Tandem switch group fault dual detection circuit and protection circuit

Abstract

The utility model belongs to the technical field of switch fault detection, and particularly relates to a series switch group fault dual detection circuit and a protection circuit. In order to overcome the defect that double detection of a series switch group is not disclosed in the prior art, the utility model adopts the following technical scheme: the series switch group fault double detection circuit comprises a series switch group which comprises a plurality of mechanical switches which are connected in series, one end of each mechanical switch is connected with the positive electrode of a first power supply Vin, the mechanical switches are switched on in normal, and the mechanical switches are switched off in fault; a plurality of single switch detection units which are respectively connected in parallel with the mechanical switches and detect whether the mechanical switches are closed or not; the resistor R3 is connected in series with the series switch group and connected with the first ground; and the total detection unit is connected between the series switch group and the resistor R3 and is used for detecting whether the series switch group is closed or not. The beneficial effects of the series switch group fault dual detection circuit are that whether a corresponding single mechanical switch is normal or not can be detected, and whether the whole series switch group is normal or not can also be detected.

Description

Technical Field

[0001] The utility model belongs to the technical field of switch fault detection, and particularly relates to a double-fault detection circuit and a protection circuit for a series switch group fault. Background Art

[0002] At present, many industrial electrical equipment in the market, such as refrigerant recovery machines, etc., have multiple switches, which are connected in series, parallel or series-parallel to achieve functions such as thermal protection. To ensure that when these switches are all normal, the industrial electrical equipment works normally, and when one of the switches fails, the electrical equipment stops working, it is necessary to detect the states of these switches and decide whether to stop the machine according to the switch states. Usually, a fault detection circuit is set for each switch for detection, and a single-chip microcomputer, etc., receives the signals of the fault detection circuit and judges whether to stop the machine.

[0003] During the use of industrial electrical equipment, when a certain switch fails, the corresponding fault detection circuit of this switch sends out a fault signal. After receiving the fault signal, a controller (such as a single-chip microcomputer) etc. shuts down the equipment at the software level. However, the program of the controller (such as a single-chip microcomputer) is relatively easy to run away (cannot operate normally). When the controller (such as a single-chip microcomputer) processes the fault signal abnormally, the industrial electrical equipment cannot stop in time, and the user cannot receive an alarm prompt, thus dangerous situations may occur.

[0004] In the prior art, although there are also detection circuits for multi-way switch faults, their application ranges are relatively narrow (not suitable for refrigerant recovery machines) or there is still room for improvement. For example, in CN203164373U - A detection circuit for multi-way switch fault signals, its detection circuit includes a high-voltage power supply, the high-voltage power supply is connected to a load through a switching device, the switching component is composed of switches connected in series, and each switch is connected to the high-voltage power supply and a PLC controller through a signal processing circuit, reducing the number of external control circuit interfaces, optimizing the system response time, and being able to reduce the number of input points of the control device. However, each switch is respectively connected to the signal processing circuit, the structure of the signal processing circuit is relatively complex, and only single detection can be achieved relying on the signal processing circuit. Most importantly, when the program of the controller runs away, it cannot stop in time.

[0005] Therefore, it is necessary to design a double-fault detection circuit for multi-way switches, so that when one or more switches fail, the fault detection circuit can send out one or more double-fault signals.

[0006] In addition, when the switch is a type such as a contact switch, during the working process of the industrial electrical equipment, the contact switch may instantaneously disconnect and then close immediately due to reasons such as vibration. To avoid mis-disconnection caused by vibration, it is also necessary to set a delay structure. Summary of the Invention

[0007] In view of the deficiency in the prior art that the double detection of the series switch group is not disclosed, the present utility model provides a double-fault detection circuit for the series switch group to detect each individual switch and all switches. The present utility model also provides a multi-channel switch protection circuit. Further, a delay structure is provided to avoid false disconnection caused by vibration.

[0008] To achieve the above object, the present utility model adopts the following technical solutions: A double-fault detection circuit for a series switch group, the double-fault detection circuit for the series switch group includes:

[0009] A series switch group, including a plurality of mechanical switches connected in series, one end connected to the positive pole of the first power supply Vin, the mechanical switches are closed when normal and opened when faulty;

[0010] A plurality of single-switch detection units, respectively connected in parallel with each mechanical switch to detect whether each mechanical switch is closed;

[0011] A resistor R3, connected in series with the series switch group and connected to the first ground GND;

[0012] A total detection unit, connected between the series switch group and the resistor R3 to detect whether the series switch group is closed.

[0013] As an improvement, the single-switch detection unit includes a series resistor and a single-switch optocoupler. The positive pole of the input end of the single-switch optocoupler is connected to the positive pole of the first power supply Vin, and the negative pole of the input end is connected to the first ground GND through the series resistor.

[0014] As an improvement, the emitter of the triode of the single-switch optocoupler is grounded, the collector is connected to the positive pole of the second power supply Vd, and a current-limiting resistor is further provided between the collector and the positive pole of the second power supply Vd. The collector is also grounded through a filter capacitor.

[0015] As an improvement, the total detection unit includes a comparator U3 and a total-switch optocoupler U4. The non-inverting input terminal of the comparator U3 is connected between the series switch group and the resistor R3. The output terminal of the comparator U3 is connected to the negative pole of the input end of the total-switch optocoupler U4. The positive pole of the input end of the total-switch optocoupler U4 is connected to the positive pole of the third power supply Vcc;

[0016] When all the mechanical switches of the series switch group are normal, the voltage at the non-inverting input terminal of the comparator U3 is greater than the voltage at the inverting input terminal of the comparator U3; when one or more mechanical switches of the series switch group are faulty, the voltage at the non-inverting input terminal of the comparator U3 is less than the voltage at the inverting input terminal of the comparator U3.

[0017] As an improvement, a series resistor R6 and a resistor R7 are provided between the positive electrode of the third power supply Vcc and the first ground GND. The resistor R6 is grounded, and the inverting input terminal of the comparator U3 is connected between the resistor R6 and the resistor R7.

[0018] As an improvement, the mechanical switch is a contact switch, and the series switch group fault double detection circuit further includes a delay unit. When one or more mechanical switches in the series switch group are disconnected, the delay unit causes the voltage at the non-inverting input terminal of the comparator U3 to change with a delay.

[0019] As an improvement, the delay unit includes a series-connected diode D1, a resistor R4, and a resistor R5 provided between the resistor R3 and the series switch group. The resistor R5 is connected to the first ground GND. The delay unit further includes a capacitor C3 provided between the negative electrode of the diode D1 and the first ground GND. The non-inverting input terminal of the comparator U3 is connected between the resistor R4 and the resistor R5.

[0020] As an improvement, a resistor R8 is provided between the comparator U3 and the main switch optocoupler U4.

[0021] The series switch group double protection circuit includes the aforementioned series switch group fault double detection circuit, and further includes a single-chip microcomputer and a relay disconnection unit. All single-switch detection units are connected to the single-chip microcomputer. When one or more mechanical switch faults are detected, the single-chip microcomputer and the relay disconnection unit cause the relay to disconnect.

[0022] As an improvement of the protection circuit, the series switch group double protection circuit further includes a plurality of filter capacitors provided at each single-switch detection unit. One end of the filter capacitor is connected to the second ground GND1, and the other end is connected to the positive electrode of the second power supply Vd through a current-limiting resistor.

[0023] As an improvement of the protection circuit, the relay disconnection unit includes a triode Q1 and a series-connected resistor R9, a resistor R10, and a resistor R11. One end of the resistor R9 is connected to the positive electrode of the second power supply Vd, and the other end is connected to the collector of the triode of the main switch optocoupler U4. The collector of the triode of the main switch optocoupler U4 is connected between the resistor R9 and the resistor R10. The emitter of the triode of the main switch optocoupler U4 is connected to the second ground GND1. The base of the triode Q1 is connected between the resistor R10 and the resistor R11. The emitter of the triode Q1 is connected to the second ground GND1, and the collector of the triode Q1 is connected in series with the relay K1.

[0024] The beneficial effects of the series switch group fault dual detection circuit of the present utility model are as follows: It includes a series switch group, a single switch detection unit, and a total detection unit. The single switch detection unit can detect whether the corresponding single mechanical switch is normal, and the total detection unit detects whether the entire series switch group is normal. The single switch detection unit is usually connected to a single-chip microcomputer. In addition to the single-chip microcomputer controlling the device through a program, it can also learn through the single-chip microcomputer which specific mechanical switch or switches are faulty; in addition to detecting the entire series switch group when the single switch detection unit fails, the total detection unit can also be connected to a relay disconnection unit, and when the single-chip microcomputer program runs abnormally, the relay is disconnected mechanically.

[0025] The series switch group dual protection circuit of the present utility model adopts the series switch group fault dual detection circuit of the present utility model, and includes a single-chip microcomputer and a relay disconnection unit. When the program of the single-chip microcomputer runs abnormally and cannot work properly, the relay disconnection unit can ensure that the relay is disconnected in time. Brief Description of the Drawings

[0026] Figure 1 It is the circuit schematic diagram of the series switch group dual protection circuit of Embodiment 1 of the present utility model.

[0027] Figure 2 It is the circuit schematic diagram of the series switch group dual protection circuit of Embodiment 2 of the present utility model. Detailed Embodiments

[0028] The technical solutions of the embodiments of the present invention will be explained and described below. However, the following embodiments are only the preferred embodiments of the present invention and not all of them. Based on the embodiments in the embodiments, other embodiments obtained by those skilled in the art without creative efforts all fall within the protection scope of the present invention.

[0029] See Figure 1 and Figure 2 For the series switch group fault dual detection circuit of the embodiment of the present utility model, the series switch group fault dual detection circuit includes:

[0030] A series switch group, including a plurality of mechanical switches connected in series, with one end connected to the positive pole of the first power supply Vin. When the mechanical switches are normal, they are closed, and when the mechanical switches are faulty, they are opened;

[0031] A plurality of single switch detection units, respectively connected in parallel with each mechanical switch to detect whether each mechanical switch is closed;

[0032] Resistor R3, connected in series with the series switch group and connected to the first ground GND;

[0033] A total detection unit, connected between the series switch group and resistor R3 to detect whether the series switch group is closed.

[0034] Single-chip microcomputer;

[0035] Relay disconnection unit;

[0036] Among them, all single-switch detection units are connected to the single-chip microcomputer. When one or more mechanical switches are detected to be faulty, the single-chip microcomputer stops the device from working, and the relay disconnection unit disconnects the relay.

[0037] The double protection circuit of the series switch group of the present utility model includes a series switch group, single-switch detection units, a total detection unit, a single-chip microcomputer, and a relay disconnection unit. The single-switch detection units can detect whether the corresponding individual mechanical switches are normal, and the total detection unit detects whether the entire series switch group is normal; the single-switch detection units are connected to the single-chip microcomputer. In addition to the single-chip microcomputer controlling the device through a program, it can also learn which specific mechanical switch or switches are faulty through the single-chip microcomputer; in addition to detecting the entire series switch group when the single-switch detection units are faulty, the total detection unit is also connected to the relay disconnection unit, and when the single-chip microcomputer program runs abnormally, the relay is disconnected mechanically through the relay disconnection unit.

[0038] Embodiment 1

[0039] See Figure 1 , the double protection circuit of the series switch group of Embodiment 1 of the present utility model includes:

[0040] A series switch group, including a plurality of mechanical switches connected in series, with one end connected to the positive pole of the first power supply Vin. When the mechanical switches are normal, they are closed, and when the mechanical switches are faulty, they are opened;

[0041] A plurality of single-switch detection units, respectively connected in parallel with each mechanical switch to detect whether each mechanical switch is closed;

[0042] Resistor R3, connected in series with the series switch group, connected to the first ground GND;

[0043] A total detection unit, connected between the series switch group and resistor R3, to detect whether the series switch group is closed.

[0044] Single-chip microcomputer;

[0045] Relay disconnection unit;

[0046] Among them, all single-switch detection units are connected to the single-chip microcomputer. When one or more mechanical switches are detected to be faulty, the single-chip microcomputer stops the device from working, and the relay disconnection unit disconnects the relay.

[0047] In this embodiment, the single-switch detection unit includes series resistors (R1, R2... Rn) and single-switch optocouplers (U1, U2... Un). The positive pole of the input end of the single-switch optocoupler is connected to the positive pole of the first power supply Vin, and the negative pole of the input end is connected to the first ground GND through the series resistor.

[0048] In this embodiment, the emitter of the triode of the single-switch optocoupler is grounded, the collector is connected to the positive pole of the second power supply Vd, a current-limiting resistor (R1', R2'... Rn') is also provided between the collector and the positive pole of the second power supply Vd, and the collector is also grounded through filter capacitors (C1, C2... Cn).

[0049] In this embodiment, the total detection unit includes a comparator U3 and a total switch optocoupler U4. The non-inverting input terminal of the comparator U3 is connected between the series switch group and the resistor R3, the output terminal of the comparator U3 is connected to the negative input terminal of the total switch optocoupler U4, and the positive input terminal of the total switch optocoupler U4 is connected to the positive pole of the third power supply Vcc.

[0050] When all the mechanical switches of the series switch group are normal, the voltage at the non-inverting input terminal of the comparator U3 is greater than the voltage at the inverting input terminal of the comparator U3; when one or more mechanical switches of the series switch group fail, the voltage at the non-inverting input terminal of the comparator U3 is less than the voltage at the inverting input terminal of the comparator U3.

[0051] In this embodiment, a series resistor R6 and a resistor R7 are provided between the positive pole of the third power supply Vcc and the first ground GND. The resistor R6 is grounded, and the inverting input terminal of the comparator U3 is connected between the resistor R6 and the resistor R7.

[0052] In this embodiment, the mechanical switch is a contact switch, and the series switch group fault double detection circuit further includes a delay unit. When one or more mechanical switches in the series switch group are disconnected, the delay unit causes the voltage at the non-inverting input terminal of the comparator U3 to change with a delay.

[0053] In this embodiment, the delay unit includes a series-connected diode D1, a resistor R4, and a resistor R5 provided between the resistor R3 and the series switch group. The resistor R5 is connected to the first ground GND. The delay unit further includes a capacitor C3. One end of the capacitor C3 is connected to the first ground GND, and the other end is connected between the diode D1 and the R4. The non-inverting input terminal of the comparator U3 is connected between the resistor R4 and the resistor R5.

[0054] In this embodiment, a resistor R8 is provided between the comparator U3 and the total switch optocoupler U4.

[0055] The working principle of the total detection switch in this embodiment for detecting whether the series switch group is faulty is as follows: Assume the voltage of the first power supply Vin is Vin, and the forward voltage drop of the diode D1 in the delay unit is Vf1. When all the mechanical switches in the series switch group are normal, the voltage Vsamp at the non-inverting input terminal of the comparator U3 is (Vin - Vf1) * R5 / (R4 + R5), and the voltage Vref at the inverting input terminal of the comparator U3 is Vcc * R6 / (R6 + R7). Through appropriate design of the component parameters, Vsamp is greater than Vref at this time;

[0056] When only one of the switches fails, assume the resistance of this switch is R1, and the forward voltage drop of the diode in the single-switch optocoupler is Vf. Then the voltage across R3 is (Vin - Vf) * R3 / (R1 + R3), the voltage Vsamp at the non-inverting input terminal of the comparator U3 is ((((Vin - Vf) * R3 / (R1 + R3)) - Vf1) * R5 / (R4 + R5)), and the voltage Vref at the inverting input terminal of the comparator U3 is Vcc * R6 / (R4 + R5). At this time, Vsamp is less than Vref;

[0057] When multiple switches fail, for example, the mechanical switches S1, S2, Sn are all open. At this time, the diodes of the single-switch optocouplers U1, U2, Un conduct, and the voltages at the collector terminals Det1, Det2, Detn of the transistors of the single-switch optocouplers U1, U2, Un are all 0V. The voltage across the resistor R3 is approximately (Vin - 3 * Vf) * R3 / (R1 + R2 + Rn + R3). The voltage across the resistor R3 at this time is lower than the voltage across the resistor R3 when only one switch fails. Therefore, as long as Vsamp < Vref is satisfied when one switch fails, Vsamp < Vref can also be satisfied when multiple switches fail. Thus, when multiple switches fail, the output voltage of pin 4 of the comparator U3 is 0V, the diode of the optocoupler U4 conducts, and the voltage at the collector terminal Det of the transistor of the optocoupler U4 is 0V. Therefore, this detection circuit can emit specific multiple-switch fault signals and also emit a centralized detection fault signal. Here, Sn does not only represent the third switch but can represent three or more switches.

[0058] In this embodiment, when one or more mechanical switches are detected to be faulty, the single-chip microcomputer disconnects the relay through the program and simultaneously issues a prompt as to which one or which ones of the mechanical switches are faulty. When the program of the single-chip microcomputer cannot run properly due to certain reasons, the relay disconnection unit can also disconnect the relay in a timely manner.

[0059] In this embodiment, the working principle of the relay disconnecting unit is as follows: when the entire series switch group is normal, the voltage Vsamp at the non-inverting input terminal of the comparator U3 is greater than the voltage Vref at the inverting input terminal. The comparator U3 outputs in open-drain mode, causing the diode path of the main switch optocoupler U4 to be open-circuited. The diode of the main switch optocoupler U4 is not conducting. Through the second power supply Vd, resistor R9, resistor R10, and resistor R11, the base of the triode Q1 is always triggered, and the triode Q1 is always conducting. The triode Q1 is in series with the circuit breaker, causing the circuit breaker to always conduct. When one or more mechanical switches in the series switch group fail, the voltage Vsamp at the non-inverting input terminal of the comparator U3 is less than the voltage Vref at the inverting input terminal. The output terminal 4 of the comparator U3 outputs a low level, which is less than the voltage of the power supply Vcc. As a result, the diode of the main switch optocoupler U4 conducts, and the triode of the main switch optocoupler U4 also conducts. The saturation voltage drop value between the collector and emitter of the triode of the main switch optocoupler U4 is very small (0.1V). The base of the triode Q1 is not triggered, the triode Q1 is disconnected, and the relay K1 is also disconnected. R9 can be selected as 3K, R10 can be selected from dozens of ohms to 1K, and R11 can be selected as 30K.

[0060] In this embodiment, the series switch group dual protection circuit further includes a plurality of filter capacitors provided at each single switch detection unit. One end of the filter capacitor is connected to the second ground, and the other end is connected to a series resistor. The filter capacitor can cooperate with the software of the single-chip microcomputer to perform filtering processing, and can filter out some interference signals.

[0061] In this embodiment, the mechanical switches (S1, S2, Sn) are contact switches, and the series switch group fault dual detection circuit further includes a delay unit. When one or more mechanical switches in the series switch group are disconnected, the delay unit causes the voltage at the non-inverting input terminal of the comparator U3 to change with a delay.

[0062] In this embodiment, the delay unit includes a series of diode D1, resistor R4, and resistor R5 connected in series between resistor R3 and the series switch group. Resistor R5 is connected to the first ground. The delay unit further includes a capacitor C3 connected between the output terminal of diode D1 and the first ground. The non-inverting input terminal of comparator U3 is connected between resistor R4 and resistor R5. Since the mechanical switch is a contact switch, when it is closed, it is similar to a wire and the voltage across both ends is 0. The voltage of Vin is all applied to R3. At this time, the voltage of R3 is Vin, and the voltage of capacitor C3 is Vin minus the voltage drop of diode D1. When the mechanical switch S1 is opened, the diode of the single-switch optocoupler U1 and the series resistor R1 will divide some voltage. Therefore, the voltage of R3 is less than Vin. At this time, due to the existence of diode D1, capacitor C3 can only discharge slowly through R4 and R5. R4 and R5 are the input resistors of comparator U3, and the resistance value can be selected to be relatively large (such as above 51 kΩ). Therefore, within a short period of time (longer than the time when the contact switch instantaneously opens and closes), the voltage of capacitor C3 will not have obvious fluctuations, so that Vsamp can be maintained greater than Vref, thus avoiding misjudgment caused by the accidental opening of the contact switch due to vibration.

[0063] The beneficial effects of the series switch group dual protection circuit of the first embodiment of the present utility model are as follows: It includes a series switch group, a single-switch detection unit, and a total detection unit. The single-switch detection unit can detect whether the corresponding single mechanical switch is normal, and the total detection unit detects whether the entire series switch group is normal; the single-switch detection unit is connected to the single-chip microcomputer. In addition to the single-chip microcomputer controlling the device through a program, it can also learn through the single-chip microcomputer which specific mechanical switch or switches are faulty; the total detection unit can not only detect the entire series switch group when the single-switch detection unit fails, but also connect to the relay disconnection unit to mechanically disconnect the relay when the single-chip microcomputer program runs abnormally; it has a filter capacitor, and the filter capacitor can cooperate with the software of the single-chip microcomputer to perform filtering processing together, and can filter out some interference signals; it has a delay unit, and the delay unit delays the change of the voltage at the non-inverting input terminal of comparator U3, thereby avoiding misjudgment caused by the accidental opening of the contact switch due to vibration.

[0064] Embodiment 2

[0065] See Figure 2 , the difference between the series switch group dual protection circuit of Embodiment 2 and that of Embodiment 1 is that it omits the filter capacitor and does not have a delay unit.

[0066] When the mechanical switch is not a contact switch and there will be no situations such as instantaneously opening and closing, etc., there is no need to set a delay unit.

[0067] The present utility model also provides a series switch group fault dual detection circuit at the same time. The series switch group fault dual detection circuit includes:

[0068] A series switch group, including a plurality of mechanical switches connected in series, with one end connected to the positive pole of the first power supply Vin. The mechanical switches are closed when normal and open when faulty.

[0069] A plurality of single-switch detection units, respectively connected in parallel with each mechanical switch to detect whether each mechanical switch is closed.

[0070] A resistor R3, connected in series with the series switch group and connected to the first ground GND.

[0071] A total detection unit, connected between the series switch group and the resistor R3 to detect whether the series switch group is closed.

[0072] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes but is not limited to the content described in the above specific implementation manner. Any modification that does not deviate from the functional and structural principles of the present invention will be included in the scope of the claims.

Claims

1. A double detection circuit for series switch group fault, characterized by: The series switch group fault dual detection circuit comprises: A series switch group includes a plurality of mechanical switches connected in series, one end of which is connected to the positive electrode of the first power supply Vin, the mechanical switches are closed when they are normal, and are opened when they fail; A plurality of single switch detection units are respectively connected in parallel with each mechanical switch to detect whether each mechanical switch is closed; The resistor R3 is connected in series with the series switch group and connected to the first ground GND; The total detection unit is connected between the series switch group and the resistor R3 to detect whether the series switch group is closed.

2. The series switch group fault dual detection circuit according to claim 1, characterized in that: The single switch detection unit comprises a series resistor and a single switch optocoupler, wherein the positive electrode of the input end of the single switch optocoupler is connected to the positive electrode of the first power supply Vin, and the negative electrode of the input end is connected to the first ground GND through the series resistor.

3. The series switch group fault dual detection circuit according to claim 2, characterized in that: The emitter of the transistor of the single switch optocoupler is grounded, the collector is connected to the positive electrode of the second power supply Vd, a current limiting resistor is provided between the collector and the positive electrode of the second power supply Vd, and the collector is also grounded through a filter capacitor.

4. The series switch group fault dual detection circuit according to claim 1, characterized in that: The total detection unit includes a comparator U3 and a main switch optocoupler U4, the non-inverting input end of the comparator U3 is connected between the series switch group and the resistor R3, the output end of the comparator U3 is connected to the negative input end of the main switch optocoupler U4, and the positive input end of the main switch optocoupler U4 is connected to the positive electrode of the third power supply Vcc; When all the mechanical switches of the series switch group are normal, the voltage at the non-inverting input terminal of the comparator U3 is greater than the voltage at the inverting input terminal of the comparator U3; when one or more mechanical switches of the series switch group fail, the voltage at the non-inverting input terminal of the comparator U3 is less than the voltage at the inverting input terminal of the comparator U3.

5. The series switch group fault dual detection circuit according to claim 4, characterized in that: A series resistor R6 and a resistor R7 are provided between the positive electrode of the third power supply Vcc and the first ground GND. The resistor R6 is grounded. The inverting input terminal of the comparator U3 is connected between the resistor R6 and the resistor R7.

6. The series switch group fault dual detection circuit according to claim 5, characterized in that: The mechanical switch is a contact switch, and the series switch group fault dual detection circuit also includes a delay unit. When one or more mechanical switches in the series switch group are disconnected, the delay unit delays the change of the voltage at the non-inverting input terminal of the comparator U3.

7. The series switch group fault dual detection circuit according to claim 6, characterized in that: The delay unit includes a diode D1, a resistor R4 and a resistor R5 connected in series between the resistor R3 and the series switch group, the resistor R5 is connected to the first ground GND, the delay unit also includes a capacitor C3 arranged between the cathode of the diode D1 and the first ground GND, and the non-inverting input terminal of the comparator U3 is connected between the resistor R4 and the resistor R5.

8. The series switch group fault dual detection circuit according to claim 4, characterized in that: A resistor R8 is provided between the comparator U3 and the main switch optical coupler U4.

9. A double protection circuit of a series switch group, characterized in that: It comprises a dual detection circuit for series switch group fault as described in any one of claims 1 to 8, and also comprises a single-chip microcomputer and a relay disconnecting unit, wherein all single switch detection units are connected to the single-chip microcomputer, and when one or more mechanical switch faults are detected, the single-chip microcomputer and the relay disconnecting unit disconnect the relay.

10. The dual protection circuit of the series switch group according to claim 9, characterized in that: The series switch group dual protection circuit further includes a plurality of filter capacitors provided at each single switch detection unit, one end of the filter capacitor is connected to the second ground GND1, and the other end is connected to the positive electrode of the second power supply Vd through a current limiting resistor; and / or The relay disconnect unit includes a transistor Q1 and a series-connected resistor R9, a resistor R10, and a resistor R11. One end of the resistor R9 is connected to the positive electrode of the second power supply Vd, and the other end is connected to the collector of the transistor of the main switch optocoupler U4. The collector of the transistor of the main switch optocoupler U4 is connected between the resistor R9 and the resistor R10, the emitter of the transistor of the main switch optocoupler U4 is connected to the second ground GND1, the base of the transistor Q1 is connected between the resistor R10 and the resistor R11, the emitter of the transistor Q1 is connected to the second ground GND1, and the collector of the transistor Q1 is connected in series with the relay K1.

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