Principle and application of piezoelectric ceramic transformer

Views: 12 Author: Site Editor Publish Time: 2020-06-18 Origin: Site

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Principle of piezoelectric ceramic transformer

Piezoelectric ceramic transformer is a new type of chip device that realizes low voltage input and high voltage output through the secondary energy conversion of electrical energy --- mechanical energy --- electrical energy. Its basic structure has many forms according to the shape, electrode and polarization direction, among which the piezoelectric transformer with a long sheet structure is the most commonly used. It has a simple structure, is easy to manufacture, and has a high step-up ratio.

Compared with the traditional electromagnetic transformer, the materials, product structure, process technology and working principle of the piezoelectric ceramic transformer are different. The main materials used in electromagnetic transformers are magnetic materials and conductive materials, which are used as the core and winding of the structure, respectively, and the energy conversion form is electric-magnet-electric. The main materials used in piezoelectric ceramic transformers are binary piezoelectric ceramic materials (PZT) such as lead zirconate titanate, ternary piezoelectric ceramic materials (PCM, PSM)-that is, add other elements and four on the basis of PZT Element-based piezoelectric ceramic materials (PMMN), etc. The product is made by high temperature sintering and high pressure polarization, and its energy conversion mode is electro-mechanical-electric.It can be seen that the energy conversion of the electromagnetic transformer needs to be completed in an orthogonal three-dimensional space according to its structural form, and the piezoelectric ceramic transformer can perform energy conversion in a plane. Therefore, the piezoelectric ceramic transformer is easy to design into a chip type structure.

The working principle of piezoelectric ceramic transformer is to use the characteristics of piezoelectric ceramic material-positive piezoelectric effect and reverse piezoelectric effect. The so-called positive piezoelectric effect is that this PZT material generates charge or voltage under the action (or deformation) of the force, and the reverse piezoelectric effect is that the material deforms or vibrates when a voltage is applied. The working principle of the piezoelectric ceramic transformer is to use the positive and reverse piezoelectric effect characteristics of the piezoelectric ceramic material by designing the orientation characteristics of the electrode and polarization direction of the piezoelectric ceramic body, and using the reverse piezoelectric effect to make the phase with the input terminal. The connected piezoelectric ceramic body generates mechanical vibration under the action of voltage, and then the positive piezoelectric effect causes the piezoelectric ceramic body connected to the output terminal to generate a voltage. When the impedance of the input terminal and the output terminal are not equal, the voltage and current at both ends are also not equal, thereby realizing the function of changing the magnitude of the voltage and current between the input terminal and the output terminal.

Piezoelectric ceramic transformer structure
The piezoelectric ceramic transformer uses piezoelectric materials,which uses the electromechanical conversion characteristics, and cooperates with the vibration part of the component and the motor of the power generation part to carry out polarization design. The input voltage makes the piezoelectric piece in resonance state, and then the positive piezoelectric effect will change the high strain Converted into voltage output, so as to achieve the effect of voltage transformation.

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Figure 1 is a schematic diagram of its long piece-type integrated structure, using special piezoelectric ceramic materials (such as modified lead zirconate titanate or lead niobium magnesium zirconate titanate), after high-pressure molding, high-temperature sintering, and high-voltage electric field polarization, etc.

Piezoelectric ceramic transformers are based on the forward and reverse piezoelectric effect. During the secondary conversion of electromechanical energy, they are boosted by in-body impedance transformation. When an alternating voltage of a certain frequency
200Khz universal transformer is added to the input end (driving part) of the piezoelectric transformer, the piezoelectric transformer generates stretching vibration along the length direction due to the inverse piezoelectric effect, and the electrical energy at the input end is converted into mechanical energy. In the power generation part, due to the presence of longitudinal vibration, the mechanical energy is converted into electrical energy through the positive piezoelectric effect, so that the output terminal has a high voltage output.

Because the reflected impedance of the piezoelectric ceramic transformer increases as the load impedance decreases, this characteristic is extremely important in high-voltage applications. When the load is short-circuited or high-voltage discharged, the input impedance of the ceramic transformer increases rapidly to ensure that the transformer and peripheral circuits will not be burned. Therefore, the use of piezoelectric ceramic transformers does not require a short-circuit protection circuit.

Use of piezoelectric ceramic transformer
Small, thin, and light-weight products:Since piezoelectric ceramic transformers have some of the characteristics outlined above, they are suitable for battery-powered consumer electronic products, such as cellular phones, notebook computers, folding computers, and integrated video and recording VTR , PAD and other products power system.

Special equipment that needs to be powered by extremely high voltage and small current, such as radar, electrostatic copier, electrostatic precipitator and other power systems.

Used in self-powered systems where battery performance, size and weight are strictly restricted, such as ultrasonic transducer transformer piezoelectric brake drive systems used in automobiles, helicopters, aerospace vehicles, satellites, sonar, medical equipment, etc. The power supply of these devices generally requires 100V~1000V, which is very different from the 9V~24V power supply of ordinary batteries, and the piezoelectric ceramic transformer can achieve this index.