What Is a Piezoelectric Transformer?
A piezoelectric transformer is a unique type of transformer that harnesses the piezoelectric and electrostrictive effects of a specific ceramic element (dielectric) to convert electrical power. Unlike conventional electromagnetic transformers with coils, piezoelectric transformers offer distinct advantages, including a simple structure, the ability to be made smaller, thinner, and lighter, a high step-up ratio, exceptional efficiency, and the absence of magnetic noise. Consequently, piezoelectric transformers have become essential components for conserving space and energy in various electrical and electronic devices.
Uses of Piezoelectric Transformers
Piezoelectric transformers find extensive use in power supplies for electrical and electronic equipment. With the increasing trend towards smaller and thinner devices like notebook PCs and mobile gadgets, there is a growing demand for compact power supplies. Piezoelectric transformers have emerged as replacements for traditional wire-wound electromagnetic transformers in such applications. For example, they are employed in power supplies for LCD backlights in notebook PCs and LCD TVs. Beyond their size advantages, piezoelectric transformers are poised for broader applications due to their high efficiency and the absence of magnetic interference.
Principles of Piezoelectric Transformers
A piezoelectric transformer consists of a rectangular dielectric material, divided into two halves: one serving as the primary side and the other as the secondary side. A voltage is applied to the primary side in the direction of its thickness, invoking the electrostrictive effect, which transforms electrical energy into mechanical vibrations. The electrostriction effect is a phenomenon in which an electric field applied to a dielectric material induces mechanical deformation. On the secondary side, the piezoelectric effect is at work, converting these mechanical vibrations back into electrical energy. This electrical energy is extracted as an output voltage in the longitudinal direction. In contrast to the electrostrictive effect, the piezoelectric effect involves the generation of voltage when pressure is applied to a dielectric. A material with this property is referred to as a piezoelectric element.
Piezoelectric transformers operate at their natural resonant frequency, determined by the dimensions of the dielectric. There are two main types based on the length of the dielectric: the λ-mode type, which operates at a full wavelength, and the λ/2-mode type, which operates at half wavelength. The transformation ratio (V2/V1) of the input voltage (V1) to the output voltage (V2) in a piezoelectric transformer is governed by the square root (√(C1/C2)) of the ratio of the primary side capacitance (C1) to the secondary side capacitance (C2). Since C1 and C2 are influenced by the thickness and length of the dielectric, the transformation ratio is primarily determined by the length-to-thickness ratio, which is also utilized to define the transformer ratio.