RS485 bus communication isolation circuit and electronic device

Abstract

The utility model provides a kind of RS485 bus communication isolation circuit and electronic equipment, the circuit includes power supply circuit, RS485 transceiver, isolated power supply filter circuit, single-ended signal input / output circuit, differential signal input / output circuit and protection circuit, power supply circuit includes power supply and power supply filter circuit, power supply filter circuit is connected to the power supply and the power supply line of RS485 transceiver;The logic side DC-DC converter of RS485 transceiver, bus side DC-DC converter are used to convert the voltage input by power supply into isolated voltage of bus side, logic side transceiver and bus side transceiver are used for signal reception and conversion;Isolated power supply filter circuit is connected to bus side DC-DC converter, for isolated voltage filtering;Protection circuit includes two TVS diodes for overvoltage protection, two differential signal lines are respectively connected to the positive pole of two TVS diodes, and the negative pole of two TVS diodes is grounded.

Description

Technical Field

[0001] This utility model belongs to the field of electronic technology, and in particular relates to an RS485 bus communication isolation circuit and electronic equipment. Background Technology

[0002] RS485 is an industrial standard developed and released by the Electronic Industries Association in 1983, based on the RS-422 industrial bus standard. The RS-485 industrial bus standard can effectively support multiple nodes, has a long communication distance, and high sensitivity to information reception. It has been widely used in many fields, such as industrial control, traffic automation control, and fieldbus communication networks.

[0003] In industrial control applications using RS-485 bus communication networks, the majority of control units are distributed geographically, leading to various types of interference and consequently, low communication efficiency and reliability. Data transmission reliability directly impacts the overall reliability of the fieldbus communication system. In practice, RS485 transceivers and external isolation power chips are still required, resulting in larger PCBA areas, more complex wiring, and relatively weaker EMI protection. Utility Model Content

[0004] The technical problem to be solved by this utility model is to provide an RS485 bus communication isolation circuit and electronic device that is low in cost, reliable in operation, and has a small PCBA area.

[0005] To solve the above-mentioned technical problems, this utility model provides the following technical solution:

[0006] An RS485 bus communication isolation circuit includes a power supply circuit, an RS485 transceiver, an isolation power supply filter circuit, a single-ended signal input / output circuit, a differential signal input / output circuit, and a protection circuit.

[0007] The power supply circuit includes a power supply and a power supply filtering circuit. The power supply is connected to the RS485 transceiver and is used to supply power to the RS485 transceiver. The power supply filtering circuit is connected to the power supply line between the power supply and the RS485 transceiver and is used to filter the output of the power supply.

[0008] The RS485 transceiver includes a logic-side DC-DC converter, a bus-side DC-DC converter, an insulating gate located between the logic-side DC-DC converter and the bus-side DC-DC converter, a logic-side transceiver, and a bus-side transceiver. The logic-side DC-DC converter and the bus-side DC-DC converter are used to convert the voltage of the power input into an isolation voltage on the bus side. The logic-side transceiver and the bus-side transceiver are used for signal transmission, reception, and conversion.

[0009] The isolation power supply filter circuit is connected to the bus-side DC-DC converter and is used to filter the isolation voltage;

[0010] The single-ended signal input / output circuit is connected to the logic-side DC-DC converter;

[0011] The differential signal input / output circuit includes two differential signal lines, which are connected to the bus-side transceiver.

[0012] The protection circuit includes two TVS diodes for overvoltage protection. The two differential signal lines are respectively connected to the positive terminals of the two TVS diodes, and the negative terminals of the two TVS diodes are connected to ground.

[0013] Furthermore, the power input terminal of the logic-side DC-DC converter is directly shorted to the power input terminal of the logic-side transceiver.

[0014] Furthermore, the isolated power output terminal of the bus-side DC-DC converter is directly shorted to the isolated power input terminal of the bus-side transceiver.

[0015] Furthermore, the power supply filtering circuit includes two first decoupling capacitors, which are connected in parallel on the power supply line of the power input terminal of the logic-side DC-DC converter, with the other end of each capacitor connected to ground.

[0016] Furthermore, the isolated power supply filter circuit includes two second decoupling capacitors, which are connected in parallel on the power line of the isolated power supply output terminal of the bus-side DC-DC converter, with the other end of each capacitor connected to ground.

[0017] Furthermore, a first terminating resistor is connected in series on each of the two differential signal lines.

[0018] Furthermore, the RS485 bus communication isolation circuit also includes a resistor voltage divider circuit, which includes a second terminating resistor and two voltage divider resistors connected in series. The second terminating resistor is connected between the two differential signal lines, and one end of each of the two voltage divider resistors is connected to one of the two differential signal lines, while the other end of each is grounded.

[0019] This utility model also provides an electronic device, which includes the above-mentioned RS485 bus communication isolation circuit.

[0020] Compared to existing technologies, the RS485 bus communication isolation circuit provided in this embodiment isolates the power supply and communication signals on the logic side and bus side of the RS485 transceiver, achieving external isolation for the overall RS485 communication. Multiple filtering circuits further enhance the filtering of power and signals, resulting in excellent communication performance and significantly improved communication quality. It boasts a high level of electrical isolation and superior performance, effectively meeting the needs of industrial applications. Furthermore, since the RS485 transceiver integrates a DC-DC converter, it eliminates the need for an external isolation power supply chip, simplifying the construction of peripheral circuits, reducing circuit complexity, and decreasing PCBA area, thus effectively saving system space and simplifying design. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model.

[0022] Figure 1 This is a schematic diagram of the RS485 bus communication isolation circuit provided in an embodiment of this utility model.

[0023] Figure 2 yes Figure 1 A simplified schematic diagram of an RS485 transceiver with an RS485 bus communication isolation circuit.

[0024] Figure 3 yes Figure 1 A schematic diagram of a resistor divider circuit for RS485 bus communication isolation circuit. Detailed Implementation

[0025] To make the objectives, features, and advantages of this utility model more apparent and understandable, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0026] Please see Figure 1This utility model embodiment provides an RS485 bus communication isolation circuit 100, including a power supply circuit 10, an RS485 transceiver 20, an isolation power supply filter circuit 30, a single-ended signal input / output circuit 40, a differential signal input / output circuit 50, and a protection circuit 60. This utility model embodiment also provides an electronic device, which includes the RS485 bus communication isolation circuit 100.

[0027] The power supply circuit 10 includes a power supply (MCU_3V3) and a power supply filter circuit. In this embodiment, the power supply is connected to the RS485 transceiver 20, and its output voltage is 3.3V, used to supply power to the RS485 transceiver 20. The power supply filter circuit is connected to the power supply line between the power supply and the RS485 transceiver 20. It includes two first decoupling capacitors (C49 and C51, 10nF and 10uF respectively), used to filter the output of the power supply to reduce power supply noise and voltage fluctuations, ensuring stable circuit operation. Specifically, the power supply is connected to the VDDL terminal of the RS485 transceiver 20 (the VDDL terminal is directly shorted to the VDDP terminal). The first decoupling capacitors C49 (10nF) and C51 (10uF) are connected in parallel, with one end of each connected to the connection line between the power supply and the RS485 transceiver 20, and the other end of each connected to ground, used to filter and stabilize the output voltage of the power supply.

[0028] RS485 transceiver 20 is used to transmit data between the CPU (e.g., MCU) and the RS485 bus, while providing electrical isolation to enhance system security and interference immunity.

[0029] Please refer to the following: Figure 2 , it is Figure 1 A simplified schematic of an RS485 transceiver, compared to Figure 1 As shown, Figure 2 Some pins have been omitted from the original text. The following descriptions of pins and their functions will still use the format specified in the original text. Figure 1 The RS485 transceiver 20 is generally divided into a primary side and a secondary side, which can also be referred to as the logic side and the bus side, respectively. An isolation barrier is located between the logic side and the bus side, providing electrical isolation while allowing energy to be transferred between the isolated logic side and bus side by the internal DC-DC converter of the RS485 transceiver 20 through optical coupling, magnetic coupling, or capacitive coupling.

[0030] Specifically, the RS485 transceiver 20 includes a logic-side DC-DC converter 21, a bus-side DC-DC converter 22, an insulating gate 23, a logic-side transceiver 24, and a bus-side transceiver 25. The internal DC-DC converters of the aforementioned RS485 transceiver 20 refer to the logic-side DC-DC converter 21 and the bus-side DC-DC converter 22. The logic-side DC-DC converter 21 and the bus-side DC-DC converter 22 are used to convert the voltage of the power input into an isolated voltage on the bus side, while the logic-side transceiver 24 and the bus-side transceiver 25 are used for signal transmission, reception, and conversion.

[0031] Please refer to it again. Figure 1 The pin functions of RS485 transceiver 20 are explained below:

[0032] Logic side: RO (pin 1) is the signal input terminal of logic-side transceiver 24, DI (pin 4) is the signal output terminal of logic-side transceiver 24, VDDP (pin 6) is the power input terminal of logic-side DC-DC converter 21, VDDL (pin 7) is the power input terminal of logic-side transceiver 24, VDDP (pin 6) and VDDL (pin 7) are directly shorted together on the PCB, GNDP1 (pin 5) is the reference ground of logic-side DC-DC converter 21, GND1 (pin 8) is the reference ground of logic-side transceiver 24, GNDP1 and GND1 are directly shorted together internally in RS485 transceiver 20. #RE (pin 2) is the receiver enable control: when RE is low, the receiver is enabled. DE (pin 3) is the driver enable control: when DE is high, the driver is enabled.

[0033] Bus side: VISOin (pin 10) is the isolated power input of bus-side transceiver 25, and VISOout (pin 11) is the isolated power output of bus-side DC-DC converter 22. VISOin and VISOout are directly shorted together on the PCB. A (pin 14) and B (pin 15) are bus input / output terminals. GND2 (pin 9) is the reference ground of bus-side transceiver 25, and GNDP2 (pin 12) is the reference ground of bus-side DC-DC converter 22. GND2 and GNDP2 are directly shorted together internally in RS485 transceiver 20. SEL (pin 13) is the output voltage selection for VISOout and VISOin: when SEL is connected to VISOin, VISOout = VISOin = 5.0V; when SEL is connected to GND2 or left floating, VISOout = VISOin = 3.3V.

[0034] In this embodiment, the RS485 transceiver 20 is powered by a single power supply. VDDP (pin 6) and VDDL (pin 7) are directly shorted together on the PCB. The power supply (MCU_3.3V) is connected to VDDP (pin 6), and SEL (pin 13) is connected to GND2 (pin 12). Two first decoupling capacitors, C49 and C51, are connected in parallel on the power line of the power input terminal of the logic-side DC-DC converter 21. After being filtered by the first decoupling capacitors C49 (10NF) and C51 (10UF), a stable 3.3V power supply is supplied to the logic-side DC-DC converter 21. After passing through the logic-side DC-DC converter 21, the insulating gate 23, and the bus-side DC-DC converter 22, an isolated power supply (3.3V) is generated on the bus side. That is, the isolated power supply is output from VISOout and then input to VISOin to power the bus-side transceiver 25. In this way, power isolation is achieved.

[0035] RS485 transceiver 20 converts the single-ended signal (CPU_TXD7A) from the CPU (not shown) into differential output signals Ext_485_A and Ext_485_B. It can also convert the differential signals Ext_485_A and Ext_485_B from the bus into the single-ended signal (CPU_RXD7A) required by the CPU. These signals are coupled to the logic side through the insulating gate 23 and then input to the CPU, thus enabling signal transmission across the insulating gate. In this embodiment, the RS485 transceiver 20 is preferably the Chuantu Micro CA-IS2092A, an isolated half-duplex RS485 transceiver with an integrated isolated DC-DC converter, eliminating the need for an external isolation power supply.

[0036] An isolation power supply filter circuit 30 is connected to the bus-side DC-DC converter 22 for filtering the isolation voltage. The isolation power supply filter circuit 30 includes two second decoupling capacitors C50 (10uF) and C48 (10NF), which are connected in parallel on the power supply line at the isolated power output of the bus-side DC-DC converter, with their other ends connected to ground. Specifically, the second decoupling capacitors C48 and C50 are connected in parallel between VISOout (pin 11) of the RS485 transceiver 20 and ground (RS485_GND1). The second decoupling capacitors C48 and C50 are used to filter out power supply noise, providing a more stable power supply environment for the isolated input power supply (VISOin) and isolated output power supply (VISOout) of the RS485 transceiver 20. This helps reduce the impact of power supply noise on the performance of the RS485 transceiver 20, improving the stability and reliability of the circuit.

[0037] The single-ended signal input / output circuit 40 is connected to the logic-side DC-DC converter 21, which includes a single-ended signal line (CPU_RXD7A) connected to RO (pin 1), a single-ended signal line (CPU_TXD7A) connected to DI (pin 4), and enable signal lines RX1_EN and TX1_EN connected to #RE (pin 2) and DE (pin 3).

[0038] The differential signal input / output circuit 50 includes two differential signal lines, A and B, which are connected to the bus-side transceiver 25. Specifically, the differential signal input / output circuit 50 includes two first terminating resistors, R58 and R59, namely, a first resistor R58 connected in series on the B differential signal line and a first resistor R59 connected in series on the A differential signal line. The first terminating resistors R58 and R59 together provide termination matching for the RS485 bus. The first terminating resistors R58 and R59 help absorb signal energy reflected at the end of the RS485 bus, reducing signal distortion and improving signal integrity. It should be noted that the first terminating resistors R58 and R59 in this embodiment are optional; their installation can be selected as needed in the circuit design.

[0039] Protection circuit 60 includes two TVS diodes (transient voltage suppressor diodes, model SM712) to provide overvoltage protection for the A and B differential signal lines. When a voltage spike occurs on the RS485 bus, the TVS diodes quickly conduct, guiding the overvoltage to ground to protect downstream circuitry. Specifically, both the A and B differential signal lines are connected to the anode of the TVS diodes, and the cathodes of the TVS diodes are connected to ground (RS485_GND) for overvoltage protection.

[0040] Please refer to the following: Figure 1 and Figure 3The RS485 bus communication isolation circuit 100 in this embodiment also includes a voltage divider circuit 70. The voltage divider circuit 70 includes a second terminating resistor R56 (120Ω) and two voltage divider resistors R57 (10KΩ) and R61 (10KΩ) connected in series. These three resistors connected in series (R56, R57, R61) form a resistor voltage divider: the second terminating resistor R56 is connected between the differential signal lines A and B, one end of each of the two voltage divider resistors R57 and R61 is connected to one of the two differential signal lines A and B respectively, and the other end of each is grounded. Specifically, voltage divider resistor R57 is connected between the B differential signal line and ground RS_GND1, and voltage divider resistor R61 is connected between the isolation voltage output VISOout line (Viso_485_1) and the A differential signal line. That is, R57 and R61 are connected to RS485_GND1 (ground) respectively, and R56 is connected to Ext_485_B1 (the B line of the RS485 bus) and Ext_485_A1 (the A line of the RS485 bus). The output is marked Viso_485_1, indicating the common-mode voltage Viso_485_1 of the RS485 bus. This resistor divider provides a stable common-mode voltage between the A and B lines of the RS485 bus. This configuration helps reduce signal reflections and electromagnetic interference, improving communication reliability. By ensuring a stable common-mode voltage between the A and B differential signal lines of the RS485 bus, communication stability and anti-interference capability are improved.

[0041] This embodiment isolates the power supply and communication signals on the logic side and bus side of the RS485 transceiver 20, achieving external isolation for the overall RS485 communication. Multiple filtering circuits further filter the power supply and signals, and with the addition of resistor divider circuits and protection circuits, excellent communication performance is achieved, significantly improving communication quality. It boasts a high level of electrical isolation and excellent performance, effectively meeting the needs of industrial applications. Furthermore, since the RS485 transceiver 20 integrates a DC-DC converter, it eliminates the need for an external isolation power supply chip, simplifying the construction of peripheral circuits, reducing circuit complexity, and decreasing PCBA area, effectively saving system space and simplifying the design.

[0042] The above is a description of the embodiments provided by this utility model. For those skilled in the art, based on the ideas of the embodiments of this utility model, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this utility model.

Claims

1. An RS485 bus communication isolation circuit, characterized in that, It includes a power supply circuit, an RS485 transceiver, an isolation power supply filter circuit, a single-ended signal input / output circuit, a differential signal input / output circuit, and a protection circuit. The power supply circuit includes a power supply and a power supply filtering circuit. The power supply is connected to the RS485 transceiver and is used to supply power to the RS485 transceiver. The power supply filtering circuit is connected to the power supply line between the power supply and the RS485 transceiver and is used to filter the output of the power supply. The RS485 transceiver includes a logic-side DC-DC converter, a bus-side DC-DC converter, an insulating gate located between the logic-side DC-DC converter and the bus-side DC-DC converter, a logic-side transceiver, and a bus-side transceiver. The logic-side DC-DC converter and the bus-side DC-DC converter are used to convert the voltage of the power input into an isolation voltage on the bus side. The logic-side transceiver and the bus-side transceiver are used for signal transmission, reception, and conversion. The isolation power supply filter circuit is connected to the bus-side DC-DC converter and is used to filter the isolation voltage; The single-ended signal input / output circuit is connected to the logic-side DC-DC converter; The differential signal input / output circuit includes two differential signal lines, which are connected to the bus-side transceiver. The protection circuit includes two TVS diodes for overvoltage protection. The two differential signal lines are respectively connected to the positive terminals of the two TVS diodes, and the negative terminals of the two TVS diodes are connected to ground.

2. The RS485 bus communication isolation circuit according to claim 1, characterized in that, The power input terminal of the logic-side DC-DC converter is directly shorted to the power input terminal of the logic-side transceiver.

3. The RS485 bus communication isolation circuit according to claim 2, characterized in that, The isolated power output terminal of the bus-side DC-DC converter is directly shorted to the isolated power input terminal of the bus-side transceiver.

4. The RS485 bus communication isolation circuit according to claim 3, characterized in that, The power filtering circuit includes two first decoupling capacitors, which are connected in parallel on the power line of the power input terminal of the logic-side DC-DC converter, and the other end of each capacitor is connected to ground.

5. The RS485 bus communication isolation circuit according to claim 4, characterized in that, The isolated power supply filter circuit includes two second decoupling capacitors, which are connected in parallel on the power line of the isolated power supply output terminal of the bus-side DC-DC converter, with the other end of each capacitor connected to ground.

6. The RS485 bus communication isolation circuit according to claim 5, characterized in that, A first terminating resistor is connected in series on each of the two differential signal lines.

7. The RS485 bus communication isolation circuit according to claim 6, characterized in that, The RS485 bus communication isolation circuit also includes a resistor voltage divider circuit, which includes a second terminating resistor and two voltage divider resistors connected in series. The second terminating resistor is connected between the two differential signal lines, and one end of each of the two voltage divider resistors is connected to one of the two differential signal lines, while the other end of each is grounded.

8. An electronic device, characterized in that, Includes the RS485 bus communication isolation circuit as described in any one of claims 1 to 7.

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