A bridge push-pull structure and transformer coupled dual operational amplifier power amplifier device

Abstract

The application relates to a bridge push-pull structure and transformer-coupled double operational amplifier power amplification device, which comprises a bridge push-pull structure power amplification circuit and a transformer-coupled isolation circuit connected with each other, wherein the bridge push-pull structure power amplification circuit is used for generating two high-voltage signals with a phase difference of 180 degrees according to an input low-voltage signal; and the transformer-coupled isolation circuit is used for converting the two high-voltage signals into a single-end signal and realizing good driving on different impedance loads based on the impedance transformation principle of a transformer. Compared with the prior art, the application has the advantages of considering the high-current driving required by an EMAT and the high-voltage output capacity on conventional loads.

Description

Technical Field

[0001] This invention belongs to the field of ultrasonic testing and designs a power amplification device, particularly a dual operational amplifier power amplification device with a bridge push-pull structure and transformer coupling. Background Technology

[0002] In the field of ultrasonic testing, improving the driving capability of transducers to generate stronger ultrasonic signals has always been a focus of research and development. Currently, commercially available power amplifiers perform adequately in conventional piezoelectric ultrasonic testing. However, in electromagnetic ultrasonic testing, due to the multiple energy conversions involved in electromagnetic ultrasonic transducers (EMAT), their conversion efficiency is lower than that of piezoelectric transducers. To obtain a detection signal with a sufficient signal-to-noise ratio, significantly higher excitation voltage and current are often required compared to piezoelectric ultrasonic testing. This places higher demands on power amplifiers.

[0003] Currently, the selection of power amplifier models in electromagnetic ultrasonic testing systems is limited because driving the EMAT requires a high current output capability without compromising the high-voltage excitation function. This type of equipment is built using discrete components, offering high design flexibility; by stacking components, ultra-high output power can be achieved. However, this approach significantly increases overall complexity, equipment size, and weight, and places stringent demands on operators. Alternatively, power amplifiers can be built using integrated chips. These solutions typically employ high-voltage operational amplifiers, resulting in a relatively simple and stable circuit structure, small size, and light weight.

[0004] However, at present, ultrasonic power amplifiers built with integrated chips are limited by semiconductor technology, resulting in restricted output power and an inability to handle both high voltage and high current. The design scheme is usually based on a basic negative feedback operational amplifier structure, and the circuit generally uses only a single chip. The upper limit of the output capability depends solely on the chip itself, making it difficult to meet the EMAT driving requirements while simultaneously possessing high voltage output capability.

[0005] Therefore, it is necessary to develop a new integrated solution for power amplifier devices. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art by providing a dual operational amplifier power amplifier device with a bridge push-pull structure and transformer coupling, which takes into account both the high current drive required for EMAT and the high voltage output capability for conventional loads, and can be used for electromagnetic ultrasonic testing and conventional ultrasonic testing.

[0007] The objective of this invention can be achieved through the following technical solutions: A dual operational amplifier power amplifier device with a bridge push-pull structure and transformer coupling includes a bridge push-pull power amplifier circuit and a transformer-coupled isolation circuit connected to each other. The bridge push-pull power amplifier circuit is used to generate two high-voltage signals with a phase difference of 180 degrees based on the input low-voltage signal. The transformer coupling isolation circuit is used to convert the two high-voltage signals into single-ended signals, and based on the impedance transformation principle of the transformer, it can effectively drive loads with different impedances.

[0008] Furthermore, the bridge push-pull power amplifier circuit is based on two PA85 operational amplifier chips to build the bridge push-pull structure.

[0009] Furthermore, the bridge push-pull power amplifier circuit includes a power input terminal that uses a TVS diode to prevent voltages exceeding a set range from entering the chip.

[0010] Furthermore, the turns ratio of the primary and secondary coils of the transformer coupling isolation circuit is optimized and determined based on the optimal load value.

[0011] Furthermore, a power resistor for limiting the static DC current is connected in series between the bridge push-pull power amplifier circuit and the transformer coupling isolation circuit.

[0012] Furthermore, the bridge push-pull power amplifier circuit includes two ground planes, namely the reference ground for the input low-voltage signal and the power supply reference ground.

[0013] Furthermore, when laying out the PCB for the bridge push-pull power amplifier circuit, the input BNC port of the low-voltage signal to be amplified and the output port of the high-voltage differential floating ground signal are set on different sides of the PCB.

[0014] Furthermore, the transformer coupling isolation circuit has a grounding terminal only on the output side.

[0015] Furthermore, the peak-to-peak voltage range of the low-voltage signal input to the device is less than or equal to 3.9 Vpp.

[0016] Furthermore, the device also includes an external bipolar high-voltage power supply for providing power.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) In terms of driving capability, this invention employs a connected bridge push-pull power amplifier circuit and a transformer-coupled isolation circuit, which can drive loads with different impedance ranges. It can also drive low-impedance EMAT, improving the adaptability of the detection system. The doubled output voltage increases the output power. The bridge push-pull amplifier circuit of this invention can achieve twice the output voltage of a single operational amplifier chip. The high-frequency transformers with different transformation ratios enable this invention to drive at near-maximum power when dealing with different loads, thus demonstrating good driving capability. Experimental results show that this invention can drive different loads, balancing the high current requirements of electromagnetic ultrasonic testing with the high-voltage output of conventional applications.

[0018] (2) From the perspective of actual measurement results, this invention can be used for measurement tasks. Complete electrical isolation is achieved through transformer coupling, allowing the originally floating differential output to be safely connected to various grounded loads, fundamentally avoiding the risk of high-voltage leakage and ensuring the safety of equipment and operators. Combined with the high driving capability of the bridge push-pull power amplifier circuit, this invention performs well when using ultrasonic transducers for measurement tasks. Experimental verification results show that this invention performs well in practical applications.

[0019] (3) The bandwidth of this invention is good for different operating frequencies. High-voltage operational amplifier chips generally have low bandwidth, while the circuit built with the PA85 chip in this invention has good bandwidth performance. Experimental verification results show that this invention maintains a good bandwidth level. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the BTL bridge push-pull structure of the present invention; Figure 3 This is a schematic diagram of the transformer coupling principle of the present invention; Figure 4 This is a circuit diagram of a bridge push-pull power amplifier circuit in an embodiment of the present invention; Figure 5 This is a schematic diagram of the PCB layout of the bridge push-pull power amplifier circuit in an embodiment of the present invention; Figure 6 This is a circuit diagram of the transformer coupling isolation circuit in an embodiment of the present invention; Figure 7 This is a schematic diagram of the PCB layout of the transformer coupling isolation circuit in an embodiment of the present invention; Figure 8 Here is the EMAT impedance curve; Figure 9This is a schematic diagram of the measured voltage signals driving different loads in an embodiment of the present invention; Figure 10 This is a schematic diagram illustrating the signal acquisition process of driving the EMAT to transmit and receive signals in an embodiment of the present invention. Figure 11 This is a schematic diagram of the overall gain-bandwidth curve of the circuit in an embodiment of the present invention. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0022] This embodiment provides a dual operational amplifier power amplifier device with a bridge push-pull structure and transformer coupling, such as... Figure 1 As shown, the device includes a bridge-type push-pull power amplifier circuit and a transformer-coupled isolation circuit connected together. The bridge-type push-pull power amplifier circuit generates two high-voltage signals with a 180-degree phase difference based on the input low-voltage signal. The transformer-coupled isolation circuit converts the two high-voltage signals into single-ended signals, achieving good driving of loads with different impedances based on the impedance transformation principle of the transformer. The device has one low-voltage input interface and one high-voltage output interface. This power amplifier combines the high current drive required for EMAT (Electromagnetic Ultrasonic Testing) with the high voltage output capability for conventional loads, and can be used for both electromagnetic ultrasonic testing and conventional ultrasonic testing.

[0023] Furthermore, a power resistor is connected in series between the bridge push-pull power amplifier circuit and the transformer-coupled isolation circuit to limit the quiescent DC current, so that more of the limited current can be allocated to the effective signal, thereby improving output capability and reducing chip heat generation. The device also includes an external bipolar high-voltage power supply for providing power.

[0024] Specifically, this embodiment uses the PA85 power amplifier chip to design a bridge push-pull amplifier circuit to generate two high-voltage signals with a 180-degree phase difference; it also uses a high-frequency transformer to design an isolation circuit, connected by a power resistor, to limit the static DC current of the amplifier circuit; and it uses the impedance transformation principle of the transformer to achieve good driving of loads with different impedances.

[0025] Specifically, such as Figure 2 As shown, the bridge push-pull power amplifier circuit uses a BTL bridge push-pull structure and sets the two amplifier chips to the same gain. In this configuration, the output high-voltage signals of the two channels have the same amplitude but opposite phase. Connecting a load across the two output channels allows the voltage across the load to reach twice the output voltage of a single amplifier chip.

[0026] In this embodiment, the circuit schematic and PCB layout diagram of the bridge push-pull power amplifier circuit are as follows: Figure 4 and Figure 5 As shown. Figure 4 As shown, the bridge push-pull power amplifier circuit includes a power input terminal, which uses a TVS diode to prevent voltages exceeding a set range from entering the chip. The bridge push-pull power amplifier circuit also includes two ground planes: a reference ground for the input low-voltage signal and a power supply reference ground. By dividing the ground plane into a low-voltage signal area and a power supply area, the return path of the power supply current can avoid the sensitive low-voltage signal reference area, thereby reducing common impedance coupling and effectively reducing the resulting crosstalk and noise.

[0027] When laying out the PCB for the bridge push-pull power amplifier circuit, the input BNC port of the low-voltage signal to be amplified and the output port of the high-voltage differential floating ground signal are placed on different sides of the PCB. Specifically, as shown... Figure 5 As shown, in the PCB layout of the bridge push-pull power amplifier circuit, the left side of the PCB is the input BNC port for the low-voltage signal to be amplified, and the top is the output port for the high-voltage differential floating ground signal. The circuit board has 2×4 through holes for connecting the mounting bolts of the two chip heat sinks. This PCB layout spatially isolates the low-voltage input from the high-voltage output and avoids long parallel wiring, effectively suppressing capacitive and inductive coupling, thereby reducing channel crosstalk and minimizing noise and oscillation risks.

[0028] Furthermore, to address the grounding compatibility issues arising from the differential floating ground output of the BTL structure, this device introduces a transformer-coupled isolation circuit after the BTL output stage. For example... Figure 3 As shown, the differential voltage of the floating ground is completely cut off from the direct electrical connection between the primary and secondary sides through the "electric-magnetic-electric" conversion of the transformer's magnetic ring, so that the secondary winding can be safely grounded.

[0029] Furthermore, the turns ratio of the primary and secondary windings in the transformer-coupled isolation circuit is optimized and determined based on the optimal load value. Based on the transformer's impedance transformation, by selecting transformers with different turns ratios, the actual load impedance is transformed. Reflected to the primary, making its equivalent impedance The load value is close to the optimal load value of the power amplifier circuit, which enables the sensor with extremely low impedance to be driven efficiently, avoiding clipping and distortion caused by excessive current. and The relational expression is as follows: .

[0030] Furthermore, to address the issue of excessive quiescent current in the transformer primary coil and chip overheating caused by the small static DC voltage difference between the two amplification channels in the BTL structure, a power resistor was connected in series between the BTL circuit output port and the transformer. This resistor presents a large impedance to DC signals to limit the quiescent current, while having minimal impact on high-frequency AC signals, ensuring normal circuit operation.

[0031] In this embodiment, the optimal load impedance of the power amplifier circuit is approximately 2 kΩ, so a 50 Ω load uses a 6.324:1 ratio, and an approximately 16 Ω EMAT uses a 13:1 ratio.

[0032] In this embodiment, the circuit schematic and PCB layout diagram of the transformer coupling isolation circuit are as follows: Figure 6 and Figure 7 As shown. Figure 6 As shown, the transformer-coupled isolation circuit has no grounding at the input, but adds grounding and copper plating to the output side. This allows the originally floating differential output to be safely connected to a grounded load, while effectively blocking high-voltage leakage paths. A power resistor is added to the differential signal side of the input terminal to limit the static DC current of the power amplifier circuit output.

[0033] The working process of the above power amplifier device is as follows: an external bipolar high-voltage power supply provides ±200V to the circuit. The power amplifier circuit inputs the original small signal to be amplified, the range of which does not exceed 3.9 Vpp, so that the output waveform just reaches the maximum undistorted peak-to-peak value. After amplification, it is converted into two differential high-voltage signals with a phase difference of 180 degrees. This signal is input to the input terminal of the transformer coupling circuit. After the static DC current is limited by the power resistor, it is coupled by the transformer and impedance converted, and finally the output voltage is obtained and connected to the ultrasonic transducer.

[0034] The aforementioned power amplification device can maintain the maximum output voltage of the power amplification circuit while ensuring that the current in the differential signal loop does not exceed the chip's upper limit of 200 mA. In this embodiment, the specific parameters are: input signal peak-to-peak value 3.9 Vpp, differential output signal peak-to-peak value 696 Vpp. Theoretically, a load with an impedance of 1740 Ω can be driven at this time. To leave a certain margin, the minimum driveable load impedance is limited to 2 kΩ. By optimizing the turns ratio of the primary and secondary coils of the transformer coupling isolation circuit, it is possible to drive loads with different impedances: for example, under the isolation drive of a 1:1 transformer, a 2 kΩ load can be connected, at which time the peak-to-peak signal voltage on the load is about 696 Vpp; if a 50 Ω load is driven, a 6.324:1 transformer can be used, at which time the conversion factor is 40 times, and the load equivalent to the primary and differential output terminals of the transformer is 2 kΩ, which meets the driving requirements; to drive the electromagnetic ultrasonic transducer, with Figure 8Taking the EMAT impedance curve shown as an example, its impedance value at the operating frequency is about 16Ω, which can be used with a 13:1 transformer. At this time, the impedance conversion factor is 169 times, and the equivalent load to the primary and differential output terminals of the transformer is 2704Ω, which meets the driving requirements.

[0035] The effectiveness of the amplification device described above will be verified through specific experiments.

[0036] (1) Adjust the input signal to approximately 3.9 Vpp. At this point, the amplified signal reaches its maximum. The test frequency is selected as a 247.25 kHz pulse signal, which is the operating frequency of the selected EMAT, to standardize the measurement conditions for each load. From Figure 9 As can be seen, when using a 1:1 transformer to drive a 2 kΩ load resistor, the peak-to-peak voltage across the load is 696 Vpp; when using a 6.324:1 transformer to drive a 50 Ω load resistor, the peak-to-peak voltage across the load is 106 Vpp; and when using a 13:1 transformer to drive the EMAT, the peak-to-peak voltage across the EMAT is 54 Vpp. The impedance of this EMAT at the operating frequency is 16 Ω, thus the peak-to-peak output current is approximately 3.3 A. The results show that this embodiment can drive different loads, balancing the high current requirements of electromagnetic ultrasonic testing with the high-voltage output of conventional applications.

[0037] (2) Using EMAT as the measuring tool, the measuring object was a 1 mm thick 6061 aluminum plate. A transformer with a transformation ratio of 13:1 was selected. The actual peak-to-peak driving current was 3.3 A. A one-to-one transmit and one-to-receive experiment was conducted at intervals of 250 mm. The received waveform results are as follows: Figure 10 As shown, the peak-to-peak value of the direct wave signal can reach 84.9 mVpp, and the wave packet is distinct. This demonstrates that this embodiment performs well in practical applications.

[0038] (3) Using a 1:1 transformer driving a 2 kΩ load as the test condition, input a 1 Vpp signal to the power amplifier and measure the voltage across the load. Calculate the overall bandwidth based on this. The results are as follows: Figure 11 As shown, its -3 dB bandwidth is approximately 45 kHz to 600 kHz, and a voltage gain of at least 120 times can be achieved within this bandwidth range. This demonstrates that this embodiment maintains a good bandwidth level.

[0039] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A dual operational amplifier power amplifier device with a bridge push-pull structure and transformer coupling, characterized in that, This includes a connected bridge push-pull power amplifier circuit and a transformer-coupled isolation circuit, wherein... The bridge push-pull power amplifier circuit is used to generate two high-voltage signals with a phase difference of 180 degrees based on the input low-voltage signal. The transformer coupling isolation circuit is used to convert the two high-voltage signals into single-ended signals, and based on the impedance transformation principle of the transformer, it can effectively drive loads with different impedances.

2. The bridge push-pull structure and transformer-coupled dual operational amplifier power amplifier device according to claim 1, characterized in that, The bridge push-pull power amplifier circuit is based on two PA85 operational amplifier chips to build the bridge push-pull structure.

3. The bridge push-pull structure and transformer-coupled dual operational amplifier power amplifier device according to claim 2, characterized in that, The bridge push-pull power amplifier circuit includes a power input terminal that uses a TVS diode to prevent voltages exceeding a set range from entering the chip.

4. The bridge push-pull structure and transformer-coupled dual operational amplifier power amplifier device according to claim 1, characterized in that, The turns ratio of the primary and secondary coils of the transformer coupling isolation circuit is determined based on the optimal load value.

5. The bridge push-pull structure and transformer-coupled dual operational amplifier power amplifier device according to claim 1, characterized in that, A power resistor for limiting static DC current is connected in series between the bridge push-pull power amplifier circuit and the transformer coupling isolation circuit.

6. The bridge push-pull structure and transformer-coupled dual operational amplifier power amplifier device according to claim 1, characterized in that, The bridge push-pull power amplifier circuit includes two ground planes: a reference ground for the input low-voltage signal and a power supply reference ground.

7. The bridge push-pull structure and transformer-coupled dual operational amplifier power amplifier device according to claim 1, characterized in that, When laying out the PCB for the bridge push-pull power amplifier circuit, the input BNC port of the low-voltage signal to be amplified and the output port of the high-voltage differential floating ground signal are set on different sides of the PCB.

8. The bridge push-pull structure and transformer-coupled dual operational amplifier power amplifier device according to claim 1, characterized in that, The transformer coupling isolation circuit has a grounding terminal only on the output side.

9. The bridge push-pull structure and transformer-coupled dual operational amplifier power amplifier device according to claim 1, characterized in that, The peak-to-peak voltage range of the low-voltage input signal to this device is less than or equal to 3.9 Vpp.

10. The bridge push-pull structure and transformer-coupled dual operational amplifier power amplifier device according to claim 1, characterized in that, The device also includes an external bipolar high-voltage power supply for providing power.

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