An Optical Coupler-Based Isolated Sampling Circuit

Abstract

This utility model discloses an optocoupler-based isolated sampling circuit. The input terminal is connected to the target AC / DC circuit, and the output terminal is connected to an HDD (High-Speed ​​ADC). It includes resistors R1-R9, capacitors C1-C2, operational amplifier U1, and two optocouplers. The target circuit is connected to the positive input terminal of U1 via R1, grounded via parallel connection C2 and R2, and its common terminal is connected to the HDD via R9. The negative input terminal of U1 is connected to R3 and the output terminal 3 of U2. The control terminal 1 of U2 is connected to the output of U1 via R4, and the control terminal 2 is connected to the control terminal 1 of U3. The control terminal 2 of U3 is grounded. The input terminals 4 of the two optocouplers are connected to the drive power supply via R5 and R6 respectively. The output terminal 3 of U3 is connected to R8, R7, and C1 in parallel. Its topology is simple, it is compatible with both AC and DC circuits, has low cost, good dynamic response, strong anti-interference, reliable isolation, and high sampling accuracy.

Description

Technical Field

[0001] This utility model relates to the field of circuit sampling technology, specifically to an isolation sampling circuit based on an optocoupler. Background Technology

[0002] In fields such as power electronics and industrial control, isolated sampling of voltage signals is a crucial step in ensuring the safe and stable operation of a system. Its core lies in achieving electrical isolation between the input and output sides, avoiding interference and safety hazards between high- and low-voltage circuits. Currently, traditional isolation sampling schemes are mainly divided into two categories: One type is the current transformer isolation sampling circuit, such as Figure 1 As shown, the circuit consists of a transformer, a voltage divider circuit, and a voltage follower. The primary winding of the transformer is connected to the power system, and the secondary winding is connected to the voltage follower, which is composed of an operational amplifier, after being divided by resistors. However, this scheme has significant limitations: it is only suitable for AC circuits and cannot meet the sampling requirements of DC signals; due to the physical structure of the transformer itself, it occupies a large volume, which is not conducive to the integration of miniaturized devices; and under high current or strong magnetic field environments, magnetic saturation is prone to occur, leading to a sharp decrease in sampling accuracy, and in severe cases, it may even damage subsequent circuits. Another type is the capacitor-isolated sampling circuit, such as Figure 2 As shown, the AMC1200 fully differential capacitor-isolated amplifier is a representative example. Its working principle involves converting the analog input signal into a digital signal and then transmitting it through a capacitor isolation barrier, combining digital modulation technology with the characteristics of an isolation barrier. However, this approach also has many problems: it is extremely sensitive to high-frequency noise; even minor high-frequency interference can cause distortion of the sampled signal, thus requiring the design of complex filtering circuits; the overall circuit structure is cumbersome, requiring various auxiliary components, which not only increases the difficulty of circuit layout but also significantly increases system cost, hindering large-scale application. Besides the two mainstream solutions mentioned above, other existing isolation acquisition schemes often require complex isolation circuit topologies to achieve isolated voltage signal acquisition. These schemes typically integrate multiple dedicated isolation devices, such as isolated power supplies and dedicated isolation chips, resulting in a bulky overall circuit structure, occupying a large layout space, and significantly increasing system costs due to the high price of dedicated components. Simultaneously, the complex circuit structure reduces system reliability and increases the difficulty of troubleshooting, making it unsuitable for scenarios with high requirements for cost, size, and reliability. Therefore, developing a simple, low-cost, widely applicable, and stable isolation sampling circuit is of significant practical importance. Utility Model Content

[0003] The purpose of this invention is to provide an optocoupler-based isolation sampling circuit to solve the problems of traditional current transformer isolation sampling which is only applicable to AC, has a large size, and is subject to magnetic saturation risk; capacitor isolation sampling which is sensitive to high-frequency noise, requires filtering, has a complex circuit and high cost; and other solutions which are cumbersome, space-consuming, and costly. The invention achieves a simple, low-cost, AC / DC universal and reliable isolation sampling.

[0004] To achieve the above objectives, the present invention employs the following technical means: An optocoupler-based isolated sampling circuit, with its input terminal connected to a target AC / DC circuit and its output terminal connected to an HD AD, includes resistors R1, R2, R3, R4, R5, R6, R7, R8, and R9, capacitors C1 and C2, operational amplifier U1, first optocoupler U2, and second optocoupler U3. The target AC / DC circuit is connected to the positive input terminal of the operational amplifier U1 through resistor R1. The target AC / DC circuit is also grounded through a parallel capacitor C2 and one end of resistor R2. The common connection terminal of resistor R1, resistor R2, and capacitor C2 is connected to HD through resistor R9. The negative input terminal of the operational amplifier U1 is grounded through resistor R3, and this negative input terminal is connected to the output terminal 3 of the first optocoupler U2. The control input terminal 1 of the first optocoupler U2 is connected to the output terminal of the operational amplifier U1 through resistor R4, and its control output terminal 2 is connected to the control input terminal 1 of the second optocoupler U3. The control output terminal 2 of the second optocoupler U3 is grounded. The input terminal 4 of the first optocoupler U2 and the input terminal 4 of the second optocoupler U3 are connected to the optocoupler driving power supply through resistors R5 and R6, respectively. The output terminal 3 of the second optocoupler U3 is grounded through resistor R8, and the output terminal 3 is also connected in parallel with capacitor C1 through resistor R7.

[0005] Preferably, resistors R1 and R2 are both 2.2KΩ, resistors R3 and R8 are both 10KΩ, resistors R4, R5, and R6 are both 100Ω, resistors R7 and R9 are both 1KΩ, and capacitors C1 and C2 are both 1UF / 25V.

[0006] Preferably, the optocoupler driving power supply is +3.3V.

[0007] Preferably, the first optocoupler U2 and the second optocoupler U3 are of the same model.

[0008] This utility model has the following beneficial effects: 1. The circuit topology is simple and efficient. It adopts an architecture combining operational amplifiers and optocouplers, eliminating the need to build complex auxiliary isolation circuits. This greatly simplifies the overall circuit structure, reduces the difficulty of circuit layout, saves layout space, and is more conducive to the integration of miniaturized devices. 2. It has AC / DC universal characteristics, breaking through the limitation of traditional current transformer isolation sampling which is only applicable to AC circuits. It can be widely adapted to AC or DC voltage acquisition scenarios, significantly expanding the scope of application. 3. Effectively reduces hardware costs. By simplifying component selection, there is no need to integrate multiple dedicated isolation devices, reducing the use of expensive dedicated chips. While ensuring performance, it significantly reduces the system's production cost, making it more conducive to large-scale promotion and application.

[0009] 4. The system has excellent dynamic response speed. Thanks to the high-speed switching characteristics of the optocoupler and the fast signal response capability of the operational amplifier, it can quickly and accurately sample and transmit the input signal, thereby improving the overall dynamic response performance of the system. 5. Enhanced anti-interference capability: Capacitor C2 can filter out high-frequency interference in the input signal, and capacitor C1 can suppress circuit oscillation, reducing the impact of high-frequency noise and other interference factors on sampling accuracy, and improving the stability and accuracy of the sampling signal. 6. Reliable isolation performance: The use of optocouplers achieves electrical isolation between the input and output sides, providing sufficient isolation and effectively avoiding interference between high and low voltage circuits. This ensures the safe and stable operation of the system and improves the reliability of circuit isolation sampling. 7. High sampling accuracy: Optocouplers of the same model and type from the same batch are selected, and their characteristics are similar. Combined with the negative feedback effect of the operational amplifier, the accuracy of signal transmission is ensured, so that the output signal can accurately reflect the input signal and improve the sampling accuracy. Attached Figure Description

[0010] Figure 1 This is a diagram of an existing current transformer isolation sampling circuit; Figure 2 This is a diagram of an existing capacitor-isolated sampling circuit; Figure 3 This is the circuit diagram of this utility model. Detailed Implementation

[0011] The technical solution of this utility model will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0012] like Figure 3As shown, an optocoupler-based isolated sampling circuit has its input connected to a target AC / DC circuit and its output connected to an HDD. It includes resistors R1, R2, R3, R4, R5, R6, R7, R8, and R9; capacitors C1 and C2; an operational amplifier U1; a first optocoupler U2; and a second optocoupler U3. Specifically, resistors R1 and R2 are both 2.2KΩ, resistors R3 and R8 are both 10KΩ, resistors R4, R5, and R6 are all 100Ω, resistors R7 and R9 are both 1KΩ, and capacitors C1 and C2 are both 1UF / 25V. The first optocoupler U2 and the second optocoupler U3 are of the same type. The target AC / DC circuit is connected to the positive input terminal of the operational amplifier U1 through resistor R1. The target AC / DC circuit is also grounded through a parallel capacitor C2 and one end of resistor R2. The common connection terminal of resistor R1, resistor R2, and capacitor C2 is connected to HD through resistor R9. The negative input terminal of operational amplifier U1 is grounded through resistor R3, and this negative input terminal is connected to the output terminal 3 of the first optocoupler U2; The control input terminal 1 of the first optocoupler U2 is connected to the output terminal of the operational amplifier U1 through resistor R4, and its control output terminal 2 is connected to the control input terminal 1 of the second optocoupler U3. The control output terminal 2 of the second optocoupler U3 is grounded. The input terminal 4 of the first optocoupler U2 and the input terminal 4 of the second optocoupler U3 are connected to the optocoupler driving power supply through resistors R5 and R6 respectively. The optocoupler driving power supply is +3.3V. The output terminal 3 of the second optocoupler U3 is grounded through resistor R8, and this output terminal 3 is also connected in parallel with capacitor C1 through resistor R7.

[0013] Working principle The input signal of the target AC / DC circuit is transmitted to the positive input terminal of operational amplifier U1 via resistor R1. Capacitor C2 is connected to ground in parallel with resistor R2, which can filter out high-frequency interference in the input signal and play a preliminary role in purifying the signal. Operational amplifier U1 forms a non-inverting proportional operational circuit. Its negative input terminal is grounded through resistor R3 and is also connected to the output terminal 3 of the first optocoupler U2, forming a negative feedback loop to ensure the stability of the operational amplifier. The output signal of operational amplifier U1 flows into the control input terminal 1 of the first optocoupler U2 through resistor R4. Since the control output terminal 2 of the first optocoupler U2 is connected to the control input terminal 1 of the second optocoupler U3, and the control output terminal 2 of the second optocoupler U3 is grounded, the two optocouplers are connected in series. The first optocoupler U2 and the second optocoupler U3 are linear optocouplers of the same batch and model, and their characteristics are similar. Therefore, under the same input signal, their sensing current is the same, and their output current is also consistent. The input terminals 4 of the first optocoupler U2 and the second optocoupler U3 are connected to the optocoupler driver power supply through resistors R5 and R6, respectively, which provides the operating voltage for the optocouplers. The output terminal 3 of the second optocoupler U3 is grounded through resistor R8, and is connected to the HD AD converter via resistor R7 and capacitor C1 in parallel. Resistors R7 and R8 form a voltage divider circuit, which converts the current signal output by the optocouplers into a voltage signal output. Due to the delay characteristic of the optocouplers, capacitor C1 effectively suppresses oscillations in the circuit, ensuring the stability of the output signal. Throughout the entire operation, the voltage at the input terminal of the non-inverting operational amplifier satisfies U3=U2=UIN (UIN is the input signal voltage). After isolation transmission by the optocoupler and subsequent circuit processing, the final output voltage Uout=UIN, thus achieving accurate isolation sampling of the target AC / DC circuit voltage signal. Example 1

[0014] Industrial motor control system voltage monitoring In an industrial motor control system, real-time monitoring of the motor's power supply voltage is required to ensure stable motor operation. The system uses a three-phase 380V AC power supply, which is subject to significant electromagnetic interference. This invention employs an optocoupler-based isolation sampling circuit. The circuit's input is connected to the motor's power supply circuit, and its output is connected to an HDD and then to the control system's microprocessor. Operational amplifier U1 is selected with low offset and high common-mode rejection ratio to improve anti-interference capability; the first optocoupler U2 and the second optocoupler U3 are linear optocouplers with fast response and good linearity. Actual operation testing shows that this circuit can accurately acquire the motor's power supply voltage signal, effectively isolate electromagnetic interference, and ensure the accuracy and stability of the control system's monitoring of the motor voltage, providing a reliable guarantee for the stable operation of the motor. Example 2

[0015] New energy vehicle battery management system In the battery management system of new energy vehicles, accurate sampling of the battery pack voltage is required to accurately assess the battery status. The battery pack consists of multiple lithium batteries connected in series, with a total voltage range of 200-400V DC, and high-frequency noise is generated during battery charging and discharging. This invention's circuit connects the input to the battery pack and the output to the main control chip of the battery management system. Based on the battery pack voltage characteristics, the parameters of components such as resistors R1 and R2 are adjusted appropriately to match the sampling requirements. Capacitor C2 effectively filters out the high-frequency noise generated during battery charging and discharging, and the optocoupler provides reliable isolation between the high-voltage side of the battery and the low-voltage control system. Actual testing shows that this circuit can accurately acquire the battery pack voltage, maintaining stable sampling accuracy even under complex charging and discharging conditions, providing reliable data support for the battery management system and ensuring the safe operation of new energy vehicles. Example 3

[0016] Smart grid distributed energy monitoring In distributed energy monitoring systems of smart grids, it is necessary to isolate and sample the output voltage of distributed power sources (such as solar photovoltaic panels and small wind turbines) to achieve effective monitoring and scheduling of energy production. Distributed power sources have both DC (e.g., output from photovoltaic panels) and AC (e.g., output from small wind turbines after inverter conversion), and their operating environment is complex with various interference sources. This invention's isolation sampling circuit is applied to this scenario, with its input connected to the output of the distributed power source and its output connected to the acquisition module of the smart grid monitoring system. Circuit parameters can be flexibly configured for different types of power source outputs. In actual operation, this circuit exhibits AC / DC compatibility, accurately acquiring the output voltage signals of various distributed power sources, effectively isolating external interference, and providing a stable and accurate data foundation for the efficient management of distributed energy by the smart grid, thereby improving the reliability and energy utilization efficiency of the smart grid.

[0017] The examples provided in this utility model are not intended to limit the implementation methods. Those skilled in the art will recognize that various variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementation methods here, and any obvious variations or modifications derived therefrom are still within the protection scope of this utility model.

Claims

1. An isolation sampling circuit based on optocouplers, characterized in that, The input terminal is connected to the target AC / DC circuit, and the output terminal is connected to the HD AD. It includes resistors R1, R2, R3, R4, R5, R6, R7, R8, R9, capacitors C1 and C2, operational amplifier U1, first optocoupler U2 and second optocoupler U3. The target AC / DC circuit is connected to the positive input terminal of the operational amplifier U1 through resistor R1. The target AC / DC circuit is also grounded through a parallel capacitor C2 and one end of resistor R2. The common connection terminal of resistor R1, resistor R2, and capacitor C2 is connected to HD through resistor R9. The negative input terminal of the operational amplifier U1 is grounded through resistor R3, and this negative input terminal is connected to the output terminal 3 of the first optocoupler U2. The control input terminal 1 of the first optocoupler U2 is connected to the output terminal of the operational amplifier U1 through resistor R4, and its control output terminal 2 is connected to the control input terminal 1 of the second optocoupler U3. The control output terminal 2 of the second optocoupler U3 is grounded. The input terminal 4 of the first optocoupler U2 and the input terminal 4 of the second optocoupler U3 are connected to the optocoupler driving power supply through resistors R5 and R6, respectively. The output terminal 3 of the second optocoupler U3 is grounded through resistor R8, and the output terminal 3 is also connected in parallel with capacitor C1 through resistor R7.

2. The optocoupler-based isolated sampling circuit according to claim 1, characterized in that, The resistors R1 and R2 are both 2.2KΩ, the resistors R3 and R8 are both 10KΩ, the resistors R4, R5, and R6 are all 100Ω, the resistors R7 and R9 are both 1KΩ, and the capacitors C1 and C2 are both 1UF / 25V.

3. The optocoupler-based isolated sampling circuit according to claim 1, characterized in that, The optocoupler drive power supply is +3.3V.

4. The optocoupler-based isolated sampling circuit according to claim 1, characterized in that, The first optocoupler U2 and the second optocoupler U3 are of the same model.

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