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JPS5647099

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DESCRIPTION JPS5647099
Description 11 Title of Invention
Piezoelectric buzzer circuit
8. Detailed Description of the Invention The present invention relates to a piezoelectric buzzer
circuit using a two-terminal type piezoelectric element having a return electrode. In particular, it
relates to a pressure buzzer circuit capable of efficiently generating an audible sound.
Conventionally, a piezoelectric buzzer circuit using a two-terminal type piezoelectric element has
been constructed as shown in FIG. In FIG. 1 (°, 1 is a two-terminal type piezoelectric element,
and 2 is a drive transistor. In the piezoelectric element 1, main electrodes 1a and 1'b are formed
on both sides of the piezoelectric body, and one side of the piezoelectric body is electrically KIN!
A refined relatively small area feedback electrode 1C is formed. The piezoelectric element 1 is
bonded to a diaphragm (not shown) and configured as a composite vibrator. Main electrode 1 a
of piezoelectric element 1, collector of ib transistor 2. Each of the emitters is connected to the
emitter, and the output of the transistor 2 causes the piezoelectric element 1 to vibrate in a
predetermined vibration mode, for example, a radial mode. "C, the composite vibrator to which
the diaphragm is attached is bent and vibrated to generate an audible sound. The feedback
electrode 1C of the piezoelectric element 1 is connected to the pace of the transistor 2 through
the base resistor 3 and the signal detected by the electrode 1C is fed back to the base "C". 4 is a
bias resistance and 5 is a collector resistance. The frequency characteristic of such a piezoelectric
buzzer circuit is as shown by a solid line B in FIG. This characteristic is obtained by removing the
capacitor 6EndPage: 1 and the resistor 7 from the measurement circuit of FIG. 3 "[In the
measurement result, one curve shows a voltage characteristic and the curve aB shows a phase
characteristic. The feedback (FB) voltage in this characteristic diagram is proportional to the
sound pressure of the audible sound generated from the composite vibrator. As is apparent from
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the same characteristic, the frequency at which the peak value of the FB voltage (sound pressure
level) and the frequency at which one phase 峨 θ is を deviate from each other. The temperature
is about ° C. On the other hand, about 10 (LB lower value. However, the sound pressure level of
the ΩΩ9 listening also decreases. So when the present invention 1g lump? An object of the
present invention is to provide a piezoelectric buzzer circuit capable of generating oscillation at a
peak value of a B voltage level and generating an audible sound at a high level of sound pressure.
That is, according to the present invention, the output of the drive transistor is applied between
the electrodes of the two-terminal type piezoelectric element to oscillate the .degree. C.
piezoelectric element and a phase shift circuit is inserted in the feedback path from the feedback
electrode to the transistor. . (3) The following is a detailed description of an embodiment of the
present invention with reference to the drawings. In FIG. 2, C, piezoelectric element 1, drive
transistor 2.
Base bias resistance3. Since the bias resistor 4 and the collector resistor 5 are the same as those
described in 1M, the same reference numerals will be appended [the description thereof will be
omitted. A phase correction capacitor 6 is connected in parallel to the base bias resistor 3C. 7 # i
bias resistance. When a CR phase shift circuit is formed by the capacitor 6 and the input
impedance of the transistor 2 and this phase shift circuit shifts the phase difference θ by about
60 °. The IFBFB voltage has a large value at the frequency of the phase difference θ = 0. As a
result, oscillation occurs at a sound pressure level that indicates a peak value during driving, and
a loud audible sound is generated. In such a circuit configuration, the FB voltage characteristic
and the phase characteristic measured by the measurement circuit of FIG. 3 are as shown by
curves A and C of FIG. 4, respectively. As is apparent from these curves A and C, the maximum FB
voltage is obtained at θ; 0 at which one shot occurs, which is due to the gain of the large town
transistor 2, and the maximum value when the gain of the transistor 2 is not considered It goes
without saying that it becomes [1clB. In the above embodiment, the phase shift circuit is
constituted of the capacitor 6 and the manual impedance of the transistor 2; The point is that a
phase shift circuit may be inserted in the feedback path from the R return electrode 1C of the
piezoelectric element 1 to the transistor 2. Since at least one phase shift circuit is inserted in the
feedback path from the piezoelectric element to the transistor as described above, the present
invention can drive the piezoelectric element at a sound pressure level indicating a peak value. It
has the effect that a large audible sound can be generated efficiently.
4. Brief description of the drawings FIG. 1 shows a conventional piezoelectric buzzer circuit, FIG.
2 shows an embodiment of the piezoelectric buzzer circuit according to the present invention,
and FIG. 3 shows characteristics of the piezoelectric buzzer circuit. FIG. 4 is a diagram showing
frequency characteristics in the prior art and the present invention. 1 ··· · · · · · · · · · · · · · · · · · · · · · · ·
························································································
· · · · · drive 6 v # 10. −コンデンサ。 Patent Assignee Murata Manufacturing Co., Ltd. EndPage: 2
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Fig. 1 Fig. 21! 1 Figure 3 ヰ EndPage: 3
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