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IntroductionLED is a new type of light source that has entered the application field in the past ten years, and it has been used in the medical field for about 6 years, showing excellent therapeutic effects in such a short period of time. LED is a cold light source, which can well moisturize the skin while treating diseases. Besides, since high-power LEDs have strong light intensity and a good effect on the deep layer of the human skin, they are widely used in various departments in hospitals. The LED light sources currently used in the medical field include red, blue and purple. The efficacy of LED in disinfection and sterilization, wound healing, wound treatment, inflammation elimination, edema reduction, and photodynamic tumor treatment has been fully affirmed in the medical field. Can LED Light Improve Your Skin?CatalogIntroductionCatalogI What is LED Light Therapy? Is it Safe?  1.1 LED  1.2 LED Light Therapy  1.3 Safety&Side EffectsII LED Light Therapy Colors: Which do you Need?  2.1 Does LED Light Therapy Actually Work?  2.2 How to Choose the LED Light Therapy Colors?III Specific Uses and Benefits of LED Light TherapyIV Procedure of Performing a LED Light Therapy  4.1 Perform a LED Light Therapy at a Professional’s Office  4.2 How to use At-home Devices?V LED Light Face Mask  5.1 Does LED Light Face Mask Work?  5.2 Are LED Face Masks Safe?VI Frequently Asked QuestionsI What is LED Light Therapy? Is it Safe?1.1 LEDLED is the abbreviation of Lighting emitting diode, which is a light-emitting diode, which is made of compounds containing gallium (Ga), arsenic (As), phosphorus (P), nitrogen (N), etc. Semiconductor. When electrons and holes are recombined, they can radiate visible light, so they can be used to make light-emitting diodes. The gallium arsenide diode emits red light, the gallium phosphide diode emits green light, the silicon carbide diode emits yellow light, and the gallium nitride diode emits blue light. Light-emitting diodes appeared as early as 1962. In the early days, it could only emit low-light red light, and later developed other monochromatic light versions. The light that can be emitted today has reached visible light, infrared light and ultraviolet light, and the light level has increased to a considerable level Degree.Figure1. LED 1.2 LED Light TherapyFor many years, scientists have studied how the sun's rays, including so-called burning rays of the sun, or ultraviolet B radiation, ultraviolet A rays, or UVA, affect the skin. Only recently have we started to talk about the effects of visible light on the skin — not necessarily LED light, but visible light in general," says Dr. Buzney, assistant professor of dermatology at Harvard Medical School. LED lights have been around since the 1960s, but have only recently been used as a skin treatment that uses varying wavelengths of light, including red, purple, green and blue. Different wavelengths of the visible light spectrum correspond to different colors of LED light and penetrate the skin to different depths. Depending on how deeply they penetrate, LED lights are thought to have different biological effects.1.3 Safety&Side EffectsAccording to Harvard Health Publishing, for the most part, these LED light therapies appear to be relatively safe, at least in the short term. The FDA has approved some products for home use. LED skin devices don't have a lot of power, so they're unlikely to burn our skin. However, it is important to shield your eyes from the light while using them. In addition, a recent study named Phototherapy with Light Emitting Diodes indicates that a device using LEDs with frequencies of 415nm (blue), 633nm (red), and 830nm (infrared) has demonstrated significant results for the treatment of medical conditions, including mild-to-moderate acne vulgaris, wound healing, psoriasis, squamous cell carcinoma in situ (Bowen’s disease), basal cell carcinoma, actinic keratosis, and cosmetic applications.  Although photodynamic therapy with the photosensitizer 5-aminolevulinic acid might cause stinging and burning, phototherapy is free of adverse events. We determined that phototherapy using LEDs is beneficial for a range of medical and aesthetic conditions encountered in the dermatology practice. This treatment displays an excellent safety profile. The above content is extracted from the journal directly, Let’s put it simple:● In the short term, LED light therapies are relatively safe, but you have to care about the device's potential to damage the eyes, especially for people with underlying eye conditions or those who are taking medication that makes the eyes more sensitive to light.● Light Therapy doesn't use UV light so there's no risk of tanning whatsoever. Therefore, you do not have to worry for regular use.● LED light therapy doesn’t cause burns compared to other anti-aging treatments such as chemical peels, dermabrasion, and laser therapy. In general, side effects are rare, but there may be(1) increased inflammation(2) Redness(3) Rashes(4) TendernessYou should not use LED therapy if having taken certain medications, such as isotretinoin (Accutane), for acne or use topical treatments that cause sensitivity to sunlight. People with skin conditions should speak to a dermatologist before using LED light therapy.Figure2. LED Light TherapyII LED Light Therapy Colors: Which do you Need?2.1 Does LED Light Therapy Actually Work?The light therapy effect of LEDs is based on the wavelengths of different spectra. Red light LEDs of 633nm to 660nm can promote collagen proliferation of the skin and even lighten fine lines and dark spots. Near-infrared LEDs with a wavelength of 780nm to 1200nm can be used Anti-inflammatory and analgesic. The blue LED and the green LED can also be used in the medical beauty market, which are respectively suitable for preventing the growth of acne and brightening, helping to absorb nutrients in skin care products, and improving the effect of allergic skin. Laura Ferguson, founder of The Light Salon, a company focused on LED beauty, said that LED light therapy has many benefits, different effects at different wavelengths, such as anti-wrinkle or blemish, and the light will not have a band that will damage the skin Intrusive, painless light therapy, it even has a mood-relieving effect. Ferguson said that LED can also solve the problem of skin sensitivity. After light therapy, the newly stimulated cells will have a protective layer to help prevent sunburn from being exposed to strong sunlight. LED light therapy is not like a solarium, so you don't have to worry about melanin precipitation. However, the current price of LED medical beauty products is still high. In the future, the price is expected to decline as the technology of LED medical products matures. At that time, consumers' choices and needs will be more and more diversified. Figure3. Four Types of LED Light2.2 How to Choose the LED Light Therapy Colors?LED light stimulates fibroblasts, which can produce collagen, thereby improving skin elasticity, scarring and enhancing skin metabolism. It can also make use of the organism's absorption of different visible light wavelengths to stimulate the mitochondria and glands to produce more energy and extend the life cycle of cells. LED light can be used in all parts of the human body, whether it is psychological or physical, scalp or toes, internal medicine or surgery, as long as the light reaches the place, it can be used for effective treatment. After laser and pulsed light, LED light therapy has become a new light therapy. (1) Red lightThe red light with a wavelength of 635nm has the characteristics of high purity, strong light source, and uniform energy density. Red light has bactericidal, repairing and pain-removing effects, which can increase cell activity and promote cell metabolism. (2) Blue LightBlue light with a wavelength of 405, 415nm has a strong bactericidal effect, which can quickly inhibit inflammation. During the formation of acne, it is mainly caused by Propionibacterium, and blue light can cause no damage to skin tissue, effectively destroy this bacteria. (3) Purple LightThe violet light with a wavelength of 313, 410nm has the advantages of sterilizing, purifying the skin, activating cells, and promoting protein and collagen synthesis. It has a good effect on specific dermatitis, vitiligo, scleroderma and so on. (4) Green Light (560nm)Natural and soft light color, which has the effect of neutralizing and stabilizing nerves, can improve anxiety or depression; regulate skin gland function, effectively dredge lymph and improve edema, improve oily skin, acne, etc. Figure4. Function of Diffrent Light III Specific Uses and Benefits of LED Light Therapy(1) PhotorejuvenationPhoton skin rejuvenation technology is defined as non-exfoliation skin rejuvenation treatment using low-energy density under continuous high pulse light. At present, it has become one of the main methods to improve skin photoaging. This technology can significantly improve skin wrinkles and texture.  Rough, irregular pigmentation and enlarged pores.Such phenomena have been recognized by many technical professionals and beauty applicants. The characteristic histological changes of skin photoaging are elastic fibrosis and collagen fiber maturation disorder in the dermal matrix, which leads to skin relaxation and wrinkles. The study found that visible to near-infrared LED light penetrated the epidermis of the skin and reached the dermal layer of the skin, and promoted the regeneration and rearrangement of elastic fibers and collagen fibers through photothermal and photochemical effects, thereby reducing skin wrinkles and increasing elasticity. (2) Prevent or treat pigmentation after inflammationPigmentation of skin after inflammation is a common and difficult to avoid phenomenon in skin physical and chemical cosmetology, and it is especially easy to appear in Asian people. For example, in order to reduce the degree of skin pigmentation after laser treatment in the clinic, generally avoid the season of excessive ultraviolet rays, ask patients to avoid sun, apply sunscreen, etc., but it is still difficult to completely avoid pigmentation after inflammation. Recent studies have found that 660nm LED light can prevent or even treat skin pigmentation that occurs after this inflammation, which will be a new research hotspot in the skin and beauty industry. (3) Promote wound healingIt can be seen that LED light of various wavelengths in the near infrared can promote the growth of epithelial cells after trauma, and promote wound healing. At the same time, it also has a good therapeutic effect on the healing of chronic ulcers in the lower extremities of diabetic patients. (4) Reduce inflammationA series of studies have shown that LED has anti-inflammatory effects. Research has found that 635nm LED light can inhibit the release of the inflammatory mediator prostaglandin E2 (PGE2) by the fibroblasts of the gum, thereby reducing the inflammatory response of the gum. Before using pulsed dye laser to treat skin photoaging, if LED light source is used to irradiate in advance, it can reduce the discomfort of skin erythema, swelling and pain caused by dye laser. The use of LED light sources in advance of radiation therapy for breast cancer patients can reduce the side effects of radiotherapy. (5) Scar preventionKeloid keloids is a skin disorder that affects beauty and is difficult to treat clinically. It is caused by excessive proliferation of connective tissue after skin damage. Patients often have a scarring constitution. It started clinically as a small, hard red pimples, which slowly increased, producing round, oval, or irregular scars, higher than the skin surface, extending outward in the shape of a crab foot, with smooth and shiny skin, which may be accompanied by Pain, itching, etc. The clinical treatment is difficult and the effect is not ideal. Studies have found that LED can significantly improve the patient's pain, itching and other discomfort, make the scar flat, and have the advantages of non-invasive. (6) Other functionsIn addition, LED can also be used as a non-ultraviolet light therapy instrument, used in photodynamic therapy, hair loss treatment, skin damage reduction after ultraviolet irradiation, and so on. In short, LED as a new type of light source has been gradually applied to dermatology. With the continuous innovation of LED lamps and the study of the biological effect of LED on medicine, the application of LED in dermatology will have unlimited prospects. . At the same time, LEDs have higher security and can be used more widely as home medical equipment.Figure5. LED Light Therapy DevicesIV Procedure of Performing a LED Light Therapy4.1 Perform a LED Light Therapy at a Professional’s OfficeWhen getting an LED treatment, you really don’t have to do much but lie in a comfy bed with your face positioned directly under panels that emanated different colored lights. Generally, LED panels will be placed a few inches away from your face after microneedling or microdermabrasion. Each session lasts approximately 15-20 minutes. At first, it feels warm, and many people report it is really like the feeling of relaxation.4.2 How to use At-home Devices?Using at-home light therapy devices is like working out by yourself and things done in the office are like working out with a trainer. Both are good. But you’re not going to get as intense of a treatment at home. This means at-home LED devices may be more convenient, but they may be less effective than professional treatments. When using an at-home device, it is important to follow the manufacturer’s instructions. These devices typically come in the form of a mask that a person applies to the face for several minutes or a wand that they use on the skin. LED light therapy is suitable for use on any body part, including the face, hands, neck, and chest.Following treatment, no recovery time is necessary.Does LED Light Therapy Really Work? Can You Do it At HOME?V LED Light Face Mask5.1 Does LED Light Face Mask Work?The LED mask was invented by John Tsagaris, a Chinese medicine doctor. It is understood that John has a degree in human biological sciences from Chinese Medicine, and also holds a graduate diploma in skin treatment and beauty care. LED blue light can play a bactericidal and anti-inflammatory effect to improve the surface skin, and has a good effect on the treatment of acne and rosacea. LED red light can promote the growth of skin collagen, for deep skin beauty care. The working principle of LED mask is similar to photosynthesis. It treats skin folds from the depth by changing the energy of LED red light. It can not only calm the skin, but also prevent the growth of bacteria inside the skin. The use of LED mask masks not only does not have a claustrophobic feeling, but the LED red light delivered to the skin in large quantities can make people feel comfortable. Just wear the LED mask for 25 minutes every day, and the LED red light can gradually improve your skin. According to a survey report from the United States, LED masks have a significant effect on eliminating wrinkles. Another report showed that 90% of people believe that LED mask can reduce skin aging, make the skin more delicate and smooth, and greatly improve the crow's feet, red blood, and melanin deposition in the corners of the eyes.Figure6. Depth of Light Energy Penetration5.2 Are LED Face Masks Safe?Actually, it is the same concern as whether LED light therapy is safe. There’s no doubt that one of the most important aspects of LED phototherapy devices is their safety. Phototherapy with Light Emitting Diodes also points out that LEDs are nonablative and nonthermal, and when used alone (i.e., without topical photosensitizers in PDT applications) do not cause damage to the epidermis or dermal tissue.  There are no adverse events associated with the use of these devices and little to no downtime for the patient. When LED phototherapy is used alone, patients do not experience redness, peeling, blistering, swelling, or pain. In fact, patients can have a treatment during their lunch hour and return to work immediately afterwards. While home use devices have been available for several years, there are many differences between those devices and those specifically designed for use by physicians. The home use devices necessarily deliver significantly less power and typically do not have light panel arrays large enough to treat the entire face at once, for example. As they often are hand-held, it might be cumbersome, time-consuming, and impractical to treat the entire face in a single session.  In contrast with the medical LED units and their protocols, home use devices have not been validated by controlled clinical studies published in peer-reviewed journals. In some cases, home units may be used adjunctively with dermatologist-provided treatment to address specific areas of concern, but they are dissimilar enough from the medical-grade units to not be considered an alternative to these tested technologies.Figure7. LED Face MasksVI Frequently Asked Questions1. Does LED light therapy actually work?LED light therapy appears to be a safe treatment for several skin conditions, including acne, skin aging, skin wounds, and other problems. Research indicates that this therapy offers promising results, although people should not expect a 100% improvement. 2. What does LED light therapy do?LED light therapy is now used by some aestheticians to help regenerate the skin from aging. It's also used for acne. Your healthcare provider uses red or blue light frequencies based on the skincare concern. Red is primarily used for anti-aging, while blue is used for acne treatment. 3. Does LED light reduce wrinkles?LED light therapy can stimulate collagen production, which reduces fine lines and wrinkles, as well as eliminate acne-causing bacteria, which improves skin clarity. 4. Can you overdo LED light therapy?Light therapy cannot be overdone for most people. If you notice any extraordinary results, stop treatment, and contact your physician. For the best results, choose the right device style and LED color, and use it as directed. 5. Does red light therapy tighten loose skin?Amber light stimulates collagen and elastin. Red light is most commonly used to promote circulation. White light penetrates the deepest and works to tighten and reduce inflammation. Blue light kills bacteria. 6. Are LED lights bad for your eyes?New findings confirm earlier concerns that "exposure to an intense and powerful [LED] light is 'photo-toxic' and can lead to irreversible loss of retinal cells and diminished sharpness of vision," the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) warned in a statement. 7. Are led masks effective?The research behind LED masks is centered on the lights used, and if you're going on those findings, LED masks can be beneficial to your skin. 8. What are the side effects of red light therapy?Red light therapy is considered safe and painless. However, there have been reports of burns and blistering from using RLT units. A few people developed burns after falling asleep with the unit in place, while others experienced burns due to broken wires or device corrosion. 9. Is red light therapy the same as laser therapy?In clinical practice, low-level laser (LLT) therapy involves exposing tissues to red and near infrared (NI) light, which are lower in energy than the lasers used in surgery. 10. How long does it take for light therapy to work?Light therapy can start to improve symptoms within just a few days. In some cases, though, it can take two or more weeks.

IntroductionA transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another, or multiple circuits. Its transmission current is AC. Transformer is commonly used to increase or decrease the supply. As one of the types, high-frequency transformers use frequencies from 20 KHz to over 1MHz. This paper tells the design process of high-frequency transformers (HFTs), that is, how to calculate high frequency transformer?How to Make High Frequency Transformer?CatalogIntroductionⅠ Transformer Core1.1 Magnetic Core Material1.2 Core Structure1.3 Core Parameters1.4 Coil Parameters1.5 Coil Turns1.6 Assembly Structure1.7 Temperature Rise CheckⅡ Types of High Frequency Transformer2.1 Transformer Classifications2.2 Design RulesⅢ Transformer Core Selection CaresⅣ Main Transformer ParametersⅤ How to Calculate High Frequency Transformer?5.1 Design Principles and Methods of Transformers5.2 AP Method Analysis5.3 Parameters of Power Supply5.4 Transformer Turns CalculationⅠ Transformer CoreIn real transformers, the two coils are wound onto the same iron core. The transformer core provides a magnetic path to channel flux. The use of highly permeable material (which describes the material's ability to carry flux), as well as better core construction techniques, helps provide a desirable, low reluctance flux path and confine lines of flux to the core. The following introduces some important aspect of the transformer core.1.1 Magnetic Core MaterialWhich material is best for high frequency transformer core? Soft ferrite is widely used in switching power supply due to its own characteristics. Its advantages are high resistivity, low AC eddy current loss, low price, and easy processing into various shapes. It also has disadvantages, including low working magnetic flux density, low permeability, large magnetostriction, and relatively sensitive to temperature changes. Choosing suitable materials can fully meet the design requirements of high-frequency transformers, and they have ideal performance and price advantage.1.2 Core StructureTransformer core as a main part, the factors to be considered when selecting the magnetic core structure are: reducing magnetic leakage and leakage inductance, increasing the heat dissipation spacing of the coil, which is beneficial to shielding, easy coil winding, and convenient assembly and wiring. Magnetic leakage and leakage inductance are directly related to the core structure. If the magnetic core does not require an air gap, a closed ring-shaped or square-shaped magnetic core is better.1.3 Core ParametersIn the design of the magnetic core parameters, special attention should be paid to the magnetic flux density on working not only limited by the magnetization curve, but also by the loss, and the working mode of power transmission. When the magnetic flux changes in one direction: ΔB=Bs-Br, which is not merely limited by the saturation magnetic flux density, but also mainly by the loss, (the loss causes a temperature rise to affect the magnetic flux density). Working magnetic flux density Bm=0.6～0.7ΔB.Opening the air gap can reduce Br to increase the magnetic flux density change value ΔB. After then, the excitation current increases, but the magnetic core volume can be reduced. For magnetic flux work in two-way: ΔB=2Bm. In this case, it is also necessary to pay attention to the fact that the volt-second area of the positive and negative changes of the excitation is not equal due to various reasons, and the DC bias problem occurs. Therefore, a small air gap can be added to the magnetic core, or a DC blocking capacitor can be added in the circuit design.1.4 Coil ParametersCoil parameters include the number of turns, wire section (diameter), wire form, winding arrangement and insulation arrangement.The wire diameter is determined by the current density of the winding. Usually J is 2.5～4A/mm2. The choice of wire diameter should consider the skin effect. If necessary, make adjustments after checking the temperature rise of the transformer.1.5 Coil TurnsGenerally used winding arrangement: The primary winding is close to the magnetic core, and the secondary winding feedback winding is gradually arranged outward. Two winding arrangements are recommended as following:1) If the voltage of the primary winding is high, and the secondary winding voltage is low, the secondary winding can be used close to the magnetic core, and next is the feedback winding, and the primary winding is in the outermost, which is beneficial to the primary winding to the magnetic core. Insulation arrangement.2) To increase the coupling between the primary and secondary windings, half of the primary windings can be close to the core, then the feedback winding and secondary windings, and another half primary windings in the outermost layer, which will reduce leakage inductance helpfully.1.6 Assembly StructureThe assembly structure of a high-frequency power transformer is divided into two types: horizontal and vertical. If using plane magnetic cores, chip magnetic cores and thin film magnetic cores, they all adopt a horizontal assembly structure.1.7 Temperature Rise CheckThe temperature rise check can be carried out by calculation and sample testing. The experimental temperature rise is lower than the allowable temperature rise by more than 15 degrees, increasing the current density and reducing the wire section appropriately. If it exceeds the allowable temperature rise, appropriately reduce the current density and increase the wire section. For example, increase the heat dissipation area of the magnetic core and wire diameter.Transformer SymbolⅡ Types of High Frequency Transformer2.1 Transformer ClassificationsPower transformers are divided into three categories according to the topology:(1) Flyback transformer(2) Forward transformer(3) Push-pull transformer (in full-bridge/half-bridge)The suitable topological structure of the magnetic core structure is shown in the table on the following:Core StructureTransformer Circuit TypeFlyback TypeForward TypePush-pull TypeE cores++0Planar E Cores-+0EFD Cores-++ETD Cores0++ER Cores0++U Cores+00RM Cores0+0EP Cores-+0P Cores-+0Ring Cores-++Remarks: "+"=Appropriate   "0"=Normal   "-"=None2.2 Design Rules1) If the DC filter inductor, and the inductor core only works in one quadrant, the inductors belonging to this type include Boost inductors, Buck inductors, Buck/boost inductors, forward and push-pull transformer filtering inductors, and single-ended transformers.2) The magnetic core of the forward transformer only works in one quadrant, so the transformer needs to be magnetically reset.3) The magnetic core of the push-pull transformer is bidirectional alternating magnetization. Converters belonging to this category include push-pull converters, half-bridge and full-bridge converters, and AC filter inductors. Ⅲ Transformer Core Selection Cares1) Soft ferrite is widely used in switching power supply due to its low price, good adaptability and high frequency performance.2) Soft ferrites are common in two series: manganese-zinc ferrite and nickel-zinc ferrite. The components of manganese-zinc ferrite are Fe2O3, MnCO3, and ZnO. It is mainly used in various filters below 1MHz, inductors, transformers, etc., with a wide range of applications. The components of nickel-zinc ferrite are Fe2O3, NiO, ZnO, etc., which are mainly used for various induction windings above 1MHz, anti-interference magnetic beads, and sharing antenna matching devices.3) Manganese-zinc ferrite cores are the most widely used in switching power supplies. Depending on their use, the choice of materials is also different. The cores used in the power input filter part are mostly high-permeability, and their material grades are mostly R4K～R10K, that is, ferrite cores with a relative permeability of 4000～10000. For main transformers and output filters, most of them have high saturation magnetic flux density, and their Bs is about 0.5T (ie 5000GS). Ⅳ Main Transformer Parametersa.Transformer TopologyWith a higher saturation magnetic flux density Bs and a lower residual magnetic flux density Br,  Bs has a certain impact on the transformer and winding results. Theoretically, if Bs is high, the number of winding turns will decrease, and the copper loss will also decrease. In practical applications, there are many circuit forms of switching power supply high-frequency converters. For transformers, their working forms can be divided into two categories:BipolarThe circuit is half-bridge, full-bridge, push-pull, etc. The positive and negative half-cycle excitation currents in the transformer primary winding are identical in magnitude and opposite in direction. Therefore, the magnetic flux changes in the transformer core also move symmetrically up and down. Maximum change range of B is △B=2Bm, and the DC component in the core basically cancels out.UnipolarThe circuit is single-ended forward, single-ended flyback, etc. The primary winding of the transformer adds a unidirectional square wave pulse voltage in one cycle (single-ended flyback is the case). The transformer core is unidirectionally excited, and the magnetic flux density varies from the maximum value Bm to the residual magnetic flux density Br. At this time, △B=Bm－Br. If Br is reduced and the saturation magnetic flux density Bs is increased, △B can be increased. It can reduce the number of turns and the copper loss. b. Low Power Loss at High FrequenciesThe power loss of ferrite not only affects the output efficiency of the power supply, but also causes the core heating, waveform distortion and other undesirable consequences. The heating problem of the transformer is extremely common in practical applications. It is mainly caused by the copper loss and core loss. If Bm is selected too low when designing the transformer, and more winding turns will cause the winding to heat up, and at the same time transfer heat to the magnetic core. Conversely, if the core is the main heating body, it will also cause the winding to heat up.When selecting ferrite materials, the power loss is required to have a negative temperature coefficient relationship. If the core loss is the main body of heat, the temperature of the transformer will rise, which will cause the core loss to increase further, eventually burn out the power tube, transformer and other components. Therefore, when developing power ferrites at home and abroad, it is necessary to solve the problem of the negative temperature coefficient of the magnetic material itself. This is also a significant feature of the magnetic material for power supply. c. PermeabilityHow much is the appropriate permeability? This should be determined according to the switching frequency of the actual circuit. Generally, materials with a relative permeability of 2000 have an applicable frequency below 300kHz, and sometimes it can be higher, less than 500kHz. For materials higher than this value, a lower magnetic permeability should be selected, generally around 1300. d. Higher Curie TemperatureThe Curie temperature is the temperature at which the magnetic material loses its magnetic properties, general above 200℃. However, the actual working temperature of the transformer should not be higher than 80℃. This is because when the temperature is above 100℃, its saturation magnetic flux density Bs has dropped to 70% of that at room temperature. Therefore, an excessively high operating temperature will cause the saturation flux density of the magnetic core to drop more severely. Furthermore, when it is higher than 100°C, its power consumption has a positive temperature coefficient, which will lead to a vicious circle. For the R2KB2 material, the temperature corresponding to its allowable power consumption has reached 110°C, and the Curie temperature is as high as 240°C, which meets the requirements for high-temperature use. Ⅴ How to Calculate High Frequency Transformer?5.1 Design Principles and Methods of TransformersThere are two principle methods for designing transformers: area product AP method. AP is the product of the core cross-sectional area Ae and the coil effective window area Aw.PT-power of transformerAe- effective cross-sectional areaAw- core window areaKo-core window utilization factor, typical value is 0.4.Kf-form factor, square wave is 4, and sine wave is 4.44.Bw-the working magnetic intensity of the magnetic coreFs-switch operating frequencyKj-current density coefficient, take 395A/cm2X-core structure coefficient5.2 AP Method AnalysisAccording to the design method of power transformer, the general steps of designing transformer with area product AP method:1. Select the core material and calculate the apparent power of the transformer.2. Determine the core cross-sectional size AP, and then select the core size according to it.3. Calculate the inductance and number of turns of the primary and secondary sides.4. Calculate the length of the air gap.5. Find the wire diameter according to the current density and the effective value current of the primary and secondary sides.6. Determine whether the copper loss and iron loss meet the requirements (allowable loss and temperature rise).5.3 Parameters of Power SupplyInput voltage: 175-264VACOutput voltage: 21VOutput power: 3AThe frequency is set at 60KHz, and the duty cycle is initially set at 0.45. Using a flyback topology, choose the core material and determine the apparent power PT of the transformer.Consider the cost, choose PC40 material here:Check the PC40 data and get Bs=0.39T, Br=0.06TBm= ΔBmax*0.6=0.198T, round it to 0.2TIn order to prevent the magnetic core from being saturated momentarily, reserve a certain margin and take Bm= ΔBmax*0.6=0.198T, take 0.2T.Transformer apparent power PT, for the flyback transformer:Calculate AP:Where:J is the current density, usually taking 395A/cm2.Ku is the effective use coefficient of the copper window, which is determined according to the safety requirements and the number of output channels, generally 0.2 to 0.4. Take 0.4 here to adapt to the sudden load current. The power supply is designed in critical mode, and the critical current I0B=0.8×I0=2.4A5.4 Transformer Turns Calculation1) Minimum input voltage: Vimin=ViACmin*1.2=210V2) Turns Ration=[Vimin/(Vo+Vf)]*[Dmax/(1-Dmax)]n=[210V/(21V+1V)]*[0.45/(1-0.45)]=7.83) Secondary Side Peak Current^IsB=2*IoB/(1-Dmax)^IsB=2*2.4A/(1-0.45)=8.72A4) Secondary Side InductanceLs=(Vo+Vf)*(1-Dmax)*[1/(Fs*1000)]/^IsB*1000000Ls=(21V+1V)*(1-0.45)*[1/(60KHz*1000)]/^8.72A*1000000=23.58uH5) Primary Side InductanceLp=n*n*LsLp=7.8*7.8*23.58uH=1434uH6) Secondary Side Peak Current (continuous mode)^IsB=Io/(1-Dmax)+(^IsB/2)^IsB=3A/(1-0.45)+(8.72A/2)=9.81A7) Primary Side Peak Current (continuous mode)^Ipp=^Isp/n^Ipp=9.81A/7.8=1.257APrimary Winding and Secondary Winding Turns1) Primary Winding TurnsNp=Lp*^Ipp(^B*Ae)Np=1434uH*1.257A/(0.2*84.8)=106.28T，round it to 106T2) Secondary Winding TurnsNs=Np/nNs=106T/7.8=13.58T，round it to Ns=14T3) Feedback TurnsNv=(Vcc+Vf)/[(Vo+Vf)/Ns]Nv=(14.5V+1V)/[(21V+1V)/14T]=9.87T, round it to Nv=10TIn order to avoid saturation of the magnetic core, an appropriate air gap is added to the magnetic circuit, and the calculation is as follows:It may be necessary to correct the number of turns based on the edge effect of the air gap flux.There are two methods for the wire diameter of the primary, secondary and auxiliary windings:Bare wire areaPrimary Winding diameter: effective currentIprms=Po/^n/ViminIprms=63W/0.8/210V=0.375AWire diameter (J current density is 4A/mm2)Use two 0.18mm diameter wires and wind them together, or use AWG #28 single stranded wire.Secondary winding diameterUse 4 wires with a diameter of 0.25mm to be wound in parallel and calculate the current skin depth:The wire diameter of multiple strands must be less than or equal to dwH. For single wire winding, if the wire diameter exceeds the dwH, it is necessary to consider the use of multiple strands.The calculation of copper loss Pcu and iron loss Pfe (transformer total loss Ploss)a) Primary winding and secondary winding losses. Among them, MLT is the average turn length of the magnetic core. b) Calculate the allowable total loss Ploss and iron loss under the efficiency η.c) Find the actual loss under the operation according to the core loss curve.Iron loss per unit weight, it actually occurredThe actual iron loss should be lower than the allowable value.d) Calculate the loss per unit area Φ=Ploss/As. If the temperature rise caused by the Φ value is less than 25 degrees, the design is good.Bw Calculation:The working magnetic flux density Bw should be met the design index requirements, Bw<Bs-Br, to avoid saturation of the magnetic core. Frequently Asked Questions about High Frequency Transformer Design1. What is high frequency transformer?The primary difference is that, as their name implies, they operate at much higher frequencies — while most line voltage transformers operate at 50 or 60 Hz, high-frequency transformers use frequencies from 20 KHz to over 1MHz. ... For any given power rating, the higher the frequency, the smaller the transformer can be. 2. What are the design aspects of high frequency transformer?Design of HF transformers. High frequency transformers transfer electric power. The physical size is dependent on the power to be transfered as well as the operating frequency. The higher the frequency the smaller the physical size. 3. What is the use of high frequency transformer?These transformers are designed to handle up to 15,000 volts safely and accurately, converting high voltage and current levels between coils by magnetic induction. High Voltage, High Frequency Transformers are relied on for applications ranging from power supplies to laser equipment and particle accelerators. 4. What is difference between high frequency and low frequency?When we talk about sound, we talk in terms of high and low-frequency waves. ... This measurement of cycles per second is expressed in Hertz (Hz), with a higher Hz representing higher frequency sound. Low-frequency sounds are 500 Hz or lower while high-frequency waves are above 2000 Hz. 5. What is the frequency of transformer?What is Transformer Frequency. The three common frequencies available are 50Hz, 60Hz and 400Hz. European power is typically 50Hz while North American power is usually 60hz. The 400 Hz is reserved for high-powered applications such as aerospace and some special-purpose computer power supplies and hand-held machine tools.

IntroductionIn electronics, what is clipper? A circuit which removes the peak of a waveform is known as a clipper. Clipper circuit is designed to prevent a signal from exceeding a predetermined reference voltage level. The clipper circuit can be designed by utilizing both the linear and nonlinear elements such as resistors, diodes, or transistors. The diode clipper, also known as a diode limiter, is a wave shaping circuit that limits positive or negative amplitude, or both. In electronics, diode clipper circuits are commonly used to process various signals. It is is a circuit designed to prevent a signal from exceeding a predetermined reference voltage level. Clipping changes the shape of the waveform and alters its spectral components.Clipper Circuits IntroductionCatalogIntroductionⅠ Clipper Circuit Types1.1 Positive Clipper Circuit1.2 Negative Clipper Circuit1.3 Combinational Limiter CircuitⅡ Clipper Circuits Analysis2.1 Clipper Circuit Structure2.2 Clipper Circuit ProblemsⅢ General Forms of Clipper Circuits3.1 Clipper Circuit Description3.2 Common Clipper Circuit ExamplesⅠ Clipper Circuit TypesDiode clipper is a limiting circuit which limits the output voltage. In electronics, a clipper is a circuit designed to prevent a signal from exceeding a predetermined reference voltage level. A basic diode limiter circuit is composed of a diode and a resistor. It is divided into three types: positive clipper circuit, negative clipper circuit and combinational clipper circuit. The positive clipper circuit produces a clipping effect when the input voltage is higher than a certain upper limit value; the negative clipper circuit produces a limit effect when the input voltage is lower than a certain lower limit value; the combinational clipper circuit produces a limit effect when the input voltage is too high or too low. In a positive clipper, the positive half cycles of the input voltage will be removed. During the negative half cycle of the input, the diode is forward biased and so the negative half cycle appears across the output. The clipper circuits are described as following.1.1 Positive Clipper CircuitThe diode in clipper circuit is connected in series to the input signal and that attenuates the positive portions of the waveform. The positive clamping circuit blocks the input signal when the diode is forward biased. During the negative half cycle of an AC signal, the diode is forward biased and allows electric current through it. In following figure, when the input signal voltage is lower than a preset upper limit voltage, the output voltage will change with the input voltage, however, when the input voltage reaches or exceeds the upper limit, the output voltage will remain at a fixed value, so that the signal amplitude is limited at the output.1.2 Negative Clipper CircuitThe diode in clipper circuit is connected in series to the input signal and that attenuates the negative portions of the waveform, is termed as negative series clipper. For the figure below, the diode is series to the input and output. If the diode has ideal switching characteristics, when iu is lower than E, D will not conduct, ou=E; when ui is higher than E, D will conduct, ou=iu. The limiting characteristic of this limiter circuit is shown in the figure.1.3 Combinational Limiter CircuitThis kind of circuit combines the positive and negative limiters together which shows in the following figure. Ⅱ Clipper Circuits Analysis2.1 Clipper Circuit StructureIn the circuit, Al is an integrated circuit (a common component), VT1 and VT2 are transistors, Rl and R2 are resistors, and VDl to VD6 are diodes.Analyzing the effect of VD1 and VD2 in the circuit mainly explains the following points.1) It can be seen from the circuit that the circuit structure of the two groups of diodes are the same. Both play the same role in this circuit, so the working principle of them are the same.2) The pin ① is connected to the base of the transistor VT1 through a resistor Rl. Obviously Rl is a signal transmission resistor. The signal output on the pin ① is added to the base of VT1 through Rl (there is no DC blocking capacitor between pin ① and VT1). From this circuit structure, it can be judged that the pin ① is an output signal pin, and it outputs a composite signal of DC and AC. The purpose of determining that the pin ① is to figure out the specific function of the diode VD1 in the circuit.3) The DC voltage output by pin ① is not high enough to make the external diode in a conducting state. The analysis is: if the DC voltage output by the pin ① is high enough, then VD1, VD2 and VD3 conduct, and the internal resistance becomes small. This will shunt the AC signal output by the pin ① to the ground, so the signal will be attenuated. However, this circuit does not need such attenuation. Therefore, the conclusion drawn from this: VD1, VD2 and VD3 are not turned on by pin ① DC voltage output.4) The output from pin ① is the superimposed signal of DC and AC, which is added to the base of the transistor VT1 through the resistor Rl. VT1 is an NPN transistor. If the amplitude of the positive half-cycle AC signal added to the base of VT1 is very large, which may burn the VT1. When the negative half-cycle signal added to the base of VT1 is large, which has no effect on VT1, because the negative signal on the base of VT1 reduces current.Follow the above circuit analysis, it can be judged that VD1, VD2, and VD3 in the circuit has clipper function, to prevent VT1 from burning out. 2.2 Clipper Circuit ProblemsIn the figure, Ul is the DC voltage in the output of pin ①, U2 is the limiting voltage value.When the AC voltage in the output signal of pin ① is relatively small, the positive half cycle of the AC signal plus the DC output voltage does not make the VD1, VD2 and VD3 conduction. Therefore, all diodes are cut off, which has no effect on the AC signal output by pin ①. Assuming that the positive half-cycle output AC signal by pin ① is very large during a certain period, as shown in the signal waveform, at this time it plus the DC voltage can conduct VD1, VD2 and VD3. If the conduction voltage of each diode is 0.7V, then three diodes is 2.1V. Since the tube voltage drop after conduction is basically the same, that is, the maximum voltage of pin ① is 2.1V. So the excess part of the positive half cycle of the AC signal is limited by the resistor. When the DC and AC output signals at pin ① is less than 2.1V, diodes will not conduct and keep cutoff state, which has no clipping effect on the signal.For the specific details of clipper circuit, there are several explanations as follows.1) The negative half cycle large signal output by the pin ④ will not cause VT1 overcurrent, because it will decrease the base voltage of the NPN transistor and the base current, so there is no need to add the limiter circuit.2) The one-way limiter circuit mentioned above, it can only limit the large signal part of the positive or negative half of the signal, and does not limit the signal in the other half. The other is the combinational limiter circuit, which can limit the positive and negative half-cycle signals at the same time.3) There are many reasons for the abnormal increase of the signal amplitude. For example, the fluctuation of the power supply voltage cause it to increase a lot at a certain moment, and the large-scale interference pulse from the outside into the circuit also causes a certain increase.4) After the three diodes VD1, VD2 and VD3 conduct, the sum of the DC and AC voltages on pin ① is 2.1V. This voltage added to the base of VT1 through resistor Rl is maximum, so as to the current of VT1.5) Since the pin ① is the same as the external circuit of pin ②, the working principle of the limiter circuit is the same. So only one circuit needs to be analyzed when analyzing the circuit.6) According to the characteristics of the series circuit, the current in the series circuit is equal everywhere. It can be known that the three series diodes VD1, VD2 and VD3 are turned on at the same time, or they will be turned off at the same time. Therefore, in the series circuit, a diode is turned on and other diodes are turned on.Ⅲ General Forms of Clipper Circuits3.1 Clipper Circuit DescriptionThere are two types of clippers namely series and parallel. In series clipper, diode is connected in series with the load. In parallel clipper, diode is in parallel to the load.1) Series clippers: if the diode is connected in series with load resistanceUnbiased series clipper: in that case the circuit diode is connected in series with load resistance and no external voltage is applied to the circuit.+ve unbiased series clipper: if the +ve portion of output is clipped its called +ve unbiased series clipper.-ve unbiased series clipper: if the -ve portion of output is clipped its called +ve unbiased series clipper.Biased series clipper: if in the circuit, diode is connected in series with load resistance and external voltage is applied to the circuit+ve biased series clipper: if the +ve portion of output is clipped its called +ve biased series clipper.-ve biased series clipper: if the -ve portion of output is clipped its called +ve biased series clipper.2) Parallel clippers: if the diode is connected in parallel with load resistanceUnbiased parallel clipper: in that case the circuit diode is connected in parallel with load resistance and no external voltage is applied to the circuit.+ve unbiased parallel clipper: if the +ve portion of output is clipped its called +ve unbiased parallel clipper.-ve unbiased parallel clipper: if the -ve portion of output is clipped its called +ve unbiased parallel clipper.Biased parallel clipper: if in the circuit, diode is connected in parallel with load resistance and external voltage is applied to the circuit+ve unbiased parallel clipper: if the +ve portion of output is clipped its called +ve biased series clipper.-ve unbiased parallel clipper: if the -ve portion of output is clipped its called +ve biased series clipper. 3.2 Common Clipper Circuit ExamplesIn general, clippers circuit are classified into two types: Series Clippers, Shunt Clippers, and Dual (Combination) Clippers.Series Clipper: The diode is connected in series with the load resistance. 👇Figure 1. Series Positive ClipperThe positive amplitude waveform is cut, and the negative amplitude waveform is retained, as follows:Figure 2. Series Positive Clipper with Positive BiasThe positive amplitude waveform is cut, and the offset positive voltage is retained on the negative amplitude waveform, as follows:Figure 3. Series Positive Clipper with Negative BiasThe waveform of positive amplitude is cut, and the negative voltage is shifted based on the waveform of negative amplitude, as follows:Figure 4. Series Negative ClipperThe negative amplitude waveform is cut, and the positive amplitude waveform is retained, as follows:Figure 5. Series Negative Clipper with Positive BiasThe negative amplitude waveform is cut, and the positive voltage is offset on the positive amplitude waveform, as follows:Figure 6. Series Negative Clipper with Negative BiasThe negative amplitude waveform is cut, and the negative voltage is offset on the positive amplitude waveform as follows: Shunt Clipper: Diode is in parallel with load resistance in circuit. 👇Figure 7. Shunt Positive ClipperFigure 8. Shunt Positive Clipper with Positive BiasFigure 9. Shunt Positive Clipper with Negative BiasFigure 10. Shunt Negative ClipperFigure 11. Shunt Negative Clipper with Positive BiasFigure 12. Shunt Negative Clipper with Negative Bias Dual (Combination) Clipper: It is desired to remove a small portion of both positive and negative half cycles. 👇Figure 13. Combination ClipperWhen the positive and negative waveforms must be limited, a combinational limiter circuit is required, as follows:Images Reference: Clipper Circuits - Series Clipper, Shunt Clipper, and Dual Clipper Frequently Asked Questions about Diode Limiter and Clipper Circuit1. What is Clipper and clamper?The major difference between clipper and clamper is that clipper is a limiting circuit which limits the output voltage while clamper is a circuit which shifts the DC level of output voltage. ... While clamper is used when we need multiples of the input voltage at the output terminal. 2. What is the function of clipper circuit?In electronics, a clipper is a circuit designed to prevent a signal from exceeding a predetermined reference voltage level. A clipper does not distort the remaining part of the applied waveform. 3. What is Clipper circuit and its types?A clipper is a device which limits, remove or prevents some portion of the wave form (input signal voltage) above or below a certain level, in other words, the circuit which limits positive or negative amplitude ,or both is called chipping circuit. The clipper circuits are of the following types. Series positive clipper. 4. What is the difference between a positive clipper and a negative Clipper?Positive Clipper and Negative Clipper. In a positive clipper, the positive half cycles of the input voltage will be removed. ... During the negative half cycle of the input, the diode is forward biased and so the negative half cycle appears across the output. 5. How does diode clipping work?The Diode Clipper, also known as a Diode Limiter, is a wave shaping circuit that takes an input waveform and clips or cuts off its top half, bottom half or both halves together. This clipping of the input signal produces an output waveform that resembles a flattened version of the input. 6. What is the main purpose of a diode limiter?The diode limiter also called Clipper as it is used to limit the input voltage. A basic diode limiter circuit is composed of a diode and a resistor. Depending upon the circuit configuration and bias, the circuit may clip or eliminate all or part of an input waveform. It limits the output voltage to a specific value. 7. What is the purpose of a clamping diode?The clamping circuit fixes the voltage lower limit to zero, that is, the start of the signal is 0 V. The positive clamping circuit blocks the input signal when the diode is forward biased. During the negative half cycle of an AC signal, the diode is forward biased and allows electric current through it. 8. What is a diode clamping circuit?A clamper circuit shifts the DC level or the reference level of the signal to the desired level without changing the shape of the waveform. The clamper circuit can be designed using the diode, resistor, and the capacitor.

IntroductionAs we all know, the most basic passive linear components are resistors (R), capacitors (C) and inductive components (L). These components can be used to form 4 different circuits: RC circuit, RL circuit, LC circuit and RLC circuit. They have some important properties for analog electronics, and can be used as passive filters. In practice, capacitors (and RC circuits) are usually used instead of inductors to form filter circuits. This is because capacitors are easier to manufacture with smaller size. This article mainly introduces the RC Circuit in series and parallel state.RC circuit (resistor–capacitor circuit), also called RC filter or RC network, has a resistor and a capacitor in series connection. When connected to a DC voltage source, the capacitor charges exponentially in time. That is, a capacitor can store energy, and when a resistor placed in series with it will control the rate at which it charges or discharges. This produces a characteristic time dependence that turns out to be exponential.RC Circuits Basic ExplainedCatalogIntroductionⅠ RC Circuit Basics1.1 What is RC Circuit?1.2 RC Circuit CharacteristicsⅡ How to Calculate RC Circuit?Ⅲ RC Circuits Classification3.1 Series and Parallel Circuits3.2 Example: RC Low Pass FilterⅣ Visualizing Filter Response4.1 Frequency Response4.2 Low Pass Filter Phase Shift4.3 Second-order Low-pass FilterⅤ ConclusionⅠ RC Circuit Basics1.1 What is RC Circuit?For a RC circuit (resistor-capacitor circuit), the primary composes of a resistor and a capacitor. According to the arrangement of resistors and capacitors, it can be divided into a RC series circuit and a RC parallel circuit. In addition, simple RC parallel circuits cannot resonate, because resistor does not store energy. However, LC parallel circuits can resonate. RC circuits are widely used in analog circuits and pulse digital circuits. If a RC parallel circuit connected in series in the circuit, it can attenuate low-frequency signals, and if it connected in parallel in the circuit, it can attenuate high-frequency signals. That is filtering.RC circuit is common element in electronic devices. It also play an important role in the transmission of electrical signals in nerve cells. A capacitor can store energy and a resistor placed in series with it will control the rate at which it charges or discharges.Figure 1. Passive Low-pass RC Circuit1.2 RC Circuit CharacteristicsIn the analog circuit, the passive RC filter circuit can be divided into a low-pass filter circuit and a high-pass filter circuit according to the connection and size of the capacitor.The low-pass filter circuit is somewhat equal to the integrator circuit (capacitor C is in parallel at the output.), but both circuits are applied to different requirements. The integrator circuit mainly uses the integration effect of the capacitor C when it is charged. In the case of square wave input, periodic sawtooth wave (triangular wave) will generate, so the capacitor C and resistor R are selected according to the square wave. While the low-pass filter circuit bypasses the higher frequency signal (because XC=1/( 2πfC), when f is larger, XC is smaller, which is equivalent to a short circuit), so the value of capacitor C is determined by referring to the value of the low frequency. For the filter circuit of the power supply, theoretically the larger the value of C, the better.Figure 2. Low Pass Filter CircuitThe high-pass filter circuit has the same form as the differential circuit or the coupling circuit. In the pulse digital circuit, due to the different relationship between RC and pulse width, it is divided into a differential circuit and a coupling circuit. In an analog circuit, choosing an appropriate capacitance C value can pass higher frequency signals selectively, even block DC and low-frequency signals. For example, a capacitor connected in series with a tweeter, is to prevent the low pitch from entering the tweeter to avoid burnout. What’s more, in the multi-stage AC amplifier circuit, the high-pass filter circuit is also a coupling circuit.Figure 3. High Pass Filter CircuitⅡ How to Calculate RC Circuit?From a mathematical point of view, suppose that the RC circuit has been connected to a DC power supply with a voltage value of U0. The voltage on the capacitor is equal to the power supply’s, and at a certain moment t0 the left end S of the resistor is grounded, then the capacitor discharges. In the theoretical analysis, the time t0 is taken as the zero point of time.According to KVL's law, establish the circuit equation: The initial condition is .This is a first-order homogeneous differential equation, and its general solution is .After substituting into the original equation: The characteristic equation is .The characteristic root is .According to , get .Therefore, the required initial value of the differential equation is It can be seen that the voltage attenuation speed on the capacitor depends on the , and its size only depends on the circuit structure and component parameters.When the unit of resistance is Ω and the unit of capacitance is F, the unit of product RC is seconds (s), which is represented by τ, then the capacitor voltage can be written as .tτ2τ3τ4τ5τ...∞uc(t)Uo0.368Uo0.135Uo0.05Uo0.018Uo0.0067Uo...∞0The τ time constant is the time it takes for the capacitor voltage to drop to 1/e=36.8% of the initial value. Specifically, it is the time required to charge the capacitor, through the resistor, from an initial charge voltage of zero to approximately 63.2% of the value of an applied DC voltage, or to discharge the capacitor through the same resistor to approximately 36.8% of its initial charge voltage. When t=4t, the capacitor voltage is very small, and it is generally considered that the circuit enters a steady state, which is also called the zero input response of the RC first-order circuit. Ⅲ RC Circuits Classification3.1 Series and Parallel CircuitsRC Series CircuitIn circuit, the capacitor cannot flow DC current, and R & C have an obstructive effect on the current. So the total impedance is determined by the resistance and capacitive reactance, and it changes with frequency. RC series circuit has a turning frequency: f0=1/2πR1C1. When the input signal frequency is greater than f0, the total impedance is basically unchanged, and it is equal to R1.RC Parallel CircuitThe RC parallel circuit can pass both DC and AC signals. It has the same turning frequency as the RC series circuit: f0=1/2πR1C1. On the one hand, when the input signal frequency is less than f0, the total impedance of the circuit is equal to R1, on the other hand, when the input signal frequency is greater than f0, the capacitive reactance of C1 is relatively small, and the total impedance is the sum of resistance and capacitance. In addition, when the frequency is high to a certain level, the total impedance is zero.Introduction to Parallel RC CircuitWhat’s more, as frequency increases, the capacitor will act like a short circuit to high frequency current in its path. At low frequencies, the capacitor tends to block current flow.3.2 Example: RC Low Pass FilterCircuit AnalysisTo create a passive low-pass filter, we need to combine the resistor elements with the reactance elements. That is a circuit consisting of a resistor and a capacitor or an inductor. Theoretically speaking, the RL low-pass topology is equivalent to the RC low-pass topology in terms of filtering ability. However, in practice, RC circuits are more common.Figure 4. RC Low-pass FilterAs shown in the figure, connecting a resistor in series with the signal path and a capacitor in parallel with the load, an RC low-pass response can be generated. In the figure, the load is a single part, but in actual circuits, it may be more complicated, such as the input stage of an analog-to-digital converter, amplifier, or oscilloscope to measure the response of the filter.If a resistor and a capacitor form a frequency-dependent voltage divider circuit, we can intuitively analyze the filtering function of the RC low-pass circuit.Figure 5. Change RC Low-pass Filter into a Voltage DividerWhen the frequency of the input signal is low, the impedance of the capacitor is high than the resistor. Therefore, most of the input voltage will drop on the capacitor (and both ends of the load, which is in parallel with the capacitor). When the input frequency is higher, the impedance of the capacitor is lower than the impedance of the resistor, which means that the resistor voltage decreases and less voltage is transferred to the load. Therefore, low frequencies pass and high frequencies are blocked.Cutoff FrequencyWhere the filter does not cause significant attenuation for a frequency range is called the passband, and the opposite is called the stopband. Analog filters, such as RC low-pass filters, always gradually transit from the passband to the stopband. This means that it cannot be recognized that the filter stops passing the signal and starts blocking one frequency of the signal. This is why the cutoff frequency concept introduced.When checking the frequency response graph of the RC filter, the signal spectrum is "cut" into two halves of the image, one of which is retained and one is discarded. Because as the frequency moves from below the cutoff point to above the cutoff value, the attenuation gradually increases.The cut-off frequency of the RC low-pass filter is actually the frequency at which the input signal amplitude is reduced by 3dB (this value is chosen because a 3dB reduction is equal to a 50% reduction in power). Therefore, the cutoff frequency is also called -3dB frequency. The term bandwidth refers to the width of the passband of the filter. For a low-pass filter, its bandwidth is equal to the -3dB frequency (as shown in the figure below).Figure 6. Cutoff Frequency -3dBFilter Response CalculationWe can discuss the theoretical behavior of the low-pass filter by a typical voltage divider. The output of the resistor divider is expressed as following:The RC filter uses an equivalent structure, using a capacitor XC replace R2. Then we need to calculate the total impedance and place it in the denominator, so there is The reactance of a capacitor represents the opposite amount of current, but unlike resistance, the opposite amount depends on the frequency of the signal passing through the capacitor. Therefore, we must calculate the reactance at a specific frequency. The equation we use for this as follows: In the above design example: R≈160Ω and C=10nF. We assume that the magnitude of VIN is 1V, so we can simply remove VIN from the calculation. First, let's calculate the amplitude of VOUT with a sine wave frequency: While suppressing noise, the amplitude of the sine wave is basically unchanged. Because the cutoff frequency (100kHz) we chose is much higher than the sine wave frequency (5kHz).Let’s see how the filter successfully attenuates the noise component.The noise amplitude is only about 20% of its original value. Ⅳ Visualizing Filter Response4.1 Frequency ResponseThe most convenient way to assess the effect of a filter on a signal is to examine the frequency response graph. That is Bode plot, which has amplitude (in decibels) on the vertical axis and frequency on the horizontal axis; the horizontal axis usually has a logarithmic scale so that the physical distance between 1Hz and 10Hz is the same as 10Hz to 100Hz and 100Hz to 1kHz. This configuration allows us to quickly and accurately evaluate the behavior of the filter over a large frequency range.Figure 7. Bode PlotEach point on the curve represents the amplitude that the output signal is 1V and the frequency is equal to the corresponding value on the horizontal axis. For example, when the input frequency is 1MHz, the output amplitude (assuming the input amplitude is 1V) will be 0.1V (because -20dB corresponds to a tenfold reduction factor).The curve in the passband is almost completely flat, and then as the input frequency approaches the cutoff frequency, it starts to drop faster. Finally, the rate of change of attenuation becomes stable, that is, for every ten times the input frequency increases, the amplitude of the output signal decreases by 20dB. 4.2 Low Pass Filter Phase ShiftThe way in which the filter modifies the amplitude of various frequency components in the signal has been discussed above. However, in addition to amplitude effects, reactive circuit elements always involve phase shifts.The concept of phase refers to the value of the periodic signal at a specific moment in the cycle. Therefore, when we say that a circuit causes a phase shift, we mean that it creates a misalignment between the input signal and the output signal. That is the input and output signals no longer start and end their periods at the same time. The phase shift value, such as 45° or 90°, indicates how much misalignment has been created.Each reactance element in the circuit introduces a 90° phase shift, but this phase shift does not occur at the same time. The phase of the output signal is the same as the amplitude of the output signal, and it changes gradually as the input frequency increases. In the RC low-pass filter, we have a reactive element (capacitor), so the circuit will eventually introduce a 90° phase shift.As with the amplitude response, the phase response can be most easily evaluated by examining the graph on the horizontal axis which represents the logarithmic frequency. The following description is the general pattern.The phase shift is initially 0°, and it gradually increases until it reaches 45° at the cutoff frequency. During this part of the response, the rate of change is increasing. With time, the phase shift continues to increase, but the rate of change is decreasing. As the phase shift approaches 90°, the change of rate becomes very small.Figure 8. Phase Shift4.3 Second-order Low-pass FilterAs above mentioned, we have assumed that the RC low-pass filter consists of a resistor and a capacitor. This configuration is a first-order filter. The "order" of passive filters is determined by the number of reactive components (ie capacitors or inductors) in the circuit. Higher-order filters have more reactive components, which lead to more phase shift and steeper roll-off.Second-order filters are usually built a resonant circuit consisting of inductors and capacitors (this topology is called "RLC", or resistor-inductor-capacitor circuit). However, it is also possible to create a second-order RC filter. As shown in the figure below, all we need to do is to cascade two first-order RC filters.Figure 9. Second-order Filter CircuitAlthough this topology can produce a second-order response, it is not widely used. Because its frequency response is usually not as good as a second-order active filter or a second-order RLC filter.Frequency ResponseWe can try to create a second-order RC low-pass filter by designing a first-order filter based on the required cutoff frequency, that is connecting two first-order stages in series. This set has a similar overall frequency response, with a maximum roll-off of 40dB/decade instead of 20dB/decade.However, we cannot simply connect these two stages together and analyze the circuit as a second-order low-pass filter. In addition, even if we insert a buffer between the two stages so that the first RC stage and the second RC stage can be used as independent filters, the attenuation at the original cut-off frequency will be 6dB instead of 3dB. Because the two stages work independently.Figure 10. Frequency Response of RC-RC FilterA limitation of the second-order RC low-pass filter is that the designer cannot tune the conversion from passband to stopband by adjusting the Q factor (this parameter indicates the degree of damping of the frequency response.) of the filter. If two identical RC low-pass filters are cascaded, the overall transfer function corresponds to the second-order response, but the Q factor is always 0.5. When Q = 0.5, the filter is at the boundary of over-damping, which results in a "sag" frequency response in the transition region. While second-order active filters and second-order resonant filters do not have this limitation, designers can control the frequency response of the transition region. Ⅴ ConclusionAll electrical signals contain a mixture of requiring frequency and unwanted ones. Undesirable frequency components are usually caused by noise and interference, and in some cases they have a negative impact on the performance of the system.Filters are circuits that react to different parts of the signal spectrum in different ways. The low-pass filter is designed to pass low frequency components and block high frequency components. The output voltage of an RC low-pass filter can be calculated by considering the circuit as a voltage divider (frequency-independent) composed of resistance and reactance.The graph of amplitude (in dB, on the vertical axis) vs. log frequency (in Hz, on the horizontal axis) is a convenient and effective way to check the theoretical behavior of the filter. You can also use phase and log frequency graph determines the amount of phase shift that will be applied to the input signal.The second-order filter provides a steeper roll-off, and its response is useful when the signal cannot provide broadband separation between the desired frequency and the unwanted one. You can make a second-order RC low-pass filter by connecting two identical first-order RC low-pass filters, but the overall -3 dB frequency will be lower than expected.In RC filtering circuit, the capacitor can store energy, and the resistor placed in series with it can control the charge-discharge rate. And this produces a characteristic time dependence that turns out to be exponential. Frequently Asked Questions about RC Filter Circuit1. What does an RC filter do?RC circuits can be used to filter a signal by blocking certain frequencies and passing others. The two most common RC filters are the high-pass filters and low-pass filters; band-pass filters and band-stop filters usually require RLC filters, though crude ones can be made with RC filters. 2. What is RC filter in electronics?A resistor–capacitor circuit (RC circuit), or RC filter or RC network, is an electric circuit composed of resistors and capacitors. ... A first order RC circuit is composed of one resistor and one capacitor and is the simplest type of RC circuit. 3. How do you calculate RC circuit?The (real value) impedance is the real part of the complex impedance Z. For a series RC circuit, we get Z=√R2+(1ωC)2 Z = R 2 + ( 1 ω C ) 2 . We see that the amplitude of the current will be V/Z=V√R2+(1ωC)2 V / Z = V R 2 + ( 1 ω C ) 2. 4. What is RC circuit used for?The RC circuit has thousands of uses and is a very important circuit to study. Not only can it be used to time circuits, it can also be used to filter out unwanted frequencies in a circuit and used in power supplies, like the one for your computer, to help turn ac voltage to dc voltage. 5. What is RC series circuit?A circuit that contains pure resistance R ohms connected in series with a pure capacitor of capacitance C farads is known as RC Series Circuit. A sinusoidal voltage is applied and current I flows through the resistance (R) and the capacitance (C) of the circuit.

IntroductionAn operational amplifier, or op amp is used in a wide variety of applications in electronics. It generally comprises a differential-input stage with high input impedance, an intermediate-gain stage, and a push-pull output stage with a low output impedance. Common 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. So what are these op-amp parameters meaning? This note tells you the typical parameters of op-amp and their definitions, also there have several examples with specific values to explain deeply for you. CatalogIntroductionⅠ How Does An Op Amp Work?Ⅱ Understanding Basic Op-amp Parameters2.1 What are the Parameters of Op Amp?2.2 Questions about Op Amp Important ParametersⅢ Common Op-amp ICs Datasheet OverviewⅣ ConclusionⅠ How Does An Op Amp Work?An op-amp is a multi-stage , direct coupled, high gain negative feedback amplifier. It is basically a three-terminal device which consists of two high impedance inputs. Ideally, it only amplifies the difference in voltage between the two, also called differential input voltage. Op-amps are still a primary building block for analog systems, performing tasks like amplification, active filtering, and signal transformation. In digital systems, op-amps are used in buffers, analog-to-digital converters, digital-to-analog converters, and regulated power supplies, to name a few applications.Ⅱ Understanding Basic Op-amp ParametersOp-amps are linear devices that are ideal for DC amplification and are used often in signal conditioning, filtering or other mathematical operations. So understanding its basic parameters is important to employ it well in circuits.Parameters Of Op-Amp2.1 What are the Parameters of Op Amp?Gain Bandwidth1) Gain bandwidth product: Due to parasitic junction capacitance and minority-carrier change storage in devices, the voltage gain of op amp decreases at high frequencies, it refers to the bandwidth and gain product.2) Unity gain bandwidth: As the input signal of the frequency increases, the open-loop gain drops off until it finally reacts to the value 1. The frequency at which the gain reduces to 1 is defined as unity gain frequency or unity-gain bandwidth.Input Offset VoltageIt is a very small voltage applied at the outputs, to make the output terminal zero of the operational amplifier. It reflects the symmetry of the the op amp circuit. The better the symmetry, the smaller the input offset voltage.Input Offset Voltage DriftThe input offset voltage drift is also called the temperature coefficient. In a given temperature range, it is the ratio of the change in the input offset voltage to the temperature change. This parameter is actually a supplement to the input offset voltage. Within a given operating range, the magnitude of the drift of the amplifying circuit depends on the temperature changes.Input Bias CurrentWhen the output current voltage of the op amp is zero, input bias current refers to the average value of the bias current of the two input terminals that flows into the inverting and non-inverting input terminals of the Op-Amp. It has a greater impact on the places where the input impedance is required, and it is generally related to the manufacturing process. The smaller the input bias current the smaller the drift.Input Offset CurrentWhen the output current voltage of the op amp is zero, input offset current means the difference between the bias currents of the two input terminals. It also reflects the symmetry of the circuit inside the op amp. The better the symmetry, the smaller the input offset current.Input Resistance1) Differential mode input impedance: when the operational amplifier is working in the linear region, it is the ratio of the voltage change at the two input terminals to the corresponding current change. It includes input resistance and input capacitance, and only refers to input resistance at low frequencies.2) Common mode input impedance: It is the ratio of the input current change when the op amp is inputting a signal, that is, the same signal is input at the two input terminals of the op amp. At low frequencies, it appears as a common-mode resistance.Output ResistanceWhen the operational amplifier works in the linear region, a voltage signal is added to the output terminal of the operational amplifier, output resistance means the ratio of the voltage change to the corresponding current change. At low frequencies, it only refers to the output resistance of the op amp. This parameter needs to be tested in an open loop state.Voltage Gain1) Open-loop gain: the amplification factor of the op amp without negative feedback (in open loop state). The ideal value is infinite, generally about thousands to tens of thousands of times, and it represents by dB and V/mV.2) Closed-loop gain: in the case of negative feedback, it refers to the amplifier magnification.Voltage SwingWhen the op amp is working in the linear region, voltage swing is the maximum voltage amplitude that the op amp can output under the specified load and the current power supply voltage.Input Voltage Range1) Differential mode input voltage range: The maximum differential mode input voltage is defined as the maximum allowable input voltage difference between the two input terminals of the operational amplifier. When the input voltage difference of the op amp exceeds it, the input stage of the op amp may be damaged.2) Common mode belongs to the rabbit voltage range: when the operational amplifier is working in the linear region, when the common mode rejection ratio of the operational amplifier deteriorates significantly is the maximum common mode input voltage. It limits the maximum common-mode input range in the input signal, therefore, special attention is required in the case of interference.Slew RateThe slew rate of the op amp is defined as the input of a large signal (including a step signal) to the input under the closed loop condition. It indicates how fast the output of OP-AMP can change in response to change in input frequency. The output rise rate of the op amp is measured from the output of the op amp. Since the op amp is in a closed loop state during conversion, the feedback loop of the op amp does not work, that is to say, the slew rate has nothing to do with the closed loop gain.CMRRThe Common Mode Rejection Ratio (CMRR) is defined as the ratio of the differential voltage gain to the common-mode voltage gain.Unity GainA unity gain amplifier is an amplifier that has a gain of 1 that also means there is no gain. The output voltage will be the same as the input voltage it is commonly known as a voltage follower amplifier.Common Mode Rejection RatioWhen the op amp works in the linear region, it means the ratio of the differential mode gain of the op amp to the common mode gain. It is an extremely important indicator, it suppresses differential mode interference signals. Since the common-mode rejection ratio is very large, the common-mode rejection ratio of most op amps is recorded and compared in decibels.Supply Voltage Common Mode Rejection RatioWhen the op amp works in the linear region, it means the input offset current of the op amp varies with the supply voltage. Supply voltage common mode rejection ratio reflects the impact of power supply changes on the output of the op amp. Pay special attention when used for DC signals or small signals.Equivalent Input VoltageA well-shielded op amp without signal input, any AC interference voltage generated at its output end, when this noise is converted to the input of the op amp, it is called the input noise voltage (sometimes also expressed by noise current).2.2 Questions about Op Amp Important ParametersWhy do op amps need negative voltage?Op-amps themselves don't have a 0V connection but their design assumes the typical signals will be more towards the center of their positive and negative supplies. Thus, if your input voltage is right at one extreme or forces the output toward one supply, chances are it won't work properly. Why op amp has high gain?The gain of an op amp represents how much greater in magnitude its output will be than its input, hence its amplification factor. This is usually defined as an open-loop gain or large signal voltage gain. Why Positive feedback is not used in op amp?In an op-amp circuit with no feedback, there is no corrective mechanism, and the output voltage will saturate with the tiniest amount of differential voltage applied between the inputs. What is CMRR?The Common Mode Rejection Ratio (CMRR) is defined as the ratio of the differential voltage gain to the common-mode voltage gain. CMRR is infinity. Why CMRR should be high?A high CMRR is required when a differential signal must be amplified in the presence of a possibly large common-mode input, such as strong electromagnetic interference (EMI). An example is audio transmission over balanced line in sound reinforcement or recording. What is the maximum gain of op amp?The maximum gain is the open loop gain. It depends on the opamp model, and can go anywhere from 60 dB to 120 dB voltage gain. The open-loop bandwidth is however very small. Another issue is that this gain is very variable between different parts of the same product number due to variations. What is slew rate of op amp?Slew rate (SR) is the maximum rate of voltage change that can be generated by the op-amp's output circuitry. It is measured as voltage relative to time, and the typical unit used in datasheets is volts per microsecond (V/µs). SR is infinity, which means the ideal op-amp will produce a change in the output instantly in response to an input step voltage. What is bandwidth of an operational amplifier?The operational amplifiers bandwidth is the frequency range over which the voltage gain of the amplifier is above 70.7% or -3dB (where 0dB is the maximum) of its maximum output value as shown below. Is higher slew rate better?Higher slew rates are not always better: Higher slew rate makes for higher operating current. This means higher power consumption. Faster slew rate will make higher bandwith. Ⅲ Common Op-amp ICs Datasheet OverviewLM741The LM741 series are general-purpose operational amplifiers which feature improved performance over industry standards like the LM709. It is intended for a wide range of analog applications. It has only one op-amp inside. An operational amplifier IC is used as a comparator which compares the two signal, the inverting and non-inverting signal.Figure 1. LM741 Op Amp PinoutTable 1: LM741 SpecificationsMax supply voltage: ±22 VVoltage gain: 200V/mVMax input voltage: ±15 VBuilt-in output short circuit protectionMax output short circuit current is 40 mA.Input resistance: 6MMax low offset voltage of 6mv and can drift 15 µV/°CApplications include comparator, dc amplifier, summing amplifier, integrator or differentiators and active Filters.Max input offset current of 70nA and can drift up-to 0.5 nA/°C.Max Bandwidth is 1.5Mhz;Max Slew rate is 0.7 V/us.Max CMRR is 90 dB.Similar Products: UA741, µA741Max peak output voltage swing is 16VOperating temperature range –50 to 125 °C LM709 SeriesThe LM709 series is a monolithic operational amplifier in tended for general-purpose applications. The precursor to the popular LM741 is the LM709. The 709 had no internal frequency compensation, unlike the 741. Frequency compensation is used to purposely limit an operator's bandwidth. As the input frequency increases, the operator's phase shift also increases. This can contribute to unnecessary oscillation, as an unintended phase-shift oscillator forms the feedback network.Figure 2. LM709 Op Amp PinoutTable 2: LM709 SpecificationsMax supply voltage: ±18VInput resistance: 750KMax input voltage: ±10VOutput resistance: 150ΩMax low offset voltage of 6mv and can drift 6 µV/°CApplication includes voltage follower, basic comparator, multivibrator and frequency generator.Max input offset current of 500nA and can drift up-to 22.8 nA/°CPackage: TO-5, Pin Nb=8Max CMRR is 70dB.Similar parts: OP77, UA70Peak output voltage swing is 24VOperating temperature range –55 to 125 °C LM1458LM1458 is a dual general purpose Operational Amplifier (Op-amp). Its has two built-in amplifiers having common power supply, and short circuits protected and require no external components for frequency.Figure 3. LM1458 Op Amp PinoutTable 3: LM1458 SpecificationsMax supply voltage: ±18 VInput resistance: 1MΩMax input voltage: ±15VMax CMRR is 90dBvoltage gain: 15V/mVbuilt-in output short circuit protectionMax low offset voltage of 6mv and can drift 15 µV/°CInput offset current of 300nA max and can drift up-to 0.5 nA/°CMax peak output voltage swing is 14V.Max bandwidth is 1MHz.Operating temperature range 0 to 70 °CApplications include summing amplifiers, portable devices, comparators, integrators, etc.Similar Products: MC1458Packages have TO-CAN, DSBGA, SOIC and PDIP. LM324The LM324 series are low−cost, quad operational amplifiers with true differential inputs. They have several distinct advantages over standard op amps. It is a single supply, high gain, internally frequency compensated quad op amp. And it can be operated from a single or split power supplies.Figure 4. LM324 Op Amp PinoutTable 4: LM1324 SpecificationsMax supply voltage: 32 VOutput resistance: 350ΩVoltage gain: 100 V/mVMax output short circuit current is 60 mAInput bias current: 100nABuilt-in output short circuit protectionMax low offset voltage of 3mv and can drift 30µV/°CMax input offset current of 30nA and can drift up-to 300 pA/°CMax CMRR is 85dB.Max peak output voltage swing is 16V.Bandwidth is 1MHzOperating temperature range 0 to 70 °CPackages: 14-pin PDIP, 14-pin CDIP, 14-pin SOIC, and 14-pin TSSOP NE5532Compared to the standard dual op amps, the NE5532 is a Dual Low Noise Op-Amp in 8-pin package commonly used as amplifiers in audio circuits for its noise immunity and high output drive capability. The Op-Amp is internally compensated for high unity gain with maximum output swing bandwidth, low distortion and high slew rate.Figure 5. NE5532 Op Amp PinoutTable 5: NE5532 SpecificationsMax supply voltage: ± 15VInput bias current: 1000nAMax supply current: 10mALow offset voltage: 5 mVInput offset current: 200nABuilt-in output short circuit protectionMax output short circuit current is 60 mAInput resistance: 300KΩMax CMRR is 100dB.Output resistance: 0.3ΩMax peak output voltage swing is 26V.Max bandwidth is 10Mhz.Max slew rate is 9 V/us.Operating temperature range -65 to 150 °CApplications include Av Receivers, Audio mixer, High-performance audio preamplifier and many more.Ⅳ ConclusionOp amps are used in a wide variety of applications in electronics. Some of the more common applications are: as a voltage follower, selective inversion circuit, a current-to-voltage converter, active rectifier, integrator, a whole wide variety of filters, and a voltage comparator. Based on your circuit requirements, you should check out datasheets of different op-amps and select one.

Ⅰ IntroductionFlyback Diodes, which are also known as freewheeling diodes, generally refer to diodes that are inversely paralleled across the ends of energy storage elements such as inductors, relays, and thyristors. When a voltage or current changes suddenly in a circuit, it protects other components in the circuit. When using a flyback diode, the circuit current can be changed more gently to avoid the occurrence of voltage spike. This article will introduce in detail what is flyback diode, how freewheeling diode works, flyback diode selection and the flyback diode function.How Freewheeling Diode WorksCatalogⅠ IntroductionⅡ DesignⅢ How It Works?Ⅳ SelectionⅤ Applications5.1 Summary5.2 In Forward Switching Power Supply5.3 In Converter Technology5.4 In Unidirectional Half Wave Silicon Control Rectifier Circuit5.5 In BUCK CircuitⅥ Something Has to CareIn electronics, a flyback voltage or an inductive flyback is a voltage spike created by an Inductor when its power supply is removed abruptly. The reason for this voltage spike is the fact that there cannot be an instant change to the current flowing through an Inductor.In addition, time constant of the inductor determines the rate at which the current can change through an inductor. This is similar to the time constant of a capacitor, which determines the rate at which its voltage can change.The freewheeling diode is named because it plays the role of freewheeling in the circuit. It is generally used in the circuit to protect components from being damaged or burned out by voltage breakdown, connected in parallel to both ends of the elements that generate the induced electromotive force(EMF), and form a loop with them, so that the high electromotive force generated in the loop is consumed by the continuous current method, thereby protecting the components in the circuits.Flyback diodes are connected in parallel at both ends of the coil. When the current passes through the coil, it will generate induced electromotive force at both ends. When the current disappears, its induced electromotive force generates a reverse voltage to the components in the circuit. When the reverse voltage is higher than the reverse breakdown voltage of the elements, it will cause damage to the elements such as triode and thyristor. When the current flowing through the coil disappears, the induced electromotive force generated by the coil is consumed by the work formed by the diode and the coil, thereby protecting the other elements in the circuit.Ⅱ DesignIn the following figure, it is showed that a flyback diode is placed across the inductor. An ideal flyback diode will have a very large peak forward current; capacity which helps in handling the voltage transients from damaging the diode, and inductor’s power supply is suited for reverse breakdown voltage and low forward voltage drop. Voltage spike can be 10times to the voltage of power supply which depends on the equipment involved and the application. So it is understood that not to underestimate the energy which contain within an energized inductor. Figure 1. Flyback DiodeFor an ideal flyback diode selection, a diode which has very large peak forward current capacity (to handle voltage transients without burning out the diode) should be selected, moreover, low forward voltage drop, and a reverse breakdown voltage fitted the inductor's power supply. Depending on the application and equipment in real requirement, some voltage surges can be upwards of 10 times the voltage of the power source, so it is critical not to underestimate the energy contained within an energized inductor.Flyback Diode Selection Note You Should KnowWhen used with a DC coil relay, a flyback diode can cause delayed drop-out of the contacts when power is turned off, due to the continued circulation of current in the relay coil and diode. When rapid opening of the contacts is important, a small value resistor can be placed in series with the diode to help dissipate the coil energy faster, at the expense of higher voltage at the switch.Schottky diodes are preferred in flyback diode applications as switching power converters, because they have the lowest forward drop (~0.2V rather than >0.7V for low currents) and are able to quickly respond to reverse bias (when the inductor is being re-energized). They therefore dissipate less energy while transferring energy from the inductor to a capacitor.When the flyback diode is used to simply dissipate the inductive energy, as with a solenoid or electric motor, cheap 1N540x and 1N400x general-purpose diodes are used instead. Ⅲ How It Works?Flyback diodes are often used with energy storage elements to prevent sudden changes in voltage and current to provide a pathway. The inductor can provide continuous current to the load through it to avoid sudden changes in load current and smooth the current. In the switching power supply, you can see a freewheeling circuit composed of a diode and a resistor connected in series, which is connected in parallel with the primary side of the transformer. When the switch is turned off, the freewheeling circuit can release the energy stored in the transformer coil to prevent the induced voltage from being too large and breakdown the switch. Generally, it is often to choose the fast recovery diode or the Schottky diode as flyback diode.Circuit Expressions Figure 2. Flyback Diode in Switching Power Supply CircuitIn Figure 2(c), when KR is turned on, the upper is positive voltage and the lower is negative voltage,  and the current direction is from top to bottom. When the VT is turned off, the current in the KR is suddenly interrupted and an induced potential is generated. The current direction is kept constant, that is, keeping the KR current direction from the top to bottom, which based on the Lenz's law. The induced potential and the power supply voltage are superimposed and applied across the VT, making it easy for the VT to breakdown. To avoid it, VD is used to short-circuit the induced potential generated by KR, that is, The current flows clockwise in the small circuits of the diodes and relays to protect the VT. R and C in Figure 2(b) also use the principle that the voltage on C cannot be abruptly changed to absorb the induced potential.In short, the flyback diode is connected in parallel to the relay or the inductor at both ends of the circuit. When the inductor is powered off, the electromotive force at both ends does not disappear immediately. At this time, the residual electromotive force is released through a freewheeling diode to reverse the reverse generated by the coil (the EMF is consumed in the form of current). It can be seen that the freewheeling diode is not a substantial component, but plays a "freewheeling" role in the circuit.For example, reversely connect a flyback diode at both ends of a relay coil or at both ends of a unidirectional thyristor. In practice, electromagnetic relays are usually controlled by triodes or MOS tubes to achieve automatic control of electrical loads (such as through a single-chip microcomputer), and the coil of the relay is a large inductance, which can store electrical energy in the form of a magnetic field. So when it pulls in, it stores a lot of magnetic field. When the triode controlling the relay changes from on to off, the coil is powered off, but there is a magnetic field in the coil. At this time, the back electromotive voltage can be as high as 1000v to destroy other circuit components. This is because the access of the diode is exactly the same as the direction of the reverse electromotive force. So that the reverse potential is neutralized by the freewheeling diode in the form of current to protect other circuit components. In addition, it is generally a diode with a fast switching speed.  Figure 3. Freewheeling Diode CircuitBecause the relay coil exists inductive load, which will absorb the self-inductive voltage of the relay coil when the triode is turned off. According to Lenz's law, when the current on the inductor decreases, a self-inductive voltage is generated. The direction of this voltage is that the forward terminal is negative and the collector of the driving tube is positive. This voltage will break through the triode, so an freewheeling diode is connected in parallel with the relay to absorb this self-inductive voltage.1) The influence of the time parameter of the circuit below the ms level on the mechanical contact is ignored.2) Even the 1N4000 reverse recovery time is far below the ms level, and the forward conduction time is shorter.3) Capacitance between the driving tubes and parasitic capacitance of the relay is enough to disable the high-speed diode.4) The consumption of inductive energy storage mainly depends on the winding resistance, which is generally in an overdamped state.It is general to use transistors as switches. As shown in Figure, a transistor TR1 is used to control the conduction of the relay coil, and the relay contact is used to control the load circuit.In a thyristor circuit, the thyristor is generally used as a contact switch, if a large inductive load is controlled, a high-voltage back electromotive force will be generated, and the principle is the same as that of a relay.Flyback diode also used on displays coils commonly used in relays. It is often used with energy storage elements to prevent sudden changes in voltage and current and provide a path. The inductor can provide continuous current to the load to avoid sudden changes in load current and smooth the current. In the switching power supply, it is common to see a freewheeling circuit composed of a diode and a resistor connected in series. The following circuit is connected in parallel with the primary side of the transformer. Figure 4. Flyback Diode in Relay CircuitThe freewheeling diode is added to both ends of the inductive load, and the inductive here is to have an inductive characteristic. The characteristic of the inductive load is that the current cannot be abruptly changed, in other words, it can't be all of a sudden. Common inductive loads include relay coils and solenoid valves.Figure 5.  Typical Freewheeling CircuitThe Figure 5 shows the typical application circuit of the flyback diode, where the resistor R determined whether it is needed or not. When the energy storage element VT is turned on, the upper voltage is positive, and the lower voltage is negative, and the current direction is from top to bottom. When the VT is turned off, the current in the energy storage element is suddenly interrupted, and an induced potential is generated at this time. This induced potential and the power supply voltage are superimposed and applied to both ends of the VT, which can easily cause VT to break down. VD can be added for this purpose, so that the induced potential generated by the energy storage element can be short-circuited to achieve the purpose of protecting the VT. Ⅳ Selection1) Based on working voltage2) Based on working current1N4007 is a not bad choice but not the best, because the PLC may be damaged before the diodes have time to play the freewheeling effect. Therefore, it is best to use FR107 to protect the freewheeling circuit, which can better protect the PLC output interface, and the cost will not rise too much. It is also possible to choose IN5819 or IN5817, which has better performance than FR107, but the cost is a little higher. Ⅴ Applications5.1 SummaryFlyback diodes are usually used with energy storage elements, and their role is to prevent sudden changes in voltage and current in the circuit and provide a power-consuming path for reverse electromotive force. The inductive coil can provide continuous current to the load through EMF, so as not to change the load current and smooth the current. In the switching power supply, a freewheeling circuit always composed of a diode and a resistor connected in series. This circuit is connected in parallel with the primary side of the transformer. When the switch is turned off, the freewheeling circuit can release the energy stored in the transformer coil to prevent the induced voltage from being too large and breakdown the switch.5.2 In Forward Switching Power SupplyIn the forward switching power supply, when the MOS is turned off, the secondary side of the transformer provides current to the outside by the energy stored in the inductor. In order to make the inductor play this role under load, a freewheeling diode is added on the secondary side of the transformer. The inductor, load, and freewheeling diodes create paths to transfer the energy in the inductor to the outside.5.3 In Converter TechnologyIn the electronic converter circuit, the single-phase bridge rectifier in the rectification section is the single-phase rectifier circuit with the most practical applications. And three-phase bridge rectification is the most widely used method for power systems, especially generator excitation systems. Both of these circuits must be connected to a flyback diode. Its function is almost the same. Take a single-phase bridge circuit as an example: When the rectifier bridge is connected to an inductive load, because the inductor current cannot be abruptly changed, during the thyristor off time, it must connect freewheeling diode at both ends of the load to provide a smoothing path  to prevent dangerous overvoltages across the inductive load, and also the thyristor can be commutated to conduct.The three-phase bridge rectifier circuits used in generator excitation systems are divided into three-phase half-control bridges and three-phase full-control bridge circuits. Therefore, in order to ensure reliable commutation of the rectifier components, the half-control bridge needs to connect flyback diodes in parallel at both ends of the inductive load, while the full-control bridge does not need to do so. In addition, when the conduction angle is changed, the average voltage and line current of the half-controlled bridge change more slowly than the full-controlled bridge.At present, current converters such as rectifiers and inverters are now used in a large number of devices, in which flyback diodes are typically added to the internal DC bus of the converter. Because if the load is an inductive element, when a large-capacity inverter on the bus fails, the DC bus will generate huge reverse surge energy. At this time, it is necessary to provide a discharge channel for this energy, otherwise it will break down or burn the converter. This channel needs a diode to form, that is a flyback diode.5.4 In Unidirectional Half Wave Silicon Control Rectifier CircuitFor unidirectional half-wave silicon control rectifier circuit with large inductive load, when the  silicon control is turned off in the negative half cycle, the inductive load will generate a high reverse induced electromotive force. This reverse electromotive force is sufficient to cause the silicon control to break down and burn. After that, the reverse electromotive force can be discharged into the forward voltage drop of the diode (about 0.7V), thereby effectively protecting the circuit components. 5.5 In BUCK Circuit Figure 6. BUCK CircuitIn the BUCK circuit, fast recovery diodes or Schottky diodes are generally selected as freewheeling diodes. It is generally used in the circuit to protect components from being broken down or burned by induced voltage. The two ends of the element form a loop with it, so that the high electromotive force generated in the loop is consumed in a continuous current manner, thereby protecting the elements in the circuit.In theory, the diode is selected at least 2 times the maximum current. In actual use, due to the strong transient overload resistance of the diode, an ultra-fast diode with a maximum current of 50A can also be used. In addition, a reasonable heat sink generally has little damage in actual use. The total impedance when conducting is the internal resistance of the motor plus the equivalent internal resistance of the drive tube. And the total impedance during freewheeling is the internal resistance of the motor plus the equivalent internal resistance of the freewheeling diode. In general, the AC equivalent internal resistance of the freewheeling diode is smaller than the AC equivalent internal resistance of the driving transistor. Therefore, in conventional design, the maximum current of the freewheeling diode is generally doubled to the maximum current of the motor.The transient current is only a moment, and the anti-overload capability of the surface-contact diode is enough, as long as it is not used in overvoltage, if necessary, a small resistor can be connected in series to limit the current. The flyback diode is to protect the switching device. The transient current during freewheeling is related to the working voltage of the motor and the internal resistance of the winding, and has nothing to do with the power of the motor. If necessary, the peak value of the transient current is the reverse self-inductance voltage minus diode junction voltage drop and then divided by the loop resistance. The reason why a diode with a certain current used is because the internal resistance of the winding of the low-voltage high-power motor is low, so the transient current will be relatively large. A series of small resistors can suppress the peak current, the transient voltage of the switch tube rises slightly because the operating voltage is not high, and now the current withstand voltage of transistors is at least 50V or more. Ⅵ Something Has to CareFreewheeling diodes are commonly used in switching power supplies, relay circuits, thyristor circuits, IGBTs, and other circuits. They are widely used, so it is necessary to pay attention to the following points when using them: 1) Fylback diode is an effective method to prevent the high voltage generated by self-inductive potential from causing damage to related components when the DC coil is powered off.2) The polarity of the flyback diode must not be connected wrongly, otherwise a short circuit situation will be caused.3) The flyback diode is always reversed to the DC voltage, that is, the negative pole of the diode is connected to the positive pole of the DC power supply.4) The flyback diode works in the forward conduction state, not in the breakdown state or the high-speed switching state, that is, the flyback diode does not used in electrical breakdown, recoverable situation, but its unidirectional conduction effect is the key point.5) Zener diodes can't be regarded as flyback diode. Because the zener diodes use reverse characteristics, and the flyback diodes use forward characteristics. Frequently Asked Questions about Flyback Diode or Freewheeling Diode1. What is a flyback diode?A flyback diode is a diode connected across an inductor used to eliminate flyback, which is the sudden voltage spike seen across an inductive load when its supply current is suddenly reduced or interrupted. 2. What is the role of freewheeling diode?A Flyback diode is also called as freewheeling diode. ... Here catch diode is used to eliminate flyback, when the abrupt voltage spike is witnessed across the inductive load when the supply current abruptly reduced. It helps the circuit from damaging. 3. What is a flyback diode used for?A flyback diode is a diode connected across an inductor used to eliminate flyback, which is the sudden voltage spike seen across an inductive load when its supply current is suddenly reduced or interrupted. 4. How does a flyback diode work?The Flyback diode makes inductor to draw current from itself in a loop until the energy is dissipated in diode and wires. When the current flow to an AC induction motor is suddenly interrupted, then the inductor tries to maintain increasing the voltage and the current by reversing polarity. 5. How do you choose a freewheeling diode?The diode reverse voltage rating should be at least the voltage applied to the relay coil. Normally a designer puts in plenty of reserve in the reverse rating. A diode in your application having 50 volts would be more than adequate. Again 1N4001 will do the job. 6. How do I choose a flyback diode for a relay?Specify a diode for at least 79.4 mA current. In your case, a 1N4001 current rating far exceeds the requirement. The diode reverse voltage rating should be at least the voltage applied to the relay coil. Normally a designer puts in plenty of reserve in the reverse rating. 7. What are the advantages of freewheeling diode?What are the advantage of free wheeling diode in a Full Wave rectifier? It reduces the harmonics and it also reduces sparking and arching across the mechanical switch so that it reduces the voltage spike seen in a inductive load. 8. Why freewheeling diode is used in controlled rectifier?When the inductive circuit is switched off, this diode gives a short circuit path for the flow of inductor decay current and hence dissipation of stored energy in the inductor. This diode is also called Flywheel or Fly-back diode. circuits, inverter circuits, and chopper circuits by making it continuous. 9. What is the effect of adding free wheeling diode?It reduces the harmonics and it also reduces sparking and arching across the mechanical switch so that it reduces the voltage spike seen in a inductive load. 10. What is the use of freewheeling diode in converter circuit?A free wheeling diode is used in converter circuits . It is connected across the load. During positive cycle of input it is reverse biased. During negative cycle of input the diode conducts and the energy stored in the circuit inductor during the previous half cycle is delivered to the load itself.