JPH0533111B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a drive circuit for an atomizer that atomizes liquid such as water using ultrasonic waves from an ultrasonic piezoelectric vibrator.

(Prior art) In an ultrasonic atomizer, during normal operation, the ultrasonic waves emitted from the ultrasonic piezoelectric vibrator are transmitted to the liquid, and one side of the vibrator is in contact with the liquid.
There is little power loss within the vibrator, and little heat is generated. However, if the vibrator is driven with very little or no liquid in the liquid tank to which the vibrator is attached, that is, if the vibrator is fired dry, the vibrations of the vibrator will not be transmitted to the air. It becomes hot inside the vibrator. As a result, the temperature inside the vibrator rises rapidly, damaging the vibrator and the transistors in the oscillation circuit for exciting the vibrator at high frequencies. To prevent such accidents, most ultrasonic humidifiers that atomize water for humidification use a float switch to stop the drive circuit that drives the vibrator when the water runs out. are doing. However, the reliability of the reed switch inside the float was not perfect, with a 0.1% to 0.2% chance of malfunction, and malfunction could also damage the vibrator or drive circuit.

Furthermore, dry heating prevention circuits have been proposed that prevent dry heating without installing a float switch, and the first one uses the conductivity and dielectric constant of the liquid.
An electrode is provided in the liquid, a voltage is applied between the electrode in the liquid and one of the grounded drive electrodes of the vibrator, and the vibrator drive circuit is controlled by changing the impedance between the two electrodes. The second type is controlled by utilizing changes in drive voltage, current, phase, etc. between opposing electrodes on both sides of the vibrator. The former has problems such as malfunctions when the electrodes become contaminated with water scale or the like, and peeling of the vibrator electrodes due to electrolytic corrosion because one drive electrode of the vibrator is energized. In addition, in the latter case, the vibrator is driven at low impedance (around 50 Ω), so the amount of change in the driving conditions due to changes in the presence or absence of liquid is small, causing problems such as temperature characteristics of the control circuit, which is not practical. It is possible to detect dry firing even when the vibrator is completely damaged and the oscillation conditions have completely changed. For this reason, it is mainly used as a secondary protection measure after the vibrator is completely damaged, and has the disadvantage that it is not possible to stop the operation of the drive circuit that excites the vibrator before the vibrator is damaged. There was.

(Objective of the Invention) The present invention aims to eliminate these drawbacks and protect the vibrator and the excitation unit that excites it by quickly and reliably detecting the dry firing state of the vibrator without using a float switch or the like. The present invention is intended to provide a drive circuit for an atomizer.

(Embodiments of the Invention) Hereinafter, embodiments of an atomizer drive circuit according to the present invention will be described with reference to the drawings.

In Fig. 1, the drive circuit of the atomizer consists of a rectifier 1 that rectifies and smoothes AC input (AC48V), an excitation unit 2 consisting of a grounded collector transistor oscillator circuit, and an ultrasonic piezoelectric vibrator TD. A control unit 3 that stops the operation of the excitation unit 2 when firing is detected.
It is composed of.

The rectifier 1 includes a rectifier 10 and a smoothing capacitor C ₁
It rectifies and smooths the AC input and outputs a DC voltage between the positive line P and the negative line E. The DC voltage of the rectifying section 1 is supplied to the excitation section 2 via an input current measuring resistor _R1 .

The excitation unit 2 is a collector-grounded transistor oscillation circuit in which an ultrasonic piezoelectric vibrator TD is connected between the collector and base of the transistor _Q1 , and the base bias circuit of the transistor _Q1 includes a variable resistor for adjusting high frequency output. VR ₁ and semi-fixed variable resistor
A series circuit of VR ₂ and transistor Q ₂ of control unit 3 is provided.

The ultrasonic piezoelectric vibrator TD has a first electrode 5 for driving formed on one side of the piezoelectric element as shown in FIG. A second electrode 6 for driving and a third electrode 7 for voltage detection are formed.

The control section 3 controls the voltage across the input current measuring resistor _R1 for measuring the input current to the excitation section 2.
An operational amplifier OP1 amplifies the voltage V ₄ smoothed by a resistor R ₂ and a capacitor C ₂ , and a voltage V ₁ appearing at the third electrode 7 of the ultrasonic piezoelectric transducer TD is smoothed by a resistor R ₂ and a capacitor C ₂ . ₃ , the voltage V ₃ rectified and smoothed by the capacitor C ₃ and the output voltage V ₂ of the operational amplifier OP1
Operational amplifier (comparator) OP2 for comparing
, transistors Q ₂ and Q ₃ , and operational amplifier OP1,
Step-down resistor to obtain power supply voltage for OP2
R ₄ , a capacitor C ₄ and a constant voltage diode D ₃ .

Note that the piezoelectric vibrator TD is provided at the bottom of a water tank of an atomizer (humidifier) that has a water tank that is maintained at a constant water level during normal operation.

In the above configuration, under normal conditions, the water tank of the atomizer is filled with a certain amount of water, and when the power is turned on in this state, a pulsed charging current is applied to each capacitor in the transistor oscillation circuit. A voltage V ₄ proportional to this is generated across the resistor R ₁ and this is applied to the operational amplifier OP in the control section 3.
1 to one input terminal. The amplification degree of this operational amplifier OP1 is (1+Rf/Ra), and the output voltage _V2 is _V2 =(1+Rf/Ra) _V4 , which is applied to one input terminal of the operational amplifier OP2. The other input terminal of operational amplifier OP2 is a resistor.
Since the time constants of R ₃ and capacitor C ₃ are set larger than the voltage V ₄ side, the voltage is approximately 0V. Therefore,
The output voltage of operational amplifier OP2 goes high and is applied to the base of transistor _Q3 . As a result, transistors Q2 and Q3 are turned on, a bias current flows to the base of oscillation transistor _Q1 of excitation section 2, and oscillation is started. When the oscillation starts, a high frequency voltage is also induced in the third voltage detection electrode 7 of the vibrator TD, and a voltage V ₁ is generated across the resistor R ₅ . This is the diode D ₁ ,
The detection voltage V ₃ is rectified and smoothed by D ₂ , resistor R ₃ and capacitor C ₃ and is applied to operational amplifier OP2. At this time, in order to maintain the output voltage of operational amplifier OP2 at a high level, the operational amplifier is set so that voltage V ₂ is approximately 50% higher than voltage V ₃ .
Set the amplification degree of OP1. For example, if the voltage V ₃ is approximately
When the voltage is 3V, the voltage _V2 should be approximately 4V. Note that this relationship also holds true when the oscillation output of the excitation section 2 is changed by adjusting the variable resistor _VR1 .
That is, when the voltage V ₁ in FIG. 3A changes from the minimum level L ₁ to the maximum level L ₂ , the voltage V ₂ proportional to the input current of the excitation section 2 also changes from the minimum level L ₃ to the maximum level as shown in FIG. 3B. Increase to level L ₄ . As a result,
The oscillation operation of the excitation unit 2 continues, and the transducer TD emits ultrasonic waves to the water in the aquarium to perform the atomization operation.

Now, normally, since the water in the water tank acts as a load on the piezoelectric vibrator TD, the voltage V ₃ obtained by rectifying and smoothing the output voltage V ₁ of the third electrode 7 of the vibrator TD is the input to the excitation section 2. Operational amplifier OP1 approximately proportional to current
_However , if for some reason there is less water to atomize and the transducer TD approaches dry firing, the voltage after time t ₁ in Figure 3A will decrease.
As can be seen from the waveform of V ₁ , the piezoelectric vibrator TD is in a substantially no-load state, and the third electrode 7 of the vibrator TD
The voltage appearing at V 3 becomes higher than normal, and therefore the voltage V ₃ obtained by rectifying and smoothing this voltage also becomes higher than normal. Therefore, at time _t2 , the output voltage of operational amplifier OP1 is approximately proportional to the input current of excitation section 2.
Voltage V ₃ becomes higher than V ₂ and the output of operational amplifier OP2, which serves as a comparator, changes to low level.
Therefore, the transistor Q ₃ is turned off, the transistor Q ₂ is also turned off, and the oscillation operation of the excitation section 2 is immediately stopped. After the oscillation stops, both input terminals of the operational amplifier OP2 become approximately 0V, and the output of the operational amplifier OP2 maintains a low level.
The user can resume the normal atomizing operation by once stopping the power supply to the drive circuit, and then supplying water to the aquarium to return it to the normal operating state, and then turning on the power.

Note that outputting an external signal when atomization is stopped can be easily achieved by using a signal from the collector of transistor _Q3 .

(Effects of the Invention) As explained above, according to the drive circuit for the atomizer of the present invention, the third electrode for detection is provided on the vibrator having the first and second opposing electrodes for drive, The voltage corresponding to the input current or voltage to the excitation unit for vibrator excitation is compared with the voltage of the third electrode to control the excitation unit on and off, so there is no need to use a conventional float switch etc. It is possible to quickly and reliably detect the dry state of the vibrator and perform an oscillation stop operation, thereby protecting the vibrator and circuit components.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the drive circuit for an atomizer according to the present invention, Fig. 2A is a plan view of an ultrasonic piezoelectric vibrator used in the embodiment, Fig. 2B is a bottom view of the same, and Fig. 3A and 3B are waveform diagrams for explaining the operation of the embodiment. 1... Rectifier section, 2... Excitation section, 3... Control section,
5...first electrode, 6...second electrode, 7...third electrode, 10...rectifier, _C1 to _C4 ...capacitor,
_D1 , _D2 , _D3 ...Diode, _R1 to _R5 ...Resistor, OP1, OP2...Operation amplifier, TD...Resonator.

Claims (1)

[Claims] 1. In a drive circuit for an atomizer that excites a vibrator provided at the bottom of a liquid tank containing a liquid, a third electrode for detection is attached to the vibrator having first and second opposing electrodes for driving. Driving an atomizer, characterized in that the excitation unit is controlled by comparing a voltage corresponding to an input current or voltage to an excitation unit that excites the vibrator with a voltage of the third electrode. circuit.