The rectangular-bar-shaped multilayer piezoelectric transformer, which employs the length extensional
vibration mode and interdigital internal electrodes, has been suggested and developed by us for the application
to AC adapters. First, the methods of increasing the power-to-volume
ratio of the transformer are investigated
experimentally. As a result, it is found that using a high driving frequency and optimizing the positions of
input and output parts increase the power-to-volume ratio. Second, to prevent characteristic degradation
resulting from spurious vibrations in its driving frequency range, the methods of controlling such spurious
vibrations are studied theoretically and experimentally. It is found that controlling the size of the transformer
can widen the driving frequency range without spurious vibrations, and that using a low order length
extensional vibration mode can decrease the number of spurious vibrations in its driving frequency range. Also,
it is found that spurious vibrations can be eliminated or weakened by properly arranging the positions of input
and output parts according to the mode pattern of the spurious
vibrations.
Optical and electrical methods of information recording on chalcogenide glassy semiconductors are compared. It is shown that techniques based on a reversible glass-crystal phase transition are similar for the optical and electrical cases and the main mechanism of phase transition is determined by thermal heating. It is supposed that the known advantages of optical and electrical information recording by short pulses are possibly related to the existence of a wide power range of pulses recording without damage, compared with the appreciably narrower range at longer pulse durations.
A piezoelectric transformer of which the structure differs from the Rosen-type structure was investigated. According to the aim of reducing the heat generation of the piezoelectric transformer, the relationship between the heat generation and vibration velocity of the transformer was investigated. The temperature of the transformer rapidly rises when the vibration velocity of the transformer increases to above a critical value. Based on analysis of the electrical equivalent circuit of the piezoelectric transformer, the vibration velocity of the transformer is proportional to the output current and inversely proportional to the force factor of the output part. As a result, new piezoelectric transformers with a strip electrode at the output part which can minimize the heat generation of transformers have been developed. The inverters with these 3, 6 and 10 W piezoelectric transformers showed more than 85% efficiency at 60–80 kHz driving.
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