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I IntroductionThis article introduces the basics of low voltage transformer, including the definition of low voltage transformer, the principle of low voltage transformer, its installation method, malfunction, and how to repair a household low voltage transformer. A transformer is an electronic instrument that we can use everywhere in our lives. For example, we are inseparable from the mobile phone chargers. The internal components also have transformers. For example, the power supply in our computers is also composed of transformers. Therefore, all electronic products are indispensable for transformers. The transformers used in electronic components are all power transformers (included low voltage transformers). The power transformer is mainly used in electronic products to convert the power supply to the voltage required by the electronic circuit.CatalogⅠIntroductionⅡ Basics of low voltage transformer2.1 Definition of low voltage transformer2.2 Types of low voltage transformers2.3 How does low voltage transformer work?2.4 Design requirements of low voltage transformer2.5 Application environmentⅢ Differences between low&high voltage transformerⅣ How to Estimate the Loss of Low Voltage TransformerV Guide to What You May be Interested in5.1 How to Install Low Voltage Transformer for Household?5.2 How to Troubleshoot a Low-Voltage Transformer5.3 Repairing a household transformer5.4 Malfunction of factory low voltage transformerVI One Question Related to Low Voltage Transformer6.1 Question (Multiple choice questions)6.2 AnswerVII FAQII Basics of Low Voltage Transformer2.1 Definition of Low Voltage Transformer Transformers are important power equipment in our life, especially low-voltage transformer. Whether it is for large-scale power plants or home circuits, it is inseparable from the transformer. There are two kinds of transformers used in our life, one is the high-voltage transformer which used in the high-voltage or ultra-high-voltage circuit, the other is the low-voltage transformer which used in the family lighting circuit or small power circuit.The so-called low-voltage transformer refers to the transformer with low load voltage. As long as the load is lower than 600V, it can be called a low-voltage transformer. The low-voltage transformer is mainly composed of primary coil, secondary coil, and a magnet iron circuit. Low voltage transformers are commonly used for low voltage lighting, which typically only uses 12 or 24 volts. 2.2 Types of Low Voltage TransformersThere are two main types of low voltage transformers: electronic and magnetic.（1）Electronic Low Voltage TransformersElectronic transformers are much smaller, lighter, and less expensive than magnetic counterparts. But they only have about a 5-6 year lifespan. Also, electronic low voltage transformers are known for being noisy.Electronic Low Voltage TransformersAdvantagesDisadvantages▪ Smaller and lighter, easier to hide▪ Less expensive▪ Shorter life span▪ Noisy▪ Heat-sensitive（2）Magnetic Low Voltage TransformersThere are two types of magnetic transformers: stack laminated and toroidal.  Stack laminated transformers have a longer lifespan, about 15 to 20 years. But they only operate at about 80 to 85 percent efficiency, also are known for being noisy.Toroidal transformers are very quiet and more energy efficient. They can operate at about 90 to 95 percent efficiency. And they are long-lived, lasting 20 to 25 years.Magnetic Low Voltage TransformersAdvantagesDisadvantages▪ Long life span of over 15 years▪ Energy efficient▪ Quiet▪ Heavy, big, and difficult to hide▪ Expensive2.3 How Does Low Voltage Transformer Work?Electricity and magnetism are two kinds of energy that can mutually transform. Electricity can generate magnetism, and magnetism can also generate electricity. The low-voltage transformer uses this principle to adjust the voltage through the mutual conversion of electricity and magnetism.A low voltage transformer consists of two electrical coils of wire, one of which is called primary winding and the other is called secondary winding. The primary side of the transformer collects power and the secondary side provides power.Figure 1. Low Voltage Transformer StructureThe two coils intertwine together on a magnet iron circuit core, but without electrically in contact with each other. The magnetic core is made of soft magnetic material, which consists of laminations connected together to help reduce core loss. The core allows power to be transferred from one coil to another. When the primary winding is connected to the power supply, the generated magnetic field transfers the voltage to the secondary winding.Figure 2.  How Does Low Voltage Transformer Work?In summary, the primary winding transforms the electrical power into magnet field when connected to the input voltage supply while secondary winding transforms alternating magnetic field into electrical power of required output.2.4 Design Requirements of Low Voltage TransformerThe low-voltage transformer should be vacuum cast, molded resin encapsulated, 60Hz, Class F insulation, comply with the requirements of IEC726, and meet the requirements of capacity, voltage, phase number, and wiring shown. Each low-voltage transformer has separate primary and secondary windings, and there are two 2.5% normal voltage full-capacity taps above and below the rated voltage on the primary side. The low-voltage transformer should be installed on a base that can isolate, reduce vibration and noise, and the iron core and coil should be properly fixed to withstand the mechanical stress generated in the event of line failure and can withstand 16460 Lite 16460-6 V2. 0 2002/ 11/ 25 Vibration and impact during shipment. Unless otherwise specified, the impedance of low-voltage transformers shall be in accordance with IEC 726. The average noise level of the low-voltage transformer should not exceed the value specified in IEC 726. Each dry-type low-voltage transformer should have appropriate terminals to accommodate the required primary and secondary wiring connections. Low-voltage transformers can be reserved for cable entry from either side or bottom.2.5 Application Environment(1) Ambient air temperature - 5 ℃ to + 40 ℃, 24-houraverage value not more than + 35 ℃(2) The altitude of the installation site shall not exceed 2000m(3) The relative humidity of the atmosphere shall not exceed50% when the ambient air temperature is + 40 ℃(4) A place without violent shaking and impact vibrationIII Differences Between Low&High Voltage Transformer Low Voltage TransformerHigh Voltage Transformerwindingcontinuous windingInterleaved WindingscoolingOil-immersed cooling or air coolingOil-immersed coolingstructureoil tank structurebell jar type oil tankⅣ How to Estimate the Loss of Low Voltage TransformerTransformer loss include copper loss and iron loss. The loss of iron loss is also called no-load loss, and the loss of copper loss is also called load loss. The open circuit of the secondary winding of the transformer applies the no-load current of rated frequency and rated voltage to the primary side, and the active loss caused by the transformer core is called the no-load loss of the transformer. The loss figure can be obtained by the unit loss of the iron core silicon steel sheet multiply the quality of the silicon steel sheet. In general, its loss is very small. For example, the S9-100/10 distribution transformer has a no-load loss of 290W. The larger the transformer capacity, the smaller the no-load loss, generally between 0.3-0.15% of the rated capacity. However, the transformer works continuously for 24 hours, and this loss cannot be ignored. The load loss: The short-circuit of the coil on the secondary side apply the rated current at the rated frequency on the primary side. The transformer loss at this time is the loss of the transformer coil and the iron core. Let's take the S9 series transformer as an example and see its load loss value:The load loss of S9-100/10000 transformer is 1500W.The load loss of S9-1000/10000 transformer is 10300W.The load loss of a transformer is generally between 0.9-1.8%. The larger the transformer, the smaller the load loss.V Guide to What You Maybe Interested in 5.1 How to Install Low Voltage Transformer for Household? First, make sure you have an outlet available. Most family homes will have several outdoor power outlets installed. Second, think about the layout of the lighting. It is important to plan ahead when installing low voltage lighting so that you can avoid any potential problems, especially with the setup.Third, choose a transformer.①Magnetic or Electronic.②Make sure to buy a transformer that can handle the lighting load you need it to.Fourth, install the transformer. Transformers are installed simply by plugging them into your outdoor outlet.5.2 How to Troubleshoot a Low-Voltage Transformer(1) First, check whether there are obvious abnormalities by observing the appearance of the transformer: such as whether the coil lead is broken, whether the insulating material has scorch marks, whether the fastening screw of the iron core is loose, whether the silicon steel sheet is rusted, and whether the winding coil is exposed Wait. (2) Test a transformer with a digital multimeter, open all secondary windings, put the multimeter in the AC block (500mA, in series into the primary winding). When the plug of the primary winding is inserted into the 220V AC mains supply, the multimeter indicates the no-load current value. This value shall not be greater than 10% - 20% of the full load current of the transformer. Generally, the normal no-load current of the power transformer of common electronic equipment should be about 100mA. If too much is exceeded, the transformer has a short-circuit fault. Low Voltage Electronic Transformer Troubleshooting Guide5.3 Repairing a Transformer(1) Understand the reasons for the problem. Generally, a transformer has failed due to some fault in the electrical circuit.(2) Check the replacement transformer. If the short circuit is caused by component failure, the new transformer may still burn out. If you replace the transformer, examine it to make sure that the incident will not occur again.(3) Check the condition of the external fuse. If the transformer has an internal fuse, there may not be a fuse on the power line. On the contrary, the device must be protected by a fuse mounted on the power circuit. Check whether the fuse is intact and replace the faulty fuse.(4) Check the secondary power consumption. Sometimes, this kind of consumption is very high, which leads to equipment failure. If the transformer has multiple ratings and the multimeter shows the value "OL" during the measurement, it may be a short circuit in the secondary winding.5.4 Malfunction of Factory Low Voltage Transformer(1) Abnormal sound in transformerThe abnormal sound inside the transformer may be caused by the following reasons:①Heavy overload causes buzzing sound inside the transformer; ② Due to poor internal contact or breakdown point, the transformer occurs crackle sound③ Some parts of the connection shaft and the core of the transformer are loose, which causes the silicon steel sheet to vibrate④ When there is a grounding or short-circuit fault in the power grid, a large current flows through the winding, which will produce strong noise⑤ The iron core, the winding discharges to the shell, or the core ground wire is disconnected. All these can make the transformer discharge sound. (2) The oil level of the transformer is too high or too lowUnder normal circumstances, the changes in oil temperature can cause a change in oil level. As the oil temperature changes, the oil level also changes accordingly. However, under abnormal conditions, abnormal oil levels can also be caused by faults such as oil seepage and water seepage and other accidents. Second, the change in oil temperature is related to load conditions, ambient temperature and other conditions. When the change of oil level is inconsistent with these elements, it may be a false oil level. (3) Transformer oil quality has deteriorated or oil temperature has suddenly increasedIn working condition, the main function of transformer oil is cooling and insulation. When running overheated for a long time or if water enters the casing and absorbs moisture, the oil quality will deteriorate. Through the oil mark, we can found  that the oil color is abnormally deepened or blackened. Through sampling and analysis, it can be detected that the oil contains carbon particles and moisture, the acid value increases, the flashpoint decreases, and the insulation strength decreases. This situation can easily lead to serious accidents. A sudden rise in oil temperature when the transformer is operating normally is often related to the overheating inside the transformer. The iron core catches fire, the internal screws are loose, the cooling device is faulty, the transformer is heavily overloaded, all may cause the oil temperature to rise suddenly. (4) Transformer on fireWhen the transformer is out of order and it is not handled in time, it may catch fire. When the transformer is on fire, the insulating oil burns and turns into gas, which makes the oil tank burst. The burning insulating oil sprays out of the transformer, which will cause equipment damage and property loss. The short circuit inside or outside the transformer wire, severe overload, a lightning strike may cause the transformer to catch fire.VI One Question Related to Low Voltage Transformer6.1 Question (Multiple choice questions)The winding of wire around a core which is connected to a source of energy is called the ______ coil.primarysecondarytertiary6.2 AnswerA、B  VII FAQ1. What are low voltage transformers?A low voltage transformer is at the heart of every landscape lighting system. It converts 120-volt current to a low voltage current (between 12-15 VAC). ... Magnetic transformers use two coils to reduce the voltage from 120 volts down to 12 volts. 2. What low voltage transformer do I need?Transformers generally range from 150- to 900-watt capacity. Matching the size of the transformer to the lighting design is important for the efficient operation and function of the system. House current, 120 volts, is reduced by a transformer to 12 to 20 volts, the current needed to operate low-voltage landscaping lights. 3. What are low voltage transformers used for?Low Voltage Transformers Low voltage transformers are power transformers that are used to change the voltage capacity of a low-voltage electrical transmission line. Typically, electronic low voltage transformers convert 120 volts into 12 volts or 24 volts. 4. How do you test a low voltage transformer?• Identify the transformer's terminals, using its label as a guide. • Turn a multimeter to its VAC function. • Test the transformer's input voltage with the multimeter, using the transformer's label as a terminal guide. • Test the transformer's output voltage with the multimeter. 5. How long do low voltage transformers last?20 to 25 years.They operate at about 90 to 95 percent efficiency and can run for a very long time, anywhere from 20 to 25 years. They also are much quieter, so you can place them close to the fixtures, rather than having to run wires a long way from the transformer to the fixture itself. 6. Can I plug a low voltage transformer into an extension cord?One warning though to be observed is to never use an extension cord between the transformer and the electrical outlet. Always plug the transformer directly into the power outlet. As you can see, low voltage outdoor lighting is not all that hard to install or maintain. 7. Can you hardwire a low voltage transformer?To hardwire a low voltage transformer, the main power should be turned off at the breaker panel before making any electrical connections. ... The polarity of these wires is not important; either wire on the output side of the transformer may be connected to either wire of the low voltage circuit. 8. Do you need a transformer for low voltage lighting?When operating low voltage lights, you need a transformer to convert your standard line voltage (120V or 277V) into low voltage (12V or 24V). This allows your lights to function properly. If you connect low voltage lights directly to line power, the higher voltage would cause them to burn out immediately. 9. How do you tell if a transformer is going bad?Symptoms of power quality issues include vibration, excessive buzzing or humming and overheating. Technicians should occasionally check the power of transformers that supply nonlinear loads, such as variable frequency drives (VFDs) or switching power supplies. 10. Can you replace a transformer with a light fitting?They will have a transformer either in the ceiling or light fitting. Some LED bulbs, like the Philips Master LED range, have in-built circuitry that can deal with most (but not all) transformers, so you don't have to change them. In other cases, you need to replace the transformer with an LED driver. 

I IntroductionThe ballast has become an important additional device in the gas discharge light source circuit. Because most gas discharge lamps are made using arc discharge characteristics and have negative characteristics (also known as negative resistance characteristics) where the voltage decreases with increasing current, it is impossible to establish a stable operating point. In order to stabilize the discharge and limit the working current of the lamp, ballast must be installed in the gas discharge light source circuit. This article will introduce what is a ballast, how does the ballast work, its function, type, fault symptoms, and how to replace a broken ballast.What is a ballast?CatalogI IntroductionII What is a Ballast?III Types of Ballasts 3.1 Inductive Ballast(Magnetic Ballast) 3.2 Electrical Ballast 3.3 Resistance Ballast 3.4 Magnetic Leakage Ballast 3.5 Capacitive Ballast 3.6 LC BallastIV The Function of the BallastV How to Replace a Ballast? 5.1 How to Tell If the Lamp is Broken or the Ballast is Broken 5.2 Symptoms of Ballast Failure 5.3 Replacement ProcedureVI Several Common Terms for Ballasts 6.1 Ballast Loss 6.2 Ballast Factor 6.3 Ballast Efficacy Factor 6.4 Crest Factor 6.5 Power FactorVII One Quiz about the BallastVIII FAQII What is a Ballast?The ballast is a device that acts as a current limiter and generates an instantaneous high voltage on the fluorescent lamp. It is made by wrapping the enameled wire around an iron core made of silicon steel. Such a coil with an iron core, when instantaneously turned on / off and powered on, will generate a high voltage by self-induction, which is added to the electrodes (filament) at both ends of the fluorescent tube. This action is carried out alternately. When the starter (bubble jump) is closed, the filament of the lamp tube conducts heat through the current limit of the ballast; when the starter is open, the ballast will generate a high voltage on the filament at both ends of the lamp tube. The filament emits electrons to hit the fluorescent powder of the tube wall, and the starter repeatedly turns on and off a few times, thereby turning on the lamp. When the lamp emits light normally, the internal resistance becomes smaller, and the starter will always maintain an open-circuit state so that the current will work stably through the lamp and the ballast to make the lamp emit light normally.Figure1. BallastIII Types of Ballasts3.1 Inductive Ballast(Magnetic Ballast)3.1.1 DefinitionInductive ballast, also known as magnetic ballast, is an iron core inductance coil. The nature of the inductance is that when the current in the coil changes, the magnetic flux will change in the coil, which will generate an induced electromotive force. Thus hindering the current changes. 3.1.2 How Does the Inductive Ballast Work?When the switch is a closed circuit of 220V, 50Hz AC power, the electric current flows through the ballast to the starter, lamp filament, the filament heating (at the beginning of the starter is broken, due to a greater than 180V AC voltage, the starter has jumped the gas inside the bubble glow discharge, jump bimetallic strip is heated inside the bubble expansion deformation, two electrodes together, forming pathways to the filament heating).Figure2. The Circuit of Inductive Ballast When the two electrodes of the starter are close together because there is no arc discharge, the bimetallic sheet cools, and the two electrodes are disconnected. Due to the inductance of the inductive ballast, when the two electrodes are disconnected, the current in the circuit suddenly disappears. Therefore, the ballast generates a high pulse voltage, which is superimposed with the power supply voltage and is added to both ends of the lamp tube to ionize the inert gas in the lamp tube and cause arc discharge. (High pulse voltage-time is about 1ms 600V ~ 1500V, the exact voltage value depends on the type of lamp). During the normal lighting process, the self-inductance of the ballast serves to stabilize the current in the circuit. 3.2 Electrical Ballast3.2.1 DefinitionAn electrical ballast is a type of ballast, which refers to an electronic device that uses electronic technology to drive an electric light source to produce the required lighting. The electronic components convert the energy of the power grid to meet the voltage and current required by the matching lamps with AC or DC power.Figure3. Electrical Ballast 3.2.2 How Does the Electrical Ballast Work?The power frequency power supply becomes a DC power supply after passing through a radio frequency interference (RFI) filter, full-wave rectification, and passive (or active) power factor corrector (PPFC or APFC). Through the DC / AC converter, output high-frequency AC power of 20K-100KHZ, which is added to the LC series resonant circuit connected to the lamp to heat the filament, and at the same time, a resonant high voltage is generated on the capacitor and added to both ends of the lamp tube. However, the "discharge" of the lamp tube is turned into the "on" state and then enters the light-emitting state. At this time, the high-frequency inductance plays a role in limiting the increase of the current and ensuring that the lamp tube obtains the lamp voltage and lamp current required for normal operation.Figure4. How an Electrical Ballast Work 3.3 Resistance BallastIt regulates the lamp current by the voltage on the resistor proportional to the current. In the gas discharge light source circuit equipped with DC power supply, the application of resistance ballast is relatively simple in design and processing, but the power consumption is large and the efficiency is low. Resistance gas ballasts are also used in gas discharge light source circuits equipped with AC power sources. For example, in self-ballasted high-pressure mercury lamp circuits, tungsten wires are used as resistance ballasts. But generally speaking, the application of a resistor ballast in an AC circuit will affect the lamp current waveform, and make the luminous efficiency of the lamp decrease and the stability deteriorate, but it can improve the circuit power factor. 3.4 Magnetic Leakage BallastThe magnetic leakage ballast is a type of LC leading peak type circuit. The fundamental wave is mutated by auto-coupling boost and local magnetic saturation, and then it resonates with the working capacitor to obtain a higher open-circuit voltage and longer-lasting lamp operating current. It is a kind of high power factor lighting circuit, the line power factor reaches 0.90 ~ 0.97, which has its unique advantages for point HID light sources.Figure5. Magnetic Leakage Ballast 3.5 Capacitive BallastA capacitor is used as a ballast in a gas discharge light source circuit equipped with an AC power source. It cannot limit the instantaneous current of the lamp, only the total amount of charge that passes through the circuit in each half-cycle. In the low-frequency AC circuit, the lamp current waveform will be seriously distorted, forming a high pulse peak current (effective value is not large), which has a very harmful effect on the lamp electrode, resulting in a significant reduction in lamp life. Therefore, capacitors are rarely used as ballasts in low-frequency AC circuits. In higher frequency (20 ～ 100kHz) AC circuits, capacitors can be used as ballasts to obtain satisfactory results. The power consumption is small, the current waveform distortion is small, the volume is small, the weight is light, and there is no noise.Figure6. Circuit for Ballast-Ignitor-Capacitor-Lamp 3.6 LC BallastThere are the following two forms. (1) Ballast composed of inductor and capacitor connected in series. The designed capacitive reactance is usually about twice the inductive reactance, and the total impedance is capacitive. It belongs to the advanced ballast, that is, the phase of the lamp current leads to the phase of the power supply voltage. Compared with resistive ballast and inductive ballast, the power consumption is small, especially with good steady current characteristics, and the short-circuit characteristics when the lamp is started are also good. Combined with the use of hysteretic inductance ballast, it can greatly improve the power factor of the circuit. However, the repetitive ionization voltage provided every half cycle when the power supply voltage is commutated is low, and the repetitive ignition ability is poor.Figure7. Circuit of the LC Ballast for T5 28W Lamps (2) Ballast composed of magnetic leakage transformer and capacitor. Generally, it belongs to the advanced ballast. If the parameters are selected properly, the circuit power factor can be better improved. Its main performance is the same as the previous form of LC ballast. If a special leakage magnetic transformer structure is selected in the design to form an LC leading peak ballast, in addition to the above advantages, it can also greatly improve repeated ignition ability. This is an ideal ballast. The disadvantage is that the design and processing are more complicated. To better understand this part, you can see more details about LC circuit. IV The Function of the BallastLimit the Starting Current of the Lamp to A Suitable RangeStarting current refers to the current through the lamp within 30 seconds after the lamp is powered on or during the lamp preheating process. In general (especially in the state of lowest temperature), the starting current is much larger than the operating current of the lamp, so each lamp has a maximum starting current. If the starting current is too large, the service life of the lamp will be shortened; if the current is too small, the lamp cannot be preheated to the normal starting state or the process from glow discharge to arc discharge cannot be completed. The starting current provided by the ballast should not only start the lamp in a short time but also not affect the normal service life of the lamp. The Open Circuit Voltage Provided Is Sufficient for the Lamp to Start SmoothlyWhen the open-circuit peak voltage of the ballast is used as the starting voltage of the lamp, it must be sufficient to ionize the gas in the gas discharge lamp, that is, to generate a peak current that causes a glow-to-arc transition discharge between the electrodes, so that the lamp can start to work. High-pressure mercury lamps and metal halide lamps are more difficult to start at low temperatures, and the open-circuit peak voltage provided by the ballast must be sufficiently high.Figure8. How Electronic Ballast Functions Prevent the Lamp Power from Changing GreatlyAlthough the lamp has a certain range of voltage values during the design and delivery of the lamp, the voltage value of the lamp changes during actual use and throughout its life. This requires the matching ballast to adjust it within a certain range so that the lamp power does not change significantly. The ideal ballast should be such that the lamp power of the newly used lamp and the lamp near the end of its life are not too different. Working Current of Automatic Control LampStable impedance within a certain voltage range is the basic condition that the impedance ballast can control the working current of the lamp. The ballast uses the time change rate of the voltage proportional to the current to adjust the working current of the lamp. When the open-circuit voltage in a certain period causes the lamp operating current to increase, the inductive effect of the ballast will limit the rate of current increase; when the current starts to decrease, the inductive effect will prevent the rate of current decrease. V How to Replace a Ballast?5.1 How to Tell If the Lamp is Broken or the Ballast is Broken(1) The fluorescent lamp requires a ballast to meet the voltage required for the fluorescent lamp to start and work. If the lamp is broken, you can try another lamp to trouble the lamp cover. If it can be lit, the lamp is broken, if it is still not lit, the ballast is broken; (2) Using a universal meter to measure the disconnection of the lamp filament can also be judged: use a universal meter to measure the two ends of the fluorescent lamp separately. If the resistance is not zero, it means that the fluorescent lamp is broken, and the light can be shorted According to the method, if the inspection of the two components of the lamp tube and the light emitter is good, the ballast is broken.Fluorescent Light Troubleshooting and Repair: starter, bulb or ballast?5.2 Symptoms of Ballast Failure(1) The shell of the lamp or ballast appears black.(2) Use an electric pen to detect the ballast. There is no electricity at the incoming and outgoing ends.(3) Use an electric pen to detect that there is electricity at the incoming end, but no electricity at the outgoing end, which means that there is a disconnection inside the ballast.(4) If the shell of the ballast is charged with an electric pen, it means that the ballast has a leakage problem.(5) Use an electric pen to detect that there is electricity at the incoming and outgoing ends. The housing is not live, but the light is off. The light is still off when the trigger is replaced.(6) Use a multimeter with a resistance level of 200 to measure the resistance of the coil. The resistance is infinite.Figure9. Flurescent Ballast Tear Down5.3 Replacement Procedure(1) Open the lampshade: There are three clips around the lampshade that can be rotated. Use a screwdriver to turn the clip away to remove the lamp cover. Place the removed clip in a fixed place so that it can be reinstalled.(2) Observe the position of each component(3) Check whether the old lamp is broken. In general, a section with a longer ring lamp will appear gray. In this case, we should know that it is caused by the sublimation of a substance inside the lamp tube under a high-temperature environment.(4) Remove the lamp: After the lamp cover is opened, remove it, you can see there is a wire slot on the ring lamp. A wire extending from the lamp holder in the center is inserted into this slot. This wire is plug-in type, just pull it out! The ring tube inside is clamped and fixed by three bent metal pieces. This piece of metal is elastic and breaks apart with a screwdriver. You can remove the ring lamp. Pay attention to the wiring inside.(5) Replace the ballast: the ballast of the ring lamp, the two white wires are 220V power cords, there is no difference between positive and negative. The four small round holes on the box are the sockets for the lamp feet. Remove the chassis, disconnect the power cord, put the ballast down, and replace it with a new one.(6) Ring lamp installation: The steps are exactly the reverse when they are removed. Fix the new lamp, and fix the lamp with the three bent metal cards. Use a screwdriver to tighten. Then connect the wires. Stick it with tape and fix it. At the same time, clamp the wire slot on the ring lamp.(7) Install the lampshade: put back the three clips that were just removed. Fix the lampshade. Turn on the power. You can test whether the light is on. If it's on, it's a good replacement lamp. Precautions:(1) Be sure to cut off the main power switch before operation;(2) When removing the lamp cover, small parts such as cards and screws must be placed. In order to reinstall it finally.Figure10. Ballast KitsVI Several Common Terms for Ballasts6.1 Ballast LossThis value represents that the energy consumed by the electronic ballast itself is converted into heat energy instead of light energy. This value can be calculated by subtracting the power consumed by all lamp tubes from the total output power. Generally speaking, the traditional 40W dual-lamp ballast consumes about 22W, while the electronic ballast consumes about 7W. 6.2 Ballast FactorThis value can show the relative effect of the light output of the electronic ballast. The value is the percentage obtained by dividing the measured light output of the electronic ballast by the light output of the standard ballast light. Generally speaking, the higher the value, the better the light output effect. For electronic ballasts, it must not be less than 0.9, but there are also electronic ballasts designed to emphasize high output values and its light output ratio can be up to 1.18 to 1.28. 6.3 Ballast Efficacy FactorThis value can be obtained by dividing the light output ratio (Ballast Factor) by the ballast input power value (Input Power). In the US market, sellers usually use this value to measure and compare the pros and cons of the efficiency of various electronic ballasts. The higher the value, the better the efficiency of the electronic ballast.Figure11. Impedance Ballast6.4 Crest FactorIt is also called wave height rate. This value has a direct and critical impact on the life of the lamp tube. Most lamp tube manufacturers recommend that this value is preferably less than 1.7. Excessively high values can easily cause blackening of the lamp tube and shorten the service life of the lamp tube. The definition of the crest factor refers to the peak current divided by the average current when an electronic ballast is used to light a fluorescent tube. 6.5 Power FactorThis value can represent the efficiency value of the electronic ballast to convert the external input voltage and current into available power. The higher the power factor value, the better the company that supplies the power system (referred to as the power company). In order to encourage consumers to use electronic ballasts with high power factors, foreign power companies have adopted a subsidy policy, but consumers generally think that the higher the PF value, the more power they save. This is a wrong concept because the amount of power saved is not related to the PF value.Figure12. Inductive BallastVII One Quiz about the BallastQuestion: Which of the following ballasts are required to have thermal protection?A. The ballast of a fluorescent luminaire installed indoors, including a replacement ballast for this type of luminaireB. A simple reactance ballast in a fluorescent luminaire with straight tubular lampsC. A ballast in a fluorescent exit luminaireD. A ballast in a fluorescent luminaire used for egress lighting and energized only during a failure of the normal supplyE. All of the aboveAnswer: A  VIII FAQ1. What does a ballast do?In a fluorescent lighting system, the ballast regulates the current to the lamps and provides sufficient voltage to start the lamps. Without a ballast to limit its current, a fluorescent lamp connected directly to a high voltage power source would rapidly and uncontrollably increase its current draw. 2. Do you need a ballast with LED lights?LED technology does not require a ballast to regulate the amount of energy flowing to the lights. LEDs require less energy and can be sensitive to excess energy. A ballast bypass is a common procedure to remove the ballast from the existing fixture. 3. What is ballast and why is it important?Ballast is defined as any solid or liquid that is brought on board a ship to increase stability. Ballasting is essential if a ship is carrying a heavy load in one hold and a lighter load in another, or when the ship is empty or facing rough seas. 4. What happens when a ballast goes bad?If the ballast is bad, then the needle won't move. If you're using a digital multimeter, often the digital readout will possibly list a ‘1’ when it doesn't find a measurable resistance. 5. Is ballast and choke the same?A choke is an inductor designed to have a high reactance to a particular frequency when used in a signal-carrying circuit. An electrical ballast (sometimes called control gear) is a device intended to limit the amount of current flowing in an electric circuit. 6. How long should a ballast last?According to the Certified Ballast Manufacturers Association, the average magnetic ballast lasts about 75,000 hours or 12 to 15 years with normal use. The optimum economic life of a fluorescent lighting system with magnetic ballasts is usually about 15 years. 7. How do I know if my ballast is T8 or T12?If no markings are available, the size in diameter of the tube is the easiest way to determine the type you have installed. T8 tubes are 1-inch in diameter and T12 tubes are 1 1/2 -inch. 8. How often does a ballast need to be replaced?A typical ballast will generally last about 20 years, but cold environments and bad bulbs can decrease this lifespan significantly. You can get a new ballast at a hardware store or home center and install it in about 10 minutes. 9. Can you bypass a ballast on a fluorescent light?If the existing fluorescent tube fixture you want to replace has a non-shunted tombstone, you can proceed with the ballast bypass procedure. Nonetheless, if the existing fixture offers a shunted tombstone, you should replace it with a non-shunted variant. 10. What's in a light ballast?They're usually rectangular black boxes with wires coming out of one or both ends. Lighting ballasts for fluorescent light bulbs and HID lamps made before 1980 may contain polychlorinated biphenyls (PCBs). When the manufacture of PCBs was banned, existing equipment containing PCBs was allowed to remain in use. 

CategoryⅠ IntroductionⅡ Development Background  2.1 Limitations of Microwave Oscillators  2.2 Origin of OEOⅢ Working Principle of OEO  3.1 The basic structure of OEO  3.2 Principle-based improvement directionⅣ Operating Characteristics of OEO  4.1 Advantage Performance  4.2 Disadvantage PerformanceⅤ Application of Optoelectronic Oscillator  5.1 Light Pulse Output  5.2 Clock ExtractionⅥ SummaryⅦ FAQ Ⅰ IntroductionThe optoelectronic oscillator (OEO) represents the first practical microwave oscillator that uses optical energy storage elements to generate signals with high spectral purity in the frequency range of several hundred MHz to more than 100 GHz. Many light wave energy storage components, such as fiber Fabry-Perot resonators, fiber ring resonators, optical micro disc resonators, etc. can be used to form OEO. It is a long fiber loop. The use of optical resonators can greatly reduce the size of OEO. Especially the optical microdisk resonator, which is a key component of integrating OEO in a single chip.  Figure1. Opto-Isolator OscillatorⅡ Development Background2.1 Limitations of Microwave OscillatorsGenerally speaking, the quality of the microwave signal generated by the microwave oscillator depends on the energy storage performance of the oscillation cavity. To produce high-quality microwave signals, a high-Q and low-loss energy storage unit is required. Current microwave oscillators are mostly based on electronics (such as dielectric oscillators) and acoustic (such as crystal oscillators) energy storage elements. When these components operate at frequencies above GHz, the energy storage characteristics will drop sharply, and the phase noise and spectral purity of the high-frequency microwaves produced will be poor. 2.2 Origin of OEOIn 1996, XSYao and L. Maleki of the California Institute of Technology Jet Power Laboratory developed a microwave oscillator based on a photonic energy storage unit during the use of photonics technology to improve the performance of a microwave system. This oscillator was named optoelectronic oscillator (OEO). Compared with microwave oscillators based on electronics and acoustic energy storage units, optoelectronic oscillators can generate high-purity microwave or millimeter-wave signals from several MHz to hundreds of GHz, and the Q value of their energy storage elements is as high as 1010, which generates high-frequency signals. The phase noise is as low as -163dBc / Hz at a frequency offset of 10kHz, and has both optical and electrical outputs. It is a very ideal high-performance microwave oscillator and is expected to be widely used in the future. Ⅲ Working Principle of OEO3.1 The basic structure of OEOThe basic structure of the optoelectronic oscillator is shown in Figure 2. It is a positive feedback loop composed of laser, electro-optic modulator, high Q optical energy storage unit (such as a certain length of optical fiber), photodetector, bandpass filter, microwave amplifier, phase shifter and microwave coupler. The energy of the oscillation comes from the injected light in front of the electro-optic modulator. After the injected light is modulated by the electro-optic modulator, it becomes an optical signal carrying a specific frequency. This optical signal is converted into an electrical signal by a photodetector, amplified, and then band-pass filtered. The filter filters out a specific frequency, part of which is used for output, and part of which is fed back into the microwave input port of electro-optic modulation to complete a cycle. After continuous cycling, a stable oscillation is finally formed. Since the optical oscillator uses a high-Q optical energy storage unit such as a low-loss long fiber, the output signal has extremely low phase noise. Figure2. Basic Structure of OEO3.2 Principle-based improvement directionIn addition, the loss in the optical energy storage unit such as optical fiber does not change with the change of microwave frequency, so theoretically the performance of the output signal of the optoelectronic oscillator will not deteriorate with increasing frequency. After nearly two decades of continuous exploration, the research on opto-electronic oscillators has made rapid progress. In the United States, opto-electronic oscillators have been successfully applied in cutting-edge technologies such as drones as high-quality local oscillators.  Nevertheless, in order to obtain a wider range of applications, optoelectronic oscillators need to be continuously improved in terms of performance and stability. Current research on optoelectronic oscillators is mainly focused on reducing phase noise, improving side mode suppression ratio, improving frequency stability, expanding output frequency, improving frequency tuning performance, miniaturization and multi-frequency oscillation, etc.Details are as follows:  (1) Phase NoiseThe phase noise of the output signal of the optoelectronic oscillator mainly comes from the thermal noise, scattered noise, and relative intensity noise of active devices such as lasers, photodetectors, and amplifiers. Phase noise can be reduced by optimizing the structure of microwave photonic links and the way the devices work. In experiments by D. Eliyahu and some others that produced extremely low phase noise (-163 dBc / Hz @ 6kHz) signals, a high power Nd: YAG laser with low relative intensity noise and an array amplifier with low phase noise were used. P.S.Devgan et al. Used low-biased Mach-Zehnder modulators and optical amplifiers to achieve an all-optical gain optoelectronic oscillator.  Compared with optoelectronic oscillators using electric amplifiers, the phase noise of this solution has been improved by 10dB. In addition, the use of high-power photodetectors can effectively reduce white noise, while the use of photodetector arrays to receive signals can effectively reduce the effects of flicker noise.Figure3. Phase Noise Modulation(2) Side Mode SuppressionIn order to obtain microwave output with low phase noise, the resonator of the photo-electric oscillator must have a very high Q value (Q = 2πfτ, f is the center frequency, and τ is the energy decay time), that is, a very large energy decay time is required. A larger τ can be obtained by increasing the fiber length, but as the fiber length increases, the longitudinal mode spacing (Δf = 1 / τ) in the cavity of the photo-electric oscillator decreases（As low as several tens of kHz）, in order to effectively suppress the non-oscillation mode and select a single oscillation frequency, a relatively narrow microwave band-pass filter is required. ①Dual-loop optoelectric oscillatorOne way to suppress side modes is to use a dual-loop optoelectronic oscillator. Two optical fiber loops of different lengths are formed in the cavity of the photo-electric oscillator. Only modes that satisfy the conditions for selecting the two loops at the same time can start oscillation. By selecting appropriate loop lengths, single-mode vibration can be achieved. The dual-loop optoelectronic oscillator scheme can be divided into an optical-domain coupled dual-loop structure and an optical-domain coupled dual-loop structure.  This research group proposed a dual-loop optoelectronic oscillator based on polarization modulation and polarization division multiplexing. The polarization beam splitter not only realizes the conversion of polarization modulation to intensity modulation, but also realizes that the incident light wave is divided into two orthogonal polarization states to form a double loop. The side-mode rejection ratio of the 10GHz signal generated by this solution reached 78dB. Compared with the electric-domain coupled dual-loop scheme, the optical-domain coupled scheme requires only one photodetector. Optical domain coupling dual loop schemes can also be implemented using wavelength division multiplexing technology.Figure4. A Dual-loop Optoelectronic Oscillator②Coupled optoelectronic oscillatorAnother method to suppress side modes is to use a coupled optoelectronic oscillator (COEO). The coupled optoelectronic oscillator includes two parts: an actively mode-locked laser loop and an optical feedback loop. The active mode-locked fiber laser loop can effectively increase the Q value of the oscillator. Therefore, a shorter fiber length can be used to obtain low phase noise. This research group used a non-pumped erbium-doped fiber to achieve a 10.7GHz stable coupled photo-electric oscillator with a phase noise below -120dBc / Hz @ 10kHz. (3) Frequency StabilityThe factors that affect the frequency stability of the optoelectronic oscillator are mainly two aspects:  ①The high-Q components in the system (including long optical fibers and narrow-band electrical filters) are susceptible to changes in the environment, and the output frequency is changed to cause the output frequency. Instability, especially the change of equivalent cavity length caused by environmental factors such as temperature. ②Because the filters used in optoelectronic oscillators usually have a relatively large passband range, they are within the gain bandwidth of the loop. There will be many side molds. One of these side modes may obtain sufficient gain during the change of cavity length to replace the original starting frequency, resulting in unstable starting frequency. In addition, the bias point drift problem of common electro-optic modulators will also affect the stability of the output frequency, but isolating the optoelectronic oscillator from the environment or using a temperature control device can reduce the impact of environmental changes on the system. For example, in experiments of XSYao, the optoelectronic oscillator was placed in a foam-filled box to isolate the influence brought by vibration. The active phase-locked loop circuit control is used to lock the oscillation signal of the optoelectronic oscillator to an external reference source, which can also effectively improve the frequency stability of the optoelectronic oscillator.Figure5. Frequency Stability(4) Working FrequencyTheoretically, the optoelectronic oscillator can generate signals from several MHz to hundreds of GHz, and the phase noise has nothing to do with frequency, but the high-frequency millimeter wave optoelectronic oscillator is difficult to realize. This is mainly due to the use of microwave devices such as photoelectric modulators, microwave couplers, microwave phase shifters, microwave amplifiers, and microwave transmission lines in optoelectronic oscillators, whose operating frequency is limited by electronic bottlenecks. Although there have been recent reports of high-frequency microwave or millimeter-wave devices, these devices are generally expensive, consume large power, and have poor performance. In response to the above problems, M. Shin et al. Used the LiNbO3 Mach-Zehnder modulator's half-wave voltage to the proportional relationship between the wavelength to achieve the simultaneous generation of 10GHz fundamental frequency and 20GHz octave signal. (5) TunabilityIn order to generate a broadband adjustable microwave signal, the optoelectronic oscillator needs to use a broadband adjustable high Q filter, which can be a tunable electrical filter, an optical filter, or a microwave photon filter. Limited by the electronic bottleneck, the tuning range of the output signal of the optoelectronic oscillator using a tunable electrical filter is limited. Optoelectronic oscillators based on microwave photonic filters usually have a large tuning range.Figure6. Schematic of The Tunable Opto-electronic Oscillator(6) Miniaturization ResearchOptoelectronic oscillators usually include laser sources, intensity modulators, long fiber delay lines, photodetectors, electrical amplifiers, electrical phase shifters, electrical bandpass filters, and other electrical or optical devices. These discrete electrical and optical components make the optoelectronic oscillator bulky and cause large power losses. By using high-Q optical resonators (such as whispering wall mode resonators) to replace fiber lengths of several kilometers, the size of the energy storage unit of a photo-electric oscillator can be significantly reduced. (7) Multi-frequency OscillationOptoelectronic oscillators usually only produce a pure single frequency signal. In applications such as wideband channelized receivers and multi-band radars, signals of multiple frequencies are required. In 2012, F. Kong et al. Used a birefringence characteristic of a phase-shifted Bragg grating to implement a dual-frequency optoelectronic oscillator. The disadvantage of this solution is that it can only generate signals of two frequencies, and the system is very sensitive to the environment. If a multi-frequency optoelectronic oscillator based on a single-phase modulator and a multi-wavelength light source are used, a single-passband tunable microwave photon filter can be formed on each optical carrier. By increasing the number of optical carriers, it will be easy to obtain more channels of different frequency signal output. Ⅳ Operating Characteristics of OEO4.1 Advantage PerformanceOptoelectronic oscillator is generally a positive feedback loop composed of light source, intensity modulator, filter and photodetector (PD). It takes advantage of the low loss characteristics of modulators and optical fibers to turn continuous light into stable, clean spectrum RF/microwave signals. The continuous light emitted by the laser is transmitted to the photodetector through the optical fiber after passing through the electro-optic modulator. The photodetector converts the light into an electrical signal and enters the frequency selection, amplification, and feedback modulation device.  During this process, the active device will generate noise disturbances of different frequencies. These disturbances are filtered by the filter at the output to the desired frequency and used to feedback and control the electro-optic modulator. The amplifier in the loop provides gain, and after several cycles of the signal, a stable oscillation can be established, and its oscillation frequency is mainly determined by the passband characteristics of the filter. 4.2 Disadvantage PerformanceAlthough the performance of the optoelectronic oscillator is outstanding, its system composition also determines some of its shortcomings. First of all, in order to obtain a high Q signal output, a long fiber is generally used in the cavity. At this time, the length of the cavity also determines the interval between the oscillation modes. The longer the cavity, the smaller the mode interval. In theory, a sufficiently narrow filter can be used to filter out unwanted modes, but it is quite difficult to obtain the device.  Secondly, in terms of the phase noise of the signal, the relative intensity noise of the light source, the photodetector and the electric amplifier will all affects the phase noise of the resulting microwave signal. Excessive bandwidth of filters and amplifiers will also reduce the signal-to-noise ratio in the passband range and affect the quality of the oscillation frequency.  Finally, because the loop is mainly composed of optical fibers, its cavity length is easily affected by environmental conditions and stress. The change causes the change of the fundamental frequency of the oscillation to cause the output frequency to drift or hop. In addition, the long optical fiber occupies a relatively large volume, which causes obstacles to the miniaturization and integration of the entire optoelectronic oscillator system. Solving the above problems is some of the key work for the final practical use of optoelectronic oscillators. Figure7. Cristal Oscillator Ⅴ Application of Optoelectronic OscillatorThe basic function of the optoelectronic oscillator is to generate high-quality optical and electrical microwave signals, but after being updated, it has also derived some new applications. In these applications, the electrical output of the photo-oscillator basically keeps the microwave signal output, but some changes occur in the light output part.5.1 Light Pulse OutputIn 1997 and 2000, X. Steve Yao and others successively analyzed and demonstrated the hybrid structure (COEO) of the optical resonator and optical oscillator loop provided by SOA to generate electric microwave signals and light pulses. This solution is similar to a regenerative mode-locked laser.  The main difference is that the photoelectric loop of COEO needs to be oscillated, and the final output mode is constrained by the selection of the two loops. In 2007, Ertan Salik demonstrated a COEO structure based on erbium-doped fiber amplifier (EDFA) to provide optical path gain, and obtained a 9.4 GHz microwave signal with ultra-low phase noise of -150 dBc / Hz (at a frequency offset of 10 to 100 kHz). Output and light pulse output with only 2 fs jitter. The optical pulse output mechanism of this structure is based on a fiber mode-locked laser. Therefore, in order to obtain high-performance output, there are high requirements on the design of the cavity length stabilization, dispersion control, and polarization maintenance of the optical cavity. Another feasible solution is to generate light pulses by changing the photoelectric modulation characteristics in the optoelectronic oscillator loop. In 2003, Jacob Lasri et al. Used electro-absorption modulator (EAM) to replace Mach-Zehnder intensity modulation (MZM) in the traditional scheme. By controlling the bias of EAM, a narrow modulation transmission window was obtained. Electric microwave signal and light pulse output. If a multi-wavelength light source is used in the light source part, this structure can also conveniently generate multi-wavelength light pulses. The structure of this scheme is relatively simple, but EAM generally has a large insertion loss, and the resulting pulse width is also wide.Figure8. Electro Absorption ModulatorIn addition, using a semiconductor laser operating under gain switching conditions or using a large-signal direct-modulation as the light source of the photo-electric oscillator, it is possible to obtain an electric microwave signal and an optical pulse output without requiring an additional modulator.5.2 Clock ExtractionBecause the structure of the optoelectronic oscillator has the function of frequency selection and amplification feedback, no matter whether the optical or electrical signal is injected into the optoelectronic oscillator, its clock signal (or frequency-divided clock) can be changed as long as it falls within the passband of the filter. The output can be recovered after locking and regeneration.  The maximum recoverable clock frequency is determined by the center frequency of the filter in the loop and the bandwidth of the modulator and the photodetector. X. Steve Yao et al.  Later, Caiyu Loun and others analyzed the extraction scheme of the frequency-divided clock based on the optoelectronic oscillator in 2002. By using the output electrical signal of the optoelectronic oscillator as a trigger signal to observe the injected optical signal on an oscilloscope, the electrical signal at this time can be determined. Whether the output is a divided clock of the injected signal, and experimentally verified the divided clock extraction under the condition of 10 Gb / s injected signal. In 2005, Hidemi Tsuchida and his partners demonstrated a frequency-divided clock extraction experiment with an injected signal rate of 40 Gb / s and 160 Gb / s. Figure9. Clock RecoveryIt should be noted that this method also provides a new idea for clock extraction of non-return-to-zero (NRZ) signals. In theory, there is no obvious clock component for NRZ signals to be extracted, but as long as the frequency selection of the optical oscillator filter is carefully adjusted. The clock signal of the injected NRZ code signal can be found and generated by the window. Li Huo et al. proposed the clock of the injected 10 Gb / s NRZ code signal, and obtained the converted zero (RZ) at the same time in the optical output part of the optoelectronic oscillator. The EAM-based optoelectronic oscillator can also complete the clock recovery of the RZ code signal. In the experiments demonstrated by Jaoob Lasri et al., In order to obtain the optical clock pulse signal at the same time, a DC light with a wavelength different from the wavelength of the injected signal light was added. Since the power change of the injected signal light will form a periodic switching window on the EAM and transfer the clock information to the simultaneously injected DC light, the wavelength of this DC light is selected by the optical filter to complete the Oscillation can generate an electrical clock signal and simultaneously obtain an optical clock pulse at that wavelength. It should be said that in addition to optical and electrical microwave sources, pulse sources and clock extraction systems, there are other applications, such as generating dual-frequency signals, inserting encoders to form multi-function signal generators, and so on. However, various applications are based on the feature that the photo-electric oscillator structure can automatically generate stable low-phase noise microwave signals. Therefore, as long as it focuses on various fields that require high-quality microwave signals, many new applications can be developed. Ⅵ SummaryIt can be seen that as a high-quality optical and electrical microwave signal generator, the optoelectronic oscillator has great advantages and wide application prospects. Various unique application methods also lay the foundation for the multifunctionalization of the optoelectronic oscillator.  However, it is undeniable that the current optoelectronic oscillator is still mainly in the laboratory research stage. There is still a period of time before it can be practically applied in the national economic construction and the development of national defense science and technology. Its main constraints focus on how to make the optoelectronic oscillator system into a compact, integrated, and compact frequency control system. The realization of these requirements depends on the development and manufacturing process of new photonic microwave devices and corresponding active devices.  Although there are no direct targets for optoelectronic oscillators, recent literature reports show some opportunities. For example, utc-pd (uni-traveling -Carrier Photodiode) in optoelectronic detection can receive high optical power and have high power electrical signal output, which can reduce or avoid the use of electric amplifiers in optoelectronic oscillators. The development of integrated semiconductor laser and modulator technology makes it possible to miniaturize the light source and feedback modulation of the photoelectric oscillator. The high Q value photonic filter with semiconductor structure is helpful to realize the system integration and tunability of optoelectronic oscillator. It is believed that with the gradual maturity of these technologies, the optotoelectric oscillator will be applied in practice and play its due contribution.  Ⅶ FAQ1. What do you mean by optoelectronic devices?Optoelectronic devices are electrical-to-optical or optical-to-electrical transducers or instruments that use such devices in their operation. ... Optoelectronics is based on the quantum mechanical effects of light on electronic materials, especially semiconductors, sometimes in the presence of electric fields. 2. What are optoelectronic devices give example?Examples of optoelectronic devices are: laser diodes, superluminescent diodes and light-emitting diodes (LEDs), converting electrical energy to light. photodetectors (e.g. photodiodes and phototransistors), converting optical signals into electrical currents. 3. What is the working principle of optoelectronic devices?Optoelectronic devices are primarily transducers i.e. they can convert one energy form to another. These devices produce light by expending electrical energy. They can also detect light and transform light signals into electrical signals for processing by a computer. 4. What are Optoelectronics used for?Optoelectronic devices refer to components used to detect or emit electromagnetic radiation, typically in the visible and near-infrared (NIR) regions of the electromagnetic spectrum. Each of these functions exploits the photoelectric effect of materials, also known as light-matter interaction. 5. Is LDR an optoelectronic device?There are two types of optoelectronic devices. These are Photoconductive devices and Photovoltaic devices. Photoconductive devices detect variations in light intensity to activate or inhibit electronic circuits. LDR, Photodiodes and Phototransistors fall in this category. 6. What are optoelectronic junction devices?Optoelectronic junction devices are p-n junction devices in which, carriers are generated by photons. Photodiodes, light-emitting diodes (LEDs) and solar cells are examples of optoelectronic devices. A photodiode is a device that is used to detect optical signals. 7. Which substance has optoelectronic property?Unlike the majority of electronic devices, which are silicon-based, optoelectronic devices are predominantly made using III–V semiconductor compounds such as GaAs, InP, GaN, and GaSb, and their alloys due to their direct bandgap. 8. Who discovered optoelectronics?Three Bell Laboratories scientists, William Shockley, John Bardeen, and Walter Brattain, demonstrated the first transistor-based on point-contact germanium (Ge) device. On the other hand, the semiconductor laser was discovered 15 years later in 1962. 9. Is solar cell an optoelectronic device?Solar Cell is another example of an Optoelectronic device based on the p-n junction, and the operating mechanism of a solar cell is essentially the same as that of Photodiode in that, a p-n junction is illuminated by light and the photogenerated carriers are separated by the built-in electric field across the p-n junction. 10. What are optoelectronic devices Name any two optoelectronic devices?Examples of optoelectronic devices include telecommunication laser, blue laser, optical fiber, LED traffic lights, photo diodes and solar cells. The majority of the optoelectronic devices (direct conversion between electrons and photons) are LEDs, laser diodes, photo diodes and solar cells. 

CategoryⅠ IntroductionⅡ Electronic Ballast Circuit Diagram Research Application 2.1 Overview 2.2 Circuit Structure of High-Performance Electronic Ballast       2.2.1 Power Factor Correction Circuit       2.2.2 Inverter Circuit       2.2.3 Lamp Circuit Network       2.2.4 Control Circuit2.3 High-Performance Electronic Ballast Dedicated Integrated Controller of ML4830 Series       2.3.1 Introduction to ML4831/32 Function       2.3.2 The Improvement of the Internal Function of ML48332.4 High-performance Electronic Ballast Built by ML4833Ⅲ FAQ Ⅰ IntroductionIn the 1970s, a worldwide energy crisis emerged. The urgency of energy conservation has led many companies to focus on energy-saving light sources and electronic ballasts for fluorescent lamps. With the rapid development of semiconductor technology, various high-return power switching devices are emerging, which provide conditions for the development of electronic ballasts. In the late 1970s, foreign manufacturers took the lead in launching the first generation of electronic ballasts, which was a major innovation in the history of lighting development. Because it has many advantages such as energy-saving, it has aroused great concern and interest around the world. It is considered to be an ideal product to replace the inductance ballast. Later, some well-known enterprises have invested considerable manpower and material resources to carry out higher-level research and development. Due to the rapid advancement of microelectronics technology, the development of electronic ballasts to high performance and high reliability has been promoted. Many semiconductor companies have introduced a series of products for dedicated power switching devices and control ICs. In 1984, Siemens developed an active power factor correction IC such as the TPA4812 with a power factor of 0.99. Subsequently, some companies have successively launched integrated electronic ballasts. In 1989, Finland's Hell Valley Company successfully launched electronically adjustable ballast monolithic integrated circuit ballasts. Electronic ballasts have been promoted and applied throughout the world, especially in developed countries. Figure 1. BallastChina's research and development of electronic ballasts started late, the technology is not advanced, early understanding of the difficulty and complexity of this product is insufficient, the development of special semiconductor devices has not kept up, the quality of products has not passed, and the market is extremely irregular. A large number of low-priced inferior goods were thrown to the market, causing losses to consumers and seriously damaging the image of electronic ballasts.  In the late 1990s, due to the rapid development and improvement of production levels, from circuit design to electronic components, the products entered a relatively mature stage, and high-quality products entered the construction project. The implementation of China's green lighting project paved the way for the promotion and application of electronic ballasts. Knowledge of Electronic Ballast for Fluorescent Lamps and Germicidal Lamps The electronic ballast is an electronic control device that uses a semiconductor electronic component to convert a direct current or low frequency alternating current voltage into a high frequency alternating current voltage, and drives a light source such as a low pressure gas discharge lamp (sterilization lamp) or a tungsten halogen lamp. The most widely used is the electronic ballast for fluorescent lamps. Due to the adoption of modern soft-switching inverter technology and advanced active power factor correction technology and electronic filtering measures, the electronic ballast has good electromagnetic compatibility and reduces the self-loss of the ballast. Ⅱ Electronic Ballast Circuit Diagram Research Application2.1 OverviewOn October 1, 1997, China's "Green Lighting Project" was officially launched. This is a major decision and measure in the field of lighting technology, which has a huge impact on China's energy, electric light source and lighting technology, and even environmental protection. As an important target of the "green lighting project", China will replace the incandescent lamp with an integrated energy-saving lamp composed of electronic ballasts and compact fluorescent lamps and promote more than 300 million energy-saving lamp, forming the terminal's ability to save 22 billion kWh, which is equivalent to saving about 49-63 billion yuan electricity construction funds. In addition to saving electricity, it can actually reduce social expenditures by 30-40 billion yuan. According to relevant experts from the Ministry of Information Industry, under the same luminous flux conditions, energy-saving lamps can save 80% of energy compared with incandescent lamps, and the cost of purchasing energy-saving lamps can be recovered in the 8-10 months of electricity savings. The use of electronic energy-saving lamps in ordinary households, enterprises and institutions, hotels, restaurants, and commercial systems is more cost-effective than incandescent lamps. However, the old-fashioned inductance ballasts currently working at the industrial frequency generally have the disadvantages of high energy consumption, low efficiency, large volume, and large amount of copper needed. Therefore, the state has set a policy which is to replace traditional inductance ballasts with high frequency electronic ballasts. Currently, some electronic ballasts have appeared on the market, and Table 1 lists the performance comparison of these electronic ballasts. According to the International Electrotechnical Commission standard IEC929 and China's professional standard ZBK74012-90, the electronic ballast should be used in "normal conditions, the lamp should be activated, but it does not cause damage to the lamp performance"; "The shortest time to apply the cathode preheating voltage should not be less than 0.4s" and "the crest factor of the open circuit voltage shall not exceed 1.8; during the minimum warm-up period, no extremely narrow voltage peaks that do not affect the rms value shall be generated", etc.  As listed in table 1, except for high grade electronic ballasts, they are unqualified products. In particular, as early as 1982, the International Electrotechnical Commission (IEC) developed a standard called “interference of household equipment and similar electrical equipment to the power supply system”, namely the IEC555-2 standard. In 1987, Europe also developed a similar EN60555-2 standard. Both standards strictly limit the power factor of the equipment to be close to 1, and it also clearly stated that, all products that do not meet the standards are not allowed to be sold. In view of the great harm caused by the low power factor, it is very important and necessary to impose regulations on the power factor of electronic equipment and products that must be close to 1. Figure 2. Brief Comparison of Low, Medium and High Grade Electronic Ballasts We believe that the high-performance electronic ballast should be a product that has both power factor correction and lamp filament preheating, lighting adjustment and lamp circuit protection, and is fully compliant with IEC555-2 and similar standards. The basic principles of the circuit structure and power factor correction circuit that must be provided for high-performance electronic ballasts are briefly discussed in this article. The integrated controllers for electronic ballasts ML4831, ML4832, ML4833 and high-performance electronic ballast circuits composed of them are highlighted. 2.2 Circuit Structure of High Performance Electronic BallastThe RFI and EMI filters in the figure filter out conducted RF interference and electromagnetic interference from the grid, while obstructing the conducted RF and electromagnetic interference generated by the ballast circuit from entering the grid. The bridge rectifier circuit converts the input AC to DC. The power factor correction circuit acts to improve the input AC current waveform, ensuring that the input current is sinusoidal and in phase with the input voltage, achieving a power factor close to or equal to one.  The inverter circuit completes the conversion of the DC high voltage to the high-frequency AC, and finally transmits the input power to the fluorescent tube through the lamp circuit network. In addition to transmitting electrical power, the lamp network will also perform preheating of the fluorescent filament, sampling and feedback of the lamp operating state signal. The feedback signal of the working state of the lamp is taken from the power factor correction circuit and the dimming signal, and processed by the control circuit to obtain the driving pulse of the switching device in the correct inverter circuit. 2.2.1 Power Factor Correction CircuitThe power factor of the system is defined as PF=γcosφ1 In the formula, γ=I1/IRMS, which is the ratio of the fundamental rms value of the input current to the rms value of the input total current and is also called the distortion factor of the current. φ1 is the phase shift angle of the fundamental current and voltage. If the input voltage of the system has no phase shift (ie, the system is purely resistive) and there is no harmonic component (ie DF=1), the PF of the system must be one. Unfortunately, the input rectification filter units that most of the current devices connect with the power frequency grid are composed of uncontrolled diodes and large-capacity electrolytic capacitors. The instantaneous value of the current on the grid side is quite high (generally about 2 to 3 times that of IRMS), the duration is very short (usually no more than 4ms), and it is severely non-sinusoidal, so the PF of the system is much lower than 1.  The power factor correction is aimed at the drawbacks of the traditional uncontrolled rectifier circuit, and adopts corresponding circuit measures. While increasing the DF value of the system, the phase shift of the input fundamental current and voltage is minimized, and finally the target with the PF value equal to 1 is achieved. As a boost-type active power factor correction circuit commonly used in electronic ballasts, the control circuit uses the input voltage signal as a reference, and the product of the input current and the output voltage signal is used as a modulation source to obtain a sinusoidal pulse width modulation (SPWM) signal to the step-up DC/DC power conversion circuit to adjust the on/off time ratio of the power switch. In the end, a stable DC high voltage is obtained.  The power switching device in the step-up power conversion circuit is driven by the SPWM signal outputted by the control circuit to turn on and off at a high speed, thereby ensuring that the current waveform flowing through the inductor connected in series with the rectifier bridge is a sine wave, and is in phase with the input voltage. Thus, the distortion factors γ=1 and φ1=0 of the system input current are obtained, that is, cosφ1=1, and the system power factor is 1. 2.2.2 Inverter CircuitThe most important function of the inverter circuit is to convert the high-voltage direct current outputted by the power factor correction circuit into a high-frequency alternating current for the fluorescent lamp. The power MOSFET push-pull tubes (V1 and V2) are alternately turned on and off under the driving pulse with a duty cycle of 50%, and is commutated when the current crosses zero in the parallel resonant loop of the power transformer primary inductance and capacitance thus to realize zero voltage switching(ZVS) and perform chopping on high voltage DC. The zero-voltage switching eliminates switching losses associated with output capacitance and parasitic capacitance charging of MOSFET tube, and the gate drive charge is minimal, which helps reduce gate losses.  Since the high frequency AC obtained by the secondary coupling of the power transformer is directly fed to the lamp network, there is no phase shift between the lamp current (ie, secondary current of the power transformer) and the output current of the inverter circuit (ie, primary current of the power transformer). Considering that the total impedance of the lamp network is reduced at high frequencies, and the negative resistance characteristic of the fluorescent lamp itself, it can be found that as the lamp current decreases (corresponding to the weakening of the light intensity of the lamp), the output current of the inverter circuit will increase. 2.2.3 Lamp Circuit NetworkThe lamp circuit network not only needs to deliver the high-frequency AC power to the lamp tube to complete the efficient conversion of electricity and light, but it also needs to implement functions such as filament warm-up, lamp current detection feedback, and auxiliary power supply for the entire electronic ballast system.  The power transformer primary T is connected to the inverter circuit, and the lamp current is directly transmitted to the lamp through the capacitor, and the secondary winding supplies the lamp with filament current for preheating and maintaining the operation. The current transformer TA performs detection and sensing of the lamp current, and sends a signal about the operation of the lamp to the control circuit at any time by the change of the lamp current. The control circuit can judge the light intensity of the lamp according to the magnitude of the lamp current (even including the disconnection and short circuit of the lamp), and then send corresponding control signals to the inverter circuit. 2.2.4 Control CircuitThe control circuit for high-performance electronic ballasts should have a series of functions including power factor correction, lighting adjustment, light-on preheating, lamp disconnection alarm, and lamp restart program control. At present, some integrated circuit controllers for electronic ballasts appearing in the domestic and international device market are mostly based on PFC control, with appropriate addition of lamp control functions, or implementation of lamp control by external circuits. It is worth mentioning that the ML4830/31/32/33 series products can be said to be integrated controllers for high-performance electronic ballasts. 2.3 High-Performance Electronic Ballast Dedicated Integrated Controller of ML4830 SeriesML4830/31/32/33 are integrated circuit controllers developed by American Micro Linear Corporation for high-performance electronic ballasts. The first generation ML4830 has been eliminated; the second generation ML4831 is manufactured by bipolar integrated circuit technology; the third generation ML4832 uses Bicmos process to replace the original bipolar process, the circuit bias current is greatly reduced, and the consumption is greatly reduced. The fourth-generation ML4833 not only adopts the Bicmos process but also has a major improvement in the internal structure, so the function is enhanced and the performance is better. Although these devices can use the functional block diagram of figure 3, the internal structure of ML4831 and ML4832 and the internal structure of ML4833 are respectively shown in figure 4 and figure 5. Figure 3. Functional Block Diagram of ML4831, 32, 33  Figure 4. Internal Block Diagram of ML4831, 32  Figure 5. Internal Structure Block Diagram of ML4833 2.3.1 Introduction to ML4831/32 FunctionThe ML4831/32 is composed of a continuous current type boosting power factor correction stage controlled by an average current. It has a dedicated control circuit for electronic ballasts with various ballast control links. Lamp start-up and restart timing can be achieved by using external circuit components to provide a wide range of control over different types of lamps. The ballast link uses an additional programmable method of frequency modulation and adjustment of the frequency range of the voltage-controlled oscillator to control the lamp power, so it is suitable for various types of output networks. The gain modulator in the ML4831/32 is highly immune to interference caused by switching high-power switching devices. The output of the gain modulator appears as a reference to the current error amplifier at the inverting input of the amplifier. Isine is the current drawn from the AC input; UEA is the output of the error amplifier (pin 1). The output of the gain modulator is limited to 1V. The PWM regulator in the PFC control section compensates for the positive voltage generated by the multiplier output through the negative voltage developed across the pin 4 sense resistor. At the same time, the power MOSFET is protected against high-speed current transients by weekly current limiting. Once the voltage at pin 4 is below 1V, the PWM cycle is terminated immediately. The overvoltage protection (OVP) terminal (pin 18) of the ML4831/32 is used to protect the power circuit from high voltage damage when the lamp is suddenly disconnected. The OVP take-off point can be set by directly tapping the voltage divider resistor to the high-voltage DC bus. As long as the voltage at pin 18 exceeds 2.75V, the power factor correction (PFC) transistor will be turned off and the ballast operation can continue.  The threshold of the OVP should be set to a value that the power device can operate safely, but is not too low to affect the operation of the boost power conversion link. The internal operational transconductance amplifier performs PFC voltage feedback, current sensing and loop amplification. The transconductance amplifier is designed with a low signal forward transconductance so that a large value resistor can be used as a load and a small (<1μF) ceramic capacitor for AC coupling in the compensation network. The compensation network can take the form of figure 6, introducing a zero point and a pole at frequencies fz and fP, respectively: fZ=1/2πR1C1fP=1/2πR1C2 It is noted that the DC-to-ground path and the output of the transconductance amplifier may be out of tune, and the offset error voltage value reflected at the input is determined by uos=iO/gm. Capacitor C1 in figure 6 is used to block DC and minimize the adverse effects of offset. All of the operational transconductance amplifiers in the ML4831/32 incorporate a Slew Rate enhancement to improve recovery under circuit power-up and transient response conditions because the transconductance amplifier changes from a small transconductance state to a large transconductance state. The response to large signals is essentially non-linear. Figure 6. Compensation Network for Transconductance Amplifier The ML4831/32 controls the output power of the lamp by frequency modulation of the non-overlapping conduction of the power switch tube in the inverter part of the ballast circuit. That is to say, during the discharge of oscillation timing capacitor CT, the output of both ballast power tubes is low. The frequency range of the voltage controlled oscillator (VCO) in the device is controlled by the output of the LFB amplifier (pin 6). As the lamp current decreases, the voltage at pin 6 rises, causing the CT charging current to drop, thus causing the oscillation frequency of the oscillator to become lower. Because the ballast output network attenuates high frequencies, the power fed to the lamp increases accordingly. In general, the frequency of the oscillator can be calculated as follows: fosc=1/（tchg＋tdis） Attention: A zero charge current occurs when LFBOUT (pin 6) is high level. Typically, the charge current varies with the two inputs to the oscillator: One is the output of the warm-up timer, and the other is the output of the lamp feedback amplifier (pin 6). During the warm-up phase, the charging current is fixed at a value of Ichg (preheat) = 2.5 / Rset (3). During normal operation, the charging current varies with the voltage of pin 6 from 0 to UOH. When the voltage at pin 6 is zero, the oscillator frequency is lowest and the lamp power is maximum. The discharge current is much larger than the current flowing through the timing resistor RT. For example, when the discharge current is 5 mA, the discharge time is：  tdis ≈ 490 × CT. The ML4831/32 also includes a parallel regulator that limits the UCC voltage to 13.5V. When the UCC is 0.7V lower than 13.5V, the quiescent current of the device will be less than 1.7mA, and the output will be turned off, allowing the device to be started directly using the resistor attached to the rectified AC bus. In addition, because the ML4831/32 contains a temperature sensing function, the ballast operation is stopped as soon as the junction temperature of the device exceeds 120 °C. In order to better utilize the internal sensing function without using an external sensor, the position of the ML4831/32 must be carefully determined on the ballast's circuit board to ensure that the device can properly transfer the operating temperature of the ballast. The chip temperature of ML4831/32 can usually be estimated by the following formula:  Tj=65TA/PD(°C/W) It is worth noting that fully and reasonably using the sensing function inside the device is useful for reducing the total cost of the ballast. The starting scheme of the device is specifically designed for the ML4831/32 in accordance with the principle of ensuring the longest lamp life and minimizing the ballast heating. Figure 7(a) contains a starting scheme including preheating of the filament and sudden breaking of the lamp. When the ballast is energized, the time that the voltage on the CX rises from 0.7V to 3.4V is called the warm-up time of the filament.  During this time, the oscillator's charging current Ichg = 2.5/Rset, the oscillator produces a very high frequency, but does not produce a voltage sufficient to start the lamp. After the filament is preheated, the frequency of the inverter circuit drops to a minimum, and a high voltage is generated to start the lamp. If the voltage of the inverter circuit does not jump when the lamp should start to work, the lamp feedback voltage entering pin 9 will rise above Uref, the CX charging current will be bypassed, and the inverter circuit will stop working until CX drops to a 1.2V threshold by RX discharge. Stopping the inverter circuit in this way can avoid the failure of the lamp to start or the inverter circuit to overheat when it is disconnected from the socket.  In general, it is better to choose a large resistance RX to make this period longer. When CX reaches the 6.8V threshold, the oscillator will turn off LFBOUT, so the lamp will be driven to full power, then dimmed, and the potential of the CX pin is clamped at approximately 7.5V. The whole process is shown in the waveform of figure 7(b). Figure 7. Lamp Start Preheat and Interrupt Timing Scheme and Its Waveform 2.3.2 The Improvement of the Internal Function of ML4833The ML4833 is a modified version of the ML4831/32. In addition to the full functionality of the ML4831/32 described above, the most prominent improvement is in the power factor correction section. The power factor correction part of the ML4833 is a step-up type PFC control circuit for peak current sensing. This form of circuit only requires voltage loop compensation, which is simpler than the ML4831/32 with average current control mode circuit. It consists of a voltage error amplifier, a current sense amplifier without compensation, an integrator, a comparator, and a logic control circuit.  In the boost type power conversion part, the correction of the power factor is performed by the current sensing resistor to output the sensing voltage and the current flowing through, and the duty ratio is adjusted by comparing the integrated voltage signal of the error amplifier with the voltage across the Rsense. The control timing of the duty ratio is as shown in figure 8. Considering that all of the high-performance electronic ballast integrated control chips of Micro-Linearity are packaged in 18-pin DIP or SOIC packages, the improvement of the device structure will inevitably bring about changes in the internal functional frame and external pin functions. Figure 8. PEC Link and Duty Cycle Control of ML4833 2.4 High-performance Electronic Ballast Built by ML4833Figure 9 shows the complete circuit diagram of a high-performance electronic ballast built by ML4833. The circuit is a typical AC/DC/AC structure: the RFI suppression filter circuit is added to the input terminal, the booster active power factor correction circuit is composed of AC/DC in the front stage, and the high-frequency inverter circuit is composed of DC/AC in the rear stage. A closed-loop is formed through T5, VD11, R23 and pin 8 of the control to make the system works stably. Figure 9. Complete Circuit Diagram of High-performance Eectronic Ballast Built with ML4833  Ⅲ FAQ1. What is the use of electronic ballast?An electronic ballast will convert power frequency to a very high frequency to initialize the gas discharge process in Fluorescent Lamps – by controlling the voltage across the lamp and current through the lamp. 2. What is the output voltage of an electronic ballast?This unit operates off the AC mains with a voltage of 230 Volts and voltages generated within the unit can reach 600 to 800 Volts. 3. What is inside an electronic ballast?Lighting ballasts generate an initial high voltage to start the arc that excites the gases in fluorescent and HID lamps and makes them shine. ... Lighting ballasts for fluorescent light bulbs and HID lamps made before 1980 may contain polychlorinated biphenyls (PCBs). 4. How do you make an electronic ballast for tube light?An electrical ballast is nothing but a simple high current, mains voltage inductor made by winding number of turns of copper wire over the laminated iron core. Basically, as we all know a fluorescent tube requires a high initial current thrust to ignite and make the electrons flow connect in between its end filaments. 5. How do you wire an electronic ballast?Connect the ballast to the power from the breaker panel by wiring the black wire from the breaker panel to the black wire on the ballast, using a wire nut. Connect the white wire from the breaker to the white wire from the ballast. 6. What's the difference between electronic and magnetic ballast?A magnetic ballast uses coiled wire and creates magnetic fields to transform voltage. ... An electronic ballast uses solid-state components to transform voltage. It also changes the frequency of the power from 60 HZ to 20,000 HZ or higher depending on the ballast. 7. How do you test an electronic ballast with a multimeter?Insert one probe of the multimeter into the wire connector holding the white wires together. Touch the remaining probe to the ends of the blue, red and yellow wires leading from the ballast. Depending on the ballast, you may have only red and blue wires. 8. Are electronic ballasts non-linear loads?Rectified input, switching power supplies and electronic lighting ballasts are the most common single-phase non-linear loads. 9. Which is not the advantage of electronic ballast?Electronic ballasts are more efficient and more compact in size and weight. They also provide the ability for continuous power adjustment in different settings. A disadvantage is that power fluctuations may cause a failure but this can be offset by adding a buffer capacitor. The operation of the ballasts generates heat. 10. Can you repair an electronic ballast?I eventually replaced the 2 switching transistors in this ballast as well and it worked. So the next time you have a problem with an electronic ballast from a fluorescent fitting open it and check before buying a new one. They can be expensive and more often than not they can be repaired. 

IntroductionThyristor is a four semiconductor layers or three PN junctions devicea solid-state semiconductor device with four layers of alternating P- and N-type materials. It is also known as “SCR” (Silicon Control Rectifier). The term “Thyristor” is dervid from the words of thyratron (a gas fluid tube which work as SCR) and Transistor. And It acts exclusively as a bistable switch in electronic circuit.What is a Thyristor?CatalogIntroductionⅠ Types of ThyristorsⅡ Thyristor Selection2.1 Specific Requirements of Applying Circuit2.2 Main Parameters of the ThyristorⅢ Replacement of ThyristorⅣ Detection of Thyristor4.1 Detection of Unidirectional Thyristors4.2 Detection of TRIACⅠ Types of ThyristorsCommonly used thyristors include unidirectional thyristors, TRIAC, and turn-off thyristors, etc., which should be selected reasonably according to the needs of the circuit.— Unidirectional ThyristorThe unidirectional thyristor is characterized in that the current can only flow from the anode A to the cathode k, and is mainly used in the control of DC power supply or pulsating direct current, AC power rectification, and DC power inverter.Unidirectional thyristors can be divided into ordinary thyristors and high-frequency thyristors (the working frequency is above 110kHz). Commonly used unidirectional thyristors are 3CT series, 3DT series, KP series and KK series (high frequency thyristors), and imported MCR series, SF series, BST series etc.— TRIACTRIAC was developed on the basis of the unidirectional thyristor and is an AC power control device. TRIAC can not only replace two unidirectional thyristors in anti-parallel, but also requires only one trigger circuit, which is more convenient to use.The characteristic of TRIAC is that alternating current can pass through it, which is mainly used in the control of AC power supply and the adjustment of AC voltage. Commonly used TRIAC include 3CTS series and KS series, as well as imported MAC series, SM series, BCR series, etc.— Gate Turn-off ThyristorThe characteristic of the gate turn-off thyristor is that it can be switched off by the control electrode. It is mainly used in gate turn-off contactless switches, DC inverters, dimmer, speed regulation and other occasions.Gate turn-off thyristors are power-type control devices developed on the basis of ordinary thyristors. After the ordinary thyristor is triggered to be turned on, its control electrode does not work. To turn off the thyristor, the power must be cut off, or the forward current flowing through the thyristor must be less than the holding current. Gate turn-off thyristor overcomes the above drawbacks. When the control electrode G is added with a positive pulse voltage, the thyristor is turned on, and when the control electrode G is added with a negative pulse voltage, the thyristor is turned off.Gate turn-off thyristors are ideal high-voltage, high-current switching devices. For example, the DG series high-power gate turn-off thyristors can reach a maximum voltage of 4500V and a maximum current of 3000A. Ⅱ Thyristor Selection2.1 Specific Requirements of Applying CircuitThere are many types of thyristors, which should be selected reasonably according to the specific requirements of the application circuit.For AC/DC voltage control, controllable rectification, AC voltage regulation, power inverter, switching power supply protection circuit, etc., ordinary thyristors can be selected.For AC switch, AC voltage regulation, AC motor linear speed regulation, lamp linear dimming, solid state relay, solid state contactor, etc., a TRIAC should be selected.For AC motor variable frequency speed regulation, chopper, power inverter and various electronic switch circuits, you can choose gate turn-off thyristor.For sawtooth wave generator, long time delay, over voltage protector and trigger circuit with power transistor, etc., BTG thyristor can be selected.In electromagnetic cookers, electronic ballasts, ultrasonic circuits, superconducting magnetic energy storage systems, switching power supplies and other circuits, reverse conducting thyristors can be selected.In the photocoupler, light detector, light alarm, light counter, photoelectric logic circuit and operation monitoring circuit of automatic production line, the light-control thyristor can be selected.2.2 Main Parameters of the ThyristorThe main parameters of the thyristor should be determined according to the specific requirements of the application circuit.The selected thyristor should have a certain power margin, and its rated peak voltage and rated current (on-state average current) should be higher than the maximum operating voltage and maximum working current of the controlled circuit by 1.5 to 2 times.The parameters of the thyristor's forward voltage drop, gate trigger current, and trigger voltage should meet the requirements of the application circuit (this refers to the control circuit of the gate), and should not be high or low, otherwise it will affect the normal operation of the thyristor. Ⅲ Replacement of ThyristorAfter the thyristor is damaged, if no thyristor of the same type is replaced, another type of thyristor with similar performance parameters can be used instead.When designing an application circuit, a large margin is generally left. When replacing the thyristor, just pay attention to its rated peak voltage (repeated peak voltage), rated current (on-state average current), gate trigger voltage and gate trigger current, especially the two indicators of rated peak voltage and rated current.The switching speed of the thyristor used for replacement should be consistent with the switching speed of the damaged thyristor. For example: After the high-speed thyristor used in the pulse circuit and high-speed inverter circuit is damaged, only the same type of fast thyristor can be used instead of the ordinary thyristor.When selecting a thyristor to be used for replacement, it is not necessary to leave too much margin for any parameter, and the parameter of it should be as close as possible to the parameter of the replaced thyristor, because an excessively large margin is not only a waste, but also sometimes has side effects, such as non-triggering or insensitive triggering.In addition, the appearance of the two thyristors should be the same, otherwise it will cause inconvenience to the installation. Ⅳ Detection of ThyristorThyristors are usually represented by the letters "SCR" in circuit schematic diagrams. For example, SCR2 refers to the thyristor numbered 2. The symbol of the thyristor in the schematic diagram is shown in figure 1. Figure 1. Symbols of Thyristor4.1 Detection of Unidirectional Thyristors(1) Discrimination of each electrode: According to the structure of an ordinary thyristor, it can be seen that there is a PN junction between the gate G and the cathode K, which has unidirectional conductive characteristics, while there are two PN junctions of opposite polarities connected in series between the anode A and the gate. Therefore, by measuring the resistance between the pins of an ordinary thyristor with the R × 100 or R × 1 k Q level of the multimeter, three electrodes can be determined.The specific method is: use the black probe of the multimeter to connect one electrode of the thyristor, and use the red probe to touch the other two electrodes in turn. If the measurement result has a resistance value of several thousand ohms (kΩ) and another resistance value of several hundred ohms(Ω), it can be determined that the black probe is connected to gate G. In the measurement with a resistance value of several hundred ohms, the red probe was connected to the cathode K, and in the measurement with a resistance value of several thousand ohms, the red probe was connected to the anode A. If the measured resistance values are both very large, it means that the black probe is not connected to gate G. Apply the same method to test other electrodes until three electrodes are found.You can also measure the forward and reverse resistance between any two pins. If the forward and reverse resistance are close to infinity, the two electrodes are anode A and cathode K, and the other pin is gate G.Each electrode of the ordinary thyristors can also be judged according to its packaging form.For example, the bolt end of the bolt-type ordinary thyristor is anode A, the thinner lead end is gate G, and the thicker lead end is cathode K.The lead end of the flat thyristor is gate G, the flat end is anode A, and the other end is cathode K.A thyristor of metal package (T0-3) is a common thyristor and its shell is anode A.The middle pin of the plastic thyristor (T0-220) is anode A, and it is mostly connected with its own heat sink. Figure 2. Pin Arrangement of Several Common Thyristors(2) Judging whether it is good or bad: Use the R×1 kΩ level of a multimeter to measure the forward and reverse resistance values between anode A and cathode K of ordinary thyristor, which should normally be infinite (∞) ; If the forward and reverse resistance values are zero or the resistance values are both small, it indicates that a breakdown short circuit or leakage occurs inside the thyristor.Measure the forward and reverse resistance values between gate G and cathode K. Normally, there should be forward and reverse resistance values similar to diodes (the actual measurement results are smaller than those of ordinary diodes), that is, the forward resistance value is small (less than 2 kΩ) and the reverse resistance value is large (greater than 80 kΩ). If the resistance values of the two measurements are both large or small, it means that the thyristor is open or short-circuited between electrode G and K. If the forward and reverse resistance values are equal or close, it indicates that the thyristor has failed, and the PN junction between its electrodes G and K has lost its unidirectional conduction effect.Measure the forward and reverse resistance value between anode A and gate G. In normal conditions, both resistances should be several hundred kiloohms (kΩ) or infinite. If the forward and reverse resistance values are not the same (there is unidirectional conduction like a diode). One of the two PN junctions connected in reverse series between gate G and electrode A has been short-circuited.(3) Detection of triggering capability: For ordinary thyristors with low power (working current is below 5A), it can be measured with R×1 level of the multimeter . During the measurement, the black probe is connected to anode A and the red probe is connected to cathode K. At this time, the watch hand does not move, and the resistance value is displayed as infinite (∞). Use tweezers or wires to make anode A and gate G of the thyristor be short-circuited(see figure 3), which is equivalent to applying a forward trigger voltage to gate G. At this time, if the resistance value is several ohms to tens of ohms (the specific resistance value will vary according to the part number of the thyristor), it indicates that the thyristor is conducting due to the forward trigger. Then disconnect electrode A and gate G(the probes on electrode A and K do not move, only the trigger voltage of gate G is cut off). If the value indicated by the watch hand is still in the position of several ohms to tens of ohms, it indicates that the triggering performance of the thyristor is good. Figure 3. Detection of Triggering CapabilityFor medium and high power ordinary thyristors with a working current above 5 A, the on-state voltage drop VT, holding current IH and the gate trigger voltage Vo are relatively large. The current provided by the R × 1 kΩ level of the multimeter is low, and the thyristor cannot be completely turned on, so a 200Ω adjustable resistor and one to three 1.5 V dry batteries can be connected in series at the end of the black probe (depending on the capacity of the thyristor being tested, if its working current is greater than 100 A, three 1.5 V dry batteries are applied), as shown in figure 4. Figure 4. Detection of Trigger VoltageYou can also use the test circuit in figure 5 to test the triggering capability of an ordinary thyristor. In the circuit, vT is the thyristor under test, HL is a 6.3 V indicator (small electric beads in a flashlight), GB is a 6 V power supply (four 1.5 V dry batteries or 6 V regulated power supply can be used), and S is the button, R is the current limiting resistor. Figure 5. Test Circuit to Test the Triggering CapabilityWhen the button S is not connected, the thyristor VT is in a blocking state, and the indicator light HL is not on (if HL is on at this time, there may be breakdown of vT or leakage damage). After pressing the button S once (turn S on for a moment to provide the trigger voltage for gate G of the thyristor VT), if the indicator HL is always on, it means that the thyristor has a good triggering capability. If the brightness of the indicator is low, it indicates that the thyristor has poor performance and a large conduction voltage drop (the conduction voltage drop should be about 1 V under normal conditions). If button S is on, the indicator light is on, and when button S is off, the indicator light is off, indicating that the thyristor is damaged and the triggering performance is poor.4.2 Detection of TRIAC(1) Discrimination of each electrode: Use the R×1 or R×10 level of the multimeter  to measure the forward and reverse resistance values between three pins of the TRIAC. If it is measured that one pin is not connected with the other two pins, then this pin is the main electrode T2.After finding the electrode T2, the remaining two pins are the main electrode T1 and the gate G3. Measuring the forward and reverse resistance values between these two pins will gain two smaller resistance values. In a measurement with a small resistance value (about tens of ohms), the black probe is connected to the main electrode T1, and the red probe is connected to gate G.One end of the bolt of the bolt-shaped TRIAC is the main electrode T2, the thinner lead end is gate G, and the thicker lead end is the main electrode T1.    The shell of the metal-encapsulated (TO-3) TRIAC is the main electrode T2.The middle pin of the plastic-encapsulated (TO-220) TRIAC is the main electrode T2, which is usually connected to its own small heat sink. Figure 6. Pin Arrangement of Several TRIAC(2) Judging whether it is good or bad: Use the R×1 or R×10 level of a multimeter to measure the forward and reverse resistance values between the main electrode T1 and the main electrode T2 and between the main electrode T2 and gate G of the TRIAC. Normally it should be close to infinity. If the measured resistance values are all very small, it means that the electrodes of the TRIAC have been broken down or are short-circuited.Measure the forward and reverse resistance of the main electrode T1 and gate G. Normally, it should be between tens of ohms (Ω) and one hundred ohms (Ω) (when the black probe is connected to electrode T1 and the red probe is connected to gate G, the measured forward resistance value is slightly smaller than the reverse resistance value). If the forward and reverse resistance values between electrode T1 and gate G are measured to be infinite, it indicates that the thyristor has been damaged by an open circuit.(3) Detection of triggering capability: For small power TRIAC with working current below 8A, it can be measured directly with R×1 level of the multimeter. When measuring, first connect the black probe to the main electrode T2 and the red probe to the main electrode T1, then use tweezers to make electrode T2 and gate G be short-circuited, and add a positive polarity trigger signal to gate G. If the resistance value measured at this time changes from infinity to more than ten ohms (Ω), it means that the thyristor has been triggered to conduct, and the conduction direction is T2 → T1.Then connect the black probe to the main electrode T1, and the red probe to the main electrode T2. Use tweezers to make electrode T2 and gate G be short-circuited, and add a negative polarity trigger signal to gate G. If the resistance value measured at this time changes from infinity to more than ten ohms (Ω), it means that the thyristor has been triggered to conduct, and the conduction direction is T1 → T2.If gate G is disconnected after the thyristor is triggered to be turned on, the low-resistance conduction state cannot be maintained between electrode T2 and T1 and the resistance value becomes infinite, it indicates that the TRIAC has poor performance or is damaged. If a positive (or negative) polarity trigger signal is added to gate G, the thyristor still does not conduct (the forward and reverse resistance values between T1 and T2 are still infinite), then the thyristor is damaged and has no trigger continuity.For medium and high power TRIAC with a working current of 8A or more, when measuring their triggering capability, one to three 1.5V dry batteries can be connected in series to a probe of a multimeter, and then measure by using R×1 level as described above.For a TRIAC with a withstand voltage of 400V or more, its trigger capability and performance can also be tested by using 220V AC voltage.Figure 7 is a test circuit of a TRIAC. In the circuit, FL is a 60W /220V incandescent bulb, VT is the TRIAC under test, R is a 100Ω current limiting resistor, and S is a button. Figure 7. TRIAC CircuitAfter the power plug is connected to the working frequency AC, the TRIAC is in the off-state and the light bulb is off. (If the bulb is glowing normally at this time, it means that electrode T1 and T2 of the thyristor under test have been broken down and short-circuited; if the light bulb is slightly light, it means that the thyristor under test is damaged by leakage). Press the button S once to provide the trigger voltage signal for gate G of the thyristor. In normal conditions, the thyristor should be immediately triggered to turn on, and the light bulb will glow normally. If the bulb fails to emit light, the internal circuit of the tested thyristor is damaged. If the light bulb is turned on when the button S is pressed, and the light bulb is turned off when the button is released, it indicates that the triggering performance of the tested thyristor is poor.When using a multimeter to detect low-power light-controlled thyristors, put the multimeter in R × 1 level, connect one to three 1.5V dry batteries in series to a black probe, and measure the forward and reverse resistance values between the two pins. Normally it should be infinite. Then use a small flashlight or laser pen to illuminate the light receiving window of the light controlled thyristor. At this time, a small forward resistance value can be measured, but the reverse resistance value is still infinite. In a measurement with a small resistance value, the black probe is connected to the anode A, and the red probe is connected to the cathode K.The following method can also be used to measure light-controlled thyristors. Turn on the power switch S and illuminate the light receiving window of the thyristor VT with a flashlight. After adding a trigger light source (high-power light-controlled thyristor has its own light source, as long as the light-emitting diode or semiconductor laser in its optical cable is added with the working voltage, no external light source is required), the indicator EL should be on. After the light source is evacuated, the indicator light EL should remain illuminated. There is only one PN junction. Therefore, you just need to measure electrode A and G with a multimeter.Put the multimeter in the R × 1 kΩ level, and the two probes can be connected to one of the two pins of the thyristor under test (measure their forward and reverse resistance values). If a pair of pins is measured with a low resistance value, the black probe is connected to the anode A, while the red probe is connected to gate G, and the other pin is the cathode K. (2) Judging whether it is good or bad: Use the R×1 level of a multimeter to measure the forward and reverse resistance values between the electrodes of the BTG thyristor. Under normal conditions, the forward and reverse resistances between the anode A and the cathode K are infinite; the forward resistance between the anode A and gate G (when the black probe is connected to electrode A) is several hundred ohms to several thousand ohms and the reverse resistance value is infinite. If the forward and reverse resistance values between two electrodes are measured to be very small, it indicates that the thyristor has been short-circuited and damaged.(3) Detection of triggering capability: Put the multimeter in the R × 1 Ω level, connect the black probe to anode A, and the red probe to cathode K. The measured resistance should be infinite. Then touch gate G with your finger and add a human body induction signal to it. If the resistance between electrodes A and K changes from infinity to low resistance (a few ohms) at this time, it indicates that the thyristor has a good triggering ability. Otherwise, the performance of the thyristor is poor. Frequently Asked Questions about Thyristors1. What is thyristor and its types?A thyristor is a four-layer device with alternating P-type and N-type semiconductors (P-N-P-N). In its most basic form, a thyristor has three terminals: anode (positive terminal), cathode (negative terminal), and gate (control terminal). The gate controls the flow of current between the anode and cathode. 2. What is thyristor diagram?In general, Thyristors are also switching devices similar to the transistors. ... SCR or Thyristor is a four-layered, three-junction semiconductor switching device. It has three terminals anode, cathode, and gate. Thyristor is also a unidirectional device like a diode, which means it flows current only in one direction. 3. Where is thyristor used?Thyristors may be used in power-switching circuits, relay-replacement circuits, inverter circuits, oscillator circuits, level-detector circuits, chopper circuits, light-dimming circuits, low-cost timer circuits, logic circuits, speed-control circuits, phase-control circuits, etc. 4. Why SCR is called Thyristor?Silicon Controlled Rectifier (SCR) is a unidirectional semiconductor device made of silicon. This device is the solid state equivalent of thyratron and hence it is also referred to as thyristor or thyroid transistor. 5. What is thyristor diagram?In general, Thyristors are also switching devices similar to the transistors. ... SCR or Thyristor is a four-layered, three-junction semiconductor switching device. It has three terminals anode, cathode, and gate. Thyristor is also a unidirectional device like a diode, which means it flows current only in one direction.

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.