Digital quantity output loop disconnection diagnosis circuit

Abstract

The utility model discloses a digital quantity output loop disconnection diagnosis circuit comprising the following steps: when disconnection diagnosis is needed, a main switch is controlled to be in a disconnection state, and a diagnosis current source is controlled to be started so as to inject a diagnosis current; the diagnostic current flows through a parallel combination of the external load and the internal resistive path; and the control unit judges the voltage level of the digital quantity output end by reading the output state of the comparator, and judges whether the external load is disconnected according to the voltage level. According to the utility model, in a power-on safety application mode and under the condition that the working state is load power loss, whether the external load is disconnected or not is judged in real time; and in the power-losing safety application mode, the working state is that the load is electrified, the diagnosis current source is inserted periodically, and the external disconnection fault result of the channel is obtained through the read-back comparator. Therefore, the load disconnection can be diagnosed under all working conditions.

Description

Technical Field

[0001] This utility model relates to the field of industrial control system technology, and more specifically, to a digital output circuit disconnection diagnosis circuit. Background Technology

[0002] In industrial control systems, load disconnection diagnosis in digital output lines is a key technology for ensuring stable equipment operation. Its core principle is to detect faults by monitoring changes in the electrical characteristics of the lines. Electrical characteristic monitoring methods rely on resistance detection, current detection, and voltage detection to detect the operating status of electrical signal lines.

[0003] The digital output circuit has two application modes: one is the power failure safety application mode, in which the load is powered on; the other is the power-on safety application mode, in which the load is de-powered.

[0004] Generally, open circuit detection is based on reading the loop current using a sampling resistor when the load is powered and functioning normally. If the load is disconnected, the loop current will be less than the current disconnection threshold. This method requires a current sensing resistor, differential operational amplifier, comparator, or A / D converter to sample the current loop current for judgment. This method is traditional and costly, and its application is in power-loss safety mode, where the circuit automatically switches to safety upon disconnection. User demand is not particularly strong in this case. Conversely, in power-on safety mode, normal operation involves the load being de-energized, requiring the diagnosis of line disconnections under power-loss conditions. Based on this requirement, even when the line is not outputting voltage, it is necessary to determine the disconnection status in the line to ensure that, under power-on safety conditions, the device can start working when the line outputs voltage. This scenario offers strong predictive capabilities, providing early warning of system line fault states.

[0005] Therefore, how to provide a digital output circuit disconnection diagnosis circuit has become a technical problem that urgently needs to be solved in this field. Utility Model Content

[0006] The purpose of this invention is to provide a circuit for diagnosing open circuits in digital output circuits.

[0007] According to the present invention, a digital output circuit disconnection diagnosis circuit is provided, including a digital output terminal for connecting an external load to ground;

[0008] The main switch has its control terminal connected to the control unit, its input terminal connected to the voltage source, and its output terminal connected to the digital output terminal, and is used to selectively connect the voltage source to the digital output terminal according to the instructions of the control unit.

[0009] A diagnostic current source, whose control terminal is connected to the control unit and whose output terminal is connected to the digital output terminal, is used to inject diagnostic current into the digital output terminal under the control of the control unit.

[0010] An internal resistor path, comprising: a first internal resistor and a second internal resistor, wherein one end of the first internal resistor is connected to a digital output terminal and the other end is connected to one end of the second internal resistor; the other end of the second internal resistor is connected to ground, providing a parallel loop for the diagnostic current.

[0011] A comparator, whose first input is connected to the other end of the first internal resistor, whose second input is connected to a reference voltage, and whose output is connected to the control unit;

[0012] The control unit is configured to: when a disconnection diagnosis is required, control the main switch to be in the off state, control the diagnostic current source to start and inject the diagnostic current; the diagnostic current flows through the parallel combination of the external load and the internal resistor path; the control unit determines the voltage level of the digital output terminal by reading the output state of the comparator, and determines whether the external load has been disconnected.

[0013] Optionally, the total resistance of the first internal resistor and the second internal resistor is set to be much greater than the typical maximum resistance of the external load in the uninterrupted state, generally more than 20 times.

[0014] Optionally, the diagnostic current value injected by the diagnostic current source is set as follows:

[0015] When the external load is not disconnected and its resistance is within the preset normal range, the voltage at the digital output terminal is lower than the reference voltage, causing the comparator to output a first preset level.

[0016] When the external load is disconnected, the diagnostic current mainly flows through the internal resistor path, causing the voltage at the digital output terminal to be higher than the reference voltage, and causing the comparator to output a second preset level.

[0017] Optionally, the first preset level is low, indicating no disconnection; the second preset level is high, indicating a disconnection; or vice versa, depending on the input connection method of the comparator and the setting of the reference voltage.

[0018] Optionally, the control unit is further configured to:

[0019] The digital output circuit is designed for a power failure safety application mode, that is, when the main switch is in the closed state during normal operation to enable the external load to be energized, the main switch is periodically controlled to be briefly opened and the diagnostic current source is activated to perform a disconnection diagnosis.

[0020] Optionally, the main switch is an electronic switch selected from MOSFET, BJT or IGBT.

[0021] Optionally, the diagnostic current source is a constant current source that is controlled to be switched on and off by the control unit.

[0022] Optionally, the low-level output of the digital output terminal is defined as being lower than a preset low-level voltage threshold.

[0023] Optionally, the value of the diagnostic current is set such that when the resistance of the external load is less than the preset maximum resistance of the unbroken circuit, the voltage of the digital output terminal is lower than the preset low-level voltage threshold and lower than the reference voltage.

[0024] Optionally, the total resistance of the internal resistance path is set such that when the external load is disconnected, the voltage generated by the diagnostic current on the internal resistance path is higher than the reference voltage of the comparator, and the total resistance is greater than a preset minimum internal resistance.

[0025] According to the technical content disclosed in this utility model, the following beneficial effects are achieved: In the power failure safety application mode, when the load is energized, the ability of the channel to be guided to safety, that is, the ability to output power failure, can be periodically confirmed. Under the condition of periodically diagnosing power failure, the disconnection diagnosis current source can be enabled, and the result of external disconnection faults in the channel can be obtained through a readback comparator. This ensures that load disconnections are diagnosed under all operating conditions.

[0026] Other features and advantages of the present invention will become clear from the following detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings. Attached Figure Description

[0027] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of the present invention and, together with their description, serve to explain the principles of the present invention.

[0028] Figure 1 This is a schematic diagram of a digital output loop disconnection diagnosis circuit provided according to an embodiment.

[0029] Explanation of reference numerals in the attached diagram: K1 - Main switch, U1 - Control unit, VDD - Voltage source, DO - Digital output terminal, Is - Diagnostic current source, R1 - First internal resistor, R2 - Second internal resistor, D1 - Diode, RL - External load, U2 - Comparator, Vref - Reference voltage, Rout1 - First path, Rout2 - Second path. Detailed Implementation

[0030] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the present invention.

[0031] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use.

[0032] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0033] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0034] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0035] According to this utility model, such as Figure 1 As shown, a digital output loop disconnection diagnostic circuit is provided, including,

[0036] The digital output terminal DO is used to connect the external load RL to ground.

[0037] The main switch K1 has its control terminal connected to the control unit U1, its input terminal connected to the voltage source VDD, and its output terminal connected to the digital output terminal DO. It is used to selectively connect the voltage source VDD to the digital output terminal DO according to the instructions of the control unit U1.

[0038] A diagnostic current source Is, whose control terminal is connected to the control unit U1 and whose output terminal is connected to the digital output terminal DO, is used to inject diagnostic current into the digital output terminal DO under the control of the control unit U1.

[0039] An internal resistor path, comprising: a first internal resistor R1 and a second internal resistor R2, wherein one end of the first internal resistor R1 is connected to the digital output terminal DO, and the other end is connected to one end of the second internal resistor R2; the other end of the second internal resistor R2 is connected to ground, providing a parallel loop for the diagnostic current.

[0040] Comparator U2 has its first input terminal connected to the other end of the first internal resistor R1, its second input terminal connected to the reference voltage Vref, and its output terminal connected to the control unit U1.

[0041] The control unit U1 is configured to: when a disconnection diagnosis is required, control the main switch K1 to be in the open state, and control the diagnostic current source Is to start to inject the diagnostic current; the diagnostic current flows through the parallel combination of the external load RL and the internal resistor path; the control unit U1 determines the voltage level of the digital output terminal DO by reading the output state of the comparator U2, and determines whether the external load RL has been disconnected.

[0042] In some embodiments, the total resistance of the first internal resistor R1 and the second internal resistor R2 is set to be much greater than the typical maximum resistance of the external load RL in the unbroken state, generally more than 20 times.

[0043] In some embodiments, the diagnostic current value injected by the diagnostic current source Is is set as follows:

[0044] When the external load RL is not disconnected and its resistance is within the preset normal range, the voltage of the digital output terminal DO is lower than the reference voltage Vref, causing the comparator U2 to output a first preset level.

[0045] When the external load RL is disconnected, the diagnostic current mainly flows through the internal resistor path, causing the voltage at the digital output terminal DO to be higher than the reference voltage Vref, and causing the comparator U2 to output a second preset level.

[0046] In some embodiments, the first preset level is low, indicating no disconnection; the second preset level is high, indicating a disconnection; or vice versa, depending on the input connection method of the comparator U2 and the setting of the reference voltage Vref.

[0047] In some embodiments, the control unit U1 is further configured to:

[0048] The digital output circuit is designed for a power failure safety application mode, that is, when the main switch K1 is in the closed state during normal operation to energize the external load RL, the main switch K1 is periodically controlled to briefly open and the diagnostic current source Is is activated to perform a disconnection diagnosis.

[0049] In some embodiments, the main switch K1 is an electronic switch selected from MOSFET, BJT or IGBT.

[0050] In some embodiments, the diagnostic current source Is is a constant current source that is controlled to be switched on and off by the control unit U1.

[0051] In some embodiments, the low-level output of the digital output terminal DO is defined as being below a preset low-level voltage threshold.

[0052] In some embodiments, the value of the diagnostic current Is is set such that when the resistance of the external load RL is less than the preset maximum unbroken resistance, the voltage of the digital output terminal DO is lower than the preset low-level voltage threshold and lower than the reference voltage Vref.

[0053] In some embodiments, the total resistance of the internal resistance path is set such that when the external load RL is disconnected, the voltage generated by the diagnostic current Is on the internal resistance path is higher than the reference voltage Vref of the comparator U2, and the total resistance is greater than a preset minimum internal resistance.

[0054] In some embodiments, the digital output circuit disconnection diagnostic circuit further includes: a diode D1; the anode of the diode D1 is connected to the output point of the diagnostic current source Is and the voltage source VDD; the cathode of the diode D1 is connected to one end of the first internal resistor R1 and the digital output terminal DO.

[0055] Control unit U1, i.e., MCU, controls switch K1. When K1 is closed, it outputs a high level (the load is energized); when K1 is open, it outputs a low level (the load is de-energized). Here, the standard value of VDD is 24V, a high-level output is defined as >15V, and a low-level output is defined as <2.4V.

[0056] An external load RL of less than 5K ohms indicates no disconnection. A load greater than 5K ohms indicates a disconnection.

[0057] When K1 is disconnected and the current source Is is working, if the external load is not disconnected, Is mainly returns through the first path Rout1, and the voltage formed at DO is Is*RL. To ensure a low-level output Is*RL < 2.4V, here when RL = 5k ohms, Is < 2.4V / 5k = 0.48mA. In the actual circuit, for a wider load range, Is = 0.2mA is chosen. At this time, the external load RL is less than 2.4V / 0.2mA = 12k ohms, which is an undisconnected load. At this time, U2 outputs a low level, indicating that there is no disconnection. If the external load RL increases, the Is current will return through the first path Rout1 and the second path Rout2. Therefore, the voltage formed by the internal impedance and the external impedance absorbing the current source Is should be > 2.5V, that is, (R1+R2) / / RL > 12Kohm.

[0058] When K1 is disconnected and the current source Is is working, when the external load RL is disconnected, Is mainly returned through the second path Rout2. The voltage formed at DO is Is*(R1+R2)>2.5V, then R1+R2>12Kohm.

[0059] By properly selecting the current source Is and the internal resistance path resistors R1 and R2, it can be determined that an external impedance greater than 15 kΩ indicates a broken wire.

[0060] The above describes the principle of disconnection diagnosis when the channel output is low (load is de-energized). To solve the problem of load disconnection under all operating conditions, specifically the problem of disconnection when the channel output is high (load is energized), the disconnection diagnosis method for load de-energization can be used.

[0061] In summary, this invention, in the power-on safety application mode (operating state where the load is de-energized), determines in real time whether there is a break in the external load; in the power-off safety application mode (operating state where the load is energized), it periodically inserts a diagnostic current source and obtains the result of an external break in the channel through a readback comparator. In the power-off safety application mode (operating state where the load is energized), it is necessary to periodically confirm the DO channel's ability to guide safely, that is, its ability to output without power. This can be achieved by enabling the break-out diagnostic current source during the periodic diagnosis of DO output power failure, and obtaining the result of an external break in the channel through a readback comparator U2. This ensures that load breaks are diagnosed under all operating conditions.

[0062] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of the present invention. The scope of the present invention is defined by the appended claims.

Claims

1. A digital output circuit disconnection diagnostic circuit, characterized in that, include: Digital output terminal, used to connect an external load to ground; The main switch has its control terminal connected to the control unit, its input terminal connected to the voltage source, and its output terminal connected to the digital output terminal, and is used to selectively connect the voltage source to the digital output terminal according to the instructions of the control unit. A diagnostic current source, whose control terminal is connected to the control unit and whose output terminal is connected to the digital output terminal, is used to inject diagnostic current into the digital output terminal under the control of the control unit. An internal resistor path, comprising: a first internal resistor and a second internal resistor, wherein one end of the first internal resistor is connected to a digital output terminal and the other end is connected to one end of the second internal resistor; The other end of the second internal resistor is connected to ground, providing a parallel loop for the diagnostic current; A comparator, whose first input is connected to the other end of the first internal resistor, whose second input is connected to a reference voltage, and whose output is connected to the control unit; The control unit is configured to: when a disconnection diagnosis is required, control the main switch to be in the off state, control the diagnostic current source to start and inject the diagnostic current; the diagnostic current flows through the parallel combination of the external load and the internal resistor path; the control unit determines the voltage level of the digital output terminal by reading the output state of the comparator, and determines whether the external load has been disconnected.

2. The digital output circuit disconnection diagnosis circuit according to claim 1, characterized in that, The total resistance of the first internal resistor and the second internal resistor is set to be more than 20 times the typical maximum resistance of the external load in the uninterrupted state.

3. The digital output circuit disconnection diagnosis circuit according to claim 2, characterized in that, The diagnostic current value injected by the diagnostic current source is set as follows: When the external load is not disconnected and its resistance is within the preset normal range, the voltage at the digital output terminal is lower than the reference voltage, causing the comparator to output a first preset level. When the external load is disconnected, the diagnostic current mainly flows through the internal resistor path, causing the voltage at the digital output terminal to be higher than the reference voltage, and causing the comparator to output a second preset level.

4. The digital output circuit disconnection diagnosis circuit according to claim 3, characterized in that, The first preset level is low, indicating no disconnection; the second preset level is high, indicating a disconnection; or vice versa, depending on the input connection method of the comparator and the setting of the reference voltage.

5. The digital output circuit disconnection diagnosis circuit according to claim 4, characterized in that, The control unit is further configured to: The digital output circuit is designed for a power failure safety application mode, that is, when the main switch is in the closed state during normal operation to enable the external load to be energized, the main switch is periodically controlled to be briefly opened and the diagnostic current source is activated to perform a disconnection diagnosis.

6. The digital output circuit disconnection diagnosis circuit according to claim 5, characterized in that, The main switch is an electronic switch, selected from MOSFET, BJT or IGBT.

7. The digital output circuit disconnection diagnosis circuit according to claim 6, characterized in that, The diagnostic current source is a constant current source that is controlled to be switched on and off by the control unit.

8. The digital output circuit disconnection diagnosis circuit according to claim 7, characterized in that, The low-level output of the digital output terminal is defined as being below a preset low-level voltage threshold.

9. The digital output circuit disconnection diagnosis circuit according to claim 8, characterized in that, The diagnostic current is set such that when the resistance of the external load is less than the preset maximum resistance of the unbroken circuit, the voltage at the digital output terminal is lower than the preset low-level voltage threshold and lower than the reference voltage.

10. The digital output circuit disconnection diagnosis circuit according to claim 9, characterized in that, The total resistance of the internal resistance path is set such that when the external load is disconnected, the voltage generated by the diagnostic current on the internal resistance path is higher than the reference voltage of the comparator, and the total resistance is greater than a preset minimum internal resistance.

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