A current-to-voltage conversion and read-back circuit based on a split device

Abstract

The utility model discloses a kind of pressure flow conversion and read-back circuit based on separation device, it is related to power electronics technical field.The circuit includes pressure flow conversion circuit and current read-back circuit, the pressure flow conversion circuit includes voltage current control circuit and pressure flow conversion output circuit, the voltage current control circuit is used to input voltage follow and current control, the pressure flow conversion output circuit is used to convert input voltage into stable output current;The current read-back circuit is used for the real-time monitoring of output current.Wherein, pressure flow conversion circuit is double operational amplifier structure, including two operational amplifiers, NMOS tube, PMOS tube and several resistors and capacitors.The utility model adopts separation device and circuit structure, realize the analog quantity output architecture with high driving ability and cost advantage, while ensuring current output high precision and stability, significantly reduce design cost, and improve the versatility and adaptability of circuit to different application scenarios.

Description

Technical Field

[0001] This utility model relates to the field of power electronics technology, specifically to a voltage-to-current conversion and readback circuit based on discrete devices. Background Technology

[0002] In industrial control systems, analog output signals are a crucial component for achieving precise process control, and their voltage-to-current conversion performance directly impacts the system's load capacity and control accuracy. Current mainstream voltage-to-current conversion technologies generally employ integrated chips (such as XTR300 / XTR305) for signal conversion. However, due to chip package size limitations, their power consumption is generally low, restricting load capacity. Furthermore, while this highly integrated chip solution simplifies design, it also incurs higher hardware costs, resulting in significant economic disadvantages. This technological situation is particularly pronounced in typical industrial applications such as variable frequency speed control and constant pressure water supply. Especially in DCS systems requiring multi-channel, high-power output, additional power amplifier circuits are often needed to compensate for the lack of drive capability, increasing system complexity and driving up overall costs.

[0003] As industrial automation evolves towards higher precision and stronger driving capabilities, existing solutions based on dedicated chips are gradually revealing their limitations. On the one hand, the inherent low-power characteristics of chips restrict their application under heavy-duty conditions; on the other hand, the high cost of chips hinders the large-scale promotion and application of the technology. This contradiction is particularly evident in industrial sectors such as power, petroleum, and chemical industries, where reliability and economy are paramount. Therefore, developing a new analog output architecture that combines high driving capability with cost advantages, and replacing traditional integrated chip solutions with discrete components or innovative circuit topologies, will be key to breaking through current technological bottlenecks and providing more flexible and economical solutions for industrial control systems.

[0004] Existing patent CN110221642A discloses a voltage / current conversion circuit and a method for adjusting its output current range, including a gain adjustment module, a voltage / current conversion module, and a zero-point adjustment module. The gain adjustment module and the zero-point adjustment module can adjust the range and zero point of the output current, expanding the range of output current values. However, this patented circuit cannot guarantee the accuracy of the output current and lacks a current readback circuit.

[0005] Existing patent CN221614847U discloses a voltage-to-current conversion circuit, including a power supply voltage circuit, a first voltage input circuit, a second voltage input circuit, a first current output circuit connected to the first voltage input circuit, and a second current output circuit connected to the second voltage input circuit. The output circuit outputs a 4-20mA current based on the current outputs from the first and second current output circuits. This patented circuit lacks a current readback circuit.

[0006] In summary, none of the aforementioned existing patents have resolved the problems in output stability and current monitoring accuracy of voltage / current conversion circuits based on dedicated chips in the prior art. Utility Model Content

[0007] Based on the aforementioned problems in the prior art, this utility model proposes a voltage-to-current conversion and readback circuit based on discrete devices. By employing discrete devices and circuit structures, this circuit achieves an analog output architecture with high driving capability and cost advantages, thereby overcoming the limitations of the prior art in terms of output stability and economy in voltage-to-current conversion.

[0008] To achieve the above objectives, this utility model proposes a voltage-current conversion and readback circuit based on a discrete device, the specific technical solution of which is as follows:

[0009] A voltage-to-current conversion and readback circuit based on a discrete device includes a voltage-to-current conversion circuit and a current readback circuit. The voltage-to-current conversion circuit includes a voltage-to-current control circuit and a voltage-to-current conversion output circuit. The voltage-to-current control circuit is used to follow the input voltage and control the current. The voltage-to-current conversion output circuit is used to convert the input voltage into a stable output current. The current readback circuit is used to monitor the output current in real time.

[0010] The voltage and current control circuit mainly includes a first operational amplifier and an N-MOS transistor;

[0011] The voltage-to-current conversion output circuit mainly includes a first operational amplifier and a P-MOS transistor.

[0012] Furthermore, the non-inverting input of the first operational amplifier is connected to the input voltage, the output of the first operational amplifier is connected to the gate of the N-MOS transistor, the inverting input of the first operational amplifier and the source of the N-MOS transistor are both grounded, the drain of the N-MOS transistor is connected to the non-inverting input of the second operational amplifier, the inverting input of the second operational amplifier is connected to the VCC terminal, the inverting input of the second operational amplifier is also connected to the source of the P-MOS transistor, and the output of the second operational amplifier is connected to the gate of the P-MOS transistor.

[0013] Furthermore, the voltage and current control circuit also includes a first resistor, a second resistor, and a first capacitor. The first resistor is connected between the output terminal of the first operational amplifier and the N-MOS transistor. One end of the second resistor is connected between the inverting input terminal of the first operational amplifier and the source terminal of the N-MOS transistor, and the other end is grounded. The first capacitor is connected between the inverting input terminal and the output terminal of the first operational amplifier.

[0014] Furthermore, the voltage and current control circuit also includes a third resistor, a fourth resistor, a fifth resistor, and a second capacitor. The third resistor is connected between the drain of the N-MOS transistor and the VCC terminal. The fourth resistor is connected between the inverting input terminal of the second operational amplifier and the VCC terminal. The fifth resistor is connected between the output terminal of the second operational amplifier and the gate of the P-MOS transistor. The second capacitor is connected between the inverting input terminal and the output terminal of the second operational amplifier.

[0015] Furthermore, the current readback circuit includes a readback sampling resistor R connected in series in the drain path of the P-MOS transistor. sense and connected in parallel to the readback sampling resistor R sense The instrumentation amplifiers at both ends are connected in sequence to the sixth resistor R6, the third capacitor C3, the over / under voltage protection circuit, and the analog-to-digital converter.

[0016] Furthermore, a gain resistor R is connected between the two input terminals of the instrumentation amplifier. gain .

[0017] Furthermore, the second resistor and the third resistor have the same resistance value, and the voltage at the VCC terminal is 24V.

[0018] Furthermore, the fourth resistor is model RMK3216-YB-200R-W, with a resistance value of 200Ω.

[0019] Furthermore, the P-MOS transistor used is model NCE60P04R, and the N-MOS transistor used is model L2N7002KLT1G.

[0020] Furthermore, the ratio of the filter cutoff frequency of the third capacitor to the sampling frequency of the analog-to-digital converter is 1:2 to 1:2.56.

[0021] Based on the above technical solution, this utility model has at least the following beneficial effects:

[0022] 1. The present invention proposes a voltage-current conversion and readback circuit based on discrete components. By selecting high-quality discrete components, which typically have better long-term stability and stronger anti-interference capabilities, the reliability of the entire circuit is improved. At the same time, it makes the debugging and maintenance of the circuit more convenient, allowing individual components to be replaced without replacing the entire chip, thus reducing maintenance costs and time.

[0023] 2. The present invention proposes a voltage-current conversion and readback circuit based on discrete devices. By selecting high-precision, low-temperature-drift resistors and low-on-resistance P-MOS transistors, the influence of temperature changes on the circuit output accuracy can be effectively reduced, thereby ensuring high accuracy and stability of current output and meeting the 0.1% accuracy output requirement.

[0024] 3. The present invention proposes a voltage-current conversion and readback circuit based on discrete devices, which significantly reduces the cost per channel. For analog output boards with multiple channels, the cost advantage will multiply with the number of channels, significantly reducing the overall design cost.

[0025] 4. This utility model proposes a voltage-to-current conversion and readback circuit based on discrete devices, with a theoretical load capacity of 989.88Ω, which is a significant improvement compared to the 800Ω load capacity of the XTR300 chip. Furthermore, the circuit's load capacity can be adjusted according to the voltage of the driving power supply. This flexibility allows the circuit to better adapt to different application scenarios, improving its versatility and adaptability. Attached Figure Description

[0026] The accompanying drawings, which form part of this specification, are used to provide a further understanding of this utility model. The illustrative embodiments and descriptions of this utility model are used to explain this utility model and do not constitute an undue limitation thereof. In the drawings:

[0027] Figure 1 This is a schematic diagram of a voltage-current conversion and readback circuit based on a discrete device proposed in this utility model. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed by the present invention.

[0029] It should be noted that, where there is no conflict, the embodiments and features in the embodiments of this utility model can be combined with each other. The present utility model will now be described in detail with reference to the accompanying drawings and embodiments.

[0030] Example

[0031] See Figure 1 As shown, this embodiment provides a voltage-to-current conversion and readback circuit based on a discrete device. The circuit includes a voltage-to-current conversion circuit and a current readback circuit. The voltage-to-current conversion circuit includes a voltage-to-current control circuit and a voltage-to-current conversion output circuit. The voltage-to-current control circuit is used to follow and buffer the input voltage and to achieve preliminary control of the current. The voltage-to-current conversion output circuit is used to convert the input voltage into a stable output current. The current loop circuit is used to monitor, control, and protect the current in the circuit in real time.

[0032] Specifically, the voltage and current control circuit includes a first operational amplifier A, a first resistor R1, a second resistor R2, a first capacitor C1, and an N-MOS transistor. The non-inverting input of the first operational amplifier A is connected to the input voltage, the inverting input of the first operational amplifier A is connected to ground after being connected to the second resistor R2, the inverting input of the first operational amplifier A is also connected to the source of the N-MOS transistor, the output of the first operational amplifier A is connected to the gate of the N-MOS transistor after being connected to the first resistor R1, and the first capacitor C1 is connected between the inverting input and the output of the first operational amplifier A. The first operational amplifier A is used to convert the input voltage into a gate drive signal for the N-MOS transistor, controlling the N-MOS transistor to operate in the linear region, making the source current (through the second resistor R2) proportional to the input voltage. The first resistor R1 is used to limit the current output from the first operational amplifier A to the gate of the N-MOS transistor, preventing the gate capacitor from charging and discharging too quickly and causing oscillation. The second resistor R2 is a current-limiting resistor to prevent the inrush current of the N-MOS transistor from being too large. The first capacitor C1 is used to compensate the feedback loop of the first operational amplifier A and suppress high-frequency oscillation. The N-MOS transistor is used to control the drain current according to the gate voltage, realizing the initial current regulation and providing a controllable current signal for subsequent circuits.

[0033] Specifically, the voltage-to-current conversion output circuit includes a second operational amplifier B, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a second capacitor C2, and a P-MOS transistor. The non-inverting input of the second operational amplifier B is connected to the drain of the N-MOS transistor. The inverting input of the second operational amplifier B is connected to the fourth resistor R4 and then to the VCC power supply. One end of the third resistor R3 is connected to the drain of the N-MOS transistor, and the other end is connected to the VCC power supply. The output of the second operational amplifier B is connected to the fifth resistor R5, which is then connected to the gate of the P-MOS transistor. The inverting input of the second operational amplifier B is also connected to the source of the P-MOS transistor. The second capacitor C2 is connected between the inverting input and output of the second operational amplifier B. The drain of the P-MOS transistor is the current output terminal. The second operational amplifier B is used to drive the P-MOS transistor and adjust its conduction to stabilize the output current. The third resistor R3 is a voltage divider resistor with the same resistance as the second resistor R2. The fourth resistor R4 is a voltage-to-current conversion resistor. The fifth resistor R5 is a current-limiting resistor to prevent excessive inrush current from the P-MOS transistor. The second capacitor C2 is used to compensate the feedback loop of the second operational amplifier B and enhance stability. The P-MOS transistor is used to control the drain current according to the gate voltage and output the current after adjustment by the second operational amplifier B.

[0034] Specifically, the current readback circuit includes readback sampling resistors R connected in sequence. senseThe instrumentation amplifier, the sixth resistor R6, the third capacitor C3, the over / under voltage protection circuit, and the analog-to-digital converter (ADC) are connected together. The gain resistor R is connected between the two input terminals of the instrumentation amplifier. gain Among them, the readback sampling resistor R sense The drain path of the P-MOS transistor is connected in series for current-to-voltage conversion; the instrumentation amplifier is connected in parallel with the readback sampling resistor R. sense The two ends are connected through the gain resistor R gain Set the amplification factor to precisely amplify the readback sampling resistor R. sense The small voltage difference across the two ends allows subsequent circuits to measure the current more accurately; the sixth resistor R6 is a current-limiting resistor, preventing excessive current due to short circuits or other abnormal conditions, thus protecting subsequent circuit components; the third capacitor C3 is a filter capacitor, making the current signal after passing through the sixth resistor R6 smoother and more stable, providing a more accurate analog signal for the analog-to-digital converter; the over / under voltage protection circuit clamps the filtered signal to ensure that the signal input to the ADC is within a safe range; the analog-to-digital converter is used to convert the filtered, amplified, and protected analog current signal into a digital signal. The digital signal can be further processed and analyzed by a microcontroller or other digital processing devices to achieve precise measurement and monitoring of the current.

[0035] In this embodiment, the current output current range of the current circuit is 4-20mA, the power supply voltage VCC is 24V, and the fourth resistor R4 in the circuit is a precision resistor of model RMK3216-YB-200R-W, using a 1206 package, with a resistance of 200Ω±0.05% and a temperature coefficient of 10PPM. This resistor has high precision and low temperature drift characteristics, ensuring the stability of the current output, and is suitable for precision measurement or industrial control scenarios. When outputting a 20mA current, the resistor power is 0.08W. Considering the 60% derating design, the rated power of the resistor should be greater than 0.14W. Therefore, a 0.25W resistor is selected to ensure long-term reliability. At the same time, a 10PPM low temperature drift resistor is selected to reduce the impact of temperature changes on the output accuracy. The final output current is calculated using the formula I... OUT =V OUT / 200Ω.

[0036] Optionally, the resistance values ​​of the second resistor R2 and the third resistor R3 are both 10KΩ.

[0037] Optionally, the P-MOS transistor used is model NCE60P04R, with an on-resistance of 120mΩ.

[0038] Optionally, the N-MOS transistor used is model L2N7002KLT1G, with an on-resistance of 2.3Ω.

[0039] Based on the above parameters, the load capacity of the current circuit is calculated. The main factors affecting the load capacity are the switching resistor, the on-resistance of the P_MOS transistor, and the readback resistor. Therefore, its theoretical load capacity is calculated as (VCC / I) - R4 - R sense -R P-MOS Finally, it was calculated that the circuit can drive a maximum load resistance of 989.88Ω.

[0040] Optional, readback sampling resistor R sense A 10Ω resistor is selected, meaning the readback voltage is 0.04-0.2V, after passing through R... gain The resistance ratio amplifies the readback voltage by 10 times, resulting in a voltage value of 0.4-2V, which meets the requirements for subsequent data acquisition.

[0041] Optionally, the amplification factor of the instrumentation amplifier can be selected according to the circuit requirements to meet the appropriate parameters for ADC readback acquisition. In this embodiment, the amplification factor is selected as 10 times.

[0042] Optionally, the sixth resistor R6 is typically a low-temperature drift, high-precision resistor, and its resistance value should be selected in conjunction with the instrumentation amplifier gain and the ADC acquisition range. In this embodiment, the ADC uses the SGM51242 chip, with an acquisition range of 0-VREF, and uses a 4.096V reference source, meaning the ADC acquisition range is 0-4.096V.

[0043] Optionally, the filter cutoff frequency of the third capacitor C3 is related to the sampling frequency of the analog-to-digital converter. The ratio of the filter cutoff frequency to the sampling frequency is generally between 1:2 and 1:2.56.

[0044] Optionally, the over / under voltage protection circuit uses a series diode connected to VCC and GND respectively. When the threshold is exceeded, the diode conducts to protect the analog-to-digital converter. The diode selection should refer to the ADC channel design parameters, i.e., the withstand voltage range of the ADC acquisition pin. In this embodiment, the ADC port withstand voltage range is -0.3-5.3V, and a Schottky diode with a small forward voltage of 0.24V is selected. That is, when the voltage is lower than -0.24V or higher than 5.24V, the protection circuit is activated.

[0045] The voltage-to-current conversion and readback circuit based on a discrete device proposed in this embodiment works as follows:

[0046] When there is no voltage input at the non-inverting input terminal of the first operational amplifier A, its negative feedback circuit is not valid, and it functions as a comparator. Since the voltages at the non-inverting and inverting input terminals are the same, the output of the first operational amplifier A is 0V. The N-MOS transistor's conduction condition is 1V-2.5V, but VGS is 0V, which does not meet the conduction condition, so the N-MOS transistor is off. The input terminal of the second operational amplifier B is in a high-impedance state, and it also functions as a comparator. Since the voltages at the positive and negative input terminals are the same, the output of the second operational amplifier B is 0V. The P-MOS transistor's conduction condition is between -1V and 2.5V, and it is off, resulting in zero output current.

[0047] When a voltage is input to the non-inverting input terminal of the first operational amplifier A, this voltage is defined as U1. At the instant the input voltage is present, the first operational amplifier A still functions as a comparator. At this moment, the voltage at the inverting input terminal U- = 0V, and the voltage at the non-inverting input terminal U+ = U1, U+ > U-. At this time, the output V of the first operational amplifier A is... OUT The voltage is high, which satisfies the conduction condition of the N-MOS transistor. The N-MOS transistor is turned on, and the second resistor R2 divides the voltage. For the first operational amplifier A, its net input voltage (U+-U-) decreases, which satisfies the condition for the formation of a negative feedback circuit. At this time, the first operational amplifier A is in a negative feedback state. Then U+=U-=U1, U2=U-=U1, so the voltage on R2 is U1.

[0048] For the second operational amplifier B, since the N-MOS transistor is turned on, the second resistor R2 divides the voltage, causing the voltage at the non-inverting input of the second operational amplifier B to drop. At this time, the voltage at the inverting input is greater than the voltage at the non-inverting input, and the output V of the second operational amplifier B is... OUT The voltage is low, satisfying the conduction condition of the P-MOS transistor, and the P-MOS transistor turns on. Before conduction, the voltage at the VCC terminal flows through the fourth resistor R4 to the negative input terminal of the second operational amplifier B, at which point the current is I1. After conduction, the current through the P-MOS transistor is I2. Since I2 effectively shunts I1, the net input current of the second operational amplifier B decreases, thus the negative feedback of the second operational amplifier B is established. Since the resistance values ​​of the second resistor R2 and the third resistor R3 are the same, the voltage drop across them is U1. At this time, the voltage at the non-inverting input terminal of the second operational amplifier B is 24V-U1. Also, since the second operational amplifier B is in a negative feedback state, the voltage at the inverting input terminal of the second operational amplifier B is 24V-U1. Therefore, the voltage drop across the fourth resistor R4 is fixed at U1. At this time, the output current value is I1 = U1 / 200. The output current enters the current feedback circuit after passing through the drain of the P-MOS transistor.

[0049] In the current readback circuit, the drain current of the P-MOS transistor flows through the readback sampling resistor R. senseThis is converted into a voltage signal, generating a voltage drop, which is then used by the instrumentation amplifier to obtain the readback sampling resistor R. sense The potential difference between the two sides is amplified and transmitted as a voltage signal to subsequent circuits. After current limiting by the sixth resistor R6, the signal enters the over / under voltage protection circuit. Simultaneously, the third capacitor C3 performs a low-pass filter to remove high-frequency noise, improving signal stability. The output of the over / under voltage protection circuit is sent to an analog-to-digital converter, converting the voltage signal into a digital signal. The MCU then reads and calculates the actual current value.

[0050] In summary, it can be seen from the above description that the embodiments of this utility model achieve the following technical effects:

[0051] 1. The present invention proposes a voltage-current conversion and readback circuit based on discrete components. By selecting high-quality discrete components, which typically have better long-term stability and stronger anti-interference capabilities, the reliability of the entire circuit is improved. At the same time, it makes the debugging and maintenance of the circuit more convenient, allowing individual components to be replaced without replacing the entire chip, thus reducing maintenance costs and time.

[0052] 2. The present invention proposes a voltage-current conversion and readback circuit based on discrete devices. By selecting high-precision, low-temperature-drift resistors and low-on-resistance P-MOS transistors, the influence of temperature changes on the circuit output accuracy can be effectively reduced, thereby ensuring high accuracy and stability of current output and meeting the 0.1% accuracy output requirement.

[0053] 3. The present invention proposes a voltage-current conversion and readback circuit based on discrete devices, which significantly reduces the cost per channel. For analog output boards with multiple channels, the cost advantage will multiply with the number of channels, significantly reducing the overall design cost.

[0054] 4. This utility model proposes a voltage-to-current conversion and readback circuit based on discrete devices, with a theoretical load capacity of 989.88Ω, which is a significant improvement compared to the 800Ω load capacity of the XTR300 chip. Furthermore, the circuit's load capacity can be adjusted according to the voltage of the driving power supply. This flexibility allows the circuit to better adapt to different application scenarios, improving its versatility and adaptability.

[0055] The above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

[0056] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0057] It should be noted that, in the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this utility model. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A voltage-to-current conversion and readback circuit based on discrete devices, characterized in that: It includes a voltage-to-current conversion circuit and a current readback circuit. The voltage-to-current conversion circuit includes a voltage-to-current control circuit and a voltage-to-current conversion output circuit. The voltage-to-current control circuit is used to follow the input voltage and control the current. The voltage-to-current conversion output circuit is used to convert the input voltage into a stable output current. The current readback circuit is used to monitor the output current in real time. The voltage and current control circuit mainly includes a first operational amplifier and an N-MOS transistor; The voltage-to-current conversion output circuit mainly includes a second operational amplifier and a P-MOS transistor.

2. The voltage-to-current conversion and readback circuit based on a discrete device according to claim 1, characterized in that: The non-inverting input of the first operational amplifier is connected to the input voltage, the output of the first operational amplifier is connected to the gate of the N-MOS transistor, the inverting input of the first operational amplifier and the source of the N-MOS transistor are both grounded, the drain of the N-MOS transistor is connected to the non-inverting input of the second operational amplifier, the inverting input of the second operational amplifier is connected to the VCC terminal, the inverting input of the second operational amplifier is also connected to the source of the P-MOS transistor, and the output of the second operational amplifier is connected to the gate of the P-MOS transistor.

3. The voltage-to-current conversion and readback circuit based on a discrete device according to claim 2, characterized in that: The voltage and current control circuit further includes a first resistor, a second resistor, and a first capacitor. The first resistor is connected between the output terminal of the first operational amplifier and the N-MOS transistor. One end of the second resistor is connected between the inverting input terminal of the first operational amplifier and the source terminal of the N-MOS transistor, and the other end is grounded. The first capacitor is connected between the inverting input terminal and the output terminal of the first operational amplifier.

4. The voltage-to-current conversion and readback circuit based on a discrete device according to claim 3, characterized in that: The voltage and current control circuit further includes a third resistor, a fourth resistor, a fifth resistor, and a second capacitor. The third resistor is connected between the drain of the N-MOS transistor and the VCC terminal. The fourth resistor is connected between the inverting input terminal of the second operational amplifier and the VCC terminal. The fifth resistor is connected between the output terminal of the second operational amplifier and the gate of the P-MOS transistor. The second capacitor is connected between the inverting input terminal and the output terminal of the second operational amplifier.

5. The voltage-to-current conversion and readback circuit based on a discrete device according to claim 4, characterized in that: The current reading circuit comprises a reading sampling resistor R connected in series in a drain path of the P-MOS sense and a voltage follower connected in parallel to both ends of the reading sampling resistor R sense and a voltage follower connected in parallel to both ends of the reading sampling resistor R A sixth resistor R6, a third capacitor C3, an over-voltage and under-voltage protection circuit, and an analog-to-digital converter are connected in sequence after the voltage follower.

6. The voltage-to-current conversion and readback circuit based on a discrete device according to claim 5, characterized in that: A gain resistor R is also connected between the two input terminals of the instrumentation amplifier. gain .

7. The voltage-to-current conversion and readback circuit based on a discrete device according to claim 4, characterized in that: The second resistor and the third resistor have the same resistance value, and the voltage at the VCC terminal is 24V.

8. The voltage-to-current conversion and readback circuit based on a discrete device according to claim 4, characterized in that: The fourth resistor is model RMK3216-YB-200R-W, with a resistance of 200Ω.

9. The voltage-to-current conversion and readback circuit based on a discrete device according to claim 4, characterized in that: The P-MOS transistor used is model NCE60P04R, and the N-MOS transistor used is model L2N7002KLT1G.

10. The voltage-to-current conversion and readback circuit based on a discrete device according to claim 5, characterized in that: The ratio of the filter cutoff frequency of the third capacitor to the sampling frequency of the analog-to-digital converter is 1:2 to 1:2.56.

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