A high-speed 485 communication interface protection circuit

Abstract

The utility model relates to the technical field of communication protection circuits, and specifically to a high-speed 485 communication interface protection circuit, which aims to solve the problem that the traditional 485 communication interface affects the signal integrity due to the excessive parasitic capacitance of the protection circuit during high-speed communication. The protection circuit includes signal lines IO485A and IO485B, and diodes, transient voltage suppression diodes (TVS) and thermistors (PTC) connected in parallel therewith. Diodes D1 and D2 are connected in series and parallel with VD1, and D3 and D4 are connected in series and parallel with VD2, respectively connected to the signal lines and grounded. PTC1 and PTC2 are respectively connected to the signal lines. Under the premise of not affecting the signal integrity, the circuit can protect the 485 communication interface from damage even when 380V or 220V strong electricity is wrongly connected, and by reducing the junction capacitance, the circuit adapts to the needs of high-speed communication, and has the advantages of simple structure, stable and reliable, and low cost.

Description

Technical Field

[0001] The utility model relates to the technical field of communication protection circuits, in particular to a high-speed 485 communication interface protection circuit. Background Art

[0002] RS-485 communication is a differential signal transmission method that uses a pair of twisted pairs to send and receive data. It has the characteristics of strong anti-interference ability and long transmission distance. RS-485 communication can work stably in harsh electrical environments and is widely used in power, industrial automation, remote monitoring and other occasions.

[0003] However, during on-site construction and wiring, there is a possibility that 220V or 380V power lines will be connected to the 485 interface. Therefore, in order to avoid equipment damage caused by wrong wiring, the 485 communication interface is often designed with a wrong connection protection circuit to ensure that the 485 communication circuit will not be damaged even if the power line is wrongly connected. However, with the widespread use of 485 communication, the requirements for communication speed are getting higher and higher. Under 485 high-speed communication, the original protection circuit will affect the integrity of the signal due to the large parasitic capacitance, resulting in communication failure.

[0004] Therefore, a high-speed 485 communication interface protection circuit is of great significance to solve the interface protection problem under 485 high-speed communication. Utility Model Content

[0005] In order to solve the problems existing in the background technology, the utility model provides a high-speed 485 communication interface protection circuit, which includes signal lines IO 485A and IO 485B; diode D1, diode D2 and transient voltage suppression diode VD1: diode D1 and transient voltage suppression diode VD1 are connected in series and then connected in parallel with diode D2, one end of the parallel circuit is connected to the signal line IO 485A, and the other end is grounded GND; diode D3, diode D4 and transient voltage suppression diode VD2: diode D3 and transient voltage suppression diode VD2 are connected in series and then connected in parallel with diode D4, one end of the parallel circuit is connected to the signal line IO 485B, and the other end is grounded GND. Thermistor PTC1 and thermistor PTC2: the two thermistors PTC1 and PTC2 are connected to the signal lines IO 485A and IO 485B respectively.

[0006] In a preferred solution, the junction capacitances of diode D1 , diode D2 , diode D3 and diode D4 are all 16 pF.

[0007] In a preferred solution, the junction capacitance of the transient voltage suppression diode VD1 and the transient voltage suppression diode VD2 are both 1000 pF.

[0008] The beneficial effects achieved by the utility model are:

[0009] The invention provides a high-speed 485 communication interface protection circuit, which has the advantages of simple circuit, stability, reliability and low cost. The interface protection circuit does not affect the signal integrity, ensures the high-speed communication of 485 under protection, and can ensure that even in the case of wrong connection of 380V or 220V strong electric wires, no damage is caused and 485 can communicate normally. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a circuit diagram of the utility model. DETAILED DESCRIPTION

[0011] The technical solution of the utility model will be clearly and completely described below in conjunction with the drawings in the utility model. In addition, the forms of the various structures recorded in the following embodiments are merely illustrative, and the utility model is not limited to the various structures recorded in the following embodiments. All other implementations obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the utility model.

[0012] Reference Figure 1 The utility model provides a high-speed 485 communication interface protection circuit, which includes signal lines IO 485A and IO 485B.

[0013] Diode D1, diode D2 and transient voltage suppression diode VD1: Diode D1 and transient voltage suppression diode VD1 are connected in series and then connected in parallel with diode D2. One end of the parallel circuit is connected to the signal line IO 485A, and the other end is grounded GND.

[0014] Diode D3, diode D4 and transient voltage suppression diode VD2: Diode D3 and transient voltage suppression diode VD2 are connected in series and then connected in parallel with diode D4. One end of the parallel circuit is connected to the signal line IO 485B and the other end is grounded GND. Thermistor PTC1 and thermistor PTC2: The two thermistors PTC1 and PTC2 are connected to the signal lines IO 485A and IO 485B respectively.

[0015] The junction capacitances of diodes D1, D2, D3 and D4 are preferably 16 pF. The junction capacitances of transient voltage suppressor diodes VD1 and VD2 are preferably 1000 pF.

[0016] When the live wire and neutral wire of 380V (220V) are connected incorrectly between the signal lines IO_485_A and IO_485_B, in the positive half cycle of the alternating current, the TVS tube VD1 breaks down, and the current flows into IO_485_A, passes through PTC1, VD1, D1, GND, D4, PTC2 in sequence, and flows out from IO_485_B; in the negative half cycle of the current, the TVS tube VD2 breaks down, and the current flows into I0_485_B, passes through PTC2, VD2, D2, GND, D3, PTC1 in sequence, and flows out from I0_485_A. The instantaneous current makes the thermistor operate, and the heating impedance of the thermistor becomes very large. The formed loop makes the 485_A and 485_B of the subsequent 485 chip short-circuited without being damaged, which plays a protective role. When the wrong connection is removed, the TVS returns to the normal open circuit state, and the circuit is normal.

[0017] In the circuit of the utility model, the junction capacitance of the diode is small, and the junction capacitance of the transient voltage suppression diode is large.

[0018] The junction capacitances of diodes D1, D2, D3, and D4 are all 16 pF. The junction capacitances of transient voltage suppressor diodes (TVS tubes) are large, and the junction capacitances of VD1 and VD2, CVD1 and CVD2, are all 1000 pF. Using the capacitors in series, the junction capacitance of 485_A is calculated as CA = CD3 + 1 / (1 / CVD1 + 1 / CD1) = 16 + 14.75 = 30.75 pF.

[0019] Similarly, the junction capacitance on 485_B is also 30.75 pF. By using the principle of series-parallel connection of junction capacitances, the junction capacitance on the signal line is reduced from 1000 pF when TVS protection is used alone to 30.75 pF in the present invention.

[0020] When the 485 high-speed communication rate is 1M (the junction capacitance on the signal line is required to be less than 50pF), normal communication can be guaranteed.

[0021] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-speed 485 communication interface protection circuit, characterized in that: It includes: Signal lines IO 485A and IO 485B; Diode D1, diode D2 and transient voltage suppression diode VD1: diode D1 and transient voltage suppression diode VD1 are connected in series and then connected in parallel with diode D2. One end of the parallel circuit is connected to the signal line IO 485A, and the other end is grounded GND. Diode D3, diode D4 and transient voltage suppression diode VD2: diode D3 and transient voltage suppression diode VD2 are connected in series and then connected in parallel with diode D4. One end of the parallel circuit is connected to the signal line IO 485B, and the other end is grounded GND. Thermistor PTC1 and thermistor PTC2: The two thermistors PTC1 and PTC2 are connected to the signal lines IO485A and IO485B respectively.

2. The high-speed 485 communication interface protection circuit according to claim 1, characterized in that: The junction capacitance of diode D1, diode D2, diode D3 and diode D4 is 16 pF.

3. The high-speed 485 communication interface protection circuit according to claim 1, characterized in that: The junction capacitance of the transient voltage suppression diode VD1 and the transient voltage suppression diode VD2 are both 1000pF.

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