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JPS54118087

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DESCRIPTION JPS54118087
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electrical circuit diagram of a piezoelectric
buzzer according to the prior art E. FIG. 2 is a top view and a sectional view of a bimorph
vibration eave used for the piezoelectric buzzer E. FIG. Fig. 4 is an electric circuit diagram
showing each embodiment of the piezoelectric buzzer according to the present invention. P:
Bimorph oscillator Tr: Transistor R3: Resistor LC: Capacitor D: Curved diode.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric
buzzer, and it is an object of the present invention to provide an extremely simple circuit
configuration which consumes less current and emits intermittent noise. An example of a
conventional piezoelectric buzzer circuit is shown in FIG. P is a bimorph oscillator having three
electrodes, Tx is a transistor, and R and R2 are resistors. Fig. 2 shows a structural example of a
bimorph oscillator P having three electrodes at its 9th port. In FIG. 2 IC, 1 is a polarized
piezoelectric ceramic, 1 'and 1' each have electrodes provided by baking silver or the like on the
piezoelectric ceramic 1, 2 is a metal plate, 3 is a piezoelectric ceramic 1 and a metal plate 2 And
adhesive. Three electrodes are formed by the electrodes 1 ′, 1 ′ ′ and the metal plate 2.
When an electric field is applied between the electrode 1 and the metal plate 2, the piezoelectric
ceramic 1 expands and contracts, whereby the whole can be flexed and vibrated. Here, 1 ′ ′ is
a feedback electrode. In FIG. 1, when a power supply voltage is applied, an electric field is applied
to the bimorph oscillator P and the oscillator P is flexed, but the base potential of the transistor
Tr rises, and the transistor TI is turned ON. At this time, the electric field to the bimorph
oscillator P disappears, and the oscillator P is released from the crooked state, and the original
state is still recoiled in the opposite direction 1, then the base potential drops and the transistor
Tr is turned off. When a force is applied, the electric field is applied to the oscillator P again to
generate the deflection. As a result of this repetition, the vibrator P continues to take an image
and generates a continuous sound. In addition, the oscillator P has a natural frequency, and its
support is usually fixed at a node when vibrating at the natural frequency. In FIG. 1, the resistor
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R1 is used to limit the collector current of the transistor Tr, and the resistor R2 is for biasing the
transistor Tr. The piezoelectric buzzer having this circuit configuration is characterized in that it
is a very thin buzzer which consumes less current because it does not use an inductance element.
However, this piezoelectric buzzer is a continuous sound, and in order to generate a so-called
intermittent sound which is intermittently generated in a desired cycle, it is necessary to
intermittently generate + d power supply voltage or to apply an external trigger. Is a fairly
complex circuit. The present invention seeks to provide a piezoelectric buzzer that generates
intermittent noise with an extremely simple circuit configuration, while taking advantage of the
features of the piezoelectric buzzer described above. FIG. 3 shows an embodiment of the present
invention, and in addition to the circuit components in the prior art shown in FIG. Connected
between base and emitter.
In addition to this, in the alternative embodiment just shown in FIG. 4, a diode D is connected in
parallel to the resistor R3. In the circuit shown in FIG. 3C, when the power supply voltage is
marked, an electric field is initially applied to the bimorph oscillator P, but the capacitor C is
charged and the voltage VBE between the base and the emitter of the transistor Tr Rises, the
transistor Tr continues to be in the OFF state until it reaches the operating power, and all losses
are halted, and when the base-emitter tlfvBE reaches the operating point, the transistor Tr
becomes 01 (and the oscillator P becomes The oscillator P is released from the flexed state, and
is in the flexed state in the original state or in the opposite direction-\ reaction. At this time, the
charge stored in the capacitor C starts to discharge, but there is no speed to compensate for the
decrease in the base potential BE, and the transistor Tr is turned off. Then, an electric field is
applied to the transducer P again, and the transducer P is swayed. Seven 71, 7 Oe, Ko. When an
electric field is applied for the 5 characteristics, a voltage of the same phase is generated, and
when released and sagging in the opposite direction: the voltage of id is generated opposite to
this. For this reason, when the transistor Tr is 0) l), the electric field of the oscillator P disappears
and the base electrode acts to lower the base potential from the dead electrode, whereby the
transistor TI is turned off and during this period the capacitor C is turned on. Discharge is
performed. When the transistor Tr is turned OFF (this time the electric field is introduced to the
vibrator P this time, the vibrator P acts to raise the base potential from the flexible feedback
electrode, and the transistor Tr is turned ON). While the transistor Tr is off, the capacitor C is
charged, but if the resistance R2 is large and the capacitor C is also much larger than the
electrostatic capacitance of the oscillator P, the time constant will be charged only immediately
or if the capacitor is large. The transistor Tr is turned on, and the capacitor C is discharged. At
this time, since the charge of the capacitor C is also discharged to the feedback electrode of the
vibrator P, more −) charges are released than in the charging time. Jτ) Therefore, summarizing
the above, when the power supply voltage is added, no oscillation occurs while the capacitor C is
charged, and charging of the capacitor C causes the base potential ■ BE to be at the operating
point of the transistor Tr. The oscillation starts from the time when it reaches, and when the
charge of the capacitor C is raised, that is, the potential of the capacitor C is lowered while
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oscillating. During this period, the base potential {circle around (BE)} oscillates at an operating
point and a potential lower than this at a period of oscillation due to the action from the feedback
electrode while the amplitude becomes large and its central potential almost matches the
potential of the capacitor C.
Eventually, the potential of the capacitor C lowers, and the oscillation is stopped when it can not
be compensated by the action of the feedback electrode. Once the oscillation stops, the action of
the feedback electrode also does not act during oscillation. The oscillation stop state continues
while the potential of the capacitor C is recovered by charging. Eventually, when the base
potential vBE reaches the operating point due to charging, oscillation starts again, that is,
intermittent noise is obtained. This intermittent cycle changes the capacity of the -4 capacitor C
and the resistance value of the resistor R3 →. よ、。 If you connect a diode as shown in Fig. 4,
when the power supply voltage is large, the action of the return electrode prevents the base
potential VBE from dropping too much during oscillation. it can. That is, the electric field to the
vibrator P is released, and a negative voltage generated when the vibrator P recoils in the
opposite direction can prevent the peak 1 of the base potential BE from greatly decreasing in the
negative direction. . As in the following -F, in the present invention, intermittent noise can be
obtained by a very simple circuit configuration, and since the use of an inductance element is not
used, the feature of low consumption current, which is an advantage of the piezoelectric buzzer,
remains. Since all of them can be made very small and thin, it is possible to provide a
piezoelectric buzzer that generates intermittent sounds of small, thin and low power
consumption at very low cost.
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