I. The basic properties of magnetic materials
1. Magnetization curve of magnetic materials
Magnetic materials are composed of ferromagnetic or subferromagnetic material, in the applied magnetic field H, there must be a corresponding magnetization strength M or magnetic induction strength B, they are called magnetization curve with the magnetic field strength H curve (M ~ H or B ~ H curve). Magnetization curve is generally non-linear, with two characteristics: magnetic saturation phenomenon and hysteresis phenomenon. That is, when the magnetic field strength H is large enough, the magnetization strength M reaches a definite saturation value Ms, and continues to increase H, Ms remains unchanged; as well as when the M value of the material reaches saturation, when the external magnetic field H is reduced to zero, M does not return to zero, but varies along the MsMr curve. The working state of the material is equivalent to a point on the M ~ H curve or B ~ H curve, which is often called the working point.
2. Common Magnetic Property Parameters of Soft Magnetic Materials
Saturation Magnetic Inductance Bs: Its magnitude depends on the composition of the material, and the physical state it corresponds to is a neat arrangement of the magnetization vectors within the material.
Residual magnetic induction Br: is a characteristic parameter on the hysteresis loop, the value of B when H returns to 0.
Rectangular ratio: Br∕Bs
Coercivity Hc: is a quantity that indicates the ease of magnetization of a material and depends on the composition of the material and defects (impurities, stresses, etc.).
Magnetic permeability μ: is the ratio of B to H corresponding to any point on the hysteresis loop, and is closely related to the device operating state.
Initial permeability μi, maximum permeability μm, differential permeability μd, amplitude permeability μa, effective permeability μe, impulse permeability μp.
Curie temperature Tc: the magnetization strength of the ferromagnetic material decreases with the temperature, and when it reaches a certain temperature, the spontaneous magnetization disappears and transforms into paramagnetism, and this critical temperature is Curie temperature. It determines the upper temperature of the magnetic device work.
Loss P: Hysteresis loss Ph and eddy current loss Pe P = Ph + Pe = af + bf2+ c Pe ∝ f2 t2 / , ρ is reduced,
Hysteresis loss Ph is to reduce the coercive force Hc; reduce the eddy current loss Pe is to thin out the thickness of the magnetic material t and increase the resistivity of the material ρ. Losses of the core in free standing air and the core temperature rise The relationship between core loss and core temperature rise in free standing air is:
Total power dissipation (mW)/surface area (cm2)
3. Conversion between magnetic parameters of soft magnetic materials and electrical parameters of devices
In the design of soft magnetic devices, the first step is to determine the voltage-current characteristics of the device according to the requirements of the circuit. The voltage-current characteristics of the device are closely related to the core geometry and magnetization state. The designer must be familiar with the magnetization process of the material and grasp the conversion relationship between the magnetic parameters of the material and the electrical parameters of the device. Designing a soft magnetic device usually involves three steps: correctly selecting the magnetic material; reasonably determining the core geometry and size; and simulating the core's operating state to obtain the corresponding electrical parameters according to the magnetic parameter requirements.
The development and types of soft magnetic materials
1. The development of soft magnetic materials
The application of soft magnetic materials in industry began in the late 19th century. With the rise of electric power workers and telecommunications technology, began to use mild steel to manufacture motors and transformers, inductor coils in telephone lines in the core of the use of fine iron powder, iron oxide, fine iron wire and so on. By the beginning of the 20th century, silicon steel sheets were developed to replace mild steel, improving the efficiency of transformers and reducing losses. Until now, silicon steel sheet in the power industry in the soft magnetic material is still in the first place. To the 20's, the rise of radio technology, promote the development of high permeability materials, the emergence of PoMo alloy and PoMo alloy magnetic powder core, etc.. From the 40's to 60's, is a period of rapid development of science and technology, radar, television broadcasting, the invention of integrated circuits, etc., the requirements of soft magnetic materials are also higher, the production of soft magnetic alloy thin strip and soft magnetic ferrite materials. Into the 1970s, with the development of telecommunications, automatic control, computer and other industries, developed a soft magnetic alloy for magnetic heads, in addition to the traditional crystalline soft magnetic alloy, and the rise of another class of materials - amorphous soft magnetic alloy.
2. Types of Commonly Used Soft Magnetic Cores
The three ferromagnetic elements, iron, cobalt, and nickel, are the basic components of magnetic materials.
By (main components, magnetic characteristics, structural characteristics) product form classification:
(1) Powder core: magnetic powder core, including: iron powder core, ferrosilicon aluminum powder core, high flux powder core (High Flux), pomo alloy powder core (MPP), ferrite cores
(2) with winding core: silicon steel sheet, pomo alloy, amorphous and nano-crystalline alloys
Three Characteristics and Applications of Commonly Used Soft Magnetic Cores
(1) Powder Cores
1. Magnetic Powder Cores
Magnetic powder cores are a kind of soft magnetic material pressed by mixing ferromagnetic powder particles with insulating medium. Because of the ferromagnetic particles are very small (0.5 ~ 5 micron used in high frequency), and by the non-magnetic insulating film material, so on the one hand, can be isolated from eddy currents, the material is suitable for higher frequencies; on the other hand, due to the gap effect between the particles, resulting in the material has a low permeability and constant permeability; and because of the small size of the particles, basically does not occur in the skin phenomenon, the change in the permeability with the frequency of the magnetic conductivity is also more stable. Stable. It is mainly used for high frequency inductors. The magnetic performance of the magnetic powder core mainly depends on the magnetic permeability of the powder material, the size and shape of the powder particles, their filling coefficient, the content of the insulating medium, molding pressure and heat treatment process.
Commonly used magnetic powder core iron powder core, PoMo alloy powder core and iron silicon aluminum powder core three.
The effective permeability of the core μe and inductance is calculated as follows: μe = DL/4N2S × 109
Which: D is the average diameter of the core (cm), L is the inductance (heng), N is the number of turns of the winding, S is the effective cross-sectional area of the core (cm2).
(1) Iron powder core
Commonly used iron powder core is composed of carbon-based ferromagnetic powder and resin carbon-based ferromagnetic powder. It is the least expensive of the powder cores. Saturation magnetic induction strength value of about 1.4T; permeability range from 22 ~ 100; initial permeability μi with frequency change stability is good; DC current superposition performance is good; but high loss at high frequencies.
Variation of initial permeability of iron powder core with DC magnetic field strength
Variation of initial permeability of iron powder core with frequency
(2). Permalloy powder cores
Permalloy powder cores are mainly molybdenum permalloy powder cores (MPP) and high flux powder cores (High Flux).
MPP is composed of 81% Ni, 2% Mo and Fe powder. The main features are: saturation magnetic induction value of about 7500Gs; wide range of permeability, from 14 to 550; the lowest loss in the powder core; excellent temperature stability, widely used in space equipment, open-air equipment, etc.; magnetostrictive coefficient is close to zero, and there is no noise generation when working at different frequencies. Mainly used in high quality factor Q filters below 300kHz, inductive load coils, resonant circuits, commonly used in LC circuits requiring high temperature stability, output inductors, power factor compensation circuits, etc., commonly used in AC circuits, and the most expensive in powder cores.
High flux powder core HF is composed of 50% Ni, 50% Fe powder. The main features are: saturation magnetic induction value of about 15000Gs; permeability range from 14 ~ 160; in the powder core has the highest magnetic induction strength, the highest DC bias capacity; core size is small. Mainly used in line filters, AC inductors, output inductors, power factor correction circuits, etc., commonly used in DC circuits, high DC bias, high DC and low AC used more. The price is lower than MPP.
(3) Iron Silicon Aluminum Powder Core (Kool Mμ Cores)
Iron Silicon Aluminum Powder Core consists of 9% Al, 5% Si, 85% Fe powder. It is mainly used as a replacement for Fe powder cores, with loss 80% lower than Fe powder cores, and can be used at frequencies above 8kHz; saturated magnetic inductance is around 1.05T; magnetic permeability ranges from 26 to 125; magnetostriction coefficient is close to 0, and there is no noise generation when working at different frequencies; it has a higher DC bias capability than MPP; and it has an optimal performance-to-price ratio. Mainly used in AC inductors, output inductors, line filters, power factor correction circuits and so on. Sometimes also replace the air gap ferrite for transformer core use.
2. Soft magnetic ferrite (Ferrites)
Soft magnetic ferrite is Fe2O3 as the main component of the ferrimagnetic oxide, using powder metallurgy production. There are Mn-Zn, Cu-Zn, Ni-Zn and other categories, of which Mn-Zn ferrite production and dosage is the largest, Mn-Zn ferrite resistivity is low, 1 ~ 10 ohm-meter, generally used in the frequency below 100kHZ. Cu-Zn, Ni-Zn ferrite resistivity of 102 ~ 104 ohm-meter, in the radio frequency band of 100kHz ~ 10 MHz. Frequency band loss is small, mostly used in radio antenna coils, radio IF transformers. There are a variety of core shapes, including E, I, U, EC, ETD shape, square (RM, EP, PQ), can shape (PC, RS, DS) and round. It is convenient in application. Since soft magnetic ferrite can get high permeability without using scarce materials such as nickel, and powder metallurgy method is suitable for mass production, so the cost is low, and because it is a sintered material with high hardness and insensitive to stress, it is convenient in application. And the magnetic permeability with frequency change characteristics of stability, in the 150kHz below basically remain unchanged. With the emergence of soft magnetic ferrite, magnetic powder core production has been greatly reduced, many of the original use of magnetic powder core are replaced by soft magnetic ferrite.
Domestic and foreign ferrite manufacturers are many, here only to the United States Magnetics company produces Mn-Zn ferrite as an example of its application. There are three types of basic materials: basic materials for telecommunications, broadband and EMI materials, and power-type materials.
The permeability of telecom ferrite ranges from 750 to 2300, with low loss factor, high quality factor Q, and stable temperature/time dependence of permeability, and it is the one with the slowest decrease of permeability in operation, which decreases by about 3% to 4% every 10 years. They are widely used in high Q filters, tuned filters, load coils, impedance matching transformers, and proximity sensors. Broadband ferrite is also often referred to as high permeability ferrite, permeability of 5000, 10,000, 15,000, respectively, which is characterized by a low loss factor, high permeability, high impedance/frequency characteristics. Widely used in *** mode filters, saturation inductors, current transformers, leakage protectors, insulation transformers, signal and pulse transformers, and more in broadband transformers and EMI. Power ferrites have a high saturation magnetic induction of 4000 to 5000 Gs. In addition, they have a low loss/frequency relationship and a low loss/temperature relationship. That is to say, with the increase of frequency, loss rise is not big; with the increase of temperature, loss change is not big. They are widely used in power chokes, parallel filters, switching power supply transformers, switching power supply inductors, and power factor correction circuits.
(II) with winding core
1. Silicon steel sheet core
Silicon steel sheet is a kind of alloy, adding a small amount of silicon in pure iron (generally below 4.5%) to form the iron-silicon alloy called silicon steel. This type of core has the highest saturation magnetic induction strength value of 20000Gs; because they have better magneto-electric properties, and easy to mass production, inexpensive, small impact of mechanical stress, etc., in the power electronics industry to obtain an extremely wide range of applications, such as power transformers, distribution transformers, current transformers and other cores. Is the soft magnetic material in the production and use of the largest amount of material. It is also the largest amount of magnetic materials for power transformers. Especially in the low-frequency, high-power is most suitable. Commonly used cold rolled silicon steel sheet DG3, cold rolled non-oriented electrical steel strip DW, cold rolled oriented electrical steel strip DQ, suitable for all kinds of electronic systems, household appliances in the middle and low power low-frequency transformers and chokes, chokes, inductors core, this kind of alloy toughness is good, can be punched, cut and other processing, the core of the stacked sheet and winding type. But the loss of high frequency increases sharply, the general use of frequency does not exceed 400 Hz. From the application point of view, the choice of silicon steel to consider two factors: magnetic and cost. For small motors, reactors and relays, can choose pure iron or low silicon steel; for large motors, can choose high silicon hot rolled silicon steel, single-orientation or non-orientation cold rolled silicon steel; for transformers often choose single-orientation cold rolled silicon steel. In the frequency of use, commonly used strip thickness of 0.2 ~ 0.35 mm; used in 400Hz, often choose 0.1 mm thickness is appropriate. The thinner the thickness, the higher the price.
2. PoMo alloy
PoMo alloy often refers to iron-nickel alloy, nickel content in the range of 30 ~ 90%. It is a very widely used soft magnetic alloy. Through the appropriate process, the magnetic properties can be effectively controlled, such as more than 105 initial permeability, more than 106 maximum permeability, coercivity as low as 2 ‰ OST, close to 1 or close to 0 rectangular coefficient, with a face-centered cubic crystal structure of the pomol alloy has a very good plasticity, and can be processed into a 1 μm of ultrathin strips and a variety of use of the form. Commonly used alloys are 1J50, 1J79, 1J85, etc. 1J50 saturation magnetic induction strength is slightly lower than that of silicon steel, but the permeability is dozens of times higher than that of silicon steel, and the iron loss is also 2 to 3 times lower than that of silicon steel. Made of higher frequency (400 ~ 8000Hz) transformer, no-load current is small, suitable for the production of 100W below the small higher frequency transformer. 1J79 has a good overall performance, suitable for high-frequency low-voltage transformers, leakage protection switch core, **** mode inductor core and current transformer core. 1J85 initial permeability can reach more than 100,000105, suitable for making a weak signal low-frequency or high-frequency input/output transformer. 1J85 initial permeability can reach more than 100,000105, suitable for making a weak signal low-frequency or high-frequency input/output transformer. The initial permeability of 1J85 can be more than 100,000105, which is suitable for weak signal low frequency or high frequency input/output transformer, ****mode inductor and high-precision current transformer.
3. Amorphous and Nanocrystalline soft magnetic alloys (Amorphous and Nanocrystalline alloys)
Silicon steel and PoMo alloy soft magnetic materials are crystalline materials, the atoms in the three-dimensional space to do the regular arrangement of the formation of a periodic array of structures, the existence of grains, grain boundaries, dislocations, interstitial atoms, the magnetic crystal anisotropy and other defects. It is unfavorable to the soft magnetic properties. From the magnetic physics, the atoms are irregularly arranged, there is no periodicity and grain boundaries of the amorphous structure to obtain excellent soft magnetic properties is very ideal. Amorphous metals and alloys are a new field of materials introduced in the 1970s. Its preparation technology is completely different from the traditional method, but the cooling rate of about one million degrees per second of the ultra-rapid cold solidification technology, from the liquid steel to the finished product of a thin strip molding, than the general cold rolled metal strip manufacturing process reduces the number of intermediate processes, this new process has been called on the traditional metallurgical process of a revolution. Due to the ultra-rapid cold solidification, alloy solidification of atoms too late to orderly arrangement of crystallization, the solid alloy is a long-range disordered structure, there is no crystalline alloy grains, grain boundaries exist, known as amorphous alloys, known as a revolution in metallurgical materials science. This amorphous alloy has many unique properties, such as excellent magnetism, corrosion resistance, wear resistance, high strength, hardness and toughness, high resistivity and electromechanical coupling properties. Because of its excellent performance and simple process, it has become the focus of research and development in the materials science community at home and abroad since the 1980s. At present, the United States, Japan, Germany has a perfect production scale, and a large number of amorphous alloy products gradually replace the silicon steel and PoMo alloy and ferrite influx to the market.
China since the 70's began the research and development of amorphous alloys, after the "Sixth Five-Year Plan", "Seventh Five-Year Plan", "Eighth Five-Year Plan" period of major scientific and technical After the completion of the "Sixth Five-Year Plan", "Seventh Five-Year Plan", "Eighth Five-Year Plan" period of major scientific and technological research projects, *** obtained 134 scientific research results, 2 national invention awards, 16 patents, there are nearly 100 varieties of alloys. The Iron and Steel Research Institute now has four amorphous alloy strip production lines and one amorphous alloy component core production line. It produces various kinds of stereotyped iron-based, iron-nickel-based, cobalt-based and nanocrystalline strips and cores, which are suitable for inverter power supply, switching power supply, power transformer, leakage protector, inductor core components, with an annual output value of nearly 20 million yuan. "Ninth Five-Year Plan" is to establish a thousand tons of iron-based amorphous production line, into the ranks of the international advanced level.
At present, the amorphous soft magnetic alloy to achieve the best single performance level:
Initial permeability μo = 14 × 104
Cobalt-based amorphous maximum permeability μm = 220 × 104
Cobalt-based amorphous coercivity Hc = 0.001 Oe
Cobalt-based amorphous rectangle ratio Br/Bs = 0.995
Cobalt-based amorphous coercivity Hc = 0.001 Oe
Cobalt-based amorphous coercivity Br/Bs = 0.995
Cobalt-based amorphous coercivity Hc = 0.995
Cobalt-based amorphous saturation magnetization strength 4πMs = 18300GsFe-based amorphous resistivity ρ= 270 μΩ/cm
Commonly used types of amorphous alloys are: iron-based, iron-nickel-based, cobalt-based amorphous alloys, and iron-based nanocrystalline alloys. Its national grade and performance characteristics are shown in the table and figure, for comparison, also lists the crystalline alloy silicon steel sheet, PoMo alloy 1J79 and ferrite the corresponding performance. These types of materials have different characteristics, in different aspects of the application.
Basic Composition and Characteristics:
1K101 Fe-Si-B system of fast-quenched soft magnetic ferroalloys
1K102 Fe-Si-B-C system of fast-quenched soft magnetic ferroalloys
1K103 Fe-Si-B-Ni system of fast-quenched soft magnetic ferroalloys
1K104 Fe-Si-B-Ni Mo Fast-quenched soft magnetic ferroalloys
1K105 Fe-Si-B-Cr (and others) fast-quenched soft magnetic ferroalloys
1K106 High-frequency, low-loss Fe-Si-B fast-quenched soft magnetic ferroalloys
1K107 High-frequency, low-loss Fe-Nb-Cu-Si-B fast-quenched soft magnetic ferroalloys with nanocrystals
1K201 High-pulse permeability, high-frequency, low-loss Fe-Si-B fast-quenched soft magnetic nanocrystalline ferroalloys
1K202 High Residual Magnetization Ratio Fast Hardening Soft Magnet Cobalt-based Alloys
1K203 High Magnetic Inductance Low Loss Fast Hardening Soft Magnet Cobalt-based Alloys
1K204 High Frequency Low Loss Fast Hardening Soft Magnet Cobalt-based Alloys
1K205 High Initial Magnetic Permeability Fast Hardening Soft Magnet Cobalt-based Alloys
1K206 Hardened high permeability cobalt-based soft magnetic alloys
1K501 Fe-Ni-P-B based fast quenching soft magnetic ferromagnetic cobalt-based alloys
1K502 Fe-Ni-V-Si-B based fast quenching soft magnetic ferromagnetic cobalt-based alloys
400 Hz: Silicon steel core Amorphous core
Power (W) 45 45
Cores Losses (W) 2.4 1.3
Excitation power (VA) 6.1 1.3
Total weight (g) 295 276
(1) Iron-based amorphous alloys (Fe-based amorphous alloys)
Fe-based amorphous alloys are composed of 80% Fe and 20% Si, B metal elements, which has a high saturation magnetic induction strength (1.0%). High saturation magnetic induction intensity (1.54T), iron-based amorphous alloys and silicon steel loss comparison
Magnetic permeability, excitation current and iron loss and other aspects are superior to the characteristics of silicon steel sheet, especially the iron loss is low (for the orientation of the silicon steel sheet 1/3-1/5), instead of silicon steel to do the distribution transformer can be energy-saving 60-70%. Iron-based amorphous alloy strip thickness of 0.03mm or so, widely used in distribution transformers, high-power switching power supplies, pulse transformers, magnetic amplifiers, intermediate-frequency transformers and inverter cores, suitable for the following 10kHz frequency
2) Fe-Ni based, cobalt-based amorphous alloy (Fe-Ni based-amorphous alloy)
Fe-Ni based-amorphous alloy is composed of 40% Ni, 40% Fe and 20% of the class of metal elements, it has a medium saturation magnetic induction strength [0.8T], high initial permeability and very high maximum permeability and high mechanical strength and excellent toughness. It has low iron loss at medium and low frequencies. Heat treatment in air does not oxidize, and a very good rectangular return line can be obtained after annealing by magnetic field. The price is 30-50% cheaper than 1J79. Iron-nickel-based amorphous alloys in the scope of application and the nickel PoMo alloy corresponds to, but the iron loss and high mechanical strength is far superior to the crystalline alloy; instead of 1J79, widely used in leakage switches, precision current transformer cores, magnetic shielding and so on. Iron-nickel-based amorphous alloy is the earliest development of domestic amorphous alloys, but also the current domestic amorphous alloys in the application of the largest amorphous varieties, the annual output of nearly 200 tons or so. Air heat treatment does not occur oxidation of iron-nickel-based amorphous alloy (1K503) to obtain the national invention patent and U.S. patent rights.
(4) Iron-based nanocrystalline alloys (Nanocrystalline alloy)
Iron-based nanocrystalline alloys are composed of iron elements, adding a small amount of Nb, Cu, Si, B elements of the alloy formed by the rapid solidification process of an amorphous material, this amorphous material can be obtained after heat treatment of 10-20 nm diameter microcrystals. This amorphous material can be obtained after heat treatment with a diameter of 10 -20 nm microcrystals, diffusely distributed in the amorphous matrix, known as microcrystalline, nanocrystalline materials or nanocrystalline materials. Nanocrystalline materials have excellent comprehensive magnetic properties: high saturation magnetic susceptibility (1.2T), high initial permeability (8×104), low Hc (0.32A/M), low high-frequency loss under high magnetic susceptibility (P0.5T/20kHz = 30W/kg), and high resistivity of 80 μΩ/cm, which is higher than that of pomolic alloys (50-60 μΩ/cm), and can be processed with a longitudinal or transverse magnetic field. High Br (0.9) or low Br value (1000Gs) can be obtained by longitudinal or transverse magnetic field treatment. It is the best material with the best comprehensive performance in the current market; applicable frequency range: 50Hz-100kHz, the best frequency range: 20kHz-50kHz. It is widely used in high-power switching power supply, inverter power supply, magnetic amplifier, high-frequency transformer, high-frequency converter, high-frequency choke cores, current transformer cores, earth leakage protection switches, and ****mode inductor cores.
(C) Comparison of the characteristics of commonly used soft magnetic cores
1. Comparison of the characteristics of magnetic powder cores, ferrite:
MPP cores: the use of ampere-turns < 200, 50Hz ~ 1kHz, μe : 125 ~ 500; 1 ~ 10kHz; μe : 125 ~ 200; > 100kHz: μe : 10 ~ 125 <
HF core: Using ampere-turns < 500, it can be used on larger power supplies, is not easily saturated under larger magnetic fields, and can ensure the minimum DC drift of the inductors, μe: 20 ~ 125
Iron Powder Cores: Using ampere-turns > 800, it can be used on higher magnetizing fields, and is not saturated, and can ensure the best stability of the inductors for AC and DC superimposed values. The frequency characteristics are stable within 200kHz; however, the high frequency loss is large, suitable for use below 10kHz.
FeSiAlF cores: Instead of iron powder cores, FeSiAlF cores can be used at frequencies greater than 8kHz, with DC bias capability between MPP and HF.
Ferrite: low saturation magnetic density (5000Gs), DC bias capability is the smallest
3. Comparison of the characteristics of silicon steel, pomolitic alloys, and amorphous alloys:
SiSiAlF and FeSiAlF materials have a high saturation magnetic induction value of Bs, but they have a low value for the effective permeability, especially in the high-frequency range;
Pomolitic alloys have a high initial permeability
Pomo alloy has high initial permeability, low coercivity and loss, stable magnetic properties, but Bs is not high enough, frequency greater than 20kHz, loss and effective permeability is not ideal, more expensive, complex processing and heat treatment;
Cobalt amorphous alloys have high permeability, low Hc, in a wide range of frequencies, low loss, near-zero saturation coefficient of magnetostriction, insensitive to stress, but the value of the Bs is low, expensive;
Fe-based amorphous alloys have high Bs values, low prices, but low effective permeability values.
Nanocrystalline alloys have magnetic permeability, Hc value close to crystalline high pomo alloys and cobalt-based amorphous, and the saturation magnetic susceptibility Bs is comparable to that of medium-nickel pomo alloys, and the heat treatment process is simple, which makes them an ideal cheap and high-performance soft magnetic material; although the Bs value of nanocrystalline alloys is lower than that of iron-based amorphous and silicon steels, but their high-frequency loss under high magnetic susceptibility is much lower than them, and they have better corrosion resistance and magnetic stability. Compared with ferrite, nanocrystalline alloys have two to three times higher operating magnetic inductance at lower than 50kHz on the basis of lower losses, and the core size can be more than twice as small.
Four, several commonly used magnetic devices in the core selection and design
Switching power supply in the use of magnetic devices, which are commonly used in soft magnetic devices: as the core device of the switching power supply main transformer (high-frequency power transformer), ****-mode chokes, high-frequency magnetic amplifiers, filtering choke, spike signal suppressor and so on. Different devices on the material performance requirements vary, as shown in the table for a variety of different devices on the performance requirements of magnetic materials.
(A), high-frequency power transformer
The size of the transformer core depends on the output power and temperature rise. Transformer design formula is as follows:
P=KfNBSI×10-6T=hcPc + hWPW
Which, P is the electric power; K is the coefficient related to the waveform; f is the frequency; N is the number of turns; S is the area of the core; B is the working magnetic inductance; I is the current; T is the temperature rise; Pc is the iron loss; PW is the copper loss; hc and hW is the coefficient determined by experiment.
From the above formula, it can be seen: a high working magnetic induction B can get a large output power or reduce the volume weight. However, the increase in B is limited by the Bs value of the material. And the frequency f can be increased by several orders of magnitude, which makes it possible to reduce the volumetric weight significantly. And low core losses reduce the temperature rise, which in turn affects the frequency of use and the selection of the operating magnetic inductance. Generally speaking, switching power supply on the main requirements of the material is: as low as possible high-frequency loss, sufficiently high saturation magnetic inductance, high permeability, sufficiently high Curie temperature and good temperature stability, some uses require a higher rectangular ratio, insensitive to stress, etc., good stability, low price. Single-ended transformer because the core operates in the first quadrant of the hysteresis loop, the requirements for the magnetic properties of the material are different from those of the main transformer described above. It is actually a single-ended pulse transformer, thus requiring a large B = Bm - Br, that is, the difference between the magnetic inductance Bm and remanent magnetization Br to be large; at the same time require a high pulse permeability. Especially for single-ended flyback switching main transformers, or energy storage transformers, the energy storage requirements are to be considered.
The amount of energy stored in the coil depends on two factors: one is the working magnetic susceptibility of the material Bm value or inductance L, and the other is the working magnetic field Hm or working current I, the energy storage W = 1/2LI2. This requires the material to have a sufficiently high value of Bs and a suitable permeability, often for a wide range of constant permeability materials. For transformers operating between ± Bm, the requirements of its hysteresis return area, especially at high frequencies, the return area should be small, and at the same time, in order to reduce no-load losses, reduce the excitation current, there should be a high permeability, the most suitable for the closed toroidal core, the hysteresis return is shown in the figure, this kind of core is used in double-ended or full-bridge operating state of the device.
Usually, metal crystalline materials to reduce iron loss at high frequencies is not easy, and for amorphous alloys, they do not exist because of the magnetic crystal anisotropy, metal inclusions and grain boundaries, etc., in addition, it does not exist in the long-range ordered atomic arrangement, its resistivity than the general crystalline alloys are 2-3 times higher, coupled with the fast cooling method of a formation of 15-30 microns in thickness Amorphous thin strip of 15-30 micron thickness, especially suitable for high frequency power output transformer. Has been widely used in inverter arc welding power supply, single-ended pulse transformer, high-frequency heating power supply, non-stop power supply, power transformer, communication power supply, switching power supply transformer and high-energy gas pedal, etc. Core, in the frequency of 20-50kHz, the power of 50kW or less, the transformer is the best core material.
In recent years the development of a new inverter arc welding power supply single-ended pulse transformer, with high-frequency high-power characteristics, so the transformer core material is required to have low high-frequency loss, high saturation magnetic induction Bs and low Br to obtain a large working magnetic induction B, so that the welder volume and weight reduction. Commonly used for high-frequency arc welding power supply core material for ferrite, although due to its high resistivity and low high-frequency loss, but its temperature stability is poor, the working magnetic inductance is low, the transformer volume and weight is large, can not meet the requirements of the new arc welding machine. The use of nanocrystalline toroidal iron core, due to its high Bs value (Bs>1.2T), high ΔB value (ΔB>0.7T), high impulse permeability and low loss, the frequency can be up to 100kHz. can make the core size and weight greatly reduced. In recent years, the inverter welder has been applied to tens of thousands of nanocrystalline iron core, users reflect the use of nanocrystalline transformer core and then with amorphous high-frequency inductors made of welder, not only small size, light weight, easy to carry, and the arc is stable, small splash, good dynamic characteristics, high efficiency and high reliability. This ring-shaped nanocrystalline iron core can also be used in high and medium frequency heating power supply, pulse transformer, non-stop power supply, power transformer, switching power supply transformer and high energy gas pedal and other devices. The core material can be selected according to the frequency of the switching power supply.
The toroidal nanocrystalline core has many advantages, but it also has the disadvantage of winding difficulties. In order to wind conveniently when the number of turns is large, high-frequency high-power C-type amorphous nanocrystalline iron core can be used. The use of low-stress binder curing and new cutting process made of amorphous nanocrystalline alloy C-type iron core performance is significantly better than silicon steel C-type iron core. At present, this kind of core has been used in batches for inverter welders and cutting machines. Inverter welding machine main transformer core and reactor core series: 120A, 160A, 200A, 250A, 315A, 400A, 500A, 630A series.
(B), pulse transformer core
Pulse transformer is a transformer used to transmit pulses. When a series of pulse duration of td (μs), pulse amplitude voltage
Um (V) for the unipolar pulse voltage added to the turns of N pulse transformer winding, at the end of each pulse, the magnetic induction intensity increment ΔB (T) in the core for: ΔB = Um td / NSc × 10-2 which Sc is the effective cross-sectional area of the core (cm2). That is, the magnetic induction increment ΔB is proportional to the area of the pulsed voltage (volt-second product). For unidirectional pulse output, ΔB = Bm-Br , and if demagnetizing windings are added to the pulse transformer core, ΔB = Bm + Br . In the pulsed state, the ratio of the ΔB of the dynamic pulse hysteresis loop to the corresponding ΔHp is the pulse permeability μp. The ideal pulse waveform is a rectangular pulse waveform, but due to the parameters of the circuit, the actual pulse waveform varies from a rectangular pulse and is often distorted. For example, the rise time tr of the pulse front is proportional to the leakage inductance Ls of the pulse transformer, the distributed capacitance Cs due to the windings and structural parts, the pulse top drop λ is inversely proportional to the excitation inductance Lm, and the eddy current loss factor also affects the output pulse waveform.
Leakage inductance of pulse transformer Ls = 4βπN21 lm / h
Primary excitation inductance of pulse transformer Lm = 4μπp Sc N2 / l × 10-9
Eddy current loss Pe = Um d2td lF / 12 N21 Scρ
β is the coefficient related to the winding structure type, lm is the average coil length, and h is the average coil length. turn length, h is the width of the winding coil, N1 is the number of primary winding turns, l is the average magnetic circuit length of the core, Sc is the cross-sectional area of the core, μp is the pulsed permeability of the core, ρ is the resistivity of the core material, d is the thickness of the core material, and F is the pulse repetition frequency.
From the above formula, it can be seen that in a given number of turns and core cross-sectional area, the larger the pulse width, the greater the change in the magnetic induction strength of the core material required ΔB; in the pulse width is given to increase the change in the magnetic induction strength of the core material ΔB, the core of the pulse transformer can be greatly reduced cross-sectional area and the number of turns of the magnetizing windings, you can reduce the size of the pulse transformer. To reduce the distortion of the pulse waveform front, the leakage inductance and distribution capacitance of the pulse transformer should be minimized, for which the number of turns of the winding of the pulse transformer needs to be as small as possible, which requires the use of materials with high pulse permeability. In order to reduce the top drop, to increase the primary excitation inductance Lm as much as possible, which requires the core material has a high impulse permeability μp. In order to reduce eddy current losses, should be used for high resistivity, as thin as possible thickness of the soft magnetic strip as the core material, especially for the repetition frequency, pulse width of pulse transformers is even more so.
Pulse transformer core material requirements are:
① high saturation magnetic induction Bs value;
② high impulse permeability, with a small core size to obtain a sufficiently large excitation inductance;
③ high power unipolar pulse transformer requires the core with a large magnetic induction increment ΔB, the use of low remanence magnetic induction material; when the use of additional DC bias, the requirements of the core with a high resistivity, the use of the core material, the use of the core material. When using additional DC bias, the core is required to have a high rectangular ratio, small coercivity Hc.
④ Small power pulse transformers require a high starting pulse permeability of the core;
⑤ Small losses.
Ferrite cores have high resistivity, wide frequency range, low cost, and are more commonly used in low power pulse transformers, but their ΔB
and μp are low, poor temperature stability, and are generally used in occasions where the top drop and trailing edge requirements are not high.
(iii). Inductor Core
The iron core inductor is a basic component, in the circuit inductor for the current change has the role of impedance, in electronic equipment in a wide range of applications. The main requirements for inductors are as follows:
① When working at a certain temperature for a long time, the rate of change of inductance over time should be kept to a minimum;
② The temperature coefficient of inductance should be kept within the allowable limit for a given range of operating temperatures;
③ Inductors should have low electrical and magnetic losses;
④ Low nonlinear divergence;
④ Low nonlinear divergence;
⑤ Low inductance and high magnetic losses;
⑥ Low inductance and high magnetic losses;
7 Low inductance and high magnetic losses.
⑤ Low price and small size.
Inductive components are closely related to inductance L, quality factor Q, core weight W, and DC resistance R of the winding.
The ability of an inductor L to resist AC current is expressed in terms of the inductive resistance value ZL: ZL = 2πfL , the higher the frequency f, the greater the inductive resistance value ZL?
Inductance L resistance to AC current is expressed by the inductance value ZL: ZL = 2πfL , the higher the frequency f, the greater the inductance value ZL?