The function of the power transformer is transmitted power and voltage transformation and insulation isolation, as a kind of main soft magnetic magnetic element, in the power supply technology and widely used in the power electronic technology. According to the size of the transmit power, the power transformer can be divided into several files: more than 10 kVA for high-power, 10 kVA ~ 0.5 kVA is in power, 0.5 kVA ~ 25 va for small power, 25 va micro power are as follows. The transmit power is different, the design of power transformer is different also, should be self-evident. Someone according to its main function is to transmit Power, the English name \"Power Transformers\" translated into \"Power transformer\", is still used in many literatures. What is called \"power transformer\", or called \"power transformer\"? To be in terms of science and technology authority to choose decision. The same English name \"Power Transformer\", also can be translated into \"Power Transformer. Power transformer is mainly used for power distribution system in the power transfer and voltage transformation and insulation isolation effect, the original side voltage of 6 kv high voltage, power minimum 5 kVA, biggest more than tens of thousands of kVA. Working principle of the power transformer and power transformer, although are based on the principle of electromagnetic induction, but the power transformer which emphasizes power transmission, and emphasizes the high insulation isolation voltage, whether in the core coil, and the design of insulation structure, with small power transmission, low voltage insulation isolation of power transformers have significant differences, more power transformer design optimization design conditions can not be regurgitated in power transformer applications. Is not the same as the design method of power transformer and power transformer, also should be self-evident. High frequency power transformer is the working frequency than medium frequency power supply transformer (10 KHZ), mainly used in high frequency switching power supply for high frequency switching power supply transformer, there are also used in high frequency inverter power supplies and high frequency inverter welding machine for high frequency inverter power supply transformer. According to the working frequency of high and low, can be divided into several levels: 10 KHZ ~ 50 KHZ, 50 KHZ to 100 KHZ, 100 KHZ to 500 KHZ, 500 KHZ to 1 MHZ, above 1 MHZ. Transmit power is larger, the work frequency is lower; Transmit power is small, working frequency is higher. In this way, the difference of both the working frequency, and the difference of transmission power, working frequency power transformer design method of different class, also should be self-evident. As mentioned above, the author of the high frequency power transformer design principles, requirements and procedures does not exist error concept, but in early July 2003, reading power technology applications, 2003, 6 particularly recommended 2 article on high frequency magnetic components design, produced doubts, feel some problems worthy of further discussion, so to write this article. As the power source technology application \"editor's note:\" concrete analysis of concrete conditions, \"the purpose of writing, it is also the most difficult in detail and try to choose one of the magnetic components of high frequency power transformer design issue clear. If there is any wrong place, please correct me authors and readers. 2 the design principle of high frequency power transformer High frequency power transformer as a kind of product, natural with the property of commodity, and therefore the design principle of high frequency power transformers and other commodities, is conducted under the specific conditions of use of specific functions in the pursuit of best price performance ratio. Sometimes may lay particular stress on performance and efficiency, and sometimes may lay particular stress on prices and costs. Now, light, thin, short, small, become the development direction of high frequency power supply, is to emphasize to reduce costs. Which become a big difficulty of high frequency power transformer, need more work in this area. So high frequency power transformer in the context of \"design\", only talk about performance, don't talk about cost, is a big drawback, if you can consider carefully the design principle of high frequency power transformer, the pursuit of a better price performance ratio, the transmission of less than 10 va monolithic switch power supply high frequency transformer, shall be designed more light, thin, short, small package. Don't talk about cost and market value rule is relentless! Many good product performance, often due to the price cannot be accepted by the market and have been left out and eliminated. Often a new product was finally cost veto. Why not some \"energy saving JieQian\" products in the market promotion worth pondering. The product cost, not only include the cost of materials, the production cost, also includes research and development costs, design costs. Therefore, in order to save time, according to past experience, iron losses of high frequency power transformer leakage inductance of the proportion of copper loss, and the proportion of excitation inductance, the original and deputy while winding loss ratio, current density, providing some reference data, filling degree of the window, winding wires and recommend some structure plan, what's wrong? Why must be according to the back and forth due to the calculation and simulation, no concept of error? The author in the 1980 s in the development of the high frequency magnetic switch power amplifier type, subject to the minimum temperature, optimization design was carried out on the high frequency power transformer. Due to heat obstruct to determine, results and the test sample is far, had to be revised again. Now some of the company's core product manuals, in order to shorten the time to design high frequency power transformer, listed some simplified design formula, some use a table to list core under a certain working frequency transmitting power. This is for the sake of users, and promote a win-win situation, the company's products is completely in line with the market rules of behavior, is no need to differentiate the wrong concepts. Problem is to provide reference data, the recommended scheme is experience summary? Is there a universal? Including some \"differentiate\" the proposed claim, need to be tested, to stand up. In conclusion, remember: the high frequency power transformer is a kind of products (goods), design principle is completed in concrete under the conditions of use of specific functions in the pursuit of best price performance ratio. The sole criterion for testing the design is a design of the products can withstand the test of the market. 3 high frequency power transformer design requirements As the starting point according to the design principle, high frequency power transformer can be put forward four design requirements: using conditions, complete functions, improve efficiency, reduce the cost. Conditions of use conditions of use include two aspects: 3.1 reliability and electromagnetic compatibility. Only pay attention to the reliability before, now due to the increasing environmental protection consciousness, must pay attention to the electromagnetic compatibility. The use of reliability refers to the specific conditions, the high frequency power transformer can work normally at the service life. General conditions of use of the high frequency power transformer is the biggest impact of the environment temperature. Some soft magnetic materials, Curie point is lower, is sensitive to temperature. For example: manganese zinc soft magnetic ferrite, Curie point is 215 ℃, the magnetic flux density, permeability and loss with the temperature changes, so in addition to the normal temperature 25 ℃, even given 60 ℃, 80 ℃, 100 ℃ when the various reference data. Therefore, limit the working temperature of manganese zinc soft magnetic ferrite core under 100 ℃, is the environment temperature of 40 ℃, the temperature rise only allow below 60 ℃, equivalent to A grade insulating material temperature. The manganese zinc soft magnetic ferrite core matching with electromagnetic wire and insulation parts, generally USES the E and B insulation materials, using class H insulation triple insulated electromagnetic wire and polyamide membrane, is a small pond? How much cost? Is it because class H insulation of high frequency power transformer optimization design, can reduce the volume of 1/2 ~ 1/3? If yes, please give the concrete instance data. The authors have developed class H insulation power frequency 50 hz, 10 kva dry type transformer, and class B insulation power frequency 50 hz, 10 kva compared to dry type transformer, reduced volume of 15% to 20%, has been considerable. Original volume is relatively small high-frequency 100 khz10va high frequency power transformer, such as the secondary winding adopts triple insulated wire, can reduce the volume of 1/2 ~ 1/3, it must be a very valuable experience. Please about the author introduced optimization design scheme for the readers to learn. Electromagnetic compatibility is refers to the high frequency power transformer does not produce electromagnetic interference of the outside world, and can withstand external electromagnetic interference. Electromagnetic interference including audible audio noise and smell of the high frequency noise. One of the main causes of high frequency electromagnetic interference with the power transformer is the core of magnetostriction. Magnetostrictive big soft magnetic materials, the electromagnetic interference. Manganese zinc, for example, soft magnetic ferrite, magnetostrictive coefficient for lambda S 21 x 10-6, more than 7 times that of oriented silicon steel, high permeability permalloy and 20 times bigger than the amorphous alloy, microcrystalline nanocrystalline alloy is more than 10 times. So the manganese zinc soft magnetic ferrite core of electromagnetic interference. The main reason of electromagnetic interference with high frequency power transformer and suction between the core and winding repulsion between the wires. These changes in power frequency in accordance with the working frequency of high frequency power transformer. Therefore, the working frequency is about 100 KHZ high frequency power transformer, no special reason is not below 20 KHZ audio noise. Since the proposed under 10 w monolithic switch power supply, audio frequency, noise of about 10 KHZ ~ 20 KHZ, there must be the reason. Because there is no noise spectrum plotted on a graph, the specific reason say not clear, but is produced by high frequency power transformer itself is unlikely, there is no need to use glass beads cement bonding magnetic core. As for adopting this bonding process audio noise can be reduced 5 db, please give examples and data, and elaborate on the cause of the noise, was believable. Is to prevent electromagnetic interference shielding, a good way to increase the high frequency power transformer electromagnetic compatibility. But in order to prevent the spread of the electromagnetic interference of high frequency power transformer, magnetic core structure in the design and structure design winding should also take corresponding measures, just by adding outer screen is not necessarily the best solution, because it can prevent radiation interference, can't stop the conducted interference. 3.2 completion High frequency power transformer completion has 3: power transmission, voltage transformation and insulation isolation. There are two ways to transfer power. The first is a transformer power transmission way, on the original winding voltage, flux change in magnetic core, make each winding induction voltage, so that the electric power transferred to the deputy from the original side. In the process of power transmission, magnetic core is divided into single magnetic flux direction changes and the two sides to change two work modes. Single direction changes in work patterns, magnetic flux density from the maximum Bm changes to the rest of the magnetic flux density Br, or varying from Br to Bm. Magnetic flux density change value Δ B = Bm - Br. In order to improve the Δ B, hope big Bm, Br. From the two sides to the changes in work patterns flux degrees + Bm changes to - Bm, or from Bm changes to + Bm. Magnetic flux density change value Δ B = 2 Bm, in order to improve the Δ B, hope Bm is big, but it does not request the Br is small, both single direction changes in work patterns and the two sides to the changes in work patterns, transformer power transmission is not directly related to core permeability. The second is inductor power transmission way, the original winding input power, make the magnetic core excitation, a magnetic energy storage, then through demagnetization winding induction voltage, into electrical energy release to the load. Transmit power depends on the magnetic core of inductive energy storage, and energy storage is determined by the original winding inductance. Inductance is associated with core permeability, high permeability, large amount of inductance, energy storage, and not directly related to the magnetic flux density. Although the power transmission way is different, the requirements of the core parameters are different, but in the high frequency power transformer design, the selection of core material and parameters is still a main content of design. In the context of power transformers \"design\", it's a pity that the lack of this one of the main content. Only in the loss of \"communication\", put forward the BAC typical value of 0.04 ~ 0.075 T. Obviously, the high frequency power transformer is to use an inductive power transfer way, why don't mention of permeability, the BAC is not clear. Check, in 2003, 1/2 power technology application, the same main switch power \"design\" written by the author, is a list of the choice of the \"core\", no mention of permeability, just put forward the maximum magnetic flux density Bm is 0.275 T. Magnetic flux density waveform change because there is no picture, not clear after the BAC and handled in the Bm is the same: why is 6.8 ~ 3.7 times from BAC and Bm? Less clear, choose what kind of soft magnetic ferrite materials? Why did you choose this type? Both the no instructions, had to let the reader to guess. Voltage transformation through the primary side and the auxiliary winding circle number ratios. Regardless of the power transmission is a kind of way, which the original and deputy while voltage transformation ratio is equal to the primary winding and the auxiliary winding turn ratio, as long as it doesn't change the rate of turn, would not affect the voltage transformation. However, winding circle number associated with the leakage inductance of the high frequency power transformer. The leakage inductance of the size and the original winding is proportional to the square of the number of turns. It is interesting to note that the leakage inductance can rule a number? Power supply technology, 2003, 6 also published two articles with a different story. \"Design\" the article said: \"for a high-frequency transformer with insulation and safety standards, the leakage inductance of the amount shall be the subordinated primary inductance of 1% ~ 3% when open\". \"Differentiate\" the article said: \"a lot of technology in the list, indicate the leakage inductance of the leakage inductance of the magnetizing inductance or = 1%.\"