JPS6233439Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a piezoelectric buzzer having a structure in which a piezoelectric ceramic thin plate is attached to a thin plate of an elastic body such as metal, and in particular, a so-called self-oscillation method that uses the resonance phenomenon of the piezoelectric buzzer to oscillate. An object of the present invention is to provide a piezoelectric buzzer that can improve the stability of self-oscillation in a piezoelectric buzzer used for.

FIG. 1 shows an example of a conventional piezoelectric buzzer used in a self-excited oscillation system, and numeral 1 is a thin metal plate on which a piezoelectric ceramic thin plate 2 is pasted. Electrodes are attached to the front and back surfaces of the piezoelectric ceramic plate, and the electrodes on the back surface are electrically connected to the metal plate 1. Further, a main electrode 3 and a return electrode 4 are provided on the surface.
This piezoelectric buzzer is held by supporting the vibration nodes as shown in FIG. 2 in order to utilize its resonance characteristics in a self-excited oscillation circuit. In FIG. 2, 5a and 5b are support stands that support the vibration nodes of the piezoelectric buzzer, and 6 is an electrode provided on the back surface. The most common self-excited oscillation circuit is the one shown in Figure 3, in which the metal plate 1 (electrode on the back side of the piezoelectric ceramic plate) of the piezoelectric buzzer shown in Figure 1 is connected to the emitter of the oscillation transistor 7 and the main electrode on the front side. 3 is electrically connected to the collector, and a return electrode 4 is electrically connected to the base. When the piezoelectric buzzer of FIG. 1 is supported as shown in FIG. 2 and a constant AC voltage is applied between the metal plate 1 and the main electrode 3 and the frequency is changed, the difference between the metal plate 1 and the return electrode 4 is The voltage appearing between them is as shown in FIG. Therefore, if the self-excited oscillation circuit shown in FIG. 3 is constructed using this piezoelectric buzzer, it will oscillate near ₁ , which is the first resonance frequency of the piezoelectric buzzer. However, the resonant frequency of a piezoelectric buzzer is not only ₁ , but also a higher-order resonant frequency _o
If the higher-order resonance level becomes higher than the first-order resonance level due to the support condition of the piezoelectric buzzer, the ambient temperature, etc., it will oscillate at that higher-order resonance frequency, making it extremely unstable. contains elements.

Therefore, the present invention was devised for the purpose of eliminating such instability of oscillation, and an embodiment of the piezoelectric buzzer of the present invention shown in FIG. 5 will be described.

In FIG. 5, 8 is a metal thin plate, 9 is a partially polarized piezoelectric ceramic thin plate, and an electrode is provided on the entire back surface of 9 and electrically connected to the metal plate. A main electrode 10 and a return electrode 11 are provided on the surface of the piezoelectric ceramic thin plate 9, and in addition to these, a third capacitive electrode 12 is provided. The ceramic plate between the main electrode 10 and the return electrode 11 and the metal plate 8 is polarized and exhibits a piezoelectric phenomenon, but the ceramic plate between the capacitive electrode 12 and the metal plate 8 is not polarized and is a mere dielectric. It's summery. When this piezoelectric buzzer is used, the electrodes 11 and 12 are electrically connected by a lead wire or the like. Note that 1 does not need to be a metal plate as long as it is a thin plate having elasticity.

As described above, the main electrode 10 and the return electrode 11 of the piezoelectric buzzer according to the present invention play the same role as the electrodes 3 and 4 in the conventional piezoelectric buzzer shown in FIG. 1, but the return electrode 11 is connected to the capacitive electrode 12. Therefore, the capacitance between the return electrode 11 and the metal plate 8 is much larger than that of a conventional piezoelectric buzzer. Therefore, the piezoelectric buzzer of the present invention is supported at the node as shown in Fig. 2, and a constant AC voltage is applied between the metal plate 8 and the main electrode, and while changing the frequency, the metal plate 8 and the return electrode (= capacitance) are applied. When measuring the voltage appearing between the electrodes, the result is as shown in Figure 6. Compared to the first resonance of the piezoelectric buzzer, the level of higher-order resonance is smaller due to the increase in the capacitance of the return electrode. Become. Therefore, this piezoelectric buzzer is the third
When used in the self-excited oscillation circuit shown in the figure (needless to say, the metal plate 8 is connected to the emitter of the transistor and the main electrode 10 is
The electrodes 11 and 12 are electrically connected to the collector and the base. ) The oscillation frequency is stably fixed at the first resonance frequency of the piezoelectric buzzer and does not jump to a higher resonance frequency. The same effect can be obtained by installing a discrete capacitor between the base and emitter of the transistor in the oscillation circuit shown in Figure 3 when using a conventional piezoelectric buzzer, but the cost of the capacitor and its installation will increase. I can't avoid it. In comparison, the present invention is a highly practical and useful device that can stabilize oscillation with almost no increase in cost.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an example of a conventional piezoelectric buzzer, FIG. 2 is a side view showing node support of the piezoelectric buzzer, and FIG. 3 is a circuit diagram of an example of a self-excited oscillation circuit using a piezoelectric buzzer. Fig. 4 is a characteristic diagram showing the resonance characteristics of a conventional piezoelectric buzzer, Fig. 5 is a plan view of a piezoelectric buzzer according to an embodiment of the present invention, and Fig. 6 is a characteristic diagram showing the resonance characteristics of the piezoelectric buzzer of the present invention. be. 8... Metal plate, 9... Piezoelectric ceramic thin plate, 10...
Main electrode, 11...return electrode, 12...capacitance electrode.

Claims (1)

[Scope of utility model registration request] It has an elastic thin plate to which a porcelain thin plate is attached, and a main electrode, a return electrode, and a capacitive electrode provided on the surface of the porcelain thin plate, and only the porcelain thin plate is between the main electrode, the return electrode, and the elastic thin plate. A piezoelectric buzzer that is polarized and has the capacitance electrode and the return electrode connected to each other.