A bipolar high-voltage pulse drive circuit and driving method for an air-coupled ultrasonic transducer

Abstract

This invention discloses a bipolar high-voltage pulse driving circuit and driving method for an air-coupled ultrasonic transducer. The driving circuit includes a control circuit, an auxiliary power supply circuit, a pulse transmitting unit, and a high-voltage output unit. The high-voltage output unit includes a high-frequency inverter circuit, a high-frequency transformer T1, and a voltage multiplier rectifier circuit. This bipolar high-voltage pulse driving circuit and driving method can generate a controllable bipolar high-voltage excitation signal while meeting the high-voltage driving requirements of the ultrasonic transducer using only a low-voltage power supply, significantly improving the received ultrasonic energy.

Description

Technical Field

[0001] This invention relates to a high-voltage pulse driving circuit and driving method, and more particularly to a bipolar high-voltage pulse driving circuit and driving method for an air-coupled ultrasonic transducer. Background Technology

[0002] To date, pulse generators developed fall into two categories: unipolar spike pulse generators and bipolar pulse generators. Unipolar spike pulse generators are most commonly used for detecting samples with low attenuation, uniformity, and fine grains, such as metals and forgings. Spike pulse generators offer the advantage of a wide frequency spectrum, providing voltages up to 800V for low-frequency sensors. However, the energy of a single-pulse excitation signal is less than that of a bipolar pulse excitation signal, resulting in insufficient ultrasonic waves to penetrate lithium battery defects, making it difficult to achieve air-coupled ultrasonic defect detection in lithium batteries.

[0003] Another approach involves using a pulse transformer to generate a bipolar pulse voltage to excite the piezoelectric ceramic inside the ultrasonic transducer. However, to achieve ultrasonic energy capable of penetrating the defects of lithium batteries, using only a single transformer for voltage boosting, with a relatively low input voltage, would result in an excessively large transformer turns ratio, leading to a larger transformer size and higher insulation requirements. Furthermore, its distributed capacitance and leakage inductance would also have a significant impact on the system. In addition, the voltage places high demands on the withstand voltage requirements of the components in the transformer's secondary rectifier circuit.

[0004] Air-coupled ultrasonic testing technology overcomes the limitations of traditional methods, and its non-contact, non-destructive, and real-time characteristics hold great potential for detecting internal defects in lithium batteries. However, there are still bottlenecks to overcome in the application of air-coupled ultrasonic technology in lithium batteries. Significant differences in acoustic impedance exist between air, the ultrasonic matching layer, and lithium battery materials. Especially when bubbles or delamination defects exist inside the battery, multiple gas-solid alternating interfaces form between the transducer and sensor, resulting in significant attenuation of ultrasonic waves. Limited by insufficient energy, ultrasonic waves may have difficulty penetrating bubble-containing areas of the lithium battery, making air-coupled ultrasonic testing less effective for detecting defects such as bubbles, electrode perforations, wrinkles, and delamination.

[0005] The shortcomings of the existing technology are: (1) The driving method of using only a single pulse transformer to generate high voltage pulses is due to the working principle of the pulse transformer. Any transformer has leakage inductance. An excessively high turns ratio will cause the magnetic core to deviate from the optimal magnetic flux density during operation, resulting in magnetic core saturation or increased hysteresis loss, thereby reducing the efficiency of the transformer; (2) In order to support a higher turns ratio, more coil turns may be required, which increases the complexity of design and manufacturing, increases the size and cost of the transformer, and when the turns ratio is too large, the voltage on the secondary coil may be too high, which may exceed the withstand voltage limit of the insulation material, increasing the risk of insulation breakdown; (3) For the traditional unipolar pulse driving method, although there is no design impact caused by transformer-related problems, the single pulse excitation signal is not as powerful as the bipolar pulse excitation signal, resulting in the emitted ultrasonic waves being insufficient to penetrate lithium battery defects, making it difficult to achieve air-coupled ultrasonic lithium battery defect detection. Summary of the Invention

[0006] The purpose of this invention is to provide a bipolar high-voltage pulse driving circuit and driving method for an air-coupled ultrasonic transducer, which can generate a bipolar high-voltage pulse signal that meets the high-voltage driving requirements of the ultrasonic transducer.

[0007] Technical Solution: The bipolar high-voltage pulse drive circuit of the air-coupled ultrasonic transducer of the present invention includes a control circuit, an auxiliary power supply circuit, a pulse emission unit, and a high-voltage output unit. The high-voltage output unit includes a high-frequency inverter circuit, a high-frequency transformer T1, and a voltage doubler rectifier circuit. The input terminal of the high-frequency inverter circuit is connected to a 12V DC input, and the output terminal of the high-frequency inverter circuit is electrically connected to the input side of the high-frequency transformer T1. The output side of the high-frequency transformer T1 is electrically connected to the input terminal of the voltage doubler rectifier circuit, and the output terminal of the voltage doubler rectifier circuit is electrically connected to the high-voltage input terminal of the pulse emission unit. The control circuit is electrically connected to the control terminal of the high-frequency inverter circuit and the control terminal of the pulse emission unit, respectively. The output terminal of the pulse emission unit is electrically connected to the input terminal of the air-coupled ultrasonic high-voltage transducer to output an ultrasonic drive signal to the air-coupled ultrasonic high-voltage transducer. The auxiliary power supply circuit supplies power to the control circuit and the pulse emission unit, respectively.

[0008] Furthermore, the pulse emission unit includes an optocoupler isolation circuit, a MOSFET driving circuit, and a power amplifier circuit; the control terminal of the optocoupler isolation circuit is electrically connected to the control circuit, and the output terminal of the optocoupler isolation circuit is electrically connected to the input terminal of the MOSFET driving circuit; the output terminal of the MOSFET driving circuit is electrically connected to the control terminal of the power amplifier circuit, and is used to drive and control the power amplifier circuit; the output terminal of the power amplifier circuit is used to be electrically connected to the input terminal of the air-coupled ultrasonic high-voltage transducer, and outputs an ultrasonic driving signal to the air-coupled ultrasonic high-voltage transducer.

[0009] Furthermore, the high-frequency inverter circuit includes MOSFETs Q1 and Q2; the voltage doubler rectifier circuit includes capacitors C1, C2, C3, and C4, diodes D1, D2, D3, and D4; the gates (G) of MOSFETs Q1 and Q2 are both electrically connected to the control circuit; the drain (D) of MOSFET Q1 is electrically connected to one end of the primary coil of the high-frequency transformer T1, and the drain (D) of MOSFET Q2 is electrically connected to the other end of the primary coil of the high-frequency transformer T1; the sources (S) of MOSFETs Q1 and Q2 are both electrically connected to the negative terminal of the 12V DC input; the midpoint of the primary coil of the high-frequency transformer T1 is electrically connected to the positive terminal of the 12V DC input. One end of the secondary coil of high-frequency transformer T1 is electrically connected to one end of capacitor C1 and one end of capacitor C3, respectively. The other end of the secondary coil of high-frequency transformer T1 is electrically connected to one end of capacitor C2, the positive terminal of diode D1, one end of capacitor C4, and the negative terminal of diode D3, respectively. The other end of capacitor C1 is electrically connected to the negative terminal of diode D1 and the positive terminal of diode D2, respectively. The negative terminal of diode D2 and the other end of capacitor C2 are electrically connected together to form the positive output terminal of the voltage doubler rectifier circuit. The other end of capacitor C4 is electrically connected to the positive terminal of diode D4. The other end of capacitor C3, the positive terminal of diode D3, and the negative terminal of diode D4 are electrically connected together to form the negative output terminal of the voltage doubler rectifier circuit.

[0010] Furthermore, the optocoupler isolation circuit includes optocoupler M1 and optocoupler M2; the MOSFET driving circuit includes MOSFET driver Q5 and MOSFET driver Q6; the power amplifier circuit includes MOSFET Q3, MOSFET Q4, resistors R1, R2, and R3, diodes D5 and D6, capacitor C5, and resistor R4; the input terminals of optocoupler M1 and optocoupler M2 are both electrically connected to the control circuit, the output terminal of optocoupler M1 is electrically connected to the input terminal of MOSFET driver Q5, and the output terminal of optocoupler M2 is electrically connected to the input terminal of MOSFET driver Q6; the output terminal of MOSFET driver Q5 is electrically connected to the gate (G) of MOSFET Q3; the output terminal of MOSFET driver Q6... The output terminal is electrically connected to the gate (G) of MOSFET Q4; the drain (D) of MOSFET Q3, one end of resistor R1, and the cathode of diode D5 are all electrically connected to the positive output terminal of the voltage doubler rectifier circuit; the source (S) of MOSFET Q3 is electrically connected to the other end of resistor R1, one end of resistor R2, one end of resistor R3, and the drain (D) of MOSFET Q4; the source (S) of MOSFET Q4 is electrically connected to the other end of resistor R2 and the anode of diode D6, and then grounded; the cathode of diode D6 is electrically connected to the other end of resistor R3, terminal a of capacitor C5, and the anode of diode D5; terminal b of capacitor C5 is electrically connected to one end of resistor R4 and serves as the output terminal of the power amplifier circuit; the other end of resistor R4 is grounded.

[0011] The present invention also provides a driving method for a bipolar high-voltage pulse driving circuit of an air-coupled ultrasonic transducer, including a high-voltage output step and an excitation output step;

[0012] The high-voltage output steps are as follows:

[0013] The control circuit alternately sends pulse drive signals K1 and K2 to the source (S) of MOSFETs Q1 and Q2. When pulse drive signal K1 is received, MOSFET Q1 turns on, and current flows into a part of the primary coil of high-frequency transformer T1 through the 12V DC input. When pulse drive signal K2 is received, MOSFET Q2 turns on, and current flows into the other part of the primary coil of high-frequency transformer T1 through the 12V DC input. Thus, a high-frequency AC voltage waveform is generated in the primary coil of high-frequency transformer T1.

[0014] The high-frequency transformer T1 outputs a boosted AC voltage on the secondary coil. Then, diodes D1 and D2, capacitors C1 and C2 convert the positive half-cycle of the AC voltage waveform into DC current, and diodes D3 and D4, capacitors C3 and C4 convert the negative half-cycle of the AC voltage waveform into DC current.

[0015] The DC output voltage is composed of the DC current converted during the positive half-cycle and the DC current converted during the negative half-cycle, and its magnitude is denoted as HVDD.

[0016] The excitation output steps are as follows:

[0017] During charging, the control circuit stops sending pulse drive signals K3 and K4 to optocoupler M1 and optocoupler M2, MOSFETs Q3 and Q4 are turned off, and the DC output voltage is charged to terminal a of capacitor C5 after being divided by resistors R1 and R2 of the same resistance value, reaching half of the potential of HVDD. Terminal b of C5 is kept at the same potential as GND through resistor R4.

[0018] When a pulse is transmitted, the control circuit sends a pulse drive signal K3 to the optocoupler M1, turning on MOS driver Q5. MOS driver Q5 pulls up the control pulse of MOS transistor Q3, while the control pulse of MOS transistor Q4 remains low. MOS transistor Q3 is on, and MOS transistor Q4 is off. The voltage at terminal a of capacitor C5 abruptly changes to HVDD through MOS transistor Q3, while the potential difference across capacitor C5 does not change instantaneously. Therefore, the voltage at terminal b of capacitor C5 becomes half of HVDD. Then, the control circuit sends a pulse drive signal K4 to the optocoupler M2, turning on MOS driver Q6. MOS driver Q6 pulls up the control pulse of MOS transistor Q4, while the control pulse of MOS transistor Q3 abruptly changes to HVDD. Simultaneously, the voltage at terminal a of capacitor C5 is pulled low, MOSFET Q4 turns on, and MOSFET Q3 turns off. The voltage at terminal a of capacitor C5 suddenly changes to GND, but the potential difference across capacitor C5 does not change instantaneously. Therefore, the voltage at terminal b of capacitor C5 becomes half of -HVDD. Then, the control circuit stops sending pulse drive signals K3 and K4 to optocouplers M1 and M2. The control pulses of MOSFETs Q3 and Q4 are pulled low at the same time, and both MOSFETs Q4 and Q3 turn off. Terminal a of capacitor C5 returns to the voltage after being divided by two resistors R1 and R2 with the same resistance, reaching half of HVDD. Terminal b of capacitor C5 remains at the same potential as GND through resistor R4, thus forming a bipolar pulse.

[0019] Repeating the charging and pulse emission process generates a bipolar high-voltage pulse train, which is used to excite the air-coupled ultrasonic transducer.

[0020] Compared with the prior art, the beneficial effects of this invention are: this invention can generate the required 1100V bipolar high-voltage pulse to drive the ultrasonic transducer with a 12V low-voltage power supply, thereby reducing the design difficulty caused by dual positive and negative power supplies. Furthermore, by using optocoupler isolation devices to effectively isolate the low-voltage drive control signal and the high-voltage pulse transmission, the safety of the circuit is improved, and the output waveform is easier to control. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall circuit structure of the present invention;

[0022] Figure 2 This is a basic schematic diagram of the air-coupled ultrasonic penetration method of the present invention;

[0023] Figure 3 This is a schematic diagram of the high-voltage output unit circuit structure of the present invention;

[0024] Figure 4 This is a timing diagram of the input control signal and output pulse of the high-voltage unit of the present invention;

[0025] Figure 5 This invention relates to a bipolar high-voltage drive circuit for an ultrasonic transducer.

[0026] Figure 6 This is a timing diagram of the drive circuit control signals and output pulses of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the embodiments described.

[0028] Air-coupled ultrasonic testing methods analyze whether a material has defects by studying the characteristic values ​​corresponding to the received ultrasonic signals after the ultrasonic waves pass through the material under test, which result in energy changes such as reflection and transmission. For example... Figure 2 As shown, the detection system utilizes a bipolar high-voltage pulse to excite a transmitting transducer, causing it to generate ultrasonic waves that are emitted towards the lithium battery. These ultrasonic waves, carrying information about the battery's internal structure, are captured by a receiving transducer, which converts the received ultrasonic waves into a received signal for analysis. The quality of the received signal is a key factor in accurately analyzing the lithium battery; therefore, improving the quality of the received signal is of great significance to the ultrasonic detection system.

[0029] like Figure 1 As shown, the bipolar high-voltage pulse drive circuit of the air-coupled ultrasonic transducer disclosed in this invention includes: a control circuit, an auxiliary power supply circuit, a pulse emission unit, and a high-voltage output unit. The high-voltage output unit includes a high-frequency inverter circuit, a high-frequency transformer T1, and a voltage doubler rectifier circuit. The input terminal of the high-frequency inverter circuit is connected to a 12V DC input, and the output terminal of the high-frequency inverter circuit is electrically connected to the input side of the high-frequency transformer T1. The output side of the high-frequency transformer T1 is electrically connected to the input terminal of the voltage doubler rectifier circuit, and the output terminal of the voltage doubler rectifier circuit is electrically connected to the high-voltage input terminal of the pulse emission unit. The control circuit is electrically connected to the control terminal of the high-frequency inverter circuit and the control terminal of the pulse emission unit, respectively. The output terminal of the pulse emission unit is electrically connected to the input terminal of the air-coupled ultrasonic high-voltage transducer to output an ultrasonic drive signal to the air-coupled ultrasonic high-voltage transducer. The auxiliary power supply circuit supplies power to the control circuit and the pulse emission unit, respectively.

[0030] The 12V DC input, combined with the +5V and +3.3V generated by the auxiliary power supply circuit, powers the control circuit, optocoupler isolation circuit, and MOSFET driver circuit. The high-voltage output unit, using the SG3525 as its control core, provides the required high-voltage DC power to the pulse transmission unit based on push-pull inverter and bipolar voltage doubler rectification. Its output amplitude can be externally controlled. The STM32F407 ARM controller embedded chip serves as the core of the control circuit. It emits ultrasonic low-voltage pulse control signals with dead time to control the subsequent pulse transmission unit. The pulse waveform is a square wave, and the frequency is consistent with the fundamental frequency required for normal transducer operation. The pulse transmission unit uses an optocoupler FODM8071 to isolate the low-voltage control signal from the high-voltage excitation signal, preventing circuit failure from burning out the main control chip. It uses the IR2213 MOSFET driver chip to drive two power MOSFETs CIM3N150D3, thereby converting the 1100V high-voltage DC provided by the high-voltage unit into a bipolar signal of the same frequency as the ARM control to drive the transducer.

[0031] Furthermore, the pulse emission unit includes an optocoupler isolation circuit, a MOSFET driving circuit, and a power amplifier circuit; the control terminal of the optocoupler isolation circuit is electrically connected to the control circuit, and the output terminal of the optocoupler isolation circuit is electrically connected to the input terminal of the MOSFET driving circuit; the output terminal of the MOSFET driving circuit is electrically connected to the control terminal of the power amplifier circuit, and is used to drive and control the power amplifier circuit; the output terminal of the power amplifier circuit is used to be electrically connected to the input terminal of the air-coupled ultrasonic high-voltage transducer, and outputs an ultrasonic driving signal to the air-coupled ultrasonic high-voltage transducer.

[0032] Furthermore, such as Figure 3As shown, the high-frequency inverter circuit includes MOSFETs Q1 and Q2; the voltage doubler rectifier circuit includes capacitors C1, C2, C3, and C4, diodes D1, D2, D3, and D4; the gates (G) of MOSFETs Q1 and Q2 are both electrically connected to the control circuit; the drain (D) of MOSFET Q1 is electrically connected to one end of the primary coil of high-frequency transformer T1, and the drain (D) of MOSFET Q2 is electrically connected to the other end of the primary coil of high-frequency transformer T1; the source (S) of MOSFETs Q1 and Q2 are both used to connect to the negative terminal of the 12V DC input; the midpoint of the primary coil of high-frequency transformer T1 is used to connect to the positive terminal of the 12V DC input; One end of the secondary coil of the high-frequency transformer T1 is electrically connected to one end of capacitor C1 and one end of capacitor C3, respectively. The other end of the secondary coil of the high-frequency transformer T1 is electrically connected to one end of capacitor C2, the positive terminal of diode D1, one end of capacitor C4, and the negative terminal of diode D3, respectively. The other end of capacitor C1 is electrically connected to the negative terminal of diode D1 and the positive terminal of diode D2, respectively. The negative terminal of diode D2 and the other end of capacitor C2 are electrically connected together to form the positive output terminal of the voltage doubler rectifier circuit. The other end of capacitor C4 is electrically connected to the positive terminal of diode D4. The other end of capacitor C3, the positive terminal of diode D3, and the negative terminal of diode D4 are electrically connected together to form the negative output terminal of the voltage doubler rectifier circuit.

[0033] The 12V DC input is boosted by a 46-fold high-frequency inverter through a high-frequency transformer T1, and then amplified into DC voltage by a 2x full-wave voltage doubler rectifier circuit that has both voltage multiplication and rectification functions, ultimately achieving a 92x voltage boost. This reduces the transformer turns ratio and design complexity, alleviates voltage stress on rectifier devices, and realizes high-gain isolated boost conversion of the circuit.

[0034] In this circuit, when the pulse drive signals K1 and K2 for MOSFETs Q1 and Q2 are pulled low, MOSFETs Q1 and Q2 are turned off, and the circuit does not operate. When a high DC voltage is required, controlled by the pulse drive signals, MOSFETs Q1 and Q2 alternately conduct in each clock cycle. When MOSFET Q1 is on, current flows through the 12V power supply into a portion of the primary coil of the high-frequency transformer T1; when MOSFET Q2 is on, current flows into the other portion of the primary coil of the high-frequency transformer T1. This alternating conduction generates a high-frequency AC voltage waveform on the primary coil of the high-frequency transformer T1. By boosting the voltage through the high-frequency transformer T1 with a turns ratio of 1:46, the AC voltage output on the secondary coil is approximately 560V peak. Diodes D1 and D2, and capacitors C1 and C2 convert the positive half-cycle AC current to DC current. Similarly, diodes D3 and D4, and capacitors C3 and C4 convert the negative half-cycle AC current to DC current, ultimately achieving a DC output voltage of 1100V.

[0035] Based on the above analysis, the timing diagram of the circuit's input signal and output voltage is as follows: Figure 4 As shown, when the pulse drive signal K1 of MOSFET Q1 and the pulse drive signal K2 of MOSFET Q2 alternately output trigger pulses, the circuit can excite a DC voltage of 1100V, which is twice the AC voltage of 560V. Using this circuit, a high voltage DC voltage of 1100V can be achieved by boosting 12V to 1100V by 92 times.

[0036] Furthermore, such as Figure 5 As shown, the optocoupler isolation circuit includes optocoupler M1 and optocoupler M2; the MOSFET driving circuit includes MOSFET driver Q5 and MOSFET driver Q6; the power amplifier circuit includes MOSFET Q3, MOSFET Q4, resistors R1, R2, and R3, diodes D5 and D6, capacitor C5, and resistor R4; the input terminals of optocoupler M1 and optocoupler M2 are both electrically connected to the control circuit, the output terminal of optocoupler M1 is electrically connected to the input terminal of MOSFET driver Q5, and the output terminal of optocoupler M2 is electrically connected to the input terminal of MOSFET driver Q6; the output terminal of MOSFET driver Q5 is electrically connected to the gate (G) of MOSFET Q3; the output terminal of MOSFET driver Q6 is electrically connected to the gate (G) of MOSFET Q3; the output terminal of MOSFET driver Q6 is electrically connected to the gate (G) of MOSFET Q3. The output terminal is electrically connected to the gate (G) of MOSFET Q4; the drain (D) of MOSFET Q3, one end of resistor R1, and the cathode of diode D5 are all electrically connected to the positive output terminal of the voltage doubler rectifier circuit; the source (S) of MOSFET Q3 is electrically connected to the other end of resistor R1, one end of resistor R2, one end of resistor R3, and the drain (D) of MOSFET Q4; the source (S) of MOSFET Q4 is electrically connected to the other end of resistor R2 and the anode of diode D6, and then grounded; the cathode of diode D6 is electrically connected to the other end of resistor R3, terminal a of capacitor C5, and the anode of diode D5; terminal b of capacitor C5 is electrically connected to one end of resistor R4 and serves as the output terminal of the power amplifier circuit; the other end of resistor R4 is grounded.

[0037] To generate a high-voltage pulse excitation signal with controllable pulse count, this invention is based on the aforementioned high-voltage output of a high-voltage circuit, and designs a system using the RC charging and discharging principle and a switching transistor cooperative operation method. Figure 5 The illustrated bipolar high-voltage ultrasonic excitation signal generation circuit utilizes the generated high voltage. This is achieved by connecting equal-value voltage divider resistors R1 and R2 in parallel across MOSFETs Q3 and Q4, respectively, to control the input voltage potential. A bipolar square wave pulse train is then generated by controlling the voltage across clamping capacitor C5 via a switching transistor. The number of excitation signal pulses is determined by the control signals for MOSFETs Q3 and Q4. This circuit effectively reduces design complexity, improves pulse drive efficiency, and isolates the high-voltage and low-voltage sections through optocoupler isolation, preventing high-voltage interference signals from damaging the ARM chip. It shows great potential in high-precision ultrasonic measurement applications.

[0038] Based on the above analysis, the timing diagram of the circuit's input signal and output voltage is as follows: Figure 6 As shown, when the pulse drive signal K3 of MOSFET Q3 outputs a trigger pulse, the circuit will generate a high-voltage pulse of equal width with a voltage of HVDD / 2. When the pulse drive signal K4 of MOSFET Q4 outputs a trigger pulse, the circuit will generate a high-voltage pulse of equal width with a voltage of -HVDD / 2. Therefore, by alternately outputting trigger pulses from pulse drive signals K3 and K4, the circuit will generate a bipolar high-voltage pulse. This circuit allows for controllable voltage amplitude and pulse width of the high-voltage pulse excitation signal.

[0039] The present invention also provides a driving method for a bipolar high-voltage pulse driving circuit of an air-coupled ultrasonic transducer, including a high-voltage output step and an excitation output step;

[0040] The high-voltage output steps are as follows:

[0041] The control circuit alternately sends pulse drive signals K1 and K2 to the source (S) of MOSFETs Q1 and Q2. When pulse drive signal K1 is received, MOSFET Q1 turns on, and current flows into a part of the primary coil of high-frequency transformer T1 through the 12V DC input. When pulse drive signal K2 is received, MOSFET Q2 turns on, and current flows into the other part of the primary coil of high-frequency transformer T1 through the 12V DC input. Thus, a high-frequency AC voltage waveform is generated in the primary coil of high-frequency transformer T1.

[0042] The high-frequency transformer T1 outputs a boosted AC voltage on the secondary coil. Then, diodes D1 and D2, capacitors C1 and C2 convert the positive half-cycle of the AC voltage waveform into DC current, and diodes D3 and D4, capacitors C3 and C4 convert the negative half-cycle of the AC voltage waveform into DC current.

[0043] The DC output voltage is composed of the DC current converted during the positive half-cycle and the DC current converted during the negative half-cycle, and its magnitude is denoted as HVDD.

[0044] The excitation output steps are as follows:

[0045] During charging, the control circuit stops sending pulse drive signals K3 and K4 to optocoupler M1 and optocoupler M2, MOSFETs Q3 and Q4 are turned off, and the DC output voltage is charged to terminal a of capacitor C5 after being divided by resistors R1 and R2 of the same resistance value, reaching half of the potential of HVDD. Terminal b of C5 is kept at the same potential as GND through resistor R4.

[0046] When a pulse is transmitted, the control circuit sends a pulse drive signal K3 to the optocoupler M1, turning on MOS driver Q5. MOS driver Q5 pulls up the control pulse of MOS transistor Q3, while the control pulse of MOS transistor Q4 remains low. MOS transistor Q3 is on, and MOS transistor Q4 is off. The voltage at terminal a of capacitor C5 abruptly changes to HVDD through MOS transistor Q3, while the potential difference across capacitor C5 does not change instantaneously. Therefore, the voltage at terminal b of capacitor C5 becomes half of HVDD. Then, the control circuit sends a pulse drive signal K4 to the optocoupler M2, turning on MOS driver Q6. MOS driver Q6 pulls up the control pulse of MOS transistor Q4, while the control pulse of MOS transistor Q3 abruptly changes to HVDD. Simultaneously, the voltage at terminal a of capacitor C5 is pulled low, MOSFET Q4 turns on, and MOSFET Q3 turns off. The voltage at terminal a of capacitor C5 suddenly changes to GND, but the potential difference across capacitor C5 does not change instantaneously. Therefore, the voltage at terminal b of capacitor C5 becomes half of -HVDD. Then, the control circuit stops sending pulse drive signals K3 and K4 to optocouplers M1 and M2. The control pulses of MOSFETs Q3 and Q4 are pulled low at the same time, and both MOSFETs Q4 and Q3 turn off. Terminal a of capacitor C5 returns to the voltage after being divided by two resistors R1 and R2 with the same resistance, reaching half of HVDD. Terminal b of capacitor C5 remains at the same potential as GND through resistor R4, thus forming a bipolar pulse.

[0047] Repeating the charging and pulse emission process generates a bipolar high-voltage pulse train, which is used to excite the air-coupled ultrasonic transducer.

[0048] As described above, although the invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A bipolar high-voltage pulse driving circuit for an air-coupled ultrasonic transducer, characterized by: The control circuit, the auxiliary power supply circuit, the pulse emission unit and the high-voltage output unit are included, the high-voltage output unit includes a high-frequency inverter circuit, a high-frequency transformer T1 and a voltage doubler rectifier circuit; the input end of the high-frequency inverter circuit is used for being connected to a 12V DC input, the output end of the high-frequency inverter circuit is electrically connected with the input side of the high-frequency transformer T1; the output side of the high-frequency transformer T1 is electrically connected with the input end of the voltage doubler rectifier circuit, and the output end of the voltage doubler rectifier circuit is electrically connected with the high-voltage input end of the pulse emission unit; the control circuit is electrically connected with the control end of the high-frequency inverter circuit and the control end of the pulse emission unit respectively; the output end of the pulse emission unit is used for being electrically connected with the input end of the air-coupled ultrasonic high-voltage transducer, and the air-coupled ultrasonic high-voltage transducer is outputted with an ultrasonic drive signal; the auxiliary power supply circuit supplies power to the control circuit and the pulse emission unit respectively. The pulse emission unit includes an optical coupling isolation circuit, a MOSFET drive circuit and a power amplifier circuit; the control end of the optical coupling isolation circuit is electrically connected with the control circuit, and the output end of the optical coupling isolation circuit is electrically connected with the input end of the MOSFET drive circuit; the output end of the MOSFET drive circuit is electrically connected with the control end of the power amplifier circuit, and is used for driving and controlling the power amplifier circuit; the output end of the power amplifier circuit is used for being electrically connected with the input end of the air-coupled ultrasonic high-voltage transducer, and the air-coupled ultrasonic high-voltage transducer is outputted with an ultrasonic drive signal. The high-frequency inverter circuit includes MOS tube Q1 and MOS tube Q2; the voltage doubler rectifier circuit includes capacitor C1, capacitor C2, capacitor C3, capacitor C4, diode D1, diode D2, diode D3 and diode D4; the G pole of the MOS tube Q1 and the MOS tube Q2 is electrically connected with the control circuit; the D pole of the MOS tube Q1 is electrically connected with one end of the primary coil of the high-frequency transformer T1, and the D pole of the MOS tube Q2 is electrically connected with the other end of the primary coil of the high-frequency transformer T1; the S pole of the MOS tube Q1 and the MOS tube Q2 is electrically connected with the negative pole of the 12V DC input; the midpoint of the primary coil of the high-frequency transformer T1 is electrically connected with the positive pole of the 12V DC input; one end of the secondary coil of the high-frequency transformer T1 is electrically connected with one end of the capacitor C1 and one end of the capacitor C3 respectively, and the other end of the secondary coil of the high-frequency transformer T1 is electrically connected with one end of the capacitor C2, the positive pole of the diode D1, one end of the capacitor C4 and the negative pole of the diode D3 respectively; the other end of the capacitor C1 is electrically connected with the negative pole of the diode D1 and the positive pole of the diode D2 respectively; the negative pole of the diode D2 and the other end of the capacitor C2 are electrically connected and serve as the positive output end of the voltage doubler rectifier circuit; the other end of the capacitor C4 is electrically connected with the positive pole of the diode D4; the other end of the capacitor C3, the positive pole of the diode D3 and the negative pole of the diode D4 are electrically connected and serve as the negative output end of the voltage doubler rectifier circuit.

2. The bipolar high-voltage pulse driving circuit for an air-coupled ultrasonic transducer of claim 1, wherein: The light coupling isolation circuit comprises a light coupling isolator M1 and a light coupling isolator M2; the MOSFET drive circuit comprises MOS drives Q5 and Q6; the power amplification circuit comprises MOS tubes Q3 and Q4, resistors R1, R2 and R3, diodes D5 and D6, and a capacitor C5 and a resistor R4; the input terminals of the light coupling isolators M1 and M2 are electrically connected to the control circuit, the output terminal of the light coupling isolator M1 is electrically connected to the input terminal of the MOS drive Q5, and the output terminal of the light coupling isolator M2 is electrically connected to the input terminal of the MOS drive Q6; the output terminal of the MOS drive Q5 is electrically connected to the G terminal of the MOS tube Q3, and the output terminal of the MOS drive Q6 is electrically connected to the G terminal of the MOS tube Q4; the D terminal of the MOS tube Q3, one end of the resistor R1 and the negative terminal of the diode D5 are electrically connected to the positive output terminal of the voltage doubling rectifier circuit; the S terminal of the MOS tube Q3 is electrically connected to the other end of the resistor R1, one end of the resistor R2, one end of the resistor R3 and the D terminal of the MOS tube Q4; the S terminal of the MOS tube Q4 is electrically connected to the other end of the resistor R2 and the positive terminal of the diode D6 and then grounded; the negative terminal of the diode D6 is electrically connected to the other end of the resistor R3, the a terminal of the capacitor C5 and the positive terminal of the diode D5; the b terminal of the capacitor C5 is electrically connected to one end of the resistor R4 and then serves as the output terminal of the power amplification circuit; and the other end of the resistor R4 is grounded.

3. A method of driving a bipolar high-voltage pulse driving circuit of an air-coupled ultrasonic transducer as claimed in claim 2, characterized in that: The method comprises a high-voltage output step and an excitation output step; The high-voltage output step is as follows: The control circuit alternately sends pulse drive signals K1 and K2 to the S terminals of the MOS tubes Q1 and Q2; when the pulse drive signal K1 is received, the MOS tube Q1 is turned on, and a current flows into a part of the primary coil of the high-frequency transformer T1 through the 12V direct-current input; when the pulse drive signal K2 is received, the MOS tube Q2 is turned on, and a current flows into another part of the primary coil of the high-frequency transformer T1 through the 12V direct-current input, thereby generating a high-frequency alternating voltage waveform in the primary coil of the high-frequency transformer T1; The high-frequency transformer T1 outputs the boosted alternating voltage on the secondary coil, and the diodes D1 and D2, the capacitor C1 and the capacitor C2 convert the positive half cycle of the alternating voltage waveform into direct current, and the diodes D3 and D4, the capacitor C3 and the capacitor C4 convert the negative half cycle of the alternating voltage waveform into direct current; The direct current converted from the positive half cycle and the direct current converted from the negative half cycle constitute a complete direct-current output voltage, which is denoted as HVDD; The excitation output step is as follows: During charging, the control circuit stops sending pulse drive signals K3 and K4 to the light coupling isolators M1 and M2, and the MOS tubes Q3 and Q4 are closed; the direct-current output voltage is divided by the resistors R1 and R2 of the same resistance value, and then charges the a terminal of the capacitor C5 to a potential of half of HVDD, and the b terminal of the capacitor C5 is kept at the same potential as GND through the resistor R4. When the pulse is emitted, the control circuit sends a pulse driving signal K3 to the opto-isolator M1, the MOS drive Q5 is turned on, the control pulse of the MOS Q3 is pulled up by the MOS drive Q5, the control pulse of the MOS Q4 is pulled down and remains unchanged, the MOS Q3 is turned on, the MOS Q4 is turned off, the voltage at the a end of the capacitor C5 is suddenly changed to HVDD through the MOS Q3 and the DC output voltage, the potential difference between the two ends of the capacitor C5 does not change instantaneously, so the voltage at the b end of the capacitor C5 becomes half of HVDD; then the control circuit sends a pulse driving signal K4 to the opto-isolator M2, the MOS drive Q6 is turned on, the control pulse of the MOS Q4 is pulled up by the MOS drive Q6, the control pulse of the MOS Q3 is pulled down at the same time, the MOS Q4 is turned on, the MOS Q3 is turned off, the voltage at the a end of the capacitor C5 is suddenly changed to GND, the potential difference between the two ends of the capacitor C5 does not change instantaneously, so the voltage at the b end of the capacitor C5 becomes half of -HVDD; then the control circuit stops sending the pulse driving signals K3 and K4 to the opto-isolators M1 and M2, the control pulses of the MOS Q3 and the MOS Q4 are pulled down at the same time, the MOS Q4 and the MOS Q3 are turned off, the a end of the capacitor C5 returns to the voltage after being divided by the two resistors R1 and R2 with the same resistance, reaches the potential of half of HVDD, the b end of the capacitor C5 keeps the same potential with GND through the resistor R4, so as to form a bipolar pulse. The above charging and emitting pulses are repeated to form a bipolar high-voltage pulse train for exciting the air-coupled ultrasonic transducer.

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