Live and zero line reverse connection detection circuit based on single-phase intelligent meter

Abstract

The invention provides a live and null line reverse connection detection circuit based on a single-phase smart meter, and relates to the technical field of electric power safety detection, the live and null line reverse connection detection circuit comprises a spring antenna induction circuit, an operational amplifier and a triode switching circuit which are connected in sequence, and the operational amplifier comprises a primary signal follower circuit and a secondary signal amplification circuit; the triode switching circuit is connected with a single-chip microcomputer. The spring antenna induction circuit comprises two spring antennas arranged beside an electric wire to be detected, the primary signal following circuit comprises a first operational amplifier, and the secondary signal amplification circuit comprises a second operational amplifier and a bias resistor; the triode switching circuit comprises a triode. According to the invention, the spring antenna induces the difference between positive and negative connection signals of the live line and the zero line, the positive and negative connection of the live line and the zero line is judged by introducing the operational amplifier hardware detection mode, the single-chip microcomputer can know the connection state of the live line and the zero line only by judging high and low levels, the software workload is reduced, the influence of module and environment temperature is avoided, and the power utilization safety is finally ensured. And the occurrence of electricity stealing events is reduced.

Description

Technical Field

[0001] This invention relates to the field of power safety detection technology, and in particular, to a live / neutral reverse connection detection circuit based on a single-phase smart meter. Background Technology

[0002] Smart meters are intelligent terminals in smart grids. They are no longer traditional electricity meters. Besides the basic electricity metering functions of traditional meters, smart meters, to adapt to smart grids and the use of new energy sources, also possess intelligent functions such as bidirectional multi-rate metering, user-end control functions, bidirectional data communication with multiple data transmission modes, and anti-theft features. Smart meters represent the future development direction of intelligent terminals for end users in energy-saving smart grids. Currently, there are various types of single-phase smart meters on the market to meet diverse customer needs.

[0003] During the installation of electricity meters, special attention must be paid to the wiring of the live and neutral wires. If the live and neutral wires are reversed—that is, the neutral wire is connected to the live wire terminal on the meter and the live wire is connected to the neutral wire terminal on the meter—the electrical appliances may become electrified when turned off, or electricity theft may occur, potentially leading to electrical accidents. Currently, there are increasingly more designs by power workers that can alarm when the live and neutral wires are reversed. For example, Chinese patent CN211402505U discloses a single-phase smart meter capable of detecting reversed live and neutral wire connections, including a main control chip U1, a live and neutral wire detection circuit, a metering circuit, a power supply circuit, a pulse circuit, a storage circuit, an alarm detection circuit, and a display circuit. The main control chip U1 is electrically connected to the live and neutral wire detection circuit, the metering circuit, the power supply circuit, the pulse circuit, the storage circuit, the alarm detection circuit, and the display circuit. The aforementioned patent can detect whether the neutral and live wires are reversed. In the event of a reversed connection, it can trigger an alarm, reducing safety hazards and improving safety.

[0004] However, the single-phase smart meters that can detect reverse connection of live and neutral wires still have the following drawbacks: Although they can basically realize the function of detecting reverse connection of live and neutral wires, the pure firmware judgment scheme occupies the microcontroller's AD port and is prone to misjudgment; other hardware solutions can realize basic functions at room temperature, but after adding modules, in high and low temperature test environments, they are easily affected by module communication or the characteristics of the device caused by the ambient temperature, resulting in misjudgment of live and neutral wires.

[0005] Therefore, in order to solve the above problems, it is necessary to design a reasonable and efficient live and neutral wire reverse connection detection circuit based on a single-phase smart meter. Summary of the Invention

[0006] The purpose of this invention is to provide a live / neutral wire reverse connection detection circuit based on a single-phase smart meter. This circuit detects the signal magnitude difference when the live and neutral wires are reversed using a spring antenna. The signal is then stabilized and amplified by an operational amplifier. Finally, the transistor outputs high and low levels when the live and neutral wires are reversed, allowing the microcontroller to determine the connection status. This reduces software workload, minimizes program space usage, and is unaffected by module and ambient temperature, ultimately ensuring electrical safety and reducing electricity theft.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A live / neutral wire reverse connection detection circuit based on a single-phase smart meter includes a spring antenna sensing circuit, an operational amplifier section, and a transistor switching circuit connected in sequence. The operational amplifier section includes a first-stage signal follower circuit and a second-stage signal amplification circuit. The transistor switching circuit is connected to a microcontroller.

[0009] The spring antenna sensing circuit includes two spring antennas placed next to the wire to be detected, thereby sensing the signal magnitude when the live and neutral wires are connected in opposite directions through the two spring antennas, and providing an AC input signal for the operational amplifier section;

[0010] The first-level signal follower circuit includes a first operational amplifier U1, which is used to follow and stabilize the AC input signal transmitted from the spring antenna sensing circuit;

[0011] The secondary signal amplification circuit includes a second operational amplifier U2 and a bias resistor. The second operational amplifier U2 is used to amplify the signal from the primary signal follower circuit, and the bias resistor boosts the AC signal to the positive voltage range.

[0012] The transistor switching circuit includes a transistor Q1, which outputs high and low level signals for the microcontroller to judge based on the comparison result between the voltage input from the secondary signal amplifier circuit and the transistor conduction threshold. This allows the microcontroller to determine whether the live and neutral wires are reversed by judging the high and low level states.

[0013] As a preferred embodiment of the present invention, a first power supply is also included; the first power supply is a 15V power supply, which is used to supply power to the first operational amplifier U1 and the second operational amplifier U2.

[0014] As a preferred embodiment of the present invention, a second power supply is also included; the second power supply is a 3.3V LDO power supply circuit, with +15V as input and +3.3V output to power the transistor, the bias resistor voltage divider, and the microcontroller.

[0015] As a preferred embodiment of the present invention, the spring antenna sensing circuit further includes a TVS transistor (TVS1) and a pull-down resistor (R1); the TVS transistor (TVS1) is connected in parallel between the output terminal of the spring antenna and ground, and one end of the pull-down resistor (R1) is connected to the output terminal of the spring antenna, while the other end is grounded.

[0016] As a preferred embodiment of the present invention, the non-inverting input terminal of the first operational amplifier U1 is connected to the output terminal of the spring antenna sensing circuit, and the inverting input terminal is connected to the output terminal to form a voltage follower.

[0017] As a preferred embodiment of the present invention, the secondary signal amplification circuit further includes a feedback resistor R2, a feedback resistor R3, and a filter capacitor C2. The bias resistors include a bias resistor R4 and a bias resistor R5, which are connected in series between the 3.3V power supply and ground, with the intermediate node connected to the non-inverting input terminal of the second operational amplifier U2. The feedback resistors R2 and R3 form a negative feedback network, wherein one end of the feedback resistor R2 is connected to the inverting input terminal of the second operational amplifier U2, and the other end is connected to the output terminal of the primary signal follower circuit. One end of the feedback resistor R3 is connected to the inverting input terminal of the second operational amplifier U2, and the other end is connected to the output terminal of the second operational amplifier U2. The filter capacitor C2 is connected in parallel between the power supply terminal of the second operational amplifier U2 and ground.

[0018] As a preferred embodiment of the present invention, the transistor switching circuit further includes a pull-up resistor R8, a voltage divider resistor R6, a voltage divider resistor R7, and a filter resistor R9; the voltage divider resistors R6 and R7 are connected in series between the output terminal of the secondary signal amplifier circuit and ground, and the intermediate node is connected to the base of the transistor Q1; one end of the pull-up resistor R8 is connected to a 3.3V power supply, and the other end is connected to the collector of the transistor Q1; one end of the filter resistor R9 is connected to the collector of the transistor Q1, and the other end serves as the output terminal OUTPUT of the circuit.

[0019] As a preferred embodiment of the present invention, the second power supply further includes a filter capacitor C3 and a filter capacitor C4; the filter capacitor C3 is connected between the +15V power supply terminal and ground; the filter capacitor C4 is connected between the +3.3V power supply terminal and ground.

[0020] As a preferred embodiment of the present invention, the length, shape, or number of the spring antennas is adjusted according to the actual magnitude of the induced signal to ensure that the induced signal is greater when the live and neutral wires are connected in the correct direction than when they are connected in the reverse direction.

[0021] The gain Av of the secondary signal amplifier circuit is -R3 / R2, and the amplification factor is changed by adjusting the resistance values ​​of R2 and R3.

[0022] The resistance values of the voltage-dividing resistors R6 and R7 are adjusted according to the magnitude of the signal amplified by the second-stage operational amplifier, so that when the live and neutral wires are correctly connected, the base voltage Ub of the triode Q1 is less than Vbe (the conduction threshold of the triode), and when the live and neutral wires are reversely connected, Ub is greater than Vbe.

[0023] The present invention also provides a single-phase smart meter, which includes a live and neutral wire reverse connection detection circuit for a single-phase smart meter as described in any one of the above, and the output end OUTPUT of the circuit is connected to the IO port of the single-chip microcomputer of the smart meter. The single-chip microcomputer determines whether the live and neutral wires are reversely connected by judging the high and low level states of the IO port.

[0024] The beneficial effects of a live and neutral wire reverse connection detection circuit for a single-phase smart meter according to the present invention are as follows: due to the difference in the magnitude of the signals induced by the spring antenna when the live and neutral wires are correctly and reversely connected, the signal is stabilized and amplified by the operation and amplification unit, and finally, when the live and neutral wires are correctly and reversely connected, the triode outputs high and low levels for the single-chip microcomputer to judge. The single-chip microcomputer only needs to judge the high and low levels to know the connection state of the live and neutral wires, reducing the software workload, not occupying too much program space, not being affected by the module and ambient temperature, ultimately ensuring electrical safety and reducing the occurrence of electricity theft incidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the overall structure of an embodiment of a live and neutral wire reverse connection detection circuit for a single-phase smart meter according to the present invention;

[0026] Figure 2 It is a circuit schematic diagram of the spring antenna induction circuit in a live and neutral wire reverse connection detection circuit for a single-phase smart meter according to the present invention;

[0027] Figure 3 It is a circuit schematic diagram of the first-stage signal follower circuit in a live and neutral wire reverse connection detection circuit for a single-phase smart meter according to the present invention;

[0028] Figure 4 It is a circuit schematic diagram of the second-stage signal amplification circuit in a live and neutral wire reverse connection detection circuit for a single-phase smart meter according to the present invention; <确]]

[0029] Figure 5 It is a circuit schematic diagram of the triode switch circuit in a live and neutral wire reverse connection detection circuit for a single-phase smart meter according to the present invention;

[0030] Figure 6 It is a circuit schematic diagram of the second power supply in a live and neutral wire reverse connection detection circuit for a single-phase smart meter according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0032] 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 and steps of the modules and steps set forth in these embodiments do not limit the scope of the invention.

[0033] At the same time, it should be understood that, for ease of description, the process shown in the attached diagram is not performed in isolation, but rather involves multiple steps that overlap.

[0034] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0035] 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.

[0036] Techniques, methods, and systems known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of this specification.

[0037] Example 1: As Figures 1 to 6 The diagram shown is merely one embodiment of the present invention. A live / neutral wire reverse connection detection circuit based on a single-phase smart meter includes a spring antenna sensing circuit, an operational amplifier section, and a transistor switching circuit connected in sequence. The operational amplifier section includes a first-stage signal follower circuit and a second-stage signal amplification circuit. The transistor switching circuit is connected to a microcontroller, such as... Figure 1 As shown;

[0038] Specifically:

[0039] The spring antenna sensing circuit includes two spring antennas placed next to the wire to be detected, thereby sensing the signal magnitude when the live and neutral wires are connected in opposite directions through the two spring antennas, and providing an AC input signal for the operational amplifier section;

[0040] In practice, two spring antennas (usually short metal springs or PCB traces) are physically insulated and placed parallel to each other near the wire to be detected (such as near the outer sheath of a power cord). They are only connected to a subsequent high-impedance, high-sensitivity detection circuit (usually an op-amp or dedicated IC). When the live and neutral wires are correctly positioned, the electric field distribution around them is fixed. Due to slight spatial asymmetry between the two antennas (e.g., slightly closer to the live wire and slightly farther from the neutral wire), the 50Hz signal strength they sense will differ slightly. The detection circuit compares the signal strength received by the two antennas. If the signal from antenna A is greater than the signal from antenna B, it is considered a connection state (e.g., correct connection). If the connection is reversed (live and neutral reversed), the electric field distribution relative to the antennas is also reversed, and the signal strength relationship becomes that the signal from antenna B is greater than the signal from antenna A. The spring antenna sensing circuit uses this to provide feedback on the signal strength difference between the live and neutral wires when they are reversed, thus converting it into an AC output signal for the operational amplifier.

[0041] The first-level signal follower circuit includes a first operational amplifier U1, which is used to follow and stabilize the AC input signal transmitted from the spring antenna sensing circuit.

[0042] The secondary signal amplification circuit includes a second operational amplifier U2 and a bias resistor. The second operational amplifier U2 is used to amplify the signal from the primary signal follower circuit, and the bias resistor boosts the AC signal to the positive voltage range.

[0043] The transistor switching circuit includes a transistor Q1, which outputs high and low level signals for the microcontroller to judge based on the comparison result between the voltage input from the secondary signal amplifier circuit and the transistor conduction threshold. This allows the microcontroller to determine whether the live and neutral wires are reversed by judging the high and low level states.

[0044] This invention discloses a live / neutral wire reverse connection detection circuit based on a single-phase smart meter. It utilizes a spring antenna to detect the signal difference when the live and neutral wires are reversed. This signal is then stabilized and amplified by an operational amplifier. Finally, the transistor outputs high and low levels when the live and neutral wires are reversed, allowing the microcontroller to determine the connection status. The microcontroller only needs to determine the high or low level to ascertain the connection status, reducing software workload, minimizing program space usage, and being unaffected by module and ambient temperature. Ultimately, this ensures electrical safety and reduces electricity theft.

[0045] Example 2, as Figures 1 to 6The diagram shown is only one embodiment of the present invention. Based on Embodiment 1, the present invention provides a live / neutral wire reverse connection detection circuit based on a single-phase smart meter, which further includes a first power supply and a second power supply. The first power supply is a 15V power supply, used to power the first operational amplifier U1 and the second operational amplifier U2. The second power supply is a 3.3V LDO power supply circuit, with +15V as input and +3.3V output to power the transistor, bias resistor voltage divider, and microcontroller. The second power supply also includes filter capacitors C3 and C4. Filter capacitor C3 is connected between the +15V power supply terminal and ground; filter capacitor C4 is connected between the +3.3V power supply terminal and ground. Figure 6 As shown.

[0046] In this invention, the spring antenna sensing circuit further includes a TVS transistor (TVS1) and a pull-down resistor (R1); the TVS transistor (TVS1) is connected in parallel between the output terminal of the spring antenna and ground, and one end of the pull-down resistor (R1) is connected to the output terminal of the spring antenna, while the other end is grounded. Figure 2 As shown.

[0047] In this invention, the non-inverting input terminal of the first operational amplifier U1 is connected to the output terminal of the spring antenna sensing circuit, and the inverting input terminal is connected to the output terminal, forming a voltage follower, such as... Figure 3 As shown.

[0048] In this invention, the secondary signal amplification circuit further includes feedback resistor R2, feedback resistor R3, and filter capacitor C2. The bias resistors include bias resistor R4 and bias resistor R5, which are connected in series between the 3.3V power supply and ground, with their intermediate node connected to the non-inverting input of the second operational amplifier U2. The feedback resistors R2 and R3 form a negative feedback network, where one end of feedback resistor R2 is connected to the inverting input of the second operational amplifier U2, and the other end is connected to the output of the primary signal follower circuit. One end of feedback resistor R3 is connected to the inverting input of the second operational amplifier U2, and the other end is connected to the output of the second operational amplifier U2. The filter capacitor C2 is connected in parallel between the power supply terminal of the second operational amplifier U2 and ground. Figure 4 As shown.

[0049] In this invention, the transistor switching circuit further includes a pull-up resistor R8, a voltage divider resistor R6, a voltage divider resistor R7, and a filter resistor R9; the voltage divider resistors R6 and R7 are connected in series between the output terminal of the secondary signal amplifier circuit and ground, with their intermediate node connected to the base of transistor Q1; one end of the pull-up resistor R8 is connected to a 3.3V power supply, and the other end is connected to the collector of transistor Q1; one end of the filter resistor R9 is connected to the collector of transistor Q1, and the other end serves as the circuit's output terminal OUTPUT, such as... Figure 5 As shown.

[0050] In the above circuit for detecting reverse connection of live and neutral wires based on a single-phase smart meter, the length, shape or number of the spring antenna is adjusted according to the actual magnitude of the induced signal to ensure that the induced signal when the live and neutral wires are correctly connected is greater than that when they are reversely connected; the gain Av of the secondary signal amplification circuit is -R3 / R2, and the amplification factor is changed by adjusting the resistance values of R2 and R3; the resistance values of the voltage-dividing resistors R6 and R7 are adjusted according to the magnitude of the signal amplified by the secondary operational amplifier, so that when the live and neutral wires are correctly connected, the base voltage Ub of the triode Q1 is less than Vbe (the conduction threshold of the triode), and when the live and neutral wires are reversely connected, Ub is greater than Vbe;

[0051] The overall working process is as follows:

[0052] Generally, a single-phase smart meter uses the live wire as the reference ground of the meter. The live wire has a sinusoidal AC signal of about 50 Hz or 60 Hz with respect to the ground, and the neutral wire is 0 V with respect to the ground. The spring antenna at the input end is used to sense the difference in the signal magnitudes when the live and neutral wires are correctly and reversely connected. The length, shape, and number of the spring antenna will all affect the magnitude of the induced signal, but the measured induced signals for both correct and reverse connections are AC signals of 50 or 60 Hz, and the signal for correct connection is greater than that for reverse connection.

[0053] When the live and neutral wires are correctly connected, the spring antenna will induce an AC signal with respect to the reference ground of the meter formed by the live wire; after being followed by the first operational amplifier U1 and amplified by the second operational amplifier U2, the signal is then voltage-divided by the resistors R6 and R7 to make the input to the triode Ub < Vbe, resulting in partial cut-off of the triode, and OUTPUT outputs a high level with a certain pulse width.

[0054] Conversely, when the live and neutral wires are reversely connected, the AC signal induced by the spring antenna is very small; finally, after voltage division by the resistors R6 and R7, Ub continuously remains greater than Vbe, and the triode continuously outputs a low level.

[0055] Finally, the signal output by the triode is transmitted to the single-chip microcomputer, and the software can distinguish whether there is a reverse connection of the live and neutral wires by judging the pulse width of the high level of the general-purpose IO port.

[0056] According to the difference in the signal magnitudes sensed by the spring antenna, adjust the resistors R5 and R4 to change the bias voltage magnitude; adjust the resistors R2 and R3 to change the gain and output voltage magnitude of the second operational amplifier; adjust the resistors R6 and R7 to control Vb near Vbe, ensuring that when correctly connected, the triode is partially conductive and outputs a high level with a certain pulse width, and when reversely connected, the triode is fully conductive and outputs a stable low level. Apply this circuit to a single-phase smart meter and install various modules for testing. This circuit has no misjudgment in both correct and reverse connections at an ambient temperature of -40 to +85 °C.

[0057] This invention introduces an operational amplifier to stabilize and amplify the weak AC signal sampled by the spring antenna, and finally outputs high and low levels through a transistor for software judgment. This circuit has been verified to be unaffected by ambient temperature (-40~+85℃) and is not subject to communication interference from various modules after installation, greatly reducing the false judgment rate and increasing reliability.

[0058] In summary, the core points of this invention are:

[0059] 1. Introducing an operational amplifier to stabilize the weak AC signal sampled by the spring antenna before amplification can significantly reduce the circuit's error rate.

[0060] 2. The detection circuit is built entirely in hardware. The firmware only needs to determine the voltage level of the microcontroller's I / O port to detect the live and neutral wire connection.

[0061] Example 3, still as before Figures 1 to 6 The diagram shown is only one embodiment of the present invention. Based on Embodiment 2, in this invention's live / neutral wire reverse connection detection circuit based on a single-phase smart meter, for ease of understanding, the parameters of the above circuit components are illustrated below: the spring antenna is a 5cm long spiral antenna; the TVS transistor TVS1 is an SMBJ6.5A; the pull-down resistor R1 is 10kΩ; both the first-stage operational amplifier U1 and the second-stage operational amplifier U2 are dual operational amplifier chips of model LM358; the bias resistors R4 and R5 are both 10kΩ, biasing the non-inverting input terminal of operational amplifier U2 at 1.65V; the feedback resistor R2 is 1kΩ; R3 is 100kΩ; at this time, the gain Av = -100k / 1k = -100 times; the filter capacitor C2 is 100nF; 3.3V The LDO power supply circuit uses an AMS1117-3.3 LDO chip; the transistor Q1 is an S9013 NPN transistor; the voltage divider resistor R6 is 100kΩ, R7 is 10kΩ; the pull-up resistor R8 is 10kΩ; and the filter resistor R9 is 100Ω.

[0062] Under these parameters, when the live and neutral wires are connected in the correct direction, the OUTPUT terminal outputs a high-level pulse with a pulse width of approximately 10ms (period of 20ms, corresponding to 50Hz); when connected in the reverse direction, the OUTPUT terminal outputs a stable low level. The microcontroller can accurately determine the status of the live and neutral wires by detecting whether a high-level pulse appears at the I / O port within a certain period of time.

[0063] Those skilled in the art can adjust the circuit parameters of the present invention according to actual application needs, such as changing the length and shape of the spring antenna, adjusting the gain of the operational amplifier, changing the ratio of the voltage divider resistors, etc., as long as they do not depart from the core concept of the present invention, they all fall within the protection scope of the present invention.

[0064] This invention discloses a live / neutral wire reverse connection detection circuit based on a single-phase smart meter. It utilizes a spring antenna to detect the signal difference when the live and neutral wires are reversed. This signal is then stabilized and amplified by an operational amplifier. Finally, the transistor outputs high and low levels when the live and neutral wires are reversed, allowing the microcontroller to determine the connection status. The microcontroller only needs to determine the high or low level to ascertain the connection status, reducing software workload, minimizing program space usage, and being unaffected by module and ambient temperature. Ultimately, this ensures electrical safety and reduces electricity theft.

[0065] Example 4: The present invention also provides a single-phase smart meter, which includes a live and neutral wire reverse connection detection circuit based on a single-phase smart meter as described in any of the above embodiments. The output terminal OUTPUT of the circuit is connected to the microcontroller IO port of the smart meter. The microcontroller determines whether the live and neutral wires are reversed by judging the high and low level states of the IO port.

[0066] This invention is not limited to the specific embodiments described above, and various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made to the above embodiments based on the technical essence of this invention should be included within the scope of protection of this invention.

Claims

1. A live / neutral wire reverse connection detection circuit based on a single-phase smart meter, characterized in that: The device includes a spring antenna sensing circuit, an operational amplifier section, and a transistor switching circuit connected in sequence. The operational amplifier section includes a first-stage signal follower circuit and a second-stage signal amplification circuit. A microcontroller is connected to the transistor switching circuit. The spring antenna sensing circuit includes two spring antennas placed next to the wire to be detected, thereby sensing the signal magnitude when the live and neutral wires are connected in opposite directions through the two spring antennas, and providing an AC input signal for the operational amplifier section; The first-level signal follower circuit includes a first operational amplifier U1, which is used to follow and stabilize the AC input signal transmitted from the spring antenna sensing circuit; The secondary signal amplification circuit includes a second operational amplifier U2 and a bias resistor. The second operational amplifier U2 is used to amplify the signal from the primary signal follower circuit, and the bias resistor boosts the AC signal to the positive voltage range. The transistor switching circuit includes a transistor Q1, which outputs a high or low level signal for the microcontroller to judge based on the comparison result between the voltage input from the secondary signal amplifier circuit and the transistor conduction threshold. This allows the microcontroller to determine whether the live and neutral wires are reversed by judging the high or low level status.

2. The live / neutral reverse connection detection circuit based on a single-phase smart meter according to claim 1, characterized in that: It also includes a first power supply; the first power supply is a 15V power supply, which is used to power the first operational amplifier U1 and the second operational amplifier U2.

3. The live / neutral wire reverse connection detection circuit based on a single-phase smart meter according to claim 1, characterized in that: It also includes a second power supply; the second power supply is a 3.3V LDO power supply circuit, with +15V as input and +3.3V output to power the transistor, bias resistor voltage divider and microcontroller.

4. The live / neutral wire reverse connection detection circuit based on a single-phase smart meter according to claim 1, characterized in that: The spring antenna sensing circuit also includes a TVS transistor (TVS1) and a pull-down resistor (R1); the TVS transistor (TVS1) is connected in parallel between the output terminal of the spring antenna and ground, and one end of the pull-down resistor (R1) is connected to the output terminal of the spring antenna, while the other end is grounded.

5. A live / neutral reverse connection detection circuit based on a single-phase smart meter according to claim 1, characterized in that: The non-inverting input of the first operational amplifier U1 is connected to the output of the spring antenna sensing circuit, and the inverting input is connected to the output, forming a voltage follower.

6. The live / neutral reverse connection detection circuit based on a single-phase smart meter according to claim 1, characterized in that: The secondary signal amplification circuit further includes feedback resistors R2 and R3, and filter capacitor C2. The bias resistors include bias resistors R4 and R5, which are connected in series between the 3.3V power supply and ground, with the intermediate node connected to the non-inverting input of the second operational amplifier U2. The feedback resistors R2 and R3 form a negative feedback network, with one end of feedback resistor R2 connected to the inverting input of the second operational amplifier U2 and the other end connected to the output of the primary signal follower circuit. One end of feedback resistor R3 is connected to the inverting input of the second operational amplifier U2 and the other end connected to the output of the second operational amplifier U2. The filter capacitor C2 is connected in parallel between the power supply terminal of the second operational amplifier U2 and ground.

7. A live / neutral wire reverse connection detection circuit based on a single-phase smart meter according to claim 1, characterized in that: The triode switching circuit further includes a pull-up resistor R8, a voltage-dividing resistor R6, a voltage-dividing resistor R7, and a filtering resistor R9; the voltage-dividing resistor R6 and the voltage-dividing resistor R7 are connected in series between the output terminal of the secondary signal amplification circuit and the ground, and the middle node is connected to the base of the triode Q1; one end of the pull-up resistor R8 is connected to the 3.3V power supply, and the other end is connected to the collector of the triode Q1; one end of the filtering resistor R9 is connected to the collector of the triode Q1, and the other end is used as the output terminal OUTPUT of the circuit.

8. A live / neutral wire reverse connection detection circuit based on a single-phase smart meter according to claim 3, characterized in that: The second power supply further includes a filtering capacitor C3 and a filtering capacitor C4; the filtering capacitor C3 is connected between the +15V power supply terminal and the ground; the filtering capacitor C4 is connected between the +3.3V power supply terminal and the ground.

9. A live / neutral reverse connection detection circuit based on a single-phase smart meter according to claim 1, characterized in that: The length, shape or number of the spring antenna is adjusted according to the actual size of the induction signal to ensure that the induction signal when the live wire and the neutral wire are correctly connected is greater than the induction signal when they are reversely connected; The gain Av of the secondary signal amplification circuit is -R3 / R2, and the amplification factor is changed by adjusting the resistance values of R2 and R3; The resistance values of the voltage-dividing resistors R6 and R7 are adjusted according to the size of the signal amplified by the secondary signal amplification circuit, so that when the live wire and the neutral wire are correctly connected, the base voltage Ub of the triode Q1 < Vbe (the triode conduction threshold), and when the live wire and the neutral wire are reversely connected, Ub > Vbe.

10. A single-phase smart meter, characterized in that, Comprising a live-neutral wire reverse connection detection circuit based on a single-phase smart meter according to any one of the above claims 1 to 9, the output terminal OUTPUT of the circuit is connected to the single-chip microcomputer IO port of the smart meter, and the single-chip microcomputer determines whether the live wire and the neutral wire are reversely connected by judging the high and low level states of the IO port.

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