Open-loop Hall current sensor with true RMS output

Abstract

The invention provides an open-loop Hall current sensor with true RMS output, and the sensor comprises a power module which is used for providing stable working voltage for all modules of the sensor; the Hall driving module is electrically connected with the power supply module, is provided with a Hall element, and is used for sensing a magnetic field generated by the detected current and outputting Hall voltage through a differential signal output end; the signal processing and amplifying module is used for amplifying the Hall voltage to obtain an amplified signal; the true virtual value conversion module is connected with the output end of the signal processing and amplifying module, comprises a true virtual value conversion chip N4 and is used for receiving the amplified signal and calculating a true virtual value to obtain a direct-current voltage signal; and the voltage / current conversion module is connected with the true RMS conversion module and is used for converting the direct-current voltage signal into a standard current output signal. According to the invention, the technical problems of poor linearity, asymmetric forward and reverse output and waveform distortion during high-frequency AC signal measurement in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of Hall current sensor technology, and specifically to an open-loop Hall current sensor with true RMS output. Background Technology

[0002] Current sensors, as key sensing components in power electronic systems, are widely used in industrial automation, new energy, and smart grids, forming the foundation for system monitoring, protection, and control. Their measurement accuracy and reliability directly affect the performance and safety of the entire system.

[0003] Currently, widely used current sensors, especially open-loop current sensors based on the Hall effect, typically operate by detecting the magnetic field generated by the current and outputting a voltage signal proportional to the magnetic field strength (i.e., the instantaneous value of the current). These sensors are technologically mature and cost-effective, but their measurement mechanisms have inherent limitations: they primarily reflect the instantaneous amplitude or peak value of the measured current.

[0004] With the rapid development of power electronics technology, the widespread use of nonlinear devices such as frequency converters and rectifier loads has caused the current waveform in the power grid to frequently deviate from the standard sine wave, exhibiting severe distortion. Under such complex operating conditions, traditional current sensors, which can only provide instantaneous value information, are inadequate. Accurately assessing the true energy consumption, efficiency, and thermal load of equipment requires the true RMS value of the current, which directly reflects the signal's power and heat generation capacity. Traditional sensors cannot perform RMS value calculations on complex non-sine waves, making them unable to meet the needs of advanced applications such as power quality monitoring, energy efficiency assessment, and precise overload protection.

[0005] Furthermore, existing open-loop Hall current sensors still have room for performance optimization. For example, their Hall element drive circuits mostly use constant voltage mode, which is susceptible to changes in operating temperature and magnetoresistive effects, leading to drift in measurement accuracy. At the same time, the overall linearity of the sensor, the consistency of forward and reverse measurements, and the output stability under high-frequency signals also need to be improved.

[0006] Existing traditional current sensors exhibit significant technical limitations when faced with the aforementioned complex operating conditions, making it difficult to meet the demands for high-precision measurement. Specifically: 1. Poor Linearity and Asymmetrical Forward and Reverse Output: Traditional current sensors, especially certain types of Hall effect sensors, are prone to core saturation under strong magnetic fields, and their signal processing circuits exhibit nonlinear characteristics. This results in a non-ideal linear input-output relationship across the entire measurement range, indicating poor linearity. Furthermore, for equal forward and reverse currents, the sensor's output gain may differ, leading to asymmetrical forward and reverse outputs. This nonlinearity and asymmetry introduce fixed measurement errors, severely impacting system control accuracy and performance in applications requiring precise bidirectional energy flow measurement (such as charging and discharging in new energy vehicles) or precise torque control.

[0007] 2. Waveform Distortion Issues in High-Frequency AC Signal Measurement: When measuring high-frequency AC signals, the bandwidth limitations and phase delay characteristics of traditional current sensors become more pronounced. Their output waveform may fail to accurately reproduce the rapid changes in the input current, exhibiting waveform distortion, blunting of the rising / falling edges, and even resonance at certain frequencies, leading to abnormal oscillations or AC trends in the output signal. This distortion prevents the sensor from accurately capturing the instantaneous current value, resulting in significant deviations in key parameters such as the effective current value (RMS) and power calculated based on the instantaneous value. Especially in frequency conversion environments dominated by pulse width modulation (PWM) waveforms, this deficiency makes it difficult for sensors to perform accurate and reliable RMS measurements of continuously fluctuating currents, failing to provide an accurate data foundation for system overcurrent protection, energy efficiency analysis, and condition monitoring. Summary of the Invention

[0008] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide an open-loop Hall current sensor with true RMS output, which solves the technical problems of poor linearity, asymmetry between forward and reverse outputs, and waveform distortion during high-frequency AC signal measurement in the prior art.

[0009] To achieve the above technical objectives, the present invention provides an open-loop Hall current sensor with true RMS output, comprising: The power supply module is used to provide a stable operating voltage for each module of the sensor. The Hall drive module is electrically connected to the power module and is equipped with a Hall element. The Hall element is used to sense the magnetic field generated by the measured current and outputs a Hall voltage through the differential signal output terminal. A signal processing and amplification module is connected to the differential signal output terminal of the Hall element and is used to amplify the Hall voltage to obtain an amplified signal. A true RMS conversion module is connected to the output of the signal processing and amplification module. The true RMS conversion module includes a true RMS conversion chip N4, which is used to receive the amplified signal and calculate the true RMS value to obtain a DC voltage signal. A voltage / current conversion module, connected to the true RMS conversion module, is used to convert the DC voltage signal into a standard current output signal.

[0010] Compared with the prior art, the beneficial effects of the present invention include: This invention discloses an open-loop Hall current sensor with true RMS output. By integrating a true RMS conversion module into a traditional open-loop architecture, it achieves a significant performance improvement. Its core advantage lies in its ability to accurately measure the true RMS value of currents of any waveform, whether it is a standard sine wave or a distorted waveform containing harmonics. It can output a DC signal that truly reflects the thermal effect and work capability, perfectly solving the problem of large errors in non-sine wave measurements by ordinary sensors.

[0011] In terms of system integration and ease of use, this sensor highly integrates sensing, amplification, true RMS calculation, and signal conversion, providing users with a "one-stop" solution. It directly outputs a stable, interference-resistant DC voltage or standard current signal, greatly simplifying the design of the backend acquisition and control system and reducing overall costs. At the same time, this design inherits the inherent advantages of open-loop Hall effect sensors, including high safety due to electrical isolation, a wide measurement range, low power consumption, and simple structure and low cost.

[0012] In summary, this sensor retains the economic advantages of open-loop technology while achieving measurement accuracy and reliability comparable to high-end closed-loop sensors through its built-in true RMS conversion function. It is particularly suitable for modern power electronic equipment such as frequency converters, inverters, and switching power supplies that have non-sinusoidal currents, providing a cost-effective and ideal choice for precise current monitoring and control.

[0013] According to some embodiments of the present invention, the true RMS conversion chip N4 performs the following computational steps through its internal circuitry to obtain the DC voltage signal: Squaring step: Squaring the input amplified signal to obtain a squared signal; The average value calculation step is to perform an average value calculation on the squared signal to obtain the average value signal; Square root step: Perform a square root operation on the average value signal, and the result is the DC voltage signal that is proportional to the true effective value of the measured current.

[0014] According to some embodiments of the present invention, the Hall drive module is a constant current drive circuit, specifically including a Zener diode VS1, a PNP transistor VT1, a current limiting resistor R7, and a current regulating resistor R8; The cathode of the Zener diode VS1 is connected to the operating voltage, and the anode is connected to the base of the PNP transistor VT1 through the current-limiting resistor R7. The emitter of the PNP transistor VT1 is connected to the operating voltage, and the collector is connected to a drive input terminal of the Hall element B1 through the current regulating resistor R8, thereby providing a constant drive current to the Hall element B1. The Hall element B1 is used to sense the magnetic field generated by the measured current, and in response to the magnetic field, outputs a Hall voltage through its differential signal output terminal.

[0015] According to some embodiments of the present invention, the power supply module includes a first linear regulator NR1, a second linear regulator NR2, and an inverter N2; The first linear regulator NR1 is used to convert the power supply VCC into the first operating voltage VCC1. The output terminal is connected in parallel with the first transistor VT2 and the second transistor VT3. The first transistor VT2 and the second transistor VT3 are used to share the power consumption of the first linear regulator NR1. The second linear regulator NR2 is used to convert the second operating voltage VCC2 of the external circuit into a positive voltage of +5V; The inverter N2 is used to convert the positive voltage +5V into a negative voltage -5V, providing the required positive and negative operating voltages for each module of the sensor.

[0016] According to some embodiments of the present invention, the true RMS conversion module includes a true RMS conversion chip N4, an adjustment circuit, and an output amplification circuit; The adjustment circuit is connected to the differential input terminal of the true RMS converter chip N4 and is used to adjust the output zero point of the true RMS converter chip N4 when the primary current is zero. The output amplifier circuit is located at the DC voltage signal output terminal of the true RMS converter chip N4 and is used to amplify the true RMS DC voltage signal.

[0017] According to some embodiments of the present invention, the adjustment circuit includes: Resistors R17, R18, and variable resistor RP1; The resistors R17 and R18 are connected in series between the positive voltage +5V and ground. The variable resistor RP1 is connected in parallel with the resistor R18. The sliding end of the variable resistor RP1 is connected to the input terminal IN2 of the differential input terminal of the true RMS conversion chip N4. By adjusting the variable resistor RP1, the potential of the input terminal IN2 is changed, thereby realizing the adjustment of the output zero point.

[0018] According to some embodiments of the present invention, the output amplifier circuit is a non-inverting amplifier circuit, including: operational amplifier N3B, resistor R20, resistor R21 and variable resistor RP2.

[0019] According to some embodiments of the present invention, the signal processing and amplification module includes a single-stage inverting amplifier circuit and two-stage inverting amplifier circuits; The first-stage non-inverting amplifier circuit includes: resistors R9, R10, R11, operational amplifier N1A, and resistor R12, which are used to initially amplify the Hall voltage and provide high input impedance. The two-stage inverting amplifier circuit is cascaded after the first-stage non-inverting amplifier circuit, wherein: The first-stage inverting amplifier circuit includes: resistor R13, resistor R15, and operational amplifier N1B; The second-stage inverting amplifier circuit includes: resistors R14 and R16, and operational amplifier N3A; The two-stage inverting amplifier circuit is used together to further amplify the signal and improve the circuit's anti-interference capability.

[0020] According to some embodiments of the present invention, the voltage / current conversion module includes a zero-adjustment circuit and a transistor VT4 for power consumption sharing; The zero-adjustment circuit includes resistor R22, resistor R24, and variable resistor RP3; Resistors R22 and R24 are connected in series, and the variable resistor RP3 is connected in parallel with resistor R24; The collector of transistor VT4 is connected to the output current path to share the circuit power consumption. The voltage / current conversion module also includes a resistor R23, used to set the voltage-to-current conversion ratio.

[0021] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, wherein the abstract drawings are to be completely consistent with one of the drawings in the specification: Figure 1 A schematic diagram of a power supply module for an open-loop Hall current sensor with true RMS output, provided in one embodiment of the present invention; Figure 2 A schematic diagram of a Hall drive circuit for an open-loop Hall current sensor with true RMS output provided in one embodiment of the present invention; Figure 3 This is a schematic diagram of a Hall drive module for an open-loop Hall current sensor with true RMS output, provided in one embodiment of the present invention. Figure 4A schematic diagram of a signal processing and amplification module for an open-loop Hall current sensor with true RMS output provided in one embodiment of the present invention; Figure 5 A schematic diagram of an improved true RMS conversion module for an open-loop Hall current sensor with true RMS output, provided as an embodiment of the present invention; Figure 6 This is a schematic diagram of a voltage / current conversion module for an open-loop Hall current sensor with true RMS output, provided as an embodiment of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] It should be noted that although functional modules are divided in the system diagram and the logical order is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than the module division in the system or the order in the flowchart. The terms "first," "second," etc., in the specification, claims, and the aforementioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0025] Reference Figures 1 to 6 , Figure 1 A schematic diagram of a power supply module for an open-loop Hall current sensor with true RMS output, provided in one embodiment of the present invention; Figure 2 A schematic diagram of a Hall drive circuit for an open-loop Hall current sensor with true RMS output provided in one embodiment of the present invention; Figure 3 This is a schematic diagram of a Hall drive module for an open-loop Hall current sensor with true RMS output, provided in one embodiment of the present invention. Figure 4 A schematic diagram of a signal processing and amplification module for an open-loop Hall current sensor with true RMS output provided in one embodiment of the present invention; Figure 5 A schematic diagram of an improved true RMS conversion module for an open-loop Hall current sensor with true RMS output, provided as an embodiment of the present invention; Figure 6 This is a schematic diagram of a voltage / current conversion module for an open-loop Hall current sensor with true RMS output, provided as an embodiment of the present invention.

[0026] In one embodiment, the open-loop Hall current sensor with true RMS output includes: a power supply module for providing a stable operating voltage to each module of the sensor; a Hall drive module electrically connected to the power supply module, equipped with a Hall element, which senses the magnetic field generated by the measured current and outputs a Hall voltage through a differential signal output terminal; a signal processing and amplification module connected to the differential signal output terminal of the Hall element, for amplifying the Hall voltage to obtain an amplified signal; a true RMS conversion module connected to the output terminal of the signal processing and amplification module, the true RMS conversion module including a true RMS conversion chip N4 for receiving the amplified signal and calculating the true RMS value to obtain a DC voltage signal; and a voltage / current conversion module connected to the true RMS conversion module for converting the DC voltage signal into a standard current output signal.

[0027] The true RMS output open-loop Hall current sensor provided by this invention, through its innovative circuit design, brings significant performance improvements and many beneficial effects compared to traditional current sensors.

[0028] This invention achieves a qualitative leap in measurement accuracy through key innovations in linearity and symmetry. Specifically, a precise adjustment circuit is built at the differential input of the true RMS conversion chip. This circuit can effectively zero the offset voltage and calibrate the gain of the Hall voltage signal after pre-amplification, ensuring that the signal fed into the true RMS conversion core has optimal signal-to-noise ratio and linearity. This technological innovation directly and significantly improves the overall linearity of the sensor and the symmetry of forward and reverse current measurements. It effectively compensates for the inherent nonlinear errors and temperature drift of the Hall element and its pre-amplifier circuit, ensuring high consistency and accuracy of measurement results across the entire operating temperature range and measurement range, regardless of whether the current is forward or reverse. This meets the stringent requirements for precise measurement in applications such as bidirectional charging and discharging of new energy vehicles.

[0029] This invention achieves significant advancements in output stability and anti-interference capabilities, completely resolving the output distortion problem during high-frequency measurements. Its core lies in the addition of a high-performance low-pass filter circuit at the output of the true RMS conversion chip. This circuit effectively filters out high-frequency switching noise generated during true RMS calculation, as well as high-frequency interference components introduced from the front end. This design significantly improves the stability of the sensor's output signal within its designed frequency range, maintaining a essentially pure and stable DC output, completely eliminating the unstable AC trend or superimposed glitches present in the output waveform of traditional sensors during high-frequency AC signal measurements. This not only provides an extremely stable and reliable feedback signal for the back-end control system but also significantly enhances the system's anti-electromagnetic interference capability, ensuring the accuracy and stability of data in complex industrial electromagnetic environments.

[0030] Through the above two core technological innovations, this invention not only successfully overcomes the technical bottlenecks of poor linearity, poor symmetry, and unstable output of traditional current sensors under complex waveforms, but also ultimately provides a solution that can accurately and reliably output the true effective value of complex current waveforms, greatly improving the system performance and reliability in modern power electronics applications such as frequency conversion and new energy.

[0031] The true RMS converter chip N4 performs the following operations through its internal circuitry to obtain a DC voltage signal: Squaring step: Squaring the amplified input signal to obtain a squared signal; Averaging step: Averaging the squared signal to obtain an average signal; Square root step: Taking the square root of the average signal, the result of which is a DC voltage signal proportional to the true RMS value of the measured current.

[0032] The true RMS converter chip brings fundamental performance advantages to this invention by performing a mathematical operation of "squaring - averaging - square root". Its core advantage lies in achieving precise measurement independent of the waveform. This operational principle physically simulates the thermal effect of current on a resistor, enabling the sensor to accurately measure the true energy value of any complex periodic waveform (including non-sinusoidal waves containing higher harmonics, square waves, or PWM waves output by frequency converters). This fundamentally overcomes the problem of huge errors in measuring distorted waveforms by traditional sensors. This process ensures that the energy of all instantaneous values ​​(regardless of positive or negative and waveform shape) is included in the calculation through the "squaring" operation, the "averaging" operation precisely corresponds to the total power within a cycle, and finally, the "square root" output is a DC voltage that strictly corresponds to the true RMS value. Furthermore, this computational process significantly improves the reliability and ease of use of measurements. Since the final output is a stable DC signal after average filtering, rather than a rapidly changing AC signal, the output results are extremely stable and almost unaffected by high-frequency noise. It also greatly simplifies the design of the back-end data acquisition system. Microprocessors or PLCs can directly obtain accurate effective values ​​without performing complex high-speed sampling and software algorithm calculations, thereby reducing the overall complexity and cost of the system.

[0033] The Hall effect drive module is a constant current drive circuit, specifically including a Zener diode VS1, a PNP transistor VT1, a current-limiting resistor R7, and a current-adjusting resistor R8. The cathode of the Zener diode VS1 is connected to the operating voltage, and the anode is connected to the base of the PNP transistor VT1 through the current-limiting resistor R7. The emitter of the PNP transistor VT1 is connected to the operating voltage, and the collector is connected to a drive input terminal of the Hall element B1 through the current-adjusting resistor R8, thereby providing a constant drive current to the Hall element B1. The Hall element B1 is used to sense the magnetic field generated by the measured current and, in response to the magnetic field, outputs a Hall voltage through its differential signal output terminal.

[0034] Constant voltage operation mode means that the driving voltage Eb of the Hall element remains constant, but due to the influence of operating temperature and magnetoresistive effect, the input resistance Rin of the Hall element will change, causing a change in the Hall current Ic, which in turn affects the Hall voltage VH. Constant current operation mode, on the other hand, means that the driving current Ic of the Hall element is constant, and in this case, the Hall element is almost unaffected by operating temperature and magnetoresistive effect. In summary, the Hall voltage VH of the Hall element has higher stability in constant current operation mode. Since the direct amplification scheme is an open-loop system, high measurement accuracy and low temperature drift coefficient of the Hall element are required; therefore, constant current operation mode is chosen.

[0035] The constant current drive circuit employed in this invention provides optimal operating conditions for the Hall element, thereby fundamentally improving the overall performance of the sensor. Its core advantage lies in providing a highly stable drive current for the Hall element. Through a precision reference and adjustment circuit composed of a Zener diode VS1, a PNP transistor VT1, and resistors, this design effectively suppresses drive current drift caused by fluctuations in operating voltage or changes in ambient temperature. This constant current characteristic ensures that the sensitivity and bias voltage of the Hall element remain constant, directly resulting in two key benefits: First, it significantly reduces measurement errors introduced by power supply ripple or noise, enhancing the sensor's anti-interference capability and long-term stability in complex electromagnetic environments; second, it provides a cleaner and more reliable initial Hall voltage signal for subsequent signal processing circuits, laying a solid foundation for the entire system to achieve high linearity and low temperature drift performance goals.

[0036] The power supply module includes a first linear regulator NR1, a second linear regulator NR2, and an inverter N2. The first linear regulator NR1 converts the power supply VCC to a first operating voltage VCC1, and its output is connected in parallel with a first transistor VT2 and a second transistor VT3. The first transistor VT2 and the second transistor VT3 share the power consumption of the first linear regulator NR1. The second linear regulator NR2 converts the second operating voltage VCC2 of the external circuit to a positive voltage of +5V. The inverter N2 converts the positive voltage of +5V to a negative voltage of -5V, providing the required positive and negative operating voltages for each module of the sensor.

[0037] The module employs a multi-linear voltage regulator and inverting design to construct a clean and stable dual positive and negative power supply system. The first linear regulator NR1 handles the front-end power supply, converting the unstable input VCC into a stable first operating voltage VCC1. The second linear regulator NR2 performs secondary voltage regulation, generating a precise +5V voltage, which is then used by the inverter N2 to generate the corresponding -5V negative voltage. This hierarchical voltage regulation and independently generated architecture provides symmetrical, low-noise operating voltages for key components in the signal chain, such as operational amplifiers and Hall elements. This is crucial for processing weak differential Hall signals, effectively ensuring that the signal is not distorted during amplification and processing due to power supply fluctuations or asymmetry, thereby fundamentally improving the measurement accuracy and signal-to-noise ratio of the entire system.

[0038] Secondly, this power module innovatively connects the first transistor VT2 and the second transistor VT3 in parallel at the output of the first linear regulator NR1. This design forms an effective power-sharing network. In a linear regulator circuit, the voltage difference between the input and output voltages is entirely consumed within the regulator, leading to significant heat generation. This not only reduces efficiency but also affects voltage regulation accuracy and can even damage the device due to increased temperature. By introducing external sharing transistors, most of the load current and corresponding power consumption are transferred to VT2 and VT3, significantly suppressing the temperature rise of the core regulator chip NR1 itself. This advantage directly translates into the power module's superior thermal stability and long-term operational reliability, ensuring that all functional modules of the sensor always receive a stable and undegraded voltage supply under wide input voltage ranges or high load current conditions. This greatly extends the equipment's lifespan and enhances its adaptability to harsh industrial environments.

[0039] The true RMS conversion module includes a true RMS conversion chip N4, an adjustment circuit, and an output amplifier circuit. The adjustment circuit is connected to the differential input terminal of the true RMS conversion chip N4 and is used to adjust the output zero point of the true RMS conversion chip N4 when the primary current is zero. The output amplifier circuit is located at the DC voltage signal output terminal of the true RMS conversion chip N4 and is used to amplify the true RMS DC voltage signal.

[0040] The adjustment circuit includes resistors R17 and R18, and a variable resistor RP1. Resistors R17 and R18 are connected in series between a positive voltage of +5V and ground. The variable resistor RP1 is connected in parallel with resistor R18. The sliding terminal of the variable resistor RP1 is connected to the differential input terminal IN2 of the true RMS converter chip N4. By adjusting the variable resistor RP1, the potential of the input terminal IN2 is changed, thereby adjusting the output zero point. The output amplifier circuit is a non-inverting amplifier circuit, including operational amplifier N3B, resistor R20, resistor R21, and the variable resistor RP2.

[0041] The adjustment circuit connected to the differential input of the true RMS converter chip N4 provides a crucial zero-point calibration mechanism for achieving extremely high measurement accuracy. In practical circuits, due to the inherent offset voltage and temperature drift of the preceding Hall element and its signal processing link, the input signal to the true RMS converter chip may not be zero even when the measured primary current is zero, resulting in a zero-point error in the final output. This adjustment circuit effectively cancels out these accumulated offsets from the preceding stage by providing a precisely adjustable compensation signal, ensuring that the output of the true RMS converter chip is also precisely zero when the primary current is zero. This advantage directly eliminates the sensor's inherent systematic error, significantly improving accuracy in low-current measurements and laying a solid foundation for excellent linearity throughout the entire measurement range, enabling the sensor to perform exceptionally well in applications requiring precision measurement and bidirectional current detection.

[0042] The output amplifier circuit located at the chip's output end greatly enhances the sensor's flexibility and signal driving capability. The DC voltage signal directly output by a true RMS converter chip typically has a fixed and limited amplitude, which may not directly meet the requirements of downstream data acquisition systems for different voltage ranges or high-standard current signals (such as 4-20mA). This output amplifier circuit, by proportionally amplifying the initially obtained true RMS DC voltage signal, can flexibly adjust the sensor's final output to a standardized, industrially applicable signal level. This design advantage allows the sensor to seamlessly interface with various types of PLCs, controllers, or display instruments, significantly improving its versatility and system integration convenience. Simultaneously, the amplified signal also has stronger anti-interference capabilities and a longer transmission distance, further ensuring reliability in complex industrial environments.

[0043] The signal processing and amplification module includes a single-stage non-inverting amplifier circuit and two stages of inverting amplifier circuits. The single-stage non-inverting amplifier circuit includes resistors R9, R10, and R11, operational amplifier N1A, and resistor R12, which are used to initially amplify the Hall voltage and provide high input impedance. The two stages of inverting amplifier circuits are cascaded after the single-stage non-inverting amplifier circuit. The first stage of the inverting amplifier circuit includes resistors R13 and R15, and operational amplifier N1B. The second stage of the inverting amplifier circuit includes resistors R14 and R16, and operational amplifier N3A. The two stages of inverting amplifier circuits are used together to further amplify the signal and improve the circuit's anti-interference capability.

[0044] The multi-stage operational amplifier architecture used in this invention forms a high-performance signal conditioning link through a precise combination of "one stage of in-phase amplification followed by two stages of in-phase amplification". Its advantages are reflected in the processing quality of weak signals and the overall stability of the system.

[0045] The first-stage in-phase amplifier circuit provides the sensor with a crucial high input impedance characteristic. This circuit is directly connected to the differential output of the Hall element, and its high input impedance minimizes the load effect on weak Hall voltage signals, ensuring that the most original and complete signal is introduced into the processing chain, effectively avoiding signal attenuation and distortion at the source. Simultaneously, this stage also performs the task of preliminary amplification of the Hall voltage, providing a signal foundation with sufficient amplitude and excellent signal-to-noise ratio for subsequent processing. This is an indispensable first step for accurately capturing and amplifying millivolt-level Hall signals.

[0046] The subsequent two cascaded inverting amplifier stages together form an optimized combination of gain distribution and noise suppression. By rationally distributing the total gain to two independent inverting amplifier stages, compared to using a single-stage amplifier to achieve the full gain, the bandwidth of the entire signal chain can be effectively widened, and the impact of the self-noise of each operational amplifier stage on the total output can be reduced. This achieves high amplification while maintaining good signal response speed and fidelity. More importantly, the inverting amplifier structure itself has a "virtual ground" node, a characteristic that naturally suppresses common-mode interference signals introduced by power supply fluctuations or lines. The series connection of the two inverting amplifier stages further enhances this common-mode interference immunity, ensuring that the signal finally sent to the true RMS conversion module is a fully amplified and "pure" differential signal, greatly improving the measurement stability and reliability of the sensor in complex electromagnetic industrial environments.

[0047] The voltage / current conversion module includes a zero-adjustment circuit and a transistor VT4 for power consumption sharing; the zero-adjustment circuit includes resistors R22 and R24 and a variable resistor RP3; resistors R22 and R24 are connected in series, and the variable resistor RP3 is connected in parallel with resistor R24; the collector of transistor VT4 is connected to the output current path to share the circuit power consumption; the voltage / current conversion module also includes resistor R23 to set the voltage to current conversion ratio.

[0048] The zero-adjustment circuit, composed of resistors R22 and R24 and a variable resistor RP3, provides a crucial calibration method for achieving high-precision standard current output. This circuit allows for fine-tuning of the signal's zero point in the final stage of voltage / current conversion. Even if the preceding circuitry has performed zero-point calibration, a slight offset may still be introduced after signal conversion and transmission, resulting in an error in the output standard current signal (e.g., 4mA) when the input is zero. By adjusting the variable resistor RP3, this residual offset can be precisely compensated, ensuring that the sensor's output current strictly corresponds to the standard value under zero-input conditions. This advantage directly enhances the sensor's applicability and interchangeability in industrial control systems, enabling seamless integration into DCS or PLC systems that adhere to standard signal protocols, and providing ultimate assurance for measurement accuracy within a small signal range.

[0049] The integration of transistor VT4 is a core design element in enhancing the module's durability and stability. When outputting large currents or handling high load voltages, the voltage / current conversion core device faces significant power consumption and heat generation, which can introduce temperature drift errors and even damage due to overheating. Connecting the collector of transistor VT4 to the output current path allows it to handle the primary power dissipation, effectively sharing the power consumption and thermal load of the core conversion chip. This advantage greatly suppresses the temperature rise of the core device, significantly improving the long-term reliability and lifespan of the entire module under harsh conditions. Furthermore, by maintaining the chip at a lower operating temperature, it ensures the stability of the conversion ratio (set by resistor R23), thereby guaranteeing the accuracy and consistency of the output current signal across the entire range.

[0050] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of the present invention.

[0051] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An open-loop Hall current sensor with true RMS output, characterized in that, include: The power supply module is used to provide a stable operating voltage for each module of the sensor. The Hall drive module is electrically connected to the power module and is equipped with a Hall element. The Hall element is used to sense the magnetic field generated by the measured current and outputs a Hall voltage through the differential signal output terminal. A signal processing and amplification module is connected to the differential signal output terminal of the Hall element and is used to amplify the Hall voltage to obtain an amplified signal. A true RMS conversion module is connected to the output of the signal processing and amplification module. The true RMS conversion module includes a true RMS conversion chip N4, which is used to receive the amplified signal and calculate the true RMS value to obtain a DC voltage signal. A voltage / current conversion module, connected to the true RMS conversion module, is used to convert the DC voltage signal into a standard current output signal.

2. The open-loop Hall current sensor with true RMS output according to claim 1, characterized in that, The true RMS converter chip N4 performs the following calculation steps through its internal circuitry to obtain the DC voltage signal: Squaring step: Squaring the input amplified signal to obtain a squared signal; The average value calculation step is to perform an average value calculation on the squared signal to obtain the average value signal; Square root step: Perform a square root operation on the average value signal, and the result is the DC voltage signal that is proportional to the true effective value of the measured current.

3. The open-loop Hall current sensor with true RMS output according to claim 1, characterized in that, The Hall effect drive module is a constant current drive circuit, specifically including a Zener diode VS1, a PNP transistor VT1, a current limiting resistor R7, and a current regulating resistor R8. The cathode of the Zener diode VS1 is connected to the operating voltage, and the anode is connected to the base of the PNP transistor VT1 through the current-limiting resistor R7. The emitter of the PNP transistor VT1 is connected to the operating voltage, and the collector is connected to a drive input terminal of the Hall element B1 through the current regulating resistor R8, thereby providing a constant drive current to the Hall element B1. The Hall element B1 is used to sense the magnetic field generated by the measured current, and in response to the magnetic field, outputs a Hall voltage through its differential signal output terminal.

4. The open-loop Hall current sensor with true RMS output according to claim 1, characterized in that, The power module includes a first linear regulator NR1, a second linear regulator NR2, and an inverter N2; The first linear regulator NR1 is used to convert the power supply VCC into the first operating voltage VCC1. The output terminal is connected in parallel with the first transistor VT2 and the second transistor VT3. The first transistor VT2 and the second transistor VT3 are used to share the power consumption of the first linear regulator NR1. The second linear regulator NR2 is used to convert the second operating voltage VCC2 of the external circuit into a positive voltage of +5V; The inverter N2 is used to convert the positive voltage +5V into a negative voltage -5V, providing the required positive and negative operating voltages for each module of the sensor.

5. The open-loop Hall current sensor with true RMS output according to claim 4, characterized in that, The true RMS conversion module includes a true RMS conversion chip N4, an adjustment circuit, and an output amplifier circuit; The adjustment circuit is connected to the differential input terminal of the true RMS converter chip N4 and is used to adjust the output zero point of the true RMS converter chip N4 when the primary current is zero. The output amplifier circuit is located at the DC voltage signal output terminal of the true RMS converter chip N4 and is used to amplify the true RMS DC voltage signal.

6. The open-loop Hall current sensor with true RMS output according to claim 5, characterized in that, The regulating circuit includes: Resistors R17, R18, and variable resistor RP1; Resistors R17 and R18 are connected in series between the positive voltage +5V and ground. Variable resistor RP1 is connected in parallel with resistor R18. The sliding end of variable resistor RP1 is connected to the input terminal IN2 of the differential input terminal of the true RMS conversion chip N4. By adjusting variable resistor RP1, the potential of input terminal IN2 is changed, thereby realizing the adjustment of the output zero point.

7. The open-loop Hall current sensor with true RMS output according to claim 5, characterized in that, The output amplifier circuit is a non-inverting amplifier circuit, including: operational amplifier N3B, resistor R20, resistor R21, and variable resistor RP2.

8. The open-loop Hall current sensor with true RMS output according to claim 1, characterized in that, The signal processing and amplification module includes a single-stage inverting amplifier circuit and two-stage inverting amplifier circuits. The first-stage non-inverting amplifier circuit includes: resistors R9, R10, R11, operational amplifier N1A, and resistor R12, which are used to initially amplify the Hall voltage and provide high input impedance. The two-stage inverting amplifier circuit is cascaded after the first-stage non-inverting amplifier circuit, wherein: The first-stage inverting amplifier circuit includes: resistor R13, resistor R15, and operational amplifier N1B; The second-stage inverting amplifier circuit includes: resistors R14 and R16, and operational amplifier N3A; The two-stage inverting amplifier circuit is used together to further amplify the signal and improve the circuit's anti-interference capability.

9. The open-loop Hall current sensor with true RMS output according to claim 1, characterized in that, The voltage / current conversion module includes a zero-adjustment circuit and a transistor VT4 for power consumption sharing; The zero-adjustment circuit includes resistor R22, resistor R24, and variable resistor RP3; Resistors R22 and R24 are connected in series, and the variable resistor RP3 is connected in parallel with resistor R24; The collector of transistor VT4 is connected to the output current path to share the circuit power consumption. The voltage / current conversion module also includes a resistor R23, used to set the voltage-to-current conversion ratio.

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