Signal output protection circuit of safety detection equipment

Abstract

The invention discloses a signal output protection circuit of safety detection equipment. The signal output protection circuit comprises a high-level module and a low-level module which are connected in parallel between a signal input end and a signal output end, the high-level module comprises a first switch tube, a second switch tube, a first resistor, a second resistor and a first current limiting unit, and the first current limiting unit is connected with a base electrode and an emitting electrode of the second switch tube and a signal output side power supply positive end and used for limiting current from the high-level module to a signal output end; the low-level module comprises a third switch tube, a fourth switch tube, a third resistor, a fourth resistor and a second current limiting unit, and the second current limiting unit is connected with the base electrode, the emitting electrode and the ground end of the fourth switch tube and used for limiting current from the signal output end to the low-level module. The problems that an output signal circuit of existing safety detection equipment is low in fault tolerance and devices are prone to being damaged are solved, and the fault tolerance and safety of use of the safety detection equipment are improved.

Description

Technical Field

[0001] The present invention relates to the field of detection technology, and in particular to a signal output protection circuit of a safety detection device. Background Art

[0002] Safety detection equipment is a safety control device that is mainly used in mechanical equipment or industrial equipment to protect operators from mechanical or electrical hazards that may cause harm. Common safety detection equipment includes safety gratings, 3D cameras, and electromagnetic door locks. Taking safety gratings as an example, it usually consists of a series of photoelectric sensors (photodiodes) installed around the machine, which emit a light beam and stop or make the equipment safe when it detects that the beam is blocked. Safety detection equipment achieves safety control by monitoring the position of people or objects in the working area of ​​the equipment, thereby preventing operators from approaching dangerous areas or unsafe incidents from occurring during equipment operation.

[0003] When an operator approaches a dangerous area, the safety detection equipment can output a danger signal to the host computer, and the host computer will then output a stop command to the equipment to shut down. If the installer connects the signal output line incorrectly, for example, when the signal line outputs a high level and is grounded, the current will be too large; when the output low level is mistakenly connected to a high voltage, the current will also be too large, which will burn out the transistors in the output circuit and cause a safety accident.

[0004] Chinese patent application CN202022854410.6 proposes a safety grating output protection circuit to achieve overcurrent and overvoltage protection for the outputs of the NPN-OUT and PNP-OUT interfaces. This solution is an open-drain output, has a weak driving capability for high-level output, and uses an op amp chip, which is relatively expensive.

[0005] In view of this, it is necessary to propose a new signal output protection circuit of a safety detection device to improve the above-mentioned problem. Summary of the invention

[0006] The purpose of the present invention is to provide a signal output protection circuit for a safety detection device. By setting a current limiting unit, the problem of low fault tolerance and easy device damage of the output signal circuit of the existing safety detection equipment is solved, thereby improving the fault tolerance and safety of the use of the safety detection equipment.

[0007] The present invention provides the following scheme:

[0008] The present invention provides a signal output protection circuit for a safety detection device, comprising a high level module and a low level module connected in parallel between a signal input terminal and a signal output terminal;

[0009] The high-level module includes a first switch tube, a second switch tube, a first resistor, a second resistor and a first current limiting unit. The base of the first switch tube is connected to the signal input terminal, the emitter is connected to the ground terminal, the collector is connected to the positive terminal of the signal output side power supply via the first resistor, and the collector is also connected to the base of the second switch tube via the second resistor; the collector of the second switch tube is connected to the signal output terminal; the first current limiting unit is connected to the base, emitter and positive terminal of the signal output side power supply of the second switch tube, and is used to limit the current from the high-level module to the signal output terminal;

[0010] The low-level module includes a third switch tube, a fourth switch tube, a third resistor, a fourth resistor and a second current limiting unit. The base of the third switch tube is connected to the signal input end, the emitter is connected to the ground end, the collector is connected to the positive end of the signal output side power supply via the third resistor, and the collector is also connected to the base of the fourth switch tube via the fourth resistor; the collector of the fourth switch tube is connected to the signal output end; the second current limiting unit is connected to the base, emitter and ground end of the fourth switch tube, and is used to limit the current from the signal output end to the low-level module.

[0011] Optionally, the first switch tube, the third switch tube and the fourth switch tube are all NPN tubes, and the second switch tube is a PNP tube.

[0012] Optionally, the first current limiting unit includes a fifth switch tube and a fifth resistor; the base of the fifth switch tube is connected to the emitter of the second switch tube, the collector is connected to the base of the second switch tube, and the emitter is connected to the positive terminal of the power supply on the signal output side; the two ends of the fifth resistor are respectively connected to the positive terminal of the power supply on the signal output side and the emitter of the second switch tube; the fifth switch tube is a PNP tube.

[0013] Optionally, the second current limiting unit includes a sixth switch tube and a sixth resistor; the base of the sixth switch tube is connected to the emitter of the fourth switch tube, the collector is connected to the base of the fourth switch tube, and the emitter is connected to the ground; the two ends of the sixth resistor are respectively connected to the emitter of the fourth switch tube and the ground; the sixth switch tube is an NPN tube.

[0014] Optionally, the high-level module includes a first reverse polarity protection unit, which is arranged in a branch from the collector of the second switch tube to the signal output end; the low-level module includes a second reverse polarity protection unit, which is arranged in a branch from the collector of the fourth switch tube to the signal output end.

[0015] Optionally, the first reverse polarity protection unit is a first Schottky diode, the anode of the first Schottky diode is connected to the collector of the second switch tube, and the cathode is connected to the signal output end; the second reverse polarity protection unit is a second Schottky diode, the cathode of the second Schottky diode is connected to the collector of the fourth switch tube, and the anode is connected to the signal output end.

[0016] Optionally, the high-level module includes a first overcurrent protection unit, which is arranged in a branch from the collector of the second switch tube to the signal output end; the low-level module includes a second overcurrent protection unit, which is arranged in a branch from the collector of the fourth switch tube to the signal output end.

[0017] Optionally, the first overcurrent protection unit is a zero-ohm resistor, and the second overcurrent protection unit is a resistance wire.

[0018] Optionally, it also includes a feedback acquisition module connected to the signal output end, the feedback acquisition module includes an eighth resistor, a ninth resistor and a Zener diode, the cathode of the Zener diode is connected to the signal output end through the eighth resistor, the anode is connected to the ground end, the ninth resistor is connected in parallel to both ends of the Zener diode, and the cathode of the Zener diode serves as a signal feedback end.

[0019] Optionally, it also includes a tenth resistor, an eleventh resistor and a twelfth resistor, the tenth resistor is connected between the base of the first switching tube and the signal input end, the eleventh resistor is connected between the base of the third switching tube and the signal input end, and one end of the twelfth resistor is connected to the signal input end, and the other end is connected to the ground or the positive end of the signal input side power supply.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] A signal output protection circuit of a safety detection device of the present invention is in a push-pull output form, has a fast switching speed, and has a strong driving capability for both high-level and low-level signal outputs; the on-current size of the second switch tube is limited by the first current limiting unit, thereby limiting the output current size provided to the signal output end, thereby preventing the switch tube device from being burned due to a large current generated when the signal output end is mistakenly connected to the ground end; the on-current size of the fourth switch tube is also limited by the second current limiting unit, thereby preventing the switch tube device from being burned due to a large current generated when the signal output end is mistakenly connected to a high level; the present invention overcomes the problem that the output signal circuit of the existing safety detection device has low fault tolerance and is prone to device damage, thereby improving the fault tolerance and safety of the use of the safety detection device;

[0022] Some embodiments of the present invention also prevent the current reversely input from the signal output terminal from damaging the circuit device by providing a first reverse polarity protection unit and a second reverse polarity protection unit;

[0023] Some embodiments of the present invention also provide a first overcurrent protection unit and a second overcurrent protection unit. When the current exceeds the limit, the first overcurrent protection unit and the second overcurrent protection unit will be disconnected, thereby protecting other circuit components. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 is a principle block diagram of some embodiments of the present invention;

[0026] Figure 2 is a principle block diagram of some embodiments of the present invention;

[0027] Figure 3 is a principle block diagram of some embodiments of the present invention;

[0028] Figure 4 is a circuit schematic diagram of some embodiments of the present invention;

[0029] Figure 5 1 is a circuit diagram of some embodiments of the present invention.

[0030] In the figure:

[0031] 100 - high level module; 110 - first current limiting unit; 120 - first reverse polarity protection unit; 130 - first overcurrent protection unit; 200 - low level module; 210 - second current limiting unit; 220 - second reverse polarity protection unit; 230 - second overcurrent protection unit. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. 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.

[0033] See also Figures 1 to 5The present invention proposes a signal output protection circuit of a safety detection device, comprising a high-level module 100 and a low-level module 200 connected in parallel between a signal input terminal and a signal output terminal. The high-level module 100 comprises a first switch tube Q1, a second switch tube Q2, a first resistor R1, a second resistor R2 and a first current limiting unit 110. The base of the first switch tube Q1 is connected to the signal input terminal, the emitter is connected to the ground terminal, the collector is connected to the positive terminal +24V of the signal output side power supply through the first resistor R1, and the collector is also connected to the base of the second switch tube Q2 through the second resistor R2; the collector of the second switch tube Q2 is connected to the signal output terminal; the first current limiting unit 110 is connected to the base, emitter and the positive terminal +24V of the signal output side power supply of the second switch tube Q2, and is used to limit the current from the high-level module 100 to the signal output terminal. The low-level module 200 includes a third switch tube Q3, a fourth switch tube Q4, a third resistor R3, a fourth resistor R4 and a second current limiting unit 210. The base of the third switch tube Q3 is connected to the signal input end, the emitter is connected to the ground end, the collector is connected to the positive end of the signal output side power supply +24V via the third resistor R3, and the collector is also connected to the base of the fourth switch tube Q4 via the fourth resistor R4; the collector of the fourth switch tube Q4 is connected to the signal output end; the second current limiting unit 210 is connected to the base, emitter and ground end of the fourth switch tube Q4, and is used to limit the current from the signal output end to the low-level module 200.

[0034] In a specific implementation, the main control device of the safety detection device outputs a signal, which is transmitted to other signal receiving devices via the signal output protection circuit of the safety detection device. The main control device of the safety detection device has a different power supply than other signal receiving devices. As an example, the signal output by the main control device of the safety detection device may be a pulse signal with a limited period and a limited width.

[0035] When the signal input end of the signal output protection circuit of the safety detection equipment receives a high-level signal, the first switch tube Q1 and the third switch tube Q3 of the high-level module 100 are both turned on, the second switch tube Q2 of the low-level module 200 is turned on, and the fourth switch tube Q4 is turned off. At this time, the positive terminal +24V of the signal output side power supply can output current to the signal output end through the first current limiting unit 110 and the second switch tube Q2. The first current limiting unit 110 is used to limit the conduction current of the second switch tube Q2, and then limit the output current provided to the signal output end, which can prevent the switch tube device from being burned due to a large current generated when the signal output end is mistakenly grounded.

[0036] When the signal input end of the signal output protection circuit of the safety detection equipment receives a low-level signal, the first switch tube Q1 and the third switch tube Q3 of the high-level module 100 are both turned off, the second switch tube Q2 of the low-level module 200 is turned off, and the fourth switch tube Q4 is turned on. At this time, there is no output current at the signal output end. If the level of the external connection of the signal output end is high, an external current flows from the signal output end and flows to the ground end through the fourth switch tube Q4 and the second current limiting unit 210. The second current limiting unit 210 is used to limit the conduction current of the fourth switch tube Q4, which can prevent the switch tube device from being burned by a large current generated when the signal output end is mistakenly connected to a high level.

[0037] The embodiment of the present invention is a push-pull output form with a fast switching speed and a strong driving capability for both high-level and low-level signal outputs. By setting the first current limiting unit 110 and the second current limiting unit 210, the problem of low fault tolerance of the output signal circuit of the existing safety detection equipment and easy device damage is overcome, thereby improving the fault tolerance and safety of the use of the safety detection equipment.

[0038] In some embodiments, see Figure 2 The first switch tube Q1, the third switch tube Q3 and the fourth switch tube Q4 are all NPN tubes, and the second switch tube Q2 is a PNP tube.

[0039] In some embodiments, see Figure 2 The first current limiting unit 110 includes a fifth switch tube Q5 and a fifth resistor R5; the base of the fifth switch tube Q5 is connected to the emitter of the second switch tube Q2, the collector is connected to the base of the second switch tube Q2, and the emitter is connected to the positive terminal +24V of the signal output side power supply; the two ends of the fifth resistor R5 are respectively connected to the positive terminal +24V of the signal output side power supply and the emitter of the second switch tube Q2; the fifth switch tube Q5 is a PNP tube.

[0040] In a specific implementation, when the signal input end of the signal output protection circuit of the safety detection device receives a high-level signal, if the load current output from the signal output end becomes larger, causing the voltage of the fifth resistor R5 to exceed 0.7V, the fifth switch tube Q5 will be turned on, thereby lowering the base voltage of the second switch tube Q2, reducing the current output by the second switch tube Q2, so that the voltage across the fifth resistor R5 can be constant at 0.7V. Since the voltage across the fifth resistor R5 is constant at 0.7V, the current of the fifth resistor R5 is also constant, so that the maximum current output from the signal output end is constant, and the specific current size can be adjusted by the resistance value of the fifth resistor R5. By limiting the maximum current output from the signal output end, the second switch tube Q2 can be prevented from being burned due to excessive conduction current.

[0041] In some embodiments, see Figure 2The second current limiting unit 210 includes a sixth switch tube Q6 and a sixth resistor R6; the base of the sixth switch tube Q6 is connected to the emitter of the fourth switch tube Q4, the collector is connected to the base of the fourth switch tube Q4, and the emitter is connected to the ground; the two ends of the sixth resistor R6 are respectively connected to the emitter of the fourth switch tube Q4 and the ground; the sixth switch tube Q6 is an NPN tube.

[0042] In a specific implementation, when the signal input end of the signal output protection circuit of the safety detection device receives a low-level signal, if the current flowing into the signal output end from the outside increases, causing the voltage of the sixth resistor R6 to exceed 0.7V, the sixth switch tube Q6 will be turned on, thereby lowering the base voltage of the fourth switch tube Q4, reducing the current output by the fourth switch tube Q4, so that the voltage across the sixth resistor R6 can be constant at 0.7V. Since the voltage across the sixth resistor R6 is constant at 0.7V, the current of the sixth resistor R6 is also constant, so that the maximum current flowing through the fourth switch tube Q4 is constant, and the specific current size can be adjusted by the resistance value of the sixth resistor R6. By limiting the maximum current, the fourth switch tube Q4 can be prevented from being burned due to excessive conduction current.

[0043] In some embodiments, see Figure 3 The high level module 100 includes a first reverse polarity protection unit 120, which is arranged in a branch from the collector of the second switch tube Q2 to the signal output end; the low level module 200 includes a second reverse polarity protection unit 220, which is arranged in a branch from the collector of the fourth switch tube Q4 to the signal output end.

[0044] In a specific implementation, the first reverse polarity protection unit 120 and the second reverse polarity protection unit 220 are used to prevent the current reversely input from the signal output terminal from damaging the circuit device.

[0045] In some embodiments, see Figure 4 The first reverse polarity protection unit 120 is a first Schottky diode D1, the anode of the first Schottky diode D1 is connected to the collector of the second switch tube Q2, and the cathode is connected to the signal output end; the second reverse polarity protection unit 220 is a second Schottky diode D2, the cathode of the second Schottky diode D2 is connected to the collector of the fourth switch tube Q4, and the anode is connected to the signal output end.

[0046] In a specific implementation, when the signal input end of the signal output protection circuit of the safety detection device receives a high-level signal, the positive terminal +24V of the signal output side power supply can output current to the signal output end through the first current limiting unit 110, the second switch tube Q2 and the first Schottky diode D1. At this time, if there is a current input in reverse from the signal output end, it will be blocked by the first Schottky diode D1; when the signal input end of the signal output protection circuit of the safety detection device receives a low-level signal, if there is a current input in reverse from the signal output end, it will flow to the ground end through the second Schottky diode D2 and the fourth switch tube Q4.

[0047] In some other embodiments, the first reverse polarity protection unit 120 and the second reverse polarity protection unit 220 may also be configured as ordinary diodes.

[0048] In some embodiments, see Figure 3 The high-level module 100 includes a first overcurrent protection unit 130, which is arranged in a branch from the collector of the second switch tube Q2 to the signal output end; the low-level module 200 includes a second overcurrent protection unit 230, which is arranged in a branch from the collector of the fourth switch tube Q4 to the signal output end.

[0049] In a specific implementation, during the control dead zone, the second switch tube Q2 and the fourth switch tube Q4 may be turned on at the same time, which will cause excessive current. The first overcurrent protection unit 130 and the second overcurrent protection unit 230 will be disconnected when the current exceeds the limit, thereby protecting other circuit components.

[0050] In some embodiments, see Figure 4 The first over-current protection unit 130 is a zero-ohm resistor R7, and the second over-current protection unit 230 is a resistor F2.

[0051] When the signal input end of the signal output protection circuit of the safety detection device receives a high level signal, a load current will flow through the first overcurrent protection unit 130. The first overcurrent protection unit 130 uses a zero-ohm resistor to avoid residual voltage drop and reduce power loss. The zero-ohm resistor will fuse when the current exceeds the limit to protect other circuit components.

[0052] In some other embodiments, the first overcurrent protection unit 130 and the second overcurrent protection unit 230 are both resistance wires.

[0053] In some embodiments, see Figure 3 , Figure 4The signal output protection circuit of the safety detection equipment also includes a feedback acquisition module 300 connected to the signal output terminal OSSD. The feedback acquisition module 300 includes an eighth resistor R8, a ninth resistor R9 and a Zener diode D3. The cathode of the Zener diode D3 is connected to the signal output terminal through the eighth resistor R8, and the anode is connected to the ground terminal. The ninth resistor R9 is connected in parallel to both ends of the Zener diode D3. The cathode of the Zener diode D3 serves as the signal feedback terminal FK_OSSD.

[0054] In a specific implementation, when the signal output terminal OSSD outputs current or receives current flowing in, the signal feedback terminal FK_OSSD can output a feedback signal of a set level to the main control device of the safety detection device. The level of the feedback signal can be set by the voltage regulator diode D3.

[0055] In some embodiments, see Figure 4 , Figure 5 , further comprising a tenth resistor R10, an eleventh resistor R11 and a twelfth resistor R12, the tenth resistor R10 being connected between the base of the first switch tube Q1 and the signal input terminal SC, the eleventh resistor R11 being connected between the base of the third switch tube Q3 and the signal input terminal SC, one end of the twelfth resistor R12 being connected to the signal input terminal, and the other end being connected to the ground terminal (such as Figure 4 as shown) or the positive power supply terminal MCU_VCC on the signal input side (as shown Figure 5 shown).

[0056] In a specific implementation, the tenth resistor R10 is used to limit the base current of the first switch tube Q1, and the eleventh resistor R11 is used to limit the base current of the third switch tube Q3. The twelfth resistor R12 is used to set the initial input level of the circuit at the moment when the device is powered on, and can be connected to the ground terminal (such as Figure 4 ) is set to low level, or connect the positive terminal MCU_VCC of the signal input side power supply (as shown Figure 5 as shown) is set to high level.

[0057] In some embodiments, the safety detection device product can also be provided with two groups of signal output protection circuits of safety detection devices at the same time, and the twelfth resistor R1 of one group is connected to the ground terminal (such as Figure 4 The twelfth resistor R1 of the other group is connected to the positive terminal MCU_VCC of the signal input side power supply (as shown in Figure 5 to be compatible with different initial signal states.

[0058] Those skilled in the art will appreciate that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the field to which the present invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless specifically defined.

[0059] It should be noted that certain words are used in this specification and claims to refer to specific components. Those skilled in the art should understand that different manufacturers and producers may use different terms to refer to the same component. This specification and claims do not use the difference in terms as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction.

[0060] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0061] In addition, those skilled in the art will appreciate that, although some embodiments described herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present invention and form different embodiments. For example, any one of the embodiments claimed in the claims can be used in any combination in the embodiments of the present invention.

[0062] Those skilled in the art will appreciate that the modules in the devices in the embodiments can be adaptively changed and set in one or more devices different from the embodiments. The modules or units or components in the embodiments can be combined into one module or unit or component, and in addition they can be divided into multiple submodules or subunits or subcomponents. Except that at least some of such features and / or processes or units are mutually exclusive, all features disclosed in this specification (including corresponding claims, abstracts and drawings) and all processes or units of any method or device disclosed in this manner can be combined in any combination. Unless otherwise explicitly stated, each feature disclosed in this specification (including corresponding claims, abstracts and drawings) can be replaced by an alternative feature that provides the same, equivalent or similar purpose.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A signal output protection circuit for a safety detection device, characterized in that: It comprises a high level module (100) and a low level module (200) connected in parallel between a signal input end and a signal output end; The high-level module (100) comprises a first switch tube (Q1), a second switch tube (Q2), a first resistor (R1), a second resistor (R2) and a first current limiting unit (110); the base of the first switch tube (Q1) is connected to the signal input end, the emitter is connected to the ground end, the collector is connected to the positive end (+24V) of the signal output side power supply via the first resistor (R1), and the collector is also connected to the base of the second switch tube (Q2) via the second resistor (R2); the collector of the second switch tube (Q2) is connected to the signal output end; the first current limiting unit (110) is connected to the base, emitter and the positive end (+24V) of the signal output side power supply of the second switch tube (Q2), and is used to limit the current from the high-level module (100) to the signal output end; The low-level module (200) comprises a third switch tube (Q3), a fourth switch tube (Q4), a third resistor (R3), a fourth resistor (R4) and a second current limiting unit (210); the base of the third switch tube (Q3) is connected to the signal input end, the emitter is connected to the ground end, the collector is connected to the positive end (+24V) of the signal output side power supply via the third resistor (R3), and the collector is also connected to the base of the fourth switch tube (Q4) via the fourth resistor (R4); the collector of the fourth switch tube (Q4) is connected to the signal output end; the second current limiting unit (210) is connected to the base, emitter and ground end of the fourth switch tube (Q4), and is used to limit the current from the signal output end to the low-level module (200).

2. The signal output protection circuit of a safety detection device according to claim 1, characterized in that: The first switch tube (Q1), the third switch tube (Q3) and the fourth switch tube (Q4) are all NPN tubes, and the second switch tube (Q2) is a PNP tube.

3. The signal output protection circuit of a safety detection device according to claim 2, characterized in that: The first current limiting unit (110) comprises a fifth switch tube (Q5) and a fifth resistor (R5); the base of the fifth switch tube (Q5) is connected to the emitter of the second switch tube (Q2), the collector is connected to the base of the second switch tube (Q2), and the emitter is connected to the positive terminal (+24V) of the signal output side power supply; the two ends of the fifth resistor (R5) are respectively connected to the positive terminal (+24V) of the signal output side power supply and the emitter of the second switch tube (Q2); the fifth switch tube (Q5) is a PNP tube.

4. The signal output protection circuit of a safety detection device according to claim 1, characterized in that: The second current limiting unit (210) comprises a sixth switch tube (Q6) and a sixth resistor (R6); the base of the sixth switch tube (Q6) is connected to the emitter of the fourth switch tube (Q4), the collector is connected to the base of the fourth switch tube (Q4), and the emitter is connected to the ground; the two ends of the sixth resistor (R6) are respectively connected to the emitter of the fourth switch tube (Q4) and the ground; the sixth switch tube (Q6) is an NPN tube.

5. The signal output protection circuit of a safety detection device according to claim 1, characterized in that: The high-level module (100) comprises a first reverse polarity protection unit (120), wherein the first reverse polarity protection unit (120) is arranged in a branch from the collector of the second switch tube (Q2) to the signal output end; The low-level module (200) comprises a second reverse polarity protection unit (220), and the second reverse polarity protection unit (220) is arranged in a branch from the collector of the fourth switch tube (Q4) to the signal output end.

6. The signal output protection circuit of a safety detection device according to claim 5, characterized in that: The first reverse polarity protection unit (120) is a first Schottky diode (D1), the anode of the first Schottky diode (D1) is connected to the collector of the second switch tube (Q2), and the cathode is connected to the signal output end; the second reverse polarity protection unit (220) is a second Schottky diode (D2), the cathode of the second Schottky diode (D2) is connected to the collector of the fourth switch tube (Q4), and the anode is connected to the signal output end.

7. The signal output protection circuit of a safety detection device according to claim 1, characterized in that: The high-level module (100) comprises a first overcurrent protection unit (130), which is arranged in a branch from the collector of the second switch tube (Q2) to the signal output end; the low-level module (200) comprises a second overcurrent protection unit (230), which is arranged in a branch from the collector of the fourth switch tube (Q4) to the signal output end.

8. The signal output protection circuit of a safety detection device according to claim 7, characterized in that: The first overcurrent protection unit (130) is a zero-ohm resistor (R7), and the second overcurrent protection unit (230) is a resistance wire (F2).

9. The signal output protection circuit of a safety detection device according to claim 1, characterized in that: The invention also comprises a feedback collection module (300) connected to the signal output end, wherein the feedback collection module (300) comprises an eighth resistor (R8), a ninth resistor (R9) and a voltage-stabilizing diode (D3), wherein the cathode of the voltage-stabilizing diode (D3) is connected to the signal output end via the eighth resistor (R8), and the anode is connected to the ground end, the ninth resistor (R9) is connected in parallel to both ends of the voltage-stabilizing diode (D3), and the cathode of the voltage-stabilizing diode (D3) serves as a signal feedback end.

10. The signal output protection circuit of a safety detection device according to claim 1, characterized in that: The invention also includes a tenth resistor (R10), an eleventh resistor (R11) and a twelfth resistor (R12), wherein the tenth resistor (R10) is connected between the base of the first switch tube (Q1) and the signal input terminal, the eleventh resistor (R11) is connected between the base of the third switch tube (Q3) and the signal input terminal, and one end of the twelfth resistor (R12) is connected to the signal input terminal, and the other end is connected to the ground terminal or the positive terminal (MCU_VCC) of the signal input side power supply.

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