engine that suddenly stalls is one of the most obvious signs of a problem with the fuel pump relay. If the fuel pump relay fails while the vehicle is in operation, the fuel pump will lose power, causing the engine to stall. A malfunctioning relay may allow the engine to be restarted after a short period of time, but a relay that has fully failed will not.• Engine does not startA non-starting engine is another indicator of a malfunctioning fuel pump relay. The gasoline pump will be left without electricity if the fuel pump relay fails. When the key is turned, the engine may still crank, but it will not start owing to a lack of fuel. This symptom could be caused by a variety of different problems, so having the vehicle professionally assessed is essential.• Loss of PowerIf the automobile suddenly loses power while driving or slows down for no apparent reason, the gasoline relay could be to blame. This does not necessarily imply that the vehicle will stall. For a short period of time, the vehicle will continue to run normally. However, if you encounter a sudden lack of power while driving, you should get your automobile inspected and repaired immediately, as there is always the possibility that the car will come to a halt again, leaving you stranded in the middle of the road.• No noise from the fuel pumpWhen the key is turned on, there is no noise from the fuel pump, which could indicate a problem with the fuel pump relay. Most fuel pumps emit a low-volume hum or whine that can be heard from inside the vehicle, or from outside the vehicle, near the fuel tank, if you listen carefully. If the fuel pump relay fails, power to the fuel pump is cut off, rendering out operation and, as a result, silent when the ignition is turned on. The gasoline pump relay is a relatively simple component, yet it is important to the vehicle's proper operation. If you notice any of the above symptoms or suspect that your fuel pump relay is failing, have your vehicle inspected by a professional to determine whether the component needs to be replaced. Ⅵ How to Replace the Fuel Pump Relay6.1  Part 1: Removing the fuel pump relayMaterials Needed• Needle nose plyers• Ratchet with metric and standard sockets• Wheel chocksStep 1: Turning on the ignition key ，wait for the gasoline pump to operate.Also, listen for any buzzing or clicking noises coming from the fuel pump relay.Figure2: listen  noise from the relayStep 2: Start the engine. Check that there is oil pressure.An oil light may be the lone signal on some automobiles. When the indicator light turns off, there will be oil pressure.Figure3: check the oil light on dashboard Step 3: Park your vehicle on a flat, hard surface.Make sure the transmission is in a park (for automatic transmissions) or first gear (for manual transmissions) (for manuals).Figure4: Parking your vehicleStep 4: Place wheel chocks around the tires.Because the rear of the car will be raised, the wheel chocks will be around the front tires in this situation.Engage the parking brake to lock the rear tires from moving.Figure5: Place wheel chocks around the tiresStep 5: Install a nine-volt battery saver into your cigarette lighter.This will keep your computer activated and your vehicle's settings current. It's fine if you don't have a nine-volt battery saver.Figure5: Install a nine-volt batteryStep 6: Open the vehicle’s hood to disconnect your battery.Remove the ground line from the negative post of the battery to turn off the power to the fuel pump and sending unit.Figure6: open your engine and disconnect your batteryStep 7: Look in the engine area for the fuse box. The fuse box's lid must be removed.Figure7: Find the fuel boxNote: Some fuse boxes are secured with hex screws or bolts and must be removed using a ratchet. Clips hold the other fuse boxes in place. Step 8: Locate the fuel pump relay using the diagram on the fuse box cover.Using the schematic on the fuse box cover, look for the fuse for the fuel pump relay when you open the fuse box. Figure8: Locate the fuel pump Step 9: Remove the fuel pump relay from the fuse box. Pay attention to how the relay comes out as the new one needs to go in the same way.If your fuse box cover doesn't have any schematics on it, you can look up the engine compartment fuse box diagram in your owner's handbook. The number adjacent to the fuel pump relay is usually stated in the owner's manual so you can discover the number on the fuse box.Note: You may need to use a pair of needle nose players to pull out the fuel pump relay.Figure9: Remove the fuel pump relay6.2 Part 2:  Installing the new fuel pump relayMaterials NeededReplacement of fuel pump relayStep1 Install relay. Install the relay into the fuse box the same way  the old relay was removed.Step2 Put on the fuse box cover. Snap it into place.Note: If you had to remove screws or bolts from the cover, make sure you put them back correctly. They will strip out if you tighten them over.Step3 Remove the fuel cap from the fuel tank.  Replace the gasoline cap and double-check that it seals properly. 6.3 Part 3: Checking for fuel pump relay operation Step1 Reattach the ground line to the negative post of the battery. Remove the cigarette lighter's nine-volt battery saver.Wait for the gasoline pump to turn on. Step2 Tighten the battery tightly. Ensure that the connection is good.Step3 Turn the ignition key on. Listen for the fuel pump to activate.When the fuel pump stops generating noise, turn off the ignition. Restart the engine and listen for a buzz or click from the fuel pump relay. To experience the buzz or clicking action, you may need to have another person touch the fuel pump relay.Note: Before starting the engine, turn the ignition key on and off three or four times to ensure the fuel rail is full of fuel.Step4 Start the engine by turning the key to start. During the cranking time, keep an eye on how long the start will be engaged.Note: Most modern vehicles will not start up until the oil pressure has built up.Step5 Wheel chocks should be removed from the wheels. Place these in a safe place. 6.4 Part 4: Test drive the vehicleStep1 Drive the auto around the block. During the test, listen for any unusual noise from the fuel pump or fuel pump relay.Also, immediately accelerate the engine to ensure that the fuel pump is working properly. Step2  Monitor the dash for any engine lights.If your engine light turns on after replacing the fuel pump relay, you may need to have the fuel pump assembly diagnosed or there could be an electrical problem with the fuel system. If the problem persists, you should contact one of Your Mechanic's qualified technicians, who will test the fuel pump relay and diagnose the issue.  Ⅶ  Frequently Asked Questions about Fuel Pump Relay Failure Analysis1. What causes a faulty fuel pump relay?A gasoline pump relay might fail due to dust, electrical power surges, and other issues. Dust and rapid voltage surges can degrade the performance of a fuel pump relay, causing an engine to fail. Passenger Side Firewall Near Dipstick. 2.  Will a fuel pump work without a relay?What is a Fuel Pump Relay, and What Does it do? A fuel pump relay is a plastic covered part connected to the fuel pump. It is one of the most important parts of your vehicle. Without the fuel pump relay, you won't even be able to drive your vehicle. 3. Can AutoZone test a fuel pump relay?AutoZone makes checking fuel pressure easier than ever. ... While testing does entail some work, few things are more rewarding than successfully troubleshooting your fuel pump relay. And with a fuel pressure test gauge from AutoZone, it's easy. 4.  How does a car act when the fuel pump is going out?You'll notice a decrease in fuel efficiency, acceleration and power in your vehicle if your fuel pump is damaged. The low pressure caused by a faulty fuel pump means your engine isn't getting the fuel and air mixture it needs to give your car that regular power. Whining in the backseat. 5.  How long does a fuel pump relay last?Over time, the fuel pump relay can begin to show signs of wear and will have to be replaced. The fuel pump relay is designed to last the life of the car, but due to the grueling conditions it is exposed to, it will not usually last that long. 6. Where is the fuel pump reset button?Look for the fuel pump switch or inertia switch. This is a small box with a plastic button on top and an electrical connector at the bottom. On some vehicle models, this will be located in the luggage compartment. Look on a side panel for a small, round button which you can pry off with a small screwdriver. 7. Will a car start with a bad fuel pump?If your vehicle's fuel pump cannot get gas from the tank to the engine, you will have trouble starting your car. The car will struggle to start and run because the pump cannot push enough gas through. A worn pump loses its pressure and the engine is being starved of gasoline. 8. What would cause a fuel pump not to get power?If you there is no power to the fuel pump or the relay, then there may be a possible electrical issue with the vehicle. ... If there is an issue with the switch or the circuit, perhaps a wiring problem, then power to the fuel system may be cut off. 9. Will a bad fuel pump give a code?Bad Fuel Pump, Fuel Pressure Sensor Can Trigger 'Check Engine' Light, P0087 Code. ... The light is part of your vehicle's on-board diagnostics (OBD) system and can indicate anything from a loose gas cap to a major repair like a catalytic converter. 

IntroductionLC circuit, also called passive filtering circuit, is commonly used for harmonic compensation, which does not require additional power supply. It is generally composed of capacitors, inductors and resistors. This kind of filtering circuit is easy to design, but its pass-band magnification and cut-off frequency vary with the load, which is not suitable for occasions with high signal processing requirements. Passive filtering circuits are usually used in power circuits, like DC power rectification, or large current loads.LC (Inductor-Capacitor) CircuitsCatalogIntroductionⅠ LC Circuit TypesⅡ LC Circuit CharacteristicsⅢ LC Circuit Working FeaturesⅣ LC Circuit FunctionsⅤ LC Circuit CalculationⅠ LC Circuit TypesCommonly used filter circuits include passive filter and active filter. If the circuit are only composed of passive components (resistors, capacitors, inductors), it is called a passive filter circuit. The main forms of passive filtering are capacitive filtering, inductive filtering and compound filtering (including inverted L-type, LC-type , LC-π type and RC-π type, etc.). The filter circuit is not only composed of passive components, but also composed of active components (bipolar tubes, unipolar tubes, integrated operational amplifiers), which is called an active filter circuit, and its main form is active RC(resistor-capacitor) circuit.The LC circuit has advantages of simple structure, high reliability, and wide range of applications. Its main feature is that the resistance of the inductor is small, and the DC loss is small. What’s more, the inductance in LC circuit to alternating current is large, so that the filtering effect is good.LC circuits are divided into LC low-pass filters, LC band-pass filters, high-pass filters, LC all-pass filters, and LC band-stop filters according to their functions. According to tuning, they are further divided into single-tuned filters, double-tuned filters and three-tuned filters and so on. The LC filter design process mainly considers its resonant frequency, capacitor withstand voltage, and inductor withstand current. In addition, it is necessary to pay attention to that passive LC circuits are not easy to integrate.  Ⅱ LC Circuit CharacteristicsThe LC circuit is generally formed by a proper combination of inductors, capacitors and resistors, and parallel with the harmonic source. It not only for filtering, but also takes into account the role of compensation.Figure 1. LC Circuit TypesThe following are the characteristics of several LC circuits:1) The load impedance of the L-type filter is high, and the source impedance is low.2) The load impedance of the inverted L filter is low, and the source impedance is high.3) The load impedance of the T-type filter is low, and the source impedance is low.4) The load impedance of the Π filter is high, and the source impedance is high.In actual use, these features are generally followed. In practice, impedance is difficult to estimate, especially in high frequency bands. Due to parasitic parameters, the circuit impedance changes greatly, and the circuit impedance is also related to the working state of the circuit, so the debugging shall prevail in practice. Ⅲ LC Circuit Working FeaturesAccording to the different impedance of reactive components to AC and DC, the basic form of the LC circuit composed of capacitor C and inductance L is shown in the figure. Because the capacitor C is open to DC and has a small impedance to AC, C is connected in parallel at both ends of the load, while the inductor L has a small impedance to DC and a large impedance to AC, so L should be connected in series with the load.In electronic circuits, the inductor coil acts on the finite current of the alternating current. From the inductance formula XL=2πfL, it can be known that the larger the inductance L, the higher the frequency f, and the larger the inductive reactance. We already know that capacitors have the ability to "block DC and pass AC", while inductors have the function of "pass DC, block AC, pass low frequencies, and block high frequencies". If the direct current accompanied by many interference signals is passed through the LC filter circuit, most of the AC interference signals will be prevented by the inductance from being absorbed and turned into magnetic induction and thermal energy, and most of the rest will be bypassed to the ground by the capacitor, which can suppress the interference. So a relatively pure DC current at the output is getting.The inductance of the power supply on PCB is generally made of a very thick enameled wire wrapped around a round magnetic core coated with various colors. In addition, there are usually several tall filter aluminum electrolytic capacitors nearby, which is a classic LC filter circuit. In addition, PCB also uses a large number of snake-type lines and chip tantalum capacitors to form an LC circuit. Few people notice, when design LC circuit, the snake line folds back and forth on the circuit board, which can also be regarded as a small inductance.In short, the principle of the LC filter circuit is actually a combination of the basic characteristics of the L and C components. Because the capacitive reactance of the capacitor xc=2nfc will decrease as the signal frequency increases, and the inductance of the inductor xl=2f will increase as the signal frequency increases. If the capacitors and inductors are connected in series, parallel or mixed together, the impedance of their combination will also vary greatly depending on the frequency of the signal. This shows that different filter circuits will present a small or large reactance to a certain frequency signal, so that it can pass or block the frequency signal. Thereby filter circuit plays a role in selecting a certain frequency signal and filtering out a certain frequency signal.Figure 2. LC Resonating CircuitsⅣ LC Circuit Functions1) LC circuit can be used as a filter circuit used in some power supplies. If the DC power with many interference signals is passed through the LC filter circuit, most of the AC interference signals will be blocked by the inductance and become magnetic induction and thermal energy. Most of them are bypassed to ground by capacitors, which can suppress the effect of interference signals and obtain relatively pure DC current output.2) Have oscillation effect, or sometimes generate a clock signal for the single-chip microcomputer (some have an external clock signal). 3) It can also be used as a frequency selection circuit, or a transmitting oscillation circuit (but it must be a circuit that can send and receive signals), and it also serves for the generation of input signals from other circuits.4) Since the output voltage of the rectifier circuit is not all pure DC, the output of the rectifier circuit observed from an oscilloscope is very different from the DC, and the waveform contains a large pulsating component, which is called ripple. In order to obtain the ideal DC voltage, it is necessary to use an LC circuit composed of reactive components (such as capacitors and inductors) with energy storage function to filter out the pulsating elements of output voltage.Ⅴ LC Circuit Calculation1) The voltage of the RC tank capacitor is:Voltage=U*exp(-t/rc)U represents the initial value of the voltage, rc represents the resistance and capacitance, t is the elapsed time, and exp (-t/rc) represents the -t/rc power of e.Time constant τ=rcNamely the product of capacitance and resistance, voltage = U*exp(-t/τ) after introducing the time constantTherefore, the voltage change with zero input response is an exponential decay process, theoretically infinite time, but generally it is considered that the decay is over after 3 to 5 time constants.Therefore, the discharge time depends on the time constant τ=rc2) For the LC oscillating circuit, it is related to the product of the LC circuit.Specifically, for the general LRC loop,R>2*sqr (L/R)R=2*sqr(L/R)R>2*sqr (L/R)sqr (X) represents the root sign (X)Divided into three situations, roughly speaking, the discharge time depends on the value of R, L, C in the circuit, U is not equal to 0 and I = 0, the capacitor discharges through L, RTwo eigenvalues can be obtained by solving second-order partial differential equations such as:p1=-(R/2L)+spr[(R/2L)*(R/2L)-1/LC]p1=-(R/2L)-spr[(R/2L)*(R/2L)-1/LC]Capacitor voltage=[U/(p2-p1)]*[p2exp(p1*t)-p1exp(p2*t)]Based on this, the relationship between capacitor discharge time and LRC can be analyzed. Frequently Asked Questions about LC Circuit1. What is meant by LC circuit?An LC circuit is a circuit that uses the elements inductor (L) and capacitor ( C). This circuit is also referred as resonating circuit, tank circuit, or tuned circuit. 2. What does an LC circuit do?LC circuits are used either for generating signals at a particular frequency, or picking out a signal at a particular frequency from a more complex signal; this function is called a bandpass filter. 3. Where are LC circuits used?The LC circuit is used to select or generate a specific frequency signal. The application of LC circuits is reflected in many electronic devices, especially radio devices, such as transmitters, radio receivers and television receivers, amplifiers, oscillators, filters, tuners and frequency mixers. 4. What are the properties of LC circuit?An LC circuit is a closed loop with just two elements: a capacitor and an inductor. It has a resonance property like mechanical systems such as a pendulum or a mass on a spring: there is a special frequency that it likes to oscillate at, and therefore responds strongly to. 5. What is LC in LC oscillation?LC oscillations- The electric current and the charge on the capacitor in the circuit undergo electrical LC oscillations when a charged capacitor is connected to an inductor. The electrical energy stored in the capacitor is its initial charge which is named as q_m.