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JPS54136972

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DESCRIPTION JPS54136972
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a conventional three-terminal type
piezoelectric acoustic device, and FIG. 2 shows a three-terminal type piezoelectric acoustic device
of the present invention. 1 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·
· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · divided electrodes, 3 · · · · ·. .
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an acoustic
generator 6 using piezoelectric elements. 1- <rtt-tsk acu. Tsuno piezoelectric acoustic device is
used for bells and buzzers widely used in alarm devices, interphones, telephones, clocks and the
like. Conventionally, all K and SR stone types have been used for these bells and buzzers, but the
electromagnet type is inexpensive, but has the disadvantages of short mechanical life with
mechanical wear and further corrosion resistance. Because there are also many structural
problems, the application of piezoelectric elements has been gradually used. The piezoelectric
buzzer j to which the piezoelectric element is applied has no mechanical consumption and there
is very little loss, so the conversion efficiency between electrical energy and acoustic energy is
extremely high, and it can be used for a long time with a small capacity power supply. In
addition, the sealed structure also improves the corrosion resistance. Conventionally, a twoterminal piezoelectric element has been used as a piezoelectric acoustic device, but a threeterminal piezoelectric element type device has also been developed recently (e.g., Japanese Utility
Model Application Laid-Open No. 50-133075). As shown in FIG. 1, this has a structure such that
G 重, a division weight from a 2-t base 6ζ piezoelectric element of a transistor is added 6ζ. The
split electrode l of the piezoelectric composite (The generated voltage is maximum at the
common frequency of the piezoelectric composite, so the return frequency to the transistor is
also the maximum at the resonant frequency i (and the oscillation is always sustained at 6ζ). Do.
However, in order to obtain high sound pressure, it is necessary to increase the power supply
voltage or to lower the resonance impedance of the piezoelectric composite. Increasing power
supply voltage is a disadvantage in equipment that uses power (a disadvantage, while lowering
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the resonant impedance of the piezoelectric composite: it is limited how to fix the rolling
composite (for example, Joint circle fixed). Furthermore, since the sound pressure also changes in
accordance with the change in resonance impedance, it is necessary to set each component so as
to obtain an optimum resonance impedance. An object of the present invention is to provide a
device that overcomes the disadvantages of such a conventional three-terminal piezoelectric
acoustic device. The device according to the present invention is a device in which a composite
formed by integrating a piezoelectric element and a diaphragm with an adhesive is driven by an
electric circuit to cause bending vibration and generate an audible sound. Forming an oscillation
circuit by dividing an electrode of the piezoelectric element of the composite to take out a
feedback signal and applying the feedback signal to a base of the transistor. A sound generator
characterized by
The device of the invention will be described with reference to the accompanying drawings. FIG.
2 is a circuit diagram of the device of the present invention, wherein (1) shows a matching
transformer, (2j is a transistor, (3) is a resistor, and (4) is a three-terminal piezoelectric
composite. When a DC voltage is applied, a current 1 flows between the base and the emitter of
the transistor (2) through the resistor (3). Then, since the current 4- of IC1 @ hfe flows between
the collector and the emitter of the transistor (2), collector electrons are lowered. Since the
winding of this old, matching transformer tl) is 6 fold so that a positive voltage is generated in
the split electrode (5), the feedback signal from the split electrode (5) is positive feedback to the
base of the transistor (2) It takes Since the amount of positive feedback is maximum at the
resonant frequency of the piezoelectric composite (4), it oscillates at the resonant frequency of
the piezoelectric composite (4). The turns ratio of the matching transformer can be set
appropriately to match the resonance impedance of the piezoelectric composite. Piezoelectric
composite (i consists of a piezoelectric element and a diaphragm, but the piezoelectric element
itself may be a conventional one, and any diaphragm may be used as long as it generates sound
from ff1ijj + iC. For example, a metal plate, a plastic plate or the like. There are no particular
limitations on the shape and size of the split electrode (5) of the piezoelectric composite. Since
the device of the present invention has the above-mentioned structure, it can drive the
piezoelectric composite at a voltage higher than the 5-2 (1) power supply voltage, and the ratio
of the turns of the lance to the piezoelectric composite By setting Gζ so as to match the
resonance impedance of the above, it is possible to obtain high sound pressure with a wide range
of power supply voltage regardless of the magnitude of the isopyance. Since it is not necessary to
strictly limit the method of fixing the piezoelectric composite and other parts (resistance and the
like) so as to obtain an optimum resonance impedance, it is easy to design an acoustic device
combination.
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