JPS5644295

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DESCRIPTION JPS5644295
Description 1, title of the invention
Piezoelectric acoustic transducer
3. Detailed Description of the Invention The present invention relates to a piezoelectric acoustic
transducer with high sounding efficiency, which is a combination of a feedback type sounding
body using a piezoelectric plate, an amplifier and a phase shifter. A conventional piezoelectric
acoustic transducer of this type is typically a drive electrode of a feedback type sounding body
X1 formed by adhering and integrating an elastic thin plate 1 also serving as a ground electrode
and a piezoelectric plate 2 as shown in FIG. 3 is connected to the collector of the transistor Q +,
and the feedback electrode 4 is connected to the base of the transistor Q via the resistor R3.
However, in such a conventional configuration, the maximum sound pressure P that the feedback
type sounding body X1 can generate. Resonant frequency f that corresponds to. Does not
oscillate and sound pressure performance is poor. In view of the above, although driving with a
power supply voltage increased using a transformer is also performed, there are drawbacks such
as an increase in size and cost, and usually the sound pressure performance is used while being
poor. The object of the present invention is to solve the drawbacks of the prior art and to fully
exhibit the original sounding performance of the feedback type sounding body so that a large
sound pressure can be obtained even if the driving voltage is low. A piezoelectric acoustic
transducer is provided. As a result of various experiments and investigations of the piezoelectric
acoustic transducer of the conventional structure, the following was found. That is, the phase
difference between the drive electrode 3 and the feedback electrode 4 of the feedback type
sounding body X1 is approximately 1800 for the sounding body alone, and the phase difference
between the base and the collector of the transistor Q1 is 180 °. The frequency is the resonance
frequency f of the feedback type sounding body X1. It should be near. However, in practice,
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phase rotation occurs due to the bias resistance such as the base resistance R3 of the transistor
QI and the equivalent capacitance of the sound generator, and as shown in FIG. 2, the resonance
frequency f. It means that it oscillates at the frequency of fl which is deviated from it. As a result,
the actual sound pressure was significantly lower than the maximum value Po of the sound
pressure. The present invention has been made based on the knowledge of such a phenomenon,
and in order to achieve the above object, as shown in FIG. 3, a feedback type sounding body X
and an amplifier 7 are used. In the self-oscillation circuit to be formed, a phase shifter 8 is
interposed, and the phase shifter 8 is configured to adjust phase rotation by the bias resistance
of the amplifier and the equivalent capacitance of the sound generator. Hereinafter, the present
invention will be described in more detail based on the drawings. First, the feedback type
sounding body exhibits an impedance characteristic 1 phase characteristic and a sound pressure
characteristic as shown in (f, (bl, (cl, respectively).
The piezoelectric speaker has a resonant frequency f represented by an LO series resonant
equivalent circuit and an antiresonant frequency f represented by a parallel resonant equivalent
circuit. In the impedance characteristic, the minimum point is the resonance frequency f2 and the
maximum point is Anti-resonance frequency f, Further, in the feedback type sounding body Xl,
the phase difference between the drive electrode 3 and the feedback electrode 4 is 180 ° at the
antiresonance frequency f and inverted as shown in FIG. 4 (bl). By the way, since the selfoscillation circuit shown in Fig. 1 is constant current property, the sound pressure P is maximum
at the antiresonance frequency f, but for the above reasons it is completely 180 ° Therefore, the
phase difference between the drive electrode 3 and the feedback electrode 40 in the feedback
type sounding body X1 is, for example, 1800 + α, and the sound pressure is P. And the
maximum value P. It will decrease more. Therefore, according to the present invention, as shown
in FIG. 3, by interposing the phase shifter 8 and adjusting the phase difference α, oscillation can
be performed at a frequency at which the sound pressure is always maximum. An example of the
specific circuit is shown in FIG. The block 7 is an amplification circuit, and the portion 8 is a
phase adjustment circuit, ie, a phase shifter. The collector of the transistor Q3 is connected to the
power source 3 via the collector current limiting resistor R0 and at the same time connected to
the drive electrode 3 of the feedback type sounding body x1. The emitter of the transistor Q is
grounded and is connected to the collector of the transistor Q via a base hash bias resistor R7.
The feedback electrode 4 of the feedback type sounding body X1 is connected to the base of the
transistor Q4, and the collector thereof is supplied with power via a collector current limiting
resistor R0. Are connected to the base of the transistor Q5 via the capacitors O, 02. The emitter
of the transistor Q4 is grounded via an emitter resistor R11, and at the same time connected to
the midpoint between the capacitors C1 and 02 via a semi-fixed resistor R1o. The base of the
transistor Q is powered via a base bias resistor R22. And, at the same time, is grounded via the
diode D1. The emitter of the transistor Q5 is grounded, and its collector is connected to the
power supply Vc via a collector current limiting resistor R13 and is fed back to the transistor Q3
via a base resistor R8. In the device configured as described above, the signal appearing at the
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feedback electrode 4 of the feedback type sounding body X is fed pack so as to be in the positive
phase to the base of the transistor Q3 through the phase shifter 8 consisting of the transistors
Q4 and Q-. Let
At this time, the phase adjustment is performed by a half fixed resistor R1o connected to the
transistor Q4. That is, by adjusting the emitter resistance R1o of the transistor Q4, the phase
difference between the drive electrode 3 and the feedback electrode 4 of the feedback type
sounding body X is made to fall within the range of -170 ° to -190 °. When the sound pressure
characteristic is determined by changing the phase difference of the open signal between the
drive electrode 3 and the feedback electrode 4, it becomes as shown in FIG. 6 (al, (b)). When the
phase difference is completely −180 °, the oscillation frequency bM feedback type sounding
body X1 is in agreement with the antiresonance frequency f, and the sound pressure has the
maximum value P. どなる。 The oscillation frequency is between f3 and 4 in the phase difference
of -170 ° to -190 °, and the sound pressure is maintained at a certain level or higher, but the
sound pressure is rapidly decreased on both sides of the sound pressure. That is, since a sound
pressure sufficiently high for practical use can be obtained in the range of f3 to f4, the phase
difference must be adjusted to fall within the range of -1700 to -190. Of course, it is best to
adjust the phase difference to -180 °. Incidentally, the sound pressure difference is about +6 dB
as compared with the case of a self-oscillation circuit having no phase adjustment function as
shown in FIG. As described above, the present invention is a self-oscillation circuit using a
feedback type sounding body, and performing phase adjustment maximizes the electro-acoustic
conversion efficiency of the sounding body and maximizes the sound pressure. In addition to
being suitable for alarm buzzers and the like that require a large sound volume because they are
oscillated, they are also suitable for buzzers for low voltage sources and the like because large
sound pressure can be obtained even with a low power supply voltage.
4. Brief description of the drawings Fang 1 is a circuit diagram showing a conventional example,
Fang 2 is the sound pressure-frequency characteristics of the feedback type sounding body and
the operating frequency f in the conventional example. Shows a block diagram showing an
example of the basic configuration of the device according to the present invention, and FIG. 4A
(al, (bl, (el represents the impedance characteristic 1 phase characteristic of the feedback type
sounding body, and the sound pressure respectively) A diagram showing the characteristics, a
symbol 5 is a circuit diagram showing an embodiment of the present invention, a symbol 6 (al,
(bl is a diagram showing the relationship between the phase difference and the frequency, the
sound pressure). 2 · · · Piezoelectric plate, 3 · · · Drive electrode, 4 · · · Feedback electrode,? ...
Amplifier, 8 ... Phase shifter, Xl ... Feedback type sounding body. Patent Assignee Fuji Electro
Chemical Co., Ltd. Atsushi Ohuka Tsumugi Estimate Araki-Tomonosuke EndPage: 3
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