TWI524649B - Polar switch circuit - Google Patents

Description

Polarity switching circuit

The present invention relates to a polarity switching circuit, and more particularly to a polarity switching circuit that can output an output AC voltage of a smooth AC waveform to drive a piezoelectric actuator.

With the advancement of technology, various 3C products have been regarded as an important force to promote market growth. Undoubtedly, such development trend will continue, and with the advancement of microelectronics technology, 3C products are not only increasingly complex in function, but their size is also becoming smaller and the portability is greatly improved. Therefore, it is easy to handle various matters with 3C products. Recently, piezoelectric actuators have been developed for use in 3C products. Piezoelectric actuators have low voltage, no noise interference, small volume, fast response, low heat generation, high precision, high conversion efficiency, and Control is easy and many other advantages.

Piezoelectric actuators typically require an alternating voltage to act to drive the piezoelectric actuator to perform periodic high-speed motion, so in practice the piezoelectric actuator requires a drive system that will drive the connected direct current. The voltage is converted to output an alternating voltage to drive the actuator. Please refer to FIG. 1, which is a circuit block diagram of a conventional drive system for driving a piezoelectric actuator. As shown in FIG. 1, the conventional driving system 1 is configured to convert a DC input voltage V _DC to generate output AC voltages V _o1 and V _o2 to drive the piezoelectric actuator 9 (as shown in FIG. 2A). A booster circuit 10, a voltage multiplying circuit 11 and a polarity switching circuit 12 are included. The booster circuit 10 is connected to the DC input voltage V _DC and boosts the DC input voltage V _DC into a transient voltage by switching operation of internal switching elements and energy storage and filtering of components such as internal inductors, capacitors and diodes. V _T . The voltage multiplying circuit 11 is connected to the transient voltage V _T and is multiplied to, for example, four times the DC high voltage V _B . The polarity switching circuit 12 converts the DC high voltage V _B into the output AC voltages V _o1 and V _o2 to drive the piezoelectric actuator 9.

Please refer to Figures 2A, 2B and 3, together with Figure 1, where Figure 2A is the internal circuit structure diagram of the polarity switching circuit shown in Figure 1, and Figure 2B is the digital signal shown in Figure 2A. f _sw is a schematic diagram of the operation of the circuit at a low level, and FIG. 3 is a voltage timing waveform diagram of the 2A or 2B diagram. As shown, the conventional polarity switching circuit 12 is mainly connected to a DC high voltage V _B , an input DC low voltage V _in and a digital signal f _sw , and is converted into output AC voltages V _o1 and V _o2 to drive the piezoelectric actuator. 9 repeated operation, wherein the polarity switching circuit 12 can be a first current limiting resistor R21, a second current limiting resistor R22, a third current limiting resistor R23, a first transistor switch Q21, a second transistor switch Q22, a third transistor The switch Q23, the fourth transistor switch Q24, the fifth transistor switch Q25, the sixth transistor switch Q26, and the seventh transistor switch Q27 are formed.

Therefore, when the digital control signal f _sw is at a high level and transmitted to the control terminals of the first and sixth transistor switches Q21 and Q26, the first and sixth transistor switches Q21 connected to the ground terminal G, Q26 is turned on. Since the first current limiting resistor R21 is connected to the first transistor switch Q21, the branch where the first current limiting resistor R21 is located is connected to the ground terminal G, and the second and fourth transistor switches Q22 at this time. Q24 will be correspondingly cut off because its control terminal is connected to the branch where the first current limiting resistor R21 is located, so that the branch where the second current limiting resistor R22 is located is at a high level due to the DC high voltage V _B , so its control The third transistor switch Q23 connected to the branch where the second current limiting resistor R22 is connected is turned on, and the control terminal of the seventh transistor switch Q27 is also connected to the high level digital control signal f _sw , so the seventh The transistor switch Q27 is turned on, because the third current limiting resistor R23 is connected to the seventh transistor switch Q27, so the branch where the third current limiting resistor R23 is located is connected to the ground terminal G, and the fifth transistor switch Q25 is controlled. The end system is connected to the branch where the third current limiting resistor R23 is located, resulting in the first Transistor switch Q25 is turned off, so that the current will be in the direction of the arrow, as shown in FIG. 2A.

When the digital signal f _sw is at a low level (Low), as shown in FIG. 2B, all the transistor switching operations are opposite to those of FIG. 2A, so that the current traveling direction is the direction of the arrow shown in FIG. 2B, thus The output AC voltages V _o1 and V _o2 outputted by the polarity switching circuit 12 form an AC square wave on the piezoelectric actuator 9, that is, the output AC voltage V _o1 and the output AC voltage V _o2 shown in FIG. Impaired waveform.

When the output AC voltages V _o1 and V _o2 outputted by the conventional polarity switching circuit 12 form an AC square wave on the piezoelectric actuator 9, the piezoelectric actuator 9 is subjected to rapid rise and rapid drop. Fast charging, although fast charging can cause the piezoelectric actuator 9 to quickly reach the top of the amplitude, but at the same time it also increases the power consumption. In addition, since the conventional polarity switching circuit 12 rapidly charges the piezoelectric actuator 9 with an alternating current square wave, the piezoelectric actuator 9 has a vibration generated at a natural resonance frequency, which causes the natural vibration to cause Large noise problems. Moreover, since the conventional polarity switching circuit 12 is configured to use a large number of transistor switches, that is, the seven transistor switches shown in FIG. 2A, not only the production cost of the conventional polarity switching circuit 12 is increased, but also The switching loss caused by the polarity switching circuit 12 due to the on or off switching of the plurality of transistor switches is increased.

Therefore, how to develop a polarity switching circuit that can improve the above-mentioned conventional technology is an urgent problem to be solved.

The main purpose of the present invention is to provide a polarity switching circuit that solves the problem that the conventional polarity switching circuit outputs an alternating square wave to drive the piezoelectric actuator, resulting in a large power loss, and the piezoelectric actuator generates noise when it is activated. In addition, since the conventional polarity switching circuit requires a large number of transistor switches, the production cost of the conventional polarity switching circuit is increased, and the switching loss is also large.

In order to achieve the above object, a broader aspect of the present invention provides a polarity switching circuit for converting a DC high voltage into an output AC voltage to drive a piezoelectric actuator, comprising: a first switching circuit that receives a first pulse width The modulation signal and the second pulse width modulation signal, wherein the first pulse width modulation signal and the second pulse width modulation signal are in anti-phase conduction, and one end of the first switching circuit is connected to the ground end, and the other end is connected to the DC a high voltage; the second switching circuit receives the first pulse width modulation signal and the second pulse width modulation signal, wherein the first pulse width modulation signal and the second pulse width modulation signal are in anti-phase conduction, and the second One end of the switch circuit is connected to the ground end, and the other end is connected to a DC high voltage; the first filter circuit is connected with the first switch circuit, the contact of the piezoelectric actuator and the ground end; and the second filter circuit and the second switch The circuit and the other contact of the piezoelectric actuator are connected to the ground; wherein the first pulse width modulation signal and the second pulse width modulation signal are alternately high-leveled When the low level switch, causes the output AC voltage to produce an AC voltage smoothing each contact of the AC input waveform to the piezoelectric actuator.

1‧‧‧Drive system
10‧‧‧Boost circuit
11‧‧‧ multiplier circuit
4, 12‧‧‧ polarity switching circuit
40‧‧‧First filter circuit
41‧‧‧Second filter circuit
8‧‧‧Fluid conveying device
9‧‧‧ Piezoelectric Actuator
90‧‧‧Acoustic film
91‧‧‧Vibration thin mold
92‧‧‧pressure chamber
V _B ‧‧‧DC high voltage
V _o1 , V _o2 , V1 , V2‧‧‧ output AC voltage
V _DC ‧‧‧DC input voltage
V _T ‧‧‧Transient voltage
V _max ‧‧‧max voltage
f _sw ‧‧‧ digital signal
V _in ‧‧‧Input DC low voltage
V _s1 ‧‧‧ first switching voltage
V _s2 ‧‧‧second switching voltage
R21‧‧‧First current limiting resistor
R22‧‧‧second current limiting resistor
R23‧‧‧ third current limiting resistor
Q21, Q41‧‧‧ first transistor switch
Q22, Q42‧‧‧Second transistor switch
Q23, Q43‧‧‧ Third transistor switch
Q24, Q44‧‧‧4th transistor switch
Q25‧‧‧ fifth transistor switch
Q26‧‧‧6th transistor switch
Q27‧‧‧ seventh transistor switch
G‧‧‧ Grounding terminal
PWM1‧‧‧ first pulse width modulation signal
PWM2‧‧‧ first pulse width modulation signal
L1‧‧‧first inductance
L2‧‧‧second inductance
C1‧‧‧first capacitor
C2‧‧‧second capacitor

Fig. 1 is a circuit block diagram of a conventional drive system for driving a piezoelectric actuator.
Fig. 2A is a diagram showing the internal circuit structure of the polarity switching circuit shown in Fig. 1.
Figure 2B: This is a schematic diagram of the operation of the circuit when the digital signal fsw shown in Figure 2A is at a low level.
Figure 3: This is a voltage timing waveform diagram of Figure 2A or 2B.
4A is a diagram showing the internal circuit structure of the polarity switching circuit of the preferred embodiment of the present invention.
Figure 4B: The first pulse width modulation signal PWM1 shown in Figure 4A is at a low level, and the second pulse width modulation signal PWM2 is in a high level and low level switching state. schematic diagram.
Figure 5A-5C: This is the voltage timing diagram for Figures 4A and 4B.
Fig. 6 is a modification of the first filter circuit and the second filter circuit shown in Fig. 4A.
7A-7B: This is a modification of the polarity switching circuit shown in Figs. 4A and 4B.
Fig. 8 is a schematic view showing an embodiment of a piezoelectric actuator shown in Fig. 4A applied to a mechanism body.

Some exemplary embodiments embodying the features and advantages of the present invention are described in detail in the following description. It should be understood that the present invention is capable of various modifications in the various aspects of the present invention, and the description and drawings are intended to be illustrative and not limiting.

Please refer to FIG. 4A and FIG. 4B , wherein FIG. 4A is an internal circuit structure diagram of a polarity switching circuit according to a preferred embodiment of the present invention, and FIG. 4B is a polarity switching circuit shown in FIG. 4A in a first pulse width modulation signal PWM1. The circuit operation diagram is a low level, and the second pulse width modulation signal PWM2 is in a high level and low level switching state. As shown in FIG. 4A and FIG. 4B, the polarity switching circuit 4 is connected to a DC high voltage line V _B, and according to a first pulse width modulation signal PWM1, and a second pulse width modulation signal PWM2 and the high DC voltage V _B The output voltages V1 and V2 are converted to drive a piezoelectric actuator 9 to be repeatedly operated, wherein the DC high voltage V _B can be output, for example, by the voltage multiplying circuit 11 shown in FIG. The polarity switching circuit 4 mainly includes a first transistor switch Q41, a second transistor switch Q42, a third transistor switch Q43, a fourth transistor switch Q44, a first filter circuit 40, and a second filter circuit. 41.

One control end of the first transistor switch Q41 is connected to the first pulse width modulation signal PWM1, and one current input end of the first transistor switch Q41 is connected to the first filter circuit 40, and one current of the first transistor switch Q41 The output terminal is connected to the ground terminal G. The control end of the second transistor switch Q42 is connected to the second pulse width modulation signal PWM2, and the current input terminal of the second transistor switch Q42 is connected to the power of the DC high voltage V _B , and the current of the second transistor switch Q42 The output terminal is connected to the first filter circuit 40 and the current input terminal of the first transistor switch Q41. The first filter circuit 40 is connected to one of the piezoelectric actuators 9 (receive output AC voltage V2) and the ground terminal G.

One control terminal of the third transistor switch Q43 is connected to the second pulse width modulation signal PWM2, and one current input terminal of the third transistor switch Q43 is connected to the second filter circuit 41, and one current of the third transistor switch Q43 The output terminal is connected to the ground terminal G. The control terminal of the fourth transistor switch Q44 is connected to the first pulse width modulation signal PWM1, and the current input terminal of the fourth transistor switch Q44 is connected to the power of the DC high voltage V _B , and the current of the fourth transistor switch Q44 The output terminal is connected to the current input terminals of the second filter circuit 41 and the third transistor switch Q43. The second filter circuit 41 is connected to another contact (receive output AC voltage V1) of the piezoelectric actuator 9 and the ground terminal G. In the above embodiment, the first transistor switch Q1 and the first transistor switch Q2 may constitute a first switch circuit, and the third transistor switch Q3 and the first transistor switch Q4 may constitute a second switch circuit.

Please refer to Figures 5A, 5B and 5C, and in conjunction with Figures 4A and 4B, wherein Figures 5A, 5B and 5C are voltage timing diagrams for Figures 4A and 4B, respectively. As shown in FIGS. 4A, 4B, 5A, 5B, and 5C, the first pulse width modulation signal PWM1 and the second pulse width modulation signal PWM2 alternately perform high-level and low-level switching, that is, when When the pulse width modulation signal PWM1 is switched between the high level and the low level, the second pulse width modulation signal PWM2 is low level, and when the second pulse width modulation signal PWM2 is at a high level When the low level is switched, the first pulse width modulation signal PWM1 is low level, in other words, the first pulse width modulation signal PWM1 and the second pulse width modulation signal PWM2 are mutually turned on.

When the first pulse width modulation signal PWM1 is in the high frequency switching of the high level and the low level, and the second pulse width modulation signal PWM2 is at the low level, the low level of the second pulse width modulation signal PWM2 will be The second transistor switch Q42 and the third transistor switch Q43 are turned off. At the same time, the first pulse width modulation signal PWM1 is in a state of high frequency switching between the high level and the low level, so that the first transistor switch Q41 and the first transistor switch The four transistor switches Q44 are in the same on or off switching state, that is, the first transistor switch Q41 and the fourth transistor switch Q44 are simultaneously in an on state or an off state, so when the first transistor switch Q41 and the fourth transistor When the crystal switch Q44 is turned on, the current traveling direction is made to be in the direction of the arrow shown in Fig. 4A.

Conversely, when the second pulse width modulation signal PWM2 is in the high frequency switching of the high level and the low level, and the first pulse width modulation signal PWM1 is at the low level, all the transistor switches operate in opposite directions, that is, the first A low level of the pulse width modulation signal PWM1 will cause the first transistor switch Q41 and the fourth transistor switch Q44 to be turned off, and at the same time, the second pulse width modulation signal PWM2 is at a high level and low level for high frequency switching. The state of the second transistor switch Q42 and the third transistor switch Q43 are in the same on or off switching state, that is, the second transistor switch Q42 and the third transistor switch Q43 are simultaneously turned on or off. Therefore, when the second transistor switch Q42 and the third transistor switch Q43 are turned on, the current traveling direction is made to be in the direction of the arrow shown in FIG. 4B.

Therefore, when the first pulse width modulation signal PWM1 and the second pulse width modulation signal PWM2 are as shown in FIG. 5A, that is, the first pulse width modulation signal PWM1 and the second pulse width modulation signal PWM2 are respectively When the high frequency gradually decreases to a low frequency and then gradually increases to a high frequency, a second switching voltage V _s2 is generated between the current input terminal of the first transistor switch Q41 and the current output terminal of the second transistor switch Q42, and A first switching voltage V _s1 generated by the current input terminal of the third transistor switch Q43 and the current output terminal of the fourth transistor switch Q44 is respectively adjusted with the first pulse width modulation signal PWM1 and the second pulse width. The variable signal PWM2 is synchronously lowered from the high frequency to the low frequency and then gradually increased to the high frequency, that is, as shown in FIG. 5B, and the first switching voltage V _s1 and the second switching voltage V _s2 are respectively passed through the second filter circuit 41. After filtering by the first filter circuit 40, the output AC voltages V1 and V2 shown in FIG. 5C are presented as smooth AC waveforms.

Referring to FIG. 5C, the driving power connected to the piezoelectric actuator 9, that is, the subtraction value of the output AC voltages V1 and V2, reaches the maximum voltage linearly in a first time when the polarity switching circuit 4 starts to operate. A first ratio value of _Vmax , such as the marker 1 to marker 2 interval, will appear after the rising rounded waveform and reach the maximum voltage _Vmax within a first set time of the marker 3, such as marker 2 to marker 3, followed by a Two times flat, such as mark 3 to mark 4, successively presenting a falling rounded waveform and decreasing to a second proportional value of the maximum voltage V _max for a second set time, such as mark 4 to mark 5, and finally linearly falling to zero The voltages, for example, marks 5 to 6, and the other half cycle (reverse direction) of the AC waveform, that is, the marks 6 to 11, are similar in characteristics to the marks 1 to 6, and therefore will not be described again. In addition, the output AC voltages V1 and V2 outputted by the polarity switching circuit 4 can be borrowed from the smooth AC waveform formed on the piezoelectric actuator 9 by the waveform rising and falling speed, the turning rounding curve and the maximum voltage V _max . The modulation is performed by the modulation pulse width variation of the first pulse width modulation signal PWM1 and the second pulse width modulation signal PWM2.

Since the output AC voltages V1 and V2 outputted by the polarity switching circuit 4 of the present invention form a smooth AC waveform which is respectively connected to the two contacts of the piezoelectric actuator 9, it is not the conventional polarity switching circuit as shown in FIG. 2A. The output AC voltages V _o1 and V _o2 of the output form a square wave on the piezoelectric actuator 9, so that the piezoelectric actuator 9 can be gradually charged in a relatively gentle manner, thereby reducing power consumption caused by rapid charging. In addition, it is also possible to reduce the occurrence of vibration at the natural resonance frequency of the piezoelectric actuator 9, thereby avoiding the noise problem generated when the piezoelectric actuator 9 is actuated, and in addition, compared with FIG. 2A The conventional polarity switching circuit 12 is configured to use seven transistor switches. The polarity switching circuit 4 of the present invention only needs to use four transistor switches (first to fourth transistor switches Q41 to Q44), so the present case The production cost of the polarity switching circuit 4 can be reduced, and the switching loss caused by the polarity switching circuit due to the on/off switching of the transistor switch can be reduced.

In other embodiments, as shown in FIG. 4A, the first filter circuit 40 can be formed by a first inductor L1 and a first capacitor C1, wherein one end of the first inductor L1 is coupled to the current of the first transistor switch Q41. The input end is connected to the current output end of the second transistor switch Q42, and one end of the first capacitor C1 is connected to one of the contacts of the piezoelectric actuator 9 and the other end of the first inductor L1, and the other end of the first capacitor C1 Then connected to the ground terminal G. The second filter circuit 41 can be composed of a second inductor L2 and a second capacitor C2, wherein one end of the second inductor L2 is connected to the current input terminal of the third transistor switch Q43 and the current output terminal of the fourth transistor switch Q44. Connected, one end of the second capacitor C2 is connected to the other contact of the piezoelectric actuator 9 and the other end of the second inductor L2, and the other end of the second capacitor C2 is connected to the ground terminal G.

In other embodiments, as shown in FIG. 6, the first filter circuit 40 may also be formed only by the first capacitor C1. At this time, one end of the first capacitor C1 is connected to one of the piezoelectric actuators 9. The current input end of the first transistor switch Q41 and the current output end of the second transistor switch Q42 are connected, the other end of the first capacitor C1 is maintained connected to the ground terminal G, and the second filter circuit 41 can also be only the second The capacitor C2 is configured. At this time, the second capacitor C2 is connected to the other contact of the piezoelectric actuator 9, the current input end of the third transistor switch Q43, and the current output end of the fourth transistor switch Q44. The other end of the capacitor C2 is maintained connected to the ground terminal G.

In some embodiments, as shown in FIG. 4A, the first to fourth transistor switches Q41-Q44 are respectively formed by NPN bipolar common-surface transistor switches (BJT), so the first to fourth electrodes are The control terminal, the current input terminal and the current output terminal of the crystal switches Q41~Q44 correspond to the base, the source and the emitter, respectively. However, in other embodiments, as shown in FIGS. 7A and 7B, the first to fourth transistor switches Q41 to Q44 may also be formed by field-corrected transistor switches (FETs), and thus the first to fourth transistor switches Q41. The control terminal, current input terminal and current output terminal of ~Q44 correspond to gate, source and drain, respectively. The structure and operation principle of the polarity switching circuit 12 shown in FIGS. 7A and 7B are similar to those of FIGS. 4A and 4B, and will not be described again.

Please refer to FIG. 8 , which is a schematic diagram of a piezoelectric actuator shown in FIG. 4A applied to a mechanism body. As shown, the mechanism body can be a fluid conveying device 8 , but not For this reason, the fluid delivery device 8 can be applied to industries such as medical technology, computer technology, printing or energy, and can transport gas or liquid, such as a pump in an inkjet printer, mainly by pressure. The electric actuator 9 converts electrical energy into mechanical energy, wherein the piezoelectric actuator 9 includes an actuating plate 90 and a vibrating thin die 91, and is respectively connected to output alternating current voltages V1 and V2 for outputting alternating current voltages V1 and V2. The driving causes the actuating sheet 90 and the vibrating thin mold 91 to perform a repetitive motion, thereby causing the volume of the pressure chamber 92 to be compressed or expanded, so that the fluid transporting device 8 can achieve the effect of transferring the fluid.

In summary, the polarity switching circuit of the present invention uses the connection and actuation of the first to fourth transistor switches and the first to second filter circuits to output an output AC voltage of a smooth AC waveform, thereby reducing power consumption, and The piezoelectric actuator is prevented from generating noise when it is actuated. At the same time, since the polarity switching circuit of the present invention only needs to be constructed by using the first to fourth transistor switches, the production cost of the polarity switching circuit of the present invention can be reduced, and the polarity can be reduced. The switching circuit is caused by the switching loss caused by the transistor switch being turned on or off.

This case has been modified by people who are familiar with the technology, but it is not intended to be protected by the scope of the patent application.

4‧‧‧Polar switching circuit

40‧‧‧First filter circuit

41‧‧‧Second filter circuit

9‧‧‧ Piezoelectric Actuator

V _B- ‧‧‧ DC high voltage

V1, V2‧‧‧ output AC voltage

V _s1 ‧‧‧ first switching voltage

V _s2 ‧‧‧second switching voltage

Q41‧‧‧First transistor switch

Q42‧‧‧Second transistor switch

Q43‧‧‧The third transistor switch

Q44‧‧‧4th transistor switch

G‧‧‧ Grounding terminal

PWM1‧‧‧ first pulse width modulation signal

PWM2‧‧‧ first pulse width modulation signal

L1‧‧‧first inductance

L2‧‧‧second inductance

C1‧‧‧first capacitor

C2‧‧‧second capacitor

Claims (11)

A polarity switching circuit converts a constant current high voltage into an output AC voltage to drive a piezoelectric actuator comprising:
a first switching circuit receives a first pulse width modulation signal and a second pulse width modulation signal, wherein the first pulse width modulation signal and the second pulse width modulation signal are in anti-phase conduction with each other, and One end of the first switch circuit is connected to a ground end, and the other end is connected to the DC high voltage;
a second switching circuit receives the first pulse width modulation signal and the second pulse width modulation signal, wherein the first pulse width modulation signal and the second pulse width modulation signal are in anti-phase conduction with each other, and One end of the second switch circuit is connected to the ground end, and the other end is connected to the DC high voltage;
a first filter circuit connected to the first switch circuit, a contact of the piezoelectric actuator and the ground; and a second filter circuit, the second switch circuit, and the piezoelectric actuator Another contact and the ground connection;
When the first pulse width modulation signal and the second pulse width modulation signal are alternately switched between the high level and the low level, the output AC voltage is generated to generate a smooth AC waveform and the AC voltage is input to the voltage. Each contact of the electric actuator. The polarity switching circuit of claim 1, wherein the first switching circuit comprises a circuit combined with a first transistor switch and a second transistor switch, and the second switch circuit comprises a third transistor A circuit in which a switch and a fourth transistor switch are combined. The polarity switching circuit of claim 2, wherein the first transistor switch to the fourth transistor switch respectively have a control terminal, a current input terminal, and a current output terminal, wherein the first The current input end of the transistor switch is connected to the current output end of the second transistor switch, and the current input end of the third transistor switch is connected to the current output end of the fourth transistor switch. The polarity switching circuit of claim 3, wherein the first filter circuit is formed by a first inductor and a first capacitor, the first inductor and the contact of the piezoelectric actuator, The current input end of the first transistor switch is connected to the current output end of the second transistor switch, and the first capacitor is connected to the contact of the piezoelectric actuator, the first inductor and the ground end, The second filter circuit is composed of a second inductor and a second capacitor, the second inductor and the other contact of the piezoelectric actuator, the current input terminal of the third transistor switch, and the fourth The current output of the transistor switch is connected, and the second capacitor is connected to the other contact of the piezoelectric actuator, the second inductor and the ground. The polarity switching circuit of claim 3, wherein the first filter circuit is formed by the first capacitor, the first capacitor and the piezoelectric actuator, the first transistor switch The current input terminal, the current output terminal of the second transistor switch, and the ground terminal are connected, the second filter circuit is formed by the second capacitor, and the second capacitor and the piezoelectric actuator are another The contact, the current input end of the third transistor switch, the current output end of the fourth transistor switch, and the ground end are connected. The polarity switching circuit of claim 2, wherein the first transistor switch to the fourth transistor switch are bipolar common junction transistors. The polarity switching circuit of claim 6, wherein the first transistor switch to the fourth transistor switch are NPN bipolar common junction transistors. The polarity switching circuit of claim 2, wherein the first transistor switch to the fourth transistor switch is a field effect transistor. The polarity switching circuit of claim 1, wherein the second pulse width modulation signal is at a low level when the first pulse width modulation signal is switched between a high level and a low level. When the second pulse width modulation signal is switched between the high level and the low level, the first pulse width modulation signal is at a low level. The polarity switching circuit of claim 1, wherein the first pulse width modulation signal and the second pulse width modulation signal are gradually reduced from a high frequency to a low frequency and then gradually increased to a high frequency. The polarity switching circuit of claim 1, wherein the AC voltage of the output smooth AC waveform is linearly reaches a first proportional value of a maximum voltage in a first period in a half cycle, and then rises and sleek. The waveform reaches the maximum voltage within a first set time, continues to be flat for a second time, continues to exhibit a falling rounded waveform, and decreases to a second ratio of the maximum voltage for a second set time, followed by a linear decrease To zero voltage.