JPS61134532A - Driver circuit for supersonic type atomizer unit - Google Patents

Abstract

PURPOSE:To enable a protection of some circuit components to be performed against their damage or burning by a method wherein a protection circuit is arranged in which an electrical current supplied from a base bias circuit is biased or shielded to terminate an oscillation or driving of a transistor. CONSTITUTION:Increased peak value of a base current turns on a transistor Q2 in a protection circuit 10, an electrical current is instantaneously flowed in the resistor R6 and the capacitor C7 through a diode D2, voltage V1 at both ends of the resistor R6 is applied to the gate of the thyristor (SCR)11 through diode D3 and SCR11 turns off. Therefore, the connection points of the resistors R1 and R2 in the base bias circuit are biased by SCR11 to the ground level, no base current is flowed in the transistor Q1 and then the oscillation is terminated. With the foregoing, the vacant operation in the Piezoelectric oscillator TD is rapidly sensed and further it is possible to protect the circuit components such as a Piezoelectric oscillator element or transistor or the like against their damage or burning.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to an ultrasonic atomizer drive circuit that atomizes liquid such as water using ultrasonic waves of an ultrasonic piezoelectric vibrator, and particularly relates to The present invention relates to an ultrasonic atomizer drive circuit equipped with a protection circuit for protecting a piezoelectric vibrator and the transistors that drive it from damage during dry firing.

(Prior art and problems) In an ultrasonic atomizer, during normal operation, the ultrasonic waves emitted from the ultrasonic piezoelectric vibrator are transmitted to the liquid, and since the vibrator surface is in contact with the liquid, the ultrasonic wave is transmitted to the liquid. The sound waves are incident on the liquid, resulting in less power loss and less heat generation within the vibrator.

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 vibration of the vibrator is difficult to transmit to the air. Most of the vibrator energy becomes heat inside the vibrator. As a result, the temperature inside the vibrator rises rapidly, damaging the vibrator and the transistors in the drive circuit for exciting it at high frequencies. To prevent such accidents, most ultrasonic humidifiers that atomize water for humidification use a 70-toe switch to stop the drive circuit that drives the vibrator when the water runs out. are doing.

FIG. 5 shows an example of a conventional ultrasonic atomizer drive circuit using a float switch. In this diagram, the AC input (A
C48V) is rectified by a rectifier DS and a hood capacitor C1, and is supplied to a flefter grounded transnoster oscillation circuit (modified col and hood type oscillation circuit). An ultrasonic piezoelectric vibrator TD is connected between the collector and base of the oscillating transistor Q1 of the transistor oscillation circuit via a capacitor C2 and a base resistor R5. A float switch FSW is inserted in the base bias circuit of the transistor Q1 in series with a variable resistor VR for output adjustment.

Note that CI, C1, C9, and C6 are capacitors, D is a diode, F is a fuse, L+, L2-L- is a coil, and R1 to R4 are resistors.

In the configuration shown in FIG. 5 above, when the liquid in the liquid tank to which the vibrator TD is attached is very low or completely absent, the float switch FSW turns off and cuts off the base current to the transistor Q. This is done to prevent dry firing.

However, the reliability of the reed switch inside the 70 switch FSW is not perfect and ranges from 0.1% to 0.
．． 2% had the possibility of malfunction, which could damage the transducer or drive circuit.

For this reason, various dry heating prevention means have been proposed to prevent dry heating without providing a float switch. The first method utilizes the electrical conductivity and permittivity of the liquid, provides an electrode in the liquid, applies a voltage between the electrode in the liquid and one of the grounded drive electrodes of the vibrator, and then The vibrator drive circuit is controlled by the impedance change between the two electrodes. The second method uses a 3nIi element type vibrator to stop the oscillation of the drive circuit by utilizing the characteristic that the amplitude of the vibrator increases when the liquid load is removed.

However, these methods for preventing dry heating have not been put into practical use due to problems such as electrolytic corrosion, impurities contained in the water that make the electrodes non-conductive, and cost.

(Measures to Solve the Problems) In view of the above points, the present invention detects the current flowing into the base of the oscillation or driving transistor in a configuration that atomizes liquid using a piezoelectric vibrator. By providing a protection circuit that bypasses or cuts off the current supplied from the base bias circuit of the transistor to stop the oscillation or drive of the transistor, the dry firing state of the piezoelectric vibrator can be quickly detected, and the The present invention aims to provide an ultrasonic atomizer drive circuit that can protect circuit components such as piezoelectric vibrators and transistors from destruction and burnout.

(Function) In the ultrasonic atomizer drive circuit of the present invention, the peak value of the base current of the oscillation or drive transistor to which the piezoelectric vibrator is connected increases several seconds after the piezoelectric vibrator becomes dry. When focusing on the phenomenon and detecting an increase in the peak value,
It is determined that a dry firing state has occurred, and the current supplied from the base bias circuit is bypassed or cut off to stop the oscillation or driving of the transistor. The phenomenon in which the peak value of the base current increases is due to the fact that when the piezoelectric vibrator enters the dry firing state, the Q temporarily decreases due to self-heating immediately before destruction.

(Example) Hereinafter, an example of the ultrasonic atomizer drive circuit according to the present invention will be described with reference to the drawings.

The ultrasonic atomizer drive circuit shown in FIG. 1 has a circuit configuration equipped with the Kobicta grounded transistor oscillation circuit (modified Colpitts type oscillation circuit) shown in FIG. This is what I did. That is, the protection circuit 10 includes transistors Q2, 5CR (Sirisk) 11
, diode D21D3, capacitor C9 and resistor R
6, and a resistor R1 proportional to the base current of the transistor Q1 between the base and emitter of the transistor Q2.
A voltage is applied across the . The function of the diode D2 is that the voltage between the base of the transistor Q1 and the ground line N2 is a waveform in which alternating current is superimposed, and the base of the transistor Q is the diode characteristic of the base and collector of the transistor Q2, and the resistor This is to prevent abnormal oscillation caused by grounding through R6. In addition, the diode D is connected to the 5C after 5CRII is turned on.
It works to prevent turning off due to negative voltage being applied to the RII date.

In the above configuration, under normal conditions, the base current of transistor Q is shown in Figure 2 (A), and the collector current is shown in Figure 2 (B).
The waveform is as follows, and the base current is approximately 0°2 to 0.4
It is A. The value of the base resistor R5 at this time is set to a value (for example, 2.degree. 2.OMEGA. in this embodiment) that the voltage generated across the base resistor does not turn on the transistor Q2.

Now, if the 70-tooth switch FSW operates normally, the liquid in the liquid tank to which the transducer TD is attached will be very low, or if there is no liquid at all, the 70-tooth switch FS will
W should be turned off and the dry firing state should be prevented, but if the 70-toe switch FSW remains closed for some reason, the vibrator TD will be dry fired, and the Q will be reduced due to its self-heating. A drop occurs after a few seconds. The base current waveform of transistor Q after several seconds of dry firing is shown in FIG. 3(A), and the collector current waveform is shown in FIG. 3(B).

It can be seen that the peak value of the base current of the transistor Q1 has increased to about twice as much due to this dry firing.
is turned on, and at this time, current momentarily flows through the diode D2 to the resistor R6 and capacitor C7, and the voltage 1 across the resistor R6 is applied to the date of SCR'll through the diode D, and as a result, 5CRII turns on. . Therefore, the connection point of the resistor R1=R2 of the base bias circuit of the transistor Q+ is bypassed by SC'RII to 7-, so that no base current flows through the transistor Q, and oscillation stops.

Furthermore, Fig. 4 (A) shows the base current waveform of the transistor Q1 after the dry firing state continues for several minutes, and Fig. 4 (B) shows the collector current waveform at that time.
shows. In the state shown in FIG. 4, the polarization of the piezoelectric vibrator begins to be lost due to heat, the off period of the transistor Q is reduced, and the collector loss is increased.

Therefore, if the oscillation is not stopped in the state shown in Figure 3,
Transistor Q1 will also be damaged soon.

(Effects of the Invention) As explained above, according to the ultrasonic atomizer drive circuit of the present invention, in a configuration that atomizes liquid using a piezoelectric vibrator, the ultrasonic atomizer drive circuit of the present invention has a structure in which liquid is atomized using a piezoelectric vibrator. By providing a protection circuit that detects current and bypasses or cuts off the current supplied from the base bias circuit of the transistor to stop oscillation or driving of the transistor, the dry state of the piezoelectric vibrator can be quickly detected. Furthermore, circuit components such as the piezoelectric vibrator and transistor can be protected from destruction and burnout. Further, the protection circuit can be constructed at low cost, and a general two-terminal type vibrator can be used as the vibrator.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the ultrasonic atomizer drive circuit according to the present invention, and tIS2 (A) is a waveform showing the base current of the oscillation transistor during normal operation of the ultrasonic atomizer drive circuit. Figure 3 (B) is a waveform diagram showing the collector current, Figure 3 (A) is a waveform diagram showing the base current of the oscillation transistor several seconds after dry firing of the ultrasonic atomizer drive circuit, B) is a waveform diagram showing the collector current, Figure 4 (A)
is a waveform diagram of the base current of the oscillating transistor released several minutes after dry firing of the ultrasonic atomizer drive circuit, Figure (B) is a waveform diagram showing the collector current, and Figure 5 is a waveform diagram of conventional ultrasonic atomization. FIG. 2 is a circuit diagram showing an example of a device drive circuit.

Claims (1)

[Claims] (1) In an ultrasonic atomizer drive circuit that atomizes liquid using a piezoelectric vibrator, a current flowing into the base of an oscillation or drive transistor is detected, and the current is supplied from the base bias circuit of the transistor. An ultrasonic atomizer drive circuit comprising a protection circuit that bypasses or cuts off the oscillation or driving of the transistor.