Digital quantity output circuit for programmable logic controller

Abstract

The invention relates to the technical field of electronic circuits, in particular to a digital quantity output circuit for a programmable logic controller, which comprises an optical coupling isolator and an NMOS (N-channel Metal Oxide Semiconductor) tube integrated chip with the model of NSO5604, when the optical coupling isolator receives a first low-level signal output by the microprocessor, connection between the first input end and the second input end is conducted. The optical coupling isolator is also used for conducting the connection between the first output end and the second output end when the connection between the first input end and the second input end is conducted, so that the second power supply outputs the power supply voltage to the first input end of the integrated chip; and the integrated chip is used for outputting a second low-level signal to the external load when receiving the power supply voltage output by the second power supply. Functional circuits of over-current protection, short-circuit protection, temperature monitoring, over-temperature protection, chip resetting, chip enabling and the like are integrated in the integrated chip, so that the occupied area of the circuits is greatly reduced, and the power consumption is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of electronic circuits, and in particular to a digital quantity output circuit for a programmable logic controller. Background Art

[0002] With the rapid development of industrial automation and information technology, programmable logic controllers (PLCs) are increasingly used in the field of industrial control. As an important industrial control device, PLC is mainly responsible for collecting, processing and outputting various signals in the production process to achieve automatic control of the production process. In the PLC system, the digital output circuit is one of the key components, which is responsible for converting the digital signal processed by the PLC into a physical signal that can be used to drive external devices.

[0003] Traditional digital output circuit designs are mostly built with discrete electronic components. This design method requires a large number of electronic components to realize the digital output function, resulting in a large footprint on the circuit board. In addition, a large number of electronic components will also generate large power consumption during operation, which not only increases energy consumption, but may also cause serious heating of the circuit, affecting the stability and service life of the equipment.

[0004] In addition, the functions of the circuits built with discrete electronic components are relatively simple and cannot meet the increasingly complex industrial control needs. With the development of industrial control technology, higher requirements are placed on the functions and performance of digital output circuits.

[0005] The above contents are only used to assist in understanding the technical solution of the present invention and do not constitute an admission that the above contents are prior art. Summary of the invention

[0006] The main purpose of the present invention is to provide a digital output circuit for a programmable logic controller, aiming to solve the technical problems that the traditional digital output circuit design is built with discrete electronic components, occupies a large area, consumes high power and has a single function.

[0007] To achieve the above object, the present invention provides a digital quantity output circuit for a programmable logic controller, the circuit comprising: an optical coupler isolator and an NMOS tube integrated chip of model NSO5604; The first input end of the optocoupler isolator is connected to the first power supply, the second input end of the optocoupler isolator is connected to the first output end of the microprocessor, the first output end of the optocoupler isolator is connected to the second power supply, the second output end of the optocoupler isolator is connected to the first input end of the integrated chip, and the first output end of the integrated chip is connected to an external load; The optical coupler isolator is used to conduct the connection between the first input terminal and the second input terminal when receiving the first low level signal output by the microprocessor; The optical coupler isolator is further used to conduct the connection between the first output terminal and the second output terminal when the connection between the first input terminal and the second input terminal is conducted, so that the second power supply outputs the power supply voltage to the first input terminal of the integrated chip; The integrated chip is used to output a second low level signal to the external load when receiving the power supply voltage output by the second power supply.

[0008] Optionally, the circuit further comprises: a switch unit; The switch unit is respectively connected to the second output terminal of the microprocessor, the first power supply and the first input terminal of the optocoupler isolator; The switch unit is used to conduct the connection between the first power supply and the first input terminal of the optocoupler isolator when the microprocessor is powered on.

[0009] Optionally, the switch unit includes: a first resistor, a second resistor and a first switch tube; Among them, the first end of the first resistor is connected to the microprocessor, the second end of the first resistor is respectively connected to the first end of the second resistor and the control end of the first switch tube, the second end of the second resistor is connected to the first power supply, the input end of the first switch tube is connected to the first power supply, and the output end of the first switch tube is connected to the first input end of the optocoupler isolator.

[0010] Optionally, the circuit further includes: a first filtering unit and a second filtering unit; Wherein, the first filtering unit is respectively connected to the first input terminal and the second input terminal of the optocoupler isolator, and the second filtering unit is respectively connected to the second output terminal of the optocoupler isolator and the first input terminal of the integrated chip; The first filtering unit is used to filter the voltage at the first input end of the optocoupler isolator; The second filtering unit is used to filter the voltage at the second output end of the optocoupler isolator.

[0011] Optionally, the first filtering unit includes: a third resistor, a fourth resistor and a first capacitor, and the second filtering unit includes: a fifth resistor, a sixth resistor and a second capacitor; Wherein, the first end of the third resistor is connected to the first output end of the microprocessor, the second end of the third resistor is connected to the first end of the fourth resistor, the first end of the first capacitor and the second input end of the optocoupler isolator, and the second end of the fourth resistor is connected to the first power supply, the second end of the first capacitor and the first input end of the optocoupler isolator; The first end of the fifth resistor is respectively connected to the first end of the sixth resistor and the second output end of the optocoupler isolator, the second end of the sixth resistor is respectively connected to the first end of the second capacitor and the first input end of the integrated chip, and the second end of the fifth resistor and the second end of the second capacitor are grounded.

[0012] Optionally, the circuit further comprises: an interface protection unit; One end of the interface protection unit is connected to the first output end of the integrated chip, and the other end of the interface protection unit is grounded; The interface protection unit is used to conduct the connection between the first output terminal of the integrated chip and the ground when an abnormal voltage appears at the first output terminal of the integrated chip.

[0013] Optionally, the interface protection unit includes: a first voltage stabilizing diode; The anode of the first voltage stabilizing diode is grounded, and the cathode of the first voltage stabilizing diode is connected to the first output terminal of the integrated chip.

[0014] Optionally, the circuit further includes: a third filtering unit and a fourth filtering unit; Wherein, the third filtering unit is connected to the first power supply, and the fourth filtering unit is connected to the second power supply; The third filtering unit is used to filter the power supply voltage output by the first power supply; The fourth filtering unit is used to filter the power supply voltage output by the second power supply.

[0015] Optionally, the third filtering unit includes a third capacitor, and the fourth filtering unit includes a fourth capacitor; The first end of the third capacitor is connected to the first power supply, the second end of the third capacitor is grounded, the first end of the fourth capacitor is connected to the second power supply, and the second end of the fourth capacitor is grounded.

[0016] Optionally, the circuit includes a plurality of the optocoupler isolators; The first input ends of the multiple optocouplers are connected to the first power supply, the second input ends of the multiple optocouplers are respectively connected to different output ends of the microprocessor, the first output ends of the multiple optocouplers are connected to the second power supply, and the second output ends of the multiple optocouplers are respectively connected to different input ends of the integrated chip. Correspondingly, different output ends of the integrated chip corresponding to different input ends are connected to an external load.

[0017] The present invention provides a digital quantity output circuit for a programmable logic controller, the circuit comprising: an optocoupler isolator and an NMOS tube integrated chip of model NSO5604; wherein the first input end of the optocoupler isolator is connected to a first power supply, the second input end of the optocoupler isolator is connected to a first output end of a microprocessor, the first output end of the optocoupler isolator is connected to a second power supply, the second output end of the optocoupler isolator is connected to the first input end of the integrated chip, and the first output end of the integrated chip is connected to an external load; the optocoupler isolator is used to conduct the connection between the first input end and the second input end when receiving a first low-level signal output by the microprocessor; the optocoupler isolator is also used to conduct the connection between the first output end and the second output end when the connection between the first input end and the second input end is conducted, so that the second power supply outputs a power supply voltage to the first input end of the integrated chip; the integrated chip is used to output a second low-level signal to the external load when receiving the power supply voltage output by the second power supply. In the present invention, the NMOS tube integrated chip model NSO5604 integrates multiple NMOS tube output circuits into one chip, and the chip also integrates overcurrent protection, short circuit protection, temperature monitoring, over-temperature protection, chip reset, chip enable and other functional circuits. The integration of many functional circuits into one chip greatly reduces the circuit occupation area and reduces power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0019] Figure 1 A structural schematic diagram of an embodiment of a digital quantity output circuit for a programmable logic controller proposed by the present invention; Figure 2 A schematic structural diagram of another embodiment of a digital quantity output circuit for a programmable logic controller proposed by the present invention; Figure 3 This is a circuit schematic diagram of an embodiment of a digital quantity output circuit for a programmable logic controller proposed by the present invention.

[0020] Description of Figure Numbers: Label name Label name 10 Switching unit 20 The first filter unit 30 The second filter unit 40 Interface protection unit 50 The third filter unit 60 Fourth filter unit OT Optocoupler Isolator U1 Integrated Chip ZD1 The first Zener diode R1~R6 The first to sixth resistors C1~C4 The first to fourth capacitors Q1 The first switch IN1~IN4 The first to fourth input terminals of U1 OUT1~OUT4 The first to fourth output terminals of U1 V1~V2 First to second power supply The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0021] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0024] In addition, the descriptions of "first", "second", etc. in the present invention are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0025] Reference Figure 1 In this embodiment, the digital quantity output circuit for the programmable logic controller includes: an optical coupler isolator OT and an NMOS tube integrated chip U1 of model NSO5604; The first input end of the optocoupler isolator OT is connected to the first power supply V1, the second input end of the optocoupler isolator OT is connected to the first output end of the microprocessor, the first output end of the optocoupler isolator OT is connected to the second power supply V2, the second output end of the optocoupler isolator OT is connected to the first input end of the integrated chip U1, and the first output end of the integrated chip U1 is connected to an external load; The optical coupler isolator OT is used to conduct the connection between the first input terminal and the second input terminal when receiving the first low level signal output by the microprocessor; The optical coupler isolator OT is further used to conduct the connection between the first output terminal and the second output terminal when the connection between the first input terminal and the second input terminal is conducted, so that the second power supply V2 outputs the power supply voltage to the first input terminal of the integrated chip U1; The integrated chip U1 is used to output a second low level signal to the external load when receiving the power supply voltage output by the second power supply V2.

[0026] It should be noted that, in this embodiment, the optocoupler isolator OT can be an optocoupler element of model LTV-217-CG, or other components that realize electrical isolation function, and this embodiment is not limited to this. The first power supply V1 can be a 3.3V DC power supply, or other power supply that can drive the first output terminal and the second output terminal of the optocoupler isolator OT to be conductive, and this embodiment is not limited to this. The second power supply V2 can be a 5V DC power supply, or other power supply that can drive the integrated chip U1 to output a second low-level signal, and this embodiment is not limited to this.

[0027] It should be understood that the microprocessor can output a corresponding first low-level signal according to the control instruction of the programmable logic controller, and the first low-level signal refers to a low-level digital signal that can be used to drive the first input terminal and the second input terminal of the optocoupler isolator OT to be turned on. The NMOS tube integrated chip U1 with model number NSO5604 can output a second low-level signal to an external load when the microprocessor outputs the first low-level signal, wherein the second low-level signal refers to a low-level physical signal used to drive the external load. The microprocessor outputs the first low-level signal, and then the integrated chip U1 outputs the second low-level signal, thereby realizing the conversion of the digital signal inside the programmable logic controller into a physical signal that can be used to drive the external load.

[0028] In addition, in this embodiment, the integrated chip U1 integrates functional circuits such as overcurrent protection, short circuit protection, temperature monitoring, over-temperature protection, chip reset, and chip enable, which enhances the functionality of the digital output circuit. In addition, many functional circuits are integrated into one chip, which greatly reduces the circuit footprint. Moreover, compared with the traditional digital quantization output circuit designed with discrete electronic components, the digital output circuit in this example also reduces power consumption by using the NMOS tube integrated chip U1 with model NSO5604.

[0029] In a specific implementation, when the microprocessor receives a control instruction from the programmable logic controller, it outputs a corresponding first low-level signal to the second input terminal of the optocoupler isolator OT. Since the first input terminal of the optocoupler isolator OT is connected to the first power supply V1, the first input terminal of the optocoupler isolator OT is connected to the second input terminal, and the optical signal of the optocoupler isolator is transmitted to the output terminal, and then the first output terminal of the optocoupler isolator is connected to the second output terminal, and the second power supply V2 outputs the power supply voltage to the first input terminal of the integrated chip U1, driving the integrated chip U1 to output a second low-level signal to the external load, thereby controlling the external load.

[0030] Furthermore, in order to prevent the first output terminal of the microprocessor from mistakenly outputting the first low-level signal to the optocoupler isolator OT during the power-on process, thereby causing the first input terminal and the second input terminal of the optocoupler isolator OT to be mistakenly connected, refer to Figure 2 , the circuit further comprises: a switch unit 10; The switch unit 10 is respectively connected to the second output terminal of the microprocessor, the first power supply V1 and the first input terminal of the optical coupler isolator OT; The switch unit 10 is used to conduct the connection between the first power supply V1 and the first input terminal of the optical coupler isolator OT when the microprocessor is powered on.

[0031] It should be noted that the switch unit 10 is used to conduct the connection between the first power supply V1 and the first input end of the optocoupler isolator OT when the microprocessor is powered on. At this time, the optocoupler isolator OT can only be turned on when the first output end of the microprocessor outputs a first low-level signal to the second input end of the optocoupler isolator OT, thereby avoiding the first output end of the microprocessor mistakenly outputting a first low-level signal to the optocoupler isolator OT during the power-on process, thereby causing the first input end and the second input end of the optocoupler isolator OT to be misconnected, thereby enhancing the output reliability of the microprocessor. Among them, the switch unit 10 can be a commonly used switching component, such as a triode, a MOS tube, or an IGBT, etc., which is not limited in this embodiment.

[0032] Specifically, refer to Figure 3, the switch unit 10 includes: a first resistor R1, a second resistor R2 and a first switch tube Q1; Among them, the first end of the first resistor R1 is connected to the microprocessor, the second end of the first resistor R1 is respectively connected to the first end of the second resistor R2 and the control end of the first switch tube Q1, the second end of the second resistor R2 is connected to the first power supply V1, the input end of the first switch tube Q1 is connected to the first power supply V1, and the output end of the first switch tube Q1 is connected to the first input end of the optocoupler isolator OT.

[0033] It should be noted that the first resistor R1 is a current limiting resistor, the second resistor R2 is a voltage dividing resistor, and the first switch tube Q1 can be a triode, a MOS tube, or other tubes that realize similar functions, which is not limited in this embodiment.

[0034] In a specific implementation, during the power-on process of the microprocessor, the second output end of the microprocessor does not output a low-level enable signal to the first resistor R1. At this time, the first switch tube Q1 is turned off. Even if the first output end of the microprocessor outputs a first low-level signal to the second input end of the optocoupler isolator OT, the optocoupler isolator OT will not be turned on, thereby avoiding the first output end of the microprocessor from mistakenly outputting a first low-level signal to the optocoupler isolator OT during the power-on process, thereby causing the first input end and the second input end of the optocoupler isolator OT to be misconnected, thereby enhancing the output reliability of the microprocessor. When the microprocessor is powered on, the second output end of the microprocessor outputs a low-level enable signal to the first resistor R1, which is output to the control end of the first switch tube Q1 after current limiting by the first resistor R1. At this time, the first switch tube Q1 is turned on, and the first output end of the microprocessor outputs a first low-level signal to the second input end of the optocoupler isolator OT, and the optocoupler isolator OT is turned on.

[0035] Furthermore, in order to ensure the stability of the input and output signals of the optocoupler isolator OT and enhance the reliability of the circuit operation, refer to Figure 2 , the circuit further includes: a first filtering unit 20 and a second filtering unit 30; The first filter unit 20 is connected to the first input terminal and the second input terminal of the optical coupler isolator OT respectively, and the second filter unit 30 is connected to the second output terminal of the optical coupler isolator OT and the first input terminal of the integrated chip U1 respectively; The first filtering unit 20 is used to filter the voltage at the first input end of the optical coupler isolator OT; The second filtering unit 30 is used to filter the voltage at the second output end of the optical coupler isolator OT.

[0036] It should be noted that the first filtering unit 20 is used to filter out the high-frequency noise and transient interference of the signal at the input end of the optocoupler isolator OT to ensure the quality of the signal at the input end of the optocoupler isolator OT, and the second filtering unit 30 is used to filter out the high-frequency noise and transient interference of the signal at the output end of the optocoupler isolator OT to ensure the quality of the signal at the output end of the optocoupler isolator OT.

[0037] Specifically, refer to Figure 3 , the first filtering unit 20 includes: a third resistor R3, a fourth resistor R4 and a first capacitor C1, and the second filtering unit 30 includes: a fifth resistor R5, a sixth resistor R6 and a second capacitor C2; Wherein, the first end of the third resistor R3 is connected to the first output end of the microprocessor, the second end of the third resistor R3 is connected to the first end of the fourth resistor R4, the first end of the first capacitor C1 and the second input end of the optocoupler isolator OT, and the second end of the fourth resistor R4 is connected to the first power supply V1, the second end of the first capacitor C1 and the first input end of the optocoupler isolator OT; The first end of the fifth resistor R5 is respectively connected to the first end of the sixth resistor R6 and the second output end of the optocoupler isolator OT, the second end of the sixth resistor R6 is respectively connected to the first end of the second capacitor C2 and the first input end of the integrated chip U1, and the second end of the fifth resistor R5 and the second end of the second capacitor C2 are grounded.

[0038] It should be noted that the third resistor R3 is used for current limiting, the fourth resistor R4 and the first capacitor C1 are connected in parallel to form a low-pass filter for filtering the high-frequency noise and transient interference of the signal at the input end of the optocoupler isolator OT, the sixth resistor R6 is used for current limiting, the fifth resistor R5 and the second capacitor C2 are connected in parallel to form a low-pass filter for filtering the high-frequency noise and transient interference of the signal at the output end of the optocoupler isolator OT.

[0039] Furthermore, in order to prevent abnormal voltage from appearing at the first output terminal of the integrated chip U1 and causing damage to the integrated chip U1, refer to Figure 2 , the circuit further comprises: an interface protection unit 40; One end of the interface protection unit 40 is connected to the first output end of the integrated chip U1, and the other end of the interface protection unit 40 is grounded; The interface protection unit 40 is used to connect the first output terminal of the integrated chip U1 to the ground when an abnormal voltage appears at the first output terminal of the integrated chip U1.

[0040] It should be noted that the interface protection circuit is used to connect the first output terminal of the integrated chip U1 to the ground when an abnormal voltage appears at the first output terminal of the integrated chip U1, such as a surge or overvoltage appears at the first output terminal, thereby releasing the abnormal voltage energy to the ground to prevent the abnormal voltage from damaging the integrated chip U1.

[0041] Specifically, refer to Figure 3 , the interface protection unit 40 includes: a first voltage stabilizing diode ZD1; The anode of the first voltage stabilizing diode ZD1 is grounded, and the cathode of the first voltage stabilizing diode ZD1 is connected to the first output terminal of the integrated chip U1.

[0042] It should be noted that when an abnormal voltage appears at the first output terminal of the integrated chip U1, such as a surge or overvoltage appears at the first output terminal, the first voltage zener diode ZD1 will be broken down and turned on, thereby connecting the first output terminal of the integrated chip U1 to the ground, thereby releasing the abnormal voltage energy to the ground, preventing the abnormal voltage from damaging the integrated chip U1.

[0043] Furthermore, in order to ensure the stability of the power supply voltage output by the first power supply V1 and the second power supply V2, refer to Figure 2 , the circuit further includes: a third filtering unit 50 and a fourth filtering unit 60; Wherein, the third filtering unit 50 is connected to the first power supply V1, and the fourth filtering unit 60 is connected to the second power supply V2; The third filtering unit 50 is used to filter the power supply voltage output by the first power supply V1; The fourth filtering unit 60 is used to filter the power supply voltage output by the second power supply V2.

[0044] It should be noted that the third filtering unit 50 is used to filter out high-frequency noise and transient interference in the power supply voltage output by the first power supply V1, thereby ensuring the stability of the power supply voltage output by the first power supply V1, and the fourth filtering unit 60 is used to filter out high-frequency noise and transient interference in the power supply voltage output by the second power supply V2, thereby ensuring the stability of the power supply voltage output by the second power supply V2.

[0045] Specifically, refer to Figure 3 The third filtering unit 50 includes a third capacitor C3, and the fourth filtering unit 60 includes a fourth capacitor C4; wherein a first end of the third capacitor C3 is connected to the first power supply V1, a second end of the third capacitor C3 is grounded, a first end of the fourth capacitor C4 is connected to the second power supply V2, and a second end of the fourth capacitor C4 is grounded.

[0046] Furthermore, in order to enhance the anti-interference performance of the digital output circuit, refer to Figure 3 , the circuit includes a plurality of the optical coupler isolators OT; The first input ends of the multiple optocouplers OT are connected to the first power supply V1, the second input ends of the multiple optocouplers OT are respectively connected to different output ends of the microprocessor, the first output ends of the multiple optocouplers OT are connected to the second power supply V2, and the second output ends of the multiple optocouplers OT are respectively connected to different input ends of the integrated chip U1. Correspondingly, different output ends of the integrated chip U1 corresponding to different input ends are connected to external loads.

[0047] It should be noted that the current digital output circuit often uses one signal channel, which makes it difficult to accurately control the external load and has insufficient anti-interference ability. For this reason, this embodiment sets up multiple signal channels, which are respectively connected to different output terminals of the microprocessor and different input terminals of the integrated chip U1, thereby improving the control accuracy of the digital output circuit. It can be understood that each signal channel can be composed of any components in the above-mentioned embodiment, and this embodiment is not limited to this.

[0048] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A digital quantity output circuit for a programmable logic controller, characterized in that: The circuit includes: an optocoupler isolator and an NMOS tube integrated chip of model NSO5604; The first input end of the optocoupler isolator is connected to the first power supply, the second input end of the optocoupler isolator is connected to the first output end of the microprocessor, the first output end of the optocoupler isolator is connected to the second power supply, the second output end of the optocoupler isolator is connected to the first input end of the integrated chip, and the first output end of the integrated chip is connected to an external load; The optical coupler isolator is used to conduct the connection between the first input terminal and the second input terminal when receiving the first low level signal output by the microprocessor; The optical coupler isolator is further used to conduct the connection between the first output terminal and the second output terminal when the connection between the first input terminal and the second input terminal is conducted, so that the second power supply outputs the power supply voltage to the first input terminal of the integrated chip; The integrated chip is used to output a second low level signal to the external load when receiving the power supply voltage output by the second power supply.

2. The digital quantity output circuit for a programmable logic controller according to claim 1, characterized in that: The circuit further comprises: a switch unit; The switch unit is respectively connected to the second output terminal of the microprocessor, the first power supply and the first input terminal of the optocoupler isolator; The switch unit is used to conduct the connection between the first power supply and the first input terminal of the optocoupler isolator when the microprocessor is powered on.

3. The digital quantity output circuit for a programmable logic controller according to claim 2, characterized in that: The switch unit comprises: a first resistor, a second resistor and a first switch tube; Among them, the first end of the first resistor is connected to the microprocessor, the second end of the first resistor is respectively connected to the first end of the second resistor and the control end of the first switch tube, the second end of the second resistor is connected to the first power supply, the input end of the first switch tube is connected to the first power supply, and the output end of the first switch tube is connected to the first input end of the optocoupler isolator.

4. The digital quantity output circuit for a programmable logic controller according to claim 1, characterized in that: The circuit further comprises: a first filtering unit and a second filtering unit; Wherein, the first filtering unit is respectively connected to the first input terminal and the second input terminal of the optocoupler isolator, and the second filtering unit is respectively connected to the second output terminal of the optocoupler isolator and the first input terminal of the integrated chip; The first filtering unit is used to filter the voltage at the first input end of the optocoupler isolator; The second filtering unit is used to filter the voltage at the second output end of the optocoupler isolator.

5. The digital quantity output circuit for a programmable logic controller according to claim 4, characterized in that: The first filtering unit includes: a third resistor, a fourth resistor and a first capacitor, and the second filtering unit includes: a fifth resistor, a sixth resistor and a second capacitor; Wherein, the first end of the third resistor is connected to the first output end of the microprocessor, the second end of the third resistor is connected to the first end of the fourth resistor, the first end of the first capacitor and the second input end of the optocoupler isolator, and the second end of the fourth resistor is connected to the first power supply, the second end of the first capacitor and the first input end of the optocoupler isolator; The first end of the fifth resistor is respectively connected to the first end of the sixth resistor and the second output end of the optocoupler isolator, the second end of the sixth resistor is respectively connected to the first end of the second capacitor and the first input end of the integrated chip, and the second end of the fifth resistor and the second end of the second capacitor are grounded.

6. The digital quantity output circuit for a programmable logic controller according to claim 1, characterized in that: The circuit further comprises: an interface protection unit; One end of the interface protection unit is connected to the first output end of the integrated chip, and the other end of the interface protection unit is grounded; The interface protection unit is used to conduct the connection between the first output terminal of the integrated chip and the ground when an abnormal voltage appears at the first output terminal of the integrated chip.

7. The digital quantity output circuit for a programmable logic controller according to claim 6, characterized in that: The interface protection unit includes: a first voltage stabilizing diode; The anode of the first voltage stabilizing diode is grounded, and the cathode of the first voltage stabilizing diode is connected to the first output terminal of the integrated chip.

8. The digital quantity output circuit for a programmable logic controller according to claim 1, characterized in that: The circuit further includes: a third filtering unit and a fourth filtering unit; Wherein, the third filtering unit is connected to the first power supply, and the fourth filtering unit is connected to the second power supply; The third filtering unit is used to filter the power supply voltage output by the first power supply; The fourth filtering unit is used to filter the power supply voltage output by the second power supply.

9. The digital quantity output circuit for a programmable logic controller according to claim 8, characterized in that: The third filtering unit includes a third capacitor, and the fourth filtering unit includes a fourth capacitor; The first end of the third capacitor is connected to the first power supply, the second end of the third capacitor is grounded, the first end of the fourth capacitor is connected to the second power supply, and the second end of the fourth capacitor is grounded.

10. The digital quantity output circuit for a programmable logic controller according to claim 1, characterized in that: The circuit includes a plurality of the optocoupler isolators; The first input ends of the multiple optocouplers are connected to the first power supply, the second input ends of the multiple optocouplers are respectively connected to different output ends of the microprocessor, the first output ends of the multiple optocouplers are connected to the second power supply, and the second output ends of the multiple optocouplers are respectively connected to different input ends of the integrated chip. Correspondingly, different output ends of the integrated chip corresponding to different input ends are connected to an external load.

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