Multistage lightning protection isolation circuit with RS485 interface

Abstract

The utility model discloses an RS485 interface multistage lightning protection isolation circuit, which belongs to the technical field of communication interfaces, and comprises an RS485 serial port, a GDT protection circuit and a TVS protection circuit which are connected in sequence, and also comprises a resettable fuse arranged between the GDT protection circuit and the TVS protection circuit. According to the utility model, the resettable fuse is additionally arranged between the GDT protection circuit and the TVS protection circuit to form a third-stage protection circuit, when the current of the circuit is too large, the resettable fuse is automatically disconnected, and the connection is automatically recovered after a certain period of time, so that a post-stage circuit can be better protected, and the service life of the circuit is prolonged. The problem that an existing RS485 interface lightning protection isolation circuit is poor in protection effect is solved.

Description

Technical Field

[0001] The utility model relates to the technical field of communication interfaces, in particular to a multi-level lightning protection isolation circuit for an RS485 interface. Background Art

[0002] The RS485 interface is a commonly used serial communication interface standard with the following features: support for multi-point communication, long transmission distance, and strong anti-interference ability. In order to ensure the normal operation and safety of the RS485 interface and its connected devices, the interface needs to be designed for lightning protection and isolation. The lightning protection and isolation design can improve the stability and reliability of the system, and ensure normal communication even when it is struck by lightning or other transient interference, reducing the risk of equipment failure and data loss.

[0003] Chinese patent CN 212435353 U proposes a lightning surge protection circuit for the RS485 port of an industrial Internet of Things gateway. The protection circuit includes a primary protection circuit and a secondary protection circuit arranged between the RS485 serial port and the network card chip, and also includes a serial port isolation power supply arranged between the RS485 serial port and the RS485 power supply chip. Among them, the primary protection circuit adopts a ceramic gas discharge tube GDT, which can withstand large surge currents, the secondary protection circuit adopts a TVS tube, which responds to surge voltages within the PS level time range, and the power supply adopts a DC / DC isolation module. When surges such as lightning arrive, the TVS starts first and accurately controls the instantaneous overvoltage at a certain level. If the surge current is large, the voltage at both ends will increase until the discharge of the front-stage gas discharge tube is driven to discharge the large current to the ground. Through this circuit structure, the surge current can be effectively discharged, the surge energy can be absorbed, and the overall surge protection level is improved, thereby effectively protecting the electronic components such as the Internet of Things gateway chip from being damaged by the surge current.

[0004] However, since the above-mentioned RS485 port lightning surge protection circuit does not have any protection devices such as fuses or fuses, when the current is too large and the GDT protection circuit (i.e., the primary protection circuit) and the TVS protection circuit (i.e., the secondary protection circuit) fail, it will still cause damage to the RS485 port or the device, and the protection effect is poor. Therefore, it is necessary to improve the existing protection circuit. Utility Model Content

[0005] The utility model proposes a multi-level lightning protection isolation circuit for an RS485 interface. A resettable fuse is added between a GDT protection circuit and a TVS protection circuit to form a third-level protection circuit. When the circuit current is too large, the resettable fuse is automatically disconnected and automatically restored to connection after a certain period of time, so that the subsequent circuit can be better protected to solve the problem that the existing RS485 interface lightning protection isolation circuit has poor protection effect.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the utility model is:

[0007] A RS485 interface multi-stage lightning protection isolation circuit comprises an RS485 serial port, a GDT protection circuit and a TVS protection circuit which are connected in sequence, and also comprises a self-recovering fuse arranged between the GDT protection circuit and the TVS protection circuit.

[0008] Furthermore, the number of the resettable fuses is two.

[0009] Furthermore, the model of the resettable fuse is nSMD020.

[0010] Furthermore, it also includes a communication circuit which is arranged at the rear stage of the TVS protection circuit and connected to the TVS protection circuit. The communication circuit includes a communication module, and the model of the communication module is MAX485ESA.

[0011] Furthermore, it also includes an MCU, and a photoelectric isolation circuit is connected between the MCU and the communication module.

[0012] Furthermore, the photoelectric isolation circuit is provided with three optical couplers, and the RX end, TX end and EN end of the communication module are respectively connected to the RX end, TX end and EN end of the MCU through the three optical couplers.

[0013] Furthermore, it also includes an isolated power supply circuit, which is electrically connected to the RS485 serial port.

[0014] Furthermore, the isolated power supply circuit includes a power supply module, the model of the power supply module is B0505S, which has pin 1, pin 2, pin 3 and pin 4; wherein pin 1 is grounded, pin 2 is connected to +5V, pin 3 is connected to the ground terminal of the RS485 serial port, and pin 4 is connected to the positive input terminal of the RS485 serial port.

[0015] Due to the adoption of the above technical solution, the utility model has the following beneficial effects:

[0016] 1. The utility model forms a third-level protection circuit by adding a resettable fuse between the GDT protection circuit and the TVS protection circuit. When the circuit current is too large, the resettable fuse automatically disconnects and automatically restores the connection after a certain period of time to ensure timely communication of the equipment. The setting of the resettable fuse can better protect the subsequent circuit. In addition, it has an automatic recovery function, and the recovery process does not require manual participation, reducing the workload of the staff.

[0017] 2. A photoelectric isolation circuit is provided between the communication module and the MCU of the utility model, which further improves the isolation effect and thus improves the safety of the RS485 interface and the MCU. In addition, the photoelectric isolation circuit uses three optical couplers, which is not only simple in structure, but also has lower cost than the existing isolation scheme. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A block diagram of a multi-stage lightning protection isolation circuit for an RS485 interface proposed in the embodiment of the utility model;

[0019] Figure 2 The schematic diagram of the GDT protection circuit, TVS protection circuit and communication circuit proposed in the embodiment of the utility model;

[0020] Figure 3 The schematic diagram of the photoelectric isolation circuit proposed in the embodiment of the utility model;

[0021] Figure 4 A schematic diagram of an isolated power supply circuit according to an embodiment of the present utility model;

[0022] Among them, the markings in the attached figure are: 1-RS485 serial port, 2-GDT protection circuit, 3-self-recovery fuse, 4-TVS protection circuit, 5-communication circuit, 6-photoelectric isolation circuit, 7-MCU, 8-isolation power supply circuit. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0024] Example

[0025] like Figure 1-4 , a RS485 interface multi-stage lightning protection isolation circuit, including an RS485 serial port 1, a GDT protection circuit 2, a TVS protection circuit 4, a self-recovery fuse 3, a communication circuit 5, a photoelectric isolation circuit 6, an MCU 7 and an isolation power supply circuit 8.

[0026] RS485 serial port 1, GDT protection circuit 2, and TVS protection circuit 4 are connected in sequence, and resettable fuse 3 is arranged between GDT protection circuit 2 and TVS protection circuit 4. There are two resettable fuses 3, which are respectively located on two lines. The model of resettable fuse 3 is nSMD020.

[0027] The communication circuit 5 is arranged at the rear stage of the TVS protection circuit 4 and connected to the TVS protection circuit 4. The communication circuit 5 includes a communication module, and the model of the communication module is MAX485ESA.

[0028] An optoelectronic isolation circuit 6 is connected between the MCU7 and the communication module. The optoelectronic isolation circuit 6 is provided with three optocouplers. The RX end, TX end and EN end of the communication module are respectively connected to the RX end, TX end and EN end of the MCU7 through the three optocouplers.

[0029] The isolated power supply circuit 8 is electrically connected to the RS485 serial port 1. The isolated power supply circuit 8 includes a power supply module, the model of the power supply module is B0505S, and it has pins 1, 2, 3 and 4. Among them, pin 1 is grounded, pin 2 is connected to +5V, pin 3 is connected to the ground terminal of the RS485 serial port 1, and pin 4 is connected to the positive input terminal of the RS485 serial port 1.

[0030] The utility model forms a third-level protection circuit by adding a resettable fuse 3 between the GDT protection circuit 2 and the TVS protection circuit 4. When the circuit current is too large, the resettable fuse 3 automatically disconnects and automatically restores the connection after a certain period of time to ensure timely communication of the device. The setting of the resettable fuse 3 can better protect the subsequent circuit. In addition, it has an automatic recovery function, and the recovery process does not require manual participation, reducing the workload of the staff.

[0031] A photoelectric isolation circuit 6 is provided between the communication module of the utility model and the MCU 7, so as to further improve the isolation effect, and thus improve the safety of the RS485 interface and the MCU 7. In addition, the photoelectric isolation circuit 6 adopts three optocouplers, which is not only simple in structure, but also has lower cost than the existing isolation scheme. The existing isolation scheme uses the ADUM1201 device (digital isolator), which has slightly better performance than the optocoupler scheme, but the price is much higher than the optocoupler scheme. ADUM1201 is a dual-channel isolation, which only isolates the signal line, and the RS485 transceiver control pin 485EN has not been isolated. If the pin needs to be isolated, the ADUM1201 device needs to be added, which is costly.

[0032] The above description is a detailed description of the preferred feasible embodiment of the utility model, but the embodiment is not used to limit the scope of the patent application of the utility model. All equivalent changes or modified changes completed under the technical spirit suggested by the utility model should fall within the patent scope covered by the utility model.

Claims

1. A RS485 interface multi-stage lightning protection isolation circuit, comprising an RS485 serial port, a GDT protection circuit and a TVS protection circuit connected in sequence, characterized in that: The invention also includes a resettable fuse arranged between the GDT protection circuit and the TVS protection circuit.

2. A RS485 interface multi-stage lightning protection isolation circuit according to claim 1, characterized in that: The number of the resettable fuses is two.

3. A RS485 interface multi-stage lightning protection isolation circuit according to claim 1, characterized in that: The model of the resettable fuse is nSMD020.

4. A RS485 interface multi-stage lightning protection isolation circuit according to claim 1, characterized in that: It also includes a communication circuit which is arranged at the rear stage of the TVS protection circuit and connected to the TVS protection circuit. The communication circuit includes a communication module, and the model of the communication module is MAX485ESA.

5. A RS485 interface multi-stage lightning protection isolation circuit according to claim 4, characterized in that: It also includes an MCU, and a photoelectric isolation circuit is connected between the MCU and the communication module.

6. A RS485 interface multi-stage lightning protection isolation circuit according to claim 5, characterized in that: The photoelectric isolation circuit is provided with three optical couplers, and the RX end, TX end and EN end of the communication module are respectively connected to the RX end, TX end and EN end of the MCU through the three optical couplers.

7. A RS485 interface multi-stage lightning protection isolation circuit according to claim 1, characterized in that: It also includes an isolated power supply circuit, which is electrically connected to the RS485 serial port.

8. A RS485 interface multi-stage lightning protection isolation circuit according to claim 7, characterized in that: The isolated power supply circuit includes a power supply module, the model of the power supply module is B0505S, which has pin 1, pin 2, pin 3 and pin 4; wherein pin 1 is grounded, pin 2 is connected to +5V, pin 3 is connected to the ground terminal of the RS485 serial port, and pin 4 is connected to the positive input terminal of the RS485 serial port.

Images