What are the characteristics of the development direction of high frequency transformers?
What are the characteristics of the development direction of high frequency transformers?
Do you know what the characteristics of high frequency transformers are? Do you know what is the density of High frequency transformers? Do you know what is the direction of high frequency transformers?
The biggest feature of high-frequency electronic transformers is high frequency. From the working principle, the working frequency is increased, which can reduce the volume and weight of the transformer, that is, to achieve short and light weight, thereby increasing the transmission power per unit volume (or weight), that is, high power density.
These are the inherent characteristics of the high-frequency transformer itself and the direct result, and can not simply high-frequency, short and light, high power density, as the development direction of high-frequency transformers.
From the aspects of the overall structure of the high-frequency transformer, the core material and structure, the coil material and the structure, some suggestions for the development direction are proposed.
1, the overall structure
In order to adapt to the increasingly light and thin electronic devices, a major development direction of high-frequency electronic transformers is to develop from three-dimensional structures to planar structures, chip structures and thin-film structures, thus forming new high-frequency electronic transformers from generation to generation: planar transformers, Chip transformer, thin film transformer. The development of the overall structure of high-frequency electronic transformers not only forms a new core structure and coil structure, but also adopts new materials, and brings new development directions in terms of design and production process. In terms of design, in addition to studying the electromagnetic field distribution of various new structures, how to achieve the optimal optimization design, we must also study the various problems of the multilayer structure. In the production process, various new processing methods are studied to ensure the consistency of performance and the mechanization and automation of the processing technology.
In the MHz-class high-frequency electronic transformers, more and more applications are using hollow transformers. It is also the research and development direction of the structure, design method, manufacturing process and application characteristics of the hollow transformer. In addition, the research on high-frequency electronic transformers with new working principles such as piezoelectric transformers is also the development direction. After nearly ten years of research and development, piezoelectric transformers have been put into practical use in some fields.
The optimization and specific design of the overall structural scheme by computer is one of the main development directions of various electronic devices, and of course, it is also a major development direction of high-frequency electronic transformers. This reduces design time, reduces material usage, shortens production cycles, and reduces costs.
2, magnetic core material and structure
The magnetic core is the most critical component in high-frequency electronic transformers that use soft magnetic materials and operate on the principle of electromagnetic induction. The main development direction of magnetic core materials is to reduce losses, widen the temperature range used and reduce costs. The main development direction of the core structure is how to form a planar core, a chip core and a thin film core with the best shape and size (parameters for electromagnetic performance, heat dissipation, amount and cost).
Nowadays, various soft magnetic materials are constantly being improved and developed to compete in the market of high frequency electronic transformers.
Soft ferrite is the main core material used in high-frequency electronic transformers. The development direction is to develop new varieties with better performance and new processes to reduce costs. In terms of new materials, TDK Corporation of Japan developed PC95, a wide temperature and low loss material in 2003, with a loss of less than 350 mW/cm3 (at 100 kHz x 200 mT) in the temperature range of 25 °C to 120 °C.
The loss is minimal at 80 ° C, 280 mW / cm 3 . Bs is 540 mT at 25 ° C, and Bs is 420 mT at 100 ° C. A high temperature and high saturation magnetic dense material PE33 was also developed, with a Curie point Tc > 290 ° C and a Bs of 450 mT at 100 ° C. At 100 ° C, 100 kHz × 200 mT, Pc ≤ 1100 mW / cm3, Japan FDK company, Germany EPCOS company, Ferrocube company also developed a similar high temperature and high saturation magnetic density material.
There are also many new varieties of high magnetic permeability materials. For example, TDK's pulse transformer uses H5C5, and μi is about 30,000. The anti-electromagnetic interference inductor uses HS10, which has good frequency characteristics and impedance characteristics. It still has a high magnetic permeability at 500 kHz, although the initial magnetic permeability is not high, only about 10,000. The high magnetic permeability and high saturation magnetic dense material DN50 has a Bs of 550 mT at 25 ° C, a Bs of 380 mT at 100 ° C, a μi of about 5200, and a Curie temperature Tc ≥ 210 ° C.
In terms of new processes, self-propagating high-temperature synthesis (SHS) is a research hotspot in recent years. Its principle is to use the chemical energy inside the reactants to synthesize materials. The whole process is extremely simple, low energy consumption, high production efficiency and product purity, no pollution to the environment, and has successfully synthesized Mg, MgZn, MnZn, NiZn ferrite, and is being industrialized.
Spark plasma sintering (SPS) can successfully produce multi-layer MnZn ferrite and permalloy composite soft magnetic material core, while having high frequency and low loss characteristics of MnZn ferrite and high permeance of permalloy The high saturation magnetic density characteristics of this composite soft magnetic material core will significantly improve the performance of high frequency electronic transformers. Other processes such as self-combustion synthesis, rapid combustion synthesis, hydrothermal synthesis, new hydrothermal synthesis, mechanical alloying, microwave sintering, etc., have carried out extensive research in recent years, all in line with the development direction of improving performance and reducing costs. .
Due to the low saturation magnetic density of soft ferrite, in the higher frequency range of 20 kHz to 100 kHz, the performance price ratio is not as obvious as the high frequency range above 100 kHz. Other soft magnetic materials are higher at 20 kHz to 100 kHz. In the frequency range, it competes fiercely with soft ferrite. All kinds of soft magnetic materials have their own characteristics. Therefore, how to make full use of the advantages of various soft magnetic materials in specific high-frequency electronic transformer products to achieve better performance and price ratio is the softness used by high-frequency electronic transformers. The direction of development of magnetic materials.
Silicon steel is characterized by high saturation magnetic density, stable performance and low price. In recent years, a series of high-frequency silicon steels have been developed, including ultra-thin silicon steel, 6.5% silicon steel, gradient silicon steel and chromium-containing silicon steel. In particular, chromium-containing silicon steel has been used in electronic transformers of 25 kHz and 70 kHz. Silicon steel is now used at frequencies up to 325 kHz. The high magnetic permeability permalloy is characterized by high magnetic permeability and good environmental adaptability, but it is expensive. In recent years, the ultra-thin band of permalloy has been used, and the working frequency has exceeded 1MHz, in special requirements and military equipment. Used in.
Cobalt-based amorphous alloy is the lowest energy loss material in existing soft magnetic materials, and it is expensive. However, it is used in high frequency above 200 kHz, the core weight is small, and the price factor is not prominent. Currently, it is at 200 kHz and 1 MHz. High-frequency electronic transformers are used in large quantities.
Soft magnetic composite materials are now a major development direction for magnetic core materials for high-frequency electronic transformers. Compared with traditional soft ferrite and soft magnetic alloys, their magnetic metal particles or films can be distributed in non-conductors and other materials. In the middle, the high frequency loss is significantly reduced, and the operating frequency is increased. At the same time, the processing technology can be processed into a powder core by hot pressing, or can be injection molded into a magnetic core of complex shape by using the current plastic engineering technology, and has the advantages of small density, light weight, high production efficiency, low cost, and product repeatability. And good consistency and other characteristics. It is also possible to use different ratios to change the magnetic properties.
An example of a composite material composed of a soft ferrite and a permalloy has been described above, and a soft magnetic composite powder core having a working frequency of 10 kHz or more has been developed, and a soft ferrite can be replaced in a high frequency filter inductor. According to the development requirements of the overall structure of the high-frequency electronic transformer, the development direction of the magnetic core structure is a planar magnetic core, a chip core and a thin film magnetic core. Previously, the planar core has been modified with the original soft ferrite core. Now there are various low-profile soft ferrite cores specifically for planar transformers. It is also possible to develop various low-profile soft magnetic composite cores in the future. In addition to further compressing the planar core, the core of the chip transformer also has a chip core manufactured by co-firing. Thin film magnetic core and magnetic material are one of the most active development directions of high-frequency electronic transformers. It will become the main core material and structure of high-frequency electronic transformers above MHz. It is possible to make the height of thin-film electronic transformers less than 1mm. Loaded into various cards.
Several centers have been established in China to study vigorously. Now I hope that the material development, electronic transformer manufacturing and application units can be united, and the thin-film soft magnetic material developed in China will be turned into a high-frequency electronic transformer core in electronic information products as soon as possible, forming a thin-film transformer with independent intellectual property rights in China.
3, coil material and structure
With the development of the overall structure of high-frequency electronic transformers, the main development direction of the coil structure is a planar coil, a chip coil and a film coil, which in turn includes a multi-layer structure. There are also some new developments in the selection of materials for various coil structures.
The high-frequency transformer coil of the three-dimensional structure, the wire material adopts a multi-strand twisted wire (Litz wire), and sometimes a flat copper wire and a copper strip, due to consideration of the skin effect and the proximity effect. The insulating material is made of a heat-resistant material to increase the allowable temperature rise and reduce the coil volume. Double-layer and three-layer insulated wires can be used to reduce the coil size. As an example, recently, China has developed a C-class insulated magnet wire that uses nanotechnology to coat mica on a copper wire. It has been applied in power frequency motors and transformers, and has achieved good results. It is estimated that it is also used in high-frequency electronic transformers. Will get applied.
The coils of the planar structure are made of copper foil, most of which are made of single-layer and multi-layer printed circuit boards, and also have a certain pattern of copper foil, which is folded in multiples. Insulating materials are generally made of B grade. The film structure coil is made of copper, silver and gold film, and is made into a comb shape, a spiral shape, a sports field shape and the like, and the insulation material is made of H grade and C grade material. There are also multilayer structures, or several multilayer coils combined, or several coils and several cores overlapped. In short, thin-film transformers are high-frequency electronic transformers that are currently being developed. Many structures are not shaped. Perhaps many new coil structures will appear.