Piezoelectric ceramic transformers lead the new trend of electronic transformer technology

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Piezoelectric ceramic transformers lead the new trend of electronic transformer technology [Copy link]

Technical Status of Electronic Transformers Electronic transformers are important components in electronic circuits, playing important roles such as insulation, isolation, voltage/current conversion, and signal transmission. Together with resistors (R), capacitors (C), and inductors (L), they constitute the basic components of electronic circuits. In the history of the development of electronic circuits, with the continuous development of electronic technology, electronic transformers have also undergone a process of continuous improvement and upgrading. In the era of electron tubes, traditional transformers wound with silicon steel sheets dominated the world. Although they do not seem delicate now, they were still matched with glass-shell electron tubes in size under the technical conditions at that time; in the era of discrete transistor components, transformers wound with silicon steel sheets seemed too large, so pulse transformers and switching power supplies with ferrite as the core were born. Electronic transformers embarked on the road of high frequency, and light, thin, short, and small electronic products were put on the agenda. At present, the working principle of iron core wire-wound electronic transformers is the electric-magnetic-electric energy conversion mechanism. The iron core plane is orthogonal to the coil plane, which must form a cube. Despite a lot of investment in materials, structures, and processes, it is still difficult to significantly compress the size on a certain geometric scale. For example, if the thickness of chip components is defined as no more than 6mm, then the window height of the core transformer cannot be greater than 3mm, or the thickness of the wire package cannot be greater than 2mm. With this size, if the thickness of the skeleton material is deducted, there will be very little effective size left, which brings insurmountable difficulties to the winding of the transformer. In the 1980s, with the development of large-scale integrated circuits (IC), surface mounted chip electronic components (SMD) came into being. Chip resistors, chip capacitors, and chip inductors successively dominated the market. The assembly density (pitch) of the whole machine developed from 1 inch (25.4mm) to 1/2 inch (12.7mm), and then to 1/4 inch (6.5mm), creating unprecedented development opportunities for portable computers and mobile communication products. Switching power supplies using pulse transformers can only be made small but difficult to be made thin. At present, pulse transformers with a thickness of 8mm are already the leaders in the market. Traditional transformers are no longer suitable for miniaturization and chip installation. Therefore, the market is more eager to require transformers to be further miniaturized, chip-typed, and even miniaturized. With the development of material technology, piezoelectric ceramic transformers provide a practical possibility for this requirement. In this sense, industry insiders generally believe that piezoelectric ceramic transformers will be a major revolution in electronic transformer systems rather than a general improvement. The birth of piezoelectric ceramic transformers Piezoelectric ceramic transformers are a new type of boost-type component that realizes the conversion of electrical energy-mechanical energy-electrical energy. Its main component, piezoelectric ceramic sheets, are new functional ceramic materials made of non-metallic materials through a series of processes such as high-temperature sintering and high-voltage polarization. Compared with traditional electromagnetic transformers, this type of transformer has the advantages of small size, light weight, simple structure, no copper and iron materials, no fear of moisture, no combustion and breakdown, and no electromagnetic interference. Piezoelectric ceramic transformers have the characteristics of high conversion efficiency, no electromagnetic radiation, small size, no combustion, safety and reliability, and are often used in CCFL drives, such as PDA, PMP, GPS, PEN-PANEL, GAME-BOX, PORTABLE DVD, CAR TV, NOTEBOOK, LCD MONITOR, LCD TV, etc. At present, the research and development and application of piezoelectric ceramic transformers are mainly concentrated in Japan, Taiwan and China. The domestic research level is leading in technology and has a certain dominance in the market. Advantages of piezoelectric ceramic transformers The advantages of piezoelectric ceramic transformers are mainly in the following aspects: ① The conversion efficiency is very high. Compared with the 60% to 85% efficiency of traditional transformers, piezoelectric ceramic transformers can easily achieve more than 90%; ② The energy density is very large, and the corresponding volume can be very small and thin; ③ There is no electromagnetic interference, because the energy conversion process is completed by mechanical vibration, not electromagnetic conversion; ④ Strong environmental applicability, resistance to low temperature, high humidity, acid and alkali, no mildew, long life; ⑤ Standard sinusoidal output, which is beneficial to the life of the lamp and has high light efficiency. Application principle of piezoelectric ceramic transformers Piezoelectric ceramic transformers use the inherent characteristics of piezoelectric effect of piezoelectric ceramics and adopt the principle of electrical-mechanical-electrical energy conversion. In most structures of piezoelectric ceramic transformers, electrical energy and mechanical energy are converted on one-dimensional coordinates. Therefore, theoretically, piezoelectric ceramic transformers can be made infinitely thin. Even with the design factors such as structural strength and power capacity, the thickness in actual components is only 1.5 to 5 mm, which is a size that iron core wire wound transformers can hardly reach. In this sense, industry insiders generally believe that piezoelectric ceramic transformers will be the third generation of high-frequency electronic transformers, and also a revolutionary progress in electronic transformers. The piezoelectric effect is divided into positive piezoelectric effect and negative piezoelectric effect. The positive piezoelectric effect is mainly used for high-voltage ignition, such as ignition devices for gas stoves and lighters. The basic principle is that an external force compresses a spring and then releases it, pushing a heavy hammer to hit the piezoelectric ceramic column to generate a high-voltage discharge spark of several thousand volts, igniting the combustible gas. The negative piezoelectric effect is mainly used in piezoelectric buzzers. The basic principle is to add an alternating electrical signal to the piezoelectric ceramic sheet, so that the piezoelectric ceramic sheet produces a corresponding deformation, that is, vibration. If the vibration frequency is within the audio band, a corresponding sound will be emitted. The negative piezoelectric effect is also common in SAWF, resonators, frequency selectors, delay lines, filters, etc. The basic structure of a piezoelectric ceramic transformer is to assemble a piezoelectric buzzer and a piezoelectric igniter. A sinusoidal electrical signal is applied to the driving end (the buzzer end, i.e., the primary end). When the fixed frequency of the signal is consistent with the resonant frequency of the piezoelectric ceramic transformer, the piezoelectric sheet vibrates, and this mechanical vibration is used to drive the power generation end (the igniter end, i.e., the secondary end) to generate a sinusoidal electrical signal. By changing the structural characteristics of the piezoelectric ceramic transformer, a step-up piezoelectric ceramic transformer with low input voltage and high output voltage can be formed, or a step-down piezoelectric ceramic transformer with high input voltage and low output voltage can be made. The signal can also be transmitted through modulation and demodulation in conjunction with a suitable transmitting unit. Application of piezoelectric ceramic transformer in inverter (I) Introduction to the application of piezoelectric ceramic transformer in inverter Piezoelectric ceramic transformer, like traditional transformers, can be used in many occasions where voltage/current conversion is required, and CCFL (cold cathode fluorescent lamp) driver used in LCD (liquid crystal display) backlight power supply is one of the typical applications, and in many aspects it has incomparable advantages over traditional inverters, as shown in: the output characteristics are completely consistent with the working characteristics of CCFL, and it has adaptive characteristics. ① The step-up ratio can be very high, which can easily drive large-size CCFL or "U"-shaped CCFL; ② High conversion efficiency, especially when used in portable LCDs, can significantly reduce the cost of batteries; ③ Good environmental adaptability, which is conducive to application in industrial and special working environments. (II) Application examples of piezoelectric ceramic transformers in inverters 1. Introduction to inverters The driving power supply for CCFL in LCDs, from the traditional ROYER, HALF BRIDGE, FULL BRIDGE, PUSH-PULL, all use a step-up transformer wound with copper wire to obtain the voltage required for CCFL lighting and operation. It should be said that people are accustomed to using this traditional method, which has relatively stable and reliable performance within a specific range, as well as price advantages, but it also has many shortcomings, which are summarized as follows: 2. Comparison between traditional inverters and piezoelectric ceramic transformer inverters 3. Application circuit of piezoelectric ceramic transformer inverter 3.1 Inverter circuit block diagram When the piezoelectric ceramic transformer is working normally, the frequency of the driving signal is required to be consistent with the inherent resonant frequency of the piezoelectric ceramic transformer itself. However, in actual applications, the resonant frequency of the piezoelectric ceramic transformer will change due to external factors such as load impedance. Therefore, it is required to feedback and adjust the frequency of the driving signal in the circuit. 3.2 Typical application circuit of inverter Since the resonance curve of the piezoelectric ceramic transformer is relatively sharp, the setting of the working point is very important. Therefore, it is necessary to ensure that the operating frequency of the circuit is near the resonance point of the piezoelectric ceramic transformer. In the actual circuit design, the input end is no different from the traditional inverter, mainly including on/off, dimming and input power supply. The output part is still the standard high-voltage output end. Most ICs in traditional applications can be well controlled and driven with appropriate peripheral circuits. 3.3 Problems of piezoelectric ceramic transformers in inverter applications At present, there are still relatively large problems in the application of piezoelectric ceramic transformers in inverter applications. As far as the piezoelectric ceramic transformer product itself is concerned, it is already relatively mature. The key problem is that a large number of application engineers, especially engineers in the R&D department, cannot correctly understand this product, and do not even fully understand the working principle of the piezoelectric ceramic transformer, let alone evaluate the piezoelectric ceramic transformer inverter, which leads to many artificial obstacles. On the other hand, due to production process reasons, the yield of piezoelectric ceramic transformers has always troubled production companies, resulting in high costs, which is also an important reason for users to stop. Of course, this part will not have any impact on the yield of the final product, the inverter. Summary Based on people's previous understanding, it is believed that the price of piezoelectric ceramic transformers is relatively high. This is of course a process. Due to the high investment in the early stage of R&D, but with the promotion of products and the increase in applications, the cost should drop sharply. In this regard, it can be achieved at the same price as traditional products or even slightly lower. Another issue that users are most concerned about is that piezoelectric ceramic transformers are prone to breakage. In fact, this is also a misunderstanding. As far as the material itself is concerned, the mechanical strength is no different from that of traditional ferrites. As a non-traditional transformer, piezoelectric ceramic transformers are considered to be an irreversible direction, especially for electronic workers engaged in technology research and development, whether from the perspective of energy saving and consumption reduction or circuit performance. One day, just like transistors replacing electron tubes, piezoelectric ceramic transformers will replace traditional winding transformers. With the continuous advancement of the piezoelectric ceramic transformer industry and the continuous promotion of applications, costs will drop rapidly, and product stability and mass production quality will be further improved. There are already mature applications in the fields of problem DVD (digital video disc player), PDA (personal digital assistant), PMP (personal multimedia center), car TV, GPS (global positioning system), monitor, notebook, LCD TV, etc.