Protection ground wire breakage detection circuit

Abstract

The technical scheme relates to the technical field of protection circuit devices, in particular to a protection ground wire breakage detection circuit, solves the technical problem that a low-voltage power supply system in the prior art lacks an effective and reliable detection mode, and provides the protection ground wire breakage detection circuit. Comprising an AC sampling circuit used for sampling a primary current to obtain a secondary sampling current and converting the secondary sampling current into a secondary sampling voltage; the high-frequency filter circuit is an active second-order circuit and is used for filtering high-frequency interference in the circuit; the precise rectifying and filtering circuit is used for rectifying to obtain direct-current voltage; the disconnection trigger circuit is used for outputting a high level with a signal of GJ; the sound-light alarm circuit is used for giving a buzzing alarm; and the operational amplifier power supply circuit is used for supplying power by using a positive single power supply. According to the technical scheme, the protection ground wire breaking condition can be detected in real time, and when the protection ground wire is broken, a sound-light alarm is given to prompt ground wire breaking.

Description

Technical Field

[0001] The utility model relates to the technical field of protection circuit devices, and particularly relates to a protection ground wire break detection circuit. Background Art

[0002] In the current method, the TN-S power supply system is mostly used in power consumption places such as residential electricity and temporary electricity at construction sites. The TN-S power supply system is a power supply system with high safety, and a separate protection ground wire is set;

[0003] However, in the actual application process, situations such as the breakage of the protection ground wire often occur, resulting in the ineffective grounding of the electrical equipment. When a circuit fault occurs, it may cause the charged body of the equipment shell, leading to major safety accidents such as electric shock or electrical fire;

[0004] In addition, low-voltage power supply systems such as temporary electricity are all large-current grounding systems, and the neutral point is grounded at the transformer, that is, the voltage between the phase line (live wire) and the ground is equal to the phase voltage. Therefore, in practice, it is possible to judge whether the ground wire is broken by detecting the voltage between the phase line (live wire) and the ground, which is a safer and more stable detection method. Content of the Utility Model

[0005] The utility model aims to solve the technical problem of the lack of an effective and reliable detection method in the existing low-voltage power supply system, and provides a protection ground wire break detection circuit.

[0006] To solve the above technical problems, the technical solution of the utility model is specifically as follows:

[0007] A protection ground wire break detection circuit includes:

[0008] An AC sampling circuit 1, which is used to obtain a secondary sampling current by sampling a primary current and convert it into a secondary sampling voltage;

[0009] A high-frequency filtering circuit 2, which is an active second-order circuit used to filter out high-frequency interference in the line;

[0010] A precision rectifier filtering circuit 3, which is used to rectify and obtain a DC voltage;

[0011] A break trigger circuit 4, which is used to output a high level with the signal of GJ;

[0012] An acoustic-optic alarm circuit 5, which is used to give a buzzer warning alarm; and

[0013] An operational amplifier power supply circuit 6, which is used to supply power with a single positive power supply.

[0014] Specifically, the AC sampling circuit 1 includes:

[0015] The first resistor R1, the second resistor R2, and the third resistor R3 connected in series with the live wire;

[0016] The fourth capacitor C4 is connected in parallel with the first resistor R1 and the transient suppression diode D1;

[0017] One side of the voltage transformer PT1 is connected to the transient suppression diode D1, and the other side is connected to the fifth capacitor C5;

[0018] The fifth capacitor C5 is connected in parallel with the fourth resistor R4 and the U2A operational amplifier U2-A.

[0019] Specifically, the fourth capacitor C4 is a Y1-class safety capacitor with a capacitance value of 1 nF, which plays a role in filtering high-frequency electromagnetic interference;

[0020] Among them, the first resistor R1, the second resistor R2, and the third resistor R3 are primary sampling resistors;

[0021] The resistance values of the primary sampling resistors are all 220 kΩ;

[0022] The transient suppression diode D1 is a TVS diode with the model SMAJ5.0A, which plays an overvoltage protection role;

[0023] The voltage transformer PT1 is a current-type voltage transformer with a turns ratio of 2000:2000;

[0024] The fifth capacitor C5 is a 100 nF filtering capacitor;

[0025] The fourth resistor R4 is a secondary sampling resistor with a resistance value of 3.3 K.

[0026] Specifically, the high-frequency filtering circuit 2 includes:

[0027] The fifth resistor R5, which is connected to the OUTA terminal of the U2A operational amplifier U2-A;

[0028] The sixth resistor R6 connected in series with the fifth resistor R5;

[0029] The second capacitor C2 connected in parallel with the fifth resistor R5;

[0030] The first capacitor C1 connected in parallel with the sixth resistor R6, which is used to connect to a ground terminal;

[0031] The second capacitor C2 and the first capacitor C1 are connected to the connection terminal of the U2B operational amplifier U2-B;

[0032] The OUTB terminal of the U2B operational amplifier U2-B is connected to a UPE;

[0033] The resistance value of the fifth resistor R5 is 3.3 kΩ, the resistance value of the sixth resistor R6 is 51 kΩ, the value of the second capacitor C2 is 10 nF, and the value of the first capacitor C1 is 2.2 nF.

[0034] Specifically, the precision rectifier filter circuit 3 includes:

[0035] A seventh resistor R7 connected to the UPE, and an eighth resistor R8 connected in parallel with the seventh resistor R7;

[0036] A ninth resistor R9 is connected in parallel with an eighth capacitor C8 and is connected to the U1B operational amplifier U1-B;

[0037] The U1B operational amplifier U1-B is connected to a second diode D2;

[0038] The U1A operational amplifier U1-A is connected to the seventh resistor and the ground protection;

[0039] The OUTA terminal of the U1A operational amplifier U1-A is connected to the second diode D2;

[0040] The OUTB terminal of the U1B operational amplifier U1-B is connected to a tenth resistor R10;

[0041] The tenth resistor R10 is connected in series with a third diode D3 and the U4B operational amplifier U4-B.

[0042] Specifically, the OUTB terminal of the U4B operational amplifier U4-B is connected to a twelfth resistor R12;

[0043] The U4B operational amplifier U4-B forms a self-loop;

[0044] Among them, the seventh resistor R7 and the eighth resistor R8 are amplification resistors, and their resistance values are both 3.3 kΩ;

[0045] Among them, the second diode D2 is a feedback diode, and its model is LL4148;

[0046] The eighth capacitor C8 is a filter capacitor, and its capacitance value is 470 nF;

[0047] The ninth resistor R9 is a discharge resistor, and its resistance value is 1 MΩ;

[0048] The tenth resistor R10 is a current-limiting resistor, and its resistance value is 10 Ω;

[0049] The third diode D3 is a feedback diode, and its model is LL4148. It forms a small-signal filter circuit loop with the U1-B operational amplifier U1-B to convert the pulsed DC signal into a smooth DC signal;

[0050] The OUTB terminal of the U4B operational amplifier U4-B is connected to a twelfth resistor R12.

[0051] Specifically, the disconnection trigger circuit 4 includes:

[0052] A reference voltage chip U3, whose REF terminal is connected to the twelfth resistor R12;

[0053] A sixteenth resistor R16 is connected in parallel with a seventh capacitor C7, and both are located between the connection line of the twelfth resistor R12 and the reference voltage chip U3;

[0054] The reference voltage chip U3 is also connected to a seventeenth resistor R17;

[0055] A sixth capacitor C6 is connected in parallel with the seventeenth resistor R17 and is connected to the U4A operational amplifier U4-A.

[0056] Specifically, the sixteenth resistor R16 is a pull-down resistor, which clamps the signal to 0V when there is no input, and its resistance value is 10kΩ;

[0057] Among them, the sixth capacitor C6 is a filtering capacitor, and its capacitance value is 100nF;

[0058] The reference voltage chip U3 has a model of TLV431 and a reference voltage of 1.24V;

[0059] VCC provides operating current for the reference voltage chip U3 through the seventeenth resistor R17, and its resistance value is 510Ω;

[0060] The U4A operational amplifier U4-A generates a signal GJ;

[0061] The U4A operational amplifier U4-A is connected to the CATHODE terminal of the reference voltage chip U3.

[0062] Specifically, the acoustic-optic alarm circuit 5 includes:

[0063] A triode Q1, when the GJ signal is at a high level, the triode Q1 conducts;

[0064] The front end of the triode Q1 is connected to a thirteenth resistor R13, and the thirteenth resistor R13 is connected to the U4A operational amplifier U4-A;

[0065] The thirteenth resistor R13 is a base resistor, and its resistance value is 1kΩ;

[0066] The fourteenth resistor R14 is a current-limiting resistor for the light-emitting diode, and its resistance value is 1kΩ;

[0067] The fifteenth resistor R15 is a current-limiting resistor for the buzzer, and its resistance value is 100Ω;

[0068] The buzzer B1 is a 5V active buzzer;

[0069] The model of the triode Q1 is S8050;

[0070] When the signal GJ is at a high level, the triode Q1 conducts, the light-emitting diode lights up, and the buzzer B1 emits an alarm sound. When the signal GJ is at a low level, the triode Q1 cuts off, the light-emitting diode goes out, and the buzzer B1 does not work.

[0071] Specifically, the operational amplifier U2 is powered by positive and negative dual power supplies, and the operational amplifiers U1 and U4 are powered by a single positive power supply.

[0072] The present utility model has the following beneficial effects:

[0073] This technical solution can detect the disconnection of the protective ground wire in real time. When the protective ground wire is disconnected, it emits an audible and visual alarm to prompt the disconnection of the ground wire. Description of the Drawings

[0074] The following further describes the present utility model in detail in conjunction with the drawings and specific embodiments.

[0075] Figure 1 is a schematic diagram of the AC sampling circuit and the high-frequency filtering circuit of the present utility model;

[0076] Figure 2 is a schematic diagram of the precision rectifier filtering circuit and the disconnection trigger circuit of the present utility model;

[0077] Figure 3 is a schematic diagram of the audible and visual alarm circuit of the present utility model;

[0078] Figure 4 is a schematic diagram of the operational amplifier power supply circuit of the present utility model. Specific Embodiments

[0079] The following will clearly and completely describe the technical solutions in the embodiments of the present utility model in conjunction with the drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all of the embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present utility model; it should be noted that in this application, for the convenience of description, the "left side" in the current view is defined as the "first end", the "right side" is defined as the "second end", the "upper side" is defined as the "first end", and the "lower side" is defined as the "second end". The purpose of such description is to clearly express the technical solution and should not be construed as an improper limitation of the technical solution of this application.

[0080] The utility model aims to solve the technical problem that the existing low-voltage power supply system lacks an effective and reliable detection method, and provides a protective ground wire breakage detection circuit.

[0081] Please refer to Figures 1-4 As shown in the figure, the protective ground wire breakage detection circuit includes:

[0082] An AC sampling circuit 1, which is used to obtain a secondary sampling current by sampling the primary current and convert it into a secondary sampling voltage;

[0083] A high-frequency filtering circuit 2, which is an active second-order circuit used to filter out high-frequency interference in the line;

[0084] A precision rectifier filtering circuit 3, which is used to rectify and obtain a DC voltage;

[0085] A breakage trigger circuit 4, which is used to output a high level with the signal of GJ;

[0086] An acoustic-optic alarm circuit 5, which is used to give a buzzer warning alarm; and

[0087] An operational amplifier power supply circuit 6, which is used to supply power with a single positive power supply.

[0088] Please refer to Figure 1 As shown in the figure, the AC sampling circuit 1 includes: a first resistor R1, a second resistor R2, and a third resistor R3 connected in series with the live wire;

[0089] A fourth capacitor C4 is connected in parallel with the first resistor R1 and the transient suppression diode D1;

[0090] One side of a voltage transformer PT1 is connected to the transient suppression diode D1, and the other side is connected to a fifth capacitor C5;

[0091] The fifth capacitor C5 is connected in parallel with a fourth resistor R4 and an operational amplifier U2-A of U2A;

[0092] Please refer to Figures 1-4 As shown in the figure, the fourth capacitor C4 is a Y1-class safety capacitor with a capacitance value of 1 nF, which plays a role in filtering out high-frequency electromagnetic interference;

[0093] Among them, the first resistor R1, the second resistor R2, and the third resistor R3 are primary sampling resistors;

[0094] The resistance values of the primary sampling resistors are all 220 kΩ;

[0095] The transient suppression diode D1 is a TVS diode with the model of SMAJ5.0A, which plays an overvoltage protection role;

[0096] The voltage transformer PT1 is a current-type voltage transformer with a turns ratio of 2000:2000;

[0097] The fifth capacitor C5 is a 100 nF filtering capacitor;

[0098] The fourth resistor R4 is a secondary sampling resistor with a resistance value of 3.3 K.

[0099] Working principle: The normal voltage between the live wire L and the protective ground wire PE is 220 V AC. The primary side current I1 = U / (R1 + R2 + R3). The turns ratio of the voltage transformer PT1 is 2000:2000. According to the principle of electromagnetic induction, the secondary side current I2 of the voltage transformer is I2 = I1 = U / (R1 + R2 + R3). The operational amplifier U2-A and the resistor R4 form a secondary sampling circuit. The non-inverting and inverting input terminals of U2-A are respectively connected to pins 1 and 2 of PT1. Using the "virtual short" and "virtual open" characteristics of the operational amplifier, it can be known that the secondary side sampling voltage U2 of the voltage transformer is U2 = -UxR4 / (R1 + R2 + R3).

[0100] Please refer to Figure 1 As shown, the high-frequency filtering circuit 2 includes:

[0101] The fifth resistor R5, which is connected to the OUTA terminal of the operational amplifier U2-A of U2A;

[0102] The sixth resistor R6 in series with the fifth resistor R5;

[0103] The second capacitor C2 in parallel with the fifth resistor R5;

[0104] The first capacitor C1 in parallel with the sixth resistor R6, which is used to connect to a grounding terminal;

[0105] The connection terminals of the second capacitor C2 and the first capacitor C1 are connected to the operational amplifier U2-B of U2B;

[0106] The OUTB terminal of the operational amplifier U2-B of U2B is connected to a UPE;

[0107] The resistance value of the fifth resistor R5 is 3.3 kΩ, the resistance value of the sixth resistor R6 is 51 kΩ, the value of the second capacitor C2 is 10 nF, and the value of the first capacitor C1 is 2.2 nF.

[0108] Please refer to Figure 2 As shown, the precision rectifier filtering circuit 3 includes:

[0109] The seventh resistor R7 connected to the UPE, and the eighth resistor R8 in parallel with the seventh resistor R7;

[0110] The ninth resistor R9 is in parallel with the eighth capacitor C8 and is connected to the operational amplifier U1-B of U1B;

[0111] The operational amplifier U1-B of U1B is connected to the second diode D2;

[0112] The operational amplifier U1A of U1 - A is connected to the seventh resistor and grounded for protection;

[0113] The OUTA terminal of the operational amplifier U1A of U1 - A is connected to the second diode D2;

[0114] The OUTB terminal of the operational amplifier U1B of U1 - B is connected to the tenth resistor R10;

[0115] The tenth resistor R10 is connected in series with the third diode D3 and the operational amplifier U4B of U4 - B.

[0116] Please refer to Figure 2 As shown, the OUTB terminal of the operational amplifier U4B of U4 - B is connected to the twelfth resistor R12;

[0117] The operational amplifier U4B of U4 - B forms a self - loop;

[0118] Among them, the seventh resistor R7 and the eighth resistor R8 are amplification resistors, and their resistance values are both 3.3 kΩ;

[0119] Among them, the second diode D2 is a feedback diode, and its model is LL4148;

[0120] The eighth capacitor C8 is a filtering capacitor, and its capacitance value is 470 nF;

[0121] The ninth resistor R9 is a discharge resistor, and its resistance value is 1 MΩ;

[0122] The tenth resistor R10 is a current - limiting resistor, and its resistance value is 10 Ω;

[0123] The third diode D3 is a feedback diode, and its model is LL4148. It forms a small - signal filtering circuit loop with the operational amplifier U1 - B of U1 - B to convert the pulsed DC signal into a smooth DC signal;

[0124] The OUTB terminal of the operational amplifier U4B of U4 - B is connected to a twelfth resistor R12.

[0125] In addition, the operational amplifier U4 - B is designed as a voltage follower to increase the input impedance, reduce the output impedance, and make the output DC voltage signal not affected by the change of the external load.

[0126] The DC voltage obtained after rectification is Ud = 1.414xUxR4 / (R1 + R2 + R3).

[0127] Please refer to Figure 2 As shown, the disconnection trigger circuit 4 includes:

[0128] The reference voltage chip U3, whose REF terminal is connected to the twelfth resistor R12;

[0129] The sixteenth resistor R16 is connected in parallel with the seventh capacitor C7, and both are located between the connection line of the twelfth resistor R12 and the reference voltage chip U3;

[0130] The reference voltage chip U3 is also connected to the seventeenth resistor R17;

[0131] The sixth capacitor C6 is connected in parallel with the seventeenth resistor R17 and is connected to the U4A operational amplifier U4-A.

[0132] Please refer to Figure 2 As shown, the sixteenth resistor R16 is a pull-down resistor, which clamps the signal to 0V when there is no input, and its resistance value is 10 kΩ;

[0133] Among them, the sixth capacitor C6 is a filtering capacitor, and its capacitance value is 100 nF;

[0134] The reference voltage chip U3, with the model number TLV431, has a reference voltage of 1.24V;

[0135] VCC provides the operating current for the reference voltage chip U3 through the seventeenth resistor R17, and its resistance value is 510 Ω;

[0136] The U4A operational amplifier U4-A generates the signal GJ;

[0137] The U4A operational amplifier U4-A is connected to the CATHODE terminal of the reference voltage chip U3.

[0138] Principle of operation: When the external AC voltage is greater than 176V, Ud > 1.24V, the inside of the reference voltage chip conducts, a low level is generated at pin 2 of U3, and after passing through the voltage follower, a low level is output, and the output signal GJ is 0; when the external AC voltage is less than 176V, Ud < 1.24V, the inside of the reference voltage chip is cut off, a high level is generated at pin 2 of U3, and after passing through the voltage follower, a high level is output, and the output signal GJ is a high level.

[0139] Please refer to Figure 3 As shown, the acoustic-optic alarm circuit 5 includes:

[0140] The triode Q1 conducts when the GJ signal is at a high level;

[0141] The front end of the triode Q1 is connected to the thirteenth resistor R13, and the thirteenth resistor R13 is connected to the U4A operational amplifier U4-A;

[0142] The thirteenth resistor R13 is a base resistor, and its resistance value is 1 kΩ;

[0143] The fourteenth resistor R14 is a current-limiting resistor for the light-emitting diode, and its resistance value is 1 kΩ;

[0144] The fifteenth resistor R15 is a current-limiting resistor for the buzzer, with a resistance value of 100Ω;

[0145] The buzzer B1 is a 5V active buzzer;

[0146] The model of the triode Q1 is S8050;

[0147] When the signal GJ is at a high level, the triode Q1 conducts, the light-emitting diode lights up, and the buzzer B1 emits an alarm sound. When the signal GJ is at a low level, the triode Q1 cuts off, the light-emitting diode goes out, and the buzzer B1 does not work.

[0148] Please refer to Figure 4 As shown, the operational amplifier U2 is powered by positive and negative dual power supplies, and the operational amplifiers U1 and U4 are powered by a single positive power supply.

[0149] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A protective ground wire disconnection detection circuit, characterized in that: include: An AC sampling circuit (1) is used to obtain a secondary sampling current by sampling a primary current and convert it into a secondary sampling voltage; A high-frequency filter circuit (2), which is an active second-order circuit, is used to filter out high-frequency interference in the circuit; A precision rectifier and filter circuit (3) for rectifying and obtaining a DC voltage; A disconnection trigger circuit (4) for outputting a high level signal of GJ; An audible and visual alarm circuit (5) is used to emit a buzzer warning alarm; as well as The operational amplifier power supply circuit (6) is used to be powered by a single positive power supply.

2. The protective ground wire disconnection detection circuit according to claim 1, characterized in that: The AC sampling circuit (1) comprises: A first resistor (R1), a second resistor (R2), and a third resistor (R3) connected in series with the live wire; A fourth capacitor (C4) is connected in parallel with the first resistor (R1) and the transient voltage suppression diode (D1); One side of the voltage transformer (PT1) is connected to the transient suppression diode (D1), and the other side is connected to the fifth capacitor (C5); The fifth capacitor (C5) is connected in parallel with the fourth resistor (R4) and the U2A operational amplifier (U2-A).

3. The protective ground wire disconnection detection circuit according to claim 2, characterized in that: The fourth capacitor (C4) is a Y1-level safety capacitor with a capacitance of 1nF, which plays a role in filtering out high-frequency electromagnetic interference; Wherein, the first resistor (R1), the second resistor (R2), and the third resistor (R3) are primary sampling resistors; The resistance of the primary sampling resistor is 220kΩ; The transient voltage suppressor diode (D1) is a TVS diode, model SMAJ5.0A, which plays an overvoltage protection role; The voltage transformer (PT1) is a current type voltage transformer with a transformation ratio of 2000:2000; The fifth capacitor (C5) is a 100nF filter capacitor; The fourth resistor (R4) is a secondary sampling resistor with a resistance of 3.3K.

4. The protective ground wire disconnection detection circuit according to claim 3, characterized in that: The high-frequency filter circuit (2) comprises: a fifth resistor (R5), connected to the OUTA terminal of the U2A operational amplifier (U2-A); a sixth resistor (R6) connected in series with the fifth resistor (R5); a second capacitor (C2) connected in parallel with the fifth resistor (R5); a first capacitor (C1) connected in parallel with the sixth resistor (R6), and used to connect to a ground terminal; The second capacitor (C2) and the first capacitor (C1) are connected to the connection end of the U2B operational amplifier (U2-B); The OUTB terminal of the U2B operational amplifier (U2-B) is connected to a UPE; The resistance value of the fifth resistor (R5) is 3.3 kΩ, the resistance value of the sixth resistor (R6) is 51 kΩ, the value of the second capacitor (C2) is 10 nF, and the value of the first capacitor (C1) is 2.2 nF.

5. The protective ground wire disconnection detection circuit according to claim 4, characterized in that: The precision rectification and filtering circuit (3) comprises: a seventh resistor (R7) connected to the UPE, and an eighth resistor (R8) connected in parallel with the seventh resistor (R7); A ninth resistor (R9) is connected in parallel with the eighth capacitor (C8) and is connected to the U1B operational amplifier (U1-B); The U1B operational amplifier (U1-B) is connected to a second diode (D2); U1A operational amplifier (U1-A) is connected to the seventh resistor and the ground protection; The OUTA terminal of the U1A operational amplifier (U1-A) is connected to the second diode (D2); The OUTB terminal of the U1B operational amplifier (U1-B) is connected to a tenth resistor (R10); The tenth resistor (R10) is connected in series with the third diode (D3) and the U4B operational amplifier (U4-B).

6. The protective ground wire disconnection detection circuit according to claim 5, characterized in that: The OUTB terminal of the U4B operational amplifier (U4-B) is connected to a twelfth resistor (R12); The U4B operational amplifier (U4-B) forms a self-loop; Wherein, the seventh resistor (R7) and the eighth resistor (R8) are amplifying resistors, and both have a resistance value of 3.3 kΩ; Wherein, the second diode (D2) is a feedback diode, model LL4148; The eighth capacitor (C8) is a filter capacitor with a capacitance of 470nF; The ninth resistor (R9) is a discharge resistor, and its resistance is 1MΩ; The tenth resistor (R10) is a current limiting resistor with a resistance of 10Ω; The third diode (D3) is a feedback diode, model LL4148, which forms a small signal filter circuit loop with the U1-B operational amplifier (U1-B) to convert the pulse DC signal into a smooth DC signal; The OUTB terminal of the U4B operational amplifier (U4-B) is connected to a twelfth resistor (R12).

7. The protective ground wire disconnection detection circuit according to claim 6, characterized in that: The disconnection trigger circuit (4) comprises: A reference voltage chip (U3), a REF terminal of which is connected to the twelfth resistor (R12); The sixteenth resistor (R16) is connected in parallel with the seventh capacitor (C7), and the two are located between the connection line of the twelfth resistor (R12) and the reference voltage chip (U3); The reference voltage chip (U3) is also connected to a seventeenth resistor (R17); The sixth capacitor (C6) is connected in parallel with the seventeenth resistor (R17) and is connected to the U4A operational amplifier (U4-A).

8. The protective ground wire disconnection detection circuit according to claim 7, characterized in that: The sixteenth resistor (R16) is a pull-down resistor, which clamps the signal to 0V when there is no input, and has a resistance of 10kΩ; Wherein, the sixth capacitor (C6) is a filter capacitor with a capacitance of 100nF; The reference voltage chip (U3) is of model TLV431, and the reference voltage is 1.24V; VCC provides working current to the reference voltage chip (U3) through the seventeenth resistor (R17), and the resistance value is 510Ω; The U4A operational amplifier (U4-A) generates a signal GJ; The U4A operational amplifier (U4-A) is connected to the CATHODE terminal of the reference voltage chip (U3).

9. The protective ground wire disconnection detection circuit according to claim 8, characterized in that: The sound and light alarm circuit (5) comprises: Transistor (Q1), when the GJ signal is at a high level, the transistor (Q1) is turned on; The front end of the transistor (Q1) is connected to a thirteenth resistor (R13), and the thirteenth resistor (R13) is connected to the U4A operational amplifier (U4-A); The thirteenth resistor (R13) is a base resistor, and its resistance is 1 kΩ; The fourteenth resistor (R14) is a current limiting resistor of the light emitting diode, and its resistance value is 1 kΩ; The fifteenth resistor (R15) is a buzzer current limiting resistor, and its resistance is 100Ω; The buzzer (B1) is a 5V active buzzer; The model of transistor (Q1) is S8050; When the signal GJ is at a high level, the transistor (Q1) is turned on, the light emitting diode is lit, and the buzzer (B1) emits an alarm sound; when the signal GJ is at a low level, the transistor (Q1) is turned off, the light emitting diode is turned off, and the buzzer (B1) does not work.

10. The protective ground wire disconnection detection circuit according to claim 9, characterized in that: The operational amplifier (U2) is powered by a dual positive and negative power supply, while the operational amplifier (U1) and the operational amplifier (U4) are powered by a single positive power supply.

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