Leakage current tester with soft start function

Abstract

The utility model discloses a kind of leakage current tester with soft start function, it is related to leakage current test equipment technical field.The tester includes power input, voltage regulator RP, isolation transformer TC and the soft start circuit being arranged between power input and voltage regulator RP.The soft start circuit includes NTC thermistor R1 in series in power supply loop and the first relay JK1 in parallel with NTC thermistor R1.The utility model adds one NTC thermistor and one relay, effectively solve the problem that instantaneous current is too large and causes circuit breaker trip due to inductive load such as voltage regulator and isolation transformer when leakage current tester starts, circuit structure is simple, low in cost, and high reliability.

Description

Technical Field

[0001] This utility model relates to the technical field of leakage current testing equipment, specifically a leakage current tester with soft-start function. Background Technology

[0002] Leakage current testing is an important part of safety testing. It aims to measure the current flowing through simulated human body impedance under normal or single-fault conditions to assess the product's electrical safety performance. During testing, the product's input voltage is typically increased to 110% or higher of the rated voltage to simulate extreme conditions caused by power grid fluctuations.

[0003] In existing leakage current testers, a common voltage boosting scheme is to use a voltage regulator in conjunction with an isolation transformer. For example... Figure 1 As shown, its circuit structure is usually as follows: after the mains power is input, it first passes through a switch and then connects to a voltage regulator. The output terminal of the voltage regulator is connected to the primary coil of the isolation transformer, and the secondary coil of the isolation transformer outputs the final test voltage.

[0004] However, since voltage regulators and isolation transformers are both inductive loads with high inductance, a surge current (or inrush current) far exceeding the normal operating current is generated at the moment the power switch is closed. This initiation current can typically be 6 to 7 times the normal operating current. Such a large instantaneous current can easily cause overcurrent protection devices such as circuit breakers or fuses on the power supply line to trip, preventing the testing instruments from starting and functioning properly, and severely impacting production testing efficiency.

[0005] Therefore, how to effectively suppress the inrush current at the start of a leakage current tester has become a technical problem that urgently needs to be solved in this field. Utility Model Content

[0006] To address the shortcomings of existing technologies, this invention provides a leakage current tester with a soft-start function, thus solving the aforementioned problems.

[0007] To achieve the above objectives, this utility model provides the following technical solution: a leakage current tester with soft-start function, comprising: Power input terminal; The voltage regulator RP has its input terminal electrically connected to the power input terminal; An isolation transformer TC, the input terminal of which is electrically connected to the output terminal of the voltage regulator RP; and A soft-start circuit is disposed between the power input terminal and the voltage regulator RP, the soft-start circuit comprising: An NTC thermistor R1 is connected in series in the power supply path between the power input terminal and the voltage regulator RP; and The first relay JK1 has its normally open contact connected in parallel across the NTC thermistor R1. The coil of the first relay JK1 is connected to an external 12V power input. After the tester is powered on, the coil of the first relay JK1 is energized and closed, causing its normally open contact to bypass the NTC thermistor R1.

[0008] Preferably, the NTC thermistor R1 is a negative temperature coefficient thermistor, which exhibits a high resistance value in the initial cold state when the tester is powered on, and is used to limit the starting current flowing through the voltage regulator RP.

[0009] Preferably, it also includes a microcontroller (MCU) and a second relay (JK4); The second relay JK4 is connected in series between the output terminal of the voltage regulator RP and the input terminal of the isolation transformer TC; The output of the microcontroller MCU is used to control the on / off state of the coil of the second relay JK4. The coil of the second relay JK4 is also connected to the external 12V power input terminal, and is used to control whether the isolation transformer TC obtains the working voltage according to the test command.

[0010] Preferably, the power input terminal is a 220V AC mains input terminal.

[0011] Beneficial effects This invention provides a leakage current tester with a soft-start function. Compared with the prior art, it has the following advantages: (1) The leakage current tester with soft start function effectively limits the surge current at the moment of power-on by connecting the NTC thermistor R1 in series in the main circuit and utilizing its high resistance in cold state. This avoids the circuit breaker tripping due to excessive current, ensuring the smooth start and reliable operation of the tester. The first relay JK1 bypasses the NTC thermistor R1, avoiding the risk of the working current continuously flowing through the NTC thermistor R1 and causing it to overheat and burn out. This improves the long-term working reliability of the circuit and the service life of the NTC component.

[0012] (2) The leakage current tester with soft start function only adds one NTC thermistor and one relay. It has fewer components, simple circuit structure, extremely low modification or production cost, and is easy to implement. At the same time, for testers with different power, it is only necessary to select the NTC thermistor and relay with a larger power level accordingly. The solution is highly adaptable. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the circuit principle of a leakage current tester in the prior art as presented in the background section; Figure 2This is the circuit diagram of the leakage current tester with soft-start function of this utility model. Detailed Implementation

[0014] 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.

[0015] Example: Please see Figure 2 This embodiment provides a leakage current tester with soft-start function. The tester mainly includes a soft-start circuit, a voltage regulator RP, an isolation transformer TC, and corresponding control components.

[0016] The soft-start circuit is located between the AC 220V AC mains power input and the input of the voltage regulator RP. Specifically, the soft-start circuit consists of an NTC thermistor R1 (negative temperature coefficient thermistor) and a first relay JK1. The NTC thermistor R1 is connected in series in the main power supply circuit of the voltage regulator RP, where the live wire (L) enters. A normally open contact of the first relay JK1 is connected in parallel across the NTC thermistor R1.

[0017] The tester is equipped with an external 12V DC power input interface (e.g. Figure 2 The "+12VGND" symbol (as shown in the image) is used to provide operating power to the coils of the first relay JK1 and the second relay JK4.

[0018] The working process of this utility model is as follows: When the main power switch of the tester is turned on, AC 220V mains power supplies power to the downstream voltage regulator RP through the NTC thermistor R1. At the instant of power-on, the NTC thermistor R1 is in a cold state, and its resistance is high, thus playing a current-limiting role and suppressing the inrush current flowing through the inductive loads such as the voltage regulator RP to a low and safe range.

[0019] Simultaneously, or with a slight delay, the external 12V power supply is also switched on, powering the coil of the first relay JK1 and energizing it. After the first relay JK1 is energized, its normally open contacts connected in parallel across the NTC thermistor R1 close, forming a low-resistance path that short-circuits (bypasses) the NTC thermistor R1. At this time, the main circuit's operating current bypasses the NTC thermistor R1 and flows directly to the voltage regulator RP through the closed relay contacts. Thus, the soft-start process is complete, and the tester enters its normal standby operating state.

[0020] When an operator needs to perform a leakage current test, they will issue a command through the human-machine interface (HMI). The command is received by the microcontroller (MCU). The MCU then outputs a control signal to connect the power supply circuit of the second relay JK4 coil, allowing current from the external 12V power supply to flow through its coil, thereby energizing and engaging the second relay JK4. The second relay JK4 is located between the voltage regulator RP and the isolation transformer TC. After its contacts close, it applies the regulated voltage output from the voltage regulator RP to the primary coil of the isolation transformer TC. The secondary coil of the isolation transformer TC then outputs a voltage higher than the rated value for product testing.

[0021] In summary, this invention cleverly adds an NTC thermistor R1 and a first relay JK1 to form a simple and efficient soft-start circuit, successfully solving the problem of leakage current testers tripping due to excessive starting current, and has significant practical value.

[0022] Furthermore, any content not described in detail in this specification is existing technology known to those skilled in the art.

[0023] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0024] 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 leakage current tester with soft-start function, characterized in that, include: Power input terminal; The voltage regulator RP has its input terminal electrically connected to the power input terminal; An isolation transformer TC has its input terminal electrically connected to the output terminal of the voltage regulator RP; as well as A soft-start circuit is disposed between the power input terminal and the voltage regulator RP, the soft-start circuit comprising: The NTC thermistor R1 is connected in series in the power supply path between the power input terminal and the voltage regulator RP; as well as The first relay JK1 has its normally open contact connected in parallel across the NTC thermistor R1. The coil of the first relay JK1 is connected to an external 12V power input. After the tester is powered on, the coil of the first relay JK1 is energized and closed, causing its normally open contact to bypass the NTC thermistor R1.

2. The leakage current tester with soft-start function according to claim 1, characterized in that, The NTC thermistor R1 is a negative temperature coefficient thermistor, which exhibits a high resistance value in the initial cold state when the tester is powered on, and is used to limit the starting current flowing through the voltage regulator RP.

3. A leakage current tester with soft-start function according to claim 1, characterized in that, It also includes a microcontroller (MCU) and a second relay (JK4); The second relay JK4 is connected in series between the output terminal of the voltage regulator RP and the input terminal of the isolation transformer TC; The output of the microcontroller MCU is used to control the on / off state of the coil of the second relay JK4. The coil of the second relay JK4 is also connected to the external 12V power input terminal, and is used to control whether the isolation transformer TC obtains the working voltage according to the test command.

4. A leakage current tester with soft-start function according to claim 1, characterized in that, The power input terminal is a 220V AC mains input terminal.

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