DI input circuit capable of preventing low-voltage false triggering

Abstract

The utility model discloses a DI input circuit capable of preventing low-voltage false triggering, which relates to the technical field of DI input and comprises an optocoupler, a first voltage stabilizing diode, a second voltage stabilizing diode, a transient suppression diode, a first resistor, a second resistor and a third resistor, a collector electrode of the optocoupler is connected with power supply voltage VCC3V3, an emitter electrode of the optocoupler is grounded, and the collector electrode of the optocoupler is grounded. The anode of the first voltage stabilizing diode is connected with the anode of the optocoupler, and the cathode of the first voltage stabilizing diode is connected with the input common end DICOM + of the DI module through the second resistor; the anode of the second voltage stabilizing diode is connected with the cathode of the optocoupler, and the cathode of the second voltage stabilizing diode is connected with the input end DI0 of the DI module through a third resistor; and two ends of the transient suppression diode are respectively connected with the second resistor and the third resistor. According to the utility model, the isolation between a field signal side and a system side is realized, the interference is reduced, the stability of the DCS system is improved, and the circuit can be effectively protected at the same time.

Description

Technical Field

[0001] The utility model relates to the technical field of DI (Digital Input), and in particular to a DI input circuit capable of preventing false triggering due to low voltage. Background Art

[0002] In a DCS (Distributed Control System), according to the principle of risk dispersion and the relative independence of the process, each typical process section needs to be equipped with a pair of redundant main controllers. The main controllers perform the following tasks cyclically under the set control cycle: collect field data from I / O devices, execute control logic operations, output control instructions to I / O devices, and exchange data with the operator station. I / O devices are used to collect field signals or output control signals, and mainly include analog input devices, analog output devices, switch input (i.e. digital input DI devices), switch output devices, pulse input devices, and some other mixed signal type I / O devices or special I / O devices. Since I / O devices collect more signals, the system needs to improve its anti-interference ability, and the circuit's surge protection ability also needs to be improved.

[0003] The existing DI input circuit, such as a DCS control system digital input circuit disclosed in the patent document with publication number CN201130324Y, adds a bypass capacitor to the input end of the DI module of the DCS control system, one end of the bypass capacitor is connected to the input end of the DI module, and the other end is grounded; the bypass capacitor is connected to the DI module in the DCS control wiring cabinet; the bypass capacitor specification is 0.22μF / 250V. This solution uses a bypass capacitor, which has the function of eliminating line-to-line induced voltage interference for the DI input of all types of control systems, and can avoid DI input misoperation. However, after careful analysis by the inventor, it was found that it was impossible to isolate the field signal side from the system side, and it was also impossible to effectively protect the circuit when encountering a surge impact circuit. Utility Model Content

[0004] The purpose of the utility model is to overcome the above-mentioned problems existing in the prior art and provide a DI input circuit that prevents false triggering of low voltage. The utility model realizes the isolation of the field signal side and the system side, reduces interference, improves the stability of the DCS system, and can effectively protect the circuit.

[0005] In order to achieve the above purpose, the technical solution adopted by the utility model is as follows:

[0006] A DI input circuit for preventing false triggering of low voltage includes an optocoupler OP1, a first zener diode ZD1, a second zener diode ZD2, a transient suppression diode TVS1, a first resistor R1, a second resistor R2 and a third resistor R3, wherein the collector of the optocoupler OP1 is connected to a power supply voltage VCC_3V3 through the first resistor R1, the emitter of the optocoupler OP1 is grounded, the anode of the first zener diode ZD1 is connected to the anode of the optocoupler OP1, the cathode of the first zener diode ZD1 is connected to an input common terminal DI_COM+ of a DI module through the second resistor R2; the anode of the second zener diode ZD2 is connected to the cathode of the optocoupler OP1, and the cathode of the second zener diode ZD2 is connected to an input terminal DI0 of the DI module through the third resistor R3; and the two ends of the transient suppression diode TVS1 are respectively connected to the second resistor R2 and the third resistor R3.

[0007] A first capacitor C1 is connected between the anode and cathode of the optical coupler OP1.

[0008] A second capacitor C2 connected in parallel with the transient voltage suppressor diode TVS1 is connected between the second resistor R2 and the third resistor R3.

[0009] A fourth resistor R4 is connected between the anode of the first zener diode ZD1 and the anode of the second zener diode ZD2.

[0010] The first resistor R1 is a 1K / 1% resistor, and the second resistor R2 and the third resistor R3 are both 1.65K / 1% resistors.

[0011] The fourth resistor R4 is a 1K / 1% resistor.

[0012] By adopting the above technical solution, the beneficial technical effects of the utility model are:

[0013] 1. The DI input circuit described in the utility model adopts an optocoupler OP1. Since the optocoupler OP1 has the functions of optical signal transmission and photoelectric isolation, it has the advantages of high-speed transmission, effective isolation of interference and noise between input and output circuits, effective resistance to various electromagnetic interference and environmental interference, and effective reduction of power consumption. At the same time, the entire circuit has no mechanical contact parts, so it also has a long service life. The first voltage zener diode ZD1 and the second voltage zener diode ZD2 used can both provide stable voltages, and have large power and voltage stabilization current, which is conducive to simplifying the volume of the circuit. The transient suppression diode TVS1 used can protect sensitive electronic devices from damage or latch effects caused by electrical overload, lightning, cable discharge events and electrostatic discharge, so that it can effectively suppress transient voltages under high voltage and high energy conditions, thereby achieving effective protection of the circuit. In addition, the first resistor R1 used can pull up the output signal of the optocoupler OP1 to avoid being suspended in an unknown state and ensure the normal operation of the circuit. The second resistor R2 and the third resistor R3 are current limiting resistors, which limit the current flowing through the optocoupler OP1 to about 5 mA, thereby ensuring that the optocoupler OP1 is not burned due to overcurrent and effectively extending the service life of the optocoupler OP1.

[0014] In summary, the DI input circuit of the utility model is not only simple in structure and easy to implement, but also can achieve effective isolation between the field signal side and the system side, reduce interference, improve the stability of the DCS system, and effectively protect the circuit.

[0015] 2. In the present invention, a first capacitor C1 is connected between the anode and cathode of the optical coupler OP1, which utilizes the filtering characteristics of the capacitor to filter out high-frequency interference and prevent false detection.

[0016] 3. The utility model has a second capacitor C2 connected in parallel with the transient suppression diode TVS1 between the second resistor R2 and the third resistor R3, which utilizes the charging characteristics of the capacitor to absorb the interference energy input by the interface and improve the system stability.

[0017] 4. In the present invention, a fourth resistor R4 is connected between the anode of the first voltage zener diode ZD1 and the anode of the second voltage zener diode ZD2. The fourth resistor R4 is a voltage dividing resistor, which can protect the optical coupler OP1 from damage and extend its service life.

[0018] 5. The utility model limits the resistance value of each resistor, which can ensure that the current of the optical coupler OP1 is about 5mA, which can not only work normally but also extend the service life of the optical coupler OP1. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a circuit schematic diagram of the utility model. DETAILED DESCRIPTION

[0020] The utility model provides a DI input circuit to prevent false triggering of low voltage, such as Figure 1 As shown, it includes an optical coupler OP1, a first voltage zener diode ZD1, a second voltage zener diode ZD2, a transient suppression diode TVS1, a first resistor R1, a second resistor R2 and a third resistor R3. Among them, the optical coupler OP1 includes an anode 1, a cathode 2, an emitter 3 and a collector 4, the collector 4 of the optical coupler OP1 is used to connect to the external MCU, and the collector 4 of the optical coupler OP1 is also connected to the power supply voltage VCC_3V3 through the first resistor R1, the emitter 3 of the optical coupler OP1 is grounded, the anode of the first voltage zener diode ZD1 is connected to the anode 1 of the optical coupler OP1, and the cathode of the first voltage zener diode ZD1 is connected to the input common terminal DI_COM+ of the DI module through the second resistor R2; the anode of the second voltage zener diode ZD2 is connected to the cathode 2 of the optical coupler OP1, and the cathode of the second voltage zener diode ZD2 is connected to the input terminal DI0 of the DI module through the third resistor R3; the two ends of the transient suppression diode TVS1 are respectively connected to the second resistor R2 and the third resistor R3.

[0021] In an embodiment of the present invention, the DI input circuit further includes a first capacitor C1 , and the first capacitor C1 is connected between the anode and the cathode of the optical coupler OP1 .

[0022] In an embodiment of the present invention, the DI input circuit further includes a second capacitor C2, which is connected between the second resistor R2 and the third resistor R3 and is connected in parallel with the transient voltage suppressor diode TVS1.

[0023] In one embodiment of the present utility model, a fourth resistor R4 is connected between the anode of the first Zener diode ZD1 and the anode of the second Zener diode ZD2, and one end of the fourth resistor R4 is located between the first capacitor C1 and the anode of the first Zener diode ZD1, and the other end is located between the first capacitor C1 and the anode of the second Zener diode ZD2.

[0024] In this embodiment, the first resistor R1 is a 1K / 1% resistor, the second resistor R2 and the third resistor R3 are both 1.65K / 1% resistors, and the fourth resistor R4 is a 1K / 1% resistor.

[0025] In one embodiment of the utility model, the model of the optical coupler OP1 is OR-3H4B-TP-G. OR-3H4B-TP-G adopts optical signal transmission, and has the characteristics of high-speed transmission; it also adopts photoelectric isolation technology, which can effectively isolate the interference and noise between the input and output circuits, and can effectively resist various electromagnetic interference and environmental interference, and can effectively reduce power consumption. And there is no mechanical contact part, and it also has a long service life.

[0026] In one embodiment of the utility model, the first voltage zener diode ZD1 and the second voltage zener diode ZD2 are both of the model MM1W5V6. MM1W5V6 can provide a stable voltage of 5.6V, with a power of 1W and a voltage stabilization current of 45mA. The package specification of MM1W5V6 is SOD-123FL, so that it occupies less space on the circuit board.

[0027] In one embodiment of the utility model, the transient suppression diode TVS1 is model SMBJ51CA. It is mainly used to protect sensitive electronic devices from damage or latch-up effects caused by electrical overload, lightning, cable discharge events and electrostatic discharge. This chip is characterized by a large cross-sectional area, which enables it to effectively suppress transient voltages under high voltage and high energy conditions. In addition, SMBJ51CA uses passivated glass chip contacts to ensure high-temperature welding, 260°C / 40 seconds for the terminal, and the plastic package has been certified by UL flammability classification 94V-O, and is halogen-free and RoHS-compliant.

[0028] The working principle of this utility model:

[0029] The utility model circuit adopts optocoupler isolation. The input common terminal DI_COM+ is generally connected to 24V. When the input terminal DI0 is connected to a low level, the optocoupler conducts the MCU_PE0 pin to the ground, and the external MCU detects a low level; when the input terminal DI0 is connected to a high level, the optocoupler is not turned on, MCU_PE0 is in a pull-up state, and the external MCU detects a high level. In order to prevent false triggering of low voltage, the reverse breakdown characteristics of the first Zener diode ZD1 and the second Zener diode ZD2 are used. Only when the reverse voltage across the first Zener diode ZD1 and the second Zener diode ZD2 is greater than 5.6V, current will pass through the two Zener diodes. In this way, a small voltage interference signal cannot turn on the optocoupler. The optocoupler can only be triggered when the input terminal DI0 and the input common terminal DI_COM+ reach a larger voltage difference threshold, which greatly enhances the anti-interference ability of the circuit.

[0030] The above description is only a specific implementation method of the present utility model. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all disclosed features, or all methods or steps in the process, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A DI input circuit for preventing false triggering due to low voltage, characterized in that: It includes an optocoupler OP1, a first zener diode ZD1, a second zener diode ZD2, a transient suppression diode TVS1, a first resistor R1, a second resistor R2 and a third resistor R3. The collector of the optocoupler OP1 is connected to the power supply voltage VCC_3V3 through the first resistor R1, the emitter of the optocoupler OP1 is grounded, the anode of the first zener diode ZD1 is connected to the anode of the optocoupler OP1, and the cathode of the first zener diode ZD1 is connected to the input common terminal DI_COM+ of the DI module through the second resistor R2; the anode of the second zener diode ZD2 is connected to the cathode of the optocoupler OP1, and the cathode of the second zener diode ZD2 is connected to the input terminal DI0 of the DI module through the third resistor R3; and the two ends of the transient suppression diode TVS1 are respectively connected to the second resistor R2 and the third resistor R3.

2. A DI input circuit for preventing false triggering due to low voltage according to claim 1, characterized in that: A first capacitor C1 is connected between the anode and cathode of the optical coupler OP1.

3. A DI input circuit for preventing false triggering due to low voltage according to claim 1, characterized in that: A second capacitor C2 connected in parallel with the transient voltage suppressor diode TVS1 is connected between the second resistor R2 and the third resistor R3.

4. A DI input circuit for preventing false triggering at low voltage according to any one of claims 1 to 3, characterized in that: A fourth resistor R4 is connected between the anode of the first Zener diode ZD1 and the anode of the second Zener diode ZD2.

5. A DI input circuit for preventing false triggering due to low voltage according to claim 1, characterized in that: The first resistor R1 is a 1K / 1% resistor, and the second resistor R2 and the third resistor R3 are both 1.65K / 1% resistors.

6. A DI input circuit for preventing false triggering due to low voltage according to claim 4, characterized in that: The fourth resistor R4 is a 1K / 1% resistor.

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