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IntroductionWhat is the difference between a three-phase AC motor and a single-phase AC motor? If you pay attention to it, you will find that single-phase AC motors have more equipment than three-phase AC motors, which is the start capacitor (starting capacitor). The most common one is in various household appliances. Almost all household appliances with motors are equipped with start capacitors. This article will start with the explanation of the principle of the motor start capacitor, and then describe in detail the failure phenomena, causes and test methods of the start capacitors in the two common home appliances, air conditioners and fans. In addition, the article will also explain some basic questions about start/run capacitors. If you want to learn the related knowledge of motor start capacitors, this article must be worthy of your reading.How to test a RUN or START CAPACITOR the CORRECT wayCatalogIntroductionCatalogI The Principle and Causes of Damage of Start Capacitor 1.1 How Does the Motor Work? 1.2 How Does the Start Capacitor Work? 1.3 Reasons for the Burning of the Start CapacitorII Troubleshooting of Start Capacitor in Air Conditioner 2.1 Functional Characteristics of Start Capacitor 2.2 How to Quickly Figure out Whether the Start Capacitor is Damaged 2.3 Why is the Start Capacitor of the Air Conditioner Outdoor Unit Easy to Damage? 2.4 Symptoms and Test MethodsIII How Test the Motor Start Capacitor of a Fan?IV Relevant Knowledge in the Step of Start Capacitor Test 4.1 How to Choose Start Capacitor? 4.2 Precautions for Replacing the Start CapacitorV How to Test the Motor Start Capacitor without a MultimeterVI Frequently Asked Questions about Start Capacitors 6.1 Which Motors are Served by the Start Capacitor? 6.2 Why Does a Three-phase Motor do not Need a Start Capacitor? 6.3 The Relationship Between Start Capacitors and Motor 6.4 What are the Functions of Start Capacitors, Run Capacitors, and Centrifugal Switches in Single-phase Motors?VII QuizⅧ FAQI The Principle and Causes of Damage of Start Capacitor1.1 How Does the Motor Work?The single-phase current flowing through a single-phase motor cannot generate a rotating magnetic field, and a capacitor is needed to separate the phases. The purpose is to make the current in the two windings produce a phase difference of nearly 90 ゜ to generate a rotating magnetic field. The capacitive induction motor has two windings, namely the starting winding and the running winding. The two windings are 90 degrees apart in space. A large-capacity capacitor is connected in series to the starting winding. When the running winding and the starting winding pass single-phase alternating current, the current in the starting winding is 90 degrees ahead of the current in the running winding due to the action of the capacitor, thus reaching the maximum value first. Two identical pulsed magnetic fields are formed in time and space so that a rotating magnetic field is generated in the air gap between the stator and the rotor. Under the action of the rotating magnetic field, an induced current is generated in the motor rotor, and the current interacts with the rotating magnetic field. The electromagnetic field torque causes the motor to rotate.Figure1. Electric-Motor1.2 How Does the Start Capacitor Work?A single-phase power supply is different from a three-phase power supply in that a three-phase rotating magnetic field is generated in the motor. The principle of capacitor starting of single-phase motor is: using the principle that the current of the capacitor in the circuit is advanced by 90 degrees so that a magnetic field of 90 degrees ahead of the main winding is generated in the starting winding so that there will be an alternating 90-degree angle in the motor. The magnetic field, to put it plainly, uses the phase-shifting principle of the capacitor to transform a single-phase power supply into a two-phase power supply of 90 degrees to each other, and a rotating magnetic field of 90 degrees to each other is generated in the motor. Maybe it is easier to understand to explain from this aspect. The start capacitor is to give the motor a thrust when the motor is started so that the motor can turn from moving to rotating. Without it, when a single-phase AC motor starts, it will shake at the origin instead of rotating; the start capacitor is a two-phase AC motor, so the magnetic field cannot exert force on the rotor without it, and of course, it is impossible to rotate.Figure2. Capacitor Start Run Induction Motor1.3 Reasons for the Burning of the Start CapacitorGenerally, the start capacitor is not easy to burn, because its working time is very short, and it is thrown off by the centrifugal switch at the moment of starting, with no current flowing through the start capacitor. However, not easy to burn does not mean that it will never burn. If the start capacitor burns out, the possible reasons are as follows:① Capacitors have low voltage resistance or poor quality, so it is best to use capacitors with a voltage resistance of 500V. ② The centrifugal switch will often produce an arc when it is turned off. It is possible to burn the switch to the motor. After the switch is started, the switch cannot be turned off. There is always current through the capacitor. It is easy to burn the secondary winding of the motor and the start capacitor within a certain period of time. ③ The capacity of the selected capacitor is too small, and the starting current exceeds the allowable value of the capacitor. ④ The motor is bored or the bearing is damaged. It is difficult for the motor to start the centrifugal switch within a certain period of time and it is difficult to reach the disconnected speed, and the start capacitor is easy to burn.Figure3. Deteriorated CapacitorII Troubleshooting of Start Capacitor in Air Conditioner2.1 Functional Characteristics of Start CapacitorThe start capacitor is an important part of the auxiliary compressor to start. The capacitor is a large-capacity capacitor (1~6uF), which is used to provide starting current for the auxiliary winding of the motor to assist the compressor to start. The start capacitor is generally fixed on the bracket or support plate above the compressor, and the pin is connected to the starting end of the compressor.2.2 How to Quickly Figure out Whether the Start Capacitor is DamagedFirst of all, it depends on what kind of capacitors are used in electrical parts.● If the compressor start/run capacitor is damaged, the compressor cannot start or run intermittently.● If the capacitor of the fan motor is damaged, some malfunctions such as excessive exhaust temperature, excessive exhaust pressure, compressor overload, and small air output will occur during the operation of the air conditioner.2.3 Why is the Start Capacitor of the Air Conditioner Outdoor Unit Easy to Damage?The capacitor of the air conditioner compressor is installed in the outdoor unit. Due to the high temperature of the outdoor unit (ambient temperature + temperature emitted by the condenser), capacitors that have been used for a long time will easily dry up and fail the electrolyte.When replacing capacitors, be sure to use high-quality capacitors. The capacity must be the same, and the withstand voltage must not be lower than the original standard.Figure4. Air Conditioner Outdoor Unit2.4 Symptoms and Test Methods① Smoke.② Cannot operate normally.③ The display cannot be displayed normally.④ The power supply cannot be charged and discharged normally.⑤ Can not heat normally.⑥ The power factor compensates the capacitor damage, resulting in a waste of electricity. Different symptoms of damage to compressor start capacitor and external motor start capacitor:There are two capacitors in the outdoor electromechanical packaging, the larger one is the compressor capacitor, and the smaller one is the external motor capacitor. Different capacitors have different failure phenomena. ① Compressor capacitor damagethe performance phenomenon is that normal compressor startup will be accompanied by loud noise and jitter. If the capacitor is damaged, you will feel a slight jitter in the compressor by pressing the casing above the compressor, and the sound is like the sound of current passing. The compressor will stop running after a period of time. ② The damage of the external motor capacitorAfter the compressor is working normally, the external motor stops working for a period of time. If there is a fault code, there will be high-pressure protection and compressor exhaust pipe temperature protection.Figure5. Basic Electrical Controls of Air-Conditioning UnitsTest methods of air conditioner start capacitor● Method 1:The start capacitor of the air-conditioning compressor is a large-capacity electrolytic capacitor. When testing, using the capacitance setting of the digital multimeter to determine whether there is any abnormality.Under normal circumstances, the capacitance of the capacitor used to detect the capacitance of a multimeter should be the same or very close to the nominal capacitance, otherwise, the start capacitor is mostly deteriorating, such as dry electrolyte, leakage, etc., which should be replaced. ● Method 2:In addition to using a multimeter to test its capacitance, the ohmic setting of a pointer multimeter can also be used to test the charge and discharge performance of the start capacitor.Steps:① Connect the red and black test leads to the two poles of the compressor start capacitor.② The multimeter gear is set in ohm gear.③ Under normal circumstances, the pointer of the multimeter first swings to the right to a position, then slowly swings to the left, and finally stops at a fixed position.④If the pointer does not swing or the swing range is small, it indicates that the performance of the compressor start capacitor is poor.Suggested Reading: 5 Ways to Test Capacitors How to replace the start capacitor?If it is ensured that the air conditioner failure is caused by the damage of the compressor start capacitor itself, the damaged compressor start capacitor needs to be replaced. Replacing the start capacitor can generally be divided into three steps: removing the start capacitor, finding a replaceable start capacitor, and replacing the start capacitor. ①Remove the start capacitorThe compressor start capacitor is located on the circuit support board above the compressor. When disassembling, unplug the connecting wire and use a screwdriver to remove the fixing screw of the snap ring. ② Looking for replaceable capacitorsAfter removing the damaged compressor start capacitor, then select a suitable new start capacitor to replace it according to the specifications and volume of the damaged start capacitor.The specific content of how to select the start capacitor will be explained in detail below. ③Replace the start capacitorAfter selecting the compressor start capacitor, install the new compressor start capacitor in the outdoor unit, fix the metal fixing ring, reconnect the connecting cable, and then power on and test the machine to complete the replacement.Figure6. Motor Start CapacitorIII How Test the Motor Start Capacitor of a Fan?①Connect all parts on the circuit board of the air conditioner completely.②Turn on the power supply.③Use the remote control to adjust the temperature to make the fan motor rotate.④Connect the ground terminal of the oscilloscope probe to the ground terminal of the circuit board.⑤Use an oscilloscope probe to detect the white lead on the Hall element plug.⑥The oscilloscope shows signal waveform. When testing the start capacitor of the fan motor, a multimeter should be used to measure the resistance of the capacitor. Due to the large size of the capacitor, it is impossible to use the capacitor input jack for testing. At this time, you can use the multimeter pen to test and judge the quality of the capacitor by the change of the value displayed by the multimeter. If the resistance value displayed by the multimeter changes from small to large and then changes to infinity, it means that this is a good capacitor with charging and discharging functions. Check again after changing the test leads, the displayed value still changes from small to large, and changes to infinity. After measuring the capacitor, if the test leads are not replaced when the test is performed again, and the resistance value is displayed as infinite, it means that charging and discharging are not performed, but it does not mean that the capacitor is damaged. Therefore, when testing the capacitance, the test leads must be replaced no matter which multimeter is used.Figure7. Fan MotorRelated recommendation: How to Test Ceramic Disc Capacitor IV Relevant Knowledge in the Step of Start Capacitor Test4.1 How to Choose Start Capacitor?● How to calculate the starting and running capacitance of a single motorrun capacitance C=120000*I/2.4*f*U*cosφWhere: I is current; f is the frequency; U is the voltage; cosφ is the power factor, taking 0.5 to 0.7. The run voltage of the run capacitor is greater than or equal to (2～2.3) U.Start capacitor capacity = (1.5 ~ 2.5) run capacitor capacity.The run voltage of the start capacitor is greater than or equal to 1.42 U.(It is best when the voltage across the capacitor is 311V during operation) The working capacitor is 1-4UF per 100W, and the start capacitor is 4-10 times the working capacitor (the motor requires a larger starting torque). Empirical data, if your motor does not exceed 200W, the start capacitor will not exceed 100uF. If you run the capacitor, you can choose several values for the power-on test, and see which capacitor has the smallest current in the whole machine, then the capacity of the capacitor is the most Good value.) The capacity of the single-phase split-phase motor capacitor can be calculated by the empirical formula C=35000I/2PUfcos&Such as I=250W/220V=1.2AC=35000x1.2/2x1x50x220X0.8=24ufCan choose 350V30uf capacitance.Figure8. Starting Capacitor Table ● How to calculate the voltage across the run capacitor of a single-phase motor?① First of all, you must know the impedance value of the secondary winding. You can measure the resistance value by measuring the DC resistance with a multimeter. Then, the secondary winding is connected to a 12V AC voltage and the current value is measured. According to the winding impedance equal to the resistance and reactance in series, it can be calculated by phasor Out the winding inductance value. ② In normal operation, the capacitor is connected in series on the secondary winding, that is, the three equivalent parameters of winding resistance, winding reactance, and capacitance are connected in series and then connected to 220V voltage. It is easy to calculate the phasor according to the formula of the series circuit. Calculate the voltage on the capacitor. ③ When a single-phase motor is running, the voltage at both ends of the capacitor is generally above 300VAC, so the capacitor voltage is generally selected for a capacitor with a withstand voltage of 400V or more, and a capacitor with a voltage of more than 450V is better. ④ For the calculation of the capacitance withstand voltage, please refer to Article 2. First, measure the resistance R and reactance XL of the secondary winding, and then select the capacitance C according to the power of the motor to calculate the capacitive reactance Xc.The actual voltage across the capacitor during operation: Uc= Xc*220/(R+jXL-jXc); the withstand voltage value of the capacitor: Uce=1.3~1.5Uc.Figure9. Single Phase Motor Starting ● Detailed selection guide of start capacitor and run capacitorSingle-phase motor capacitor selection.Withstand voltage formula: U (capacitance) is greater than or equal to 1.5*USingle-phase run capacitor formula: C=1950×I/U×cosφ (using a capacitor, which is both a start capacitor and a run capacitor, is commonly used for small-capacity motors such as electric fans and washing machines)Start capacitor capacity formula: C=3500*I/U*cosφ (a capacitor is only used when starting, disconnected during normal operation, and switched with a transfer switch or a centrifugal switch.Dual-value capacitor run capacitor capacity formula: C=1200*I/U*cosφ (use 2 capacitors, one for operation and one for startup)Dual-value capacitor start capacitor capacity formula: C=(2～3)*C (run capacitor) C: Capacitor capacity: I: motor rated current, U: motor rated voltage, cosφ: power factor 0.7.Generally, there is no need to calculate. The run capacitor is 2~3μF per 100W, and the start capacitor is 2~3 times the run capacitor. The capacitor selection of the motor has strict requirements on the voltage, and it must be equal to or greater than 1.5 times the rated voltage of the motor. For a power supply with a rated voltage of 220V, the rated voltage of the capacitor cannot be lower than 400V. The capacitance value has a certain broadness, it doesn't matter if it is larger or smaller, especially the start capacitor, which can be selected at 2-6 times the working capacitor. ● How to choose the capacitor of single-phase asynchronous capacitor start the motorWe can calculate according to the following formulaPhase start capacitor capacity:C=350000*I/2p*f*U*cosφIn the formula: I---current;f-frequency;U---voltage;2p-the larger power factor is 2, and the smaller power factor is 4; cosφ---power factor (0.4～0.8).Split-phase start capacitor withstand voltage:The capacitor withstand voltage is greater than or equal to 1.42*U. Run capacitor capacity:C=120000*I/2p*f*U*cosφIn the formula: I---current;f-frequency;U---voltage;2p-take 2.4;cosφ---power factor (0.4～0.8). Run capacitor withstand voltage:The withstand voltage of the capacitor is greater than or equal to (2～2.3)*U.start capacitor capacity of double-value capacitor motor:C=(1.5～2.5)*operating capacitor capacity.Withstand voltage of start capacitor:The capacitor withstand voltage is greater than or equal to 1.42*U.4.2 Precautions for Replacing the Start CapacitorThe start capacitor is an important part of the electronic circuit. Once the start capacitor is broken, the motor cannot be started. The damaged start capacitor will only make a buzzing sound when it is energized for a short time, causing the current to surge, and long-time energization will cause severe overheating and even burn the motor, so it should be replaced immediately. And it is not difficult to judge that the start capacitor is broken. Most of the damaged start capacitors are bulging, and the surface will be burnt due to excessive current, and the rotor speed will be slow and weak. Of course, the most intuitive and accurate way is to use the capacitance setting of a multimeter to measure the quality. Once we have confirmed that the start capacitor has failed, the things that should be noted when replacing the start capacitor:① After the start capacitor is discharged, there will still be part of the residual charge that cannot be discharged for a while, and an artificial discharge should be performed again. ② Since the failed start capacitor may have poor lead contact, internal disconnection or fuse blown, etc., part of the charge may not be discharged. Therefore, the maintenance personnel should wear insulating gloves before touching the failed start capacitor. Using the short-circuit wire to short the two poles of the faulty capacitor first, and then it can be removed and replaced by hand. ③ If multiple start capacitors are used in series, they should be discharged separately.Figure10. Replace the Start Capacitor④ When handling or replacing a malfunctioning start capacitor, disconnect the power supply of the start capacitor, disconnect the switch or unplug the plug, and discharge the start capacitor. ⑤ When discharging, first connect the grounding terminal of the grounding wire, and then use the grounding rod to discharge the start capacitor several times until there is no discharge spark or discharge sound, and then fix the grounding terminal. ⑥ It should also be noted that general users often ignore the instruction manual, and the precautions for use must be carefully understood and followed during installation. As we all know, the impedance of a capacitor is inversely proportional to frequency. As the frequency increases, the loss also increases. Measures should be taken to limit the harmonics and inrush current in the circuit. Capacitors always generate heat, so pay special attention to ventilation and cooling. After the reactive power compensation device is installed, during the trial operation, the system should be tested, and measures should be taken in time if over-voltage, over-current, oscillation, and harmonics are found, which is very necessary for the normal operation of the capacitor. V How to Test the Motor Start Capacitor without a MultimeterA DC voltmeter can be connected to the capacitor in parallel, and an insulating shaker can be used to charge the capacitor (note the + and-poles)(1) See if the voltage can rise to the rated voltage of the capacitor:① 0V, the capacitor is short-circuited.② Slowly rise to the rated voltage of the capacitor, it proves that the capacitor is good.③ Raised quickly to the rated voltage of the capacitor, and the insulation resistance is about the internal resistance of the DC voltmeter, then the capacitor is open.(2) When it is stable at the rated voltage value of the capacitor, look at the insulation resistance of the capacitor:①The insulation resistance is close to the internal resistance of the DC voltmeter, so the capacitance is good.②If the insulation resistance is less than the internal resistance of the DC voltmeter, it means that the leakage of the capacitor is large, and it is easy to generate heat and cannot be used.VI Frequently Asked Questions about Start Capacitors6.1 Which Motors are Served by the Start Capacitor?Although some electrical appliances seem to have similar principles, they are different in the selection of motors, such as electric fans and air conditioners. Most electric fans use single-phase motors. Single-phase motors have only one 220v live wire and one neutral wire, while air conditioners often uses the three-phase motor, which has three wires, 220v live wire, neutral wire, and 380v live wire. The most obvious difference between a single-phase motor and a three-phase motor is that the number of start capacitors is different. A single-phase motor is equipped with a start capacitor, while a three-phase motor has no start capacitor.6.2 Why Does a Three-phase Motor do not Need a Start Capacitor?Because the three-phase motor itself has three running windings and can generate a magnetic field by itself, the appearance of the magnetic field can effectively replace the start capacitor, so the three-phase motor is generally not equipped with a start capacitor. However, the start capacitor still plays an irreplaceable role in a single-phase motor, because there is only one running winding in a single-phase motor, which cannot form a rotating magnetic field, and the operation of electrical appliances can only rely on the start capacitor. In addition to the start capacitor in a single-phase motor, there is also a run capacitor. Although these two capacitors work together, the function of the start capacitor is much greater than that of the run capacitor, so once they start capacitor is damaged, the fan will make a lot of noise, The blade speed is reduced. If this happens to your electric fan, you might as well try to replace a start capacitor, the problem should be solved.6.3 The Relationship Between Start Capacitors and MotorAt present, in single-phase motors with low-power motors, the start capacitor is connected in series with the starting coil and then connected in parallel with the running coil to work at the same time. In order to speed up the start-up time of the high-power motor, a large capacitor to help start is added. After the motor is started, the additional large start capacitor is disconnected by the centrifugal switch. The smaller capacitor connected in series with the starting coil is responsible for the phase shift required during normal operation. Electric current, the power supply machine is operating normally. Is there a single-phase motor that is connected to the starting coil and connected in parallel with the running coil in the circuit from start to run and does not require other large capacitors to help start? Low-power motors are always used in the circuit. High-power motors have to add additional capacitors due to their large power and large starting distance.Figure11. Torque-speed characteristic6.4 What are the Functions of Start Capacitors, Run Capacitors, and Centrifugal Switches in Single-phase Motors?The start capacitor is used for phase separation, and the purpose is to make the current in the two windings produce a phase difference close to 90 ゜ to generate a rotating magnetic field, allowing the motor to run quickly in a static state. There is an automatic clutch switch in the motor. When the motor is started, the motor will continue to run due to inertia. When the speed reaches a certain speed, the start capacitor will be separated by centrifugal action and automatically connected to the run capacitor, and the motor will enter the normal working state. The function of the run capacitor is to keep the current in the two windings with a phase difference of 90° to generate a continuous rotating magnetic field. For motors with start capacitors, the rotational torque generated by the start capacitors is larger than that of the run capacitors, which is more suitable for starting with a load. Motors without start capacitors are not suitable for starting with a larger load.VII QuizThe starting capacitor of a single phase motor is(A) Electrolytic capacitor(B) Ceramic capacitor(C) Paper capacitor(D) None of the above.Answer: AⅧ FAQ1. What happens when a start capacitor goes bad?A motor connected to a run and start capacitor may still attempt to start if one or both of the capacitors has failed, and this will result in a motor that hums and will not remain running for long. ... In most cases of capacitor problems, such as damage or a loss of charge, the capacitor will need to be replaced. 2. What's the difference between a run capacitor and a start capacitor?The start capacitor creates a current to voltage lag in the separate start windings of the motor. The current builds up slowly, and the armature has an opportunity to begin rotating with the field of current. A run capacitor uses the charge in the dielectric to boost the current which provides power to the motor. 3. How do you test a start capacitor with an ohmmeter?To test the capacitor with a multimeter, set the meter to read in the high ohms range, somewhere above 10k and 1m ohms. Touch the meter leads to the corresponding leads on the capacitor, red to positive and black to negative. The meter should start at zero and then moving slowly toward infinity. 4. How to test a motor start capacitor?Motor run capacitor failure symptoms include warm air flowing from the vents inside the home, the air conditioner taking more time than usual to kick on or it turns off before it is programmed to, or there is a constant low hum emitting from the machine that isn't typical. 5. How do I test a capacitor with a multimeter?To test the capacitor with a multimeter, set the meter to read in the high ohms range, somewhere above 10k and 1m ohms. Touch the meter leads to the corresponding leads on the capacitor, red to positive and black to negative. The meter should start at zero and then moving slowly toward infinity. 6. How do you check if a capacitor is bad with a multimeter?If the capacitance value is within the measurement range, the multimeter will display the capacitor's value. It will display OL if a) the capacitance value is higher than the measurement range or b) the capacitor is faulty. 7. How do I test a capacitor without a multimeter?Just connect those two ends of the capacitor to a single-phase supply and switch it ON for a few seconds. Then take that two-terminal and short it, you will get a spark. 8. How can I check a capacitor?Put the Analog Multimeter in the Ohmmeter position and if there are multiple ranges, choose a higher range. Connect the leads of the capacitor to the multimeter probes and observe the readings on the multimeter. For a good capacitor, the resistance will be low in the beginning and will gradually increase. 9. Can I replace a start capacitor with a run capacitor?Start capacitors give a large capacitance value necessary for motor starting for a very short period of time (usually seconds long). A start capacitor can never be used as a run capacitor because it cannot handle current continuously. 10. Which is bigger, start or run capacitor?A lot of torque is necessary to start up an AC system, so a start capacitor will have greater capacitance than a run capacitor. 

Ⅰ IntroductionThe vacuum tube was an essential part of early radios, used to create and amplify the electrical signals needed for the radio to work. The vacuum tube radio was a new stuff of the early 20th century, and immediately became the "new favorite" of that era with the launch of the radio show. Due to the continuous development of technology and the emergence of transistors, vacuum tubes were swept away by the powerful transistors in the 1960s and 1970s. With the improvement of people's lives, they have a new understanding of sound quality, and people are once again interested in the beautiful sound of vacuum tube radios.Vacuum Tube Radio RepairCatalogⅠ IntroductionⅡ Vacuum Tube Radio Circuit2.1 Input Circuit2.2 Converter Stage2.3 Detection Stage2.4 Intermediate Amplifier Stage2.5 Audio Voltage Amplifier2.6 Audio Power Amplifier Stage2.7 RectifierⅢ Classification3.1 AM Radio3.2 Heterodyne Radio3.3 FM Radio3.4 Service LifeⅣ Audio Maintenance PrincipleⅤ Specific Troubleshooting5.1 Tube Inspection5.2 Resistor Inspection5.3 Capacitor Inspection5.4 Transformer InspectionⅥ One Question Related to Vacuum Tube Radio and Going FurtherCompared with the semiconductor radio, the biggest advantage of the tube radio is that the sound quality is obviously better than that of the semiconductor radio. The second is that it is stable and elegant, with classical temperament. In addition, the history of tube radios is far greater than that of semiconductor radios, which are more valuable for collection. Ⅱ Vacuum Tube Radio CircuitFigure 1. 12AV6 Vacuum Tube Radio Circuit2.1 Input CircuitThe circuit from the antenna of the radio to the input of the first-stage tube is called the input circuit. It has two tasks to complete: One is to transmit the high-frequency signal voltage induced on the antenna to the grid of the first electron tube (usually the frequency conversion stage). To accomplish this task, there should be a certain coupling between the radio antenna and the input circuit to facilitate signal transmission. Second, because the antenna induces a lot of signals, it is necessary to select the radio broadcast signal you want to listen to  suppress unnecessary signals. To accomplish this task, the input circuit should be composed of a selective resonant circuit, so the input circuit should compose of coupling elements and the resonant circuit.Depending on the coupling form of the antenna and the resonance circuit. The input circuit can be divided into three types: inductive coupling (transformer coupling) circuit, capacitive coupling circuit, and inductive capacitive coupling circuit. Since the voltage transmission coefficient of the inductive coupling circuit is relatively high and uniform, tube radio usually adopts this type. In order to improve the suppressing ability of mid-frequency interference (because the intermediate-frequency detuning is smaller for medium wave, and it is larger for short wave.). An intermediate-frequency trap circuit is also applied in the antenna loop.2.2 Converter StageThe converter stage is located between the input circuit and the intermediate amplifier stage. Its function is to change the high-frequency amplitude modulation signal into a fixed intermediate-frequency amplitude modulation signal. In order to complete the task, the frequency converter should be composed of four parts: oscillator (generating a high frequency constant-amplitude oscillating voltage with an intermediate-frequency different from the frequency of the external radio signal), a high frequency circuit (used to select the radio signal, usually it is the input circuit), non-linear components (usually pentagrid converter, used to change the frequency), the intermediate-frequency loop.The converter stage of a tube radio is generally composed of a pentagrid converter tube. The high-frequency circuit is connected to the third grid (signal grid). The oscillator is composed of the screen grid (oscillation anode), the first grid (oscillation grid) and the cathode. The anode load is an intermediate frequency resonance circuit. Therefore, the main mark that distinguishes the converter stage from the tube amplifier is the pentagrid tube and three resonant circuits. The frequency converter can be divided into single-grid converter and double-grid converter according to the different ways of inputting signal voltage and local oscillation voltage. The single-grid inverter applies the signal voltage and the local oscillation voltage to the same electrode of the inverter tube, so the traction effect is large, and the operation is unstable. The double-gate inverter adds the signal voltage and the local oscillation voltage to the different electrodes of the inverter tube separately, the traction effect is greatly reduced, thus double-bar frequency converters are commonly used in tube radios.The structural feature of pentagrid tubes is that there are two metal sheets on the second grid, called the collection screen. It blocks the electrons moving to the anode. There are two metal rods on the third grid in the gap of the collecting screen, which carry negative potential. When the electrons passing through the second grid hit the negatively charged metal rod while advancing, the electrons flying to the anode is divided into two streams, one flying to the anode, and the other being collected by the collecting screen without returning to the cathode. In this way, when the signal grid voltage changes, it will only affect the distribution of the two currents, and has little effect on the total current. Because the local oscillator adopts the total current feedback, the oscillator is basically not affected, so the oscillation frequency is stable. There are many types of frequency converter circuits with different performances, but their principle difference lies in the way of local oscillation feedback. 2.3 Detection StageThe detection stage is located between the intermediate amplifier stage and the audio voltage amplifier stage. Its task is to transform the intermediate-frequency signal into the original modulated audio signal. To complete the task of frequency conversion, the detector must consist of an intermediate-frequency signal circuit (it is the output circuit of an intermediate-frequency amplifier), a non-linear elements (usually a diode), and a load (resistor). 2.4 Intermediate Amplifier StageThe intermediate amplifier stage is located between the frequency converter stage and the detection stage, and specifically amplifies the 465kHz intermediate-frequency signal. The main feature of the intermediate amplifier stage is: in order to achieve automatic gain control, the intermediate amplifier tube generally uses a remote cut-off tube. The intermediate-frequency transformer is the main component of the intermediate-frequency amplifier, and its quality directly affects the quality of the radio. In addition, a shielding cover is usually used to avoid the parasitic coupling between the intermediate-frequency loop and the eternal to improve the working stability. The shielding cover is made of good conductors such as aluminum and copper, and is attached to the case (ground potential), to isolate the entry of high frequency electromagnetic fields. 2.5 Audio Voltage AmplifierTo make the power amplifier stage output a certain amount of power, its anode current must have a certain amount of AC component, which requires that the grid audio signal voltage used to control the anode current must have a sufficiently large amplitude (voltage). The output voltage of the detector stage is usually very low. Therefore, between the power amplifier stage and the detector stage, there is always one or several audio voltage amplifier stages. Its function is to amplify the audio signal voltage to meet the input signal requirements.The audio voltage amplifier stage can be divided into a resistance-capacitance coupling amplifier and a transformer-coupled amplifier according to the different anode load forms. In the vacuum tube radio, the resistance-capacitance coupling amplifier is used mostly. The audio voltage amplifier stage and the detection stage usually share an electron tube. The input signal is generally controlled by a volume control potentiometer to adapt to different broadcasts and listening situations. Some radios have a tone control circuit connected to the output end of the audio voltage amplifier stage to flexibly change the frequency characteristics of the amplifier to make the sound pleasant. Due to the different forms of volume and tone control circuits. There are many types of audio voltage amplifier stages. 2.6 Audio Power Amplifier StageThe audio power amplifier stage is the last stage of the tube radio, and its function is to output a certain amount of audio power to make the speaker work normally. Someone may wonder, can a voltage amplifier be used instead of a power amplifier? This will not work. Although there is no difference between the basic circuits of a power amplifier and a voltage amplifier, due to the different tasks of the two, there are significant differences in the selection of electron tubes, the circuit components, and the nature of the load. It should be pointed out that the so-called power amplifier does not amplify the input power itself, but uses the control function of the electron tube grid voltage to convert the power supplied by the anode circuit DC power supply into the required audio power. From the viewpoint of energy conversion, the power amplifier is an energy converter. 2.7 RectifierThe rectifier stage of the tube radio is composed of three parts: power transformer, rectifier tube and filter. There are many forms of rectifier circuits, and the most common is a full-wave rectifier circuit.Ⅲ Classification3.1 AM RadioIn the era when tube radios were popular. AM radios were the mainstream products. Amplitude modulation is to modulate the high frequency carrier with audio signal. Its waveform is symmetrical up and down, and the amplitude is the same as the modulated signal. After detection, the highfrequency component is filtered out to obtain the audio signal. The frequency of the carrier signal (the frequency of the broadcasting station) is the carrier frequency.AM radios can receive medium wave and short wave broadcasts, and some can receive long wave broadcasts. Since the mid-band frequency interval has been unified to 9KHz, its highest audio frequency is only 4KHz. The sound quality is affected, and electromagnetic interference is relatively large.There are two main types of AM radios: direct-amplifier type and heterodyne type.1)Direct-amplified radio, also known as high-amplification radio, its typical circuit structure is such as: High-amplification→Detection→Low-amplification→Power amplifierA circuit that uses a grid detector circuit and a high-frequency positive feedback, called a regenerative radio, can achieve better sensitivity and selectivity. It can receive AM telegraph signals with high-amplifier and short-wave. Old Japanese-made radios mostly have this circuit. High-frequency signals of direct-amp radios are prone to self-excitation, and the high-end and low-end gains are uneven, and there is no high-amplifier regeneration. Widespread use of reed speakers with poor sound quality made it obsolete. Out of nostalgia, some enthusiasts are still keen on getting recycled radios. The regenerative circuit can not only be applied to direct-amplified radios, but also in simple heterodyne radios, because proper positive feedback can also be used to improve sensitivity.Simple regenerative radios often use reed speakers, which have high impedance (about 10K) and high sensitivity, and can be directly used as the load of the power amplifier tube. Its frequency range is only 350~3000Hz, so the sound quality is poor. Later regenerative radios used moving coil speakers, and the sound quality was better. However, due to the low impedance, an output transformer is needed, and its primary impedance must match the load impedance of the power amplifier tube. Moving coil speakers are divided into permanent magnet, constant magnet and excitation type. In addition, excitation horns are used in AC tube radios, and their excitation coils can also be used as filter chokes. 3.2 Heterodyne RadioThe heterodyne radio uses a frequency conversion circuit. The signal generated by the high-frequency oscillation circuit is different from the input signal at a certain frequency. After the two are combined, a fixed intermediate frequency signal (455~465KHz) is generated. The oscillation circuit needs independent vacuum tube as a part before the emergence of the dedicated frequency conversion tube. Some people call the oscillation frequency higher than the signal frequency by a heterodyne type.Heterodyne plus intermediate-frequency amplifier circuit is called superheterodyne. This type of circuit requires a single electron tube to oscillate. Later a multi-pole or composite tube dedicated to frequency conversion appears, such as 1A2, 6A2, 6SA7GT, 6U1, 6K8, etc. The superheterodyne type is the most common circuit of commercial radios. It has an automatic volume control circuit and can add tuning instructions. The superheterodyne radio can obtain more stable and higher gain due to the fixed frequency amplified. The disadvantage is that there is image frequency interference.The circuit structure of a typical superheterodyne radio is as follows:Frequency conversion→Middle amplifier→Detection→Low amplifier→Power amplifier 3.3 FM RadioFM is to use audio signal to modulate the frequency of high-frequency carrier. Its advantages are strong anti-interference ability, high signal-to-noise ratio, good frequency bandwidth and sound quality, and the audio frequency can reach 20~15000Hz. Because the FM audio work in the ultra-high frequency band, it can accommodate many radio stations. Because of its linear propagation characteristics, the same frequency can be reused at a distance of hundreds of kilometers, which can effectively solve the problem of congestion of medium and short-wave radio stations.Modern FM broadcasting is compatible with stereo and mono (in the early days of stereo broadcasting, two frequencies were used and received by two radios). Amateurs like to use a simple super-regenerative circuit to receive FM broadcasts. Because it works in a self-oscillation state, it is unstable and has strong super noise. 3.4 Service LifeThe general design life of the valves is 2000 hours (special tube has 5000~10000 hours), but in reality, many electron tubes break after using 2000 hours, for example, there is no sound. Its performance is not up to the design standard. When there is not any sound from the actual tube, it may have reached 3000 hours or more. The actual service life of the amplifier tube of the front stage is longer. To cite the simplest example: the old picture tube (picture tube is also a kind of vacuum tube) of a TV set, the actual life span usually excesses 10 years.If use it for 5 hours a day, you need to change the tube once a year to meet the actual design performance, and the replaced tube can also be used for other purposes.Ⅳ Audio Maintenance PrincipleHow to repair the failure of the vacuum tube radio depends on the difficulty of the failure. Under normal circumstances, the following steps are used.First point is to seek clues. What is the difference in the use of the radio before and after the failure, thinking about whether it has been repaired, or what components have been replaced, etc.Second point is the fault display. For faults such as flashover, smoking, burning, etc. Turn off the power immediately and find the factor to avoid damage to the audio. According to the displayed failure phenomenon, rotate audio button to compress the failure to clarify where the failure may occur, and to provide necessary information for analysis and judgment.Third point is analysis and judgment. Make comprehensive analysis and judgment based on the information obtained by self-examination inference and fault display. List all possible direct causes of the failure, and develop a scientific inspection procedure. This not only prevents blind movement, but also accumulates maintenance experience and improves efficiency.Fourth point is troubleshooting. Gradually narrow the scope of the fault, and accurately detect the fault point. Sometimes it refers to (such as electron tubes, capacitors, resistors, coils, transformers, etc.) connecting wires, welding points of a certain component. Determine where the failure occurred, which is important for fault repair. Tube radios are usually divided into high-frequency part, intermediate frequency part, audio part, power supply part and auxiliary circuit according to their working frequency and circuit function. The fault should be compressed to a specific circuit, such as DC circuit, AC circuit, or the anode circuit, the screen grid circuit, grid circuit, cathode circuit, etc. Since each loop in the electronic tube circuit affects each other, a failure of a component may affect several loops at the same time. Therefore, in the inspection process, comprehensive analysis should be performed, that is, each circuit should not be isolated.Fifth point is repairing practice. The repair test can be performed after determining the cause of the failure.Sixth point is repair inspection. In the actual maintenance process, if a failure point is detected, it must be immediately eliminated and repaired. After all the faults are investigated, the radio should be inspected as necessary to ensure the quality of the repair. The specific content of the inspection depends on the specific fault and the type and quantity of the instrument. The simplest one should also be auditioned and take general technical observations.Ⅴ Specific TroubleshootingA radio is composed of many components, and component damage is the main cause of radio failure. When the fault location is gradually reduced, the quality of the components must be checked to determine the fault. Therefore, inspecting components is one of the main methods to find the cause of failure.5.1 Tube InspectionThe common faults of electronic tubes are mostly filament broken, poor contact of the electric board, broken pole, pole touching, leakage, breakdown between the cathode and the filament, aging, air leakage, and micro-sound effects. When the radio is turned on, if the filament of a certain tube does not light up, the filament may be broken or a serious leak. The tube shell is cold when the filament is broken, and the tube shell is often warm when the gas leaks. Unplug the tube for further inspection. Use a multimeter to measure the filament resistance at the "R×1"gear. If the meter indicates infinite, the filament is disconnected. If the indicator of the needle is zero, it means that the tube is short-circuit. When the indicator of the needle indicates a constant value, it means that there is leakage between the electrodes. The smaller the resistance, the more serious the leakage. At this time, the top of the tube is usually milky white.The electron tube electrode is in poor contact, intermittently electrode touching (some are hot electrode touching), and the radio will sometimes have no sound or noise. This type of failure is characterized by being greatly affected by vibration. Therefore, you can tap the tube shell lightly. If there is no sound or noisy sound (sometimes there may be no sound or normal sound after tapping), it means that the tube electrode is in poor contact or intermittently electrode touching. When the fault is serious, the electrode is completely disconnected, which means a broken pole. The tube does not work, and the radio is silent.When the electron tube ages, the positive current and the amplification will decrease. If it was frequency conversion tube, the local oscillator will oscillate abnormally, resulting in the radio cannot receive the radio signal, low sound, or the high frequency end of the band can receive one or two radio stations, and the low-frequency end cannot receive the radio signal. The micro-phonic effect of the vacuum tube is often caused by improperly fixing the electrode, and it can be judged by tapping the tube case lightly. Sometimes it is difficult to determine whether the valve is normal or not. The easiest way is to replace it with the same type of electron tube. If the failure disappears, it means that there is a problem with the vacuum tube. 5.2 Resistor InspectionThere are two types of resistors used in radios: fixed resistors and variable resistors (potentiometers). They are not easy to damage. Possible damages include: resistor burnout, resistor body broken or lead broken, internal open circuit, or poor lead contact, etc. Some of failure can be observed. For example, the increase of fault current in a certain part of the circuit, which means the resistor is burned out. At this time, the paint layer on the outside of the resistor is burnt and hot. If the resistor is internally disconnected or the resistance value changes, it can be checked by measuring the ohm gear of a multimeter. If the meter indicates infinity, it means that the resistor is internally open; if the measurement result is too far from the nominal value (the error exceeds 20%), it means that the resistance has deteriorated.The lead of the resistor body is in poor contact and will be broken unbroken, which will cause noise or sound from the radio. This kind of failure is very susceptible to vibration and produces vibration noise. Therefore, you can gently shake the resistor body to see if the sound changes. It can also be measured with a multimeter. When measuring, shake the resistor body. If the pointer is unstable, it means that the contact is bad.The potentiometer that controls the volume of the radio usually has a power switch. The common faults of the potentiometer are: dirty carbon film, wear of the carbon film, poor contact of the sliding contact, loose lead-out piece, burnt of the carbon film, broken bakelite frame of the sliding contact, leakage, and damage to the power switch. When the potentiometer is normal, the radio can only hear a very light sound after power on. If the potentiometer is closed, the broadcast voice should not be heard. After turning off the power, there is no sound. If you cannot control the power on and off, it indicates that the power switch is partially damaged; if the noise is very loud, especially when the volume is adjusted, the loudspeaker has a large sound or interrupted sound, it means that the potentiometer is in poor contact. 5.3 Capacitor InspectionThere are two types of capacitors used in radios: fixed capacitors and variable (semi-variable) capacitors. The faults of fixed capacitors are usually leakage, breakdown, internal open circuit, poor internal contact, broken lead, or capacity failure, etc. The common faults of variable capacitors are bump, short circuit, leakage and so on. 5.4 Transformer InspectionCommon faults in transformers are coil mold breakage, a partial short circuit, leakage and other faults. A multimeter can also check out the coil mold. When high-frequency coils and intermediate-frequency transformers are locally short-circuited, it is not easy to measure. The substitution method can be employed to test or adjust the loop frequency to figure problems out.Ⅵ One Question Related to Vacuum Tube Radio and Going Further6.1 QuestionWhy do vacuum tubes sound better?6.2 AnswerTubes sound better because their distortion products are more musical. Those are the fundamental reasons why tubes simply sound better. Vacuum tubes are the more linear and require less feedback. Tubes are voltage amplifiers as opposed to transistors which are current amplification devices. Frequently Asked Questions about Vacuum Tube Radio1. What is a vacuum tube radio?VACUUM TUBE RADIO. Vacuum Tube Radio. By the late 1920s, vacuum tube radio equipment replaced the primitive spark-gap systems on most merchant ships. This new equipment could send and receive signals virtually worldwide, by using high frequency or "short-wave" bands. 2. How do radio vacuum tubes work?The basic working principle of a vacuum tube is a phenomenon called thermionic emission. It works like this: you heat up a metal, and the thermal energy knocks some electrons loose. ... When the cathode is heated, and a positive voltage is applied to the anode, electrons can flow from the cathode to the anode. 3. Why are vacuum tubes better for audio?Tube amplifiers sound better because of the euphonic distortions they add to the music, as well as plenty of other reasons I'll cover below. ... We use tubes simply because they make the music we create sound better: smoother, warmer and cleaner. Ditto for guitar amplifiers used in creating music. 4. How do you know if a vacuum tube is bad?When a vacuum tube develops an air leak (a small crack or bad seal by a pin for example) this getter color will change to pure white. If you see this you know with 100% certainty that the tube is bad. Third, look for a purple glow that is very focused around specific elements inside the tube.

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.

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.

Ⅰ Introduction1.1 Diode Structure and SymbolThis Video Clearly Explains the  P-N Junction Semiconductor DiodeBasic diode consist of a tube, a case and two electrodes. The tube is a PN junction, and a pin is drawn at each end of the PN junction. Use plastic, glass, or metal material to make a package shell, as shown in the following figure. The electrode drawn out of the P area is called a positive electrode or anode, and the electrode drawn out of the N area is called a negative electrode or cathode.Figure 1. Simple Diode Structure and SymbolCatalogⅠ Introduction  1.1 Diode Structure and Symbol  1.2 Classification StandardⅡ Common Diodes DescriptionⅢ Diodes Comparison  3.1 Schottky Diode vs Common Diode  3.2 Transient Voltage Suppressor vs ESD Protection Diode  3.3 Light Emitting Diode vs Laser DiodeⅣ Diode Application  4.1 Rectification  4.2 Switch  4.3 Amplitude Limit  4.4 Freewheeling Role  4.5 DisplayⅤ Question Related to Diode types and Going Further  5.1 Question  5.2 Answer1.2 Classification Standard1) According to the material, it can be divided into germanium diode (Ge tube) and silicon diode (Si tube).2) According to the structure, it can be divided into point-contact diodes, surface-contact diodes and planar diodes. The point-contact diode has a small PN junction and cannot pass through a large forward current and withstand a high reverse voltage. However, it has good performance in high-frequency and is suitable for high-frequency detection circuits and switching circuits. The surface-contact diode has a large PN junction, can pass a large current and withstand a high reverse voltage, and is suitable for use in a rectifier circuit. When the planar diode is used as a switching tube in a pulse digital circuit, the PN junction contact is small, but the PN junction area is large when used for high-power rectification. There are two types of SMD diodes, leaded and leadless, and their common shapes are cylindrical and rectangular.3) According to use: include rectifier diode, detection diode, zener diode, varactor diode, photodiode, light emitting diode, switching diode, fast recovery diode, etc.Ⅱ Common Diodes DescriptionRectifier DiodesRectifier diodes can rectify AC power into pulsating DC power using the unidirectional conductivity characteristics. Because the forward current of the rectifier diode is relatively large, the structure always adopt to the surface-contact type. But this structure will cause a large junction capacitance. Generally, the operating frequency of the rectifier diode is less than 3KHz. Fully sealed metal structure packaging and plastic packaging are common for rectifier diodes. The rectifiers with a forward rated current of more than 1A are packaged in a metal shell to dissipate heat fully; the rectifiers with a forward rated current of less than 1A are mostly packaged with full plastic.Figure 2. RectifierWhen selecting a rectifier diode, the parameters such as its maximum rectified current, maximum reverse operating current, cut-off frequency and reverse recovery time are mainly considered. The rectifier tube used in the common series stabilized power supply circuit, its reverse recovery time of the cut-off frequency is not strict, therefore, only the maximum rectification current and the maximum reverse working current that meets circuit requirements can be selected. In addition, the rectifier circuit of the switching power supply and the pulse rectifier circuit should use rectifiers with high operating frequency and short reverse recovery time. Detection DiodesThe detection diode is a device that filters out the low-frequency signal superimposed on the high-frequency carrier. It has high detection efficiency and good frequency characteristics, and mostly uses a glass packaging structure. The detection diode has the characteristics of small forward voltage drop, high detection efficiency, small junction capacitance, and good frequency characteristics. When selecting a detection diode, high operating frequency, small reverse current, and sufficiently large forward current should be considered according to the circuit design requirements. Switching DiodesThe forward bias on-resistance of the switching diode is very low under, and the off-resistance is very large when the reverse bias is applied. Using the unidirectional conduction characteristics of the diode, the current can be turned on and off, so the tube is called a switching diode.Figure 3. Switching DiodeMedium-speed switch circuit and detector circuit can use 2AK series ordinary switch diode. High-speed switching circuit can choose RLS series, 1S series, 1N series, 2CK series high-speed switching diodes. The specific model of the switching diode should be selected according to the main parameters of circuits, such as forward current, maximum reverse voltage, reverse recovery time, etc. For example, the reverse recovery time (trr) refers to a time from the on-state to the fully off-state. Generally, the electron cannot be stopped immediately after being turned off, and a certain amount of reverse current flows, and the greater the leakage current, the greater the loss. The key characteristic of the switching diode is the fast on/off speed, which can meet the needs of high-frequency and ultra-high-frequency circuits. So it is often used in pulse digital circuits and automatic control circuits.Figure 4. Reverse Recovery Time (trr)Zener DiodesZener diodes achieve the purpose of voltage regulation according to the characteristic that the voltage basically does not change with the change of current when the PN junction reverses breakdown. It is divided according to the breakdown voltage, and its voltage regulation value is the breakdown voltage value. As a voltage regulator or voltage reference component, zener diodes can be connected in series to obtain a higher voltage regulation value. When selecting, the zener diode should comply with the circuit parameter requirements. For example, the stable voltage value of the zener diode should be the same as the reference voltage of the application circuit, and the maximum stable current should be higher around 50% than the maximum load current of the application circuit.Recommended Reading: Zener Diodes Tutorial: What is the Principle of Zener Diode? Avalanche DiodesThe avalanche diode is a microwave power device drew up on the basis of the voltage regulator technology. It can produce high-frequency oscillation under the effect of an external voltage. Avalanche diodes use avalanche breakdown to inject carriers into the crystal. Because the carrier takes a certain amount of time to travel across the semiconductor wafer, its current lags the voltage for a while. If the transit time is properly controlled, there will be a negative resistance effect on the current-voltage relationship, resulting in high-frequency oscillations. As for application, It is often used in microwave communications, radar, tactical missiles, remote control, telemetering, and other equipment. Fast Recovery DiodesThe fast recovery diode is a new type of semiconductor diode, which has sound switching characteristics and short reverse recovery time, and is usually used as a rectifier diode in high-frequency switching power supplies.The reverse recovery time is an important parameter for fast recovery diode. The definition of it is the time required for the diode to change from the forward on state to the cut-off state quickly, from zero output pulse to the reverse power supply to recover to 10% of the maximum reverse current.Super fast recovery diodes (SRD) are developed on the basis of fast recovery diodes, and their principal difference is that the shorter reverse recovery time. The reverse recovery time of an ordinary fast recovery diode is several hundred nanoseconds, and is generally several tens of nanoseconds for a SRD. The smaller the value, the higher the working frequency of diodes. When the operating frequency is in the range of tens to hundreds of kHz, the time for voltage changes of the ordinary rectifier diode is slower than the recovery time, and diodes cannot work normally based on unidirectional conduction. In this case, a fast recovery rectifier diode is required. Therefore, rectifier diodes used in switching power supplies for color TVs and other household appliances. Otherwise, electrical appliances may not work properly with ordinary rectifier diodes. Step Recovary Diodes Its structural characteristics are: a steep impurity distribution area at the boundary of the PN junction, thereby forming a "self-help electric field". Because the PN junction is under forward bias, it conducts with a small number of carriers, and has a charge storage effect near the PN junction, so that its reverse current needs a "storage time" before it can fall to the minimum (reverse saturation current value). The self-help electric field shortens the storage time, cuts off the reverse current quickly, and generates rich harmonic components. Utilizing these harmonic components, a special spectrum generating circuit can be designed, which mainly used in pulse and higher harmonic circuits. Schottky DiodesSchottky diode is a low-power, high-current, ultra-high-speed semiconductor device, its reverse recovery time is extremely short (can be as small as a few nanoseconds), the forward voltage drop is only about 0.4 V, but the rectified current can reach thousands of amps. These excellent characteristics are unmatched by fast recovery diodes.Figure 5. V-A CurveSchottky diode is a metal-semiconductor device made of precious metal (gold, silver, aluminum, platinum, etc.) as the positive electrode, and N-type semiconductor as the negative electrode, and the barrier formed on the contact surface of the two has rectifying characteristics. Schottky diodes are usually used in high-frequency, high-current, low-voltage rectifier circuits. In addition, some switching power supplies require it.Recommended Reading: Schottky Diode Characteristics and Its Applications Transient Voltage Suppressor (TVS)Transient voltage suppressor(TVS) is a commonly used circuit protection device, and has fast response time (sub-nanosecond level) and a fairly high surge absorption capacity. As its two ends are subjected to an instantaneous high-energy impact, the TVS can change the impedance value between the two ends from a high impedance to a low impedance at a very high speed to absorb an instantaneous large current and clamp the voltage on a predetermined value, to protect the subsequent circuit components from transient high voltage spikes. Its response to overvoltage is faster than the varistor or gas discharge tube. It is widely used in computers, electronic instruments, communication equipment, household appliances, and airborne/marine and automotive electronic equipment, also it can be used as a protective element such as overvoltage shock or lightning strikes.TVS can be divided into four categories according to their peak pulse power: 50W, 1000W, 1500W, and 5000W. It will turn on instantaneously when the voltage at both ends is higher than the rated value, and the resistance at both ends will change from high resistance to low resistance at a very high speed, absorbing a huge current and clamping the voltage at a predetermined value across the tube.Recommended Reading: Transient Voltage Suppressor Tutorial and Applications Light Emitting Diodes (LED)The light-emitting diodes are made of semiconductor materials such as gallium phosphide and gallium arsenide phosphide. In addition to the unidirectional conductivity characteristic of ordinary diodes, they can directly convert electrical energy into light energy. When a forward voltage is applied to the light-emitting diode, it is also in a conducting state. A forward current flows through the tube, it will emit light.The light-emitting color of the light-emitting diode is mainly determined by the material of the tube and the type of impurities incorporated. At present, the common light-emitting diodes have blue, green, yellow, red, orange, white and so on. The working current of the LED is usually 2～25mA. The operating voltage varies with different materials: ordinary green, yellow, red, and orange light-emitting diodes are about 2v; the operating voltage of white light-emitting diodes is usually higher than 2.4V, and the operating voltage of blue light-emitting diodes is usually higher than 3.3V. The working current of the LED cannot exceed the rated value, otherwise, there is a risk of burning. Therefore, a current limiting resistor is usually connected in series in the LED circuit. Infrared light-emitting diode is a special light-emitting diode, its shape is similar to LED, but it emits infrared light, which is invisible to human eyes under normal circumstances. Their working voltage is about 1.4V, and the working current is generally less than 20mA. In addition to single-color LEDs, there are two-color and three-color LEDs that can emit more than two colors of light.The PN junction of the light-emitting diode is packaged in a transparent plastic shell, and the shape is square, rectangular and round. Light-emitting diodes have the advantages of low driving voltage, small working current, strong anti-vibration and impact capabilities, small size, high reliability, power saving and long life, thus they are commonly used in circuits such as signal indication.Recommended Reading: Light-emitting Diode Basics Tutorial     LED Driver Basics and Its Circuit Design Laser DiodesLaser diodes are a type of diode similar to LEDs. They have similar characteristics to diodes, but in forward bias mode, they emit light and the voltage drop across ends acts as a load. The laser diode has the advantages of high efficiency, small size and long life, but its output power is small (generally less than 2mW). Their linearity is poor, also monochromaticity is not very good, so its application in the cable TV system is greatly restricted and cannot transmit multichannel and high-performance analog signals.There are two common laser diodes:①PIN photodiodeWhen it receives power to generate photocurrent, it will bring quantum noise.② Avalanche photodiodeIt can provide internal signal amplification, and the transmission distance is longer than the PIN photodiode, but its quantum noise is greater. PhotodiodesThe shell of a photodiode is equipped with a glass window to facilitate receiving light. Its characteristic is that when light is irradiated to its PN junction, free electrons and holes can be generated in pairs, so that the concentration of minority carriers in the semiconductor is increased. Under a certain reverse bias voltage, the reverse current increases. Therefore, its reverse current increases linearly with increasing light intensity. When there is no light, the volt-ampere characteristics of the photodiode are the same as ordinary diodes. As a light control element, the photodiode can be used for various object detection, photoelectric control, automatic alarm, etc. When a large photodiode is made, it can be used as an energy source called a photovoltaic cell. At this time, it does not need an external power supply, and can directly convert light energy into electrical energy.Recommended Reading: Avalanche Photo Diode Diode for Alternating Current (DIAC)The DIAC is a diode that conducts electrical current only after its breakover voltage has been reached momentarily. It is a silicon bidirectional voltage trigger switching device. When the voltage applied across the diode exceeds its breakdown voltage, the two ends are turned on, and the conduction will not stop until the current is interrupted or it drops to the minimum of the holding current of the device. DISC is usually used in overvoltage protection circuits, phase shift circuits, thyristor trigger circuits, and timing circuits. Varicap or Varactor DiodesVaractor diodes are special semiconductor devices that use reverse bias to change the capacitance of a PN junction. It is equivalent to a variable-capacity capacitor. The capacitance of the PN junction between its two electrodes changes with the magnitude of the reverse voltage applied to the two ends. As the voltage increases, the capacity of the varactor diode decreases. Owing to this characteristic, it is mainly used in electric tuning circuits (such as the LNB of color TV sets), as an automatic fine-tuning capacitor controlled by voltage.When choosing a varactor diode, it should be focused on operating frequency, maximum reverse operating voltage, maximum forward current, and zero bias junction capacitancc in the circuit. The varactor diode with low revere leakage current and various junction capacitance should be selected. Freewheeling DiodesGenerally, a fast recovery diode or a Schottky diode is selected as a "freewheeling diode". It is generally used in the circuit to protect the component from breakdown by induced voltage or burned out. Connect in parallel to the two ends of the element that generates the induced electromotive force(EMF), and forms a loop with it, so that the high EMF generated in the loop is consumed by the current, thereby protecting the components in the circuit.Freewheeling diodes are often used with energy storage elements to prevent sudden changes in voltage and current, and provide a path. The inductor can provide a continuous current to the load through it, so as to prevent the load current from abruptly changing and play a role in smoothing  current. In the switching power supply, a freewheeling circuit composed of diodes and resistors connected in series. The freewheeling diode of this circuit is connected in parallel with the transformer. When the switching tube is turned off, the freewheeling circuit can release the energy stored in the transformer coil to prevent the induced voltage from being too high to damage the switch tube. In fact, freewheeling diode is not a substantial component, it is just having freewheeling function in the circuit.Recommended Reading: What Is A Flyback Diode or Freewheeling Diode and It's Applications Gunn DiodeGunn diode, also called transferred electron device (TED), is a form of diode used in high-frequency electronics. Unlike ordinary diodes that have both a N-type region and a P-type region, it consists of N-type impurity semiconductor only.The Gunn diode has three regions: the two ends are N-type impurity doped regions, and there is a lightly doped thin layer between them. When a voltage is applied across the Gunn diode, electrical gradients at the central thin layer are the largest. Because in the conductor material, the current is proportional to the voltage, conductivity will be generated. Eventually, a higher electric field value will be generated at the central thin layer, resulting in a higher resistance to prevent further increase in conductivity, thus the current will start to decrease. This means that the Gunn diode has a negative resistance effect, or called negative differential resistance. It is commonly used to generate microwave signals and has been used as a simple and effective form of microwave generator in many RF circuit designs. Tunnel DiodesIt is a crystal diode with a tunneling current as the main current, and is a two-terminal active device. The base materials are gallium arsenide and germanium. The N-type region and the P-type region is highly doped (ie, with a high concentration of impurities). The tunneling current is produced by the quantum mechanical effect of semiconductors, which has the following three conditions: the conduction band and the full band are Fermi level; the width of the space charge layer must be narrow (below 0.01 microns); the holes in the P-type and N-type regions of will overlap with electrons at the same energy level. Tunnel diodes can be used in high-frequency amplifiers with low noise and high-frequency oscillators (whose operating frequency can reach the millimeter), and can also be used in high-speed switching circuits. PIN DiodesThis is a crystal diode with a layer of intrinsic semiconductor (or semiconductor with low concentration of impurities) between the P region and the N region. When its operating frequency exceeds 100MHz, due to the storage effect of minority carriers and the transit time effect in the intrinsic layer, diode loses rectifying function and becomes an impedance element, and its impedance value varies with the bias voltage. Therefore, the PIN diode can be used as a variable impedance element. It is often used in high-frequency switches such as microwave switches, phase-shifting, modulation, amplitude limit and other circuits. Damper Diodes Damper diode has a lower voltage drop and a higher operating frequency, can withstand a higher reverse operating voltage and peak current, and has a small forward voltage drop. It is similar to a high-frequency high-voltage rectifier diode, and used for damper and booster rectification. Vacuum DiodesVacuum diode, also called electron diode or valve, or vacuum tube. A tube with only one cathode and one anode. It is conducted by the electron emitted by the cathode based on heated filament. Because the filament has heat loss, the performance is poor than that of the semiconductor diode.When the anode potential is higher than the cathode, the electrons emitted by the cathode move to the anode to form an electron flow under the action of the electric field. When the cathode voltage is higher than the anode, the electric field force received by the electrons pulls the electrons back to the cathode, and cannot generate current. That is unidirectional conductivity. It is generally used for rectification and detection. There are two types of vacuum tube, vacuum and gas (filled with an inert gas). The latter can also be used for voltage stabilization, indication and system control.Recommended Reading: What is Vacuum Tube? Basic Structure and TypesFull Diode Symbols Display Ⅲ Diodes Comparison3.1 Schottky Diode vs Common DiodeFor common diode, the initial conduction voltage drop of the silicon tube is about 0.5V, the normal conduction voltage drop is about 0.7V, the conduction voltage drop is about 1V when it is close to the limit current. The initial conduction voltage drop of the germanium tube is about 0.2V, the normal turn-on voltage drop is about 0.3V, and the turn-on voltage drop is about 0.4V when it is close to the limit current. For Schottky diode, the initial turn-on voltage drop is about 0.4V, the normal turn-on voltage drop is about 0.5V, and the turn-on voltage drop is about 0.8V when it is approaching limit current.Both diodes are unidirectional and can be used in rectification applications. The difference is that the withstand voltage of common silicon diodes can be higher, but its recovery time is long, and it can only be used for low-frequency rectification. If it is used in high frequency, reverse leakage will occur to cause tube burned. Withstand voltage of Schottky diode is low, but its recovery time is short and can be used in high frequency occasions. 3.2 Transient Voltage Suppressor vs ESD Protection DiodeTVS is mainly for transient voltage suppression, and ESD is mainly used for electrostatic discharge protection. As for anti-static, it requires low capacitance value, generally between 1 ~ 3.5PF is the best, ESD meets the requirements well. However, TVS cannot do this, because the capacitance of TVS is relatively high. 3.3 Light Emitting Diode vs Laser DiodeLED uses the spontaneous emission of carriers injected into the active area to emit light, while LD emits light from laser radiation. The direction of the light emitted by the LED is random, and the LD light is in the same direction and phase. The LD has an optical resonant cavity, so that the generated photons oscillate and amplify in the cavity, and the LED has no that. The LED has no critical value, the spectral density is several orders of magnitude higher than that of the LD, the LED light output power is small, and the divergence angle is large. LEDs are commonly used in the indicator light of electrical equipment such as traffic lights. They have the characteristics of long service life and high photoelectric conversion efficiency. While LD is widely used in low-power photoelectric devices such as CD drives on computers and print part of laser printers.Ⅳ Diode Application4.1 RectificationAccording to the unidirectional conductivity, a diode can transform the alternating current into a pulsed direct current with a single direction.4.2 SwitchUnder the action of forward voltage, the resistance of the diode is very small, it is in the on state, which is equivalent to a switch on; under the action of the reverse voltage, the resistance is large, and it is in the off state, just like a switch off. Using the switching characteristics of the diode, various logic circuits can be made.4.3 Amplitude LimitAfter the diode is forward-conducted, its forward voltage drop remains basically the same (0.7V for silicon tube and 0.3V for germanium tube). Using this feature, diode often regarded as a limiting element in the circuit to limit the signal amplitude to a certain range.4.4 Freewheeling RoleIt plays a freewheeling role in the inductance of the switching power supply and inductive loads such as in relays.4.5 DisplayDiodes are commonly used in VCD, DVD, traffic lights and other displays. Ⅴ Question Related to Diode types and Going Further5.1 QuestionHow are diodes classified? 5.2 AnswerDiodes are classified according to their characteristics and are offered in a number of different types based on circuit requirements, including rectifier diodes, switching diodes, light emitting diodes, Schottky diodes, Zener diodes, and diodes designed for high-frequency applications, etc. Frequently Asked Questions about Different Types of Diode1. What are the different types of diode?Different Types of DiodesSmall Signal DiodeLarge Signal DiodeZener DiodeLight Emitting Diode (LED)Constant Current DiodesSchottky DiodeShockley DiodeStep Recovery Diodes 2. What is diode and its types?A diode is a two-terminal electrical device, that allows the transfer of current in only one direction. ... Most of the diodes are made from semiconductors such as Si (silicon), but in a few cases, Ge (germanium) is also used. It is sometimes beneficial to summarize the different types of diodes are existing. 3. How do you identify a Schottky diode?The Schottky diode is measured in both forward And reverse directions. If the re a, the measurement in Figure 8-25 indicates that the tube is a silicon diode. If it is a germanium diode, the forward voltage reading should be less than 0.3V. 4. What is the application of a diode?The application areas of diodes include communication systems as limiters, clippers, gates; computer systems as logic gates, clampers; power supply systems as rectifiers and inverters; television systems as phase detectors, limiters, clampers; radar circuits as gain control circuits, parameter amplifiers, etc.

I IntroductionA capacitor is an electronic component composed of an insulator between two conductors, like a sandwich. We can understand it as a container that holds the electric charge. In actual capacitors, two conductors are filled with an insulating dielectric. There are numerous types of dielectrics, so the types of capacitors formed are also different. For example, according to dielectric materials, capacitors can be divided into gas dielectric capacitors, liquid dielectric capacitors, inorganic solid dielectric capacitors, and organic solid dielectric capacitors; according to polarity, they can be divided into polarized capacitors and non-polarized capacitors. This article will introduce the various types of capacitors in detail and some additional basic knowledge of them, mainly explaining from the perspective of the manufacturing process and structure.Capacitors: types, use and testing. CatalogI IntroductionII The Basic Principle of CapacitorsIII Film Capacitor  3.1 Metal Foil Film Capacitor  3.2 Metallized Film CapacitorIV Electrolytic Capacitor  4.1 Aluminum Electrolytic Capacitors  4.2 Tantalum Electrolytic Capacitors  4.3 Niobium Electrolytic CapacitorsV Ceramic Capacitor  5.1 Ceramic Disc Capacitor  5.2 Multi-layer Ceramic Capacitor  5.3 Monolithic Capacitors  5.4 Classification of Ceramic MediaVI SupercapacitorVII Fixed, Trimmer and Variable Capacitors  7.1 Mica Capacitor  7.2 Paper Capacitor  7.3 Trimmer Capacitor  7.4 Variable CapacitorVIII Comparison of Polarized Capacitors and Non-polarized Capacitors  8.1 Medium  8.2 Performance  8.3 Capacity  8.4 Structure  8.5 Application Environments and UseIX Axial and Radial Leaded CapacitorsX A Quiz About Capacitor TypesⅪ FAQII The Basic Principle of CapacitorsCapacitors, along with inductors and resistors, are the three basic passive devices in electronics. The function of the capacitor is to store electrical energy in the form of electric field energy.Taking the parallel plate capacitor as an example, we briefly introduce the basic principle of capacitance.Figure1. Parallel Plate CapacitorAs shown in the figure above, a DC voltage is applied to two metal plates that are close to each other and are parallel to each other (the dielectric between the plates). After stabilization, the metal plate connected to the positive electrode of the voltage will exhibit a certain amount of positive charge, while the metal plate connected to the negative electrode of the voltage will exhibit an equal amount of negative charge. In this way, an electrostatic field is formed between the two metal plates, so the capacitor stores electrical energy in the form of electric field energy, and the stored charge is Q. The amount of charge stored in the capacitor Q is related to the voltage U and its own property (that is, the capacitance value C), that is, Q=U*C. According to the theoretical derivation, the capacitance formula of the parallel plate capacitor is as follows:In this formula:C is the capacitance value, the unit is F (Farad)ε is the dielectric constant of the medium, F/mS is the area of the metal flat plate, m²d is the distance between metal plates, mThe ideal capacitor contains a dielectric, and there is no free charge, so it is impossible to produce charge movement, which is the current.  How does the ideal capacitor pass AC power? AC PowerVoltage can form an electric field inside the capacitor, and alternating voltage will produce an alternating electric field. According to the law of full current in Maxwell's equations:This means that either a current or a changing electric field can generate a magnetic field. Maxwell defines ε(∂E/∂t) as a displacement current, which is an equivalent current and represents the change of the electric field. (The current here represents the current density, or J)Let the AC voltage change sinusoidally, ie:The actual displacement current is equal to the current density times the area:Therefore, the capacitive reactance of the capacitor is 1/ωC. When the frequency is high, the capacitive reactance will be very small, which means passing the high frequency. DC BlockingThe DC voltage does not change with time, the displacement current ε(∂E/∂t) is 0, and the DC component cannot pass through.The characteristics of actual capacitors are non-ideal and have some parasitic effects; therefore, a more complicated model is needed to represent the actual capacitors. The commonly used equivalent model is as follow:Figure2. Equivalent ModelSince the medium is not absolutely insulated, there is a certain conductivity; therefore, any capacitor has a leakage current, expressed by the equivalent resistance Rleak;The conductors and electrodes of the capacitor have a certain resistivity, and there is a certain dielectric loss of the dielectric; these losses are uniformly expressed as the equivalent series resistance ESR;There is a certain inductance in the conductor of the capacitor, which has a greater impact at high frequencies, expressed as the equivalent series inductance ESL;In addition, there is a certain hysteresis in any medium, that is, after the capacitor is quickly discharged, the voltage is suddenly disconnected, and the capacitor will recover part of the charge, which is represented by a series RC circuit（Related post: LC circuit）.Most of the time, the main concern is the ESR and ESL of the capacitor. Quality FactorAs with inductors, the quality factor of the capacitor can be defined, which is the Q value, which is the ratio of the stored power of the capacitor to the power loss:Qc=(1/ωC)/ESRThe Q value is a relatively important parameter for high-frequency capacitance. Self-Resonance FrequencyBecause of the existence of ESL, a resonant circuit is formed together with C, and its resonant frequency is the self-resonant frequency of the capacitor. Before the self-resonant frequency, the impedance of the capacitor becomes smaller as the frequency increases; after the self-resonant frequency, the impedance of the capacitor becomes smaller as the frequency increases, which is inductive. As shown in the following figure:Figure3. Self-Resonance FrequencyAccording to the capacitance formula, in addition to the size of the capacitor, the size of the capacitance is related to the Permittivity of the dielectric. The performance of the dielectric affects that of the capacitor, and different media are suitable for different manufacturing processes.Capacitors can be divided into three main categories according to the manufacturing process: Film Capacitor Electrolytic Capacitor Ceramic CapacitorIII Film CapacitorFilm capacitors are made by winding two plastic films with metal electrodes into a cylindrical shape, and finally encapsulated; because its medium is usually plastic material, also known as plastic film capacitors. Its internal structure is rough as shown in the following figure:Figure4. The Structure of Film CapacitorFilm capacitors can be divided into two categories according to the manufacturing process of their electrodes:3.1 Metal Foil Film Capacitor For metal foil film capacitors, a thin metal foil, usually aluminum foil, is directly added to the plastic film as an electrode. This process is relatively simple, the electrode is easy to lead out, and can be applied to large current occasions.3.2 Metallized Film CapacitorMetalized film capacitors form a thin metal surface directly on the surface of the plastic film by vacuum deposition process as an electrode. Because the thickness of the electrode is very thin, it can be wound into a capacitor with a larger capacity. However, due to the thickness of the electrode, it is only suitable for small current applications.Figure5. Metallized Film ConstructionThe metalized film capacitor has the function of self-repair, that is, if there is a breakdown point inside the capacitor, an avalanche effect will occur at the damaged place, and the vaporized metal will form a vaporized assembly surface at the damaged place, the short circuit disappears, and the damaged point is repaired. Therefore, the reliability of the metalized thin film capacitor is very high, and will not fail due to a short circuit. There are two winding methods for film capacitors:Inductive winding method Before winding, the lead has been connected with the internal electrode.After the non-inductive winding method, gold plating and other processes are used to connect the internal electrodes of the two end surfaces into one surface, so that a smaller ESL can be obtained, and the high frequency performance should be higher.In addition, there is a laminated type non-inductive capacitor, the structure is similar to MLCC, the performance is better, and it is easy to make SMD package.Figure6. Winding MethodsThe characteristic of the film capacitor is that it can achieve large capacity and high withstand voltage. However, due to process reasons, its size is difficult to be small, and it is usually used in strong electric circuits, such as the power electronics industry.Figure7. Winding MethodsIV Electrolytic CapacitorElectrolytic capacitors use metal as an anode, and form a metal oxide film on the surface as a medium, and then wet or solid electrolyte and metal as a cathode. Electrolytic capacitors are mostly polarized. If the metal on the cathode side also has an oxide film, it is a non-polarized electrolytic capacitor.Depending on the metal used, there are three types of electrolytic capacitors:4.1 Aluminum Electrolytic CapacitorsAluminum electrolytic capacitors should be the most widely used electrolytic capacitors and the cheapest. Its basic structure is shown in the following figure:Figure8. The Structure of Aluminum Electrolytic CapacitorThe manufacturing process of aluminum electrolytic capacitors is roughly as follows:First, the aluminum foil will form a very rough surface by electroetching process, which increases the surface area of the electrode and can increase the capacitance;The anode is oxidized by a chemical method to form an oxide layer as a medium;Then, a layer of electrolytic paper is added between the anode aluminum foil and the cathode aluminum foil as a separator, and is pressed and wound;Finally, fill the electrolyte, the electrolytic paper will absorb the electrolyte, and the package is molded.Wet aluminum electrolytic capacitors using electrolyte are the most widely used, with the advantages of large capacitance, high rated voltage, and low cost. The disadvantages are also obvious, that is, shorter life, poor temperature characteristics, and larger ESR and ESL. For hardware development, it is necessary to avoid over-design. In the case of meeting performance requirements, cheap is the biggest advantage.Recommendation: How to Test Aluminum Electrolytic Capacitors4.2 Tantalum Electrolytic CapacitorsThe most widely used tantalum electrolytic capacitor should use manganese dioxide as a solid electrolyte. The internal structure of the solid tantalum electrolytic capacitor is rough as shown in the figure below:Figure9. The Internal Structure of the Solid Tantalum Electrolytic CapacitorCompared with aluminum electrolytic capacitors, the dielectric constant of tantalum oxide (tantalum pentoxide) is much higher than that of aluminum oxide (aluminum oxide). With the same volume, the capacity of tantalum capacitors is larger than that of aluminum electrolytic capacitors. Tantalum capacitors have a longer life and more stable electrical performance.Figure10. The Internal Structure of the Solid Tantalum Electrolytic CapacitorTantalum capacitors also use conductive polymer as electrolyte, the structure is similar to the manganese dioxide tantalum capacitor in the above figure, which is to replace manganese dioxide with a conductive polymer. Conductive polymers have higher conductivity than manganese dioxide, so ESR will be lower. In addition, there are wet tantalum capacitors, which are characterized by super large capacity, high withstand voltage, and low DC leakage current, which is mainly used in military and aerospace fields.Figure11. Wet Tantalum Capacitors4.3 Niobium Electrolytic CapacitorsNiobium electrolytic capacitors are similar to tantalum electrolytic capacitors, in that niobium and its oxides replace tantalum. The dielectric constant of niobium oxide (niobium pentoxide) is higher than that of tantalum oxide (tantalum pentoxide). The performance of niobium capacitors is more stable and more reliable.V Ceramic CapacitorCeramic capacitors use ceramic materials as dielectric materials. There are many types of ceramic materials with different dielectric constants and stability, which are suitable for different occasions.Ceramic capacitors mainly include the following:5.1 Ceramic Disc CapacitorThe main advantage of the ceramic capacitor is that it can withstand high voltage, and it is usually used as a safety capacitor, which can withstand 250V AC voltage. Its appearance and structure are shown below:Figure12. The Structure of Ceramic Disc Capacitor5.2 Multi-layer Ceramic CapacitorMulti-layer ceramic capacitors, that is, MLCCs, chip multi-layer ceramic capacitors are currently the most widely used capacitor types in the world. Their standardized packaging and small size are suitable for automated high-density chip production.The internal structure of the multilayer ceramic capacitor is shown below:Figure13. Internal Structure of Chip Multilayer Ceramic Capacitor5.3 Monolithic CapacitorsBecause multilayer ceramics need to be sintered and porcelainized to form an integrated structure, the multilayer ceramic capacitors in lead packages are also called monolithic capacitors.The structure of monolithic capacitors is that several ceramic film blanks are covered with electrode paddle material, and after being laminated, they are wound into an inseparable whole at a time, and the outside is encapsulated with resin.Monolithic capacitors are a new type of capacitors with small volume, large capacity, high reliability and high-temperature resistance. Low-frequency monolithic capacitors with high dielectric constant also have stable performance and are actively small.5.4 Classification of Ceramic MediaAccording to EIA-198-1F-2002, ceramic media are mainly divided into four categories:Class I: Ceramic medium with temperature compensation characteristics, the dielectric constant is mostly low, not more than 200. It is usually a paraelectric medium. Under temperature, frequency and bias voltage, the dielectric constant is relatively stable and the change is small. The loss is also very low, the dissipation factor is less than 0.01.Figure14. Coding of Class 1 Capacitors According to EIA SpecificationThe most stable and most used is the C0G capacitor, or NP0. NP0 is the code name for the IEC/EN 60384-1 standard as Negative Positive Zero, using N and P for Positive and Negative deviations.Due to the low dielectric constant, the capacitance value of C0G capacitor is small and can be up to 0.1uF. The 0402 package usually has a maximum of 1000pF. Class II, III: Among them, the temperature characteristic A-S belongs to Class II, and the dielectric constant is about several thousand. The temperature characteristic T-V belongs to Class III, and the dielectric constant can be as high as 20000. It can be seen that the performance of Class III is more unstable. According to the classification of IEC, both Class II and III belong to the second category, high dielectric constant media. For example, X5R and X7R are Class II capacitors, which are widely used in power supply decoupling, while Y5V belongs to Class III capacitors, and their performance is not stable.Figure15. EIA Coding of Class 2 and 3 CapacitorsThe capacitance value of Class II and III capacitors can be up to several hundred uF, but due to the high dielectric constant medium, most of them are ferroelectric medium (Ferroelectric), and the temperature stability is poor. In addition, the dielectric constant of ferroelectric media will decrease under DC bias voltage. Class IV: The manufacturing process is different from the usual ceramic materials. The internal ceramic particles are all a thin oxide layer on the outside, and the core is a conductor. This type of capacitor has a large capacity but a small breakdown voltage. Due to the unstable performance and high loss of these capacitors, they have been basically eliminated.VI SupercapacitorSupercapacitor refers to a new type of energy storage device between a traditional capacitor and a rechargeable battery. There are two ways to store charge: EDLC and pseudocapacitance. It not only has the characteristics of rapid charge and discharge of the capacitor but also has the energy storage characteristics of the battery. The capacity of the supercapacitor is particularly large. It can replace the battery as a power supply device, and can also be used in conjunction with the battery. Supercapacitors charge fast, can be fully charged and discharged, and can be charged to any desired voltage, as long as the rated voltage is not exceeded. There are many applications of supercapacitors, for example, many cities in China have supercapacitor electric buses. There are also applications in some electronic products, such as some driving recorders, which can continue to supply power for several days.Figure16. SupercapacitorsVII Fixed, Trimmer and Variable CapacitorsA capacitor with a fixed capacitance is called a fixed capacitor. According to the different media can be divided into ceramics, mica, paper, film, electrolysis. Having described film capacitors, electrolytic capacitors, and ceramic capacitors, let's look at the other two types of fixed capacitors.  7.1 Mica CapacitorMica capacitors can be divided into foil type and silver type. Silver electroplating is very direct on mica sheets by vacuum evaporation or sintering method. Due to the elimination of the air gap, the temperature coefficient is greatly reduced and the capacitance stability is higher than foil type. Mica capacitors are widely used in high-frequency electrical appliances and can be used as standard capacitors. The glaze capacitor is made of a special mixture with a concentration suitable for spraying into a film. The medium is then sintered with a silver layer electrode to form a "monolithic" structure. Glass glaze capacitor is comparable to a mica capacitor in performance and can withstand various climates. It can generally work at 200℃ or higher, with rated working voltage up to 500 V and loss tan = 0.0005 ~ 0.008.Figure17. Silver Mica Capacitors7.2 Paper CapacitorPaper capacitors are widely used in radio and electronic equipment. Generally, two aluminum foils are used as electrodes, which are separated by overlapping winding of capacitor paper with a thickness of 0.008 ~ 0.012 mm. Simple manufacturing process, low price, can obtain a large capacitance, generally below 0.25 F, but the capacity error is large and difficult to control, good quality is ±10%, loss (tan ≤ 0.015), temperature and frequency characteristic stability is poor. The paper capacitors commonly used in the past are non-sealed, impregnated only with ground wax, paraffin wax and chlorinated diphenyl, etc., which are prone to aging and poor stability. They are easily affected by humidity, insulation resistance decreases after being affected by moisture, and atmospheric pressure also affects them. The paper capacitor whose core is sealed inside the metal or ceramic tube is of good quality and has little influence on the external climatic conditions. It can be normally used in the situation with the relative humidity up to 95 ~ 98 %. The electrode of metalized paper capacitor uses vacuum evaporation to directly attach the metal to the capacitor paper, which is only about 1/4 of the volume of the ordinary paper capacitor. Its main feature is its "self-recovery" function, that is, it can be "self-healing" after a breakdown. It is an improved type of paper capacitor. Oil-immersed capacitors have a higher voltage than ordinary paper capacitors, good stability, suitable for high-voltage circuits.Paper capacitors are intermediate frequency capacitors, which are generally used in low-frequency circuits and usually cannot be used in frequencies higher than 3 ~ 4 MHz.Figure18. Paper Capacitor7.3 Trimmer CapacitorTrimmer capacitors, also called semi-variable capacitors, have a capacitance that can be adjusted within a small range and fixed to a certain capacitance value after adjustment.Ceramic trimmer capacitors are of high quality and small size, and can usually be divided into two types: round tube type and round chip type.Trimmer capacitors for mica and polystyrene media are usually of spring-loaded structure, which is simple in structure but less stable.The wire-wound porcelain trimmer capacitor is used to change the capacitance by removing the copper wire (external electrode), so the capacitance can only be reduced and is not suitable for repeated debugging.7.4 Variable CapacitorAs the name implies, a variable capacitor means that the capacitance value can vary over a large range and can be determined to a certain value. Variable capacitors are divided into two forms: film medium and air medium. It is commonly used in coupling and tuning circuits, such as double capacitors, ceramic capacitors and so on.VIII Comparison of Polarized Capacitors and Non-polarized Capacitors8.1 MediumWhat is the medium? To put it bluntly, is the substance between the two plates of the capacitor. Most polarized capacitors use an electrolyte as the dielectric material. Generally, capacitors of the same volume have large polar capacitance. In addition, different electrolytic materials and processes produce polarized capacitors of the same volume. Furthermore, pressure resistance is also closely related to the use of dielectric materials. There are likewise many non-polarized capacitor dielectric materials, most of which use metal oxide film and polyester. Because the reversible or irreversible performance of the medium determines the use environment of polarized and non-polarized capacitors.8.2 PerformancePerformance is the requirement for use, and maximum demand is the requirement for use. If the metal oxide film capacitor is used for filtering in the power supply part of the TV, the capacitor capacity and withstand voltage required by the filtering must be achieved. Maybe only a power supply can be installed in this case. Therefore, only polarized capacitors can be utilized for filtering, and these capacitors are irreversible. In other words, the positive electrode must be connected to the high potential end, and the negative electrode must be connected to the low potential end. Generally, the electrolytic capacitor is above 1 microfarad for coupling, decoupling, power supply filtering, etc. Non-polarized capacitors are mostly below 1 microfarad, participating in resonance, coupling, frequency selection, current limiting, etc. Of course, there are also large-capacity and high-pressure-resistant ones, which are mostly used for reactive power compensation of electric power, phase shifting of motors, and frequency shifting power supply. There are many types of non-polarized capacitors, so this article won’t go into detail.Figure19. Classification of Capacitors8.3 CapacityAs mentioned earlier, the electrical media of the same volume are different, so the capacity is not equal.8.4 StructureIn principle, any shape capacitors can be used in the environment without considering the tip discharge. The electrolytic capacitors (polarized capacitors) that are usually used are round, and the square ones are rarely utilized. The shape of non-polarized capacitors varies. Like tube shape, deformed rectangle, sheet shape, square shape,combined square shape and round shape, etc., see where it is used. Of course, there are invisible. Intangible here refers to distributed capacitance. The distributed capacitance must not be ignored in high-neck and intermediate-frequency devices.8.5 Application Environments and UseIn the repair of home appliances, all of the above may be found. If you want to understand in a simple way, you have to find out by yourself.Because of the relationship between its internal materials and construction, the capacity of polarized capacitors (such as aluminum electrolysis) can be very large, but its high-frequency characteristics are not good, so it is suitable for power supply filtering and other occasions, but there are also good high-frequency characteristics. Polarized capacitor-tantalum electrolysis, its price is relatively high; Non-polarized capacitors are small in size, low in price, and satisfactory in high-frequency characteristics, but they are not suitable for large capacity. Like ceramic capacitors, monolithic capacitors, and polyethylene (CBB) capacitors, ceramic capacitors are generally used in high-frequency filtering and oscillation circuits.Figure20. Axial and Radial Type ConstructionIX Axial and Radial Leaded CapacitorsOne method of packaging capacitors is the lead structure. 　　Axial capacitance refers to the capacitance of the two pole leads on the same axis. Generally, it is a non-inductive structure. It is made of metalized polyester film as the dielectric/electrode. The wire is tinned copper clad steel wire (or flexible wire), the outer layer is wrapped with polyester tape, and both ends are sealed with epoxy resin.Figure21. Axial Lead StructureAxial leads (the leads are on the same plane as the capacitor axis) are radial leads. The figure below shows an example of a radial lead. The lead is in the radial position of the capacitor. Critical dimensions are lead spacing "S", height "H", length "L" and thickness "P'. Because they are inserted on the printed circuit board rather than on the surface of the circuit board like surface mount components, axial And radial elements are collectively referred to as "plug-in elements".Figure22. Radial Lead StructureX A Quiz About Capacitor TypesQuestion:The capacitors which use chemical reactions to store charge are calledA.ceramic capacitorsB.fixed capacitorsC.parallel plate capacitorsD.electrolytic capacitorsAnswer:D Ⅺ FAQ1. How do you identify a capacitor?Ceramic types of capacitors generally have a 3-digit code printed onto their body to identify their capacitance value in pico-farads. Generally, the first two digits indicate the value of the capacitor and the third digit indicates the number of zero's to be added. 2. What are the 2 types of capacitors?Capacitors are divided into two mechanical groups: Fixed capacitors with fixed capacitance values and variable capacitors with variable (trimmer) or adjustable (tunable) capacitance values. The most important group is the fixed capacitors. Many got their names from the dielectric. 3. Can a 440v capacitor be used for a 230v application?The 440 volts listed on the cap is the maximum allowable voltage the capacitor can handle. You could actually use a 370-volt cap on 230 volts. ... Capacitor is connected in series with the auxiliary winding of the motor. Since winding is inductive, the voltage across the capacitor is much higher than the supply voltage. 4. What side of the capacitor is positive?Electrolytic capacitors have positive and negative sides. To tell which side is which, look for a large stripe or a minus sign (or both) on one side of the capacitor. The lead closest to that stripe or minus sign is the negative lead, and the other lead (which is unlabeled) is the positive lead. 5. What does 50 uF mean on a capacitor?It's a symbol that means micro so 50 μF means 50 microfarads or 000050 Farads. The farad is such a large unit that the microfarad is the practical unit for capacitance. 6. What are capacitors in parallel called?When capacitors are connected in parallel, the total capacitance is the sum of the individual capacitors' capacitances. If two or more capacitors are connected in parallel, the overall effect is that of a single equivalent capacitor having the sum total of the plate areas of the individual capacitors. 7. Are AC and DC capacitors interchangeable?You can use AC caps on DC. AC caps have a much higher DC rating. All capacitors have microscopic air bubbles between the foil layers. DC is just a special case where the polarity of the voltage does not change, so you can use AC capacitors - as is - in a DC application. 8. Which type of capacitor is polarized?The only type of capacitor that is polarized (works differently depending on which way the current is flowing) is the electrolytic capacitor. Electrolytic capacitors have higher capacitance, but for most purposes, the non-polarized capacitor is preferred. 9. What is the main function of the capacitor?A capacitor is an electronic component that stores and releases electricity in a circuit. It also passes alternating current without passing direct current. A capacitor is an indispensable part of electronic equipment and is thus almost invariably used in an electronic circuit. 10. What happens if you use the wrong size capacitor?If the wrong run capacitor is installed, the motor will not have an even magnetic field. This will cause the rotor to hesitate at those spots that are uneven. This hesitation will cause the motor to become noisy, increase energy consumption, cause performance to drop, and cause the motor to overheat.