JP2001145849A - Driving circuit for ultrasonic probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving circuit for an ultrasonic probe which is stable in operation and high in reliability and prevents the breakage of circuit elements such as a transistor and a piezoelectric vibrator even when the load applied to the piezoelectric vibrator is changed. SOLUTION: A transistor self-exciting oscillation circuit for driving the piezoelectric vibrator of an ultrasonic probe is provided. A protective circuit 10 for controlling the increase of base voltage when it exceeds a prescribed value is formed in the base bias circuit of the transistor Q1 for oscillation of the oscillation circuit. The protective circuit 10 is connected with a transistor circuit having a transistor Q2 for protection between the base bias circuit and the emitter side power source line of the transistor Q1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit used for an ultrasonic probe of a health cosmetic device for promoting penetration of a chemical solution, lotion, etc. onto the skin, and more particularly to a self-excited oscillation for driving a piezoelectric vibrator. The present invention relates to a driving circuit for an ultrasonic probe which has improved reliability by preventing the oscillation transistor, the piezoelectric vibrator, and the like from being destroyed when the circuit is unloaded.

[0002]

2. Description of the Related Art FIG. 4 shows an example of an ultrasonic probe. A piezoelectric vibrator T for generating ultrasonic waves is provided on the bottom inside a metal cap 1.
D is bonded, and is driven by the high frequency power of the ultrasonic probe drive circuit 3 connected by the lead wire 2.

FIG. 5 shows a conventional example of the ultrasonic probe driving circuit 3 shown in FIG. 4, which uses a self-excited Colpitts oscillation circuit with a grounded collector. In this figure, a capacitor C1 is connected between the + power supply line and the − power supply line, the collector of the oscillation transistor Q1 is connected to the + power supply line, and the emitter is connected to the − power supply line via the coils L1 and L2. A piezoelectric vibrator TD for generating ultrasonic waves is connected between the collector and the base of the transistor Q1. A capacitor C2 is connected between the collector of the transistor Q1 and a connection point between the coils L1 and L2, and the base and the coil L
A capacitor C3 is connected between the connection point of L1 and L2. Further, a bias current is supplied to the base of the transistor Q1 via the filter circuit of the bias resistor R1 and the coil L3 and the capacitor C4 connected in series.

In the configuration of FIG. 5, the capacitor C
2 and the coil L2 equivalently form a parallel resonance circuit, the coil L1 is a compensation coil for waveform shaping, and the capacitor C1 works to reduce the high-frequency impedance between the + power supply line and the − power supply line. . The parallel resonance circuit is capacitive, the piezoelectric vibrator TD is inductive, and the Colpitts oscillation circuit oscillates to obtain an output.

[0005]

When the piezoelectric vibrator of an ultrasonic probe is driven by a driving circuit for an ultrasonic probe having a transistor self-oscillation circuit, the circuit configuration becomes simple, but the following problems arise. Occurs.

When a self-excited oscillation circuit is used for an application in which the load applied to the piezoelectric vibrator TD fluctuates, when the piezoelectric vibrator is not loaded, the oscillation voltage increases and a large voltage is applied to the oscillation transistor Q 1. You. For this reason, a voltage higher than the rated voltage is applied to the transistor Q1, and the transistor may be destroyed.

Since the energy of the vibration of the piezoelectric vibrator TD is not easily transmitted to the air, most of the vibration energy becomes heat and damages the piezoelectric vibrator.

[0008] Because of the above-mentioned problems, conventionally, an ultrasonic atomizer or the like using a piezoelectric vibrator for generating ultrasonic waves,
The power switch is turned off when there is no more water to be atomized by a float switch or the like. Alternatively, in applications where the load of the piezoelectric vibrator fluctuates, measures are taken to use a separately-excited drive circuit. However, the protection means by the float switch cannot be applied to anything other than the atomizer, and the circuit configuration of the separately-excited drive circuit is complicated.

Further, as disclosed in Japanese Patent Publication No. 3-16579, the applicant of the present invention has proposed to add a no-load interruption circuit to a transistor self-excited oscillation circuit. However, the use of a health / cosmetic device probe cannot be adopted because the unloaded state (when not applied to the skin) frequently occurs during use.

In view of the above, the present invention provides a stable and highly reliable ultrasonic wave that does not break down circuit elements such as transistors and piezoelectric vibrators even when the load applied to the piezoelectric vibrator fluctuates. It is an object to provide a drive circuit for a probe.

Other objects and novel features of the present invention will be clarified in embodiments described later.

[0012]

In order to achieve the above object, the present invention relates to an ultrasonic probe driving circuit having a transistor self-oscillation circuit for driving a piezoelectric vibrator of an ultrasonic probe. A protection circuit is provided in the base bias circuit of the oscillation transistor of the oscillation circuit, which suppresses a rise in the base voltage when the base voltage exceeds a predetermined value.

In the ultrasonic probe driving circuit,
The protection circuit may have a configuration in which a forward diode is connected in series or a transistor circuit or a constant voltage diode is connected between the base bias circuit and the power supply line on the emitter side of the oscillation transistor.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a drive circuit for an ultrasonic probe according to the present invention.

FIG. 1 shows a first embodiment of a drive circuit for an ultrasonic probe according to the present invention. In this figure, a protection circuit 10 including a protection transistor Q2 and resistors R2 and R3 is provided in addition to the configuration of the conventional example shown in FIG. That is, the series circuit of the resistors R2 and R3 is connected between the connection point S1 of the coil L3, the capacitor C4 and the bias resistor R1, and the negative power supply line (the power supply line on the emitter side of the oscillation transistor Q1). Transistor Q2
Is connected between the connection point S1 and the power supply line, and the base of the protection transistor Q2 is connected to the connection point of the resistors R2 and R3. Other configurations are the same as those in FIG. 5, and the same or corresponding portions are denoted by the same reference characters and description thereof is omitted.

In the first embodiment, when a load is applied to the skin by the ultrasonic probe, the piezoelectric vibrator TD
Q is low, the oscillation voltage does not become excessive, the base voltage of the oscillation transistor Q1 is within an appropriate voltage range, and the oscillation transistor Q1 is not damaged. Also, the ultrasonic energy of the piezoelectric vibrator TD is transmitted to the skin,
Since power consumption inside the piezoelectric vibrator TD is small, the piezoelectric vibrator TD is not damaged.

When no load is applied to the piezoelectric vibrator TD, the Q of the piezoelectric vibrator TD increases. When the oscillation voltage rises due to this, the base voltage that is fed back to the base side of the oscillation transistor Q1 also tries to increase, but the oscillation voltage is divided by the coil L3 and the capacitor C4 or the coil L3 and the resistor R1. Therefore, the voltage at the connection point S1 between the coil L3, the capacitor C4, and the bias resistor R1 also varies in proportion to the oscillation voltage. Since the protection transistor Q2 and the bias resistors R2 and R3 are connected between the connection point S1 and the -power supply line, respectively, when the voltage of the connection point S1 becomes higher than a certain voltage, the connection point of the bias resistors R2 and R3 is connected. Since the base potential rises and the protection transistor Q2 operates to allow the collector current to flow and suppress the rise of the base voltage, the base voltage of the oscillation transistor Q1 does not exceed a certain value. For this reason, the oscillation voltage is limited so as not to exceed a certain value, so that the oscillation transistor Q1 is not broken. In addition, since the oscillation voltage is limited, the input power under no load does not increase unnecessarily, so that the power applied to the piezoelectric vibrator TD is limited and the piezoelectric vibrator is not broken.

According to the first embodiment, in the ultrasonic probe driving circuit having the transistor self-oscillation circuit for driving the piezoelectric vibrator TD of the ultrasonic probe, the oscillation transistor of the transistor self-oscillation circuit is provided. Since the protection circuit 10 having the protection transistor Q2 for suppressing the rise of the base voltage when the base voltage exceeds a certain value is provided in the base bias circuit of Q1, even if the self-excited oscillation circuit has a simple circuit configuration, the load is reduced. The ultrasonic probe can be used in an unstable place, and the ultrasonic probe can be driven by an inexpensive circuit.

FIG. 2 shows a second embodiment of the ultrasonic probe drive circuit according to the present invention. In this figure, a bias adjustment transistor Q3, a resistor R4, and a variable voltage source VE1 are a base bias current control circuit of the oscillation transistor Q1, and are provided between the bias resistor R1 and the + power supply line for the purpose of controlling the ultrasonic output. It is connected. That is, the bias adjustment transistor Q3 is inserted in series with the bias resistor R1, and the DC voltage of the variable voltage source VE1 is applied to the base of the transistor Q3 via the resistor R4. By increasing or decreasing the voltage of the variable voltage source VE1, the base bias current of the oscillation transistor Q1 can be increased or decreased.

Further, between a connection point S1 between the coil L3, the capacitor C4 and the bias resistor R1, and a minus power supply line (a power supply line on the emitter side of the oscillation transistor Q1).
A protection circuit 20 composed of two forward diodes D1 and D2 connected in series is connected. Other configurations are shown in FIG.
The same or corresponding parts have the same reference characters allotted, and description thereof will not be repeated.

According to the second embodiment, the coil L
Since the voltage at the connection point S1 of the capacitor 3, the capacitor C4 and the bias resistor R1 does not exceed the sum of the forward voltage drops of the diodes D1 and D2 (because they are clipped by D1 and D2), the oscillation voltage is limited ( Oscillation transistor Q1 is not destroyed. Also,
The ultrasonic output can be controlled by the variable voltage source VE1. Other functions and effects are the same as those of the first embodiment.

FIG. 3 shows a third embodiment of the ultrasonic probe drive circuit according to the present invention. In this case, a constant voltage diode ZD is connected instead of the diodes D1 and D2 of the second embodiment. That is, the protection circuit 30 including the constant voltage diode ZD is connected between the connection point S1 of the coil L3, the capacitor C4, and the bias resistor R1, and the minus power supply line (the power supply line on the emitter side of the oscillation transistor Q1). I have. Other configurations are the same as those in FIG. 2, and the same or corresponding portions are denoted by the same reference characters and description thereof is omitted.

According to the third embodiment, the coil L
3, the voltage at the connection point S1 between the capacitor C4 and the bias resistor R1 does not exceed the Zener voltage, which is the forward voltage drop of the constant voltage diode ZD, so that the oscillation voltage is limited (the rise of the base voltage is suppressed). The oscillation transistor Q1 is not destroyed. Other functions and effects are the same as those of the above-described second embodiment.

Although the embodiments of the present invention have been described above, it is obvious to those skilled in the art that the present invention is not limited to the embodiments and that various modifications and changes can be made within the scope of the claims. There will be.

[0025]

In a place where the load is unstable, the oscillation transistor could be destroyed in the conventional self-excited oscillation circuit, so that it could not be used as a drive circuit of the ultrasonic probe. According to the present invention, it is possible to prevent the destruction of circuit components such as the piezoelectric vibrator and the transistor at the time of no load, and it is possible to use the device at a place where the load is unstable. The ultrasonic probe can be driven.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of a drive circuit for an ultrasonic probe according to the present invention
FIG. 3 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention.

FIG. 4 is a configuration diagram illustrating an example of an ultrasonic probe.

FIG. 5 is a circuit diagram showing a conventional example of a driving circuit for an ultrasonic probe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal cap 2 Lead wire 3 Drive circuit for ultrasonic probe 10, 20, 30 Protection circuit C1, C2, C3, C4 Capacitor D1, D2 Diode L1, L2, L3 Coil Q1, Q2, Q3 Transistor R1, R2, R3 R4 Resistance TD Piezoelectric vibrator VE1 Variable voltage source ZD Constant voltage diode

[Procedure amendment]

[Submission date] February 1, 2001 (2001.2.1)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

According to the third embodiment, the coil L
3, the voltage at the connection point S1 between the capacitor C4 and the bias resistor R1 does not exceed the Zener voltage, which is the reverse voltage drop of the constant voltage diode ZD, so that the oscillation voltage is limited (the rise of the base voltage is suppressed). The oscillation transistor Q1 is not destroyed. Other functions and effects are the same as those of the above-described second embodiment.

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Figure 3

[Correction method] Change

[Correction contents]

FIG. 3

Claims (2)

[Claims] 1. An ultrasonic probe driving circuit having a transistor self-oscillation circuit for driving a piezoelectric vibrator of an ultrasonic probe, wherein a base voltage is fixed to a base bias circuit of an oscillation transistor of the transistor self-oscillation circuit. A drive circuit for an ultrasonic probe, comprising a protection circuit for suppressing an increase in a base voltage when the above is provided. 2. The protection circuit according to claim 1, wherein a series connection of a forward diode, a transistor circuit, or a constant voltage diode is connected between the base bias circuit and an emitter-side power supply line of the oscillation transistor. Drive circuit for ultrasonic probe.