RS485 isolating circuit

Abstract

The utility model discloses an RS485 isolation circuit, and relates to the technical field of communication isolation, the RS485 isolation circuit comprises a single-chip microcomputer serial port signal output circuit, a power supply isolation circuit and a bus protection circuit, the single-chip microcomputer serial port signal output circuit comprises a 485 isolation transceiver, the input end of the 485 isolation transceiver is electrically connected with the serial port level output end of a single-chip microcomputer, and the input end of the 485 isolation transceiver is electrically connected with the serial port level output end of the single-chip microcomputer. The output end of the 485 isolation transceiver is electrically connected with the power supply isolation circuit, and the output end of the 485 isolation transceiver is also electrically connected with the RS485 bus through the bus protection circuit. According to the RS485 isolation circuit provided by the invention, an isolation type RS485 circuit is realized by using a small number of electronic components, a transceiver and a single chip microcomputer can be well protected when the electric transient noise amplitude is relatively large and the duration time is relatively long, the circuit protection level is improved, the stability of communication on an RS485 bus is improved, and the product cost is reduced.

Description

Technical Field

[0001] This application relates to the field of communication isolation technology, and particularly relates to an RS485 isolation circuit. Background Art

[0002] At present, many industrial controls use the RS485 bus for communication between devices, and the I / O of device cables is vulnerable to electrical transient noise from various signal sources. If the electrical transient noise has sufficient amplitude and duration, it may cause damage to the transceiver or adjacent sensitive circuits; therefore, in order to perform RS485 communication more stably and safely, it is particularly important to isolate the serial port of the single-chip microcomputer from the RS485 bus. Summary of the Utility Model

[0003] For this reason, this application provides an RS485 isolation circuit to solve the problem that the existing RS485 circuit may cause damage to the transceiver or adjacent sensitive circuits when the electrical transient noise has a large amplitude and a long duration.

[0004] To achieve the above object, this application provides the following technical solutions:

[0005] An RS485 isolation circuit includes a single-chip microcomputer serial port signal output circuit, a power isolation circuit, and a bus protection circuit. The single-chip microcomputer serial port signal output circuit includes a 485 isolation transceiver. The input end of the 485 isolation transceiver is electrically connected to the serial port level output end of the single-chip microcomputer. The output end of the 485 isolation transceiver is electrically connected to the power isolation circuit. The output end of the 485 isolation transceiver is also electrically connected to the RS485 bus through the bus protection circuit; wherein, the single-chip microcomputer serial port signal output circuit is used to input the serial port level signal of the single-chip microcomputer to the 485 isolation transceiver and control the 485 isolation transceiver to receive or send data; the power isolation circuit is used to isolate the power supply used by the single-chip microcomputer and the power supply of the 485 isolation transceiver bus end; the bus protection circuit is used to protect the RS485 bus.

[0006] Preferably, the model of the 485 isolation transceiver is ISO3082DWR.

[0007] Preferably, the data transmission pin of the 485 isolation transceiver is electrically connected to the receiving port of the serial port level of the single-chip microcomputer through a first LED and a first resistor, and the data receiving pin of the 485 isolation transceiver is electrically connected to the sending port of the serial port level of the single-chip microcomputer through a second LED and a second resistor.

[0008] Preferably, the power isolation circuit includes an isolated power module, and the model of the isolated power module is B0505S-1WR3.

[0009] Preferably, the power isolation circuit further includes a first capacitor, a second capacitor, a third capacitor, and a fourth capacitor. One end of the first capacitor and the second capacitor in parallel is electrically connected to the 5V network and the input voltage pin of the isolated power module, and the other end is grounded and electrically connected to the ground wire pin of the isolated power module; one end of the third capacitor and the fourth capacitor in parallel is electrically connected to the 5V-1 network and the positive power pin of the isolated power module, and the other end is grounded and electrically connected to the negative power pin of the isolated power module.

[0010] Preferably, the bus protection circuit includes a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a first unidirectional TVS diode, a second unidirectional TVS diode, a bidirectional TVS diode, a first fuse, and a second fuse;

[0011] One end of the third resistor and the first fuse in series is electrically connected to the output end of the 485 isolated transceiver, and the other end is electrically connected to the B network of the RS485 bus. One end of the fourth resistor and the second fuse in series is electrically connected to the output end of the 485 isolated transceiver, and the other end is electrically connected to the A network of the RS485 bus; the sixth resistor and the bidirectional TVS diode are connected in parallel between the third resistor and the first fuse and between the fourth resistor and the second fuse; one end of the fifth resistor is connected between the third resistor and the first fuse, and the other end is grounded; one end of the first unidirectional TVS diode is connected between the third resistor and the first fuse, and the other end is grounded; one end of the seventh resistor is connected between the fourth resistor and the second fuse, and the other end is grounded; one end of the second unidirectional TVS diode is connected between the fourth resistor and the second fuse, and the other end is grounded.

[0012] Compared with the prior art, the present application has at least the following beneficial effects:

[0013] The present application provides an RS485 isolation circuit, which includes a single-chip microcomputer serial port signal output circuit, a power isolation circuit, and a bus protection circuit. The single-chip microcomputer serial port signal output circuit includes a 485 isolation transceiver. The input end of the 485 isolation transceiver is electrically connected to the serial port level output end of the single-chip microcomputer, and the output end of the 485 isolation transceiver is electrically connected to the power isolation circuit. The output end of the 485 isolation transceiver is also electrically connected to the RS485 bus through the bus protection circuit. Among them, the single-chip microcomputer serial port signal output circuit is used to input the serial port level signal of the single-chip microcomputer to the 485 isolation transceiver and control the 485 isolation transceiver to receive or send data. The power isolation circuit is used to isolate the power supply used by the single-chip microcomputer and the power supply of the 485 isolation transceiver bus terminal. The bus protection circuit is used to protect the RS485 bus. The RS485 isolation circuit provided by the present application realizes an isolated RS485 circuit with a small number of electronic components. It can play a good protective role for the transceiver and the single-chip microcomputer when the amplitude of the electrical transient noise is large and the duration is long, improves the circuit protection level, enhances the stability of communication on the RS485 bus, and reduces the product cost. Description of the Drawings

[0014] To more intuitively illustrate the prior art and the present application, exemplary drawings are given below. It should be understood that the specific shapes and structures shown in the drawings generally should not be regarded as limiting conditions when implementing the present application. For example, those skilled in the art are capable of making routine adjustments or further optimizations to the addition / deletion / attribution division of certain units (components), specific shapes, positional relationships, connection methods, dimensional proportional relationships, etc. based on the technical concept disclosed in the present application and the exemplary drawings.

[0015] Figure 1 It is a schematic block diagram of an RS485 isolation circuit provided by the present application;

[0016] Figure 2 It is a schematic circuit diagram of the single-chip microcomputer serial port signal output circuit provided by the present application;

[0017] Figure 3 It is a schematic circuit diagram of the power isolation circuit provided by the present application;

[0018] Figure 4 It is a schematic circuit diagram of the bus protection circuit provided by the present application.

[0019] Description of the Reference Numerals:

[0020] 1. Single-chip microcomputer serial port signal output circuit; 2. Power isolation circuit; 3. Bus protection circuit. Detailed Embodiments

[0021] The following further details the present application through specific embodiments in conjunction with the drawings.

[0022] In the description of this application: Unless otherwise specified, the meaning of "a plurality of" is two or more. The terms "first", "second", "third", etc. in this application are intended to distinguish the objects being referred to, and do not have special significance in terms of technical connotations (for example, they should not be understood as emphasizing importance or order, etc.). Expressions such as "including", "comprising", "having", etc. also mean "not limited to" (certain units, components, materials, steps, etc.).

[0023] In this application, terms such as "upper", "lower", "left", "right", "middle", etc. that are cited are usually indications of the general relative position relationship for the convenience of intuitively understanding with reference to the accompanying drawings, and are not absolute limitations on the position relationship in the actual product.

[0024] Please refer to Figure 1 , this application provides an RS485 isolation circuit, including a single-chip microcomputer serial port signal output circuit 1, a power isolation circuit 2, and a bus protection circuit 3. The single-chip microcomputer serial port signal output circuit 1 includes a 485 isolation transceiver. The input end of the 485 isolation transceiver is electrically connected to the serial port level output end of the single-chip microcomputer, and the output end of the 485 isolation transceiver is electrically connected to the power isolation circuit 2. The output end of the 485 isolation transceiver is also electrically connected to the RS485 bus through the bus protection circuit 3; wherein, the single-chip microcomputer serial port signal output circuit 1 is used to input the serial port level signal of the single-chip microcomputer to the 485 isolation transceiver and control the 485 isolation transceiver to receive or send data; the power isolation circuit 2 is used to isolate the power supply used by the single-chip microcomputer and the power supply at the bus end of the 485 isolation transceiver; the bus protection circuit 3 is used to protect the RS485 bus.

[0025] Please refer to Figure 2 , the model of the 485 isolation transceiver (chip U3) is ISO3082DWR. The data transmission pin (RO, that is, the 3rd pin) of the 485 isolation transceiver is electrically connected to the receiving port (USART1_RX) of the serial port level of the single-chip microcomputer through the first LED D3 and the first resistor R9. The data receiving pin (DI, that is, the 6th pin) of the 485 isolation transceiver is electrically connected to the sending port (USART1_TX) of the serial port level of the single-chip microcomputer through the second LED D4 and the second resistor R14.

[0026] Specifically, pin 1 of the 485 isolation transceiver is connected to the 5V network, pins 2, 7, and 8 are connected to GND, pin 3 is connected to the USART1_RX network and one end of the R9 chip resistor, pins 4 and 5 are connected to the 485_DIR network, and pin 6 is connected to the USART1_TX network and one end of the R14 chip resistor; one end of the R9 chip resistor is connected to the cathode of the D3 chip LED; one end of the R14 chip resistor is connected to the cathode of the D4 chip LED; the anodes of the D3 chip LED and the D4 chip LED are commonly connected to the 3.3V network.

[0027] Please refer to Figure 3 , the power isolation circuit 2 uses an isolated power module (chip U7) to isolate the power supply used by the single-chip microcomputer and the power supply at the bus end of the 485 isolation transceiver, thereby reducing the impact of the high level on the RS485 bus on the single-chip microcomputer circuit. The model of the isolated power module is preferably B0505S-1WR3.

[0028] Specifically, the power isolation circuit 2 further includes a first capacitor C16, a second capacitor C17, a third capacitor C18, and a fourth capacitor C19. After the first capacitor C16 and the second capacitor C17 are connected in parallel, one end is electrically connected to the 5V network and the input voltage pin (VIN, i.e., pin 2) of the isolated power module, and the other end is grounded and electrically connected to the ground pin (GND, i.e., pin 1) of the isolated power module; after the third capacitor C18 and the fourth capacitor C19 are connected in parallel, one end is electrically connected to the 5V-1 network and the positive power supply pin (V + , i.e., pin 4) of the isolated power module, and the other end is grounded and electrically connected to the negative power supply pin (V - , i.e., pin 4) of the isolated power module.

[0029] In other words, pin 1 of the isolated power module is connected to one end of the C17 chip capacitor and the C16 chip capacitor, and they are commonly connected to the GND network; pin 2 is connected to one end of the C17 chip capacitor and the C16 chip capacitor, and they are commonly connected to the 5V network; pin 3 is connected to one end of the C18 chip capacitor and the C19 chip capacitor, and they are commonly connected to the GND-1 network; pin 4 is connected to one end of the C18 chip capacitor and the C19 chip capacitor, and they are commonly connected to the 5V-1 network.

[0030] Please refer to Figure 4, the bus protection circuit 3 is a protection circuit for the RS485 bus, used to ensure the integrity of the signals on the bus and protect the 485 isolation transceiver from being damaged by electrical breakdown. The bus protection circuit 3 includes a third resistor R10, a fourth resistor R12, a fifth resistor R8, a sixth resistor R13, a seventh resistor R16, a first unidirectional TVS diode T4, a second unidirectional TVS diode T5, a bidirectional TVS diode T3, a first fuse F1, and a second fuse F2; one end of the series connection of the third resistor R10 and the first fuse F1 is electrically connected to the output end of the 485 isolation transceiver, and the other end is electrically connected to the B network of the RS485 bus. One end of the series connection of the fourth resistor R12 and the second fuse F2 is electrically connected to the output end of the 485 isolation transceiver, and the other end is electrically connected to the A network of the RS485 bus; a sixth resistor R3 and a bidirectional TVS diode T3 are connected in parallel between the third resistor R10 and the first fuse F1 and between the fourth resistor R12 and the second fuse F2; one end of the fifth resistor R8 is connected between the third resistor R10 and the first fuse F1, and the other end is grounded; one end of the first unidirectional TVS diode T4 is connected between the third resistor R10 and the first fuse F1, and the other end is grounded; one end of the seventh resistor R16 is connected between the fourth resistor R12 and the second fuse F2, and the other end is grounded; one end of the second unidirectional TVS diode T5 is connected between the fourth resistor R12 and the second fuse F2, and the other end is grounded.

[0031] In other words, pin 9 and pin 10 of the 485 isolation transceiver (chip U3) are connected to the GND-1 network, pin 11 is left floating, pin 12 is connected to one end of the R12 chip resistor, pin 13 is connected to one end of the R10 chip resistor, pin 14 is left floating, pin 15 is connected to the GND-1 network, and pin 16 is connected to the 5V-1 network; one end of the R10 chip resistor is connected to one end of the R8 chip resistor, one end of the R13 chip resistor, the cathode of the T4 unidirectional TVS diode, one end of the T3 bidirectional TVS diode, and one end of the F1 chip fuse; one end of the R12 chip resistor is connected to one end of the R16 chip resistor, one end of the R13 chip resistor, the cathode of the T5 unidirectional TVS diode, one end of the T3 bidirectional TVS diode, and one end of the F2 chip fuse; one end of the R8 chip resistor is connected to the GND-1 network; one end of the R16 chip resistor is connected to the 5V-1 network; one end of the F1 chip fuse is connected to the A network; one end of the F2 chip fuse is connected to the B network.

[0032] It should be noted that Figure 4 the "A" network and the "B" network in refer to A and B on the RS485 bus.

[0033] An RS485 isolation circuit provided by the present application realizes an isolated RS485 circuit with a small number of electronic components. It can play a good protective role for transceivers and single-chip microcomputers when the amplitude and duration of electrical transient noise are large, improve the circuit protection level, reduce the risk of damage to expensive control circuits, enhance the stability of communication on the RS485 bus, and reduce product costs.

[0034] The technical features of the above embodiments can be combined arbitrarily (as long as there is no contradiction in the combination of these technical features). For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described; these embodiments not explicitly written out should also be regarded as within the scope described in this specification.

Claims

1. An RS485 isolation circuit, characterized in that: It includes a single-chip microcomputer serial port signal output circuit, a power isolation circuit and a bus protection circuit. The single-chip microcomputer serial port signal output circuit includes a 485 isolation transceiver. The input end of the 485 isolation transceiver is electrically connected to the serial port level output end of the single-chip microcomputer. The output end of the 485 isolation transceiver is electrically connected to the power isolation circuit. The output end of the 485 isolation transceiver is also electrically connected to the RS485 bus through the bus protection circuit. The single-chip microcomputer serial port signal output circuit is used to input the serial port level signal of the single-chip microcomputer to the 485 isolation transceiver and control the 485 isolation transceiver to receive or send data. The power isolation circuit is used to isolate the power used by the single-chip microcomputer and the power of the bus end of the 485 isolation transceiver. The bus protection circuit is used to protect the RS485 bus.

2. The RS485 isolation circuit according to claim 1, characterized in that: The model of the 485 isolation transceiver is ISO3082DWR.

3. The RS485 isolation circuit according to claim 2, characterized in that: The data transmission pin of the 485 isolation transceiver is electrically connected to the serial port level receiving port of the single-chip microcomputer through the first LED lamp and the first resistor, and the data receiving pin of the 485 isolation transceiver is electrically connected to the serial port level transmitting port of the single-chip microcomputer through the second LED lamp and the second resistor.

4. The RS485 isolation circuit according to claim 1, characterized in that: The power isolation circuit includes an isolated power module, and the model of the isolated power module is B0505S-1WR3.

5. The RS485 isolation circuit according to claim 4, characterized in that: The power isolation circuit also includes a first capacitor, a second capacitor, a third capacitor and a fourth capacitor. After the first capacitor and the second capacitor are connected in parallel, one end is electrically connected to the 5V network and the input voltage pin of the isolated power supply module, and the other end is grounded and electrically connected to the ground pin of the isolated power supply module; after the third capacitor and the fourth capacitor are connected in parallel, one end is electrically connected to the 5V-1 network and the positive power pin of the isolated power supply module, and the other end is grounded and electrically connected to the negative power pin of the isolated power supply module.

6. The RS485 isolation circuit according to claim 1, characterized in that: The bus protection circuit includes a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a first unidirectional TVS diode, a second unidirectional TVS diode, a bidirectional TVS diode, a first fuse and a second fuse; After the third resistor and the first fuse are connected in series, one end is electrically connected to the output end of the 485 isolation transceiver, and the other end is electrically connected to the B network of the RS485 bus. After the fourth resistor and the second fuse are connected in series, one end is electrically connected to the output end of the 485 isolation transceiver, and the other end is electrically connected to the A network of the RS485 bus; the sixth resistor and the bidirectional TVS diode are connected in parallel between the third resistor and the first fuse and between the fourth resistor and the second fuse; one end of the fifth resistor is connected between the third resistor and the first fuse, and the other end is grounded; one end of the first unidirectional TVS diode is connected between the third resistor and the first fuse, and the other end is grounded; one end of the seventh resistor is connected between the fourth resistor and the second fuse, and the other end is grounded; one end of the second unidirectional TVS diode is connected between the fourth resistor and the second fuse, and the other end is grounded.

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