50 Years Of Piezoelectric Transformers. Trends In The Technology
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50 Years Of Piezoelectric Transformers. Trends In The Technology Alfredo Vázquez Carazo Department of R&D Engineering, Face Electronics, LC th 427 W. 35 Street, Norfolk, Virginia 23508, U.S.A
ABSTRACT The initial concept of a piezoelectric transformer (PT) was proposed by C.A. Rosen, K. Fish, and H.C. Rothenberg and is described in the U.S. Patent 2,830,274, applied for in 1954. Fifty years later, this technology has become one of the most promising alternatives for replacing the magnetic transformers in a wide range of applications. Piezoelectric transformers convert electrical energy into electrical energy by using acoustic energy. These devices are typically manufactured using piezoelectric ceramic materials that vibrate in resonance. With appropriate designs it is possible to step-up and step-down the voltage between the input and output of the piezoelectric transformer, without making use of wires or any magnetic materials. This technology did not reach commercial success until early the 90s. During this period, several companies, mainly in Japan, decided to introduce PTs for applications requiring small size, high step-up voltages, and low electromagnetic interference (EMI) signature. These PTs were developed based on optimizations of the initial Rosen concept, and thus typically referred to as “Rosen-type PTs”. Today’s, PTs are used for backlighting LCD displays in notebook computers, PDAs, and other handheld devices. The PT yearly sales estimate was about over 20 millions in 2000 and industry sources report that production of piezoelectric transformers in Japan is growing steadily at a rate of 10% annually. The reliability achieved in LCD applications and the advances in the related technologies (materials, driving circuitry, housing and manufacturing) have currently spurred enormous interest and confidence in expanding this technology to other fields of application. This, consequently, is expanding the business opportunities for PTs. Currently, the industry trend is moving in two directions: low-cost product market and valueadded product market. Prices of PTs have been declining in recent years, and this trend is expected to continue. Soon (if not already), this technology will become a serious candidate for replacing the magnetic transformers in cost-sensitive applications. Currently, leading makers are reportedly focusing on more value-added products. Two of the key value-added areas are miniaturization and higher output power. Piezoelectric transformers for power applications require lower output impedances, high power capabilities and high efficiency under step-down conditions. Among the different PT designs proposed as alternatives to the classical Rosen configuration, Transoner laminated radial PT has been demonstrated as the most promising technology for achieving high power levels. Higher powers than 100W, with power densities in the range of 30-40 W/cm2 have been demonstrated. Micro-PTs are currently being developed with sizes of less than 5mm diameter and 1mm thickness allowing up to 0.5W
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