Switching circuit and circuit board
By introducing an anti-error circuit into the photoelectric switch circuit, the cutoff characteristics of the filter circuit and the transistor switch circuit are used to solve the problem of mis-passing by the photoelectric sensor due to environmental factors, and the reliability and detection accuracy of the equipment are improved.
Patent Information
- Application Number
- CN202420489726.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-03-14
- Publication Date
- 2025-01-17
- Estimated Expiration
- 2034-03-14
AI Technical Summary
In actual use, photoelectric sensors are prone to mis-connection due to the influence of the product itself and external environmental factors, resulting in damage to industrial precision instruments or failure of functions.
A switching circuit including a photoelectric switch circuit and an anti-error circuit was designed. The photoelectric switch circuit consists of an optocoupler, a current limiter, a filter circuit and a transistor switch circuit. The anti-error circuit prevents non-error circuits through the filter circuit and the transistor switch circuit. Expect frequency signals to prevent misdirection.
Effectively prevent misdirection of the photoelectric switch circuit due to the product itself and external environmental factors, and improve the reliability and detection accuracy of the equipment.
Smart Images
Figure CN222366258U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of electronic circuits, in particular to a switch circuit and a circuit board. Background Art
[0002] Photoelectric switch (photoelectric sensor) is the abbreviation of photoelectric proximity switch. It uses the blocking or reflection of the light beam by the detected object to select the circuit by the synchronous circuit to detect the presence or absence of the object. The photoelectric switch converts the input current into a light signal on the transmitter, and the receiver detects the target object according to the intensity or presence of the received light. Therefore, it is often used in the field of industrial control technology.
[0003] However, in actual use, due to the influence of various factors such as the product itself and the external environment, photoelectric sensors may suffer various damages and failures, resulting in false connection, thereby damaging industrial precision instruments or causing them to fail in function. Utility Model Content
[0004] The embodiments of the utility model provide a switch circuit and a circuit board, which are helpful to prevent the photoelectric switch circuit from being misconnected due to the influence of factors such as the product itself and the external environment.
[0005] On one hand, an embodiment of the utility model provides a switch circuit, which includes: a photoelectric switch circuit and an anti-misconnection circuit, wherein:
[0006] The photoelectric switch circuit includes an optical coupler, which includes a transmitter and a receiver. The transmitter is used to transmit light, and the receiver outputs a voltage of corresponding magnitude according to the strength of the received light. The output end of the receiver is connected to the input end of the anti-false connection circuit.
[0007] The anti-false-connection circuit includes a filter circuit and / or a transistor switch circuit.
[0008] Optionally, the photoelectric switch circuit also includes a first current limiter and a second current limiter, the first current limiter is connected between the first power supply and the input end of the transmitter to limit the current of the transmitter; the second current limiter is connected between the second power supply and the input end of the receiver to limit the current of the receiver.
[0009] Optionally, the first current limiter is a constant current source, or a first resistor, or includes at least two second resistors connected in parallel;
[0010] The second current limiter is a third resistor.
[0011] Optionally, the filtering circuit includes a fourth resistor and a capacitor, a first end of the fourth resistor is connected to the output end of the photoelectric switch circuit, a second end of the fourth resistor is connected to the first end of the capacitor, and a second end of the capacitor is grounded;
[0012] The second end of the fourth resistor is also connected to the first input pin of the controller.
[0013] Optionally, the transistor switch circuit includes a fifth resistor, a triode, a sixth resistor, a seventh resistor and a light emitting diode; the control electrode of the triode is connected to the first end of the fifth resistor, the emitter of the triode is connected to the second end of the fifth resistor and is grounded, the collector of the triode is connected to the first end of the sixth resistor and the cathode of the light emitting diode, the anode of the light emitting diode is connected to the first end of the seventh resistor, and the second end of the seventh resistor is connected to the second end of the sixth resistor and a third power supply;
[0014] The cathode of the light emitting diode is also connected to the second input pin of the programmable logic controller.
[0015] Optionally, the switch circuit further includes an operational amplifier, the input end of the operational amplifier is connected to the output end of the photoelectric switch circuit, and the output end of the operational amplifier is connected to the input end of the anti-false connection circuit.
[0016] Optionally, the positive input terminal of the operational amplifier is connected to the output terminal of the photoelectric switch circuit, the negative input terminal of the operational amplifier is connected to the output terminal of the operational amplifier, and the output terminal of the operational amplifier is connected to the input terminal of the anti-false connection circuit.
[0017] Another aspect of the present invention provides a circuit board, which includes a first PCB board and a second PCB board, wherein at least two switch circuits of the first aspect are welded on the first PCB board, the input ends of at least two of the switch circuits are connected in series, and the output ends of at least two of the switch circuits are respectively connected to the input pins of the controller;
[0018] An optical coupler is welded on the second PCB board, and the second PCB board is welded on the first PCB board by direct insertion, and the pins of the optical coupler are connected with the pins of the first PCB board via the second PCB board.
[0019] The switch circuit provided by the embodiment of the utility model includes a photoelectric switch circuit and an anti-false connection circuit. The photoelectric switch circuit includes an optical coupler. The optical coupler includes a transmitter and a receiver. The transmitter is used to transmit light. The receiver outputs a voltage of a corresponding magnitude according to the intensity of the received light. The output end of the receiver is connected to the input end of the anti-false connection circuit.
[0020] The anti-false conduction circuit connected to the photoelectric switch circuit includes a filter circuit and / or a transistor switch circuit. The filter circuit only allows signal components within a certain frequency range to pass normally, while preventing signal components of another frequency from passing through the circuit, thereby helping to prevent the photoelectric switch circuit from being falsely conducted due to the influence of factors such as the product itself and the external environment; the transistor switch circuit utilizes its cut-off characteristics to realize the switching function, which can also help to prevent the photoelectric switch circuit from being falsely conducted due to the influence of factors such as the product itself and the external environment. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In order to more clearly illustrate the embodiments of the utility model 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 utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0022] Figure 1 It is a structural schematic diagram of a photoelectric switch circuit provided by an embodiment of the utility model;
[0023] Figure 2 It is a structural schematic diagram of a filter circuit provided by an embodiment of the utility model;
[0024] Figure 3 It is a structural schematic diagram of a transistor switch circuit provided by an embodiment of the utility model;
[0025] Figure 4 It is a structural schematic diagram of a first switching circuit provided by an embodiment of the utility model;
[0026] Figure 5 It is a structural schematic diagram of a second switch circuit provided by an embodiment of the utility model;
[0027] Figure 6 It is a structural schematic diagram of a third switch circuit provided by an embodiment of the utility model;
[0028] Figure 7 It is a structural schematic diagram of a fourth switch circuit provided in an embodiment of the utility model. DETAILED DESCRIPTION
[0029] The specific implementation of the utility model will be described in more detail below in conjunction with the schematic diagram. The advantages and features of the utility model will become clearer according to the following description and claims. It should be noted that the drawings are all in a very simplified form and are not in precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the utility model.
[0030] In the description of the present invention, it should be understood that the terms "center", "up", "down", "left", "right", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.
[0031] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying 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 one or more of the features. In the description of the present utility model, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.
[0032] Please refer to Figure 1 , Figure 1 The photoelectric switch circuit 100 includes an optical coupler 110, and the optical coupler 110 includes a transmitter 111 and a receiver 112. The transmitter 111 is used to transmit light, and the receiver 112 outputs a voltage of a corresponding magnitude according to the intensity of the received light.
[0033] The transmitter 111 may be an infrared light emitting diode that converts electrical energy into light of a specific wavelength. There may be a closed optical channel (also called a dielectric channel) between the transmitter 111 and the receiver 112. The receiver may sense light of a specific wavelength and convert the light into electrical energy. The receiver 112 may be a photoresistor, a photodiode, a phototransistor, a silicon controlled rectifier (SCR) or a triode for alternating current (TRIAC). In addition to emitting light, a light emitting diode can also be used as a light sensing element. Therefore, a light emitting diode can be used as a light sensing element, which is a symmetrical bidirectional optical coupler.
[0034] Optionally, the photoelectric switch circuit also includes a first current limiter 120 and a second current limiter 130, the first current limiter 120 is connected between the first power supply 140 and the input end of the transmitter 111 to limit the current of the transmitter 111; the second current limiter 130 is connected between the second power supply 150 and the input end of the receiver 120 to limit the current of the receiver 120.
[0035] The voltage output by the second power supply may be equal to the voltage output by the first power supply, or may not be equal to the voltage output by the first power supply, which is not limited here.
[0036] Further, when the receiver 112 is a phototransistor, the collector of the transistor (ie, the output end of the receiver 112) is connected to the second current limiter 130 and the anti-false connection circuit 200, and the emitter of the transistor is grounded. When the transmitter 111 is a light emitting diode, the cathode of the light emitting diode is grounded.
[0037] Optionally, the first current limiter is a constant current source, or a first resistor, or includes at least two second resistors connected in parallel;
[0038] The second current limiter is a third resistor.
[0039] The above-mentioned current limiter can reduce the voltage on the input side to prevent the resistor from overheating due to excessive resistor power.
[0040] Please refer to Figure 2 , Figure 2 The filter circuit 210 includes a fourth resistor 211 and a capacitor 212, wherein a second end 211b of the fourth resistor 211 is connected to a first end 212a of the capacitor 212, and a second end 212b of the capacitor 212 is grounded.
[0041] Please refer to Figure 3 , Figure 3 1 is a schematic diagram of a transistor switch circuit provided by an embodiment of the utility model. The transistor switch circuit 220 includes a fifth resistor 221, a triode 222, a sixth resistor 223, a seventh resistor 224 and a light emitting diode 225; the control electrode of the triode 222 is connected to the first end 221a of the fifth resistor 221, the emitter of the triode 222 is connected to the second end 221b of the fifth resistor 221 and is grounded, the collector of the triode 222 is connected to the first end 223a of the sixth resistor 223 and the cathode of the light emitting diode 225, the anode of the light emitting diode 225 is connected to the first end 224a of the seventh resistor 224, and the second end 224b of the seventh resistor 224 is connected to the second end 223b of the sixth resistor 223 and the third power supply 226.
[0042] The third power source may be equal to or different from the first power source and the second power source, which is not limited here.
[0043] The conduction of the transistor 222 requires a certain current, so false triggering can be prevented to a certain extent.
[0044] Please refer to Figure 4 , Figure 4 1 is a schematic diagram of the structure of the first switch circuit provided by the embodiment of the utility model. The switch circuit comprises: a photoelectric switch circuit 100 and an anti-false connection circuit 200. The anti-false connection circuit 200 comprises a filter circuit 210.
[0045] The photoelectric switch circuit 100 includes an optical coupler 110, and the optical coupler 110 includes a transmitter 111 and a receiver 112. The transmitter 111 is used to transmit light, and the receiver 112 outputs a voltage of a corresponding magnitude according to the strength of the received light. The photoelectric switch circuit 100 also includes a first current limiter 120 and a second current limiter 130. The first current limiter 120 is connected between the first power supply 140 and the input end of the transmitter 111 to limit the current of the transmitter 111; the second current limiter 130 is connected between the second power supply 150 and the input end of the receiver 120 to limit the current of the receiver. Among them, the first current limiter is a constant current source, or a first resistor, or includes at least two second resistors in parallel; the second current limiter is a third resistor.
[0046] The filter circuit 210 includes a fourth resistor 211 and a capacitor 212 . The second end 211 b of the fourth resistor 211 is connected to the first end 212 a of the capacitor 212 , and the second end 212 b of the capacitor 212 is grounded.
[0047] Among them, the output end of the photoelectric switch circuit 100 (i.e. the output end of the receiver 112) is connected to the input end of the filter circuit 210 (i.e. the first end 211a of the fourth resistor 211); the output end of the filter circuit 210 (i.e. the second end 211b of the fourth resistor 211) can also be connected to the first input pin of the controller.
[0048] The controller may be a programmable logic controller (PLC) or a single chip microcomputer.
[0049] The switch circuit provided by the embodiment of the utility model includes a photoelectric switch circuit and an anti-false connection circuit. The photoelectric switch circuit includes an optical coupler. The optical coupler includes a transmitter and a receiver. The transmitter is used to transmit light. The receiver outputs a voltage of a corresponding magnitude according to the intensity of the received light. The output end of the receiver is connected to the input end of the anti-false connection circuit.
[0050] The anti-false conduction circuit connected to the photoelectric switch circuit includes a filter circuit. The filter circuit only allows signal components within a certain frequency range to pass normally, while preventing other frequency signal components from passing through the circuit, thereby preventing the photoelectric switch circuit from being falsely conducted due to the influence of factors such as the product itself and the external environment.
[0051] Please refer to Figure 5 , Figure 5 1 is a schematic diagram of the structure of a second switch circuit provided by an embodiment of the utility model. The switch circuit comprises: a photoelectric switch circuit 100 and an anti-false connection circuit 200. The anti-false connection circuit 200 comprises a transistor switch circuit 220.
[0052] The photoelectric switch circuit 100 includes an optical coupler 110, and the optical coupler 110 includes a transmitter 111 and a receiver 112. The transmitter 111 is used to transmit light, and the receiver 112 outputs a voltage of a corresponding magnitude according to the strength of the received light. The photoelectric switch circuit 100 also includes a first current limiter 120 and a second current limiter 130. The first current limiter 120 is connected between the first power supply 140 and the input end of the transmitter 111 to limit the current of the transmitter 111; the second current limiter 130 is connected between the second power supply 150 and the input end of the receiver 120 to limit the current of the receiver. Among them, the first current limiter is a constant current source, or a first resistor, or includes at least two second resistors in parallel; the second current limiter is a third resistor.
[0053] The transistor switch circuit 220 includes a fifth resistor 221, a triode 222, a sixth resistor 223, a seventh resistor 224 and a light-emitting diode 225; the control electrode of the triode 222 is connected to the first end 221a of the fifth resistor 221, the emitter of the triode 222 is connected to the second end 221b of the fifth resistor 221 and to ground, the collector of the triode 222 is connected to the first end 223a of the sixth resistor 223 and the cathode of the light-emitting diode 225, the anode of the light-emitting diode 225 is connected to the first end 224a of the seventh resistor 224, and the second end 224b of the seventh resistor 224 is connected to the second end 223b of the sixth resistor 223 and the third power supply 226.
[0054] Among them, the input end of the transistor switch circuit 220 (i.e., the first end 221b of the fifth resistor 221) is connected to the output end of the photoelectric switch circuit 100 (i.e., the output end of the receiver 112), and the output end of the transistor switch circuit 220 (i.e., the cathode of the photodiode) is also connected to the second input pin of the controller.
[0055] The controller may be a PLC or a single-chip microcomputer. The second input pin may be connected to Figure 4 The first input pins in the embodiment may be the same or different, which is not limited here.
[0056] The switch circuit provided by the embodiment of the utility model includes a photoelectric switch circuit and an anti-false connection circuit. The photoelectric switch circuit includes an optical coupler. The optical coupler includes a transmitter and a receiver. The transmitter is used to transmit light. The receiver outputs a voltage of a corresponding magnitude according to the intensity of the received light. The output end of the receiver is connected to the input end of the anti-false connection circuit.
[0057] The anti-false conduction circuit connected to the photoelectric switch circuit includes a transistor switch circuit. The transistor switch circuit can utilize its cut-off characteristics to realize the switching function, which is beneficial to prevent the photoelectric switch circuit from being falsely conducted due to the influence of factors such as the product itself and the external environment.
[0058] Please refer to Figure 6 , Figure 6 1 is a schematic diagram of the structure of the third switch circuit provided by the embodiment of the utility model. The switch circuit comprises: a photoelectric switch circuit 100 and an anti-false connection circuit 200. The anti-false connection circuit 200 comprises a filter circuit 210 and a transistor switch circuit 220.
[0059] The photoelectric switch circuit 100 includes an optical coupler 110, and the optical coupler 110 includes a transmitter 111 and a receiver 112. The transmitter 111 is used to transmit light, and the receiver 112 outputs a voltage of a corresponding magnitude according to the strength of the received light. The photoelectric switch circuit 100 also includes a first current limiter 120 and a second current limiter 130. The first current limiter 120 is connected between the first power supply 140 and the input end of the transmitter 111 to limit the current of the transmitter 111; the second current limiter 130 is connected between the second power supply 150 and the input end of the receiver 120 to limit the current of the receiver. Among them, the first current limiter is a constant current source, or a first resistor, or includes at least two second resistors in parallel; the second current limiter is a third resistor.
[0060] The filter circuit 210 includes a fourth resistor 211 and a capacitor 212 . The second end 211 b of the fourth resistor 211 is connected to the first end 212 a of the capacitor 212 , and the second end 212 b of the capacitor 212 is grounded.
[0061] The transistor switch circuit 220 includes a fifth resistor 221, a triode 222, a sixth resistor 223, a seventh resistor 224 and a light-emitting diode 225; the control electrode of the triode 222 is connected to the first end 221a of the fifth resistor 221, the emitter of the triode 222 is connected to the second end 221b of the fifth resistor 221 and to ground, the collector of the triode 222 is connected to the first end 223a of the sixth resistor 223 and the cathode of the light-emitting diode 225, the anode of the light-emitting diode 225 is connected to the first end 224a of the seventh resistor 224, and the second end 224b of the seventh resistor 224 is connected to the second end 223b of the sixth resistor 223 and the third power supply 226.
[0062] Among them, the output end of the photoelectric switch circuit 100 (i.e., the output end of the receiver 112) is connected to the input end of the filter circuit 210 (i.e., the first end 211a of the fourth resistor 211); the output end of the filter circuit 210 (i.e., the second end 211b of the fourth resistor 211) can also be connected to the input end of the transistor switch circuit 220 (i.e., the first end 221a of the fifth resistor 221), and the output end of the transistor switch circuit 220 (i.e., the cathode of the photodiode) is also connected to the second input pin of the controller.
[0063] The controller may be a PLC or a single chip microcomputer.
[0064] The switch circuit provided by the embodiment of the utility model includes a photoelectric switch circuit and an anti-false connection circuit. The photoelectric switch circuit includes an optical coupler. The optical coupler includes a transmitter and a receiver. The transmitter is used to transmit light. The receiver outputs a voltage of a corresponding magnitude according to the intensity of the received light. The output end of the receiver is connected to the input end of the anti-false connection circuit.
[0065] The anti-false conduction circuit connected to the photoelectric switch circuit includes a filter circuit and a transistor switch circuit. The filter circuit only allows signal components within a certain frequency range to pass normally, and prevents signal components of another frequency from passing through the circuit, thereby helping to prevent the photoelectric switch circuit from being falsely conducted due to the influence of factors such as the product itself and the external environment; the transistor switch circuit utilizes its cut-off characteristics to realize the switching function, which can also help to prevent the photoelectric switch circuit from being falsely conducted due to the influence of factors such as the product itself and the external environment.
[0066] Please refer to Figure 7 , Figure 7 1 is a schematic diagram of the structure of the fourth switch circuit provided by the embodiment of the utility model. The switch circuit includes: a photoelectric switch circuit 100, an anti-false connection circuit 200 and an operational amplifier 300. The input end of the operational amplifier 300 is connected to the output end of the photoelectric switch circuit 100, and the output end of the operational amplifier 300 is connected to the input end of the anti-false connection circuit 200.
[0067] Optionally, the positive input terminal of the operational amplifier 300 is connected to the output terminal of the photoelectric switch circuit 100 , the negative input terminal of the operational amplifier 300 is connected to the output terminal of the operational amplifier 300 , and the output terminal of the operational amplifier 300 is connected to the input terminal of the anti-false-connection circuit 200 .
[0068] Another aspect of the present invention provides a circuit board, which includes a first PCB board and a second PCB board, wherein at least two switch circuits of the first aspect are welded on the first PCB board, the input ends of at least two of the switch circuits are connected in series, and the output ends of at least two of the switch circuits are respectively connected to the input pins of the controller;
[0069] An optical coupler is welded on the second PCB board, and the second PCB board is welded on the first PCB board by direct insertion, and the pins of the optical coupler are connected with the pins of the first PCB board via the second PCB board.
[0070] Among them, the angle of the direct plug welding is the first angle, and the first angle can be, for example, 80°, 85°, 90°, 95°, 100°, etc., which is not limited here.
[0071] The volume of a single switch circuit module in the embodiment of the present application can be 4mm*5mm*5mm, while the volume of the finished optical switch module on the market is 20mm*15mm*20mm. Therefore, at least two of the above-mentioned switch circuits can be soldered on the first PCB board, and the integration level is higher than that of the finished optical switch modules on the market. At the same time, the slot width of the existing finished optical switch modules is too wide, which may cause the object to be measured to be unable to be completely shielded from light, resulting in low detection accuracy. The slot width of the switch circuit in the embodiment of the present application is narrower, which can increase the shading range of the object to be measured and improve the detection accuracy.
[0072] Furthermore, in specific applications, for example, when it is necessary to simultaneously determine the arrival of materials at multiple points on the equipment, some relatively sophisticated equipment cannot use finished optical switch modules on the market due to limited internal space, because it will cause numerous wiring difficulties and take up space. In the embodiment of the present application, 7 of the above-mentioned switch circuits can be welded on the first PCB board, and 7 IO signals of PLC or single-chip microcomputer can be output for detection, and only 9 wires (including two power lines) are needed, which further reduces the wiring.
[0073] In addition, the installation method of the switch circuit provided in the embodiment of the present application is also different from the existing one. The existing photoelectric switch needs to be installed on the PCB board through a metal mounting plate and screws, and then the pins of the photoelectric switch are welded to the PCB board. This installation method is complicated. In the embodiment of the present application, a plurality of the above-mentioned switch circuits are welded on the first PCB board, and an optical coupler is welded on the second PCB board. The second PCB board is welded on the first PCB board by direct plug-in. The pins of the optical coupler are connected to the pins of the first PCB board through the second PCB board. The switch is first welded on the mounting board, which has good integrity and is easy to install. The series installation method can also achieve the purpose of reducing voltage to control the temperature of components.
[0074] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example" or "specific example" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the utility model. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.
[0075] The above are only preferred embodiments of the present invention and do not limit the present invention in any way. Any technician in the relevant technical field, without departing from the scope of the technical solution of the present invention, may make any equivalent replacement or modification to the technical solution and technical content disclosed in the present invention, which shall be deemed as the content of the technical solution of the present invention and still fall within the protection scope of the present invention.
Claims
1. A switching circuit, characterized in that: The switch circuit includes: a photoelectric switch circuit and an anti-misconnection circuit, wherein: The photoelectric switch circuit includes an optical coupler, and the optical coupler includes a transmitter and a receiver. The transmitter is used to transmit light, and the receiver outputs a voltage of a corresponding magnitude according to the strength of the received light. The output end of the receiver is connected to the input end of the anti-misconnection circuit; The anti-false-connection circuit includes a filter circuit and / or a transistor switch circuit.
2. The switch circuit according to claim 1, characterized in that: The photoelectric switch circuit further includes a first current limiter and a second current limiter, wherein the first current limiter is connected between the first power supply and the input end of the transmitter to limit the current of the transmitter; The second current limiter is connected between the second power supply and the input terminal of the receiver to limit the current of the receiver.
3. The switch circuit according to claim 2, characterized in that: The first current limiter is a constant current source, or a first resistor, or comprises at least two second resistors connected in parallel; The second current limiter is a third resistor.
4. The switch circuit according to claim 1, characterized in that: The filter circuit comprises a fourth resistor and a capacitor, a first end of the fourth resistor is connected to the output end of the photoelectric switch circuit, a second end of the fourth resistor is connected to the first end of the capacitor, and a second end of the capacitor is grounded; The second end of the fourth resistor is also connected to the first input pin of the controller.
5. The switch circuit according to claim 1, characterized in that: The transistor switch circuit includes a fifth resistor, a triode, a sixth resistor, a seventh resistor and a light emitting diode; the control electrode of the triode is connected to the first end of the fifth resistor, the emitter of the triode is connected to the second end of the fifth resistor and is grounded, the collector of the triode is connected to the first end of the sixth resistor and the cathode of the light emitting diode, the anode of the light emitting diode is connected to the first end of the seventh resistor, and the second end of the seventh resistor is connected to the second end of the sixth resistor and a third power supply; The cathode of the light emitting diode is also connected to the second input pin of the programmable logic controller.
6. The switch circuit according to claim 1, characterized in that: The switch circuit further comprises an operational amplifier, the input end of the operational amplifier is connected to the output end of the photoelectric switch circuit, and the output end of the operational amplifier is connected to the input end of the anti-false connection circuit.
7. The switch circuit according to claim 6, characterized in that: The positive input terminal of the operational amplifier is connected to the output terminal of the photoelectric switch circuit, the negative input terminal of the operational amplifier is connected to the output terminal of the operational amplifier, and the output terminal of the operational amplifier is connected to the input terminal of the anti-false connection circuit.
8. A circuit board, characterized in that: The circuit board comprises a first PCB board and a second PCB board, at least two switch circuits according to any one of claims 1 to 7 are welded on the first PCB board, the input ends of at least two of the switch circuits are connected in series, and the output ends of at least two of the switch circuits are respectively connected to the input pins of the controller; The optical coupler is welded on the second PCB board, and the second PCB board is welded on the first PCB board by direct plug-in, and the pins of the optical coupler are connected with the pins of the first PCB board via the second PCB board.