A bus isolation transmission circuit

Abstract

This application discloses a bus isolation transmission circuit, including a power module circuit and an isolation protection circuit. The isolation protection circuit includes an RS485 chip circuit using the ADM2483 chip, a DC-to-DC isolation power supply, a VCC power supply, an RS485-VCC power supply, an RS485 ground wire, a TVS tube protection circuit, and an MCU processor. The MCU processor side is powered by the VCC power supply to achieve TTL levels. The VCC power supply is connected to the RS485-VCC power supply via a DC-to-DC isolation power supply. The TVS tube protection circuit side is powered by the RS485-VCC power supply to achieve RS485 levels. It can be seen that the bus isolation transmission circuit has an RS485-level VCC power supply and ground wire, and the internal power supply of the ADM2483 chip is separate. The ADM2483 chip has an isolation circuit that can significantly increase the signal isolation voltage, enabling the complete isolation of the RS485 bus.

Description

Technical Field

[0001] The present application relates to the field of circuit technology, and more specifically, to a bus isolation transmission circuit. Background Art

[0002] RS485 bus transmission is a standard for multi-point communication within the physical layer of the OSI model, with electrical characteristics specified as two-wire, half-duplex, balanced transmission lines. Digital communication networks implementing this standard can efficiently communicate over long distances in environments with electronic noise. RS485 bus products include repeaters and various USB-to-RS485 bus devices. However, current RS485 bus products have very limited control over controlled slave devices. The RS485 bus lacks full isolation technology and power output capabilities, so researchers are using RS495 bus isolation technology to achieve isolation.

[0003] like Figure 1 As shown in the figure, this circuit is a common circuit diagram, which is simple and cheap, but it does not have RS485 bus signal isolation technology and is easily affected by noise. Figure 2 This circuit, shown in Figure 1, is a common RS485 bus transceiver isolator. Some versions are available with or without a power supply. However, only the RS485-A and RS485-B lines are isolated using optocouplers. The RS485 power supply is still connected to the control system's power and ground wires, so lightning strikes and strong signal interference can affect the main control system MCU, demonstrating that the RS485 bus is not fully isolated.

[0004] How to design a bus transmission circuit with significant isolation effect is an issue that needs attention. Summary of the Invention

[0005] In view of the above problems, the present application provides a bus isolation transmission circuit to improve the circuit isolation effect.

[0006] In order to achieve the above objectives, the following specific plans are proposed:

[0007] A bus isolation transmission circuit includes a power module circuit and an isolation protection circuit;

[0008] The isolation protection circuit includes an RS485 chip circuit using an ADM2483 chip, a DC-to-DC isolation power supply, a VCC power supply, an RS485-VCC power supply, a ground wire, an RS485 bus ground wire, a TVS tube protection circuit, and an MCU processor;

[0009] The VCC power supply is connected to the RS485-VCC power supply through the DC-to-DC isolated power supply;

[0010] The MCU processor is connected to the external interface through the RS485 chip circuit and the TVS tube protection circuit in sequence;

[0011] The side of the RS485 chip circuit located at the MCU processor is powered by the VCC power supply to have a TTL level; the side of the RS485 chip circuit located at the TVS tube protection circuit is powered by the RS485-VCC power supply to have an RS485 level;

[0012] The MCU processor and the RS485 chip circuit are connected to the ground line on one side thereof, and the TVS tube protection circuit and the RS485 chip circuit are connected to the RS485 bus ground line on one side thereof.

[0013] Optionally, the power module circuit includes a DC power supply, a diode, a MOS tube, a first TVS tube, a first resettable fuse and a MOS tube switch;

[0014] The positive electrode of the DC power supply is output to the external interface through the MOS tube, the diode and the first self-recovery fuse in sequence; wherein the third pin of the MOS tube is connected to the diode;

[0015] The MOS transistor switch is connected between the first pin and the second pin of the MOS transistor to control the on and off of the MOS transistor;

[0016] The negative electrode of the DC power supply is connected between the diode and the first resettable fuse through the first TVS tube.

[0017] Optionally, the RS485 chip circuit includes an RS485 bus transceiver;

[0018] The TVS tube protection circuit includes a second resettable fuse, a third resettable fuse, a second TVS tube for protecting the RS485-A line, a third TVS tube for protecting the RS485-B line, a first through-core magnetic bead and a second through-core magnetic bead;

[0019] Pin 13 of the RS485 bus transceiver is connected to the RS485-A line through the second resettable fuse and the first through-hole magnetic bead, and the pin 13 is connected to the RS485 bus ground line through the second TVS tube;

[0020] Pin 12 of the RS485 bus transceiver is connected to the RS485-B line through the third resettable fuse and the second through-core ferrite bead in sequence, and pin 12 is connected to the RS485 bus ground line through the third TVS tube.

[0021] Optionally, the TVS tube protection circuit further includes a first matching resistor for RS485 level signals, a second matching resistor for RS485 level signals, and a third matching resistor for RS485 level signals;

[0022] The negative electrode of the output end of the DC-to-DC isolated power supply is connected to pin 16 of the RS485 bus transceiver through the first matching resistor of the RS485 level signal, the second matching resistor of the RS485 level signal and the third matching resistor of the RS485 level signal in sequence. The resistance value of the first matching resistor of the RS485 level signal is the same as the resistance value of the third matching resistor of the RS485 level signal, and the two ends of the second matching resistor of the RS485 level signal are respectively connected to pin 13 and pin 12.

[0023] Optionally, the TVS tube protection circuit further includes a first ceramic gas discharge tube and a second ceramic gas discharge tube;

[0024] The pin No. 12 is connected to the first ceramic gas discharge tube through the third resettable fuse;

[0025] The pin No. 13 is connected to the second ceramic gas discharge tube through the second resettable fuse.

[0026] Optionally, the isolation protection circuit further includes a third ceramic gas discharge tube;

[0027] The negative electrode of the output end of the DC-to-DC isolated power supply is connected to the third ceramic gas discharge tube.

[0028] Optionally, the isolation protection circuit further includes a machine housing ground wire, a resistor and a first capacitor;

[0029] The RS485 bus ground wire is connected to the machine housing ground wire through the resistor;

[0030] The first capacitor is connected to both ends of the resistor;

[0031] The first ceramic gas discharge tube, the second ceramic gas discharge tube and the third ceramic gas discharge tube are connected to the ground wire of the machine housing.

[0032] Optionally, the power module circuit further includes a fourth ceramic gas discharge tube and a fifth ceramic gas discharge tube;

[0033] The negative electrode of the DC power supply is connected to the fourth ceramic gas discharge tube;

[0034] The positive electrode of the DC power supply is connected to the fifth ceramic gas discharge tube through the MOS tube, the diode and the first resettable fuse in sequence.

[0035] Optionally, the isolation protection circuit further includes a second capacitor, and the second capacitor is connected between the output positive electrode and the output negative electrode of the DC-to-DC isolated power supply.

[0036] Optionally, the negative output electrode of the DC-to-DC isolated power supply is connected to the RS485 bus ground line.

[0037] By means of the above technical solution, the bus isolation transmission circuit of the present application includes a power module circuit and an isolation protection circuit, wherein the isolation protection circuit includes an RS485 chip circuit using an ADM2483 chip, a DC-to-DC isolation power supply, a VCC power supply, an RS485-VCC power supply, a ground wire, an RS485 bus ground wire, a TVS tube protection circuit and an MCU processor, wherein the VCC power supply is connected to the RS485-VCC power supply through the DC-to-DC isolation power supply, and the MCU processor is connected to the RS485 chip circuit and the TVS tube protection circuit in turn. As for the external interface, the RS485 chip circuit on the side of the MCU processor is powered by the VCC power supply to provide a TTL level. The RS485 chip circuit on the side of the TVS tube protection circuit is powered by the RS485-VCC power supply to provide an RS485 level. The MCU processor and the RS485 chip circuit on the side of the MCU processor are connected to the ground wire. The TVS tube protection circuit and the RS485 chip circuit on the side of the TVS tube protection circuit are connected to the RS485 bus ground wire. It can be seen from this that the bus isolation transmission circuit has a VCC power supply and ground wire at the RS485 level, and the internal power supply of the ADM2483 chip is separate. The ADM2483 chip has an isolation circuit that can significantly increase the signal isolation voltage, enabling the complete isolation of the RS485 bus. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0039] Figure 1 The first commonly used RS485 bus transmission circuit provided by this application;

[0040] Figure 2 The second commonly used RS485 bus transmission circuit provided by this application;

[0041] Figure 3 An RS485 bus isolation transmission circuit with power output provided in an embodiment of the present application;

[0042] Figure 4 A circuit diagram of an ADM2483 chip provided in an embodiment of the present application;

[0043] Figure 5 A system circuit diagram of an RS485 bus isolation transmission circuit with power output provided in an embodiment of the present application. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0045] Figure 3 A bus isolation transmission circuit is provided in an embodiment of the present application, such as Figure 3 As shown, the circuit may include: a power module circuit and an isolation protection circuit.

[0046] Specifically, the power module circuit is Figure 3 The upper part consists of the power supply BT3 and the diode 1N4007. The positive and negative poles of the power supply BT3 are output to OUT-24V+ and OUT-24V- respectively, and are connected to the external interface.

[0047] The isolation protection circuit may include an RS485 chip circuit using the ADM2483 chip, a DC-to-DC isolation power supply, a VCC power supply, an RS485-VCC power supply, a ground wire (GND), an RS485 bus ground wire (RS485-GND), a TVS tube protection circuit, and an MCU processor.

[0048] The MCU processor is powered by the BT4 power supply. The ADM2483 chip has 16 pins.

[0049] The VCC power supply is connected to the RS485-VCC power supply through a DC-to-DC isolated power supply.

[0050] Specifically, the isolation voltage of the DC-to-DC isolated power supply can be 3000 VDC, which can be used as.

[0051] The MCU processor is connected to the RS485 bus external interface through the RS485 chip circuit and the TVS tube protection circuit in sequence.

[0052] Specifically, the RS485 bus external interface may include a 24+ interface, a 24- interface, an RS485-GND interface, an RS485-B line interface, an RS485-A line interface, and a machine casing ground (PE-GND) interface.

[0053] The RS485 chip circuit on the MCU processor side is powered by the VCC power supply to provide TTL level. The RS485 chip circuit on the TVS tube protection circuit side is powered by the RS485-VCC power supply to provide RS485 level.

[0054] Specifically, the pins 1 to 8 on the MCU processor side of the ADM2483 chip are TTL level parts, and the pins 9 to 16 on the TVS tube protection circuit side of the ADM2483 chip are RS485 level parts. Figure 4 As shown, the internal power supply of the ADM2483 chip is separated. The ADM2483 chip has an isolation circuit that allows the signal isolation voltage to reach 2500V, and the RS485 signal lines A and B are isolated inside the chip.

[0055] The MCU processor and the RS485 chip circuit are connected to GND on one side of the MCU processor, and the TVS tube protection circuit and the RS485 chip circuit are connected to RS485-GND on one side of the TVS tube protection circuit.

[0056] The bus isolation transmission circuit provided in this embodiment includes a power module circuit and an isolation protection circuit. The isolation protection circuit includes an RS485 chip circuit using an ADM2483 chip, a DC-to-DC isolation power supply, a VCC power supply, an RS485-VCC power supply, a ground wire, an RS485 bus ground wire, a TVS tube protection circuit, and an MCU processor. The VCC power supply is connected to the RS485-VCC power supply through the DC-to-DC isolation power supply, and the MCU processor is connected to the external power supply through the RS485 chip circuit and the TVS tube protection circuit. The RS485 chip circuit on the MCU processor side is powered by the VCC power supply to provide a TTL level. The RS485 chip circuit on the TVS tube protection circuit side is powered by the RS485-VCC power supply to provide an RS485 level. The MCU processor and the RS485 chip circuit on the MCU processor side are connected to the ground line. The TVS tube protection circuit and the RS485 chip circuit on the TVS tube protection circuit side are connected to the RS485 bus ground line. This shows that the bus isolation transmission circuit has a VCC power supply and ground line at the RS485 level, and the internal power supply of the ADM2483 chip is separate. The ADM2483 chip has an isolation circuit that can significantly increase the signal isolation voltage, enabling complete isolation of the RS485 bus.

[0057] In some embodiments of the present application, the power module circuit mentioned in the above embodiment is introduced, such as Figure 5 As shown, the power module circuit may include a DC power supply P1, a diode 1N4007, a MOS transistor Q4, a first TVS transistor DZ3, a first resettable fuse RT1 and a MOS transistor switch S76.

[0058] The positive electrode of the DC power supply P1 is output to the external interface through the MOS tube Q4, the diode 1N4007 and the first resettable fuse RT1 in sequence.

[0059] The resettable fuse is an electronic overcurrent protection component. It's made by mixing conductive particles with a high-molecular-weight organic polymer under high-voltage, high-temperature, and vulcanization conditions, then undergoing a specialized process. Traditional fuses only provide overcurrent protection once and require replacement if they burn out. However, resettable fuses offer dual functions: overcurrent and overheat protection, along with automatic recovery. Therefore, the first resettable fuse, RT1, provides overcurrent and overheat protection for the power module circuit.

[0060] Specifically, the DC power supply P1 outputs DC24V. The third pin of the MOS tube Q4 is connected to the diode 1N4007.

[0061] The MOS transistor switch S76 is connected between the first and second pins of the MOS transistor Q4 to control the on and off of the MOS transistor Q4, thereby achieving the purpose of 24V switch output.

[0062] The negative electrode of the DC power supply P1 is connected between the diode 1N4007 and the first resettable fuse RT1 through the first TVS tube DZ3.

[0063] The TVS (transient voltage suppressor) diode, also known as the transient voltage suppressor diode, is a new product developed based on the Zener diode process. Its circuit symbol and appearance are identical to those of a conventional Zener diode. When a TVS diode experiences a sudden, high-energy surge, its impedance drops dramatically at an extremely high rate (up to 10^-12 seconds), while simultaneously absorbing a large current and clamping the voltage across it to a predetermined value. This protects subsequent circuit components from damage caused by the transient high-energy surge. Therefore, the first TVS diode, DZ3, can be a 28V TVS diode, providing protection for the power module circuit.

[0064] Furthermore, the power module circuit may further include a fourth ceramic gas discharge tube E3 and a fifth ceramic gas discharge tube E6.

[0065] The negative electrode of the DC power supply P1 is connected to the fourth ceramic gas discharge tube E3.

[0066] The positive electrode of the DC power supply P1 is connected to the fifth ceramic gas discharge tube E6 through the MOS tube, the diode and the first resettable fuse RT1 in sequence.

[0067] As you can understand, a ceramic gas discharge tube (GDT) is a discharge gap sealed in a ceramic cavity. The cavity is filled with an inert gas to stabilize the discharge voltage of the tube. Its main features include high current flow energy, reaching tens to hundreds of kA, extremely high insulation resistance, no leakage, no aging failure, non-polarity bidirectional protection, and extremely low static capacitance. This makes it particularly suitable for coarse protection of high-speed network communication equipment. CDTs are widely used for first-level lightning surge protection of various power and signal lines. Therefore, the fourth GDT E3 and the fifth GDT E6 can provide protection for the fifth GDT E6.

[0068] Furthermore, the fourth ceramic gas discharge tube E3 and the fifth ceramic gas discharge tube E6 may be connected to the ground wire PE-GND of the machine casing.

[0069] In some embodiments of the present application, the TVS tube protection circuit mentioned in the above embodiment is introduced, such as Figure 5 As shown, the TVS tube protection circuit includes a second self-resettable fuse PT1, a third self-resettable fuse PT2, a second TVS tube for protecting the RS485-A line, a third TVS tube for protecting the RS485-B line, a first through-core magnetic bead F1 and a second through-core magnetic bead F2.

[0070] The RS485 chip circuit may include an RS485 bus transceiver.

[0071] Specifically, the RS485 bus transceiver is the ADM2483 differential bus transceiver, an integrated galvanic isolation device suitable for bidirectional data communication on multipoint bus transmission lines. Designed for balanced transmission lines, the RS485 bus transceiver complies with ANSI TIA / EIA RS-485-A and ISO 8482:1987(E) standards. It integrates a three-channel isolator, a three-state differential line driver, and a differential input receiver into a single package.

[0072] Pin 13 of the RS485 bus transceiver is connected to the RS485-A line through the second resettable fuse PT1 and the first through-core ferrite bead F1, and pin 13 is connected to RS485-GND through the second TVS tube.

[0073] Pin 12 of the RS485 bus transceiver is connected to the RS485-B line through the third resettable fuse PT2 and the second through-core ferrite bead F2, and pin 12 is connected to RS485-GND through the third TVS tube.

[0074] Figure 5 TVS1 includes the second and third TVS diodes, which are 24V PESD1CAN diodes and protect the RS485 A and B lines. The second and third resettable fuses, PT1 and PT2, are SMD0805-010-15V, providing current protection when the voltage exceeds 15V and the current exceeds 0.1A. The first and second feedthrough beads, F1 and F2, are devices with ferrite beads added to the outside of the conductors to provide interference resistance.

[0075] Furthermore, the TVS tube protection circuit may further include a first matching resistor R42 for RS485 level signals, a second matching resistor R43 for RS485 level signals, and a third matching resistor R47 for RS485 level signals. R42, R43 and R47 are all matching resistors for RS485 level signals.

[0076] Among them, the negative electrode of the output end of the DC-to-DC isolated power supply is connected to pin 16 of the RS485 bus transceiver through the RS485 level signal first matching resistor R42, the RS485 level signal second matching resistor R43 and the RS485 level signal third matching resistor R47 in sequence.

[0077] The resistance of the first RS485 level signal matching resistor R42 is the same as the resistance of the third RS485 level signal matching resistor R47. The two ends of the second RS485 level signal matching resistor R43 are connected to pin 13 and pin 12 respectively.

[0078] In some embodiments of the present application, the TVS tube protection circuit mentioned in the above embodiment is further introduced, such as Figure 5 As shown, the TVS tube protection circuit may further include a first ceramic gas discharge tube E5 and a second ceramic gas discharge tube E4.

[0079] Specifically, pin 12 is connected to the first ceramic gas discharge tube E5 through the third resettable fuse PT2. Pin 13 is connected to the second ceramic gas discharge tube E4 through the second resettable fuse PT1.

[0080] It can be understood that the first ceramic gas discharge tube E5 and the second ceramic gas discharge tube E4 can be used for the first-level lightning surge protection of the TVS tube protection circuit.

[0081] In some embodiments of the present application, the isolation protection circuit mentioned in the above embodiment is further introduced, such as Figure 5 As shown, the isolation protection circuit may further include a third ceramic gas discharge tube E2.

[0082] Specifically, the negative electrode of the output end of the DC-to-DC isolated power supply is connected to the third ceramic gas discharge tube E2.

[0083] It can be understood that the third ceramic gas discharge tube E2 can be used for the first level lightning surge protection of the isolation protection circuit.

[0084] In some embodiments of the present application, the isolation protection circuit mentioned in the above embodiment is further introduced, such as Figure 5 As shown, the isolation protection circuit may further include a machine housing ground wire PE-GND, a resistor R48 and a first capacitor CY2.

[0085] Among them, RS485-GND is connected to the machine casing ground wire PE-GND through resistor R48.

[0086] It can be understood that PE-GND can be the ground wire of the device casing, which can be safely grounded. PE-GND is used to wrap the RS485 bus shield for transmission at the external port labeled P2. Therefore, by transmitting the RS485 bus with a ground wire, the RS485 A line and B line can be stabilized.

[0087] The first capacitor CY2 is connected to both ends of the resistor R48 to release the voltage on RS485-GND to PE-GND to stabilize RS485-GND.

[0088] The first ceramic gas discharge tube E5, the second ceramic gas discharge tube E4 and the third ceramic gas discharge tube E2 are connected to the ground wire PE-GND of the machine casing.

[0089] In some embodiments of the present application, the isolation protection circuit mentioned in the above embodiment is further introduced, such as Figure 5 As shown, the isolation protection circuit may further include a second capacitor C62.

[0090] Specifically, a second capacitor C62 is connected between the output positive electrode and the output negative electrode of the DC-to-DC isolated power supply.

[0091] In addition, the negative output pole of the DC-to-DC isolated power supply can also be directly connected to RS485-GND.

[0092] Finally, it should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

[0093] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referenced to each other.

[0094] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A bus isolation transmission circuit, characterized in that: Including power module circuit and isolation protection circuit; The isolation protection circuit includes an RS485 chip circuit using an ADM2483 chip, a DC-to-DC isolation power supply, a VCC power supply, an RS485-VCC power supply, a ground wire, an RS485 bus ground wire, a TVS tube protection circuit, and an MCU processor; The VCC power supply is connected to the RS485-VCC power supply through the DC-to-DC isolated power supply; The output negative electrode of the DC-to-DC isolated power supply is connected to the RS485 bus ground wire; The MCU processor is connected to the external interface through the RS485 chip circuit and the TVS tube protection circuit in sequence; The side of the RS485 chip circuit located at the MCU processor is powered by the VCC power supply to have a TTL level; the side of the RS485 chip circuit located at the TVS tube protection circuit is powered by the RS485-VCC power supply to have an RS485 level; The MCU processor and the RS485 chip circuit are connected to the ground line on one side thereof, and the TVS tube protection circuit and the RS485 chip circuit are connected to the RS485 bus ground line on one side thereof. The internal power supply of the ADM2483 chip is separate. The ADM2483 chip has an isolation circuit that allows the signal isolation voltage to reach 2500V, and the RS485 signal lines A and B are isolated inside the chip.

2. The bus isolation transmission circuit according to claim 1, characterized in that: The power module circuit includes a DC power supply, a diode, a MOS tube, a first TVS tube, a first resettable fuse and a MOS tube switch; The positive electrode of the DC power supply is output to the external interface through the MOS tube, the diode and the first self-recovery fuse in sequence; wherein the third pin of the MOS tube is connected to the diode; The MOS transistor switch is connected between the first pin and the second pin of the MOS transistor to control the on and off of the MOS transistor; The negative electrode of the DC power supply is connected between the diode and the first resettable fuse through the first TVS tube.

3. The bus isolation transmission circuit according to claim 1, characterized in that: The RS485 chip circuit includes an RS485 bus transceiver; The TVS tube protection circuit includes a second resettable fuse, a third resettable fuse, a second TVS tube for protecting the RS485-A line, a third TVS tube for protecting the RS485-B line, a first through-core magnetic bead and a second through-core magnetic bead; Pin 13 of the RS485 bus transceiver is connected to the RS485-A line through the second resettable fuse and the first through-hole magnetic bead, and the pin 13 is connected to the RS485 bus ground line through the second TVS tube; Pin 12 of the RS485 bus transceiver is connected to the RS485-B line through the third resettable fuse and the second through-core ferrite bead in sequence, and pin 12 is connected to the RS485 bus ground line through the third TVS tube.

4. The bus isolation transmission circuit according to claim 3, characterized in that: The TVS tube protection circuit also includes a first matching resistor for RS485 level signals, a second matching resistor for RS485 level signals, and a third matching resistor for RS485 level signals; The negative electrode of the output end of the DC-to-DC isolated power supply is connected to pin 16 of the RS485 bus transceiver through the first matching resistor of the RS485 level signal, the second matching resistor of the RS485 level signal and the third matching resistor of the RS485 level signal in sequence. The resistance value of the first matching resistor of the RS485 level signal is the same as the resistance value of the third matching resistor of the RS485 level signal, and the two ends of the second matching resistor of the RS485 level signal are respectively connected to pin 13 and pin 12.

5. The bus isolation transmission circuit according to claim 4, characterized in that: The TVS tube protection circuit also includes a first ceramic gas discharge tube and a second ceramic gas discharge tube; The pin No. 12 is connected to the first ceramic gas discharge tube through the third resettable fuse; The pin No. 13 is connected to the second ceramic gas discharge tube through the second resettable fuse.

6. The bus isolation transmission circuit according to claim 5, characterized in that: The isolation protection circuit further includes a third ceramic gas discharge tube; The negative electrode of the output end of the DC-to-DC isolated power supply is connected to the third ceramic gas discharge tube.

7. The bus isolation transmission circuit according to claim 6, characterized in that: The isolation protection circuit further includes a machine housing ground wire, a resistor and a first capacitor; The RS485 bus ground wire is connected to the machine housing ground wire through the resistor; The first capacitor is connected to both ends of the resistor; The first ceramic gas discharge tube, the second ceramic gas discharge tube and the third ceramic gas discharge tube are connected to the ground wire of the machine housing.

8. The bus isolation transmission circuit according to claim 2, characterized in that: The power module circuit further includes a fourth ceramic gas discharge tube and a fifth ceramic gas discharge tube; The negative electrode of the DC power supply is connected to the fourth ceramic gas discharge tube; The positive electrode of the DC power supply is connected to the fifth ceramic gas discharge tube through the MOS tube, the diode and the first resettable fuse in sequence.

9. The bus isolation transmission circuit according to claim 1, characterized in that: The isolation protection circuit further includes a second capacitor, and the second capacitor is connected between the output positive electrode and the output negative electrode of the DC-to-DC isolated power supply.

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