Multi-waveform current source for ground resistance detection

Abstract

The invention provides a multi-waveform current source for ground resistance detection, which is characterized in that an ultra-low temperature drift precision operational amplifier is used as a core device to establish a voltage-current conversion loop, the in-phase end and the anti-phase end of the operational amplifier are respectively connected with a high-precision 10k omega resistor, and an equivalent resistor is respectively used as a positive feedback resistor and a negative feedback resistor. The current source circuit takes an analog operational amplifier closed loop and push-pull output as a core, and has the remarkable advantages that the structure is simple, the cost is low, device errors are effectively suppressed through double operational amplifier compensation, the push-pull stage optimizes the low-current loading capacity, the high-precision requirement in a small-current scene can be met, and the requirement of large-current output can also be met.

Description

Technical Field

[0001] This invention specifically relates to a multi-waveform current source for grounding resistance detection. Background Technology

[0002] As a crucial component of tower grounding resistance testers, the test current's type and accuracy determine the tester's operating environment and the accuracy of the results. Currently, grounding resistance testers on the market typically output either DC current or alternating frequency current. DC power supply technology is mature and effectively avoids power frequency interference. However, since DC current can alter the properties of some substances in the soil, alternating current is required in these cases. Different application scenarios require different solutions: DC solutions are suitable for grounding resistance testing of small equipment, while AC solutions are suitable for grounding resistance testing of wider grounding grids. At the application level, in the field of electronic measurement, component testing and instrument calibration rely heavily on reference current signals, with error requirements typically below 0.1%. Industrial control and energy sectors require simulating complex current conditions to verify the accuracy and reliability of equipment. Scientific research and metrology fields have extremely high requirements for resolution and harmonic distortion. Technological evolution has focused on overcoming challenges related to accuracy, stability, and flexibility. In terms of accuracy, it has evolved from simple circuits with errors exceeding 1% in the early stages to breakthroughs with errors below 0.01% achieved through digital control, precision sampling, and closed-loop feedback, combined with technologies such as Hall sensors. Regarding stability, it employs isothermal control, low-temperature coefficient materials, and grid isolation technology to control drift at the ppm level. In terms of waveform flexibility, it utilizes DDS technology to achieve multi-waveform output, extending the frequency to over 1MHz, with distortion as low as -100dB. Its architecture has evolved from analog to analog-digital fusion and even fully digital, while continuously developing based on advancements in power electronics, metering, and communication technologies. Current trends are moving towards higher performance, intelligence, and miniaturization, continuously providing strong support for cutting-edge fields.

[0003] Currently, the main methods for generating current sources are as follows: 1. Operational amplifier-based current pump technology, such as the Howland current pump, utilizes the negative feedback characteristics of operational amplifiers to convert voltage signals into current output. Its core lies in using the negative feedback of operational amplifiers to convert the input voltage signal into a stable output current. In implementation, the non-inverting input of the operational amplifier is connected to a reference voltage, and the inverting input is connected to the output through a sampling resistor, forming a closed loop. By adjusting the reference voltage or the resistance value of the sampling resistor, the output current can follow the reference voltage change proportionally, thus outputting a stable small current. 2. Low-power digital-to-analog converter (DAC) driving technology, which converts digital signals into corresponding analog current signals. In implementation, a digital quantity is input through a digital interface, the DAC chip internally converts it into a corresponding analog voltage, and then the conversion circuit converts the voltage signal into a current output. Combined with a microcontroller, the digital quantity can be flexibly set, thereby controlling the magnitude of the small output current. 3. Sampling technology in closed-loop feedback, which detects the small output current in real time and feeds the detection signal back to the control terminal for precise regulation. In implementation, components such as Hall sensors or shunt resistors are used to detect the current. Hall sensors obtain current information by sensing a magnetic field, while shunt resistors use the voltage drop generated by the current flow to reflect the current magnitude. The detected signal is processed and fed back to the front-end control circuit.

[0004] Operational amplifier-based low-current pump technology is widely used in low-current scenarios, but it is limited by the characteristics of the devices themselves. The input bias current of the operational amplifier (especially bipolar op-amps, which typically reach the nA level) is directly added to the output current, which significantly increases the error percentage at the microampere level. Furthermore, even with temperature drift as low as 10ppm / ℃, the precision resistors used in the circuit can cause the microampere current drift to exceed the allowable range during long-term operation. In addition, the output current of this technology is mostly constant DC, which cannot meet the current output requirements of specific waveforms.

[0005] While low-power digital-to-analog converter (DAC) driver technology improves controllability and enriches the waveform of output current through digitalization, the resolution bottleneck becomes particularly prominent under low current conditions. For example, a 16-bit DAC has a minimum step size of 15nA when outputting 1mA at full scale, but in practical applications, nanoampere-level adjustment is often required. This necessitates relying on a higher bit-level DAC, which leads to a sharp increase in cost. Furthermore, the stepped signal output by the DAC needs to be smoothed by a low-pass filter, and leakage current in the filter capacitor (especially in high-temperature environments) can cause significant interference to the nanoampere-level current, resulting in baseline drift.

[0006] The sampling error in closed-loop feedback is further amplified in low-current scenarios. When Hall sensors detect microampere-level currents, the signal-to-noise ratio drops sharply, making them susceptible to external electromagnetic interference. On the other hand, the voltage signal generated by the shunt resistor sampling method is very weak at low currents (e.g., a 1mA current flowing through a 1kΩ resistor only produces a 1mV voltage), requiring a high-gain amplifier. However, its own noise (e.g., 1μV input voltage noise) directly introduces current measurement errors, leading to a decrease in feedback regulation accuracy. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a multi-waveform current source for grounding resistance detection, which can effectively solve the aforementioned problems.

[0008] To achieve the above requirements, the technical solution adopted by the present invention is to provide a multi-waveform current source for grounding resistance detection, wherein the multi-waveform current source for grounding resistance detection uses a precision operational amplifier with ultra-low temperature drift as the core device to establish a voltage-current conversion loop.

[0009] Preferably, a high-precision 10kΩ resistor is connected to both the non-inverting and inverting inputs of the operational amplifier, and an equal-value resistor is used as the positive and negative feedback resistors respectively.

[0010] Preferably, based on the voltage division relationship of the resistors and the principle of virtual short and virtual open of the op-amp, the following calculation formula can be obtained: Vi + V3 = 2V2, V6 = 2V1, V1 = V2; a voltage follower is connected on both the positive and negative feedback paths; according to the characteristics of the voltage follower, the following voltage relationship can be obtained: V3 = V5, V4 = V6; substituting this relationship into the previous formula, the following voltage relationship can be obtained: V4 = V3 + Vi, that is, V3 - V4 = Vi; V4 - V3 is the voltage difference across the twelfth resistor. When the input Vi is a constant value, the sum of the currents flowing through these two resistors is constant, and this current will change with the input voltage Vi; according to the virtual open of the op-amp, the current at the non-inverting terminal of the voltage follower is approximately zero, and the current flowing through these two resistors flows out from the 0Ω thirteenth resistor to supply power to the load.

[0011] Preferably, it specifically includes: a first amplifier, a second amplifier, a third amplifier; a first general-purpose diode, a second general-purpose diode; an NPN transistor; a PNP transistor; capacitors: a first capacitor, a second capacitor, a third capacitor, a fourth capacitor; resistors: a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, and a twelfth resistor; one end of the first resistor is connected to the inverting input terminal of the first amplifier, and the other end is connected to analog ground; one end of the second resistor is connected to the non-inverting input terminal of the first amplifier, and the other end is connected to the input signal; one end of the first capacitor is connected to analog ground, and the other end is connected to a second power supply; one end of the second capacitor is connected to analog ground, and the other end is connected to a second power supply; pin 8 of the first amplifier is connected to the second power supply, and pin 4 is connected to the second power supply; one end of the fifth resistor is connected to pin 1 of the first amplifier (output terminal), and the other end is connected to the cathode of the first general-purpose diode and the anode of the second general-purpose diode; one end of the tenth resistor is connected to the second power supply, and the other end is connected to the anode of the first general-purpose diode; one end of the eleventh resistor is connected to... The second power supply is connected to the cathode of the second general-purpose diode; one end of the eighth resistor is connected to the anode of the first general-purpose diode, and the other end is connected to the base of the NPN transistor; one end of the sixth resistor is connected to the second power supply, and the other end is connected to the collector of the NPN transistor; one end of the third capacitor is connected to the second power supply, and the other end is connected to analog ground; one end of the ninth resistor is connected to the cathode of the second general-purpose diode, and the other end is connected to the base of the PNP transistor; one end of the seventh resistor is connected to the second power supply, and the other end is connected to the collector of the PNP transistor; one end of the fourth capacitor is connected to analog ground, and the other end is connected to the second power supply; one end of the twelfth and eleventh resistors are connected to the emitters of the NPN and PNP transistors and the non-inverting input of the third amplifier, and the other end is connected to the output and the non-inverting input of the second amplifier; the inverting input of the second amplifier is connected to its output; the inverting input of the third amplifier is connected to its output; one end of the third resistor is connected to the output of the second amplifier, and the other end is connected to the inverting input of the first amplifier; one end of the fourth resistor is connected to the non-inverting input of the first amplifier, and the other end is connected to the output of the third amplifier.

[0012] The advantages of this multi-waveform current source for grounding resistance detection are as follows:

[0013] This circuit, centered on a closed-loop analog operational amplifier with push-pull output, offers significant advantages: simple structure and low cost. Dual operational amplifier compensation effectively suppresses component errors, and the push-pull stage optimizes low-current load capacity, successfully avoiding the complex defects inherent in DACs and high-end sampling in precision low-current scenarios. Furthermore, it provides diverse output waveforms, with the output current waveform fully inheriting the type and frequency of the input waveform. This circuit is suitable for cost-sensitive, low-current (mA-A level), and conventional frequency (e.g., within the audio range) simple applications, such as debugging small electronic devices and powering simple sensors. For achieving nanoampere-level ultra-high precision, extremely wide frequency range, or complex waveform output, it can be combined with DACs, low-temperature drift operational amplifiers, and quantum references. Traditional low-current precision sources rely on high-precision operational amplifiers, but bias current still adds to the nA-level output. In this circuit, the dual op-amp feedback + push-pull stage design, through dynamic adjustment via dual feedback loops, can offset the influence of the op-amp's own bias current to a certain extent. Furthermore, the base current of the push-pull stage transistor is driven by the op-amp. Compared to the method of "op-amp directly outputting small current", the current amplification effect of the transistor can reduce the proportion of the op-amp bias current in the total output current. In the small current range of mA, the output accuracy is less affected by the device bias, while enhancing the driving capability of the load. Attached Figure Description

[0014] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, use the same reference numerals to denote the same or similar parts. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0015] Figure 1 A schematic diagram of a multi-waveform current source for grounding resistance detection according to an embodiment of this application is shown.

[0016] Figure 2 A schematic diagram of a multi-waveform current source for grounding resistance detection according to an embodiment of this application is shown.

[0017] Among them: 1. First amplifier; 2. Second amplifier; 3. Third amplifier; 4. First general-purpose diode; 5. Second general-purpose diode; 6. NPN transistor; 7. PNP transistor; 8. First capacitor; 9. Second capacitor; 10. Third capacitor; 11. Fourth capacitor; 12. First resistor; 13. Second resistor; 14. Third resistor; 15. Fourth resistor; 16. Fifth resistor; 17. Sixth resistor; 18. Seventh resistor; 19. Eighth resistor; 20. Ninth resistor; 21. Tenth resistor; 22. Eleventh resistor; 23. Twelfth resistor; 24. Thirteenth resistor. Detailed Implementation

[0018] To make the objectives, technical solutions and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and specific embodiments.

[0019] In the following description, references to "an embodiment," "an embodiment," "an example," "example," etc., indicate that the described embodiment or example may include a particular feature, structure, characteristic, property, element, or limitation, but not every embodiment or example necessarily includes that particular feature, structure, characteristic, property, element, or limitation. Furthermore, the repeated use of the phrase "an embodiment according to this application," while possibly referring to the same embodiment, does not necessarily refer to the same embodiment.

[0020] For simplicity, certain technical features known to those skilled in the art are omitted in the following description.

[0021] According to one embodiment of this application, the multi-waveform current source for grounding resistance detection includes:

[0022] First amplifier 1, second amplifier 2, third amplifier 3;

[0023] First general-purpose diode 4, second general-purpose diode 5;

[0024] NPN transistor 6;

[0025] PNP transistor 7;

[0026] Capacitor 1: 8; Capacitor 2: 9; Capacitor 3: 10; Capacitor 4: 11;

[0027] Resistors: 12 (first resistor), 13 (second resistor), 14 (third resistor), 15 (fourth resistor), 16 (fifth resistor), 17 (sixth resistor), 18 (seventh resistor), 19 (eighth resistor), 20 (ninth resistor), 21 (tenth resistor), 22 (eleventh resistor), 23 (twelfth resistor);

[0028] One end of the first resistor 12 is connected to the inverting input terminal of the first amplifier 1, and the other end is connected to analog ground;

[0029] One end of the second resistor 13 is connected to the non-inverting input terminal of the first amplifier 1, and the other end is connected to the input signal.

[0030] One end of the first capacitor 8 is connected to analog ground, and the other end is connected to the second power supply 25 (VCC_5V).

[0031] One end of the second capacitor 9 is connected to analog ground, and the other end is connected to the second power supply 25 (VCC-5V).

[0032] Pin 8 of the first amplifier 1 is connected to the second power supply 25 (VCC_5V), and pin 4 is connected to the second power supply 25 (VCC_-5V).

[0033] One end of the fifth resistor 16 is connected to the output terminal of pin 1 of the first amplifier 1, and the other end is connected to the cathode of the first general-purpose diode 4 and the anode of the second general-purpose diode 5.

[0034] One end of the tenth resistor 21 is connected to the second power supply 25 (VCC_5V), and the other end is connected to the anode of the first general-purpose diode 4;

[0035] One end of the eleventh resistor 22 is connected to the second power supply 25 (VCC-5V), and the other end is connected to the cathode of the general-purpose second general-purpose diode 5;

[0036] One end of the eighth resistor 19 is connected to the anode of the first general-purpose diode 4, and the other end is connected to the base of the NPN transistor 6;

[0037] One end of the sixth resistor 17 is connected to the second power supply 25 (VCC_5V), and the other end is connected to the collector of the NPN transistor 6;

[0038] One end of the third capacitor 10 is connected to the second power supply 25 (VCC_5V), and the other end is connected to analog ground;

[0039] One end of the ninth resistor 20 is connected to the cathode of the second general-purpose diode 5, and the other end is connected to the base of the PNP transistor 7.

[0040] One end of the seventh resistor 18 is connected to the second power supply 25 (VCC-5V), and the other end is connected to the collector of the PNP transistor 7.

[0041] One end of the fourth capacitor 11 is connected to analog ground, and the other end is connected to the second power supply 25 (VCC_5V).

[0042] One end of the twelfth resistor 23 and the eleventh resistor 22 are connected to the emitter of the NPN transistor 6 and the PNP transistor 7 and the non-inverting input of the third amplifier 3, and the other end is connected to the output and the non-inverting input of the second amplifier 2.

[0043] The inverting input terminal of the second amplifier 2 is connected to its output terminal;

[0044] The inverting input of the third amplifier 3 is connected to its output.

[0045] One end of the third resistor 14 is connected to the output terminal of the second amplifier 2, and the other end is connected to the inverting input terminal of the first amplifier 1;

[0046] One end of the fourth resistor 15 is connected to the non-inverting input of the first amplifier 2, and the other end is connected to the output of the third amplifier 3.

[0047] According to one embodiment of this application, a multi-waveform current source for grounding resistance detection is provided, using a precision operational amplifier with ultra-low temperature drift as the core device to establish a voltage-to-current conversion loop. Figure 2It can be seen that both the non-inverting and inverting inputs of operational amplifier U43 are connected to a high-precision 10kΩ resistor, and an equal-value resistor is used as the positive and negative feedback resistors respectively. Based on the voltage division relationship of the resistors and the principle of virtual short and virtual open of the op-amp, the following calculation formula can be obtained:

[0048] Vi + V3 = 2V2, V6 = 2V1, V1 = V2;

[0049] A voltage follower is connected to both the positive and negative feedback paths. Based on the characteristics of the voltage followers, the following voltage relationship can be obtained:

[0050] V3=V5, V4=V6;

[0051] Substituting this relationship into the previous formula yields the following voltage relationship:

[0052] V4 = V3 + Vi, that is, V3 - V4 = Vi; V4 - V3 is the voltage difference across the twelfth resistor 23. Therefore, when the input Vi is constant, the sum of the currents flowing through these two resistors is constant, and this current will change with the input voltage Vi. According to the virtual open circuit of the op-amp, the current at the non-inverting input of the voltage follower is almost zero. The current flowing through these two resistors both flows out from the 0Ω thirteenth resistor 24 to supply power to the load.

[0053] The push-pull emitter follower here serves as a current amplifier. Since the output current of a precision operational amplifier is typically only tens of mA, adding this current amplifier significantly increases the load driving capability of the current source, reaching the several amperes level. The circuit uses two precision resistors connected in parallel to generate the ideal current because the parallel resistors reduce errors caused by temperature drift.

[0054] According to one embodiment of this application, the multi-waveform current source for tower grounding detection balances diverse input waveforms, high precision, and large load-carrying capacity. Both the feedback resistor and the sampling resistor in the circuit are high-precision resistors. For the current sampling resistor, a non-inductive power resistor is recommended to increase overcurrent capability and reduce temperature drift. A 10R sampling resistor is set, and tests are performed for different input signals, output accuracy, and output current capability.

[0055] This study examines different input signals. The circuit's output is connected to a 10Ω power resistor as a load. When the input signal is a sinusoidal AC signal with an amplitude of 1V and a frequency of 100Hz, the voltage across the load is measured using an oscilloscope, yielding a sinusoidal AC signal with an amplitude of 1V and a frequency of 100Hz. When the input signal is a square wave signal with an amplitude of 1V and a frequency of 1kHz, the same square wave signal is obtained. The rising and falling edges of the square wave appear slightly smoother after amplification, which is determined by the op-amp's slew rate. When the input signal is a DC voltage with an amplitude of 1V, the oscilloscope measures the voltage across the load, yielding a level with an amplitude of 1V. This case illustrates that regardless of the input waveform, the output waveform always satisfies I... out =V IN / R 采样 .

[0056] This study investigates input signals of varying strengths. The load resistance was measured to be 9.998R using a precision impedance meter. When the input signal is a 1V DC voltage, the theoretical current is 100mA. The multimeter measured the voltage across the load to be 0.999V, and the calculated current is 0.999 / 9.998 = 0.09992mA, with an accuracy of 99.9%. When the input signal is a 100mV DC voltage, the theoretical current is 10mA. The multimeter measured the voltage across the load to be 99.6mV, and the calculated current is 99.6 / 9.998 = 99.62mA, with an accuracy of 99.6%. This case demonstrates that the current output accuracy error of this circuit is <1%.

[0057] Regarding the output current capability: When the theoretical output current is set to 5mA, the measured voltage across the load is 49.9mV. When the theoretical output current is set to 50mA, the measured voltage across the load is 499.8mV. When the theoretical output current is set to 200mA, the measured voltage across the load is 2.002V. When the theoretical value reaches 250mA, the voltage across the load is less than 2.5V because the maximum input voltage of the circuit is 5V, limiting further increases in potential. If a larger current is required, the input voltage can be increased. This case illustrates that within the permissible voltage range, the output current can reach the ampere level.

[0058] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A multi-waveform current source for grounding resistance detection, characterized in that: A voltage-to-current conversion loop is established using a precision operational amplifier with ultra-low temperature drift as the core component.

2. The multi-waveform current source for grounding resistance detection according to claim 1, characterized in that: The non-inverting and inverting inputs of the operational amplifier are each connected to a high-precision 10kΩ resistor, and an equal-value resistor is used as the positive and negative feedback resistors respectively.

3. The multi-waveform current source for grounding resistance detection according to claim 2, characterized in that: Based on the voltage division relationship of resistors and the principles of virtual short and virtual open circuits of operational amplifiers, the following calculation formula can be obtained: Vi + V3 = 2V2, V6 = 2V1, V1 = V2; A voltage follower is connected to both the positive and negative feedback paths; Based on the characteristics of the voltage follower, the following voltage relationship can be obtained: V3=V5, V4=V6; Substituting this relationship into the previous formula yields the following voltage relationship: V4 = V3 + Vi, that is, V3 - V4 = Vi; V4-V3 is the voltage difference across the twelfth resistor. When the input Vi is constant, the sum of the currents flowing through these two resistors is constant, and this current will change with the input voltage Vi. According to the virtual open circuit of the op-amp, the current at the non-inverting terminal of the voltage follower is approximately zero. The current flowing through these two resistors flows out from the 0Ω resistor and the thirteenth resistor to supply power to the load.

4. The multi-waveform current source for grounding resistance detection according to claim 1, characterized in that, Specifically, it includes: First amplifier, second amplifier, third amplifier; First general-purpose diode, second general-purpose diode; NPN transistor; PNP transistor; Capacitors: First capacitor, Second capacitor, Third capacitor, Fourth capacitor; Resistors: First resistor, Second resistor, Third resistor, Fourth resistor, Fifth resistor, Sixth resistor, Seventh resistor, Eighth resistor, Ninth resistor, Tenth resistor, Eleventh resistor, Twelfth resistor; One end of the first resistor is connected to the inverting input of the first amplifier, and the other end is connected to analog ground; One end of the second resistor is connected to the non-inverting input of the first amplifier, and the other end is connected to the input signal; One end of the first capacitor is connected to analog ground, and the other end is connected to the second power supply. One end of the second capacitor is connected to analog ground, and the other end is connected to the second power supply; Pin 8 of the first amplifier is connected to the second power supply, and pin 4 is also connected to the second power supply. One end of the fifth resistor is connected to the output terminal of pin 1 of the first amplifier, and the other end is connected to the cathode of the first general-purpose diode and the anode of the second general-purpose diode. One end of the tenth resistor is connected to the second power supply, and the other end is connected to the anode of the first general-purpose diode; One end of the eleventh resistor is connected to the second power supply, and the other end is connected to the cathode of the general-purpose second general-purpose diode; One end of the eighth resistor is connected to the anode of the first general-purpose diode, and the other end is connected to the base of the NPN transistor; One end of the sixth resistor is connected to the second power supply, and the other end is connected to the collector of the NPN transistor; One end of the third capacitor is connected to the second power supply, and the other end is connected to analog ground; One end of the ninth resistor is connected to the cathode of the second general-purpose diode, and the other end is connected to the base of the PNP transistor. One end of the seventh resistor is connected to the second power supply, and the other end is connected to the collector of the PNP transistor. One end of the fourth capacitor is connected to analog ground, and the other end is connected to the second power supply; One end of the twelfth and eleventh resistors is connected to the emitter of the NPN and PNP transistors and the non-inverting input of the third amplifier, while the other end is connected to the output and the non-inverting input of the second amplifier. The inverting input of the second amplifier is connected to its output. The inverting input of the third amplifier is connected to its output. One end of the third resistor is connected to the output terminal of the second amplifier, and the other end is connected to the inverting input terminal of the first amplifier; One end of the fourth resistor is connected to the non-inverting input of the first amplifier, and the other end is connected to the output of the third amplifier.

Images