In general, to drive a PT, either a sine wave or a square wave voltage can be used. Numerous efforts were undertaken in this area mainly with magnetic components. Resonant converters were originally considered in the early 1990s as an extension of the general approach undertaken in power electronics to use high frequency switching circuits to minimize the size of DC-DC and AC-DC converters. Due to its small size, the cost of the piezoelectric transformers was relatively low and competitive for this application, rapidly enabling high-volume production.
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In this application, the piezoelectric transformer enabled thinner, lighter, and more efficient CCFL backlighting modules, thus allowing the reduction of LCD screen thickness and improving the battery life of portable devices. The main application was to generate high voltage for backlighting the small cold cathode fluorescent lamps (CCFLs) used in liquid crystal displays (LCDs) of the increasingly popular portable cell phones and computers.
Ltd., Nihon Cement Kabushiki Kaisha (Tokyo, Japan) and others, reconsidered the use of PTs, taking advantage of improvements in novel piezoelectric materials, more reliable manufacturing technology, including multilayer co-firing processes, new concepts on integrated circuits, and housing solutions. (Tokyo, Japan), Matsushita Electric Industrial Co. In the late 1980s, several Japanese companies, including NEC Corp.
In the 1980s, Siemens (Berlin, Germany), Figure 7c, and General Electric (Schenectady, NY, USA) were among some companies working on the application of PTs for triggering power switch gates such as triacs, thyristors, Mosfets, etc., with galvanic decoupling. ), in small engine applications (Briggs & Straton (Milwaukee, WI), Figure 7a) and in automobiles (Nippon Soken, Nishio, Japan) ). Several attempts were also reported for using piezoelectric transformers as igniter in gas-based stoves (Matsushita Electric Industrial Co. (Osaka, Japan), focused their attention to PTs for generating the high voltage required for the cathode-ray tubes in black and white television receivers (see Figure 7b for a typical example). (Tokyo, Japan), and Matsushita Electric Industrial Co. and Japanese companies, like Motorola, Inc. Jaffe, at Clevite Corporation, were unquestionably world leaders in this subject area. Over the decade of the 1960s, the group led by B. Berlincourt (all at Clevite Corporation) and others, which led to the evolution of the entire family of PZT piezoceramics. Jaffe’s studies were followed by more detailed studies by Hans Jaffe (not a relative of B. Jaffe was the head of the research center of the piezoelectric division at the then Clevite Corporation, Bedford, OH, USA, which later became known as Vernitron Corporation, and today is known as Morgan Ceramics. This situation changed when, in 1954, Bernard Jaffe recognized the importance of the morphotropic phase boundary in the Lead Zirconate Lead Titanate (PZT) family of ceramics. Most of the work of the General Electric team on piezoelectric transformers during the 1950s–1960s was based on Barium Titanate, the only commercially available ferroelectric material at the time.
Rosen needed just one unit to prove his concept, but manufacturers had to be able to produce them reliably. The concept was great but the results were poor, because it was very difficult to make a bipolarized block that would not break into pieces when the alternating current was applied. The total length of the ceramic block determines the resonant frequency of the transformer, while the ratio of the input and output sections determines the voltage conversion. Half of the block was polarized in the longitudinal direction and the other half in the thickness direction. Rosen created the two zones by applying separated electrodes and different polarizing voltages to the halves of the block. Unlike the earlier attempts by Nicolson to make piezoelectric transformers using two pieces of piezoelectric solid crystals bonded together and clamped with an external structure, Rosen's approach involved the use of a single rectangular block of BaTiO 3 polycrystalline ceramic comprising two distinct polarization zones ( Figure 3).
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