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IntroductionPCB exists in every electronic device. A fully functional PCB is mainly used to create connections between components, such as resistors, capacitors, inductors, diodes, transistors, integrated chips, etc. It is the carrier of the entire logic circuit. Sound PCB design can save production costs, and achieve good circuit performance and heat dissipation effect. PCB designs vary in complexity according to product needs. This article mainly talks about wiring, one of the basics of PCB design.PCB Design: From Idea to Schematic to PCBCatalogIntroductionⅠ PCB Basics: Wiring RulesⅡ Three PCB Wiring MethodsⅢ PCB Design: Wire InspectionⅣ Complete PCB Design Projects Inspection4.1 General PCB Design Inspection Projects4.2 PCB Electrical Characteristics Checking Projects4.3 PCB Physical Characteristics Checking Projects4.4 PCB Mechanical Design Factors4.5 PCB Installation Requirements4.6 PCB Pull-out Requirements4.7 PCB Mechanical Considerations4.8 PCB Electrical Considerations4.9 Electronics Inspection Before Into A PCBⅤ ConclusionⅠ PCB Basics: Wiring Rules1. The area within 1mm from the edge of the PCB board and within 1mm around the mounting hole will not take wiring.2. The power line width should not be less than 18mil; the signal line width should not be less than 12mil; the cpu input and output lines should not be less than 10mil (or 8mil); the line spacing should not be less than 10mil.3. It is necessary noted that the power line and the ground line should be as radial as possible, and the signal line must not be looped.4. Ground circuit rulesThe loop area formed by the signal line should be as small as possible. The smaller the loop area, the less external radiation and the less interference from the outside. An example is shown in the figure below:5. Crosstalk controlHere crosstalk refers to the mutual interference caused by long parallel wiring between different networks on the PCB, which caused by the distributed capacitance and inductance between the parallel lines. The main measures to overcome it are:a. Increase the spacing of parallel wiring and follow the 3W rule. To ensure that the distance between the lines is large enough, when the distance between the line and the center of the line is not less than 3 times the line width (as shown in the figure below). If the line center distance is not less than 3 times the line width, 70% of the line electric fields will not interfere with each other, which is called 3W rule.b. Insert a grounded isolation wire between the parallel wires. Reduce the distance between the wiring layer and the ground plane.6. The direction control rules of routing:The routing directions of adjacent layers are orthogonal. Different signal lines in the same direction on adjacent layers should be avoided to reduce unnecessary interlayer crosstalk. When the signal rate is high, use a ground plane to isolate each wiring layer, in other words, isolate each signal line with ground line. The neighbouring wires used in the input and output end of the circuit shouldn’t be parallel to prevent the feedback, and it is best to add a ground wire between these wires.7. Open loop inspection rules for wiring:Generally, it is not allowed to have a floating wiring at one end, because of the "antenna effect" and unnecessary interference radiation and reception, which may bring unpredictable results.8. Impedance matching inspection rulesThe wiring width of the same network should be kept the same. Line width variations will bring uneven line characteristic impedance, and reflection will occur when the transmission speed is high. This situation should be avoided in the design. Under certain conditions, such as the lead wires of the connector and the similar structure of the lead wires of the BGA package, the change of the line width may not be avoided, so that the length of the middle inconsistent part should be minimized.9. Wiring closed loop inspection rules:Prevent signal lines from forming self-loops between different layers. Such problems are prone to occur in multilayer board design, and it will cause radiation interference. As shown below:10. The branch length control rule of wiring:Try to control the length of branches, and the general requirement is Tdelay≤Trise/20.11. Resonance rules of wiring:For high-frequency signal design, the wiring length must not be an integer multiple of its wavelength to avoid resonance.12. Line length control rules:In fact, it refers to the short-circuit rule. When designing, you should keep the wiring length as short as possible to reduce interference problems caused by unnecessary lines. Especially for some important signal lines, such as clock lines, be sure to place oscillators close to the device. In the case of driving multiple devices, the network topology should be decided according to the specific situation.13. Parallel input and output wires on the PCB board should be avoided as far as possible to avoid parallel. It is best to place a ground wire between the two wires to avoid circuit feedback coupling.14. Digital ground and analog ground should be separated. For low-frequency circuits, single-point parallel grounding should be used. High-frequency circuits should be grounded in series with multiple points. For digital circuits, the ground wire should be closed into a loop to improve anti-noise capability.15. The wiring and via distribution of the whole circuit board should be uniformity. When the outer signal of the circuit board has a large blank area, auxiliary lines should be added to make the lines distribution on the board basically balanced.16. The low-frequency circuit can be grounded at a single point in parallel, and the actual wiring can be connected in series and then grounded in parallel. The high-frequency circuit can be grounded in series with multiple points. The ground wire should be short and thick. For high-frequency components, a large area ground foil can be used. The ground wire should be as thick as possible. If the ground wire is a very thin, the ground potential will change with the current, which reduces the noise resistance.17. Multilayer boards should be as symmetrical as possible when designing the laminated structure, as well as the wiring density and copper layout of each layer to reduce warpage and reduce EMI during soldering.18. The signal line should not cross the power supply and ground. The signal reference plane should be as complete as possible.19. Impedance controlThe signal lines that need impedance control must be wired in strict accordance with the calculated data, in addition, it is necessary to tell manufacturers it. For signal lines that do not require it, the impedance should be calculated to prevent unnecessary interference.20. Grid copper should be used less in low frequency circuits. Although it can effectively reduce the problem of large area copper skin blistering. When using grid copper, you need to consider the electrical length of the grid line and the working frequency of the circuit board. If using grid copper, the power supply should also be coated with solid copper as much as possible.21. A group of buses with the same attribute should be wired side by side as much as possible, and the length should be as equal as possible. Ⅱ Three PCB Wiring MethodsThe wires should take the shortest route between components according to the specified wiring rules. Limit the coupling between parallel wires as much as possible. Good PCB design requires the minimum number of wiring layers, and also requires fair use of the widest wire and the largest pad size corresponding to packaging density. For example, rounded corners and smooth inner corners design may avoid some electrical and mechanical problems, therefore, sharp corners and sharp corners in the wire should be avoided. Here introduces three main PCB routing methods; right-angle wiring, differential wiring, and serpentine wiring to illustrate PCB layout:A. The influence of right-angle wiring on the signal is mainly reflected in three aspects:1. The corner can be equivalent to the capacitive load on the transmission line to slow down the rise time.2. Discontinuous impedance will cause signal reflection.3. The EMI generated by the right-angle tip reaches the RF field above 10GHz. Such a right-angle is likely to develop into the source of high-speed problems. B. To figure out what is differential wiring, you must first understand what is differential signal. In a word, the driving end sends two equal and inverted signals, and the receiving end judges the logic state "0" or "1" by comparing the difference between the two voltages. The pair of traces carrying differential signals is called differential traces. Compared with ordinary single-ended signal traces, differential signals have the most obvious advantages in the following three aspects:1. Have Strong anti-interference ability. Because the coupling between the two differential traces occurs, when there is noise interference from the outside, they are almost coupled to the two lines at the same time. However, the receiving end only cares about the difference between the two signals. Therefore, the external common mode noise can be completely canceled.2. It can effectively suppress EMI. Due to the opposite polarity of the two signals, the electromagnetic fields radiated by them can cancel each other out. What’s more, the tighter the coupling, the less the electromagnetic energy leaked to the outside world.3. The timing positioning is accurate. Because the switch change of the differential signal is located at the intersection of the two signals. Unlike ordinary single-ended signals, which rely on the high and low threshold voltages to judge. Timing positioning is less affected by the process and temperature, and also more suitable for circuits with low amplitude signals. The current popular LVDS (low voltage differential signaling) refers to this small amplitude differential signaling technology. C. Serpentine line is a type of wiring method often used in PCB layout. Its main purpose is to adjust the delay to meet the system timing design requirements. The two most critical parameters are the parallel coupling length (Lp) and the coupling distance (S). Obviously, when a signal is transmitted on a serpentine trace, the parallel line segments will be coupled in a differential mode. The smaller the S, the greater the Lp, the greater the coupling. It may cause the transmission delay to be reduced, also the signal quality is greatly reduced due to crosstalk. The mechanism can refer to the analysis of common mode and differential mode crosstalk. The following are some suggestions when dealing with serpentine wring:1. Try to increase the distance (S) of parallel lines, at least more than 3H(H refers to the distance from the signal trace to the reference plane). As long as S is large enough, the mutual coupling effect can be almost completely avoided.2. Reduce the coupling length Lp. When the double Lp delay approaches or exceeds the signal rise time, the crosstalk generated will reach saturation.3. The signal transmission delay caused by the strip-line or embedded micro-strip line is less than that of the micro-strip. Theoretically, the strip-line will not affect the transmission rate due to differential mode crosstalk.4. For signal lines with high-speed and strict timing requirements, try not to take serpentine lines, especially in a small area.5. You can often use s-shaped routing at any angle, which can effectively reduce the mutual coupling.6. In high speed, the serpentine line has no ability so-called filtering or anti-interference, and can only reduce the signal quality, so it is better to use for timing matching.7. Sometimes you can consider the spiral routing method for winding. Simulation shows that its effect is better than normal serpentine routing.Ⅲ PCB Design: Wire Inspection1.Wire SpacingThe minimum spacing of wires must be determined to eliminate voltage breakdown or arcing between adjacent wires. The spacing is variable, it mainly depends on the following factors:1) Peak voltage between adjacent wires2) Atmospheric pressure (maximum working altitude)3) Coating layer4) Capacitive coupling parametersComponents with critical impedance or high-frequency components should be placed very close to reduce the critical stage delay. There is something need to pay attention to. Transformers and inductive components should be isolated to prevent coupling. Inductive signal wires should be laid orthogonally at right angles. Components that generate any electrical noise due to magnetic field movement should be isolated or rigidly installed to prevent excessive vibration.2. Whether the wire is short and straight without sacrificing function.3. Whether the restrictions on the wire width are complied with.4. There must be a minimum distance between wires, wires and mounting holes, wires and pads.5. Whether to avoid all the wires (including component leads) closer to parallel wiring.6. Whether sharp corners (≤90℃) are avoided in the wire pattern. Ⅳ Complete PCB Design Projects Inspection4.1 General PCB Design Inspection Projects1) Has the circuit been analyzed? Is the circuit divided into basic units to smooth the signal?2) Does the circuit allow short or isolated key leads?3) Where must be shielded, are they effectively shielded?4) Have you made full use of the basic grid graphics?5) Is the best size of the printed circuit board?6) Do you use the available wire width and spacing as much as possible?7) Has the preferred pad size and hole size been used?8) Are the base plate and the sketch consistent?9) Is less cross-wiring used? Do cross wires pass through components and accessories?10) Are the letters visible after assembly? Are their size and model correct?11) In order to prevent blistering, is there any window on the large area of copper foil?12) Are there tool positioning holes?4.2 PCB Electrical Characteristics Checking Projects1) Have you analyzed the influence of wire resistance, inductance, and capacitance, as well as the critical voltage drop on the ground?2) Does the wire spacing and shape meet the insulation requirements?3) Has the insulation resistance value been controlled and specified in key areas?4) Is the polarity fully recognized?5) According to geometric view, has the effect of wire spacing on leakage resistance and voltage been measured?6) Has the medium for changing the surface coating been identified?4.3 PCB Physical Characteristics Checking Projects1) Are all pads and their positions suitable for final assembly?2) Can the assembled PCB meet the shock and vibration conditions?3) What is the required spacing of standard components?4) Are the components that are not firmly installed or the heavier parts fixed?5) Is the heating element heat dissipation and cooling normally? Or is it isolated from the printed circuit board and other heat-sensitive elements?6) Are the voltage divider and other multi-lead components placed correctly?7) Is the arrangement and orientation of components easy to check?8) Has it eliminated all possible interference on the printed circuit board?9) Is the size of the positioning hole correct?10) Are the tolerances complete and reasonable?11) Have you controlled and signed the physical properties of all coatings?12) Is the ratio of via hole and lead diameter within an acceptable range?4.4 PCB Mechanical Design FactorsThe printed circuit board adopts mechanical methods to support the components, however, it cannot be used as an unique structural part of the entire device. On the edge of the printing plate, at least every 5 inches for a certain support. The factors that must be considered when selecting and designing printed circuit boards are as follows:1) The size and shape of the printed circuit board.2) The type of mechanical accessories and plug (seat) required.3) The environmental adaptability of circuits.4) According to some factors, such as heat and dust, install the printed circuit board vertically or horizontally.5) Some environmental factors that require special attention, such as heat dissipation, ventilation, shock, vibration, and humidity, dust, and radiation, etc.6) Physical support7) Install and fix.8) Disassemble4.5 PCB Installation RequirementsAccording to practical experience, the distance between the supporting points of a printed circuit board with a thickness of 0.031-0.062 inches should be at least 4 inches. For a printed circuit board with a thickness greater than 0.093 inches, the distance between the supporting points should be at least 5 inches. Taking this measure can improve the rigidity of the printed circuit board and avoid possible resonance. The following factors should be considered before deciding which mounting technology they use.1) PCB structure.2) Input and output terminals.3) Available equipment space.4) Convenience of loading and unloading.5) Type of attachments.6) Required heat dissipation.7) Required shieldability.8) The type of circuit and its relationship with other circuits.4.6 PCB Pull-out Requirements1) The influence of plugging tools on the installation distance between two printed circuit boards.2) When the plug-in tool used in the equipment, its size should be considered.3) A plug-in device is required, which is usually fixed to the printed circuit board assembly with rivets.4) As for the mounting frame of the printed circuit board, special design such as load bearing flange is required.5) The adaptability of the plug-in tool used and the size, shape and thickness of the printed circuit board.4.7 PCB Mechanical ConsiderationsThe characteristics of the board substrate that have an important influence on the printed circuit assembly are: water absorption, thermal expansion coefficient, heat resistance, flexural strength, impact strength, tensile strength, shear strength and hardness. All these characteristics affect the function and the production efficiency of the printed circuit board structure. For most applications, the dielectric substrate materials of the printed circuit board are as following:1) Phenolic impregnated paper2) Acrylic-polyester impregnated randomly arranged glass mat3) Epoxy impregnated paper4) Epoxy impregnated glass clothEach substrate can be flame retardant or combustible. The first 3 types mentioned above can be processed. The most common used material for printed circuit boards with metalized holes is epoxy-glass cloth. Its dimensional stability is suitable for high-density circuits and can minimize the occurrence of cracks in the metalized holes. One disadvantage of epoxy-glass cloth laminate is that it is difficult to punch in the usual thickness range of printed circuit boards. For this, all holes are usually drilled and copied and milled to form a print shape of the circuit board.4.8 PCB Electrical ConsiderationsIn DC or low-frequency AC applications, the most important electrical characteristics of insulating substrates are: insulation resistance, anti-isolation, printed wire resistance, and breakdown strength. In high frequency and microwave applications, include: dielectric constant, capacitance, and dissipation factors. In all applications, the current carrying capacity of printed wires is important.4.9 Electronics Inspection Before Into A PCB1) Check the rationality and correctness of the schematic diagram.2) Check the correctness of the component packaging of the schematic.3) The distance between strong and weak current lines, and the distance between isolation areas.4) Check the schematic diagram and PCB diagram to prevent the loss of the network table.5) Whether the package of the component matches the physical object.6) Whether the placement of the components is appropriate.7) Whether the components are easy to install and disassemble.8) Whether the temperature sensitive element is too close to the heating element.9) Whether the distance and direction of the mutual inductance components are appropriate.10) Whether the placement between the connectors is smooth.11) Easy to plug in and plug out12) Input and output13) Strong current and weak current14) digital and analog should be interlaced.15) Arrangement of elements on the upside and downside16) Check whether the directional component has been wrong flipped instead of rotated.17) Check whether the mounting holes of the component pins are suitable and whether it is easy to insert.18) Check whether the empty pin of each component is normal and whether it is a missing line.19) Check whether there are vias between the upper and lower wiring of the same net table. And the pads are connected through the holes, to prevent disconnection and ensure the integrity of the circuit.20) Silk screen printing should be clear, so that the operation of welding or maintenance can be easy.21) The arrangement of power and signal lines in the socket should ensure signal integrity and anti-interference.22) Pay attention to the proper ratio of pads and solder holes.23) Each plug should be placed on the edge of the PCB board as much as possible and easy to operate.24) Whether the size and distribution of the mounting holes on the PCB are appropriate to reduce the PCB bending stress.25) Pay attention to the height distribution of the components on the PCB to ensure easy assembly.Ⅴ ConclusionBased on the above mentioned rules, drawing the PCB schematics you need becomes easier. Decide what PCB you want to and install a PCB design software. PCB software is really helpful and powerful. Also a software can check your design to make sure the design does not contain errors such as traces that incorrectly touch, traces too skinny, or drill holes that are too small. For example, run the Electrical Rules Checker (ERC) to see if you’ve made any typical errors. There is less thing stopping you from making your first PCB, right? Frequently Asked Questions about PCB Design Diagram1. Which side of PCB is correct for soldering?The bottom side of the PCB is usually the side without components and the side that touches the solder wave during assembly. That is why sometimes it is also called SOLDER side. However more often, PCB are populated on both sides and the assembly process does not require wave soldering. 2. Which soldering method is suitable for soldering printed circuit board?Soldering Iron – Used to melt solder and connect component pins to board pads. A cheap soldering pencil may be sufficient, but a temperature-controlled solder station is best for high performance boards. Solder – An alloy of tin and lead with a low melting point. 3. What is PCB diagram?A PCB schematic is a simple two-dimensional circuit design showing the functionality and connectivity between different components. ... Once the blueprint has been completed, the PCB design comes next. The design is the layout, or physical representation of the PCB schematic and includes the copper track and hole layout. 4. Why we use PCB in soldering?PCB soldering is another term for the process of soldering electrical circuit boards. ... As the soldering iron melts this metal, it is then used a bit like glue to stick to pieces together. As the solder metal cools, it will re-harden into one large shape that connects the two parts. 5. How do you read a PCB board?Start with an easy analog circuit, such as a guitar distortion pedal, and work your way up to more complicated versions. Make a drawing of the top of the circuit board. Show the positions of the capacitors, integrated circuits, resistors, transistors and other components. Review it to make sure everything is included.

IntroductionLED lights cannot directly use the conventional mains grid voltage, because of the characteristics of LED lighting. In order to meet the special voltage and current requirements of LEDs, a specially designed voltage conversion device must be used to make LEDs work normally. This device is an LED driver. LED drivers are usually switching mode devices that convert the input voltage (Typically 120-220 VAC or 12 VDC) into a voltage at which the current drawn by the LED's is equal to its drive current. The drive current is regulated for optimum brightness, led service life, and battery life. A drive current lower than the maximum drive current of an LED can greatly prolong service life. As a key part of LED lighting, the quality of LED drivers directly affects the performance of LED lighting.Choose the Correct LED Drivers For LED LightsNo matter how good the quality of the LED driver is, failure and maintenance are inevitable. This article will analyze the 10 failures in LED lighting design and its application based on the relevant technology and practical experience of the LED driver.CatalogIntroductionⅠ LED Driver Failure Analysis1.1 Forward Voltage Drop (Vf) Range1.2 Power Margin and Derating Requirements1.3 LED Working Characteristics1.4 Test Session1.5 Different Load with Different Test Results1.6 LED Driver Circuit Problem1.7 Wrong Phase Wring1.8 Grid Fluctuation1.9 Frequent Line Trips1.10 Drive CoolingⅡ LED Driver Maintenance2.1 Multimeter to Detect LED Driver2.2 Identify LED Power SupplyⅢ LED Driver Circuit Modulation3.1 Pulse Width Modulation (PWM)3.2 Pulse Frequency Modulation (PFM)3.3 Sliding-Mode ModulationⅣ One Question Related to LED DriverⅠ LED Driver Failure AnalysisThe LED driver is measuring current passing through LEDs using sense resistor and then increase or decrease the voltage to maintain constant current continuously. LEDs are kind of diode so they need DC voltage to operate so most of the LED drivers are boost and can vary output supply in wide range (example, 16V to 38V). They also have dimming control by PWM signal from microcontroller OR by having a manual potentiometer to change sense resistor. According to them, LED driver failures are complex, but we can follow the steps below to analyse.1.1 Forward Voltage Drop (Vf) RangeLED lamp load end is generally composed of a number of LEDs connected in series, and its working voltage Vo=Vf×Ns, where Ns represents the number of LEDs. And the Vf of an LED varies with temperature. Generally, at a constant current, Vf becomes lower at high temperatures and becomes higher at low temperatures. The LED lamp load working voltage is VoL at high temperature, and VoH represents a value at low temperature. When selecting an LED driver, consider that the driver output voltage range is greater than VoL～VoH.If the maximum output voltage of the LED driver is lower than VoH, the maximum power of the lamp may not reach the actual power required at low temperature. If the minimum voltage of the selected LED driver is higher than VoL, the output of the driver may exceed the working range at high temperature. And LED driver will work unstable, making the lights flicker.Considering the overall cost and lamp efficiency, don’t blindly pursue the ultra-wide output voltage range of the LED driver. Because the driver voltage is only in a certain range, its efficiency is the highest. When the range is exceeded, the efficiency and power factor (PF) will deteriorate. In addition, if the design of the driver output voltage range is too wide, high costs and unoptimized efficiency will be made. 1.2 Power Margin and Derating RequirementsIn general, the nominal power of the LED driver refers to the data measured under the rated environment and rated voltage. Taking into account different applications, most LED driver suppliers will provide power derating curves in their product specifications (common load vs. ambient temperature derating curves and load vs. input voltage derating curves).As shown in Figure 1, the red curve represents the power derating curve when the input is 120Vac, and its load varies with the ambient temperature. When the ambient temperature is lower than 50℃, the LED driver is allowed to be 100% full load. When the ambient temperature is as high as 70℃, the LED driver can only be derated to 60% of the load. When the ambient temperature changes between 50℃~70℃, the driver load varies with the temperature linearly.Figure 1. Power Derating Curve (Load vs Ambient Temperature)The blue curve represents the power derating curve when the input is 230Vac or 277Vac, and its load varies with the ambient temperature. The principle is similar to the above mentioning.As shown in Figure 2, the blue curve represents the derating curve of the LED driver when the ambient temperature is 55°C, its output power varies with the input voltage. When the input voltage is 140Vac, the load of the driver is allowed to be 100%, and the input voltage will be adjusted downward. If the output power remains the same, the input current will rise, resulting in input terminal loss and lower efficiency. When the device temperature rises, exceeding the rated temperature, which may cause the device to fail.Figure 2. Power Derating Curve (Load vs Input Voltage)Therefore, when the input voltage is less than 140Vac, the output load of the LED driver is required to linearly decrease as the input voltage decreases. According to the above derating curve and corresponding requirements, when choosing a LED driver, actual applying needs are important, as well as the derating margin. 1.3 LED Working CharacteristicsWhen the required input power is a fixed value, such as a fixed error of 5%, the output current can only be adjusted to the specified power for each lamp. Due to different working ambient temperature and different lighting time, the power of each lamp will vary greatly.Although there are considerations for marketing and business factors. However, the volt-ampere characteristic of the LED lamp determines that the LED driver is a constant current source, and its output voltage varies with the series voltage Vo of the LED load. When the efficiency of the driver is basically unchanged, its input power changes with Vo. And meanwhile, the overall efficiency of the LED driver will increase after thermal equilibrium. Under the same output power, the input power will decrease compared to the boot time.Therefore, when formulating requirements, LED driver users should first understand the operating characteristics of LEDs. Avoid suggesting indicators that do not meet the principles of operating characteristics, and indicators that far exceed actual requirements, resulting in excess quality and cost waste. 1.4 Test SessionSample test problems, for example, multi-brand LED driver samples all failed during the test. The reason is that a self-dual voltage regulator is used to directly power the LED driver for testing. After power on, the voltage regulator is gradually adjusted from 0Vac to the rated operating voltage of the LED driver. This kind of test operation can easily make the LED driver start and work with the load when the input voltage is very small, but this situation will cause the input current to be far greater than the rated value. And the internal input terminal related components, such as fuses, rectifier bridges, thermistors, etc. will fail due to excessive current or overheating, damaging the LED driver.The correct test method is to adjust the voltage regulator to the rated operating voltage range of the LED driver, and then connect the driver to power-on test. Of course, technically improving the design can also avoid the failure caused by this kind of test misoperation. That is, a starting voltage limit circuit and an input undervoltage protection circuit are set at the input of the driver. When the input does not reach the start-up voltage set by the driver, the driver does not work. When the input voltage drops to the input undervoltage protection point, the driver enters the protection state. Although the driver has a self-protection function and will not fail, you must carefully understand whether the purchased LED driver product has this protection before testing (considering the actual application environment of the LED driver, most LED drivers currently do not have this set). 1.5 Different Load with Different Test ResultsOn the one hand, when the LED driver is tested with LED lights, the result is normal; on the other hand, when driver tested with an electronic load, the result may be abnormal. Usually this phenomenon has the following reasons:1) The output instantaneous voltage or power of the driver exceeds the working range of the electronic load instrument. (Especially in CV mode, the maximum test power should not exceed 70% of the maximum power of the load. Otherwise, the load may instantaneously have overpower protection when loading, causing the driver to fail to work.)2) The characteristics of the electronic load instrument used are not suitable for measuring constant-current device. And the load voltage gear jumping, result in the drive to fail to work.3) Because there is a large capacitor inside the input of the electronic load meter. The test is equivalent to connecting a large capacitor in parallel with the driver output, which may cause the driver's current sampling work to be unstable. As we all known, the LED driver is designed to meet the working characteristics of LED lamps. The most practical test method is to use the LED lamp as a load, and connects an ammeter and a voltmeter in series to test. 1.6 LED Driver Circuit ProblemThe following conditions often cause damage to the LED driver:Connect AC to the DC output terminal of the driver, causing the driver to fail.Connect AC to the DC/DC output or input of the driver, causing the driver to fail.Connect the output terminal of the constant current to the dimming light, causing the driver to fail.Connect the phase wire to the ground wire causing the driver has no output and the housing is charged. 1.7 Wrong Phase WringTake an international example: the rated working voltage between each phase line and the neutral line is 220V, and the voltage between the phase line and the phase line is 380V. If the driver is connected to two phase wires, after power on, the LED driver input voltage exceeds the rated range, which cause the product to fail.As shown in Figure 3, V1 represents the first phase voltage, V2 represents the second phase voltage, and R1 and R2 respectively represent the drivers normally installed on the line. When the neutral line (N) on the circuit is disconnected, the drivers R1 and R2 on the two branches are connected to the 380V voltage after being connected in series. Because of the difference in input internal resistance, when one of the drivers is charged to start, the internal resistance becomes smaller. Most of the voltage may be applied to another driver, causing the overvoltage damage. Therefore, it is recommended that switches or short-circuiters on the same distribution branch should be disconnected together, not just cut off the neutral line. What’s more, do not put the power distribution fuse on the neutral line to avoid bad effect of the neutral line on the circuit.Figure 3. Neutral Line Open Circuit Diagram 1.8 Grid FluctuationWhen wires of a transformer grid branch is too long and there is large power equipment on the branch, the grid voltage will fluctuate sharply when the large equipment starts and stops. It even causes the grid to be unstable. When the grid voltage exceeds 310V, the drive may be damaged (even if there is an LED lightning protection device, it is useless. Because the lightning protection device is to deal with pulse spikes of tens of uS level, and the fluctuation of the grid may reach tens of mS, or even hundreds of mS) . Therefore, special attention should be paid when there is large electric machinery on the street lighting branch power grid. It is best to monitor the fluctuation range of the power grid or to supply power to the grid transformer separately. 1.9 Frequent Line TripsToo many lights are connected on the same branch, which leads to overload on a certain phase and uneven power distribution among the phases, resulting in frequent line trips. 1.10 Drive CoolingAlthough the LED has high luminous efficiency, only a small part of the energy flowing through the LED is radiated in the form of visible light. And most of the remaining energy is consumed in the LED in the form of heat, so the LED generates more serious heat. When the driver is installed in a non-ventilated environment, the driver housing should be in contact with the lamp housing as much as possible. If possible, apply thermal glue or a thermal pad on the contact surface between the housing and the lamp housing to improve the heat dissipation of the LED driver and ensure the reliability of the driver.Ⅱ LED Driver Maintenance2.1 Multimeter to Detect LED DriverMeasuring the output voltage of the no-load LED driver with a multimeter, if the output voltage is not detected, does it mean that the driver is broken? Look at the following steps:1) The voltage of the non-isolated LED power supply in the no-load state is about 300V tested with a multimeter, and it is about 220V with a PFC.2) Isolating the LED power supply, the voltage in the no-load state, tested with a multimeter, is about 3-5V more than the total voltage of the rated LED series. However, although the output voltage can be tested under no load, it does not mean that it can be normal under load. At this time, it is necessary to connect the corresponding LED light board to see the performance of the LED lighting. If there is no flicker, the output voltage is also equal to the total voltage of LED lights in series connection. This situation can be considered normal, otherwise it fails. If there is no output voltage at no load, the power supply must be broken. 2.2 Identify LED Power SupplyThe LED power supply is widely used in many applications. So how to distinguish the quality of LED power supply is particularly important. A few methods are briefly introduced below. LED Driver ICThe power of IC drive, the quality of IC directly affects the whole power supply. The lighting manufacturer should understand the IC design solution and calculate the cost of the driver, so as to purchase power products at a reasonable price. TransformersThe control chip can be regarded as the brain center of the power supply, while the transformers determine the power and temperature resistance. The transformer is responsible for the transfer of "AC to DC". However, the energy overload will damage the device. The core of the transformer is the magnetic core and the wire package. Electrolytic Capacitors and Ceramic CapacitorsThe quality and life requirements of input electrolytic capacitors are important. However, people tend to ignore the quality requirements of the output capacitor. In fact, the life of the output capacitor also has a great impact on the life of the power supply. The output end has a switching frequency of up to 60,000 times per second, which causes the parasitic resistance of the capacitor to heat up and produce substances similar to scale. Finally, the electrolyte heats up and bursts. Ceramic capacitors: The materials are divided into X7R, X5R and Y5V, and the actual capacitance value of Y5V can only reach 1/10 of the actual value. In addition, the nominal capacitance value only refers to when a capacitor works at 0V. Therefore, this tiny chip with poor options will also lead to a price difference in cost and greatly shorten the life of the power supply. Circuit Design and Welding ProcessJudgment of the pros and cons of the design: Aside from the professional point of view, it can be distinguished by some intuitive methods, such as the neat layout of the components, and soldering points. As for flying leads and manually adding components, it is a serious lack of techniques and efficiency. As we all know, the quality of mechanized production of wave soldering process is definitely better than manual welding. Because the machining process is more neat and uniform. Identification method: whether there is red glue on the back board.The flashing phenomenon of the lamp after a period of use is basically caused by the power supply or the weak welding of the lamp beads. However, it is extremely difficult to detect the virtual welding of products through aging, so AOI must be used to detect the quality of the power supply. Batch Inspection of Aging Racks and High Temperature Aging RoomsNo matter how good the power products are controlled by materials and production processes, they still need to be tested for aging. Because the incoming inspection of electronic components and transformers is difficult to control. Only through the aging of the entire batch of power supplies and the high temperature sampling inspection of the high temperature room. This is a wide-ranging screening to determine whether the materials have safety hazards. Ⅲ LED Driver Circuit ModulationThe LED driver circuit is divided into constant-voltage type and constant-current type according to the power supply to the LED. Constant-current switch type LED driver circuit samples the current flowing through the LED lamp, and gives the output control signal to control the on and off of the switching power tube, which aims to adjust the output current as the set value. The dimming control circuit mainly includes SCR dimming circuit, pulse width modulation (PWM), pulse frequency modulation (PFM), sliding mode control, PWM_PFM, PSM, etc. Let's take pulse width modulation (PWM), pulse frequency modulation (PFM), and sliding mode modulation to introduce in detail below. 3.1 Pulse Width Modulation (PWM)Pulse width modulation, shown in the figure below, refers to the stability of the output voltage by changing the on-time of the switching power tube in each cycle at a specific frequency. That is adjusting the duty cycle to obtain stable output voltage. When the output voltage changes due to the working environment, noise and other factors, the error amplifier samples the voltage change and sends the signal to the control circuit. The control circuit adjusts the duty cycle of the switching power tube signal to maintain the stability of the output voltage.Figure 4. PWM Modulation Based on BUCK StructureFigure 4 (a). Voltage ModeFigure 4 (b). Peak Current ModeFigure 4 (c). Average Current Mode3.1.1 Advantages of PWM(1) The PWM modulation method has high efficiency under heavy load, and has a good dynamic response to load changes.(2) The output ripple voltage is small and the linearity is high.(3) The frequency is stable, the duty cycle adjustment is not restricted, the control is simple, and both the current control mode and the voltage control mode are applicable.3.1.2 Disadvantages of PWM(1) The efficiency of PWM modulation method decreases at light load.(2) The transient response is slow during constant-voltage driving, and a more complicated compensation circuit is required.(3) Accurate current detection circuit is required for constant-current driving. 3.2 Pulse Frequency Modulation (PFM)The pulse frequency modulation is shown in the figure below. Under the condition of a certain on-time of the switching power tube, the output voltage can be controlled by adjusting the off time. When the output voltage changes, the error amplifier samples the feedback signal and sends the output signal compared with the reference signal to the control circuit. The control circuit analyzes the error signal and generates a square wave signal with constant pulse width and varying frequency to control the switch power tube to maintain the stability of the output voltage.Figure 5. Pulse Frequency Modulation Based on BUCK Structure3.2.1 Advantages of PFM(1) The PFM modulation has very high efficiency, better frequency characteristics and higher voltage regulation rate at light load.(2) The PFM modulation has a relatively high transmission signal-to-noise ratio and a good anti-interference ability.(3) The output voltage has a large adjustable range and low power consumption.3.2.2 Disadvantages of PFM(1) The efficiency of the PFM modulation will decrease under heavy load.(2) The frequency spectrum of the output ripple is scattered and irregular.(3) The load adjustment range is very small, resulting in high filtering costs. 3.3 Sliding-Mode ModulationSliding-mode modulation mode, the full name is sliding mode variable structure control,  is a discontinuous control. As shown in Figure 6, the sliding mode makes the system structure change purposefully according to its current state, which force the system to make small amplitude and high frequency up and down movements along the designed trajectory under response conditions. That is, sliding mode movement. Reduce the system's sensitivity to disturbances and load jumps.Figure 6. Sliding Mode Control Based on BUCK Structure3.3.1 Advantages and Disadvantage of Sliding ModeIt has the advantages of fast dynamic response, strong robustness and wide stability range, but it also has a problem that the operating frequency is not fixed. Ⅳ One Question Related to LED Driver4.1 QuestionHow long do LED drivers last?4.2 AnswerWhile the light function of an LED may last for years, drivers can give out much sooner. This is why we recommend name brand LED bulbs for the home, especially those with 25,000 hour rated lives. In general, high power white LEDs use much more current, and need of more complicated drivers. Frequently Asked Questions about LED Drivers Failure Analysis and Maintenance1. What is a LED driver IC?They are configured as either inductorless (charge pump) or switching regulator-based LED drivers that support driving white LEDs in series, parallel or combination. ... Topologies include boost regulator, buck regulator, buck/boost, SEPIC topology LED drivers, and more. 2. What is a LED driver used for?LED drivers are electrical devices that prevent damage to LEDs by regulating the forward voltage (VF) of the LED that changes with temperature, avoiding thermal runaway while delivering a constant current to the LED. LED drivers also aid efforts to meet new energy requirements (e.g., Energy Star). 3. How do I choose an LED driver?Use an LED driver with at least the same value as your LED(s). The driver must have a higher output power than your LEDs require for extra safety. If the output is equivalent to the LED power requirements, it is running at full power. Running at full power may cause the driver to have a shorter life span. 4. Why do LED drivers fail?LED FailureThe LEDs usually fail, because they have been connected to a constant LED driver in parallel. If the LEDs have failed you may want to also replace the LED driver. We usually recommend using a model with an adjustable output, and trimming down the output voltage slightly, to avoid over powering the LEDs. 5. How long do LED drivers last?Namely, the life of the driving circuit expires prior to when the LED stops emitting light or has its brightness dropped. The typical nominal lifetime of these elements is often times less than 25,000 hours, while the lifetime of LED itself could be as long as 50,000-100,000 hours. 6. Why do my LED drivers get hot?If the LED driver is trying to draw DC (not a balanced load circuit) then that can also cause the transformer to overheat.7. What is the difference between a transformer and an LED driver?LED drivers and electronic transformers for retrofit LED lighting are not interchangeable. They differ in output and load compatibility i.e. which LED lights they will work with. The fundamental difference between the two is that LED drivers output DC while electronic halogen transformers output 12VAC.

Ⅰ IntroductionAs for operational amplifier applications, in electronic circuit, it is usually combined with a feedback network to form a certain functional module, with a special coupling circuit and feedback. Its output signal can be input signal addition, subtraction or differentiation, integration, etc, which early used in analog computers to do mathematical operations. Now they widely used in the electronics industry, regarded as precision AC and DC amplifiers, active filters, oscillators and voltage comparators.This Video is Introducing Operational Amplifier Applications in the CircuitCatalogⅠ Introduction1.1 Integrated Op AmpⅡ Op-amp ParametersⅢ Application MattersⅣ Classic Amplifier CircuitsⅤ One Question Related Op Amp and Going Further5.1 Question5.2 Answer1.1 Integrated Op Amp1.1.1 Evaluation AnalysisIntegrated operational amplifiers are one of the most widely used devices in analog integrated circuits. In various systems, because of different application requirements, the performance requirements of operational amplifiers are also different.Where there are no special requirements, try to use a universal integrated operational amplifier as much as possible, which can reduce costs and easily replace. When using multiple op amps in a system, use as many op amp integrated circuits as possible. For example, LM324 and LF347 always integrate four op amps together in a circuit.The evaluation of integrated op amps depends on their overall performance. Generally, the merit coefficient K is used to measure the excellent degree of integrated operational amplifiers, which is defined as: where SR is the slew rate and the unit is V / ms. The larger the value, the better the AC characteristics of the operational amplifier; The input bias current of the amplifier is lib, the unit is nA; VOS is the input offset voltage in mV. The smaller the Iib and VOS values, the better the DC characteristics of the op amp. Therefore, for circuits that amplify AC signals such as audio and video, op amps with large SR are better; for circuits that handle weak DC signals, op amps with high accuracy are more suitable (both offset current, offset voltage and temperature drift are relatively small).When selecting an integrated op amp, some factors should be considered in addition to the figure of merit coefficient K. For example, the signal source is a voltage source or a current source; the nature of the load, and whether the output voltage and current of the integrated op amp meet the requirements; operating voltage range, power consumption, and volume of the integrated op amp.Figure 1. Using Operational Amplifier as a Comparator1.1.2 Integrated Op Amp Basics Power supplyThe integrated op amp has two power terminals + VCC and -VEE, with different power supply methods. For different power supply modes, the requirements for input signals are different.1) Dual power supplyOp amps are mostly powered in this way. The positive power (+ E) and negative power (-E) relative to the common terminal (ground) are connected to the + VCC and -VEE pins of the op amp, respectively. In this way, the signal source can be directly connected to the input pin of the op amp, and the amplitude of the output voltage can make the positive and the negative symmetrical.2) Single power supplySingle-supply operation connects the -VEE pin of the op amp to ground. At this time, in order to ensure that the internal unit circuit of the operational amplifier has a suitable static operating point, a DC potential must be added to the input end of the op amp. Zero settingDue to the influence of the input offset voltage and input offset current of the integrated op amp, when the input signal is zero, the output is often not equal to zero. In order to improve the operation accuracy of the circuit, it is required to compensate the error caused by the offset voltage and the offset current. This is the zero setting of the operational amplifier. Commonly used zeroing methods include internal zeroing and external zeroing. For integrated op amps without internal zeroing terminals, external zeroing methods should be used. Self oscillationThe operational amplifier is a high-amplitude multi-stage amplifier. Under the condition of deep negative feedback, it is easy to cause self-excited oscillation. To make the amplifier work stably, a certain frequency compensation network must be added to eliminate the self oscillation. In addition, to prevent low-frequency oscillation or high-frequency oscillation caused by the internal resistance of the power supply, an electrolytic capacitor (10mF) and a high-frequency filter capacitor (0.01 mF ~ 0.1mF) should be connected. Device protectionThere are three aspects to the protection of the integrated op amp safety: power protection, input protection and output protection.1) Power protectionCommon faults of power supply are reverse polarity and voltage jump. For a power supply with poor performance, voltage overshoot often occurs at the moment when the power is turned on and off. Protection measures such as the use of FET current source and voltage regulator clamping protection. The voltage regulator’s voltage value is greater than the normal operating voltage of the integrated op amp and less than the maximum allowable operating voltage of the integrated op amp, and the current of the FET tube should be greater than the normal operating current of integrated op amp.2) Input protectionIf the input differential/common mode voltage of the integrated op amp is too high beyond the limit parameter range of the integrated op amp, it will be damaged.3) Output protectionWhen the integrated op amp is overloaded or the output is shorted, the op amp will be damaged if there is no protection circuit. However, some integrated op amps have internal current limit protection or short circuit protection, and no additional output protection is required to use these devices.Figure 2. An Inverting Op Amp CircuitⅡ Op-amp ParametersTo use the op amp better in the circuit, you must have a certain understanding of its internal parameters. Here are the technical parameters closely related to the op amp: Unity-gain bandwidth Definition: Under the condition that the closed-loop gain of the op amp is 1 time, a constant amplitude sinusoidal small signal is input to the input end of the op amp, and the closed-loop voltage gain measured from the output end of the op amp is reduced by 3dB (or equivalent to 0.707 times of the input signal of the op amp), that is to say, the frequency at which the output signal is reduced by -3dB is unity-gain bandwidth. It is a very important indicator. For a sinusoidal small signal amplification, the unity-gain bandwidth is equal to the product of the input signal frequency and the maximum gain at that frequency. In other words, when you know the frequency and gain of the signal to be processed, the unity-gain bandwidth (gain bandwidth = amplification * signal frequency) can be calculated to select the appropriate op amp. The higher the bandwidth, the higher the frequency of the signal that can be processed, and the better the high frequency characteristics, otherwise the signal will be easily distorted.    For small signals, the unity-gain bandwidth is also called the gain-bandwidth product, which can roughly show the ability of the op amp to process the frequency of the signal. For example, the gain bandwidth of a certain operational amplifier is 1MHz, if the actual closed-loop gain is 100, then the maximum frequency for theoretical processing of small signals is 1MHz / 100 = 10KHz.For the bandwidth of a large signal, that is, the power bandwidth, the influence of the slew rate SR is the major factor, and the unit is V/uS. In this case, the power bandwidth calculated by FPBW = SR / 2πVp-p, that is, the gain bandwidth and power bandwidth must be satisfied at the same time when designing the circuit.For DC signals, bandwidth issues are generally not considered, and accuracy and interference are mainly considered.When the amplification factor of an amplifier is n times, it does not mean that all input signals are amplified n times. When the signal frequency increases, the amplification capability decreases. Open bandwidthThe open-loop bandwidth is defined as: inputting a constant-amplitude sinusoidal small signal to the input of the op amp, the frequency measured at which the open-loop voltage gain decrease 3dB from the output of the op amp to the dc gain of the op amp. This is used for very small signal processing. Slew rate SRWith the op amp connected in a closed loop, a large signal (including a step signal) is input to the input of the op amp, and the output rise rate of the op amp is measured from the output of the op amp called SR. Because the input stage of the op amp is switched during the conversion, the feedback loop of the op amp does not work, that is, the conversion rate is independent of the closed-loop gain. The slew rate is a very important index for large signal processing. For general op amps, the slew rate SR <= 10V / μs, and the slew rate of high speed op amps is SR> 10V / μs. The highest conversion rate SR of current high-speed op amps reaches 6000V / μs. The larger the SR, the better the response of the op amp to the input signal changing at high speed. The larger the signal amplitude, the higher the frequency, and the greater the SR. This is used for op amp selection in large signal processing. Full-power bandwidthAt the rated load, under the condition that the closed-loop gain of the op amp is 1 time, a constant-amplitude sinusoidal large signal is input to the input end of the op amp, so that the output frequency of the op amp reaches the maximum (allowing certain distortion) signal. This frequency is limited by the slew rate SR of the op amp. Approximately, full power bandwidth is calculated by formula SR / 2πVop (Vop is the peak output amplitude of the op amp). It is a very important indicator for op amp selection in large signal processing. Setting timeAt the rated load, under the condition that the closed-loop gain of the op amp is 1 time, the time required to input a step large signal to the input of the op amp to increase the output from 0 to a given value. Because it is a step large signal input, a certain jitter will occur after the output signal reaches a given value. This jitter time is called the stabilization time. At this moment, stabilization time + rise time = settling time. For different output accuracy, there is a big difference in the stabilization time. The higher the accuracy, the longer the stabilization time. Equivalent input noise voltageIt refers to any AC random interference voltage generated at the output of an op amp with good shielding and no signal input. When this noise voltage is converted to the input of the op amp, it is called the input noise voltage of the op amp (sometimes expressed by noise current). For broadband noise, the effective value of the input noise voltage of ordinary op amps is about 10 ~ 20μV. This value often corresponds to a certain frequency band. Output impedanceIt refers to the ratio of the change in voltage to the corresponding change in current when the signal voltage is applied to the output of the op amp working in the linear region. At low frequencies it only refers to the output resistance of the op amp. Common mode input resistenceRefers to the ratio of the change in the input voltage of the common mode to the corresponding change in the input current when the two inputs of the op amp input the same signal. At low frequencies, it behaves as a common mode resistance. Generally, the common mode input impedance of the op amp is much higher than the differential mode input impedance, with a typical value above 108Ω. Common mode rejection ratioSame as the definition in the differential amplifier circuit, it is the ratio of the differential mode voltage gain to the common mode voltage gain, which is usually expressed in decibels. It is a parameter that measures the degree of symmetry of the input stage differential amplifier and the ability of the integrated op amp to suppress common mode interference signals. The larger the value, the better. Power supply rejection ratioThe power supply voltage rejection ratio is defined as the change ratio of the input offset voltage of the op amp with the power supply voltage in the linear region. The power supply voltage rejection ratio reflects the effect of power supply changes on the output of the op amp. At present, the power supply voltage suppression ratio is only about 80dB. Therefore, when used for DC signal or small signal processing for analog amplification, the power supply of the op amp needs to be carefully set. Of course, an op amp with a high common mode rejection ratio can compensate a part of the power supply voltage rejection ratio. In addition, when using dual power supplies, the power supply voltage rejection ratio of the positive and negative power supplies may be different. Differential mode input resistanceRefers to the ratio of the change in voltage at the two input terminals to the corresponding change in current at the input terminals when the op amp is operating in the linear region. The differential mode input impedance includes the input resistance and input capacitance, and refers only to the input resistance at low frequencies. General products specification only give input resistance. The input resistance of the op amp using the bipolar transistor as the input stage is not greater than 10MΩ; the input resistance of the op amp as the input stage of the field effect transistor is generally greater than 109Ω. Input offset voltageWhen the input voltage is zero, the output voltage is divided by the voltage gain, plus the negative sign, which is the offset voltage converted to the input. It is the compensation voltage applied at the input when the output voltage is zero. The input offset voltage actually reflects the circuit symmetry inside the op amp. The better the symmetry, the smaller the input offset voltage. The input offset voltage is a very important indicator of the op amp, especially when it is a precision op amp or used for DC amplification.The input offset voltage has a certain relationship with the manufacturing process. It is between ± 1 and 10 mV when op amps use the bipolar process (that is, the standard silicon process). If the field effect tube is used as the input stage, it will be greater. For precision op amps, it is generally below 1mV. The smaller the input offset voltage, the smaller the intermediate zero offset during DC amplification, and the easier it is to handle. Therefore, it is an extremely important index for precision op amps. Input offset voltage driftWithin the specified operating temperature range, it is the ratio of the change in input offset voltage with temperature to the change in temperature. It is actually a supplement to the input offset voltage, which is convenient for calculating the drift of the amplifier circuit due to temperature changes within a given operating range. It is an important indicator for measuring the temperature effect to the op amp. Under normal circumstances, it is about (10 ~ 30) uV / C (degree Celsius), the high quality can be <0.5uV / C. Input offset currentIt is defined as the difference between the base current of the differential pair of the differential input stage when the output DC voltage of the op amp is zero. Used to characterize the degree of asymmetry of the differential input current. The better the symmetry, the smaller the input offset current. Input offset current is a very important indicator for op amps, especially for precision operational amplifier or DC amplifier. The input offset current is approximately one to one-tenth of the input bias current. It has an important impact on small signal precision amplification or DC amplification, especially when a large resistor is used outside the op amp. The effect of input offset current may exceed the effect of input offset voltage on accuracy. The smaller the input offset current, the smaller the intermediate zero offset during DC amplification, and the easier it is to handle. Therefore, it is an extremely important index for precision op amps. Input offset current temperature driftWithin the specified operating temperature range, the ratio of the amount of change in input offset current with temperature to the amount of temperature change. It refers to the temperature coefficient of within the specified operating range, and is also an important indicator to measure the temperature effect on the op amp. It is usually about (1-50) nA / C, and the high quality is about several pA / C. This value is only given in the precision op amp parameters, and it needs attention when it is used for DC signal processing or small signal processing. Input bias current   It is defined as the average value of the bias currents of the two input terminals when the output DC voltage of the op amp is zero, in other words, it is the average current flowing into the input terminal when the operational amplifier is operating in the linear region. The input bias current has a greater impact on the places where input impedance is required, such as high-impedance signal amplification and integrator circuits. The input bias current has a certain relationship with the manufacturing process. If a field effect tube is used as the input stage, the input bias current generally lower than 1nA. It always used to measure the input current of the differential amplifier pair. Maximum differential mode input voltageIt is a voltage that the two input ends of the op amp can withstand. When it is exceeded, the reverse breakdown of the differential tube will occur. The NPN tube made by the plane process has a value of about 5V, and the Vidmax of the horizontal PNP tube can reach more than 30V. Maximum common mode input voltageIt an allowable range of common mode input voltage under normal operating conditions of the op amp. When the input differential pair saturates, the amplifier loses common mode rejection ability. In the case of interference, it is necessary to pay attention to this problem in the use of the circuit. Output peak to peak voltageWorking in the linear region, under the specified load, when the op amp is powered by the large power supply, it is the maximum voltage amplitude that the op amp can output. Except for low voltage op amps, the output peak-to-peak voltage of general op amps is greater than ± 10V, but less than the power supply voltage. This is due to the design of the output stage. The output stage of modern low-voltage op amps has been specially treated. The output peak-to-peak voltage is close to within 50mV of the power supply voltage, so it is called a full-scale output op amp, also known as a rail-to-raid op amp. It should be noted that the output peak-to-peak voltage of the op amp is related to the load, and the value is different for different loads; the positive and negative output voltage swings of the op amp are not necessarily the same. For practical applications, the closer the output peak-to-peak voltage is to the supply voltage, the easier the power supply design.Figure 3. Input Offset Voltage of an Op-ampⅢ Application Matters1) A single-supply op amp must be DC biased, otherwise it will not work properly. For the virtual ground design, in addition to the DC potential, it is necessary to pay attention to the voltage stabilization (it is best to use the reference voltage chip), and also to ensure low impedance AC decoupling, that is, low-frequency decoupling parallel to at least 10uF and high frequency decoupling under 0.1uF.2) The input of the non-inverting amplifier must be biased to ground as a DC path.3) Ordinary op amps cannot directly drive capacitive loads. If there is need, you must use capacitors for phase compensation or output series resistors and then connect the load.4) For the op amp input of the external interface, a TVS tube must be connected in parallel to the positive and negative input pins to prevent the op amp from reversing the polarity due to the too large input voltage signal, forming a parasitic false signal output.5) For amplifier circuits with a gain of more than 10 times, pay attention to controlling the bandwidth gain of the op amp to prevent the device from self oscillation.6) The output of the power amplifier needs to be protected by switching diodes to the power supply and ground, especially when inductive loads are connected.7) When using multiple op amps to process multiple signals, care must be taken to prevent the instantaneous changes in one of the signals from causing crosstalk to the other signal. Therefore, it is recommended not to use one op amp to process multiple signals.8) Most op amp chips are ESD sensitive devices, so pay more attention when using them.9) The pins of unused op amps (excess channels in multiple op amps) should not be left floating, and  grounded or connected to positive and negative power supplies. It is recommended to connect it as a follower (the output is connected to the reverse input) and the non-inverting input is connected to a potential between the power rails (the ground of the dual power system or any suitable point in the circuit). They can also used as buffer amplifiers and add them to a small impact location in the system.Figure 4. Op Amp 741Ⅳ Classic Amplifier CircuitsFigure 5. Inverting AmplifierFigure 5: The grounded non-inverting terminal of op amp is 0V. The inverting and non-inverting terminals are short-circuit, so the inverting end is also 0V. The input resistance of the inverting input terminal is very high, and it is virtual open. In other words, there is almost no current pass through. Therefore, the current flowing through each component in a series circuit is the same, that is, the current flowing through R1 and R2 are the same.Current flowing through R1: I1 = (Vi-V-)/R1Current flowing through R2: I2 = (V--Vout)/R2V- = V+ = 0, I1 = I2Solve the above algebraic equation to get Vout = (-R2/R1)*Vi, it is the input-output relationship of the inverting amplifier. Figure 6. Non-inverting AmplifierIn Figure 6, Vi and V- are virtual short, where Vi = V-. Because of the virtual open, there is no current flow through at the reverse input terminal, then R1=R2. If the current is I, which is obtained by Ohm's law: I = Vout/(R1+R2);Vi is equal to the partial voltage on R2, that is: Vi = I*R2.Virtual short: Vi = V-, R1=R2Ohm's law: I = Vout/(R1+R2), Vi = I*R2Where Vout=Vi*(R1+R2)/R2, represents the non-inverting amplifier. Figure 7. AdderFigure 7: Knowing from the Kirchhoff's law and virtual open theory, the sum of the current through R2 and R1 is equal to the R3, V- = V+ = 0 (short circuit), so (V1 – V-)/R1 + (V2 – V-)/R2 = (Vout – V-) /R3 can be transferred as V1/R1 + V2/R2= Vout/R3. If R1=R2=R3, then the formula becomes Vout=V1+V2, which is an adder. Figure 8. AdderIn Figure 8, because of the virtual open, no current flows through the non-inverting terminal, where V+ = V-, R1=R2, R4=R3, therefore, (V1 – V+)/R1 = (V+-V2)/R2, (Vout – V-)/R3 = V-/R4 can be simplified as V+ = (V1 + V2)/2 V- = Vout/2. So Vout = V1 + V2 is also an adder. Figure 9. SubtractorFigure 9 shows that the current through R1 is equal to the R2, and R4=R3, therefore, (V2– V+)/R1 = V+/R2, (V1 – V-)/R4 = (V--Vout)/R3. If R1=R2, then V+ = V2/2; if R3=R4, then V- = (Vout + V1)/2, because of V+ = V-, so Vout =V2-V1 is a subtractor. Figure 10. Integrator CircuitIn Figure 10, the input voltage at the inverting terminal is equal to the non-inverting terminal because of short circuit; the current through R1 is equal to the C1 because of virtual open. The current flowing through R1 and C1 are Ri=V1/R1, Ci=C*dUc/dt=-C*dVout/dt, respectively. So Vout=((-1/(R1*C1))∫V1dt, which is a integrator circuit. If V1 is a constant voltage U, then the above formula is transformed to Vout = -U*t/(R1*C1)t, then the Vout is a straight line that changes with time. Figure 11. Differential CircuitIn Figure 11, the current through capacitor C1 and resistor R2 is equal because of virtual open; V+ = V- because of short circuit, where Vout = -i * R2 = -(R2*C1)dV1/dt, which is a differential circuit. If V1 is a DC voltage, the output Vout corresponds to a pulse in the opposite direction to V1. Figure 12. Differential Amplifier CircuitFigure 12:Vx = V1……a, Vy = V2……bthen R1, R2, R3 can be regarded as a series, R1=R2=R3, the current I=(Vx-Vy)/R2……cwhere Vo1-Vo2=I*(R1+R2+R3) = (Vx-Vy)(R1+R2+R3)/R2 ……dIf R6=R7, then Vw = Vo2/2 ......e, similarly, if R4=R5, then Vout – Vu = Vu – Vo1, so Vu = (Vout+Vo1)/2 ……fdue to short circuit, Vu = Vw ……g, based on efg formulas, Vout = Vo2 – Vo1 ……hGet from dh, Vout = (Vy – Vx) (R1+R2+R3)/R2, where (R1+R2+R3)/R2 is a fixed value. This value determines the amplifier multiple of the difference (Vy-Vx), thus it is a differential amplifier circuit. Figure 13. Amplifier CircuitIt is a relatively common amplifier circuit. Many controllers accept 0~20mA or 4~20mA current from various measuring instruments. The circuit converts the current into voltage signal to become a digital signal by ADC. Figure 13 is such a typical circuit. As shown in Figure, 4~20mA current flows through the sampling 100Ω resistor R1, there will be a voltage difference of 0.4~2V on R1. Due to virtual open circuit, R3= R5 and R2=R4.Therefore: (V2-Vy)/R3 = Vy/R5 ……a  (V1-Vx)/R2= (Vx-Vout)/R4 ……bShort circuit: Vx = Vy ……cCurrent changes from 0~20mA, then V1 = V2 + (0.4~2) ……dPut cd formulas into b formula: (V2 +(0.4~2)-Vy)/R2 = (Vy-Vout)/R4 ……eIf R3=R2 , R4=R5, then e-a gets Vout =-(0.4~2)R4/R2 ……fIn Figure 13, R4/R2=22k/10k=2.2, then f formula Vout = -(0.88~4.4)V, that is to say, the current of 4~20mA is converted into a voltage range of -0.88~-4.4V. Current can be converted into voltage, and voltage can also be converted into current. Figure 14 is such a circuit. The negative feedback in the above figure does not directly feedback through the resistor, but the emitter junction of the transistor Q1 is connected in series. But it isn't a comparator. As long as it is an amplifying circuit, the law of short circuit and virtual open still conforms.Figure 14. Amplifier CircuitDue to virtual open, no current flows through the input of the op amp,Then (Vi – V1)/R2 = (V1 – V4)/R6 ……aSimilarly (V3 – V2)/R5 = V2/R4 ……bsince short circuit, V1 = V2 ……cIf R2=R6, R4=R5, then V3-V4=Vi can be obtained from abc.The above formula shows that the voltage across R7 is equal to the input voltage Vi, then the current through R7 is I=Vi/R7. If the load RL<100KΩ, the current through R1 and R7 are basically the same. Ⅴ One Question Related to Op Amp and Going Further5.1 QuestionWhat the Application of an Op Amp as a Phase Shifter?5.2 AnswerIn electronic circuit, op amp is used for direct coupling procedure and so DC voltage level at the emitter terminal increases from phase to phase. This rapidly increasing DC level is likely to shift the operating point of the upcoming stages. Thus to move down the increasing voltage swing, this phase shifter is applied.The phase shifter performs by adding a DC voltage level to the output of fall stage to pass the output to a ground level. Frequently Asked Questions about Operational Amplifier Applications1. Why is it called operational amplifier?It's called an “operational” amplifier because it performs a mathematical operation. The most obvious one is multiplication - it amplifies an input signal by a constant. ... But many different 'operations' can be performed by different circuit topologies. 2. What is inside an operational amplifier?Operations amplifiers — op-amps for short, are integrated circuits, constructed mostly out of transistors and resistors. These integrated circuits multiply an input signal to a larger output. You can use these components with voltage and current in both DC and AC circuits. 3. What are operational amplifiers used for?Op amps are used in a wide variety of applications in electronics. Some of the more common applications are: as a voltage follower, selective inversion circuit, a current-to-voltage converter, active rectifier, integrator, a whole wide variety of filters, and a voltage comparator. 4. What are linear applications of op amp?A linear amplifier like an op amp has many different applications. It has a high open loop gain, high input impedance and low output impedance. It has high common mode rejection ratio. Due to these favourable characteristics, it is used for different application. 5. How does an operational amplifier work?An operational amplifier, or op amp, generally comprises a differential-input stage with high input impedance, an intermediate-gain stage, and a push-pull output stage with a low output impedance (no greater than 100 Ω). ... That is, the output gets fed back to the inverting input through some impedance. 6. What do you mean by differential amplifier?A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. It is an analog circuit with two inputs and and one output in which the output is ideally proportional to the difference between the two voltages. 7. What are the non linear applications of op amp?Non-Linear Applications of Op AmpVoltage comparator.Two applications of comparator as window detector and zero crossing detector.Schmitt trigger circuit with the extension of regenerative comparator.Multivibrator circuits.Precision rectifier or super diode with the combination of op amp as voltage follower and a diode. 8. Why do we use differential amplifier?Differential amplifiers are used mainly to suppress noise. ... Noise is generated in the wires and cables, due to electromagnetic induction, etc., and it causes a difference in potential (i.e., noise) between the signal source ground and the circuit ground. 9. What does an operational amplifier do?An operational amplifier is an integrated circuit that can amplify weak electric signals. An operational amplifier has two input pins and one output pin. Its basic role is to amplify and output the voltage difference between the two input pins. 10. What is an ideal operational amplifier?Operational amplifier: The ideal op amp is an amplifier with infinite input impedance, infinite open-loop gain, zero output impedance, infinite bandwidth, and zero noise. It has positive and negative inputs which allow circuits that use feedback to achieve a wide range of functions.

Ⅰ IntroductionIn electronics, the transient interference of voltage and current source is the main cause of damage to circuits and equipment, and it often causes immeasurable losses to the society. These disturbances usually come from the  the starting and stopping operation of power equipment, instability of the AC grid, lightning interference and electrostatic discharge, etc. They are almost ubiquitous and always present. Therefore, scientists have developed a high-efficiency circuit protection device TVS to effectively suppress transient interference.TVS (transient voltage suppressor) is a new product developed on the basis of Zener diode technology. Its circuit symbol is the same as that of ordinary Zener diode. As a common circuit protection component, it is widely used in various fields: automotive electronics, consumer electronics, power drives, industrial power distribution, renewable energy, telecommunications, home appliances, measuring instruments, medical electronics, industrial control, lighting, security systems, building control and automation, audio / video equipment, computers, etc. Learn more about tvs diode, let's check the following transient voltage suppressor tutorial. TVS Diode Tutorial: Transient Voltage SuppressorCatalogⅠ IntroductionⅡ Terminology2.1 Basic Characteristics2.2 Electrical Characteristics2.3 Main ParametersⅢ TVS SelectionⅣ TVS vs Varistor, CapacitorⅤ Application Examples5.1 Lighting Protection5.2 Transistor Protection5.3 Electric Relay Protection5.4 Silicon Control Protection5.5 Integrated Op Amp Protection5.6 Integrated Circuit (IC) Protection5.7 Microcomputer System Protection5.8 DC Regulated Power Supply Protection5.9 Suppression of Electromagnetic Pulse Interference Ⅱ Terminology2.1 Basic CharacteristicsTVS diode, under the specified reverse application conditions, when subjected to a high-energy transient overvoltage pulse, due to it has a very fast response time (sub-nanosecond) and a very high  surge absorption ability, its working impedance can be immediately reduced to a very low on value, allowing large currents to pass, and clamping the voltage to a predetermined level, thereby effectively protecting precision components in electronic circuits from damage. TVS can withstand instantaneous pulse power up to kilowatts, and its clamp response time is only 1ps (10-12S). The forward surge current allowed by TVS can reach 50 ~ 200A under the conditions of TA = 250C and T = 10ms.TVS diodes work similarly to common Zener diodes. If the breakdown voltage is higher than the mark, the TVS diode will conduct. Compared with the Zener diode, the TVS diode has a higher current conduction capability. When the two poles of a TVS diode are subjected to reverse transient high-energy shocks, the high impedance between the two poles of the TVS diode becomes low at a speed of the order of 10 ^ -12S, while absorbing surge power of up to several kilowatts. The clamped voltage between the two poles is at a safe value, which effectively protects precision components in electronic circuits from being damaged by surge pulses. Figure 1. Working Characteristic Curve of TVS DiodeWhen the reverse voltage of the two poles of the TVS is greater than the maximum reverse voltage, it starts to conduct reversely; after the reverse voltage is greater than the breakdown voltage, it begins to be broken down, while the current starts to change suddenly; when the reverse voltage is greater than the maximum clamping voltage, the tube is in an avalanche breakdown state. At this time, the current flowing through the tube increases sharply, and the voltage difference across the tube does not change much (the voltage is clamped).Under specified reverse application conditions, the TVS diode will provide a low-impedance path, and the instantaneous current flowing to the protected component will be shunted to the TVS diode through a large current method, while the voltage across the protected component will be limited to the clamping voltage of TVS. When the overvoltage condition disappears, the TVS diode returns to a high impedance state.  Note: Unidirectional and Bidirectional TVS DiodesUnidirectional TVS SymbolBidirectional TVS Symbol1) Look at the signs: for unidirectional tvs diode, there is a thin color ring, connected to the positive electrode, and for bidirectional tvs diode, there are two rings in the middle, or there is no sign, no polarity.2) Look at the specifications: bidirectional tvs is bidirectional conduction, and unidirectional tvs is unidirectional conduction.3) Look at the model: The model name of the tvs tube is regular, and most of the tvs diode models can see the parameters on the case. For details, it is necessary to consult the manufacturer.4) Using multimeter tool: the unidirectional has voltage, while avalanche breakdown characteristics are available on the DC side; voltage is on both sides, and the DC side is symmetrical on both sides.Bidirectional tvs diodes can absorb instantaneous large pulse power in both forward and reverse directions and clamp the voltage to a predetermined level. In addition, bidirectional TVS is suitable for AC circuits, and unidirectional TVS is generally used for DC circuits. 2.2 Electrical Characteristicsa. Unidirectional TVS (V-I characteristic) Figure 2. Unidirectional TVS DiodeThe unidirectional tvs diode has the same forward characteristics as ordinary Zener diodes, and the reverse breakdown inflection point is approximately “right angle” as a hard breakdown and is a typical PN junction avalanche device. The curve segment from the breakdown point to the VC value indicates that when there is a transient overvoltage pulse, the current of the device increases sharply while the reverse voltage rises to the clamped voltage value and remains at this level.b. Bidirectional TVS (V-I characteristic) Figure 3. Bidirectional TVS DiodeThe V-I characteristic curve of the bidirectional tvs diode is similar to the two back-to-back unidirectional tvs diodes combination. Its forward and reverse directions have the same avalanche breakdown characteristics and clamping characteristics. The symmetry relation of the breakdown voltage on both sides of the positive and negative is as follows: 0.9≤ VBR(positive)/(inverse) ≤1.1, once the interference voltage at both ends of it exceeds the clamping voltage will be immediately suppressed, thus the bidirectional tvs are very convenient for ac loop application.  2.3 Main Parameters1) breakdown voltage V(BR)In the region where the device breaks down, the voltage across the device is measured at the specified test current I (BR), which is called the breakdown voltage. In this area, the tvs diode becomes a low impedance path.2) maximum reverse pulse peak current IPPIn reverse operation, IPP refers to the maximum pulse peak current allowed by the device under specified pulse conditions. The product of IPP and the maximum clamping voltage VC (max) is the maximum value of the transient pulse power.The TVS should be properly selected during use, so that the rated transient pulse power PPR is greater than the maximum transient surge power that may occur in the protected device or wires.When the instantaneous pulse peak current appears, the TVS is broken down and its breakdown voltage value rises to the maximum clamping voltage value. As the pulse current decreases exponentially, the clamping voltage also decreases and returns to the original state. Therefore, TVS diode can suppress the impact of possible pulse power to effectively protect the electronic circuits.The test waveform of the TVS peak current uses a standard wave (exponential waveform), which is determined by TR / TP.Peak current rise time TR: The time from when the current reaches 0.9 IPP from 0.1 IPP.Half-peak current time TP: The time after the current passes through the maximum peak from zero and then drops to 0.5 IPP.The TR / TP values of typical test waveforms are listed below:A. EMP wave: 10ns / 1000nsB. Lightning wave: 8μs / 20μsC. Standard wave: 10μs / 1000μs3) Maximum reverse working voltage VRWMWhen the device operates in reverse, the voltage across the device is called the maximum reverse operating voltage VRWM under the specified IR, usually VRWM = (0.8 ~ 0.9) V(BR). At this voltage, the power consumption of the device is small. When used, VRWM should not be lower than the normal working voltage of the protected device or circuits.4) Maximum clamping current VC(max)The maximum voltage value across the device under the peak pulse current IPP is called the maximum clamping voltage. When used, VC (max) should not be higher than the maximum allowable safe voltage of the protected device. And the ratio of the maximum clamping voltage to the breakdown voltage is called the clamping coefficient.Clamping coefficient = VC(max) / V(BR), the general clamping coefficient is about 1.3.5) Reverse pulse peak power PPRThe PPR of TVS depends on the pulse peak current IPP and the maximum clamping voltage VC (max). In addition, it is also related to the pulse waveform, pulse time and ambient temperature.When the pulse time Tp is constant, PPR = K1‧K2‧VC (max) ‧IPP(K1 is the power coefficient, and K2 is the temperature coefficient of the power) The typical pulse duration tp is 1MS. When the pulse time tp applied to the transient voltage suppression diode is shorter than the standard pulse time, its peak pulse power will increase as tp is shortened.Figure 4. Peak Pluse Power vs Pluse TimeTVS reverse pulse peak power PPR is related to the pulse waveform subjected to surge, expressed by the power coefficient K1: E=∫i(t)‧V(t)dt     i (t) is the pulse current waveform, and V (t) is the clamping voltage waveform.This rated energy value is not reproducible to TVS in a very short time. However, in practical applications, surges often occur repeatedly. In this case, even if the single pulse energy is much smaller than the pulse energy that the TVS device can withstand, if repeat, these single pulse energy will accumulated, in some cases, it will exceed the pulse energy that the TVS device can withstand. Therefore, the circuit design must carefully consider and select the TVS device, so that the accumulation of pulse energy repeatedly applied within the specified interval does not exceed the pulse energy rating of the TVS device.6) Capacitance CPP  Figure 6. The Capacitance of TVS CircuitThe capacitance of TVS is determined by the area of the silicon sheet and the bias voltage. In the case of zero bias, the capacitance value decreases with the increase of the bias voltage. The value of the capacitance will affect the response time of the TVS device.7) Leakage current IRWhen the maximum reverse working voltage is applied to the TVS, the TVS tube has a leakage current IR. When the TVS is used in a high impedance circuit, the leakage current is an important parameter. In practice, especially in automotive electronics, this parameter affects static current.  Ⅲ TVS SelectionWhen selecting tvs diode, the specific conditions of the circuit must be considered, and generally the following principles should be followed:1) The clamping voltage VC (max) is not greater than the maximum allowable safe voltage of the circuit.2) The maximum reverse working voltage VRWM is not lower than the maximum working voltage of the circuit. Generally, VRWM can be selected to be equal to or slightly higher than the maximum working voltage of the circuit.3) The rated maximum pulse power must be greater than the maximum transient surge power present in the circuit. Ⅳ TVS vs Varistor, Capacitor1) TVS diode and varistor do not have switching characteristics like switching elements, but have voltage regulation characteristics like zener diodes.2) The varistor can withstand a larger surge current, and the larger the varistor can withstand the larger surge current, which can reach tens of kA to hundreds of kA at the maximum; but the non-linear characteristics of the varistor are poor and the limiting voltage is higher at large current, and the leakage current is larger at low voltage.3) The non-linear characteristics of TVS diodes are the same as those of Zener tubes. Leakage current before breakdown is very small. After the breakdown, it is in a standard voltage stabilization. Compared with varistors, the maximum clamping voltage of TVS diode is smaller, but its current capability is poor than a varistor. Since the breakdown voltage VBR and the clamping voltage VC of the varistors are relatively high, the current flow capability is relatively strong, and the surge pulse absorption capability is stronger, so it is more suitable for ESD or surge protection of the power interface.4) For the reaction speed, the response speed of the TVS is fast (ps level), while the varistor’s is slow ( ns level). In addition, the capacitance of both is large (ps: TVS also have low capacitance products).5) The TVS tube has high reliability, and a long service life, while the varistor has poor reliability, easy aging and short service life.Other ViewCompared with ceramic capacitors, TVS diodes can withstand a voltage of 15 kV, but ceramic capacitors have a lower ability to withstand high voltages. A 5 kV shock will cause about 10% of the ceramic capacitor to fail, and by 10 kV, its damage rate will reach 60%. Ⅴ Application Examples5.1 Lighting ProtectionIn thunderstorm-prone areas, lightning-induced voltage often breaks down some of the integrated circuits in a computer network. The reason is that cables are damaged due to transient high voltage caused by lightning induction, by installing tvs diodes in the microcomputer, it is useful to reduce damages and commercial loss. And the result shows that it is very practical, and it can improve the reliability of the whole machine application.TVS also have many other applications, for example, for VMOS high power transistors, the tvs diodes between the gate and the source and the machine can prevent gate breakdown and improve the reliability of the VMOS power tube application. 5.2 Transistor ProtectionVarious transient voltages can cause damage to the EB junction or CE junction of the transistor. Especially when the collector of the transistor has an inductive load (coil, transformer, motor), a high-voltage back-EMF can be generated, which often causes the transistor to be damaged. It is necessary to use a tvs diode as a protector. 5.3 Electric Relay ProtectionRelay contacts often use large currents to switch on and off high-current inductive loads such as motors, and the inductor has a high back electromotive force when switching, and has a large amount of energy. What’s more, the contacts are burned or broken to produce an arc, and the surge current generated by the arc is very large. To protect the contacts by suppressing the occurrence of arcs to protect the relays, adding a tvs diode is more effective. In the past, a capacitor or a capacitor series resistor, a diode or a diode series resistor and other suppression methods were used. 5.4 Silicon Control ProtectionThe thyristor may has wrong trigger and cause malfunction. The control electrode current cannot be too large and the voltage cannot be too high, in order to do it, TVS can be used for protection. 5.5 Integrated Op Amp ProtectionIntegrated op amps are very sensitive to external electrical stress. In the process of using op amps, if having excessive voltage or current due to operating errors or abnormal working conditions, especially surges and electrostatic pulses, it is easy to damage the op amp. In the integrating circuit, if the capacitor is charged and discharged to a high potential, and then the power supply voltage is cut off, a transient voltage will be generated at the input terminal, and a large discharge current will occur, resulting in damage to the operational amplifier. At this time, tvs protection method adopted at the input terminal of op amp to avoid device damage. If the capacitance value is large (such as greater than 0.1μF), the protecting effect will be very significant. 5.6 Integrated Circuit (IC) ProtectionAs integrated circuits become more integrated, their withstand voltages are getting lower and lower, and they are easily damaged by transient voltages. Protective measures must be taken, for example, adding tvs diode in the circuit, the CMOS circuit has a protection network at its input and output ends. 5.7 Microcomputer System ProtectionIn a typical microcomputer system, various interference or transient voltages entering through the power line, input line, and output line may cause the microcomputer to malfunction and fail, especially from the switching power supply. The on-off motor near the microcomputer, voltage surges and transients of AC power, electrostatic discharges, etc. may cause the system to fail, and in severe cases may damage the device. Connecting the tvs diode to the input and output lines of the power supply of the microcomputer can prevent the transient voltage from entering the “microcomputer” bus, strengthen the microcomputer's resistance to external interference, ensure the normal operation, and improve its reliability. 5.8 DC Regulated Power Supply ProtectionA DC regulated power supply with a transistor that expands the current output, adding a tvs diode to its regulated output can protect the equipment, and can also absorb peak voltage from the collector to the emitter in the circuit to protect the transistor. In a word, adding a tvs diode at the output end of each voltage stabilization source can greatly improve the reliability of the whole operation. 5.9 Suppression of Electromagnetic Pulse InterferenceA nuclear explosion will cause a strong electromagnetic pulse, which causes induced voltage in the wire. If the induced voltage exceeds the breakdown voltage of the device, it may cause the breakdown of the component, especially for long-term transmission, it is more easily to cause high voltage.TVS diodes are connected in parallel to the signal and power lines, which can absorb the induced voltage caused by electromagnetic pulses, ensure the reliability of the system, and avoid radiation damage to components. Frequently Asked Questions about Transient Voltage Suppression Diode1. How does a transient voltage suppressor work?Transient Voltage Suppressor Diode is a clamping device, so whenever the induced voltage exceeds the avalanche breakdown voltage, it absorbs the excess energy of the overvoltage event, and then it automatically resets after overvoltage condition. 2. What does a transient suppressor do?A transient voltage suppressor or TVS is a general classification of an array of devices that are designed to react to sudden or momentary overvoltage conditions. ... This makes TVS devices or components useful for protection against very fast and often damaging voltage spikes. 3. What is a transient voltage surge suppressor?A transient voltage surge suppressor is a device which is installed on an AC or DC power line to act as a cutoff if there is a momentary surge of electrical power, also known as a “transient.” TVSS devices are considered crucial to the protection of sensitive equipment which would result in circuitry damage or data. 4. What is a voltage transient?A transient voltage is a temporary unwanted voltage in an electrical circuit that range from a few volts to several thousand volts and last micro seconds up to a few milliseconds. ... Faulty contactors and lightning are the most common source of transients. 5. How does a transient voltage suppressor diode work?Transient Voltage Suppressor Diode is a clamping device, so whenever the induced voltage exceeds the avalanche breakdown voltage, it absorbs the excess energy of the overvoltage event, and then it automatically resets after overvoltage condition. 6. Which device can be used as a transient suppressor?Transient voltage suppression diodeOne such common device used for this purpose is known as the transient voltage suppression diode that is simply a Zener diode designed to protect electronics device against overvoltages. 7. What does a suppression diode do?A transient-voltage-suppression (TVS) diode, also transil or thyrector, is an electronic component used to protect electronics from voltage spikes induced on connected wires. 8. What is the difference between Zener and TVS diode?Zener diodes are used to make the voltage more stable. They act as a regulator as well as a protective device. TVS diode is intended to prevent high voltage transients such as Surge and ESD damaging. 9. Where are transient voltage most dangerous?Transient voltages are most dangerous while taking measurements on equipment. Should someone turn something off it could cause a transient voltage spike. 10. What is transient protection?Transients (momentary spikes in voltage or current) can disrupt or damage the products connected to signal or power lines. The most common transient protection schemes limit the voltage amplitude, current amplitude or transition times on the circuit they are protecting.

Ⅰ IntroductionAn operational amplifier, or op-amp for short, is fundamentally a voltage amplifying device designed to be used with external feedback components such as resistors and capacitors between its output and input terminals. Learn more about the most common opamp basics, essential knowledge when selecting and using an op amp in electronics. We can conclude our section and look at Op Amp basics with the following properties and questions. Opamp Basics: Op-Amp CircuitsCatalogⅠ IntroductionⅡ Amplifier Figures of MeritⅢ Q & AⅣ Application: LM358 Classic CircuitsⅡ Amplifier Figures of MeritNegative FeedbackIt is a important technique to improve bandwidth and distortion and control gain.Open-loop GainIt refers to the ratio of the voltage change at the output of the amplifier to the voltage change at the input when the amplifier input and output are open. Common-mode Rejection Ratio (dB)It is the ratio of the amplifier's amplification factor of the differential voltage signal to the amplification factor of the common mode voltage signal.Input Current NoiseIt is the equivalent current noise applied in parallel with the input of the noiseless amplifier.Output CurrentIt refers to the current driven by the load at the output of the op amp. It is usually a function: input overdrive, correlation between output voltage and power supply, temperature, source, and drain characteristics will differ.Phase MarginIt is the phase shift between an output of the same frequency and an inverting input in an open-loop circuit.Voltage GainIt is the ratio of the change in output voltage to the change in input voltage.Programmable Gain BufferIt can set the gain resistance of the op amp (integrated on the template), and the gain can be set to +1, +2, or -1 through simple external connections.Saturation VoltageIt is the voltage between the collector and emitter of the transistor under saturation conditions. In the saturated state, the emitter-base and collector-base are forward biased, so that the voltage between the collector-emitter is very low.Rise TimeThis refers to the time required for the output voltage to change from 10% of its final value to 90% of its final value.Unity-gain BandwidthIt refers to the frequency at which the amplifier's open-loop gain is equal to one. If the op amp frequency response has a single-pole roll-off, the unity-gain bandwidth is equal to 1UGBW.Strobe “OFF” VoltageThe strobe “OFF” voltage is the minimum voltage at the strobe pulse and is guaranteed not to interfere with the comparator operation.Input Current IndexIt refers to the average of the current drawn from the two input pins. In addition, the input current is also commonly called bias current.Gain Bandwidth ProductIt refers to the product of the amplifier's bandwidth and the gain at which the bandwidth is measured.Large Signal Voltage GainIt refers to the ratio of the change in output voltage to the change in input voltage. This parameter is usually specified at a large output voltage, smaller than the maximum output voltage, which is the typical value under direct current conditions.Offset Voltage Temperature CoefficientIt refers to the average rate of change in offset voltage due to changes in junction temperature within a specified temperature range.Output High VoltageIt refers to the high DC output voltage of the comparator, which produces the high output current. And it is usually related to the totem pole or push-pull output of the comparator.Input Source CurrentIt refers to the maximum output positive current produced under the comparator's push-pull output state.Total Harmonic Distortion (THD)When a pure sinusoidal signal is input to the op amp as Vin (w) = Vpsin (wt):Input harmonic distortion: Vout(w)a1Vpsin(wt)+a2Vpsin(wt)+...+anVpsin(nwt)The expression of THD is: THD(%)=[sqrt(a2xa2+a3xa3+...+anxan)/a1]x100Common-Mode Input Impedance (RINCM)It refers to the ratio of the change in the common-mode input voltage to the change in the input current at the inverting or non-inverting terminal.Output Low VoltageIt refers to a low DC output voltage. The output drive is a low voltage sink current. This specification is usually related to the totem pole or push-pull output of the comparator.Using a CMOS op amp as the output driver, although the circuit works well, but requiring a 1m shielded cable, and the oscillation of the operational amplifier is about 1MHz when there is no input signal. If shorten the cable to 10cm, the oscillation is stable.Some op amps are not suitable for driving capacitive loads directly, such as long shielded cables, which is a capacitive load. In addition, coaxial cables have about 60-100pF capacitance per meter.Harmonic DistortionIt refers to the unwanted spurious signals generated at the amplifier output due to the non-linearity of the signal line. When the input is a sinusoidal signal, these spurious signals will appear as integer times of the input frequency (for example, second harmonic, third harmonic).Output Leakage Current (ILEAKAGE)It means that the current enters the comparator output (the output is driven high). It often appears at the output of open collector and open drain.Power Supply Rejection Ratio (PSRR)It refers to the ratio of the change in the input offset voltage to the change in the power supply voltage, PSRR (dB) = 20log10 (DVOS / DVS)Linear Phase DeviationIt refers to how a closed-loop phase response of an operational amplifier approaches and follows the linear relationship between phase change and frequency in a specific frequency band.-3dbIt refers to the frequency when the value of the small signal output amplitude of the closed-loop amplifier decreases to 3dB.Common-mode Voltage RangeIt refers to the typical value of the voltage range at the input, which determines the performance of the amplifier.Specified Power Supply RangeIt describes the power supply voltage required for the operational amplifier to operate.Output Absorption CurrentIt refers to the highest output negative current of the comparator.Output Voltage SwingIt refers to the maximum peak-to-peak swing of the output voltage under a specific load and power supply voltage.Current FeedbackIt refers to a technology used in current feedback amplifiers whose output signal reflects the value of the current input to the inverting input (transimpedance gain function). In some aspects, this topology has operational advantages over traditional voltage feedback.Closed Loop BufferIt refers to an amplifier with high input impedance and low output impedance and a fixed gain of +1. Its typical applications are used for isolation, increased output drive, capacitive load, etc., in addition, there is no need to set the gain resistance.Closed-loop Gain It is the ratio of the change in the output voltage to the change in the input voltage after the feedback and input network added. Generally, this value is set using an external resistance.Common-mode RangeThe common-mode range, also known as the input voltage range, is a measure of the range of input voltages that the input pins of an op amp can accept. This specification is usually relative to the power supply amplitude.Output ImpedanceIt refers to the ideal series output impedance of the ideal operational amplifier when there is no impedance, which is the approximate output impedance of the op amp measured under AC  conditions.Transient ResponseIt refers to the step function response of the closed-loop system of the amplifier under the condition of small signal (usually less than 100mV).Slew RateWhen given a transition or square wave input, the amount of change in the amplifier's output from one level to another. Typical values are averages of values measured based on a change in total output voltage from 10% to 90%.Response TimeIt is the time interval when the input step function makes the output from the initial value to the logic threshold voltage.Unity Gain FrequencyIt refers to the frequency at which the gain of the voltage feedback op amp is 1 (0 dB). For an ideal operational amplifier, its gain-bandwidth product is equal.Intercept PointIt refers to the output power of the fundamental frequency, which is equal to the power value of the fundamental frequency in the specified distortion term (2nd, 3rd, or 3rd intermodulation).Input Offset CurrentIt refers to the current difference between the two inputs.Voltage OverdriveIt means that a certain amount of input step voltage exceeds the minimum drive input voltage required by the comparator to change from one logic level to the opposite logic level.Differential Gain & Differential PhaseDifferential gain refers to the change in the input and output of the gain, and differential phase refers to the phase change in the input stage. They are video measurements, and are a standard measurement in the broadcasting field to measure relative changes in the interpretation of video signal consistency.Voltage FeedbackA technique used in traditional operational amplifiers, where part of the output voltage is fed back to the input, and the voltage difference between the two inputs is amplified by the operational amplifier. Avol Open-loop Voltage Gain“A” is a sign of gain. The letter “V” written below indicates the gain of voltage, and the letter “ol” also written below is an abbreviation for open loop. Open-loop voltage gain refers to the gain (Vout / Vin) of the amplifier without feedback. Due to the existence of the bias voltage, these errors must be compensated.Logic Threshold VoltageIt refers to the voltage that causes the comparator output state to change when the input offset voltage is exceeded.Output ResistanceIt refers to the value of the series resistance at the output of an ideal op amp with zero output resistance, which measured under DC conditions.Gain FlatnessIt refers to the volume of gains “violently increasing” and “rapidly decreasing” in a given bandwidth range measured in decibels (dB), which affects the most important parameter specifications such as phase margin, gain margin, and closed-loop gain.Offset Current Temperature CoefficientIt refers to the average rate of change in deviation current due to changes in junction temperature within a specified temperature range.Input ImpedanceIt is the ratio of input AC voltage to input AC current.Input Voltage NoiseIt refers to the equivalent voltage noise in series with a noiseless amplifier.Input Offset VoltageIt is the product of the DC error voltage between the inputs and the closed-loop gain, because of the non-ideal balance between the input stage and the output is caused by the DC error voltage of the input terminals.Gain MarginOpen loop gain when the phase between the inverting input and output crosses zero at a certain frequency.Supply CurrentIt refers to the current required from the power supply to the unloaded amplifier and to the power supply at the output midpoint.Settling TimeIt refers to the time between the input step function initial value and the output voltage reaching the specified error band. The error band refers to the percentage of the total voltage change.Differential Input ResistanceIt is the ratio of the change in the input voltage to the change in the input current.Ⅲ Q & AQ1: What is the difference between a voltage feedback amplifier and a current feedback amplifier?A: The internal circuits of these two op amps are different. The voltage feedback op amp is restricted by the internal design, and it only has a very low input bias current, but there is no internal limit on the differential input voltage, because it is limited only when external feedback is required. In contrast, for a current feedback amplifier, its differential input voltage is subject to internal design, but it does not limit its input bias current, so it is limited only when external feedback is required.Q2: What is the difference between open and closed loops?A: The open loop gain is actually the internal gain of the op amp without feedback, and usually takes any value between 1,000 and 10,000. Closed loop gain is the gain of the entire circuit, which is equal to the open loop gain divided by 1 plus the loop gain (the improvement coefficient). In fact, the gain of the op amp when there is no feedback is the open loop gain, and the gain when feedback is considered is closed-loop gain.Q3: If the op amp has ideal AC characteristics, the Bode plot (gain-frequency response) is a unipolar system. What is the gain slip rate in dB / decade?A: In a unipolar system, the gain drops (or decreases) at 20dB / decade, which is 6dB / octave. This is responsive to any single pole, and it is also suitable for a simple RC filter or an ideal operational amplifier. However, because op amps have more high-frequency poles, the phase shift will begin to increase as the frequency approaches the unity gain frequency of the op amp.Q4: What is the difference between unity gain bandwidth, gain bandwidth product (GBP), and -3dB frequency?A: Many op amps have an open-loop gain reduction rate of -20db / decade when the frequency is stable. At any point during this descent phase, the GBW is a constant. If the unity-gain operation of the op amp is stable, then the unity-gain bandwidth, or the frequency at which the open-loop gain is 1, is usually equal to GBP. In addition, GBP is not equal to (usually higher than) the unity gain bandwidth. The -3dB frequency is a measure of the bandwidth of an operational amplifier when it is operating in a closed loop. The -3dB point is the frequency at which the gain of the overall closed-loop system drops by 3dB. The unity gain frequency for closed loop applications can be calculated using BW=GBP/Av. The -3dB frequency and unity-gain bandwidth applied depend on the feedback gain setting, output swing, load, and circuit layout.Q5: Why do some amplifiers oscillate with a capacitive load?A: The output impedance of the op amp and the capacitance of the capacitive load may form a resistance-capacitance oscillation. Also they form an R-C oscillation at the output stage, which causes additional phase lag in the feedback signal. CMOS amplifiers have a high output impedance which will cause the electrodes to be approached or lower the unity gain frequency of the op amp. The additional phase lag of the electrodes will weaken the phase margin of the op amp The total phase lag of the amplifier causes the phase angle of the unity gain frequency to increase by more than 180 degrees to cause the total feedback phase shift in unity gain to exceed 180. degree. In addition, the output impedance of a CMOS amplifier is between 100 and 500, causing a relatively low pole frequency. And meanwhile, the output impedance of the high-speed bipolar operational amplifier is in the range of 1 to 100, which causes the pole frequency to be much higher than that of the CMOS operational amplifier, so that the pole is far from the unity gain frequency of the device. The drive of a CMOS amplifier to a capacitive load can be improved by placing an output resistor at the output and an external positive feedback capacitor.Q6: If the output of the op amp stays close to the voltage rail, that is, the output rail, what is the reason?A: There are many ways for operational amplifiers to “rail”. The difficulty is keeping it away from the "rail". If the input exceeds the input voltage range, the output is usually near to a supply voltage rail. In theory, if the output exceeds the actual supply voltage, and a higher supply voltage is given, the op amp will go to rail output again. If there is no feedback or the polarity of the feedback is wrong, the op amp goes to rail output again. At the same time, if the non-inverting input is higher than the negative inverting input, the op amp also goes to rail output. The application of the operational amplifier should be analyzed to ensure that the power supply voltage used has a proper input and gain, so that in normal operation, its input voltage is within the rated value and the output voltage is within the normal range.Q7: What is the difference between the common-mode voltage and input voltage range of an op amp?A: Common mode voltage means that one voltage is applied to both inputs at the same time. Input voltage range is the range of voltages that can be accepted by the input pins. It is necessary to remember that the op amp should suppress the common-mode voltage, and amplify the difference between the two input pins only.Q8: The SPICE model of the bipolar operational amplifier works well, but the SPICE model of the CMOS operational amplifier does not work. Is there a need to set SPICE?A: To input the appropriate bias current to the model, the SPICE model applied on CMOS operational amplifier needs to set the default GMIN option to the largest SPICE package value.Q9: What is the difference between the amplifier's output current and short-circuit current?A: Short circuit current refers to the current generated by the device if the output is connected directly to the power line. This indicates that the output current is limited depending on the design of the device. However, the short-circuit current does not represent the true output of the drive capability of the output. Due to the impedance characteristics of the output stage, the maximum output current is determined by the swing of the output voltage under load. In facet, the smaller the load, the larger the output swing; the larger the load, the smaller the output swing.Q10: How to check the stability of an op amp circuit?A: Check the stability of the control loop, such as the pulse load and related changes in output voltage. The pulse load may be a load current with a pulse or step change, so that the output of the op amp circuit should be connected to a series R-C circuit. The greater the circuit swing or vibration, the worse the stability of the circuit.Q11: Are there any good ways to minimize noise when amplifying a low-level DC signal?A: To obtain a high signal-to-noise ratio, the circuit must be well designed. This includes choosing the best amplifier bandwidth and knowing the impedance of the input signal. If the input signal source has a fairly high impedance, it makes no sense to choose a low voltage noise amplifier, which has high current noise.Q12: How should design a low frequency (<1Hz) differentiator to minimize the output noise?A: The only reason that the output of the differentiator contains noise is because there is a lot of gain and the input is noisy. The traditional differentiator uses Rs-Cs in series at the input and the Rf-Cf in parallel near the operational amplifier. It is not necessary to try more Rs or Cf to minimize noise. The noise of the output come from the differentiator does not mean that it is harmful, because it also amplifies useful signals. In addition, if disconnect a loop, the differential output noise may be beneficial and will stabilize the loop. If the output of the differentiator is quite noisy or has too much input noise, analyze which are the real sources of them.Q13: How to protect the amplifier input from being higher or lower than the supply voltage?A: What must be done is either to clamp the input of the device, or to limit the input current of the device, or ideally, do both. The easiest way is to choose a current limiting resistor to limit this current. The selection is based on the fact that the current generated by the circuit input at the maximum input voltage is less than the maximum current rating of the input pin. Usually, a 1K to 100K resistor in series with this input pin is effective. However, since the signal is usually connected directly to a non-inverting input pin, a non-inverting amplifier may need a protective resistor connected to this pin. For high impedance circuits, a large resistor and or low leakage current diode can be used.Q14: What is the difference between a single-supply amplifier and a dual-supply amplifier?A: There is no difference in the actual circuit, layout, and characteristics of the amplifier. When an operational amplifier is designated as dual power supply, the output load is usually referenced to ground (GND), while a single power supply operational amplifier is usually referenced to the midpoint voltage of a single supply, and it is usually specified to operate on lower voltages, but this is not a necessary requirement. Therefore, whether the op amp is powered by a single 5V power supply and ground (GND), or powered by +2.5 and -2.5V, these is no different. Ⅳ Application: LM358 Classic CircuitsThis Video is Going to Show Top 5 Electronics Project Using OP-AMP LM358The LM358 includes two independent, high-gain, internal frequency-compensated dual operational amplifiers. It is suitable for single-supply operation with a wide range of power supply voltages. It is also suitable for dual-supply operation. LM358 applications include sensor amplifiers, DC gain modules and all other operational amplifiers that can be powered by a single power supply. The classic circuits of LM358 are as shown as following:Figure 1. Active DC-coupled Low Pass RC Filter Figure 2. LED Driver Figure 3. Transistor-Transistor-Logic (TTL) Drive Circuit Figure 4. Active RC Band Pass Filter Figure 5. Squareware Oscillator Figure 6. Hysteresis ComparatorFigure 7. Active Band Pass filter Figure 8. Lamp Driver Figure 9. Current Monitor Figure 10. Low Drift Peak Detector Figure 11. Voltage Follower Figure 12. Power Amplifier Peripheral CircuitFigure 13. Voltage Controlled Oscillator VCOFigure 14. Fixed Current Source Figure 15. Pulse Generator Figure 16. AC Coupled Non-inverting Amplifier Figure 17. AC Coupled Inverting Amplifier Figure 18. Adjustable Gain Instrumentation Amplifier Figure 19. DC Amplifier Figure 20. Pulse Generator Figure 21. Bridge Current Amplifier Figure 22. Introducing Differential Input Signal Figure 23. DC Differential Amplifier Frequently Asked Questions about Op Amps Basics1. What is an op amp basics for dummies?An op amp is a super-sensitive electronic amplifier circuit that's designed to amplify the difference of two input voltages. Thus, an op amp has two inputs and one output. ... Most op amps require both a positive and a negative voltage power supply, with voltages usually ranging from 6 V to 18 V. 2. What is the basic use of op amp?An operational amplifier is an integrated circuit that can amplify weak electric signals. An operational amplifier has two input pins and one output pin. Its basic role is to amplify and output the voltage difference between the two input pins. 3. What is operational amplifier and its types?An operational amplifier (op amp) is an analog circuit block that takes a differential voltage input and produces a single-ended voltage output. Op amps usually have three terminals: two high-impedance inputs and a low-impedance output port. 4. Which purpose the op amp is used?As the name suggests, the purpose of an amplifier or an op amp is to amplify or increase the input signal to produce an output signal which is much larger than that of the input, with a similar waveform as that of the input. The main change in the output signal will be the increase in the power level. 5. What does it mean when an op amp saturates?Originally Answered: What happens when an op-amp is saturated? that means the amplification or gain is so high as to make the output signal with a given input signal, so large as to exceed the compliance range of the power supply of the ope amp. More simply put, if you have an op amp supplied with +/-15V supply rails.

IntoductionAn operational amplifier, or op-amp for short is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. In this configuration, an op-amp produces an output potential that is typically hundreds of thousands of times larger than the potential difference between its input terminals, and is a voltage amplifying device designed to be used with external feedback components such as resistors and capacitors between its output and input terminals. They are used extensively in signal conditioning, filtering or to perform mathematical operations such as add, subtract, integration and differentiation.In this video, the basic introduction of the Operational Amplifier (Op-Amp) has been given and different characteristics of ideal and real Op-amp (General Purpose 741 Op-Amp) has been discussed. CatalogIntroductionⅠ Operational Amplifier Basics1.1 Amplification Principle1.2 Balance Resistor1.3 Feedback Resistor in Parallel with a Capacitor 1.4 Pulling Down Resistor and Pulling Up the Capacitor1.5 Parasitical Resistor as an Integrator1.6 Parasitical Resistors and Capacitors1.7 Balance Resistor Failure1.8 Magnification, Input Impedence, Voltage1.9 Open Loop Gain1.10 Virtual ShortⅡ Op Amp ApplicationⅢ Op Amp SamplingⅣ Op Amp Reference VoltageⅤ Importance of Op AmpⅠ Operational Amplifier BasicsWhen using op amp, there will be more problems confusing us, what are they? Listing all of them is impossible, but we can seek the core of these problems, which are the following lists.1.1 Amplification PrincipleThere are many types of op amps with many functions, and their circuits are inconsistent, but the internal block diagrams are basically the same. It consists of three parts: input stage, intermediate stage, and output stage. The input stage consists of a differential amplifier circuit that uses circuit symmetry to improve overall circuit, and the main function of the intermediate voltage amplifier stage is to increase the voltage gain. It can be composed of one or more stages of amplifying circuits; the output stage has a voltage gain of 1, but can provide a certain amount of power, and the circuit consists of two power supplies V+ and V-. The entire amplifier circuit is designed with two inputs P and N, and one output O. The voltages of the three terminals are represented by Vp, Vn, and Vo, respectively. The two ends of P and N are respectively called the non-inverting input terminal and the inverting input terminal, which means that when the P terminal is added with the voltage signal Vp (Vn = 0), it is obtained at the output end. The voltage Vo is in-phase with Vp, when the voltage signal Vn (Vp = 0) is applied to the N terminal, the output voltage Vo obtained at the output is inverted from Vp.The operational amplifier is actually a differential amplifier. Look at its structure, two transistors are connected back to back to share the crossing current source. One of the transistors is the positive input of the op amp and the other is the inverting input. The positive input is amplified and sent to a power amplifier circuit to amplify the output. Thus, if the voltage at the forward input rises, the output naturally becomes larger. If the voltage at the inverting input rises, the reverse current is large, and the forward current is small, because the inverting tertiary tube and the forward tube share a same current source.1.2 Balance ResistorGenerally, there is a balance resistor in the inverting / non-inverting amplifier circuit. What is the role of this balance resistor?(1) Provide a suitable static bias for the transistors inside the chip.The internal circuit of the chip is usually directly coupled, and it can automatically adjust the static operating point, but if an input pin is directly connected to the power supply or the ground, its automatic adjustment function can not work normally. Because the voltage of the ground cannot be raised by the inside transistors, and the voltage of the power supply cannot be reduced, which causes the chip to fail to meet the conditions of virtual short and virtual open.(2) Eliminate the influence of the static base current on the output voltage, and the value should be balanced with the equivalent resistance value of the external DC of the two input terminals.(3) In non-inverting op amp circuit, if it not connecting a balance resistor, the op amp will be burned, because the resistor acts as a voltage divider. 1.3 Feedback Resistor in Parallel with a Capacitor What is the role of the feedback resistor in parallel with a capacitor when using non-inverting op amp?(1) The feedback resistor and capacitor form a high-pass filter, so that local high-frequency amplification is particularly noticeable.(2) Prevent self-excitation. 1.4 Pulling Down Resistor and Pulling Up the CapacitorWhat role does the role of pulling down resistor and pulling up the capacitor at the input of the op amp play?To get positive feedback and negative feedback, depending on the specific circuit connection. For example, if the input voltage signal and the output voltage signal are taken to the input, the partial output signal passes through the balance resistor to obtain a new voltage value, that is, shunting the input voltage to make the input voltage smaller, and this is a negative feedback. Since the signal output from the signal source is always constant, the output signal can be corrected by negative feedback. 1.5 Parasitical Resistor as an IntegratorWhat is the function of the resistor RF connected to the op amp as an integrator at the two ends of the integrating capacitor?Adjust resistance to prevent the output voltage from running out of control. 1.6 Parasitical Resistors and CapacitorsWhy are resistors and capacitors connected in series at the input of the op amp?Regardless of the type of op amp, it consists of transistors or MOS transistors. In the absence of an external components, the op amp is a comparator actually. When the voltage of the non-inverting terminal is high, it will output a level similar to the positive voltage, and vice versa, but this op amp does not seem to have much use. Only when the external circuit is formed to generate the feedback will make the real op amp function. 1.7 Balance Resistor FailureWhat is the consequence of the balance resistor doesn't work well in non-inverting amplifier circuit?(1) The non-inverting end is unbalanced. For example, there will be an output although the input is 0. When the input signal is output, the output value is always larger (or smaller) than the theoretical output value by a fixed number.(2) The error caused by the input bias current cannot be eliminated. 1.8 Magnification, Input Impedence, VoltageWhat is the amplification factor and input impedence of an ideal integrated operational amplifier? What is the voltage between the non-inverting input and the inverting input?The magnification is infinite, the input impedance is infinitesimal, and the voltage is almost the same (the voltage is not 0V, for example, the non-inverting end is 10V and the inverting end is 9.99V). 1.9 Open Loop GainWhy is the open loop gain of an ideal op amp infinite?1) The actual open loop gain of the op amp is very large, so imagine it as infinity and derive the virtual ground from it.2) Deriving virtual ground is not only an inverting amplifier for the negative feedback connection, because there is no virtual ground for positive feedback.The open-loop gain of the op amp is infinite, when design the circuit, the closed-loop gain can be independent of the open-loop gain, and only depends on the external components. It is to use the large open loop gain in exchange for the stability of the closed loop gain.3) Assuming that the gain is small, the difference between the voltages applied across the op amp is relatively large for an output voltage. If it is connected to a negative feedback state, the voltage across the op amp will be different, causing amplification.We all know that the op amp’s output voltage Vo is equal to the difference Vid between the non-inverting input voltage and the inverting input voltage, multiplied by the op amp’s open-loop gain A, that is, Vo = Vid * A = (VI + - VI-) * A ( 1 ). Since the output voltage of the op amp does not exceed the supply voltage in practice, it is a finite value. In this case, if A is large, (VI+ - VI-) is necessarily small; if (VI+ - VI-) is small enough, then we can actually treat it as 0, at this time,  there will be VI+ = VI-, that is, the voltage at the non-inverting input of the op amp is equal to the voltage at the inverting input. This is what we call “virtual short”. Note that they are not really connected together, and there is resistance between them.In the above discussion, how did we get the result of “virtual short”? Our starting point is the formula (1), which is based on the characteristics of the op amp. Then, we made two important assumptions, one is that the output voltage of the op amp is limited, and it not exceed the power supply voltage; the second is that the open loop gain A of the op amp is large. The A of a normal op amp usually reaches 106 or 107 or even larger, but the actual open loop gain of the op amp is also related to its working state. For example, if the op amp is not working in the linear area, the value A may be small, so second assumption is conditional.Therefore, we know that when the open loop gain A of the op amp is large, the op amp can have a virtual short. But it is one of the possibilities, and it is not suitable for every op amp in any case to say their inputs are virtual short, in other words, virtual short can only be achieved in circuits under certain conditions.The conditions of virtual short:a. The open-loop gain of operational amplifier should be large enough.b. There should be a negative feedback circuit. From the above we know when we need to analyze the virtual short in the circuit. In reality, condition (1) is true for most op amps, and the important point is to look at the work area. If it is a circuit drawing, judge by calculation; if it is an actual circuit, it is reasonable to use the instrument to measure amplifier output voltage.There is also a situation related to virtual short called “virtual ground”, that is, there is a virtual short when the input is grounded. Some books say that virtual short will be exist under deep negative feedback conditions, but in reality, the op amp is more likely to work in the linear region under this situation. But this is not absolute, when the input signal is too large, the op amp with deep negative feedback will still be saturated. Therefore, it should be judged to be the most reliable with the output voltage value. 1.10 Virtual ShortAdd the input signal directly to the non-inverting input, and the inverting input is grounded through the resistor. Why is U-= U+ = Ui≠0? Is it not a virtual short? What are the conditions that the virtual ground exists?(1) In the non-inverting amplifier circuit, the output affects by the feedback, so that U(+) automatically tracks U(-), so they will be close to zero. It seems that the two ends are short circuit, so it is called virtual short.(2) Due to the virtual short phenomenon and the high input resistance of the op amp, the current flowing through the two input terminals is small, approaching 0. This phenomenon is called virtual open, which is derived from virtual short.(3) The virtual ground is in the inverting op amp circuit, the (+) terminal is grounded, and the (-) is connected to the input and feedback network. Due to the virtual short, U(-) and U(+) are very close, which is said to be virtual ground.(4) About the conditions: the virtual short is an important feature of the closed-loop (negative feedback) operating state of the non-inverting amplifier circuit; the virtual ground is an important feature of the inverting amplifier circuit in the closed-loop operating state. Ⅱ Op Amp ApplicationWhen a operational amplifier is connected as a non-inverting amplifier, the potentials of the two inputs are the same. If the waveform of the input is measured, it will be the same. This is like a common-mode signal. In fact, there are still small differential mode signal on the two inputs, but the differential mode signal can not be measured by the general instrument. As a result, the virtual short artificially increases the common-mode signal at the two inputs, which poses a challenge to the performance of the operational amplifier. Why is an op amp used like this?(1) The common mode signal of the non-inverting amplifier is much larger than the inverting amplifier, and strict to the common mode rejection ratio.(2) For single-ended input, the equivalent common-mode value is half of the input value, whether non-inverting or inverting input. However, since the input impedance of the non-inverting amplifier is usually larger than the inverting amplification, the anti-interference ability is a little poor.As mentioned above, when the inverting input is performed, the voltage at the inverting terminal is almost zero, so the differential influence on the tube collector voltage that has only one tube change. When the input is in phase, the voltage at the inverting terminal is equal to the non-inverting terminal voltage, so the common mode voltage and the input voltage are equivalent. That is to say, the collector voltage of the differential tube has variable quantity that changes in the same direction when the two tubes have portions that change in different directions at the same time, which is the common mode output voltage. It is added in phase with the voltage of one of the tubes. Therefore, it is easy to cause the tube to become saturated (or cut off), fortunately, the amplification of the common mode voltage is only tens of thousands of parts of the differential mode amplification.However, this does not mean that the common mode rejection suppression ratio of the differential mode input and the common mode input of the amplifier is different. It should be that the non-inverting input is added with a common mode signal equivalent to the input volume, so it should be careful to use non-inverting amplification mode when the input signal is large. Ⅲ Op Amp SamplingWhy is the amplifier circuit composed of operational amplifiers generally sampling the inverting input mode?(1) The significant difference between the inverting input and the non-inverting input mode is:When inverting input, because there is a balanced resistor connected to the ground at the same phase, and there is no current on this resistor (because the input resistance of the op amp is extremely large), this non-inverting terminal is approximately equal to the ground potential, and  the potential at the non-inverting terminal is extremely close to the inverting terminal, so there is a virtual ground at the inverting end. The advantage of having a virtual ground is that there is no common mode input signal, even if the common mode rejection ratio is not high, there is no common mode output. The non-inverting input mode has no virtual ground. When a single-ended input signal is used, a common-mode input signal is generated. Even if an operational amplifier with a high common-mode rejection ratio is used, there is still a common-mode output. Therefore, it is best to use the inverting input method.(2) The positive phase is the oscillator, and the inverting can stabilize the amplifier and access the negative feedback.(3) From the principle point of view, it is possible to connect to the same analog circuit. However, the signal (differential mode signal) that is amplified during the actual application tends to be small, thus it is necessary to pay attention to suppressing noise (usually expressed as a common mode signal). In the same way, the amplification circuit has a poor ability to suppress the common mode signal, and the signal that needs to be amplified is submerged in the noise, which is not conducive to post processing. Therefore, an inverting proportional amplification circuit with better suppression capability is good.Ⅳ Op Amp Reference VoltageSome op amps will have an output even if no voltage is input after power-on, and the output is not small, so VCC/2 is often used as the reference voltage.The output is output signal without any input, this is called the input offset voltage Vos, which is caused by the asymmetry of the design structure of the op amp. It is a very important performance indicator of the op amp. The op amp commonly used VCC/2 as the reference voltage is because the op amp is in a single power supply state. At this time, the real reference of the op amp is VCC/2, so a DC offset of VCC/2 is often provided at the positive terminal of the op amp. When having positive and negative dual power supply, it is often referenced to the ground.The selection of op amps requires attention to many things. Under less stringent conditions, it is often necessary to consider the operating voltage, output current, power consumption, gain bandwidth product, and price of the op amp. Of course, when using it under special conditions, different factors must be considered in practice. Ⅴ Importance of Op Amp(1) If the voltage on both inputs of the op amp is 0V, the output voltage should also be equal to 0V. But in fact, there is always some voltage at the output, that is, the offset voltage Vos. If the offset voltage at the output is divided by the noise gain of the circuit, the calculated result is called the input offset voltage or the input reference offset voltage. The Vos is considered to be a voltage source in series with the inverting input of the op amp. A differential voltage must be applied to both inputs of the amplifier to produce a 0V output.(2) The input impedance of an ideal op amp is infinite, so no current flows into the input. However, a real op amp using a bipolar junction transistor (BJT) in the input stage requires some operating current, which is called bias current (IB). There are usually two bias currents: IB+ and IB-, which flow into the two inputs, respectively. The range of IB values is large, with bias currents of lower at 60fA for special op amps and up to tens of mA for some high-speed op amps.(3) The power supply voltage range required for the first single-chip op amp to operate normally is ±15V. Today, op amps are moving toward low voltages due to increased circuit speeds and power supplies from low-power sources such as batteries. Although the op amp’s voltage specifications are usually specified as symmetrical two-pole voltages ±15V, these voltages do not necessarily require a symmetrical voltage or a two-pole voltage. For an op amp, as long as the input is biased in the active region (within the common-mode voltage range), the ±15V supply is equivalent to a +30V/0V supply, or a +20V/-10V supply. The op amp does not have a ground pin unless the negative voltage rail is grounded in a single-supply application.The input voltage swing of high speed circuits is smaller than that of low speed devices. The higher the speed of the device, the smaller its geometry, which means the lower the breakdown voltage. Due to the low breakdown voltage, the device must operate at a lower supply voltage. Today, op amps typically have a breakdown voltage of around ±7V, so high-speed op amps can work at a supply voltage of ±5V, and they can also operate at a single supply voltage of +5V.For general-purpose op amps, the supply voltage can be as low as +1~8V. These op amps are powered by a single power supply, but this does not mean that a low supply voltage must be used. Because the terms single supply voltage and low voltage are two related and independent concepts. Frequently Asked Questions about Operational Amplifiers Problems1. How can you tell if an op amp is blown?Re: how to tell whether an op amp is burned out? measure the DC voltage at the +input. then measure the DC voltage at the output. if the results are significantly different, the opamp is most likely shot. 2. How do I know if my op amp is broken?measure the DC voltage at the +input. then measure the DC voltage at the output. if the results are significantly different, the opamp is most likely shot. if they are the same, the opamp is most likely ok and the problem is something else. 3. What errors you have to consider with real operation amplifiers?These errors include input bias current, input offset current, input offset voltage, CMRR, PSRR, and finite input impedance. In reality, all these errors will occur at the same time. 4. How do op amps fail?The common failures I have seen including with comparators involve either the output being shorted or open to one supply or the input differential pair or input protection circuits being damaged causing excessive input bias current and/or input offset voltage which usually ends up pinning the undamaged output. 5. Why do op amps fail?The common failures I have seen including with comparators involve either the output being shorted or open to one supply or the input differential pair or input protection circuits being damaged causing excessive input bias current and/or input offset voltage which usually ends up pinning the undamaged output.