JPS6012619Y2 - Piezoelectric vibrator excitation circuit for ultrasonic liquid atomization device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a piezoelectric vibrator excitation circuit for an ultrasonic liquid atomization device that continuously varies oscillation output.

Generally, an ultrasonic liquid atomizer uses a case molded from synthetic resin, and therefore, countermeasures against radiation noise emitted from the piezoelectric vibrator excitation circuit become a problem.

FIG. 1 shows a conventional piezoelectric vibrator excitation circuit using a grounded collector Colpitts self-excited oscillation circuit.

In this figure, an AC voltage applied between power supply terminals A and 8 is rectified by a rectifier 1, smoothed by a smoothing capacitor 2, and then supplied to a positive line P and a negative line N as a DC voltage.

The collector of the transistor 3 is directly connected to the positive line P, and the emitter is connected to the negative line N via the coils 4 and 5.

A piezoelectric vibrator 6 for generating ultrasonic waves is connected between the collector and base of the transistor 3.

Here, the ultrasonic radiation surface side terminal of the piezoelectric vibrator 6 is connected to the positive line P, and the positive line P is grounded.

Further, a capacitor 7 is connected between the collector of the transistor 3 and the connection point between the coils 4 and 5, and a capacitor 8 is connected between the base and the connection point between the coils 4 and 5.

Furthermore, a bias resistor 9 and an extension line 1 in series therewith are provided.
A bias current is supplied to the base of the transistor 3 through a variable resistor 11 connected at zero.

In the above configuration, the capacitor 7 and the coil 5 equivalently form a parallel resonant circuit, the coil 4 is a compensation coil for waveform shaping, and the capacitor 2 is connected between the positive line P and the negative line N. It works to reduce the high frequency impedance of.

The parallel resonant circuit is capacitive, the piezoelectric vibrator 6 is inductive, and the Colpitts oscillation circuit performs an oscillation operation to obtain an output of several tens of watts.

According to the above configuration, since the collector of the transistor 3 can be grounded, noise radiation from the collector side is prevented, but radiation noise from the extension line 10 connected to the base becomes a problem.

That is, the variable resistor 11 for varying the oscillation output is usually attached to the case of the ultrasonic liquid atomizer for convenient adjustment, and the extension line 10 tends to be long. Because high frequency current flows through the
This results in radio wave radiation from this part.

In view of the above points, the present invention has been developed by inserting a filter circuit into the base bias circuit of the oscillation transistor.
It is an object of the present invention to provide a piezoelectric vibrator excitation circuit for an ultrasonic liquid atomizer that can continuously vary the oscillation output and reduce radiation noise.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a piezoelectric vibrator excitation circuit for an ultrasonic liquid atomization device according to the present invention will be described below with reference to the drawings.

In FIG. 2, a filter circuit consisting of a coil 20 and a capacitor 21 is inserted into the base bias circuit of the oscillation transistor 3, and is connected in series with a bias resistor 9 via this filter circuit 22 by an extension line 10. A variable resistor 11 is connected between the collector and base of the transistor 3.

In this case, one end of the variable resistor 11 is connected to the positive side line P via the extension line 10.

The other configurations are the same as in FIG. 1. According to the above embodiment, the high frequency impedance of the base bias circuit can be made sufficiently high by inserting the filter circuit 22 compared to the driving impedance of the piezoelectric vibrator 6, and the high frequency current flowing through the base bias circuit can be significantly reduced. be able to.

Therefore, radiation noise caused by radio wave radiation from the extension line 10 can be reduced, and it is also possible to make the extension line 10 long to some extent.

Furthermore, by providing the variable resistor 11 on the positive line P side, the bias resistor 9 can attenuate high frequencies, so the coil 20 of the filter circuit 22 and the capacitor 2
The effect of 1 becomes even greater.

FIG. 3 shows another embodiment of the present invention in which the oscillation section is shielded in order to more actively reduce radiation noise.

In this figure, the oscillation section 30 is the filter circuit 2 of FIG.
2, the power supply line of the oscillation unit 30 is led out from the shield case 32 through a feedthrough capacitor 31, and connected to a power supply circuit 34 via a power supply noise filter 33.

Note that the piezoelectric vibrator 6 is attached to the bottom of the container 35, and a terminal on the ultrasonic emission surface side that is in contact with the liquid 36 in the container 35 is connected.

Further, the variable resistor 11 is connected to the oscillation section 30 by an extension line 10.

According to the embodiment shown in FIG. 3, not only the radiation noise on the extension line side but also the noise on the power supply side can be removed.

Note that when a shield and a noise filter similar to those shown in Fig. 3 are added to the circuit configuration shown in Fig. 1, the electric field strength of the radiated noise is approximately 55 dB (□ dB = 1 μV/m). Capacitor 21 is 10.0O
In the example shown in FIG. 3 in which the OPF and coil 20 are set to 100 μH, the result is approximately 40 dB, and extremely effective results were obtained by inserting the filter circuit 22 into the base bias circuit.

In each of the above embodiments, the case where the collector of the N-P-N transistor is grounded is illustrated, but it is clear that the same effect can be obtained even if the collector of the P-N-P transistor is grounded.

As described above, according to the piezoelectric vibrator excitation circuit of the ultrasonic liquid atomizer according to the present invention, even when a variable resistor is provided in the base bias circuit to adjust the output, the base bias of the filter circuit remains unchanged. By inserting it into the circuit, radiation noise can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a piezoelectric vibrator excitation circuit of a conventional ultrasonic liquid atomizer, and FIG. 2 is a circuit diagram showing an embodiment of a piezoelectric vibrator excitation circuit of an ultrasonic liquid atomizer according to the present invention. , 3rd
The figure is a block diagram showing another embodiment of the present invention. 1... Rectifier, 2. 7. 8. 21...
...Capacitor, 3...Transistor, 4,
5.20... Coil, 6... Piezoelectric vibrator, 9... Bias resistor, 10...
Extension line, 11... Variable resistor, 22...
...Filter circuit, 30...Oscillation section, 31...
...Feedthrough capacitor, 32...Shield case, 33...Power supply noise filter.

Claims (1)

[Scope of utility model registration request] An ultrasonic liquid atomizer having an automatic oscillation circuit with a grounded collector that drives a piezoelectric vibrator for generating ultrasonic waves, and a variable resistor for varying the output in the base bias circuit of the transistor of the automatic oscillation circuit. In the piezoelectric vibrator excitation circuit,
A piezoelectric vibrator excitation circuit for an ultrasonic liquid atomizer, characterized in that a filter circuit is inserted into the base bias circuit of the transistor, and the variable resistor is connected to the base of the transistor via the filter circuit.