Isolation 485 communication circuit

Abstract

The utility model provides an isolation 485 communication circuit, which belongs to the technical field of external communication of an industrial automatic control system and comprises a communication signal processing part, a power conversion part and a controller. The communication signal processing part comprises a communication interface protection circuit, an RS485 transceiver circuit and a digital isolator circuit; the power supply conversion part comprises an isolation power supply module and a control power supply. According to the utility model, the mode that the integrated RS485 transceiver is matched with the digital isolation chip is adopted, and a single power supply is adopted for power supply. In addition to the advantages of a common magnetic isolator, the magnetic isolator also has extremely high integration level and stability and extremely small PCB usable area, and perfect isolation of an RS485 interface is realized. And the circuit connection, the PCB use and the usability are far better than those of an optocoupler. Compared with performance test results, waveform delay, waveform rising / falling time and the like are superior to those of an optocoupler.

Description

TECHNICAL FIELD

[0001] The utility model relates to the technical field of industrial automatic control system external communication, and specifically, especially relates to an isolation 485 communication circuit. BACKGROUND

[0002] RS485 is a differential signal communication protocol, which uses a pair of twisted pair to transmit signals, and the two lines represent the positive and negative voltage difference, that is, the differential signal. RS485 can realize multi-point communication, that is, multiple devices can be connected on the network, and bus arbitration can be performed to ensure the accuracy of data transmission. It is widely used in industrial and commercial environments and is favored because it can support long-distance communication and multi-device network. However, in some application scenarios, in order to improve the reliability and safety of the system, isolation communication has become a necessary technology.

[0003] In some special application scenarios, such as high-noise environments, communication between devices with different voltage levels, or occasions that require enhanced data transmission security, isolation communication is particularly important. Isolation communication can prevent the generation of ground loop, reduce electromagnetic interference, and improve the stability and safety of the system.

[0004] RS485 interface usually needs to be isolated to ensure the stability of bus network communication. The main purposes of isolation are generally as follows:

[0005] 1. Safety consideration: protect equipment and personal safety, and isolate potential high-voltage hazards.

[0006] 2. Improve communication stability: eliminate the influence of ground potential difference.

[0007] 3. Improve device reliability: eliminate ground loop effects.

[0008] 4. Low coupling: improve system compatibility.

[0009] The core of isolation communication is electrical isolation, that is, there is no direct electrical connection between the sending end and the receiving end. This is achieved by using isolation devices or isolation modules. Isolation devices can cut off the direct path of electrical signals without damaging the integrity of the signal, thereby achieving electrical isolation.

[0010] For many years, the isolation of RS485 interface has always used the traditional optical coupling isolation scheme. Two optical couplings and external current limiting and driving circuits composed of discrete components are required for isolation of one RS485 interface, which increases the use of circuit board space and cost, and also increases the complexity of the circuit, leading to longer design time and unstable circuit performance. UTILITY MODEL CONTENTS

[0011] The technical problems in the background art are solved by providing an isolated 485 communication circuit.

[0012] The technical means adopted by the utility model are as follows:

[0013] An isolated 485 communication circuit comprises a communication signal processing part, a power conversion part and a controller.

[0014] The communication signal processing part comprises a communication interface protection circuit, an RS485 transceiver circuit and a digital isolator circuit; the power conversion part comprises an isolated power module and a control power supply.

[0015] An input RS485 signal is connected to the input end of the communication interface protection circuit, and the output end of the communication interface protection circuit is connected to the RS485 transceiver circuit; the output end of the RS485 transceiver circuit is connected to the input end of the digital isolator circuit through a TXD data stream; the output end of the digital isolator circuit is connected to the input end of the RS485 transceiver circuit through an RXD data stream.

[0016] The output end of the digital isolator circuit is connected to the input end of the controller through TXDA; the output end of the controller is connected to the input end of the digital isolator circuit through RXDA.

[0017] The control power supply provides a 5VA power supply to the isolated power module; the isolated power module converts the 5VA power supply into an isolated 5V power supply; the output end of the isolated power module is connected to the input end of the RS485 transceiver circuit.

[0018] Further, the RS485 transceiver circuit comprises a MAX13487EE chip and a protection circuit.

[0019] The protection circuit comprises a connector CN1, protection tubes Z1 and Z2, resistors R1, R2, R3, R4 and R5, diodes D1A and D1B, capacitors C2 and C3.

[0020] Further, pin 1 of the connector CN1 is connected to the ground; pin 2 of the connector CN1 is connected to the cathode of the protection tube Z1 through the resistor R3, and the anode of the protection tube Z1 is grounded; pin 3 of the connector CN1 is connected to the cathode of the protection tube Z2 through the resistor R4, and the anode of the protection tube Z2 is grounded; the anodes of the diodes D1A and D1B are respectively connected to the cathodes of the protection tubes Z1 and Z2; the cathodes of the diodes D1A and D1B are connected to one end of the resistor R2, and the other end of the resistor R2 is connected to the ground.

[0021] One end of the resistor R2 is connected to +5V power supply through the capacitor C1; the capacitor C2 is connected in series with the resistor R5, and then connected between ground and +5V power supply; the pin 1 of the MAX13487EE chip is connected to +5V power supply through the resistor R1; the pin 2, the pin 3, the pin 4 and the pin 6 of the MAX13487EE chip are connected to ground respectively; the pin 5 of the MAX13487EE chip is connected with the capacitor C3 and ground; the pin 7 of the MAX13487EE chip is connected to +5V power supply.

[0022] Further, the digital isolator circuit is ISO7221AD digital isolator.

[0023] Further, the pin 6 of the ISO7221AD digital isolator is connected with the pin 4 of the MAX13487EE chip; the pin 7 of the ISO7221AD digital isolator is connected with the pin 1 of the MAX13487EE chip; the pin 1 and the pin 8 of the ISO7221AD digital isolator are connected with +5V power supply; the pin 4 and the pin 5 of the ISO7221AD digital isolator are connected to ground.

[0024] Further, the maximum isolation voltage of the isolator circuit is 4000VPK; the data transmission rate of the isolator circuit is 1000Kbps.

[0025] Further, the isolation power module is B0505XT-1WR2.

[0026] Further, the isolation voltage +5V generated by the voltage +5VA of the control side is used for power supply of the RS485 transceiver and the digital isolator.

[0027] Compared with the prior art, the utility model has the advantages that:

[0028] The utility model adopts the way that integrated RS485 transceiver cooperates with digital isolation chip, adopts single power supply power supply. In addition to having the advantages of general magnetic isolator, also have very high integration and stability, very small PCB use area, realized perfect isolation of RS485 interface. The performance test result comparison, waveform delay, waveform rise / fall time and the like are superior to photoelectric coupler. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0030] Fig. 1 The circuit topology structure diagram of the present application.

[0031] Fig. 2 The circuit principle diagram of the present application. DETAILED DESCRIPTION

[0032] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0033] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0034] It should be noted that the terms used herein are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form, and in addition, it should be understood that when the terms "comprise" and / or "include" are used in the specification, there is a feature, step, operation, device, component and / or combination thereof.

[0035] The foregoing description, for purposes of explanation, sets forth specific values and arrangements of components and steps that are subject to many options. The intent is to be accurate in describing the principles and novel features of the application. Thus, although the application has been described with reference to specific embodiments thereof, it will be apparent to those of ordinary skill in the art that a number of changes can be made to the embodiments described without departing from the spirit and scope of the application. For example, the various features of the application can be combined in any combination, where possible. Accordingly, the scope of the application is to be construed as encompassing modifications and variations of the specific examples described herein, subject only to the conditions of the prior art.

[0036] In the description of the present application, it should be understood that the orientation words such as "front, back, up, down, left, right", "horizontal, vertical, perpendicular, horizontal" and "top, bottom" and the like indicated orientation or position relationship are usually based on the orientation or position relationship shown in the drawings, only for the convenience of describing the present application and simplifying the description, without making the opposite statement, these orientation words do not indicate and imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, therefore, it cannot be understood as a limitation on the protection scope of the present application: the orientation words "inner, outer" refer to the inner and outer of the contour of each component itself.

[0037] For the convenience of description, spatial relative terms such as "on", "above", "upper surface", "upper" and the like can be used herein to describe the spatial position relationship of one device or feature with other devices or features as shown in the drawings. It should be understood that the spatial relative terms are intended to include different orientations in use or operation in addition to the orientation of the device described in the drawings. For example, if the device in the drawing is inverted, the device described as "above" or "on" other devices or structures will be positioned "below" or "under" other devices or structures. Thus, the example term "above" can include both "above" and "below" orientations. The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative description used herein is interpreted accordingly.

[0038] In addition, it should be noted that the use of "first", "second" and the like words to limit parts, only for the convenience of distinguishing the corresponding parts, if there is no further declaration, the above words have no special meaning, therefore, it cannot be understood as a limitation on the protection scope of the present application.

[0039] AsFigs. 1-2 The utility model provides a kind of isolated 485 communication circuit, comprising: communication signal processing part, power conversion part and controller.

[0040] As preferred implementation, in the present application, communication signal processing part includes: communication interface protection circuit, RS485 transceiver circuit and digital isolator circuit;Power conversion part includes: isolated power module and control power supply.

[0041] Input RS485 signal is connected with the input end of communication interface protection circuit, and the output end of communication interface protection circuit is connected with RS485 transceiver circuit;The output end of RS485 transceiver circuit is connected with the input end of digital isolator circuit through TXD data stream;The output end of digital isolator circuit is connected with the input end of RS485 transceiver circuit through RXD data stream;The output end of digital isolator circuit is connected with the input end of controller through TXDA;The output end of controller is connected with the input end of digital isolator circuit through RXDA;

[0042] Control power supply provides 5VA power supply to isolated power module;Isolated power module transforms 5VA power supply into isolated 5V power supply;The output end of isolated power module is connected with the input end of RS485 transceiver circuit.

[0043] Further, RS485 transceiver circuit includes: MAX13487EE chip and protection circuit.Protection circuit includes: connector CN1, protection tube Z1, protection tube Z2, resistance R1, resistance R2, resistance R3, resistance R4, resistance R5, diode D1A, diode D1B, capacitor C2 and capacitor C3.

[0044] Pin 1 of connector CN1 is connected to ground;Pin 2 of connector CN1 is connected to the cathode of protection tube Z1 through resistance R3, and the anode of protection tube Z1 is grounded;Pin 3 of connector CN1 is connected to the cathode of protection tube Z2 through resistance R4, and the anode of protection tube Z2 is grounded;The anodes of diode D1A and diode D1B are respectively connected to the cathodes of protection tube Z1 and protection tube Z2;The cathodes of diode D1A and diode D1B are connected to one end of resistance R2, and the other end of resistance R2 is connected to ground;One end of resistance R2 is connected to +5V power supply through capacitor C1;Capacitor C2 and resistance R5 are connected in series, and then connected between ground and +5V power supply;Pin 1 of MAX13487EE chip is connected to +5V power supply through resistance R1;Pin 2, pin 3, pin 4 and pin 6 of MAX13487EE chip are respectively connected to ground;Pin 5 of MAX13487EE chip is connected with capacitor C3 and ground;Pin 7 of MAX13487EE chip is connected to +5V power supply.

[0045] The protection tube Z1 / Z2 ensures the input RS485 communication signal level stable, which will not exceed the pin range of U1 chip. The resistance R3 / R4 and the capacitor C2 / C3 are used as the absorption circuit to prevent the current impact from damaging the chip. The R2 / R5 is used as the bus level matching resistance to ensure the bus is still in a steady state when idle, so as to avoid the mis-triggering of communication. The above discrete components together form the protection circuit of the RS485 communication interface, which ensures the stability and service life of the RS485 transceiver chip in the later stage.

[0046] The MAX13487EE chip is the RS485 transceiver, and can automatically detect the receiving and transmitting control, without the separate control chip for the receiving and transmitting pin. It is more convenient in use, and also makes the programming more portable. The U1 chip decodes the RXD and TXD data stream after analyzing the RS485 communication protocol.

[0047] As a preferred embodiment, in the present application, the digital isolator circuit is ISO7221AD digital isolator. The pin 6 of the ISO7221AD digital isolator is connected with the pin 4 of the MAX13487EE chip; the pin 7 of the ISO7221AD digital isolator is connected with the pin 1 of the MAX13487EE chip; the pin 1 and the pin 8 of the ISO7221AD digital isolator are connected with the +5V power supply; and the pin 4 and the pin 5 of the ISO7221AD digital isolator are connected to the ground. The ISO7221AD chip digital isolator is the key of the isolated communication, and the chip isolation voltage is as high as 4000VPK. The chip has two different direction digital isolation channels, and the highest data transmission rate reaches 1000Kbps, which fully meets the requirements of RS485 communication. When the chip is used with the isolation power supply, the high voltage and the isolation ground can be prevented, and the noise current on the data bus or other circuits can be prevented from entering the local ground or causing interference or damage to the sensitive circuit. In terms of the power supply of the chip, the 3.3V or 5V power supply is compatible, which greatly facilitates the matching of the control circuit level.

[0048] The isolation power supply module B0505XT-1WR2 is selected in the isolation power supply aspect, which has small volume and the isolation voltage reaches 1500VDC / min. The isolation voltage +5V generated by the voltage +5VA on the control side is used to supply power for the RS485 transceiver and the digital isolator.

[0049] Finally, it should be noted that: the above embodiments are used to illustrate the technical solutions of the present application, but not limited to them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An isolated 485 communication circuit, characterized in that, include: Communication signal processing unit, power conversion unit, and controller; The communication signal processing unit includes: a communication interface protection circuit, an RS485 transceiver circuit, and a digital isolator circuit; the power conversion unit includes: an isolation power supply module and a control power supply. An input RS485 signal is connected to the input terminal of the communication interface protection circuit, and the output terminal of the communication interface protection circuit is connected to the RS485 transceiver circuit; the output terminal of the RS485 transceiver circuit is connected to the input terminal of the digital isolator circuit via a TXD data stream; the output terminal of the digital isolator circuit is connected to the input terminal of the RS485 transceiver circuit via an RXD data stream. The output of the digital isolator circuit is connected to the input of the controller via TXDA; the output of the controller is connected to the input of the digital isolator circuit via RXDA. The control power supply provides 5VA power to the isolation power module; the isolation power module converts the 5VA power into an isolated 5V power; the output terminal of the isolation power module is connected to the input terminal of the RS485 transceiver circuit.

2. The isolated 485 communication circuit according to claim 1, characterized in that, The RS485 transceiver circuit includes: a MAX13487EE chip and a protection circuit; The protection circuit includes: connector CN1, protection tube Z1, protection tube Z2, resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, diode D1A, diode D1B, capacitor C2, and capacitor C3.

3. The isolated 485 communication circuit according to claim 2, characterized in that, Pin 1 of connector CN1 is connected to ground; pin 2 of connector CN1 is connected to the cathode of protective tube Z1 through resistor R3, and the anode of protective tube Z1 is grounded; pin 3 of connector CN1 is connected to the cathode of protective tube Z2 through resistor R4, and the anode of protective tube Z2 is grounded; the anodes of diodes D1A and D1B are respectively connected to the cathodes of protective tube Z1 and protective tube Z2; the cathodes of diodes D1A and D1B are connected to one end of resistor R2, and the other end of resistor R2 is connected to ground. One end of resistor R2 is connected to the +5V power supply through capacitor C1; capacitor C2 is connected in series with resistor R5, and then connected between ground and the +5V power supply; pin 1 of the MAX13487EE chip is connected to the +5V power supply through resistor R1; pins 2, 3, 4, and 6 of the MAX13487EE chip are respectively connected to ground; pin 5 of the MAX13487EE chip is connected to capacitor C3 and ground; pin 7 of the MAX13487EE chip is connected to the +5V power supply.

4. The isolated 485 communication circuit according to claim 1, characterized in that, The digital isolator circuit is an ISO7221AD digital isolator.

5. The isolated 485 communication circuit according to claim 4, characterized in that, Pin 6 of the ISO7221AD digital isolator is connected to pin 4 of the MAX13487EE chip; pin 7 of the ISO7221AD digital isolator is connected to pin 1 of the MAX13487EE chip; pins 1 and 8 of the ISO7221AD digital isolator are connected to a +5V power supply; and pins 4 and 5 of the ISO7221AD digital isolator are connected to ground.

6. The isolated 485 communication circuit according to claim 1, characterized in that, The isolator circuit has a maximum isolation voltage of 4000VpK and a data transmission rate of 1000Kbps.

7. The isolated 485 communication circuit according to claim 1, characterized in that, The isolated power supply module is B0505XT-1WR2.

8. The isolated 485 communication circuit according to claim 1, characterized in that, The +5VA voltage on the control side generates an isolation voltage of +5V, which powers the RS485 transceiver and digital isolator.

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