Folding characteristics
Electronic transformer, the input is AC220V, the output is AC12V, and the power can reach 50W-300W. It is mainly a transformer circuit developed on the basis of a high-frequency electronic ballast circuit. It has stable performance, small size, and high power, thus overcoming the disadvantages of traditional silicon steel sheet transformers such as large, heavy and high price.
An electronic transformer is an unregulated switching power supply, which is actually a kind of inverter. First, the AC power is rectified into DC power. Then, a high-frequency oscillator is used to form a high-frequency oscillator with electronic components to convert the DC power into a high-frequency AC power. The required voltage is output through a switching transformer and then rectified twice for use by electrical appliances. Switching power supply has the advantages of small size, light weight and low price, so it is widely used in various electrical appliances.
According to the different driving modes of the high-frequency switch tube, it can be divided into self-excited oscillation type and separately excited type.
use
The application of electronic transformers in traditional lighting fixtures is very common, such as fluorescent lamps, desk lamps, energy-saving lamps, advertising lamps, etc. Almost all can use electronic transformers, and after adopting electronic transformers, starters can be omitted. In LED lighting, most new products also use electronic transformers. Mainly, the electronic transformer has high efficiency, low cost, saving iron and copper materials, small structure and light weight in terms of voltage transformation function. The disadvantage is that the withstand voltage and high current impact performance is worse than that of ferrous transformers.
Application in power supply technology
The electronic transformer in the power supply device generally uses an electronic transformer (soft magnetic electromagnetic element) made of a soft magnetic core. Although there are air-core electronic transformers and piezoelectric ceramic transformers that do not use soft magnetic cores, by the beginning of the 21st century, most electronic transformers in power supply devices still use soft magnetic cores.
Therefore, discuss the relationship between power supply technology and electronic transformers: the role of electronic transformers in power supply technology, the requirements of power supply technology for electronic transformers, the influence of new soft magnetic materials and new magnetic core structures in electronic transformers on the development of power supply technology, certain Will arouse the interest of friends in the power supply industry and soft magnetic materials industry. Baidu Baike puts forward some opinions in order to facilitate dialogues, exchanges and common development between the power supply industry and the electronic transformer industry and the soft magnetic material industry on the related issues of electronic transformers and soft magnetic materials.
1. The requirements of power supply technology for electronic transformers
The requirement of power supply technology for electronic transformers, like all products as commodities, is to pursue the best performance-to-price ratio while completing specific functions under specific conditions of use. Sometimes price and cost may be emphasized, and sometimes efficiency and performance may be emphasized. Light, thin, short, and small are the development directions of electronic transformers, emphasizing cost reduction. Starting from the general requirements, four specific requirements can be drawn for electronic transformers: use conditions, complete functions, improve efficiency, and reduce costs.
2. Use conditions The use conditions of electronic transformers include two aspects:
Reliability and electromagnetic compatibility. Reliability means that the electronic transformer can work normally to the end of its service life under specific conditions of use. In general use conditions, the environmental temperature has the greatest impact on electronic transformers. The parameter that determines the strength of electronic transformers affected by temperature is the Curie point of soft magnetic materials. Soft magnetic materials have a high Curie point and are less affected by temperature; soft magnetic materials have a low Curie point and are more sensitive to temperature changes and are greatly affected by temperature.
For example, the Curie point of Mn-Zn ferrite is only 215°C, which is relatively low. The magnetic flux density, permeability and loss all change with temperature. In addition to the normal temperature of 25°C, 60°C and 80°C are required. , Various parameter data at 100℃. Therefore, the operating temperature of Mn-Zn ferrite cores is generally limited to below 100°C, that is, when the ambient temperature is 40°C, the temperature rise must be less than 60°C. The Curie point of cobalt-based amorphous alloys is 205°C, which is also low, and the operating temperature is also limited to below 100°C. The Curie point of iron-based amorphous alloy is 370℃, and it can be used below 150℃~180℃. The Curie point of high permeability permalloy is 460℃ to 480℃, and it can be used below 200℃~250℃. The Curie point of microcrystalline nanocrystalline alloy is 600℃, and the Curie point of oriented silicon steel is 730℃, and it can be used at 300℃~400℃. (Electromagnetic compatibility means that electronic transformers neither produce electromagnetic interference to the outside world, but also can withstand external electromagnetic interference. Electromagnetic interference includes: audible audio noise and inaudible high-frequency noise. The main reason for electronic transformer electromagnetic interference It is the magnetostriction of the magnetic core. Soft magnetic materials with a large magnetostriction coefficient will produce large electromagnetic interference.) The magnetostriction coefficient of iron-based amorphous alloys is usually the maximum (27~30)×10-6, which must be used Measures to reduce noise suppression interference. The magnetostriction coefficient of high-permeability Ni50 permalloy is 25×10-6, and the magnetostriction coefficient of manganese-zinc ferrite is 21×10-6. The above three kinds of soft magnetic materials are materials that are prone to electromagnetic interference, so pay attention to them in application. The magnetostriction coefficient of 3% oriented silicon steel is (1~3)×10-6, and the magnetostriction coefficient of microcrystalline nanocrystalline alloy is (0.5~2)×10-6. These two kinds of soft magnetic materials are relatively easy to produce electromagnetic interference materials. The magnetostriction coefficient of 6.5% silicon steel is 0.1×10-6, the magnetostriction coefficient of high permeability Ni80 permalloy is (0.1~0.5)×10-6, and the magnetostriction coefficient of cobalt-based amorphous alloy is 0.1 ×10-6 or less. These three soft magnetic materials are materials that are not prone to electromagnetic interference. The frequency of electromagnetic interference generated by magnetostriction is generally the same as the operating frequency of an electronic transformer. If there is electromagnetic interference lower or higher than the operating frequency, it is caused by other reasons.
3. Complete function The electronic transformer is divided into two main types: transformer and inductor in terms of function.
The functions performed by special components are discussed separately.
There are 3 functions completed by the transformer: power transmission, voltage conversion, and insulation isolation;
The inductor has two functions: power transmission and ripple suppression. There are two ways of power transfer.
The first is the transformer transmission method, that is, the alternating voltage applied to the primary winding of the transformer produces a magnetic flux change in the magnetic core, causing the secondary winding to induce a voltage, which is applied to the load, so that the electric power is transmitted from the primary side to the secondary side. . The size of the transmitted power is determined by the induced voltage, which is determined by the magnetic flux density variable ΔB per unit time. ΔB has nothing to do with magnetic permeability, but with saturation magnetic flux density Bs and residual magnetic flux density Br. From the perspective of saturation magnetic flux density, the order of Bs of various soft magnetic materials from large to small is: iron-cobalt alloy is 2.3~2.4T, silicon steel is 1.75~2.2T, iron-based amorphous alloy is 1.25~1.75T, The iron-based microcrystalline nanocrystalline alloy is 1.1~1.5T, the iron-silicon aluminum alloy is 1.0~1.6T, the high magnetic permeability iron-nickel permalloy is 0.8~1.6T, the cobalt-based amorphous alloy is 0.5~1.4T, iron-aluminum The alloy is 0.7-1.3T, the iron-nickel-based amorphous alloy is 0.4-0.7T, and the manganese-zinc ferrite is 0.3-0.7T. As the core materials of electronic transformers, silicon steel and iron-based amorphous alloys are dominant, while manganese-zinc ferrite is at a disadvantage. Power transfer
The second is the inductor transmission method, that is, the electrical energy input to the inductor winding causes the magnetic core to be energized and converted into magnetic energy for storage, and then demagnetized into electrical energy and released to the load. The size of the transmitted power is determined by the energy storage of the inductor core, which is determined by the inductance of the inductor. The inductance is not directly related to the saturation magnetic flux density, but is related to the magnetic permeability. The magnetic permeability is high, the inductance is large, the energy storage is large, and the transmission power is large. The order of permeability of various soft magnetic materials is as follows: Ni80 permalloy is (1.2~3)×106, cobalt-based amorphous alloy is (1~1.5)×106, iron-based microcrystalline nanocrystalline alloy It is (5~8)×105, iron-based amorphous alloy is (2~5)×105, Ni50 permalloy is (1~3)×105, silicon steel is (2~9)×104, manganese zinc ferrite The body is (1~3)×104. As the magnetic core material of the inductor, Ni80 permalloy, cobalt-based amorphous alloy, and iron-based microcrystalline nanocrystalline alloy are dominant, while silicon steel and manganese-zinc ferrite are at a disadvantage. The size of the transmission power is also related to the number of transmissions per unit time, that is, related to the working frequency of the electronic transformer. The higher the operating frequency, the greater the transmitted power under the same size of magnetic core and coil parameters. The voltage conversion is completed by the turns ratio of the primary winding and the secondary winding of the transformer. Regardless of the size of the power transmission, the voltage transformation ratio of the primary side and the secondary side is equal to the ratio of the primary winding and the secondary winding turns. Insulation isolation is accomplished by the insulation structure of the primary winding and the secondary winding of the transformer. The complexity of the insulation structure is related to the magnitude of the applied and transformed voltage. The higher the voltage, the more complex the insulation structure. Ripple suppression is achieved by the self-induction potential of the inductor. As long as the current passing through the inductor changes, the magnetic flux generated by the coil in the magnetic core will also change, causing a self-induced potential at both ends of the inductor's coil, the direction of which is opposite to the direction of the applied voltage, thereby preventing the current from changing. The change frequency of the ripple is higher than the fundamental frequency, and the current frequency of the current ripple is larger than the fundamental frequency, so it can be more suppressed by the self-induction potential generated by the inductor. The ability of inductors to suppress ripple depends on the size of the self-induced potential, that is, the magnitude of the inductance, which is related to the permeability of the magnetic core. Ni80 permalloy, cobalt-based amorphous alloy, iron-based microcrystalline nanocrystalline alloy The magnetic permeability is high, which is at an advantage, while silicon steel and manganese-zinc ferrite have low magnetic permeability and are at a disadvantage.
4. Improving efficiency is a universal requirement for power supplies and electronic transformers.
a. Improve the efficiency of electronic transformers.
For example: 100VA power transformer, when the efficiency is 98%, the loss is only 2W and not much. But with hundreds of thousands and millions of power transformers, the total loss may reach hundreds of thousands of watts, or even millions of watts. In addition, many power transformers have been running for a long time, and the total annual loss is considerable, possibly reaching tens of millions of kWh. Obviously, improving the efficiency of electronic transformers can save electricity. After saving power, fewer power stations can be built. After building fewer power stations, less coal and oil can be consumed, CO2, SO2, NOx, waste gas, sewage, soot and ash can be reduced, and environmental pollution can be reduced. It not only saves energy, but also has the dual social and economic benefits of protecting the environment. Therefore, improving efficiency is a major requirement for electronic transformers.
b. Design of electronic transformer
The loss of electronic transformer includes core loss (iron loss) and coil loss (copper loss). Iron loss exists as long as the electronic transformer is put into operation, and is the main part of the loss of the electronic transformer. Therefore, selecting the core material based on the iron loss is the main content of the electronic transformer design, and the iron loss has also become a main parameter for evaluating soft magnetic materials. The core loss is related to the working magnetic flux density and working frequency of the magnetic core of the electronic transformer. When introducing the core loss of soft magnetic materials, it must be explained under what working magnetic flux density and what working frequency the loss is.
For example: P0.5/400, which means the iron loss under the working magnetic flux density of 0.5T and working frequency of 400Hz. P0.1/100k represents the iron loss at a working magnetic flux density of 0.1T and a working frequency of 100kHz. Soft magnetic materials include hysteresis loss, eddy current loss and residual loss. The eddy current loss is inversely proportional to the resistivity ρ of the material. The larger the ρ, the smaller the eddy current loss. The order of ρ of various soft magnetic materials from large to small is: 108~109μΩ?cm for manganese-zinc ferrite, 150~180μΩ?cm for iron-nickel-based amorphous alloys, and 130~150μΩ?cm for iron-based amorphous alloys. cm, cobalt-based amorphous alloy is 120~140μΩ?cm, high permeability permalloy is 40~80μΩ?cm, iron-silicon-aluminum alloy is 40~60μΩ?cm, iron-aluminum alloy is 30~60μΩ?cm, silicon steel is 40~50μΩ?cm, iron-cobalt alloy is 20~40μΩ?cm. Therefore, the ρ of Mn-Zn ferrite is 106 to 107 times higher than that of metallic soft magnetic materials, and the eddy current is small in high frequency, and the application is dominant. But when the working frequency exceeds a certain value, the insulator in the magnetic particles of Mn-Zn ferrite is broken down and melted, ρ becomes quite small, and the loss rapidly rises to a high level. This working frequency is the same as that of Mn-Zn ferrite. Limit operating frequency.
The role of each part
Electronic transformer for spotlights, downlights, etc. used in general shop lighting. 220v AC to DC 12v50W, there is a 7-terminal magnet coil inside. 3 resistors, 6 diodes, 4 capacitors, 2 transistors. Its functions are:
Resistance: 1 start resistance, 2 current limiting resistance, 3 stabilizing resistance
Diodes: Four diodes are used for rectification, the other two are also used for rectification
Capacitor: filtering
Triode: One is a switching transistor, the other is for starting