Line finder transmitting circuit

Abstract

The utility model relates to a line finder transmitting circuit, which belongs to the technical field of line finding devices and comprises a line finding signal generating circuit, a voltage amplifying circuit, a power amplifying circuit, a bidirectional frequency selecting circuit and a protection circuit. The voltage amplification circuit converts the square wave signal into a quasi-sinusoidal signal through low-pass filtering processing; the power amplification circuit adopts a push-pull amplification structure to avoid waveform distortion; the bidirectional frequency selection circuit is composed of a primary side resonance branch circuit and a secondary side resonance branch circuit, and by setting the resonance frequency, power frequency interference is effectively restrained, and commercial power line connection is achieved. The protection circuit provides overvoltage protection through a fuse and a surge protection resistor. According to the utility model, non-target frequency interference can be efficiently isolated, line hunting requirements in a commercial power environment can be satisfied, and strong anti-interference capability and equipment protection characteristics are possessed.

Description

Technical Field

[0001] This utility model belongs to the technical field of wire finding devices, specifically relating to a wire finder transmitting circuit. Background Technology

[0002] In the field of power cable inspection and communication maintenance, cable finders need to inject specific frequency signals into the target cable through a transmitting circuit and rely on signal characteristics to achieve accurate positioning. However, with the development of smart grids, the electromagnetic environment of live lines is becoming increasingly complex. The superposition of power frequency harmonics, carrier communication signals, and high-frequency noise causes serious interference to the transmission and identification of cable finding signals. Traditional cable finder transmitting circuits mostly adopt single-stage amplification and fixed-frequency filtering designs, which have the following technical limitations: First, the power amplification stage mostly relies on a single-tube amplification structure, which is prone to waveform distortion due to current saturation when driving low-impedance or capacitive loads, affecting signal penetration and demodulation accuracy at the receiving end; Second, conventional frequency selection circuits are mostly unidirectional filtering designs, which can only suppress interference at the receiving end and cannot block power frequency noise from the mains side, resulting in a decrease in the signal-to-noise ratio of the transmitted signal; Third, the circuit lacks multi-dimensional protection mechanisms, and abnormal operating conditions such as mains surges, electrostatic discharge, and load short circuits can easily damage core components, resulting in insufficient equipment reliability. In addition, existing technologies are poorly adapted to live lines, often requiring power outages to avoid interference from mains power, which greatly limits on-site work efficiency.

[0003] Chinese patent CN207321251U discloses a novel network cable locating device adaptable to fast and high-speed switches. The device includes a transmitter for sending an FM signal to a target cable and a receiver for receiving and amplifying the FM signal. The transmitter comprises a signal amplification module, a signal shaping module, and a power amplification module connected in sequence. Current source modules are connected to the signal shaping module and the power amplification module to maintain a constant voltage amplitude of the output signal. The receiver comprises a signal receiving module, an intermediate frequency selector module for filtering interference waves, a frequency discriminator module for demodulating the modulated signal into an audio signal, and a power amplifier module for amplifying the signal power and emitting a cable locating prompt tone. This modulation and demodulation method effectively filters interference signals within the audio signal range and possesses strong adaptability and penetration power, capable of penetrating shielding layers, thus achieving excellent cable locating capabilities.

[0004] The problems with the aforementioned existing technology are that the device cannot effectively isolate mains power frequency interference, the line-finding signal is easily interfered with by other signals when transmitted through a live line, the signal is prone to distortion when connected to a low-impedance load, and there is a risk of damage to the equipment due to mains overvoltage. Utility Model Content

[0005] The purpose of this invention is to provide a line finder transmitting circuit to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, this utility model provides the following technical solution:

[0007] A line finder transmitting circuit includes a line finding signal generating circuit, a voltage amplification circuit, a power amplification circuit, a bidirectional frequency selection circuit, and a protection circuit;

[0008] The input terminal of the voltage amplifier circuit is connected to the output terminal of the line-finding signal generation circuit, and the output terminal of the voltage amplifier circuit is connected to the input terminal of the power amplifier circuit; the output terminal of the power amplifier circuit is connected to the input terminal of the bidirectional frequency selection circuit; the output terminal of the bidirectional frequency selection circuit is connected to the input terminal of the protection circuit; and the output terminal of the protection circuit is connected to the mains power line.

[0009] The bidirectional frequency selection circuit is a transformer-coupled double resonant structure, used to extract and transmit the line-finding signal of the target frequency, and to bidirectionally isolate interference signals of non-target frequencies.

[0010] The protection circuit is used to suppress mains surge impacts and maintain the transmission of line-following signals on energized mains lines.

[0011] In a preferred embodiment, the voltage amplification circuit includes an amplifier;

[0012] The non-inverting input terminal of the amplifier is connected to one end of the eighth resistor and one end of the fourth capacitor, respectively. The other end of the eighth resistor is connected to the output terminal of the line-finding signal generation circuit, and the other end of the fourth capacitor is connected to one end of the third capacitor and ground.

[0013] The inverting input terminal of the amplifier is connected to one end of the sixth resistor and one end of the seventh resistor, respectively, and the other end of the sixth resistor is connected to the other end of the third capacitor.

[0014] The output terminal of the amplifier is connected to the other end of the seventh resistor and the power amplifier circuit, respectively.

[0015] In a preferred embodiment, the power amplifier circuit includes a first transistor, a second transistor, a first diode, and a second diode;

[0016] The base of the first transistor is connected to one end of the first resistor and the anode of the first diode, the other end of the first resistor is connected to the positive terminal of the power supply and the collector of the first transistor, and the emitter of the first transistor is connected to one end of the third resistor, the emitter of the second transistor and the bidirectional frequency selection circuit.

[0017] The base of the second transistor is connected to one end of the second resistor and the cathode of the second diode, respectively; the other end of the second resistor is connected to the collector of the second transistor and grounded, respectively.

[0018] The cathode of the first diode is connected to the other end of the third resistor, the anode of the second diode, and the output terminal of the amplifier, respectively.

[0019] In a preferred embodiment, the bidirectional frequency selection circuit includes a transformer, a first capacitor, and a second capacitor;

[0020] One end of the primary inductance of the transformer is connected to the emitter of the first transistor through the first capacitor, and the other end of the primary inductance of the transformer is grounded.

[0021] One end of the secondary inductance of the transformer is connected to the protection circuit through a second capacitor, and the other end of the secondary inductance of the transformer is connected to the protection circuit.

[0022] The primary inductance and the first capacitor of the transformer form the primary resonant branch, and the secondary inductance and the second capacitor of the transformer form the secondary resonant branch. The resonant frequencies of the primary and secondary resonant branches are both the target line-finding signal frequency.

[0023] In a preferred embodiment, the protection circuit includes a fuse and a surge protection resistor;

[0024] One end of the fuse is connected to one end of the secondary inductance of the transformer and one end of the surge protection resistor through the second capacitor. The other end of the fuse is connected to the mains power line. The other end of the surge protection resistor is connected to the other end of the secondary inductance of the transformer and grounded.

[0025] In a preferred embodiment, a fifth resistor is also included, one end of which is connected to one end of the second capacitor and one end of the fuse, and the other end of which is connected to the other end of the surge protection resistor.

[0026] In a preferred embodiment, a fourth resistor and a bidirectional Zener diode are also included;

[0027] One end of the fourth resistor is connected to the emitter of the first transistor, and the other end of the fourth resistor is connected to the first capacitor and one end of the bidirectional Zener diode.

[0028] The other end of the bidirectional Zener diode is connected to the other end of the primary inductance of the transformer.

[0029] In a preferred embodiment, the turns ratio of the primary inductor to the secondary inductor is 1:1 to 1.2.

[0030] Compared with the prior art, the beneficial effects of this utility model are:

[0031] 1. High-efficiency interference suppression: Bidirectional frequency selection is achieved through the primary and secondary side dual resonant branches, presenting a low-impedance path for the line-finding signal and a high impedance to power frequency interference;

[0032] 2. Mains power adaptability: It can be directly connected to live power lines, breaking through the limitation of traditional line finders that require power off operation;

[0033] 3. Waveform fidelity design: Through push-pull power amplification and micro-conduction bias, the output signal waveform is ensured to be undistorted;

[0034] 4. Multiple safety protections: The combination of fuses and surge protection resistors can withstand mains surge impacts, and the bidirectional Zener diodes limit the output voltage, ensuring the safe and stable operation of the overall circuit device. Attached Figure Description

[0035] Figure 1 This is a circuit diagram of the present invention. Detailed Implementation

[0036] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0037] It should be understood that the step numbers used in the text are for ease of description only and are not intended to limit the order in which the steps are performed.

[0038] It should be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0039] The terms “comprising” and “including” indicate the presence of the described feature, whole, step, operation, element and / or component, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0040] The term “and / or” refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes these combinations.

[0041] As attached Figure 1 As shown, a line finder transmitting circuit includes a line finding signal generating circuit, a voltage amplification circuit, a power amplification circuit, a bidirectional frequency selection circuit, and a protection circuit.

[0042] The input terminal of the voltage amplifier circuit is connected to the output terminal of the line-finding signal generation circuit, and the output terminal of the voltage amplifier circuit is connected to the input terminal of the power amplifier circuit; the output terminal of the power amplifier circuit is connected to the input terminal of the bidirectional frequency selection circuit; the output terminal of the bidirectional frequency selection circuit is connected to the input terminal of the protection circuit; and the output terminal of the protection circuit is connected to the mains power line.

[0043] The line-finding signal generating circuit is used to generate the original line-finding signal at the target frequency;

[0044] The bidirectional frequency selection circuit is a transformer-coupled double resonant structure, used to extract and transmit the line-finding signal of the target frequency, and to bidirectionally isolate interference signals of non-target frequencies.

[0045] The protection circuit is used to suppress mains surge impacts and maintain the transmission of line-following signals on energized mains lines.

[0046] In a preferred embodiment of this utility model, the voltage amplification circuit includes amplifier U2;

[0047] The non-inverting input terminal of the amplifier U2 is connected to one end of the eighth resistor R8 and one end of the fourth capacitor C4, respectively. The other end of the eighth resistor R8 is connected to the output terminal NET1 of the line-finding signal generation circuit. The other end of the fourth capacitor C4 is connected to one end of the third capacitor C3 and ground.

[0048] The inverting input terminal of the amplifier U2 is connected to one end of the sixth resistor R6 and one end of the seventh resistor R7, respectively, and the other end of the sixth resistor R6 is connected to the other end of the third capacitor C3.

[0049] The output terminal of the amplifier U2 is connected to the other end of the seventh resistor R7 and the power amplifier circuit, respectively.

[0050] In this embodiment, amplifier U2 can be an SGM722 operational amplifier. The original line-following signal waveform generated by the line-following signal generation circuit has a small amplitude. The amplitude of the original line-following signal waveform is amplified by the voltage amplification circuit. In the voltage amplification circuit, the eighth resistor R8 and the fourth capacitor C4 form a low-pass filter circuit to filter out multiple harmonics of the line-following square wave signal, thereby processing the square wave signal into a quasi-sinusoidal signal.

[0051] In a preferred embodiment of the present invention, the power amplifier circuit includes a first transistor Q1, a second transistor Q2, a first diode D1, and a second diode D2;

[0052] The base of the first transistor Q1 is connected to one end of the first resistor R1 and the anode of the first diode D1, respectively. The other end of the first resistor R1 is connected to the positive terminal of the power supply and the collector of the first transistor Q1, respectively. The emitter of the first transistor Q1 is connected to one end of the third resistor R3, the emitter of the second transistor Q2, and the bidirectional frequency selection circuit, respectively.

[0053] The base of the second transistor Q2 is connected to one end of the second resistor R2 and the cathode of the second diode D2; the other end of the second resistor R2 is connected to the collector of the second transistor Q2 and grounded.

[0054] The cathode of the first diode D1 is connected to the other end of the third resistor R3, the anode of the second diode D2, and the output terminal of the amplifier U2, respectively.

[0055] In this embodiment, the power amplifier circuit amplifies the line-finding signal, which has passed through the voltage amplifier circuit, by one time, enabling the line-finding signal to have a certain current output capability. This prevents waveform distortion when the transmitter of the line-finding transmitter is connected to a load with low impedance, thus avoiding impact on transmission efficiency. Specifically, the first diode D1 and the second diode D2 keep the first transistor Q1 and the second transistor Q2 in a slightly conducting state, preventing crossover distortion in the amplified waveform. The source current and sink current at the output of the power amplifier circuit flow into the power supply and ground wires through Q1 and Q2 respectively, avoiding waveform distortion.

[0056] In a preferred embodiment of this utility model, the bidirectional frequency selection circuit includes a transformer U1, a first capacitor C1, and a second capacitor C2.

[0057] One end of the primary inductance L1 of the transformer U1 is connected to the emitter of the first transistor Q1 through the first capacitor C1, and the other end of the primary inductance L1 of the transformer U1 is grounded.

[0058] One end of the secondary inductance L2 of the transformer U1 is connected to the protection circuit through the second capacitor C2, and the other end of the secondary inductance L2 of the transformer U1 is connected to the protection circuit.

[0059] The primary inductance L1 and the first capacitor C1 of the transformer U1 form the primary resonant branch, and the secondary inductance L2 and the second capacitor C2 of the transformer U1 form the secondary resonant branch. The resonant frequencies of the primary and secondary resonant branches are both the target line-finding signal frequencies.

[0060] In this embodiment, the bidirectional frequency selection circuit consists of the primary inductance L1 and the first capacitor C1 of transformer U1, and the secondary inductance L2 and the first capacitor C2 of transformer U1, forming the primary resonant branch and the secondary resonant branch, respectively. The resonant frequencies of both the primary and secondary sides are designed to be close to the line-finding signal frequency (200kHz), i.e.:

[0061]

[0062] In the formula: f is the target frequency of the line-finding signal; L1 is the inductance value of the primary resonant branch; C1 is the capacitance value of the primary resonant branch; L2 is the inductance value of the secondary resonant branch; C2 is the capacitance value of the secondary resonant branch.

[0063] The 200kHz component of the line-finding signal is transmitted to transformer U1 via the primary resonant branch, using a low-impedance path. During this process, power frequency interference, due to its frequency being far from the resonant point, is suppressed in the primary branch by its high impedance and cannot enter subsequent circuits. After being coupled by the transformer, the line-finding signal is further filtered out by secondary resonance in the secondary resonant branch, where the non-200kHz components are filtered out. The high impedance characteristic of the secondary branch prevents external power frequency interference from entering the circuit from the mains power line in the reverse direction.

[0064] In a preferred embodiment of this utility model, the protection circuit includes a fuse U3 and a surge protection resistor U4;

[0065] One end of the fuse U3 is connected to one end of the secondary inductance L1 of the transformer U1 and one end of the surge protection resistor U4 through the second capacitor C2. The other end of the fuse U3 is connected to the mains power line NET2. The other end of the surge protection resistor U4 is connected to the other end of the secondary inductance L2 of the transformer U1 and grounded.

[0066] In this embodiment, when the external mains voltage is too high, the fuse U3 and the surge protection resistor U2 can operate in a timely manner to disconnect the circuit and protect the line-finding transmitter.

[0067] In a preferred embodiment of the present invention, a fifth resistor is also included, one end of which is connected to one end of the second capacitor and one end of the fuse, and the other end of which is connected to the other end of the surge protection resistor.

[0068] In this embodiment, the fifth resistor R5 is a discharge resistor, which is generally set to a parameter of more than 1 MΩ, to prevent the accumulation of static electricity in the second capacitor C2.

[0069] In a preferred embodiment of this utility model, a fourth resistor and a bidirectional Zener diode are also included;

[0070] One end of the fourth resistor is connected to the emitter of the first transistor, and the other end of the fourth resistor is connected to one end of the primary inductance of the transformer and one end of the bidirectional Zener diode through the first capacitor.

[0071] The other end of the bidirectional Zener diode is connected to the other end of the primary inductance of the transformer.

[0072] In this embodiment, the fourth resistor R4 is set to a 10-ohm resistor to limit the current in the signal circuit and prevent the first transistor Q1 and the second transistor Q2 from burning out when the external signal is too large; the bidirectional protection diode D3 is used to ensure that the output voltage of the power amplifier circuit is within a certain range and to prevent the power amplifier circuit from burning out.

[0073] In a preferred embodiment of this utility model, the turns ratio of the primary inductor to the secondary inductor is 1:1 to 1.2.

[0074] In this application embodiment, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent the existence of A alone, A and B simultaneously, or B alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, at least one of a, b, and c can represent: a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, and c can be single or multiple.

[0075] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A line finder transmitter circuit comprising a line finder signal generating circuit, characterized in that It also includes voltage amplifier circuits, power amplifier circuits, bidirectional frequency selection circuits, and protection circuits; The input terminal of the voltage amplifier circuit is connected to the output terminal of the line-finding signal generation circuit, and the output terminal of the voltage amplifier circuit is connected to the input terminal of the power amplifier circuit; the output terminal of the power amplifier circuit is connected to the input terminal of the bidirectional frequency selection circuit; the output terminal of the bidirectional frequency selection circuit is connected to the input terminal of the protection circuit; and the output terminal of the protection circuit is connected to the mains power line. The bidirectional frequency selection circuit is a transformer-coupled double resonant structure, used to extract and transmit the line-finding signal of the target frequency, and to bidirectionally isolate interference signals of non-target frequencies. The protection circuit is used to suppress mains surge impacts and maintain the transmission of line-following signals on energized mains lines.

2. A line finder transmitting circuit according to claim 1, characterized in that: The voltage amplification circuit includes an amplifier; The non-inverting input terminal of the amplifier is connected to one end of the eighth resistor and one end of the fourth capacitor, respectively. The other end of the eighth resistor is connected to the output terminal of the line-finding signal generation circuit, and the other end of the fourth capacitor is connected to one end of the third capacitor and ground. The inverting input terminal of the amplifier is connected to one end of the sixth resistor and one end of the seventh resistor, respectively, and the other end of the sixth resistor is connected to the other end of the third capacitor. The output terminal of the amplifier is connected to the other end of the seventh resistor and the power amplifier circuit, respectively.

3. A line finder transmitting circuit according to claim 2, characterized in that: The power amplifier circuit includes a first transistor, a second transistor, a first diode, and a second diode; The base of the first transistor is connected to one end of the first resistor and the anode of the first diode, the other end of the first resistor is connected to the positive terminal of the power supply and the collector of the first transistor, and the emitter of the first transistor is connected to one end of the third resistor, the emitter of the second transistor and the bidirectional frequency selection circuit. The base of the second transistor is connected to one end of the second resistor and the cathode of the second diode, respectively. The other end of the second resistor is connected to the collector of the second transistor and grounded, respectively; The cathode of the first diode is connected to the other end of the third resistor, the anode of the second diode, and the output terminal of the amplifier, respectively.

4. A line finder transmitting circuit according to claim 3, characterized in that: The bidirectional frequency selection circuit includes a transformer, a first capacitor, and a second capacitor; One end of the primary inductance of the transformer is connected to the emitter of the first transistor through the first capacitor, and the other end of the primary inductance of the transformer is grounded. One end of the secondary inductance of the transformer is connected to the protection circuit through a second capacitor, and the other end of the secondary inductance of the transformer is connected to the protection circuit. The primary inductance and the first capacitor of the transformer form the primary resonant branch, and the secondary inductance and the second capacitor of the transformer form the secondary resonant branch. The resonant frequencies of both the primary and secondary resonant branches are the target line-finding signal frequencies.

5. A line finder transmitting circuit according to claim 4, characterized in that: The protection circuit includes a fuse and a surge protection resistor; One end of the fuse is connected to one end of the secondary inductance of the transformer and one end of the surge protection resistor through the second capacitor. The other end of the fuse is connected to the mains power line. The other end of the surge protection resistor is connected to the other end of the secondary inductance of the transformer and grounded.

6. A line finder transmitting circuit according to claim 5, characterized in that: It also includes a fifth resistor, one end of which is connected to one end of the second capacitor and one end of the fuse, and the other end of the fifth resistor is connected to the other end of the surge protection resistor.

7. A line finder transmitter circuit as claimed in claim 4 or 5, characterized in that: It also includes a fourth resistor and a bidirectional Zener diode; One end of the fourth resistor is connected to the emitter of the first transistor, and the other end of the fourth resistor is connected to the first capacitor and one end of the bidirectional Zener diode. The other end of the bidirectional Zener diode is connected to the other end of the primary inductance of the transformer.

8. A line finder transmitting circuit according to claim 4, characterized in that: The turns ratio of the primary inductor to the secondary inductor is 1:1 to 1.2.

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