JPH07185457A - Supersonic wave oscillator drive circuit - Google Patents

Abstract

PURPOSE:To provide a supersonic wave oscillator drive circuit which can be made compact and miniaturized at low cost and at the same time, drives an oscillator resonantly using a constant current. CONSTITUTION:A supersonic wave oscillator drive circuit which drives a supersonic oscillator 1 is equipped with a matching inductance 39 connected in parallel to a supersonic oscillator 1, and a low-pass filter 38 connected to the supersonic wave oscillator 1 and the matching inductance 39 connected side by side. Thus, the out-off frequency of the low-pass filter 38 coincides or is caused to almost coincide with the resonance drive frequency of the supersonic wave oscillator 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic oscillator drive circuit for driving an ultrasonic oscillator at a resonance point.

[0002]

2. Description of the Related Art Generally, in a device for generating a strong ultrasonic wave such as an ultrasonic scalpel for surgical operation or an ultrasonic processing device, in order to obtain a large ultrasonic vibration amplitude, an ultrasonic vibrator (hereinafter, simply The oscillator) is driven at or near its resonance frequency. As such a vibrator drive circuit, for example, one based on a PLL (phase locked loop) system that compares the drive voltage and the current of the vibrator and controls the drive frequency of the vibrator to match the resonance frequency. It has been known.

FIG. 5 shows a configuration of such a PLL type vibrator drive circuit. In FIG. 5, the vibrator 1 is driven by the power amplifier 15. In this vibrator driving circuit, since the vibrator 1 is used for medical purposes, a transformer 3 is provided between the vibrator 1 and the power amplifier 15. It is separated by insulation. Further, since the oscillator 1 is represented by an equivalent circuit in which a damping capacitance is connected in parallel to a series resonance circuit of an inductance, a capacitance, and a resistance, in FIG. 5, the matching inductance Ld is connected in parallel with the oscillator 1. , Oscillator 1
The braking capacity of is canceled. Therefore, the frequency characteristic of the impedance of the vibrator 1 includes only the actual resistance component at the resonance frequency, and the phase difference between the driving voltage and the current of the vibrator 1 becomes 0, and the frequency at that time is equal to the resonance frequency of the vibrator 1. Become.

In the vibrator drive circuit shown in FIG. 5, the vibrator 1
In order to drive the oscillator at the resonance frequency, the drive voltage and current of the vibrator 1 are detected by the transformers 4 and 5, respectively, and their outputs are amplified by the amplifier circuits 6 and 7, respectively,
Binarization circuits 8 and 9 perform binarization, and the outputs thereof are supplied to a phase comparison circuit 10 to compare the phases of voltage and current. The comparison output of the phase comparison circuit 10 is passed through a low pass filter (LPF) 11 and a voltage controlled oscillation circuit (VC).
O) 12 to output an oscillation signal corresponding to the phase difference, and the oscillation signal output is output to a voltage controlled oscillation amplifier (VC).
After being amplified by A) 13, it is supplied to the power amplifier 15 through the low-pass filter 14 to drive the vibrator 1.

On the other hand, the drive current of the vibrator 1 is set by the current value setting circuit 17 and supplied to one input terminal of the differential amplifier circuit 18. An actual drive current output from the amplifier circuit 7 is rectified by the rectifier circuit 16 and supplied to the other input terminal of the differential amplifier circuit 18, and the output of the differential amplifier circuit 18 is supplied to the low-pass filter 19. The voltage is then supplied to the voltage-controlled oscillation amplifier 13 so that the drive current of the vibrator 1 is controlled to be the constant drive current set by the current value setting circuit 17.

[0006]

However, in the above-mentioned conventional PLL type oscillator drive circuit, since the linear amplifier is used as the power amplifier 15,
There is a problem in that downsizing of the device and cost reduction are hindered because the drive circuit becomes large and measures against heat generation and a heat dissipation structure are required.

In order to solve such a conventional problem, the present applicant proposes a switching type vibrator driving circuit as shown in FIGS. 6 (a) and 6 (b), for example, in Japanese Patent Laid-Open No. 4-247268. is doing. Figure 6
The oscillator drive circuit shown in (a) has two switching M
The sources of the OS transistors 21 and 22 are commonly connected,
Those drains are connected to the primary side input terminal of the transformer 23 for insulation and separation, the oscillator 1 is connected to the secondary side of the transformer 23, and the oscillator drive signal is passed through the buffer 24 to one of the switching MOS transistors. 21 is applied to the gate of the other switching MOS transistor 22 through the inverting amplifier 25 and between the source of the switching MOS transistors 21 and 22 and the center tap of the primary side of the transformer 23. The output voltage of the connected DC drive power source 26 is switched to drive the vibrator 1. Further, the vibrator driving circuit shown in FIG. 6B is the vibrator driving circuit shown in FIG. 6A in which an inductance 27 is connected in series with the vibrator 1 on the secondary side of the transformer 23.

However, various experiments conducted by the present inventor have revealed that the above switching method has the following points to be improved. That is, FIG.
In the oscillator drive circuit shown in (a), the waveform of the oscillator drive voltage due to switching is a rectangular wave, and the drive current waveform is a differential waveform of the voltage waveform. Further, in the oscillator drive circuit shown in FIG. 6 (b), Since the inductance 27 is connected in series to the vibrator 1, the inductance 27 and the vibrator 1
The waveforms of the oscillator drive voltage and the drive current each approach a sine wave due to the braking capacity of, but include a large amount of high-frequency components. For this reason, in these oscillator drive circuits, PLL driving for driving the oscillator 1 at the resonance point becomes extremely difficult.

Such a problem is caused by connecting the inductance Ld in parallel with the vibrator 1 in order to cancel the damping capacity of the vibrator 1 as shown in FIG. Even if only is the actual resistance component, the oscillator drive voltage and current waveforms are still distorted, so that the same occurs.

As described above, the conventional switching-type vibrator drive circuit can be downsized and reduced in cost,
Since resonance point driving cannot be performed and constant current driving of the vibrator has not been realized, it has not reached a practical range in a drive circuit for resonance driving the vibrator with a constant current.

The present invention has been made in view of the above-mentioned conventional problems, and it is possible to achieve size reduction and cost reduction, and to appropriately configure the resonator so that it can be resonantly driven by a constant current. An object is to provide an ultrasonic transducer drive circuit.

[0012]

In order to achieve the above object, the present invention is an ultrasonic vibrator driving circuit for driving an ultrasonic vibrator, wherein a matching inductance connected in parallel to the ultrasonic vibrator is provided. And a low-pass filter connected to these ultrasonic transducers and a matching inductance connected in parallel, and the cut-off frequency of the low-pass filter is matched or substantially matched with the resonance drive frequency of the ultrasonic transducer.

[0013]

In this structure, the damping capacitance of the ultrasonic oscillator is canceled by the matching inductance connected in parallel with the ultrasonic oscillator, and the impedance of the ultrasonic oscillator has only the actual resistance component at the resonance point. When a drive voltage is applied to a parallel circuit of this ultrasonic transducer and a matching inductance through a low-pass filter whose cutoff frequency matches or almost matches the resonant drive frequency of the ultrasonic transducer, the input of the low-pass filter Even if the drive voltage waveform on the side is rectangular, the drive voltage waveform is shaped into a sine wave by the low-pass filter. Therefore, since the drive voltage waveform and the drive current waveform of the ultrasonic oscillator have sinusoidal waveforms, the ultrasonic oscillator can be driven at the resonance drive frequency by PLL control by phase comparison between them. In addition, during resonance drive, the impedance of the ultrasonic transducer is only the actual resistance component, so it is possible to drive the ultrasonic transducer at a constant current regardless of changes in the actual resistance component due to changes in the oscillator load. Becomes

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the construction of the essential parts of a first embodiment of the present invention. In this embodiment, the vibrator 1 is driven by the switching method. For this reason, for example, two switching means 31, 32 such as n-type power MOS field effect transistors are used to apply the drive signal of the vibrator 1 to the gate of one switching means 31 via the buffer 33, and The voltage is applied to the gate of the other switching means 32 via the inverting amplifier 34. The sources of the switching means 31 and 32 are commonly connected and connected to a reference potential terminal of a DC drive power source (not shown), and their drains have a center tap and the primary side of a step-up transformer 35 for insulation separation with a step-up ratio of 1: n. Connect to. The primary side center tap of the step-up transformer 35 is connected to the high potential output terminal of the DC drive power source.

Also, the vibrator 1 is connected to the secondary side of the step-up transformer 35 via a low-pass filter 38 having a coil 36 and a capacitor 37, and a matching capacitor for canceling the braking capacity of the vibrator 1 is connected. Coil 39
Are connected in parallel with the vibrator 1. Here, the values of the coil 36 and the capacitor 37 are set so that the cutoff frequency of the low-pass filter 38 matches or substantially matches the resonance drive frequency of the vibrator 1. Further, the impedance seen from the secondary side of the step-up transformer 35 is 0 [Ω] as much as possible.
The impedance of the step-up transformer 35 and the on-resistances of the switching means 31 and 32 are reduced so as to be close to

The operation of this embodiment will be described below. Figure 1
When a drive signal of the resonance drive frequency of the vibrator 1 is applied to the gate of the switching means 31 via the buffer 33 and to the gate of the switching means 32 via the inverting amplifier 34, the switching means 31, 32 Perform a complementary switching operation, whereby the output voltage of a DC drive power supply (not shown) is switched, and a push-pull switching output 2n times the power supply voltage appears on the secondary side of the step-up transformer 35. The output voltage on the secondary side of the step-up transformer 35 is the low-pass filter 3
8 is applied to the matching coil 39 and the vibrator 1,
As a result, the vibrator 1 is driven at the resonance drive frequency.

Since the cut-off frequency of the low-pass filter 38 matches or almost matches the resonance drive frequency of the vibrator 1, the rectangular-wave switching output voltage waveform and its differential-wave drive current waveform are: By passing through the low-pass filter 38, a sine wave having a resonance drive frequency is obtained. Therefore, in the vibrator 1, the damping capacity is canceled by the matching coil 39, and the impedance becomes only the actual resistance component, and the phase difference between the vibrator drive voltage and the current disappears.

According to this embodiment, even if the vibrator 1 is driven by the switching method, the switching output is shaped into the sine wave by the low-pass filter 38 and applied to the vibrator 1, so that the switching means 31, 32 are provided. It becomes possible to drive the resonator 1 in resonance by generating a drive signal to be applied to the resonator 1 by the resonance point tracking circuit as described in FIG.

Further, if the cutoff frequency of the low-pass filter 38 and the resonance frequency of the vibrator 1 match or substantially match, the impedance of the vibrator 1 at the time of resonance driving has only the actual resistance component, so that the vibration is generated. The current flowing through the child 1 is always constant irrespective of the change in the actual resistance component of the vibrator 1 due to the fluctuation of the vibrator load. Therefore, the input voltage of the low-pass filter 38 and the coil 36 and the capacitor 37 forming the low-pass filter 38. The oscillator 1 can be driven with a constant current by a current value uniquely determined by the value of.

FIG. 2 shows the low-pass filter 3 in FIG.
8 shows the oscillator drive current characteristics when the actual resistance component of the oscillator changes depending on the ratio between the cutoff frequency of 8 and the resonance frequency of the oscillator 1. As is apparent from FIG. 2, even when the cutoff frequency of the low-pass filter 38 and the resonance frequency of the vibrator 1 are not completely matched and are in a substantially matched state, within a certain range of the vibrator actual resistance component variation range, It can be seen that it exhibits constant current characteristics. Therefore, when the oscillator load variation based on the actual usage state of the oscillator 1, that is, the oscillator actual resistance change range is taken into consideration, the cutoff frequency of the low-pass filter 38 does not completely match the resonance frequency of the oscillator 1. It is understood that For example, when the actual resistance component of the vibrator 1 fluctuates to about 1 [kΩ], the cutoff frequency of the low-pass filter 38 may be matched within ± 2% of the resonance frequency. It will be.

On the other hand, in FIG. 1, when the actual resistance component of the vibrator 1 increases, the low-pass filter 3 increases in accordance with the increase.
The input impedance of 8 decreases. Therefore, if the output impedance of the step-up transformer 35 is large, the vibrator 1
The secondary output voltage of the step-up transformer 35 drops as the resistance increases, and as a result, the current flowing through the vibrator 1 drops and constant current characteristics are not exhibited.

FIG. 3 shows this state, and shows how the constant current characteristic of the oscillator current deteriorates due to the difference in the secondary output impedance r of the step-up transformer 35. In order to prevent the characteristic deterioration of the constant current, as described above,
The output impedance (internal resistance) of the circuit connected to the low-pass filter 38 is made as close to 0 as possible, that is, an ideal state. This is because, for example, the impedance of the step-up transformer 35, the ON resistance of the switching means 31 and 32 is reduced, or the drive power supply voltage is increased to increase the step-up transformer 35.
It can be achieved to some extent by reducing the step-up ratio of (1), and thereby the constant current characteristic deterioration can be minimized.

As described above, according to this embodiment, the resonator 1 is resonantly driven by the switching drive,
The constant current drive is possible at the same time, and not only high efficiency drive by the switching amplifier can be performed, but also the control for the constant current drive is not required, and the constant current drive can be achieved only by the passive components. Therefore, as compared with the conventional drive circuit using the linear amplifier and the drive circuit having the constant current control circuit, the oscillator 1 can be driven by the constant current resonance with a dramatically simple structure, and the number of parts of the oscillator drive circuit can be reduced. ,
The cost can be reduced and the circuit and the device can be downsized.

FIG. 4 shows a second embodiment of the present invention. This embodiment is the same as the embodiment shown in FIG.
The elements that perform the LL control and the constant current control are the same as those in FIG. 1, and the same reference numerals are given to the elements, and the description thereof will be omitted. In order to perform the PLL control, the transformer 41 for detecting the drive voltage is provided on the secondary side of the step-up transformer 35.
Are connected in parallel, and a transformer 42 that detects a drive current is connected in series. These transformers 41 and 42
The drive voltage signal and the drive current signal respectively detected at 2 are amplified by amplifier circuits 43 and 44, respectively, and then 2
The binarizing circuits 45 and 46 binarize the signals and supply their outputs to the phase comparing circuit 47 to compare the phases of the voltage and the current. The comparison output of the phase comparison circuit 47 is low-pass filtered by a low-pass filter (LPF) 48 as necessary, and then supplied to a voltage controlled oscillation circuit (VCO) 49, where an oscillation signal corresponding to the phase difference is output. And supplies the oscillation signal output to the buffer 33 and the inverting amplifier 34.

On the other hand, in order to perform constant current control, a variable power supply circuit 50 with a variable output voltage is used as a driving power supply for the vibrator 1, and its reference potential output terminal is used as the switching means 31, 32.
The high potential output terminal is connected to the primary side center tap of the step-up transformer 35, respectively. Further, in order to set the drive current of the vibrator 1, a current value setting circuit 51 is provided,
The set value is supplied to one input terminal of the differential amplifier circuit 52. The actual drive current output from the amplifier circuit 44 is supplied to the other input terminal of the differential amplifier circuit 52.
3 is rectified and supplied, and the output of the differential amplifier circuit 52 is passed through a low-pass filter (LPF) 54 and the variable power supply circuit 50.
To control the output voltage.

In this embodiment, the low pass filter 3
8 is configured such that its cutoff frequency matches or almost matches the resonance drive frequency of the vibrator 1 as in the first embodiment. Therefore, as in the first embodiment, the rectangular drive waveform by the switching drive is shaped into a sine wave by the low pass filter 38, so that the oscillator 1 has a phase difference of 0 between its drive voltage and drive current. As described above, the driving frequency by the PLL is controlled and resonance driving is performed.

Further, since the cutoff frequency of the low-pass filter 38 matches or almost matches the resonance drive frequency of the vibrator 1, the vibrator drive current is applied to the vibrator load as in the first embodiment. Regardless of the constant current. here,
In the case of the first embodiment, as described above, the output impedance of the step-up transformer 35, that is, the step-up transformer 35.
If the output impedance of the switching circuit including is large, the drive current decreases as the load of the vibrator increases, and the vibrator 1 cannot be driven with a constant current. However, in this embodiment, the differential amplifier circuit 52 is used. At, in accordance with the set value in the current value setting circuit 51, a control signal for correcting the change in the actual drive current detected by the transformer 42 is generated, and the output of the variable power supply circuit 50 is generated based on this control signal. Since the voltage is controlled, the vibrator 1 is always driven with the set current value.

Therefore, according to this embodiment, not only can the resonator 1 be resonantly driven by the switching method, but even if the output impedance (internal resistance) of the circuit connected to the low-pass filter 38 is so large that it cannot be ignored. The vibrator 1 can be driven with a constant current without being affected.

It should be noted that the present invention is not limited to the above-described embodiments, and many variations and modifications are possible. For example, in the above-described embodiment, the drive power supply is switched by the push-pull switching method and the switching output is applied to the vibrator through the step-up transformer. However, for example, when the drive power supply is switched by the single-end switching method, The present invention can be effectively applied even when the step-up transformer is not used. Further, the present invention can be effectively applied not only to the driving by the switching system but also when a linear amplifier is used. In this case, at the time of resonance drive, the oscillator is driven with a constant current at a current value that is uniquely determined by the input voltage of the low-pass filter and the values of the coil and the capacitor that form the low-pass filter. A circuit is not required, and the number of parts can be reduced, the cost can be reduced, and the size can be reduced accordingly.

[0030]

As described above, according to the present invention, the ultrasonic vibrator can be resonantly driven by the switching drive and at the same time the constant current can be driven. Therefore, the ultrasonic vibrator can be efficiently driven by the switching amplifier. It becomes possible to drive, and constant current drive can be performed only by passive components. Therefore, compared to a conventional drive circuit using a linear amplifier and a constant current drive circuit, the ultrasonic transducer can be driven with constant current resonance with a simple structure, reducing the number of parts, reducing the cost, and downsizing the circuit and the device. Can be planned.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a main part of a first embodiment of the present invention.

FIG. 2 is a diagram showing oscillator drive current characteristics with a parameter of a ratio between a cutoff frequency of a low pass filter and a resonant drive frequency of an oscillator in the configuration shown in FIG.

FIG. 3 is a diagram showing a state of constant current characteristic deterioration of a vibrator current due to a difference in secondary side output impedance of the step-up transformer in the configuration shown in FIG. 1.

FIG. 4 is a diagram showing a second embodiment of the present invention.

FIG. 5 is a diagram showing an ultrasonic transducer drive circuit using a conventional linear amplifier.

FIG. 6 is a diagram showing two examples of main parts of an ultrasonic transducer drive circuit according to a conventional switching method.

FIG. 7 is a diagram showing another example of the main part of an ultrasonic transducer drive circuit according to the conventional switching method.

[Explanation of symbols]

 1 Ultrasonic Transducer 31, 32 Switching Means 33 Buffer 34 Inverting Amplifier 35 Boosting Transformer 36 Coil 37 Capacitor 38 Low Pass Filter 39 Matching Coil 41, 42 Transformer 43, 44 Amplifying Circuit 45, 46 Binarizing Circuit 47 Phase Comparing Circuit 48 Low pass filter (LPF) 49 Voltage controlled oscillator circuit (VCO) 50 Variable power supply circuit 51 Current value setting circuit 52 Differential amplification circuit 53 Rectifier circuit 54 Low pass filter (LPF)

Claims (1)

[Claims] 1. An ultrasonic vibrator driving circuit for driving an ultrasonic vibrator, comprising: a matching inductance connected in parallel to the ultrasonic vibrator; and an ultrasonic vibrator and a matching inductance connected in parallel. An ultrasonic transducer driving circuit, comprising: a connected low-pass filter, wherein a cut-off frequency of the low-pass filter is matched or substantially matched with a resonance driving frequency of the ultrasonic transducer.