At present, piezoelectric ceramic transformer has been widely used in a series of fields, including household appliances and high-tech military products. One of the most typical applications is to drive cold cathode fluorescent lamp. This is because the voltage and current characteristics of piezoelectric ceramic transformer input and output are very suitable for cold negative fluorescent lamp. The characteristics of the device are having the high output impedance, low output current and large output voltage variation with impedance. While the cold fluorescent lamp needs 1 000 V start-up voltage when it is started, it needs much lower voltage when Pzt piezo ceramics is in stable working state, which is about half of the start-up voltage, and its impedance is much lower than that when it is started. In addition, the cold fluorescent lamp needs much lower current. These characteristics of cold fluorescent lamps are very similar to those of piezoelectric ceramic transformers. Another important application area of piezoelectric ceramic transformers is DC and DC converters. Besides that, there are many applications of piezoelectric ceramic transformers, such as those used in safe explosion-proof systems. Electric batons, anti-theft nets, withdrawal boxes, cash carriers and safe cabinets, image tubes, cold cathode tubes in liquid crystal displays, neon lamps, laser tubes or X-ray tubes, high-voltage electrostatic spraying, high-voltage electrostatic flocking and radar display tubes, high-voltage pulse igniters in ignition systems, and photocopiers, laser printers, fax machines, and quieters electric generator, electrostatic copier, medical equipment, air freshener, ozone disinfection cabinet, military and aerospace equipment, etc. it is worth of pointing out that when trying to replace the traditional wound electromagnetic transformer with piezoelectric ceramic transformer, we should not blindly replace it, because the piezoelectric ceramic transformer has strict requirements for its peripheral circuit. At present, manufacturers usually sell the transformer as a complete set and seldom sell the isolated piezoelectric ceramic transformer separately.
Material Research of Piezoelectric Ceramic Transformer
Piezoelectric ceramic materials have been widely used in filters, ultrasonic transducers, piezoelectric actuators and sensors. Different devices require different performance parameters of piezoelectric ceramic materials. The working principle of piezoelectric ceramic transformers is realized by using the positive and negative piezoelectric effects of piezoelectric materials. In the piezoelectric ceramic transformer, the piezo ceramic disc transducers are used as transformers. At the input end of the device, the alternating energy of the input piezoelectric ceramic transformer is converted into mechanical vibration energy through the inverse piezoelectric effect. At the output end of the piezoelectric ceramic transformer, the mechanical vibration is converted into alternating electric energy through the positive piezoelectric effect, and the impedance is transformed in the two transformations of energy, thus the resonant frequency of the piezoelectric ceramic transformer is realized. In order to achieve the highest energy conversion efficiency, piezoelectric ceramics with specific properties must be selected. For piezoelectric ceramics used for piezoelectric ceramic transformers, higher electromechanical coupling coefficient, higher mechanical quality factor and electrical quality factor as well as the lowest possible are required. The development of piezoelectric ceramic transformer is inseparable from the development of piezoelectric ceramic material because of its temperature coefficient. In the early stage of research on piezoelectric ceramic transformer, piezoelectric ceramic material is mainly monolithic, and its important representative is barium titanate ceramics. Although this kind of piezoelectric ceramic material has high dielectric constant, its temperature is stable. These characteristics of barium titanate piezoelectric ceramics are not conducive to the development and application of high-power piezoelectric ceramic transformers.
Lead zirconate titanate is a binary piezoelectric ceramic material, which has very strong and very stable piezoelectric properties. Compared with barium titanate piezoelectric ceramics, lead zirconate titanate piezoelectric ceramics have many kinds of materials. PZT-4 material is a kind of emission. PZT-8 material is a kind of piezoelectric ceramics with low mechanical and dielectric losses, large AC depolarization field, large dielectric constant, electromechanical coupling coefficient and piezoelectric constant. It is especially suitable for the excitation of strong electric field and large mechanical amplitude, so it is often used in the transmitting transducers and piezoelectric transformers. The dielectric constant, electromechanical coupling coefficient and piezoelectric constant of PZT-4 material piezoelectric ceramics are slightly lower than those of PZT-4, but their tensile strength and stability are better than those of PZT-4 material. They also have higher mechanical quality factor and are more suitable for high mechanical amplitude excitation. Therefore, they are widely used for the piezoelectric ceramic transformers. In order to meet the development needs of high-power piezoelectric ceramic transducers and piezoelectric ceramic transformers, ternary piezoelectric ceramics were developed on the basis of binary lead zirconate titanate piezo ceramic crystal quartz. Ternary piezoelectric ceramics were made of fine particle size materials, which were characterized by good sintering performance, low sintering temperature, low porosity and high quality. The ternary piezoelectric ceramics are commonly used as lead niobium magnesium zirconate titanate, lead niobium zinc zirconate titanate and lead tellurium manganese zirconium titanate. In order to further improve the performance of piezoelectric ceramics transformers, quaternary piezoelectric ceramics have been developed on the basis of ternary piezoelectric ceramics. Their main characteristics are similar to ternary piezoelectric ceramics, but their electromechanical coupling coefficient, mechanical quality factor and electrical quality factor are higher. It is more suitable for the requirement of high power piezoelectric ceramic transformer.
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