Over-current protection circuit for digital quantity output module of programmable logic controller

Abstract

The invention relates to the technical field of electronic circuits, in particular to an overcurrent protection circuit for a digital quantity output module of a programmable logic controller, which comprises a voltage acquisition unit, a first switch unit and a second switch unit, the voltage acquisition unit is used for acquiring power supply voltage output by a power supply and outputting a conduction signal to the first switch unit when the power supply voltage is greater than a preset voltage threshold value; the first switch unit is used for conducting power supply connection between the power supply and the second switch unit when receiving a conduction signal; and the second switch unit is used for disconnecting the power supply from the load when the power supply connection is conducted. The power supply voltage is monitored in real time through the voltage acquisition unit, the first switch unit quickly responds and conducts a control signal, the second switch unit quickly disconnects load power supply after receiving the signal, and the problems of high cost and low reliability in an existing overcurrent protection scheme are effectively solved.

Description

Technical Field

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

[0002] In the field of industrial automation, programmable logic controllers (PLCs) are key devices for realizing various control functions and are widely used in automation of simple mechanical control and complex production processes. PLCs are connected to external actuators (such as motors, valves, indicator lights, etc.) through their digital output modules to achieve precise control of these devices. However, due to the complexity of the actual application environment, especially the diversity of external loads and possible operational errors or failures, the output modules of PLCs are often faced with the risk of overcurrent. Overcurrent may not only cause damage to the output module itself, but may also cause more serious equipment failures and even safety hazards, greatly affecting production efficiency and safety.

[0003] At present, in order to deal with this problem, there are several overcurrent protection solutions on the market. For example, as a simple and common protection measure, the fuse can automatically disconnect the circuit when the current exceeds the preset value, but its disadvantage is that once triggered, it needs to be replaced, the maintenance cost is high, and the response time is long; although the overcurrent relay can achieve automatic reset, its setting is not flexible enough, and the physical contacts are easy to wear, which affects the service life; although the traditional electronic overcurrent protection circuit can provide faster response speed and higher reliability, the design is complex and the cost is relatively high. It can be seen that the existing overcurrent protection solutions generally have the problems of high cost and low reliability, and cannot fully meet the needs of industrial sites for overcurrent protection of PLC output modules.

[0004] 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

[0005] The main purpose of the present invention is to provide an overcurrent protection circuit and system for a digital output module of a programmable logic controller, aiming to solve the technical problems of high cost and low reliability in existing overcurrent protection solutions, such as fuses, overcurrent relays or traditional electronic overcurrent protection circuits.

[0006] To achieve the above object, the present invention provides an overcurrent protection circuit for a digital output module of a programmable logic controller, the circuit comprising: a voltage acquisition unit, a first switch unit, and a second switch unit; The voltage acquisition unit is connected to the power supply and the first switch unit respectively, the first switch unit is connected to the power supply and the second switch unit respectively, and the second switch unit is connected to the power supply and the load; The voltage acquisition unit is used to acquire the power supply voltage output by the power supply, and output a conduction signal to the first switch unit when the power supply voltage is greater than a preset voltage threshold; The first switch unit is used to conduct the power supply connection between the power supply and the second switch unit when receiving the conduction signal; The second switch unit is used to disconnect the power supply and the load when the power supply connection is turned on.

[0007] Optionally, the voltage acquisition unit includes: a first resistor; The first end of the first resistor is connected to the power supply and the first switch unit respectively, and the second end of the first resistor is connected to the second switch unit and the first switch unit respectively.

[0008] Optionally, the first switch unit includes: a second resistor, a third resistor, a fourth resistor, a fifth resistor, a first switch tube and a second switch tube; Among them, the first end of the second resistor is respectively connected to the first end of the first resistor and the input end of the first switch tube, the second end of the second resistor is respectively connected to the control end of the first switch tube, the input end of the second switch tube and the first end of the third resistor, the second end of the third resistor is connected to the second switch unit and the second end of the first resistor, the output end of the first switch tube is respectively connected to the second switch unit, the first end of the fourth resistor and the control end of the second switch tube, the output end of the second switch tube is connected to the first end of the fifth resistor and the second end of the fourth resistor, and the second end of the fifth resistor is grounded.

[0009] Optionally, the circuit further comprises: a first capacitor; The first capacitor is connected in parallel at both ends of the second resistor.

[0010] Optionally, the second switch unit includes: a first diode, a second diode, a sixth resistor, a seventh resistor, and a third switch tube; Among them, the anode of the first diode is connected to the first switch unit, the cathode of the first diode is connected to the first end of the sixth resistor, the first end of the seventh resistor and the control end of the third switch tube, the second end of the sixth resistor is connected to the drive signal generator, the second end of the seventh resistor is respectively connected to the power supply and the input end of the third switch tube, the output end of the third switch tube is respectively connected to the load and the cathode of the second diode, and the anode of the second diode is grounded.

[0011] Optionally, the second switch unit includes: a third diode, a first voltage stabilizing diode, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a second capacitor and a photocoupler; Among them, the positive electrode of the third diode is connected to the first switching unit, the negative electrode of the third diode is connected to the first end of the eighth resistor, the second end of the eighth resistor is connected to the negative electrode of the first voltage regulator diode, the positive electrode of the first voltage regulator diode is respectively connected to the first end of the ninth resistor and the first input end of the photoelectric coupler, the second end of the ninth resistor and the second input end of the photoelectric coupler are grounded, the first output end of the photoelectric coupler is respectively connected to the first end of the tenth resistor and the first end of the eleventh resistor, the second output end of the photoelectric coupler is grounded, the second end of the tenth resistor is connected to the signal power supply, the second end of the eleventh resistor is respectively connected to the first end of the second capacitor and the microprocessor, the microprocessor is used to control the digital output module to stop outputting signals, and the second end of the second capacitor is grounded.

[0012] Optionally, the circuit further comprises: a filtering unit; Wherein, the filtering unit is connected to the power supply and the voltage acquisition unit respectively; The filtering unit is used to filter the power supply voltage output by the power supply, and output the filtered power supply voltage to the voltage acquisition unit; The voltage acquisition unit is further configured to output a conduction signal to the first switch unit when the filtered power supply voltage is greater than a preset voltage threshold.

[0013] Optionally, the filtering unit includes: a third capacitor and a fourth capacitor; The first end of the third capacitor and the first end of the fourth capacitor are connected to the output end of the power supply, and the second end of the third capacitor and the second end of the fourth capacitor are grounded.

[0014] Optionally, the circuit further comprises: a voltage protection unit; Wherein, the voltage protection unit is connected to the power supply and the voltage acquisition unit respectively; The voltage protection unit is used to check whether the power supply voltage output by the power supply has an abnormally high voltage phenomenon and / or a circuit reverse connection phenomenon. If so, the power supply voltage is subjected to voltage abnormality processing, and the power supply voltage after abnormal processing is output to the voltage acquisition unit; The voltage acquisition unit is further configured to output a conduction signal to the first switch unit when the power supply voltage after the abnormality processing is greater than a preset voltage threshold.

[0015] Optionally, the voltage protection unit includes: a fourth diode and a bidirectional voltage regulator diode; Among them, the first end of the bidirectional voltage regulator diode is respectively connected to the output end of the power supply and the anode of the fourth diode, the second end of the bidirectional voltage regulator diode is grounded, and the cathode of the fourth diode is connected to the voltage acquisition unit.

[0016] The present invention provides an overcurrent protection circuit for a digital output module of a programmable logic controller, the circuit comprising: a voltage acquisition unit, a first switch unit, and a second switch unit; wherein the voltage acquisition unit is connected to a power supply and the first switch unit respectively, the first switch unit is connected to the power supply and the second switch unit respectively, and the second switch unit is connected to the power supply and a load; the voltage acquisition unit is used to acquire the power supply voltage output by the power supply, and output a conduction signal to the first switch unit when the power supply voltage is greater than a preset voltage threshold; the first switch unit is used to conduct the power supply connection between the power supply and the second switch unit when receiving the conduction signal; the second switch unit is used to disconnect the connection between the power supply and the load when the power supply connection is conducted. The present invention monitors the power supply voltage in real time through the voltage acquisition unit, the first switch unit quickly responds to and conducts the control signal, and the second switch unit quickly disconnects the load power supply after receiving the signal, effectively solving the problems of high cost and low reliability in the existing overcurrent protection scheme. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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.

[0018] Figure 1 A schematic structural diagram of an embodiment of an overcurrent protection circuit for a digital output module of a programmable logic controller proposed by the present invention; Figure 2 A schematic structural diagram of another embodiment of an overcurrent protection circuit for a digital output module of a programmable logic controller proposed by the present invention; Figures 3 to 5 This is a circuit schematic diagram of an embodiment of an overcurrent protection circuit for a digital output module of a programmable logic controller proposed by the present invention.

[0019] Description of Figure Numbers: Label name Label name 10 Voltage acquisition unit 20 The first switch unit 30 The second switch unit 40 Filter unit 50 Voltage protection unit R1~R11 The first to eleventh resistors C1~C4 The first to fourth capacitors Q1~Q3 The first switch tube to the third switch tube D1~D4 The first to fourth diodes ZD1 The first Zener diode ZD2 Bidirectional Zener Diode OT Optocoupler 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

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] Reference Figure 1 In this embodiment, the overcurrent protection circuit for the digital output module of the programmable logic controller includes: a voltage acquisition unit 10, a first switch unit 20, and a second switch unit 30; The voltage acquisition unit 10 is connected to the power supply and the first switch unit 20 respectively, the first switch unit 20 is connected to the power supply and the second switch unit 30 respectively, and the second switch unit 30 is connected to the power supply and the load; The voltage acquisition unit 10 is used to acquire the power supply voltage output by the power supply, and output a conduction signal to the first switch unit 20 when the power supply voltage is greater than a preset voltage threshold; The first switch unit 20 is used to conduct the power supply connection between the power supply and the second switch unit 30 when receiving the conduction signal; The second switch unit 30 is used to disconnect the power supply and the load when the power supply connection is turned on.

[0025] It should be noted that the main task of the voltage acquisition unit 10 is to monitor the power supply voltage output by the power supply in real time. It converts the voltage signal of the power supply into a processable electrical signal through a high-precision voltage sensor or a voltage divider circuit. When it is detected that the power supply voltage exceeds the preset voltage threshold, the voltage acquisition unit 10 will immediately output a conduction signal to the first switch unit 20. By monitoring the power supply voltage in real time, protective measures can be taken in time when the power supply voltage exceeds the safety range to prevent overcurrent caused by overvoltage.

[0026] A high-precision voltage sensor or voltage divider circuit can be used to ensure the accuracy of voltage monitoring and reduce the possibility of false alarms and missed alarms. The first switch unit 20 receives the conduction signal from the voltage acquisition unit 10, and decides whether to conduct the power supply connection between the power supply and the second switch unit 30 according to the state of the signal. When receiving the conduction signal, the first switch unit 20 is quickly turned on to provide a control signal to the second switch unit 30. The first switch unit 20 can use a high-speed switching element (such as MOSFET or IGBT), which can complete the conduction operation in a very short time, has a fast response speed, and effectively prevents voltage mutations before overcurrent occurs.

[0027] Secondly, solid-state switch elements can be used without mechanical contacts, which reduces faults caused by contact wear and improves the reliability of the circuit. After receiving the on-signal from the first switch unit 20, the second switch unit 30 disconnects the connection between the power supply and the load. By disconnecting the power supply connection of the load, the PLC output module can be effectively protected from damage due to overcurrent. After the voltage acquisition unit 10 detects overvoltage and triggers the first switch unit 20, the second switch unit 30 quickly disconnects the power supply connection of the load to ensure the safety of the load and the PLC output module. By disconnecting the load power supply in time, equipment damage and safety accidents caused by overcurrent can be prevented, thereby improving the safety of the entire system.

[0028] In this embodiment, an overcurrent protection circuit for a digital output module of a programmable logic controller is provided, the circuit comprising: a voltage acquisition unit 10, a first switch unit 20, and a second switch unit 30; wherein the voltage acquisition unit 10 is connected to a power supply and the first switch unit 20 respectively, the first switch unit 20 is connected to the power supply and the second switch unit 30 respectively, and the second switch unit 30 is connected to the power supply and a load; the voltage acquisition unit 10 is used to acquire the power supply voltage output by the power supply, and when the power supply voltage is greater than a preset voltage threshold, output a conduction signal to the first switch unit 20; the first switch unit 20 is used to conduct the power supply connection between the power supply and the second switch unit 30 when receiving the conduction signal; the second switch unit 30 is used to disconnect the connection between the power supply and the load when the power connection is conducted. The present invention monitors the power supply voltage in real time through the voltage acquisition unit 10, the first switch unit 20 quickly responds to and conducts the control signal, and the second switch unit 30 quickly disconnects the load power supply after receiving the signal, effectively solving the problems of high cost and low reliability in the existing overcurrent protection scheme. Its low cost, quick response, flexible setting and high reliability make this protection circuit have broad application prospects in the field of industrial automation and can significantly improve the safety and stability of PLC systems.

[0029] Further, refer to Figure 3 , the voltage acquisition unit 10 includes: a first resistor R1; The first end of the first resistor R1 is connected to the power supply and the first switch unit 20 respectively, and the second end of the first resistor R1 is connected to the second switch unit 30 and the first switch unit 20 respectively.

[0030] It should be noted that the function of the first resistor R1 is to form a simple voltage divider circuit for detecting whether there is an overcurrent phenomenon in the circuit. When the current flowing through the first resistor R1 increases, the voltage drop across the first resistor R1 increases accordingly. The voltage drop across the first resistor R1 can be output as a voltage signal to the first switch unit 20. When the voltage drop reaches a certain threshold, it can trigger the first switch unit 20 to turn on.

[0031] It should be understood that the resistance of the first resistor R1 is usually small. When the current flowing through the first resistor R1 in the circuit is at a normal current level, the voltage drop of the first resistor R1 is small, and the output voltage drop is insufficient to turn on the first switch unit 20. When the current flowing through the first resistor R1 in the circuit increases, the voltage drop of the first resistor R1 increases accordingly until the first switch unit 20 is triggered to turn on.

[0032] Furthermore, the first switch unit 20 includes: a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a first switch tube Q1 and a second switch tube Q2; Among them, the first end of the second resistor R2 is respectively connected to the first end of the first resistor R1 and the input end of the first switch tube Q1, the second end of the second resistor R2 is respectively connected to the control end of the first switch tube Q1, the input end of the second switch tube Q2 and the first end of the third resistor R3, the second end of the third resistor R3 is connected to the second switch unit 30 and the second end of the first resistor R1, the output end of the first switch tube Q1 is respectively connected to the second switch unit 30, the first end of the fourth resistor R4 and the control end of the second switch tube Q2, the output end of the second switch tube Q2 is connected to the first end of the fifth resistor R5 and the second end of the fourth resistor R4, and the second end of the fifth resistor R5 is grounded.

[0033] It should be noted that when there is an overcurrent phenomenon in the circuit, the voltage drop across the first resistor R1 increases, and accordingly, the voltage drop between the control end and the input end of the first switch tube Q1 increases, so that the first switch tube Q1 is turned on. After the first switch tube Q1 is turned on, a high level is output to the control end of the second switch tube Q2. At this time, the second switch tube Q2 is turned on. Since the second switch tube Q2 is turned on, the voltage drops of the second resistor R2 and the third resistor R3 will cause the first switch tube Q1 to continue to be turned on. At this time, even if the external overcurrent or short-circuit conditions disappear, the overcurrent signal will be maintained, thereby reliably protecting the circuit; preventing the circuit from frequently and continuously experiencing overcurrent or short-circuit.

[0034] It should be understood that the second resistor R2 and the third resistor R3 function to divide voltage, the fourth resistor R4 and the fifth resistor R5 function to limit current, and the first switch tube Q1 and the second switch tube Q2 can be MOS tubes, triodes or IGBTs, which are not limited in this embodiment.

[0035] Furthermore, the circuit further comprises: a first capacitor C1; The first capacitor C1 is connected in parallel at both ends of the second resistor R2.

[0036] It should be noted that the first capacitor C1 can filter the overcurrent protection circuit to enhance the stability of the circuit. Secondly, different overcurrent signal filtering delay effects can be achieved by adjusting the capacitance of the first capacitor C1, so that it can flexibly adapt to the realization of the overcurrent protection function in different usage environments. For example, after the capacitance of the first capacitor C1 is adjusted to 1nf, the delay time of the overcurrent signal is only 700ns, and the response is very fast, which is suitable for environments that require faster overcurrent response.

[0037] Further, refer to Figure 4 , the second switch unit 30 includes: a first diode D1, a second diode D2, a sixth resistor R6, a seventh resistor R7, and a third switch tube Q3; Among them, the anode of the first diode D1 is connected to the first switch unit 20, the cathode of the first diode D1 is connected to the first end of the sixth resistor R6, the first end of the seventh resistor R7 and the control end of the third switch tube Q3, the second end of the sixth resistor R6 is connected to the drive signal generator, the second end of the seventh resistor R7 is respectively connected to the power supply and the input end of the third switch tube Q3, the output end of the third switch tube Q3 is respectively connected to the load and the cathode of the second diode D2, and the anode of the second diode D2 is grounded.

[0038] It should be noted that, in this embodiment, the third switch tube Q3 can be a PMOS tube with model number WMS09P06TS. Taking this PMOS tube as an example, the overcurrent signal can be transmitted unidirectionally to the gate of the PMOS tube through the first diode D1. At this time, the gate voltage of the PMOS tube is pulled up, thereby turning off the output of the PMOS tube.

[0039] In a specific implementation, the driving signal output by the driving signal generator is transmitted to the gate of the PMOS tube after voltage division through the sixth resistor R6 and the seventh resistor R7, and the overcurrent signal is transmitted to the gate of the PMOS tube through the first diode D1. The drain of the PMOS tube is connected to the load and the cathode of the second diode D2.

[0040] Further, refer to Figure 5 In another feasible implementation manner, the second switch unit 30 includes: a third diode D3, a first voltage stabilizing diode ZD1, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a second capacitor C2 and a photocoupler OT; Among them, the anode of the third diode D3 is connected to the first switching unit 20, the cathode of the third diode D3 is connected to the first end of the eighth resistor R8, the second end of the eighth resistor R8 is connected to the cathode of the first voltage zener diode ZD1, the anode of the first voltage zener diode ZD1 is respectively connected to the first end of the ninth resistor R9 and the first input end of the photoelectric coupler OT, the second end of the ninth resistor R9 and the second input end of the photoelectric coupler OT are grounded, the first output end of the photoelectric coupler OT is respectively connected to the first end of the tenth resistor R10 and the first end of the eleventh resistor R11, the second output end of the photoelectric coupler OT is grounded, the second end of the tenth resistor R10 is connected to the signal power supply, the second end of the eleventh resistor R11 is respectively connected to the first end of the second capacitor C2 and the microprocessor, the microprocessor is used to control the digital output module to stop outputting signals, and the second end of the second capacitor C2 is grounded.

[0041] In this embodiment, the overcurrent signal passes through the third diode D3 and reaches the first end of the eighth resistor R8. The overcurrent signal is transmitted to the cathode of the first voltage stabilizing diode ZD1 through the eighth resistor R8. After the first voltage stabilizing diode ZD1 stabilizes the LED of the photocoupler OT, the phototransistor is turned on, and the output end is stabilized to a low level through the eleventh resistor R11 and the second capacitor C2. The microprocessor receives the low-level signal, determines that an overcurrent phenomenon has occurred, and controls the digital output module to stop outputting signals, thereby protecting the PLC output module and the load device.

[0042] Further, refer to Figure 2 , the circuit further comprises: a filtering unit 40; Wherein, the filtering unit 40 is connected to the power supply and the voltage acquisition unit 10 respectively; The filtering unit 40 is used to filter the power supply voltage output by the power supply, and output the filtered power supply voltage to the voltage acquisition unit 10; The voltage acquisition unit 10 is further configured to output a conduction signal to the first switch unit 20 when the filtered power supply voltage is greater than a preset voltage threshold.

[0043] It should be noted that, by introducing the filter unit 40 , the entire overcurrent protection circuit can work more stably, reducing false alarms and missed alarms caused by power supply fluctuations and noise.

[0044] Further, refer to Figure 3 , the filtering unit 40 includes: a third capacitor C3 and a fourth capacitor C4; The first end of the third capacitor C3 and the first end of the fourth capacitor C4 are connected to the output end of the power supply, and the second end of the third capacitor C3 and the second end of the fourth capacitor C4 are grounded.

[0045] It should be noted that the third capacitor C3 and the fourth capacitor C4 are connected in parallel between the output terminal of the power supply and the ground to filter out high-frequency noise and instantaneous spikes in the power supply voltage to ensure that the power supply voltage received by the voltage acquisition unit 10 is stable.

[0046] Further, refer to Figure 2 , the circuit further includes: a voltage protection unit 50; Wherein, the voltage protection unit 50 is connected to the power supply and the voltage acquisition unit 10 respectively; The voltage protection unit 50 is used to check whether the power supply voltage output by the power supply has an abnormally high voltage phenomenon and / or a circuit reverse connection phenomenon. If so, the power supply voltage is subjected to voltage abnormality processing and the power supply voltage after abnormal processing is output to the voltage acquisition unit 10; The voltage acquisition unit 10 is further configured to output a conduction signal to the first switch unit 20 when the power supply voltage after the abnormality processing is greater than a preset voltage threshold.

[0047] It should be noted that the voltage protection unit 50 ensures the stability of the power supply voltage and prevents damage to the circuit caused by abnormally high voltage and reverse connection.

[0048] Further, refer to Figure 3 , the voltage protection unit 50 includes: a fourth diode D4 and a bidirectional voltage regulator diode ZD2; The first end of the bidirectional voltage regulator diode ZD2 is respectively connected to the output end of the power supply and the anode of the fourth diode D4 , the second end of the bidirectional voltage regulator diode ZD2 is grounded, and the cathode of the fourth diode D4 is connected to the voltage acquisition unit 10 .

[0049] It should be noted that the bidirectional voltage regulator diode ZD2 has the characteristic of being turned on when the forward and reverse voltages exceed its voltage regulation value. Assume that the voltage regulation value of the bidirectional voltage regulator diode ZD2 is set to a safe voltage, such as 30V. When the output voltage of the power supply exceeds 30V, the bidirectional voltage regulator diode ZD2 will conduct in the forward or reverse direction, clamping the voltage within a safe range to prevent excessive voltage from causing damage to the subsequent circuit. Through the conduction of the bidirectional voltage regulator diode ZD2, the excessive voltage is led to the ground to protect the circuit from the influence of high voltage. The fourth diode D4 is used to prevent the power supply from being reversed and ensure the safety of the circuit. When the power supply is positively connected, the fourth diode D4 is forwardly conducted, and the voltage of the power supply is transmitted to the voltage acquisition unit 10 through the fourth diode D4. When the power supply is reversely connected, the fourth diode D4 will reversely block to prevent the current from flowing into the subsequent circuit through the fourth diode D4 in the reverse direction, protecting the circuit from damage caused by reverse connection.

[0050] 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. An overcurrent protection circuit for a digital output module of a programmable logic controller, characterized in that: The circuit comprises: a voltage acquisition unit, a first switch unit, and a second switch unit; The voltage acquisition unit is connected to the power supply and the first switch unit respectively, the first switch unit is connected to the power supply and the second switch unit respectively, and the second switch unit is connected to the power supply and the load; The voltage acquisition unit is used to acquire the power supply voltage output by the power supply, and output a conduction signal to the first switch unit when the power supply voltage is greater than a preset voltage threshold; The first switch unit is used to conduct the power supply connection between the power supply and the second switch unit when receiving the conduction signal; The second switch unit is used to disconnect the power supply and the load when the power supply connection is turned on.

2. The overcurrent protection circuit for a digital output module of a programmable logic controller according to claim 1, characterized in that: The voltage acquisition unit includes: a first resistor; The first end of the first resistor is connected to the power supply and the first switch unit respectively, and the second end of the first resistor is connected to the second switch unit and the first switch unit respectively.

3. The overcurrent protection circuit for a digital output module of a programmable logic controller according to claim 2, characterized in that: The first switch unit includes: a second resistor, a third resistor, a fourth resistor, a fifth resistor, a first switch tube and a second switch tube; Among them, the first end of the second resistor is respectively connected to the first end of the first resistor and the input end of the first switch tube, the second end of the second resistor is respectively connected to the control end of the first switch tube, the input end of the second switch tube and the first end of the third resistor, the second end of the third resistor is connected to the second switch unit and the second end of the first resistor, the output end of the first switch tube is respectively connected to the second switch unit, the first end of the fourth resistor and the control end of the second switch tube, the output end of the second switch tube is connected to the first end of the fifth resistor and the second end of the fourth resistor, and the second end of the fifth resistor is grounded.

4. The overcurrent protection circuit for a digital output module of a programmable logic controller according to claim 3, characterized in that: The circuit further includes: a first capacitor; The first capacitor is connected in parallel at both ends of the second resistor.

5. The overcurrent protection circuit for a digital output module of a programmable logic controller according to claim 1, characterized in that: The second switch unit includes: a first diode, a second diode, a sixth resistor, a seventh resistor, and a third switch tube; Among them, the anode of the first diode is connected to the first switch unit, the cathode of the first diode is connected to the first end of the sixth resistor, the first end of the seventh resistor and the control end of the third switch tube, the second end of the sixth resistor is connected to the drive signal generator, the second end of the seventh resistor is respectively connected to the power supply and the input end of the third switch tube, the output end of the third switch tube is respectively connected to the load and the cathode of the second diode, and the anode of the second diode is grounded.

6. The overcurrent protection circuit for a digital output module of a programmable logic controller according to claim 1, characterized in that: The second switch unit includes: a third diode, a first voltage stabilizing diode, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a second capacitor and a photoelectric coupler; Among them, the positive electrode of the third diode is connected to the first switching unit, the negative electrode of the third diode is connected to the first end of the eighth resistor, the second end of the eighth resistor is connected to the negative electrode of the first voltage regulator diode, the positive electrode of the first voltage regulator diode is respectively connected to the first end of the ninth resistor and the first input end of the photoelectric coupler, the second end of the ninth resistor and the second input end of the photoelectric coupler are grounded, the first output end of the photoelectric coupler is respectively connected to the first end of the tenth resistor and the first end of the eleventh resistor, the second output end of the photoelectric coupler is grounded, the second end of the tenth resistor is connected to the signal power supply, the second end of the eleventh resistor is respectively connected to the first end of the second capacitor and the microprocessor, the microprocessor is used to control the digital output module to stop outputting signals, and the second end of the second capacitor is grounded.

7. The overcurrent protection circuit for a digital output module of a programmable logic controller according to claim 1, characterized in that: The circuit further comprises: a filtering unit; Wherein, the filtering unit is connected to the power supply and the voltage acquisition unit respectively; The filtering unit is used to filter the power supply voltage output by the power supply, and output the filtered power supply voltage to the voltage acquisition unit; The voltage acquisition unit is further configured to output a conduction signal to the first switch unit when the filtered power supply voltage is greater than a preset voltage threshold.

8. The overcurrent protection circuit for a digital output module of a programmable logic controller according to claim 7, characterized in that: The filtering unit comprises: a third capacitor and a fourth capacitor; The first end of the third capacitor and the first end of the fourth capacitor are connected to the output end of the power supply, and the second end of the third capacitor and the second end of the fourth capacitor are grounded.

9. The overcurrent protection circuit for a digital output module of a programmable logic controller according to claim 1, characterized in that: The circuit further comprises: a voltage protection unit; Wherein, the voltage protection unit is connected to the power supply and the voltage acquisition unit respectively; The voltage protection unit is used to check whether the power supply voltage output by the power supply has an abnormally high voltage phenomenon and / or a circuit reverse connection phenomenon. If so, the power supply voltage is subjected to voltage abnormality processing, and the power supply voltage after abnormal processing is output to the voltage acquisition unit; The voltage acquisition unit is further configured to output a conduction signal to the first switch unit when the power supply voltage after the abnormality processing is greater than a preset voltage threshold.

10. The overcurrent protection circuit for a digital output module of a programmable logic controller according to claim 9, characterized in that: The voltage protection unit includes: a fourth diode and a bidirectional voltage regulator diode; Among them, the first end of the bidirectional voltage regulator diode is respectively connected to the output end of the power supply and the anode of the fourth diode, the second end of the bidirectional voltage regulator diode is grounded, and the cathode of the fourth diode is connected to the voltage acquisition unit.

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