Current loop transmission circuit

Abstract

The utility model discloses a current loop transmission circuit, which comprises a transmitting circuit, the transmitting circuit comprises a first optocoupler module, a first switch driving module, a selection protection module and a current limiting module, the input end of the first optocoupler module is used for receiving signals, and the output end of the first optocoupler module is connected with the input end of the first switch driving module; the output end of the first switch driving module is connected with the input end of the selection protection module, the protection output end of the selection protection module is connected with a first ground end, the signal output end of the selection protection module is connected with the input end of the current limiting module, and the output end of the current limiting module is used for outputting signals. The selection protection module is arranged in the circuit, when pulse voltage or high voltage signals appear in the circuit, the pulse voltage or high voltage signals are connected to the ground end through the selection protection module, elements in the circuit are protected, the accuracy and stability of signal transmission of the circuit are guaranteed, the service life is prolonged, and the cost is reduced.

Description

Technical Field

[0001] This utility model relates to the field of electricity meter communication, and in particular to a current loop transmission circuit. Background Technology

[0002] In the field of electricity meter communication, current loop communication is already quite common. Current loop is an informally published serial communication standard. The flow of current through the communication loop indicates the transmission of data signals (logic 1), and the absence of current through the communication loop indicates that the data signal is empty (logic 0). This communication method has long-distance, high-speed communication capabilities and strong anti-interference and noise suppression capabilities.

[0003] The current loop, as an important control technique, is widely used in motor control, industrial instrumentation, and other fields. It detects the motor current and feeds it back to the MCU (microcontroller unit) to achieve stable control of the motor current, thereby stabilizing the motor torque. As the innermost loop of the control system, the bandwidth of the current loop directly affects the bandwidth of the outer loops, thus occupying a crucial position in the control system.

[0004] Existing current loop communication uses a scheme that controls multiple transistors together to achieve current loop communication of data. This circuit is costly, and when there are pulse voltages or high voltage signals in the circuit, it will affect the components in the circuit, reduce their lifespan, or even damage the devices, making the circuit cost even higher. Summary of the Invention

[0005] This utility model provides a current loop transmission circuit to solve the problems of circuit component damage and high circuit cost caused by pulse voltage or high voltage signals in traditional current loop communication circuits.

[0006] To achieve the above objectives, in one embodiment, a current loop transmission circuit is provided, comprising: a transmitting circuit, the transmitting circuit including: a first optocoupler module, a first switch driving module, a selection protection module, and a current limiting module, wherein the input terminal of the first optocoupler module is used to receive signals, the output terminal of the first optocoupler module is connected to the input terminal of the first switch driving module, the output terminal of the first switch driving module is connected to the input terminal of the selection protection module, the protection output terminal of the selection protection module is connected to a first ground terminal, the signal output terminal of the selection protection module is connected to the input terminal of the current limiting module, and the output terminal of the current limiting module is used to output signals.

[0007] In one embodiment, the selection protection module includes: a first diode, a second diode, a first current-limiting resistor, and a Zener diode, wherein the input terminal of the first diode is connected to the output terminal of the first switch driving module, the output terminal of the first diode is connected to the input terminal of the second diode and the input terminal of the current-limiting module, the output terminal of the second diode is connected to one end of the first current-limiting resistor, the other end of the first current-limiting resistor is connected to the third terminal of the Zener diode, and the first terminal of the Zener diode is connected to a first ground terminal.

[0008] In one embodiment, the first switch driving module includes a first switch transistor and a second switch transistor, wherein the base of the first switch transistor is connected to the output terminal of the first optocoupler module, the collector of the first switch transistor is connected to a first power supply terminal and the base of the second switch transistor, the emitter of the first switch transistor is connected to a first ground terminal, the collector of the second switch transistor is connected to the first power supply terminal, and the emitter of the second switch transistor is connected to the input terminal of the selection protection module.

[0009] In one embodiment, a receiving circuit is further included, the receiving circuit comprising: a second optocoupler module and a second switch driving module, wherein the second switch driving module comprises: a third switch transistor, the base of the third switch transistor is used to receive signals, the base of the third switch transistor is also connected to the selection protection module, the emitter of the third switch transistor is connected to a first ground terminal, the collector of the third switch transistor is connected to the input terminal of the second optocoupler module, and the output terminal of the second optocoupler module is used to output signals.

[0010] In one embodiment, a transient protection module is further included, wherein a first transient protection diode and a second transient protection diode are provided in the transient protection module. The anode of the first transient protection diode is connected to the output terminal of the first diode and the input terminal of the second diode, and the anode of the first transient protection diode is connected to a first ground terminal. The anode of the second transient protection diode is connected to the cathode of the first transient protection diode and the base of the third switching transistor, and the cathode of the second transient protection diode is connected to the first ground terminal.

[0011] In one embodiment, the system further includes a microcontroller unit, the output of which is connected to the input of the transmitting circuit, and the input of which is connected to the output of the receiving circuit. The output of the microcontroller unit is used to output a signal to the transmitting circuit, and the input of the microcontroller unit is used to receive the signal output by the receiving circuit.

[0012] In one embodiment, the first optocoupler module includes: a first optocoupler, a first resistor, and a second resistor. A first end of the first optocoupler is connected to a second power supply terminal, a second end of the first optocoupler is connected to the microcontroller unit through the first resistor, a third end of the first optocoupler is connected to a third power supply terminal, and a fourth end of the first optocoupler is connected to the input terminal of the first switch driving module through the second resistor.

[0013] In one embodiment, the first switch driving module further includes a third resistor and a fourth resistor. One end of the third resistor is connected to the base of the first switch transistor, and the other end of the third resistor is connected to the emitter of the first switch transistor. One end of the fourth resistor is connected to the first power supply terminal and the collector of the second switch transistor, and the other end of the fourth resistor is connected to the base of the second switch transistor and the collector of the first switch transistor.

[0014] In one embodiment, the receiving circuit further includes a fifth resistor and a sixth resistor, wherein one end of the fifth resistor is connected to the base of the third switching transistor, the other end of the fifth resistor is connected to the emitter of the third switching transistor, one end of the sixth resistor is connected to the collector of the third switching transistor, and the other end of the sixth resistor is connected to the input terminal of the second optocoupler module.

[0015] In one embodiment, the second optocoupler module includes a second optocoupler, a seventh resistor, and an eighth resistor, wherein a first end of the second optocoupler is connected to a third power supply terminal, a second end of the second optocoupler is connected to the sixth resistor, a third end of the second optocoupler is connected to a second ground terminal, a fourth end of the second optocoupler is connected to a second power supply terminal through the eighth resistor, and the fourth end of the second optocoupler is also connected to a microcontroller unit through the seventh resistor.

[0016] The aforementioned current loop transmission circuit, by incorporating a selective protection module, conducts pulse voltage or high voltage signals within the circuit. Traditional current loop circuits suffer from reduced lifespan or even damage to components that are not voltage-resistant due to excessively high pulse voltage or high voltage signals. However, by connecting the pulse voltage or high voltage signal to ground through the selective protection module, the components in the circuit are protected from interference by the pulse voltage or high voltage signal, ensuring the accuracy and stability of signal transmission in the current loop transmission circuit, extending the circuit's lifespan, and reducing costs. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments of this utility model will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the connection of each module of the current loop transmission circuit in one embodiment of this utility model;

[0019] Figure 2 This is a current loop transmission circuit diagram in one embodiment of the present invention;

[0020] Figure 3 This is a software flowchart of data transmission in one embodiment of the present invention.

[0021] Reference numerals: 1. Transmitting circuit; 101. First optocoupler module; 102. First switch driver module; 103. Selection protection module; 104. Current limiting module; 2. Receiving circuit; 201. Second switch driver module; 202. Second optocoupler module; 3. Transient protection module; 4. Microcontroller unit. Detailed Implementation

[0022] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present utility model.

[0023] It should be understood that this invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of this invention to those skilled in the art. In the drawings, for clarity, the dimensions of layers and regions, as well as their relative dimensions, may be exaggerated. The same reference numerals denote the same elements throughout.

[0024] It should be understood that when an element or layer is referred to as "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or portions, these elements, components, areas, layers, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, area, layer, or portion from another element, component, area, layer, or portion. Therefore, without departing from the teachings of this utility model, the first element, component, area, layer, or portion discussed below may be referred to as the second element, component, area, layer, or portion.

[0025] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein for convenience of description to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, then the element or feature described as “below,” “under,” or “below” other elements or features will be oriented “above” other elements or features. Therefore, the exemplary terms “below” and “under” can include both above and below orientations. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptive terms used herein will be interpreted accordingly.

[0026] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0027] To fully understand this utility model, detailed structures and steps will be presented in the following description to illustrate the technical solution proposed by this utility model. Preferred embodiments of this utility model are described in detail below; however, in addition to these detailed descriptions, this utility model may have other embodiments.

[0028] In one embodiment, a current loop transmission circuit is provided, such as Figure 1 and Figure 2 As shown, it includes: a transmitting circuit 1, which includes: a first optocoupler module 101, a first switch driving module 102, a selection protection module 103, and a current limiting module 104. The input terminal of the first optocoupler module 101 is used to receive signals, the output terminal of the first optocoupler module 101 is connected to the input terminal of the first switch driving module 102, the output terminal of the first switch driving module 102 is connected to the input terminal of the selection protection module 103, the protection output terminal of the selection protection module 103 is connected to the first ground terminal G485, the signal output terminal of the selection protection module 103 is connected to the input terminal of the current limiting module 104, and the output terminal of the current limiting module 104 is used to output signals.

[0029] Among them, the current limiting module 104 uses a thermistor, model SPMZB-6, with a resistance value of 30-60Ω.

[0030] The operation of the above current loop transmission circuit is as follows:

[0031] The input terminal of the first optocoupler module 101 of the transmitting circuit 1 receives the signal. After passing through the first optocoupler module 101, the signal is output to the input terminal of the first switch driving module 102. After passing through the first switch driving module 102, the signal is output to the input terminal of the selection protection module 103.

[0032] When the circuit is working normally, the protection module 103 outputs the signal through the signal output terminal to the input terminal of the current limiting module 104, and the signal is output after passing through the current limiting module 104.

[0033] When a pulse voltage or high voltage signal appears in the circuit, the protection module 103 selects the pulse voltage or high voltage signal to the first ground terminal G485 through the protection output terminal to protect the circuit.

[0034] In this embodiment, by setting a selective protection module in the circuit, when a pulse voltage or high voltage signal appears in the circuit, it is conducted in the circuit. Because the voltage of the pulse voltage or high voltage signal is too large, it reduces the service life of the components that are not withstand voltage in the traditional current loop circuit, or even damages the components. However, by connecting the pulse voltage or high voltage signal to the ground terminal through the selective protection module, the components in the circuit can be protected from the interference of the pulse voltage or high voltage signal, ensuring the accuracy and stability of the signal transmission of the current loop transmission circuit, extending the service life of the circuit, and reducing costs. When the temperature of the circuit rises, the resistance value of the current limiting module increases, limiting the current passing through the current limiting module, protecting the downstream electronic components from high temperature damage, keeping the circuit operating within a safe temperature range, and improving the reliability and service life of the circuit.

[0035] In one embodiment, such as Figure 2 As shown, the selection protection module 103 includes: a first diode D701, a second diode D702, a first current-limiting resistor R067, and a Zener diode D46. The input terminal of the first diode D701 is connected to the output terminal of the first switch drive module 102, the output terminal of the first diode D701 is connected to the input terminal of the second diode D702 and the input terminal of the current-limiting module 104, the output terminal of the second diode D702 is connected to one end of the first current-limiting resistor R067, the other end of the first current-limiting resistor R067 is connected to the third terminal of the Zener diode D46, and the first terminal of the Zener diode D46 is connected to the first ground terminal G485.

[0036] Optionally, the first diode D701 and the second diode D702 are of type LBAV199LT1G, the first current-limiting resistor R067 is of type 0603CR472J, and the Zener diode D46 is of type LMBZ5248BLT1G.

[0037] The working process of the above-mentioned protection module is as follows:

[0038] The input terminal of the protection module 103 receives the signal output by the first switch drive module 102;

[0039] When the circuit is working normally, the first diode D701 is turned on, so that the signal passes through the first diode D701 and reaches the current limiting module 104, and then the signal is output.

[0040] When a pulse voltage appears in the circuit, the pulse voltage will form a loop through the second diode D702, the first current-limiting resistor R067 and the Zener diode D46, and the first ground terminal G485, introducing the pulse voltage into the first ground terminal G485. The Zener diode D46 stabilizes the voltage at 18V.

[0041] In this embodiment, the first diode and the second diode have low forward voltage drop and conduct in the forward direction when the circuit is working normally, so that the current can pass through with a small voltage loss, which can reduce power consumption and improve circuit transmission efficiency. They also have high reverse voltage withstand capability, which can withstand high reverse voltage without being broken down, increasing the safety and reliability of the circuit. The Zener diode stabilizes the pulse voltage to 18V and can withstand a large power loss without being damaged, further improving the stability of the current loop transmission circuit.

[0042] In one embodiment, such as Figure 2As shown, the first switch driving module 102 includes a first switch transistor T451 and a second switch transistor Q321. The base B of the first switch transistor T451 is connected to the output terminal of the first optocoupler module 101. The collector C of the first switch transistor T451 is connected to the first power supply terminal VHH2 and the base B of the second switch transistor Q321. The emitter E of the first switch transistor T451 is connected to the first ground terminal G485. The collector C of the second switch transistor Q321 is connected to the first power supply terminal VHH2. The emitter E of the second switch transistor Q321 is connected to the input terminal of the selection protection module 103.

[0043] Optionally, the first switching transistor T541 is model MMBT3904LT1, and the second switching transistor G321 is model 2SCR553PGZET100.

[0044] The working process of the first switch driver module mentioned above is as follows:

[0045] The input terminal of the first switch driving module 102 receives the output signal of the first optocoupler module 101;

[0046] When the received signal is low, the base B of the first switch transistor T541 is at a low voltage, the first switch transistor T541 is cut off, the first power supply terminal VHH2 reaches the base B of the second switch transistor Q321, making the second switch transistor Q321 conduct, and the signal is output to the selection protection module 103 after passing through the second switch transistor Q321.

[0047] When the received signal is high, the first switch transistor T541 is turned on, and the first power supply terminal VHH2 is connected to the first ground terminal after passing through the first switch transistor T541. The signal detected by the selection protection module 103 is low.

[0048] In this embodiment, both the first and second switching transistors have low saturation voltages. When switching states, they can control the circuit's on / off states with minimal voltage loss, reducing circuit power consumption. Furthermore, these transistors can quickly respond to changes in the input signal, achieving fast and accurate switching actions without being damaged by excessive current. Using transistors as switching transistors in the switch driver module enables the circuit to be turned on and off in a very short time, achieving precise control of the current loop transmission circuit.

[0049] In one embodiment, such as Figure 2As shown, it also includes a receiving circuit 2, which includes a second optocoupler module 202 and a second switch driving module 201. The second switch driving module 201 includes a third switch transistor T450. The base B of the third switch transistor T450 is used to receive signals. The base B of the third switch transistor T450 is also connected to the selection protection module 103. The emitter E of the third switch transistor T450 is connected to the first ground terminal G485. The collector C of the third switch transistor T450 is connected to the input terminal of the second optocoupler module 202. The output terminal of the second optocoupler module 202 is used to output signals.

[0050] Optionally, the third switching transistor T450 is model MMBT3904LT1.

[0051] The operation of the above receiving circuit is as follows:

[0052] The base B of the third switching transistor T450 is used to receive signals;

[0053] When the signal is high, the third switch T450 is turned off, the input terminal of the second optocoupler module 202 detects a low-level signal, and after processing by the second optocoupler module 202, a high-level signal is output at the output terminal of the second optocoupler module 202.

[0054] When the signal is low, the third switch T450 is turned on. After the signal is processed by the second optocoupler module 202, a low-level signal is output at the output terminal of the second optocoupler module 202, thus completing the data reception.

[0055] In this embodiment, the input signal is sent to the base of the third switch to control the turn-on and turn-off of the third switch, thereby controlling the signal output by the second optocoupler module to realize the transmission function of the current loop circuit.

[0056] In one embodiment, such as Figure 2 As shown, it also includes a transient protection module 3, which is provided with a first transient protection diode TVS9 and a second transient protection diode TVS5. The anode of the first transient protection diode TVS9 is connected to the output terminal of the first diode D701 and the input terminal D702 of the second diode. The anode of the first transient protection diode TVS9 is connected to the first ground terminal G485. The anode of the second transient protection diode TVS5 is connected to the cathode of the first transient protection diode TVS9 and the base B of the third switching transistor T450. The cathode of the second transient protection diode TVS5 is connected to the first ground terminal G485.

[0057] Optionally, the first transient protection diode TVS9 is of model number SMBJ24A, and the second transient protection diode TVS5 is of model number SMAJ8.0CA.

[0058] The operation process of the above transient protection module is as follows:

[0059] During data transmission, when a pulse voltage or high voltage signal appears in the circuit, the pulse voltage or high voltage signal passes through the first diode D701, the first transient protection diode TVS9, and the second transient protection diode TVS5 and is then connected to the first ground terminal G485, thus introducing the pulse voltage or high voltage signal in the circuit to the ground terminal.

[0060] During data reception, when a pulse voltage or high voltage signal appears in the circuit, the pulse voltage or high voltage signal is led to the first ground terminal G485 after passing through the second transient protection diode TVS5. At the same time, the pulse voltage or high voltage signal is introduced into the selection protection module 103 through the first transient protection diode TVS9 and the second diode D702 to protect the circuit.

[0061] In this embodiment, the first transient protection diode can withstand peak pulse power of up to 600W, providing efficient protection for the circuit and preventing circuit damage caused by transient voltage surges. Moreover, the transient protection diode has a very fast response time, which can protect the circuit before the voltage spike arrives, ensuring the reliability of the circuit's long-term operation. The second transient protection diode has a high surge absorption capability, can withstand peak pulse power of 400W, and has a low leakage voltage when the circuit is operating normally, which can reduce power consumption and save costs.

[0062] In one embodiment, such as Figure 1 As shown, it also includes a microcontroller unit 4. The output terminal of the microcontroller unit 4 is connected to the input terminal of the transmitting circuit 1, and the input terminal of the microcontroller unit 4 is connected to the output terminal of the receiving circuit 2. The output terminal of the microcontroller unit 4 is used to output a signal to the transmitting circuit 1, and the input terminal of the microcontroller unit 4 is used to receive the signal output by the receiving circuit 2.

[0063] In microcontroller unit 4, a software program is added to process the data to be sent and then send it to transmitting circuit 1. The software flowchart is shown below. Figure 3 As shown.

[0064] In this embodiment, code for corresponding function processing is added inside the microcontroller unit. After processing, the code is sent to the receiving circuit via serial port. The signal transmission communication is completed through the current loop transmission circuit. Encoding chips are no longer used, which saves costs, facilitates hardware debugging, and makes current loop transmission simpler and more convenient.

[0065] In one embodiment, such as Figure 2As shown, the first optocoupler module 101 includes: a first optocoupler N21, a first resistor R245 and a second resistor R71. The first end of the first optocoupler N21 is connected to the second power supply terminal VOP. The second end of the first optocoupler N21 is connected to the microcontroller unit 4 through the first resistor R245. The third end of the first optocoupler N21 is connected to the third power supply terminal V485. The fourth end of the first optocoupler N21 is connected to the input terminal of the first switch drive module 102 through the second resistor R71.

[0066] Optionally, the first optocoupler N21 is model QX816D-CuH-ST, the first resistor R245 is model 0402CR472J, and the second resistor R71 is model 0402CR101J.

[0067] The working process of the first optocoupler module mentioned above is as follows:

[0068] When the microcontroller unit 4 outputs a high-level signal, the first optocoupler N21 is turned off, and the third terminal of the first optocoupler N21 outputs a low-level signal to the input terminal of the first switch drive module 102.

[0069] When the microcontroller unit 4 outputs a low-level signal, the first optocoupler N21 is turned on, and the third power supply terminal V485 is output through the fourth and third terminals of the first optocoupler N21, and the input terminal of the first switch drive module 102 is a high-level signal.

[0070] In this embodiment, the first optocoupler is a specially designed optocoupler for electricity meters, meeting the State Grid standard, and used to achieve isolation and transmission of electrical signals. It can solve the problem of initial pulses and has the function of electrical isolation, protecting sensitive circuits from the influence of high voltage or noise, and improving the stability and reliability of the circuit. A first resistor is connected to the second end of the first optocoupler to limit the current through the light-emitting diode, protecting the light-emitting diode from damage by excessive current and extending the service life of the first optocoupler. A second resistor is connected to the third end of the first optocoupler to limit the current and prevent excessive current from damaging other devices in the downstream circuit.

[0071] In one embodiment, such as Figure 2As shown, the first switch driving module 102 further includes a third resistor R247 and a fourth resistor R890. One end of the third resistor R247 is connected to the base B of the first switching transistor T451, and the other end of the third resistor R247 is connected to the emitter E of the first switching transistor T451. One end of the fourth resistor R890 is connected to the first power supply terminal VHH2 and the collector C of the second switching transistor Q321, and the other end of the fourth resistor R890 is connected to the base B of the second switching transistor Q321 and the collector C of the first switching transistor T451.

[0072] Optionally, the third resistor R247 is model number 0402CR222J, and the fourth resistor R890 is model number 0603CR202J.

[0073] In this embodiment, the third resistor provides a stable bias current, maintains the stability of the circuit operation, increases circuit damping, reduces high-frequency gain, and suppresses oscillation. At the same time, because the third resistor accelerates the charge consumption of the base of the first switching transistor, the first switching transistor can switch between the on and off states more quickly, reducing switching time and improving circuit efficiency. The fourth resistor can limit the current, prevent excessive current from damaging the second switching transistor, and also balance circuit parameters, stabilize the circuit, and improve efficiency.

[0074] In one embodiment, such as Figure 2 As shown, the receiving circuit 2 further includes a fifth resistor R670 and a sixth resistor R252, wherein one end of the fifth resistor R670 is connected to the base B of the third switching transistor T450, the other end of the fifth resistor R670 is connected to the emitter E of the third switching transistor T450, one end of the sixth resistor R252 is connected to the collector C of the third switching transistor T450, and the other end of the sixth resistor R670 is connected to the input terminal of the second optocoupler module 202.

[0075] Optionally, the fifth resistor R670 is model number 0603CR510F, and the sixth resistor R252 is model number 0402CR102J.

[0076] In one embodiment, such as Figure 2 As shown, the second optocoupler module 202 includes: a second optocoupler N23, a seventh resistor R250, and an eighth resistor R248. The first end of the second optocoupler N23 is connected to the third power supply terminal V485, the second end of the second optocoupler N23 is connected to the sixth resistor R252, the third end of the second optocoupler N23 is connected to the second ground terminal GND, the fourth end of the second optocoupler N23 is connected to the second power supply terminal VOP through the eighth resistor R248, and the fourth end of the second optocoupler N23 is also connected to the microcontroller unit 4 through the seventh resistor R250.

[0077] Optionally, the second optocoupler N23 is model QX816D-CuH-ST, the seventh resistor R250 is model 0402CR102J, and the eighth resistor R248 is model 0402CR222J.

[0078] In this embodiment, the second optocoupler is a specially designed optocoupler for electricity meters that meets the State Grid standard. It has electrical isolation function, protects sensitive circuits from high voltage or noise, and improves the stability and reliability of the circuit. A sixth resistor is connected to the second end of the second optocoupler to prevent excessive current from damaging other devices in the downstream circuit. A seventh and eighth resistor are connected to the second end of the second optocoupler to limit the current to the microcontroller unit, protect the microcontroller unit from damage, and extend its service life.

[0079] Combination Figure 1 and 2 As shown, the data transmission process of the above current loop transmission circuit is as follows:

[0080] When microcontroller unit 4 sends a high level, the first optocoupler N21 is not turned on, the base B of the first switch T541 is at a low level, and the first switch T541 is turned off. The first power supply terminal VHH2 provides current to the base B of the second switch Q321 through the fourth resistor R890, causing the second switch Q321 to turn on. After passing through the first diode D701 and the current limiting module 104, a high-level signal is output at ECL-A.

[0081] When the microcontroller unit 4 sends a low level, the first optocoupler N21 is turned on, and the third power supply terminal V485 reaches the base B of the first switch transistor T541 through the second resistor R71, providing current to turn on the first switch transistor T541. The first power supply terminal VHH2 forms a loop with the first ground terminal G485 through the fourth resistor R890 and the first switch transistor T451. The second switch transistor Q321 is turned off, so that a low level signal is generated at ECL-A.

[0082] When a pulse voltage or high voltage signal appears in the circuit, the pulse voltage or high voltage signal passes through the second diode D702, the first current-limiting resistor R067 and the Zener diode D46 and forms a loop with the first ground terminal G485. At this time, the Zener diode D46 is clamped at 18V, stabilizing the voltage in the circuit at 18V. At the same time, it passes through the first transient protection diode TVS9 and the second transient protection diode TVS5 and is connected to the first ground terminal G485, introducing the pulse voltage or high voltage signal in the circuit to the ground terminal, thereby protecting the circuit.

[0083] The data reception process of the above current loop transmission circuit is as follows:

[0084] When a high level is sent at ECL-B, the third switch T450 is turned off, the second optocoupler N23 is turned off, and the 3.3V second power supply terminal VOP outputs a high level signal to the microcontroller unit 4 after passing through the eighth resistor R248 and the seventh resistor R250.

[0085] When a low level is sent at ECL-B, the third switch T450 is turned on, and the second optocoupler N23 is also turned on. The third power supply terminal V485 forms a loop with the first ground terminal G485 after passing through the second optocoupler N23, the sixth resistor R252 and the third switch T450. The 3.3V second power supply VOP is connected to the second ground terminal GND after passing through the eighth resistor R248 and the second optocoupler N23, and outputs a low level signal to the microcontroller unit 4.

[0086] When the signal input through ECL-B carries a pulse voltage or high voltage signal, it forms a loop with the first ground terminal G485 after passing through the second transient protection diode TVS5, leading the pulse voltage or high voltage signal to the first ground terminal G485. At the same time, it forms a loop with the first ground terminal G485 after passing through the first transient protection diode TVS9, the second diode D702, the first current limiting resistor R067, and the Zener diode D46, leading the pulse voltage or high voltage signal to the ground terminal, thereby protecting the circuit.

[0087] The above-described embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model, and should all be included within the protection scope of this utility model.

Claims

1. A current loop transmission circuit, characterized in that, include: The transmitting circuit includes: a first optocoupler module, a first switch driving module, a selection protection module, and a current limiting module. The input terminal of the first optocoupler module is used to receive signals, the output terminal of the first optocoupler module is connected to the input terminal of the first switch driving module, the output terminal of the first switch driving module is connected to the input terminal of the selection protection module, the protection output terminal of the selection protection module is connected to a first ground terminal, the signal output terminal of the selection protection module is connected to the input terminal of the current limiting module, and the output terminal of the current limiting module is used to output signals.

2. The current loop transmission circuit according to claim 1, characterized in that, The selected protection module includes: a first diode, a second diode, a first current-limiting resistor, and a Zener diode. The input terminal of the first diode is connected to the output terminal of the first switch driving module, the output terminal of the first diode is connected to the input terminal of the second diode and the input terminal of the current-limiting module, the output terminal of the second diode is connected to one end of the first current-limiting resistor, the other end of the first current-limiting resistor is connected to the third terminal of the Zener diode, and the first terminal of the Zener diode is connected to the first ground terminal.

3. The current loop transmission circuit according to claim 1, characterized in that, The first switch driving module includes a first switch transistor and a second switch transistor, wherein the base of the first switch transistor is used to connect to the output terminal of the first optocoupler module, the collector of the first switch transistor is connected to a first power supply terminal and the base of the second switch transistor, the emitter of the first switch transistor is connected to a first ground terminal, the collector of the second switch transistor is connected to the first power supply terminal, and the emitter of the second switch transistor is connected to the input terminal of the selection protection module.

4. The current loop transmission circuit according to claim 2, characterized in that, It also includes a receiving circuit, which includes a second optocoupler module and a second switch driving module. The second switch driving module includes a third switch transistor. The base of the third switch transistor is used to receive signals. The base of the third switch transistor is also connected to the selection protection module. The emitter of the third switch transistor is connected to a first ground terminal. The collector of the third switch transistor is connected to the input terminal of the second optocoupler module. The output terminal of the second optocoupler module is used to output signals.

5. The current loop transmission circuit according to claim 4, characterized in that, It also includes a transient protection module, which is provided with a first transient protection diode and a second transient protection diode. The anode of the first transient protection diode is connected to the output terminal of the first diode and the input terminal of the second diode, and the cathode of the first transient protection diode is connected to a first ground terminal. The anode of the second transient protection diode is connected to the cathode of the first transient protection diode and the base of the third switching transistor, and the cathode of the second transient protection diode is connected to a first ground terminal.

6. The current loop transmission circuit according to claim 4, characterized in that, It also includes a microcontroller unit, the output of which is connected to the input of the transmitting circuit, and the input of which is connected to the output of the receiving circuit. The output of the microcontroller unit is used to output a signal to the transmitting circuit, and the input of the microcontroller unit is used to receive the signal output by the receiving circuit.

7. The current loop transmission circuit according to claim 6, characterized in that, The first optocoupler module includes: a first optocoupler, a first resistor, and a second resistor. A first end of the first optocoupler is connected to a second power supply terminal. A second end of the first optocoupler is connected to the microcontroller unit through the first resistor. A third end of the first optocoupler is connected to the input terminal of the first switch drive module through the second resistor. A fourth end of the first optocoupler is connected to a third power supply terminal.

8. The current loop transmission circuit according to claim 3, characterized in that, The first switch driving module further includes a third resistor and a fourth resistor. One end of the third resistor is connected to the base of the first switch transistor, and the other end of the third resistor is connected to the emitter of the first switch transistor. One end of the fourth resistor is connected to the first power supply terminal and the collector of the second switch transistor, and the other end of the fourth resistor is connected to the base of the second switch transistor and the collector of the first switch transistor.

9. The current loop transmission circuit according to claim 4, characterized in that, The receiving circuit further includes a fifth resistor and a sixth resistor, wherein one end of the fifth resistor is connected to the base of the third switching transistor, the other end of the fifth resistor is connected to the collector of the third switching transistor, one end of the sixth resistor is connected to the emitter of the third switching transistor, and the other end of the sixth resistor is connected to the input terminal of the second optocoupler module.

10. The current loop transmission circuit according to claim 9, characterized in that, The second optocoupler module includes a second optocoupler, a seventh resistor, and an eighth resistor. The first end of the second optocoupler is connected to the third power supply terminal, the second end of the second optocoupler is connected to the sixth resistor, the third end of the second optocoupler is connected to the second ground terminal, the fourth end of the second optocoupler is connected to the second power supply terminal through the eighth resistor, and the fourth end of the second optocoupler is also connected to the microcontroller unit through the seventh resistor.

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