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JPH1155783

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Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
financial decisions, should not be based on machine-translation output.
DESCRIPTION JPH1155783
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric speaker transformer suitable for driving a piezoelectric speaker.
[0002]
2. Description of the Related Art As a conventional transformer for a piezoelectric speaker, for
example, one disclosed in Japanese Utility Model Laid-Open Publication No. 64-29986. This will
be described with reference to FIG. The transformer 1 has a rectangular plate-shaped toroidal
core 2, a primary winding 3 wound on the lower side of the magnetic core 2 in the drawing, and
a primary winding on the upper side of the magnetic core 2 in the drawing. It comprises a
secondary winding 4 provided separately from the winding 3 and wound. The primary winding 3
is connected to the input terminal 5 of an amplifier (not shown) for driving the speaker, and the
secondary winding 4 is connected to the sounding body 6 made of a piezoelectric material, The
piezoelectric speaker device 7 is configured.
[0003]
Then, when the audio signal amplified by the amplifier is input from the input terminal 5 to the
primary winding 3, a magnetic field is generated in the primary winding 3, and power is induced
in the secondary winding 4 by this magnetic field, An electrical signal by this power is added to
the sounding body 6, and sound is reproduced.
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[0004]
Generally, the output impedance of an amplifier is approximately 0 Ω, and the frequency
characteristics of the transformer connected to the amplifier and the sounding body made of a
piezoelectric material are determined by the inductance on the secondary winding side of the
transformer. It is determined by the inductance on the secondary winding side when the primary
winding side is shorted, and this is called a leakage inductance.
[0005]
Then, assuming that the resonance frequency of the speaker device at this time is f, it is
expressed by the equation f = (2π (LC) 1/2) −1.
Here, L is a leakage inductance and C is a capacitance of the piezoelectric body.
The leakage inductance is dependent on the degree of coupling between the primary winding
and the secondary winding. For example, as the degree of coupling between the primary winding
and the secondary winding increases, the leakage inductance tends to decrease. The frequency
characteristic of the transformer connected to the sounding body is represented by a curve as
shown in FIG. 5, and the frequency at which the response represented by the vertical axis tends
to decrease is referred to as the high cutoff frequency. Here, in the curve indicated by the solid
line and the curve indicated by the broken line, the curve indicated by the broken line represents
the case where the leakage inductance is larger. Then, assuming that the high cutoff frequency of
the curve of the solid line is f1 and the high cutoff frequency of the curve of the broken line is f2,
then f2 <f1 and the value of the high cutoff frequency decreases as the leakage inductance
increases. . The response indicates the efficiency of the signal input to the sound generator.
[0006]
In addition, when a sounding body made of a piezoelectric material is driven at a constant
voltage, the sounding body made of a piezoelectric material is capacitive, so the impedance is
high at low frequencies and the impedance is low at high frequencies. The sound pressure
characteristic is represented by a curve as shown in FIG. Note that no transformer is connected
to the sounding body.
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[0007]
And it is thought that the graph of FIG. 5 and FIG. 6 overlaps by utilizing the leakage inductance
of a transformer to the sounding body which consists of piezoelectric materials, and as shown in
FIG. Shows a flat sound pressure characteristic.
[0008]
Here, in the piezoelectric speaker device shown in the conventional example, when the
transformer is used, for example, from the low frequency band around 20 Hz, the characteristics
of the low frequency band are extremely distorted and deteriorated due to the iron loss of the
magnetic core.
As a means to improve this, it is conceivable to reduce the influence of core loss of the core by
largely increasing the number of turns. However, in this case, the leakage inductance described
above is increased. When the leakage inductance is increased as described above, the high cutoff
frequency is lowered as described with reference to FIG. That is, since the frequency band is cut
off at a low frequency, as shown by the broken line curve in FIG. 7, the sound pressure is reduced
at the time of sound reproduction, and the sound expansion in the high frequency band is lost.
[0009]
Therefore, in order to improve the sound pressure characteristics in the low frequency band
without increasing the number of turns, the cross-sectional area of the magnetic core used for
the transformer may be expanded. In that case, the transformer itself becomes large.
[0010]
In addition, although the expansion of the sound in the high frequency band can be improved by
reducing the capacity of the piezoelectric body, in this case the sound in the low frequency band
runs short and the signal input to the piezoelectric body is converted into sound. Efficiency will
decrease.
[0011]
Therefore, an object of the present invention is to solve the above-mentioned problems, and it is
possible to combine the primary winding and the secondary winding even if the number of turns
of the transformer winding is increased to increase the leakage inductance. Piezoelectric speaker
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in which sufficient sound pressure characteristics can be obtained from a low frequency band to
a high frequency band without reducing the capacity of the piezoelectric body by using the
transformer as a piezoelectric speaker. To provide a transformer for the
[0012]
SUMMARY OF THE INVENTION In order to achieve the above object, a transformer for a
piezoelectric speaker according to the present invention is used for a piezoelectric speaker
provided with a sound generator made of a piezoelectric material, and has a magnetic core, a
primary winding and a secondary winding. And both ends of the primary winding are connected
to an input terminal for inputting a drive signal for driving the sounding body, both ends of the
secondary winding are connected to the sounding body, and the secondary winding is It is
divided into 2 parts, and the core is wound by overlapping one divided secondary winding of the
secondary winding, the primary winding, and the other divided secondary winding of the
secondary winding in this order on the magnetic core. It is characterized by being
[0013]
As a result, the contact area between the primary winding and the secondary winding is more
than doubled as compared to that of the conventional transformer, so the degree of coupling
between the primary winding and the secondary winding is also improved.
[0014]
Also, by using this piezoelectric speaker transformer as a piezoelectric speaker, the degree of
coupling between the primary winding and the secondary winding is sufficient even if the
number of turns of the transformer winding is increased to increase the leakage inductance. In
addition, since the leakage inductance of the piezoelectric speaker is smaller than the
conventional one, sufficient sound pressure characteristics can be obtained from the low
frequency band to the high frequency band.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
described in detail with reference to the drawings.
FIG. 1 shows a piezoelectric speaker transformer according to an embodiment of the present
invention.
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The piezoelectric speaker transformer 10 includes an E-shaped magnetic core 11.
An inner secondary winding 12 a corresponding to the number of turns divided into about half of
the number of turns of the secondary winding 12 is wound around the axial portion of the
magnetic core 11.
Then, the primary winding 13 is wound from above the inner secondary winding 12 a around the
shaft portion of the magnetic core 11 in a state in which the inner secondary winding 12 a is
wound.
Further, the number of turns of the remaining half of the secondary winding 12 from above the
primary winding 13 corresponds to the axial portion of the magnetic core 11 in a state in which
the inner secondary winding 12a and the primary winding 13 are wound. The external secondary
winding 12b is wound.
Then, an I-shaped core 16 is provided at the open portion of the E-shaped magnetic core 11, and
the piezoelectric speaker transformer 10 is configured as an EI core-type transformer.
[0016]
Thus, the piezoelectric speaker transformer 10 has a structure in which the primary winding 13
is sandwiched between the secondary windings 12, and the contact area between the primary
winding 13 and the secondary winding 12 is The size is larger than that of the conventional
piezoelectric speaker transformer, and hence the degree of coupling between the primary
winding and the secondary winding is also improved.
[0017]
An explanatory view in the case where this piezoelectric speaker transformer 10 is used for a
piezoelectric speaker is shown in FIG.
The piezoelectric speaker 20 includes a sounding body 15 made of a piezoelectric body. The
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primary winding 13 of the piezoelectric speaker transformer 10 is connected to the input
terminal 14 of an amplifier (not shown) for driving the sounding body 15 of the piezoelectric
speaker 20, and the secondary winding 12 is It is connected to the sound generator 15 of the
piezoelectric speaker 20.
[0018]
Then, when an audio signal amplified by the amplifier is input from the input terminal 14 to the
primary winding 13, a magnetic field is generated in the primary winding 13, and power is
induced in the secondary winding 12 by this magnetic field, An electrical signal by this power is
applied to the sounding body 15, and sound is reproduced. FIG. 2 schematically shows a state in
which the secondary winding 12 is divided into two, and in the drawing, with respect to the
magnetic core 11, the inner secondary winding 12a, the primary winding 13, and the outer The
secondary windings 12b are arranged adjacent to each other, but in fact, as shown in FIG. 1, the
inner secondary winding 12a is wound around the magnetic core 11, and the primary winding
13 is wound thereon. Further, the external secondary winding 12b is wound thereon. And as an
example of the sounding body 15 made of a piezoelectric body, although not shown in the
drawings, a vibration made of a sounding body having a vibrating body made of a hemispherical
shell-like or spherical shell-like piezoelectric ceramic or a plate-like piezoelectric ceramic If the
sounding body etc. which have a body etc. are mentioned and the sounding body comprised with
the piezoelectric material, the shape etc. will not be specifically limited.
[0019]
The piezoelectric speaker using the piezoelectric speaker transformer 10 of this sandwich
winding structure has a large degree of coupling between the primary winding and the
secondary winding of the piezoelectric speaker transformer 10, and the leakage inductance is
compared with that of the conventional piezoelectric speaker And become smaller. As a means of
improving the sound pressure characteristic deterioration of the low frequency band by the iron
loss of the magnetic core 11 when the piezoelectric speaker transformer 10 is used from the low
frequency band around 20 Hz, the number of turns is significantly increased. When the influence
of loss is reduced, the leakage inductance is increased, but since the degree of coupling between
the primary winding and the secondary winding is originally sufficiently large, the leakage
inductance is sufficiently small compared to the conventional piezoelectric speaker. Therefore,
the high cutoff frequency of the piezoelectric speaker 20 becomes a high value, and the speaker
can reproduce the wide range from the low range to the high range with a sufficient sound
pressure.
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[0020]
Also, as a matter of course, there is no need to reduce the capacity of the piezoelectric body of
the sounding body 15, so that no decrease in the sound of the low frequency range occurs and
the efficiency (response) that the signal input to the sounding body is converted into sound.
There will be no decline.
[0021]
In the above embodiment, although the secondary winding is wound with the number of turns
being divided into about half, the primary winding may be formed into a sandwich, without being
limited to the division of the number of turns. The number of turns of the secondary winding is
not limited to half, as long as the secondary winding is divided and wound so as to sandwich it.
[0022]
In addition, as shown in FIG. 3, the frequency characteristic between the piezoelectric speaker
transformer and the sounding body is a curve having a convex peak near the high cutoff
frequency f0, as shown by a broken line, where the high cutoff frequency is f0. Or, it may be a
curve showing a gradual decreasing tendency from before the high frequency cutoff frequency
f0.
This is caused by the influence of resonance between the leakage inductance and the capacitance
of the piezoelectric material. In this case, the winding resistance is changed by changing the wire
diameter of the primary winding or the secondary winding, as shown by a solid line. It can be
approximated to the curve of such an ideal state.
[0023]
As described above, in the transformer for piezoelectric speaker according to the present
invention, the primary winding is sandwiched between the secondary windings, and the primary
winding and the secondary winding The contact area is increased compared to the conventional
piezoelectric speaker transformer, and the degree of coupling between the primary winding and
the secondary winding is also improved.
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In addition, even if the number of turns of the winding of the piezoelectric speaker transformer is
increased to increase the leakage inductance, a sufficient degree of coupling can be obtained
between the primary winding and the secondary winding. Since the leakage inductance is smaller
than the conventional one, sufficient sound pressure characteristics can be obtained from the low
frequency band to the high frequency band.
[0024]
Brief description of the drawings
[0025]
1 is a cross-sectional view showing the structure of a piezoelectric speaker transformer according
to an embodiment of the present invention.
[0026]
2 is an explanatory view showing a case where the piezoelectric speaker transformer according
to one embodiment of the present invention is used for a piezoelectric speaker.
[0027]
3 is an explanatory view showing the frequency characteristics of the piezoelectric speaker
transformer and the sound generator according to the present invention.
[0028]
4 is an explanatory view showing a conventional piezoelectric speaker transformer.
[0029]
5 is an explanatory view for explaining the frequency characteristics of the piezoelectric speaker
transformer to which the sounding body is connected.
[0030]
6 is an explanatory view for explaining the sound pressure characteristics of the sounding body
made of a piezoelectric body in the state where the piezoelectric speaker transformer is not
connected.
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[0031]
7 is an explanatory view for explaining the sound pressure characteristics when the leakage
inductance of the piezoelectric speaker transformer is used for the sounding body made of a
piezoelectric body.
[0032]
Explanation of sign
[0033]
DESCRIPTION OF REFERENCE NUMERALS 10 piezoelectric speaker transformer 11 magnetic
core 12 secondary winding 13 primary winding 14 input terminal 15 sounding body 20
piezoelectric speaker
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