AC residual current detection circuit

By designing an AC residual current detection circuit based on leakage transformer CT1 and operational amplifier U1, combined with RC low-pass and high-pass filters, the problem of low leakage detection accuracy of AC equipment is solved, achieving cost reduction and improved detection accuracy.

CN120652161APending Publication Date: 2025-09-16SICHUAN YONGGUI SCI & TECH CO LTD
View PDF 0 Cites 0 Cited by

Patent Information

Application Number
CN202510701107.7
Authority / Receiving Office
CN · China
Patent Type
Applications(China)
Current Assignee / Owner
Filing Date
2025-05-28
Publication Date
2025-09-16

AI Technical Summary

Technical Problem

The leakage detection circuit of existing AC equipment has the problem of low detection accuracy, especially the inaccurate processing of the leakage transformer output signal.

Method used

An AC residual current detection circuit consisting of a leakage transformer CT1, an operational amplifier U1 and a reference power supply is used. Combined with an RC low-pass filter and a high-pass filter, an active filter circuit is designed to improve detection accuracy.

Benefits of technology

The invention reduces costs, reduces components, simplifies circuit structure and improves the accuracy of leakage detection.

✦ Generated by Eureka AI based on patent content.

Smart Images

  • Figure CN120652161A_ABST
    Figure CN120652161A_ABST
Patent Text Reader

Abstract

The invention discloses an alternating-current residual current detection circuit which comprises an electric leakage mutual inductor CT1, an operational amplifier U1 and a reference power source, the positive end RCD + of an induction coil of the electric leakage mutual inductor CT1 is connected with one end of a detection resistor R4, the negative end RCD-of the induction coil of the electric leakage mutual inductor CT1 is connected with the other end of the detection resistor R4, and the positive end RCD + and the negative end RCD-of the induction coil of the electric leakage mutual inductor CT1 are jointly connected to a reference voltage source. Two stages of RC low-pass filters are connected in series between a positive end RCD + of an induction coil of the electric leakage mutual inductor CT1 and an in-phase input end of the operational amplifier U1, the reference voltage source is used as a reference plane by the first-stage filter, GND is used as a reference plane by the second-stage filter, a high-pass filter is arranged between the reference voltage source and an inverted input end of the operational amplifier U1, and the high-pass filter is connected with the operational amplifier U1. A low-pass RC filter circuit is arranged between the output end of the operational amplifier U1 and the IO port of the single-chip microcomputer. The invention has the advantages of cost reduction, device reduction, circuit simplification and detection accuracy improvement.
Need to check novelty before this filing date? Find Prior Art

Description

Technical Field

[0001] The present invention relates to the technical field of new energy vehicle charging, and in particular to an AC residual current detection circuit. Background Art

[0002] The input lines of AC equipment are typically equipped with a leakage detection circuit to detect whether there is leakage. When the leakage detection circuit detects leakage exceeding national standards, it usually immediately cuts off the power supply to ensure that the AC access equipment is always in a safe power state, effectively preventing electric shock accidents. The current common method is to use a leakage transformer, but the processing of the leakage transformer's output signal has many drawbacks. Either the detection accuracy is low, for example, the output signal is only passively filtered, or the detection accuracy is low, for example, the active filtering circuit is not well designed. Summary of the Invention

[0003] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide an AC residual current detection circuit, which has the advantages of reducing cost, reducing components, simplifying circuits and improving detection accuracy.

[0004] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: an AC residual current detection circuit, comprising: a leakage transformer CT1, an operational amplifier U1 and a reference power supply, the positive terminal RCD+ of the induction coil of the leakage transformer CT1 is connected to one end of the detection resistor R4, the negative terminal RCD- is connected to the other end of the detection resistor R4, and both are connected to the reference voltage source, a two-stage RC low-pass filter is provided in series between the positive terminal RCD+ of the induction coil of the leakage transformer CT1 and the non-inverting input terminal of the operational amplifier U1, wherein the first-stage filter uses the reference voltage source as a reference plane, and the second-stage filter uses GND as a reference plane, a high-pass filter is provided between the reference voltage source and the inverting input terminal of the operational amplifier U1, and a low-pass RC filter circuit is provided between the output terminal of the operational amplifier U1 and the IO port of the single-chip microcomputer.

[0005] As a further improvement of the present invention, the first-stage filter includes a resistor R1 and a capacitor C1, one end of the resistor R1 is connected to the positive end RCD+ of the induction coil of the leakage transformer CT1, the other end of the resistor R1 is connected to one end of the capacitor C1, and the other end of the capacitor C1 is connected to the reference voltage source.

[0006] As a further improvement of the present invention, the secondary filter includes a resistor R2 and a capacitor C2, one end of the resistor R2 is connected to the common end of the resistor R1 and the capacitor C1, the other end of the resistor R2 is connected to one end of the capacitor C2, and the other end of the capacitor C2 is grounded.

[0007] As a further improvement of the present invention, the high-pass filter includes a resistor R3 and a capacitor C3, one end of the resistor R3 is connected to the inverting input terminal of the operational amplifier U1, the other end of the resistor R3 is connected to one end of the capacitor C3, and the other end of the capacitor C3 is connected to the reference voltage source.

[0008] As a further improvement of the present invention, the low-pass RC filter circuit includes a resistor R6 and a capacitor C4, one end of the resistor R6 is connected to the output end of the operational amplifier U1, the other end of the resistor R6 is respectively connected to the IO port of the microcontroller and one end of the capacitor C4, and the other end of the capacitor C4 is grounded.

[0009] As a further improvement of the present invention, a resistor R7 is provided between the common end of the resistor R6 and the capacitor C4 and the IO port of the single chip microcomputer.

[0010] As a further improvement of the present invention, a resistor R5 is provided between the inverting input terminal and the output terminal of the operational amplifier U1.

[0011] The beneficial effects of the present invention are:

[0012] The present invention has the advantages of reducing cost, reducing components, simplifying circuits and improving detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the circuit structure of an embodiment of the present invention. DETAILED DESCRIPTION

[0014] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0015] Example

[0016] like Figure 1 As shown, an AC residual current detection circuit is shown, in which one end RCD+ of the induction coil of the leakage transformer CT1 is connected to one end of the detection resistor R4; the other end RCD- is connected to the other end of the detection resistor R4, and both are connected to a reference voltage source of +2.5V; one end of the resistor R1 of the first-stage low-pass filter for the signal at the non-inverting input end of the operational amplifier U1 is connected to the resistor R4, and the other end is connected to one end of the capacitor C1, and the other end of the capacitor C1 is connected to the reference voltage source of +2.5V; one end of the resistor R2 of the second-stage low-pass filter for the signal at the non-inverting input end of the operational amplifier U1 is connected to the resistor R1, and the other end is connected to the non-inverting input end of the operational amplifier U1; one end of the capacitor C2 is connected to the non-inverting input end of the operational amplifier U1, and the other end is connected to the ground plane GND.

[0017] One end of the high-pass filter's capacitor C3 is connected to a +2.5V reference voltage source, and the other end is connected to one end of resistor R3. The other end of resistor R3 is connected to the inverting input of op amp U1. One end of balancing resistor R6 is connected to the inverting input of op amp U1, and the other end is connected to the output of op amp U1. The output of op amp U1 is connected to one end of resistor R6, which is connected to current-controlled resistor R7. One end of capacitor C4 is connected between resistors R6 and R7, and the other end is connected to ground plane GND. The other end of current-controlled resistor R7 is connected to the microcontroller IO port, namely RC_DET.

[0018] The principle of this embodiment is described below:

[0019] First, a high-gain, rail-to-rail op amp is selected as the core component of the leakage signal processing circuit (active filter). A high-precision detection resistor, namely resistor R4, is connected in parallel between the two ends of the induction coil RCD+ and RCD- of the leakage transformer CT1. This resistor is used for current-voltage conversion, converting the induced leakage current into a small AC voltage signal, namely the acquisition signal.

[0020] First, design an external +2.5V reference voltage source to raise the voltage during the negative half-cycle of the AC circuit to above 0V. Connect the non-inverting input of op amp U1 to a two-stage RC low-pass filter. The first filter uses +2.5V as the reference plane, while the second uses GND as the reference plane. A high-pass filter is placed between the +2.5V reference voltage source and the inverting input of op amp U1 to ensure voltage stability at the inverting input.

[0021] A high-value resistor, R5, is connected in parallel between the inverting input and output of op amp U1 to balance the effects of the op amp's bias current on the output. A low-pass RC filter circuit is designed at the output of op amp U1 to stabilize and maintain the output during AD sampling. A current control element, R7, is placed after the RC low-pass filter circuit at the output of op amp U1 to ensure that the output voltage signal has a certain load capacity after passing through the resistor.

[0022] The above-described embodiments merely represent specific implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. An AC residual current detection circuit, characterized in that: include: Leakage transformer CT1, operational amplifier U1 and reference power supply, the positive end RCD+ of the induction coil of the leakage transformer CT1 is connected to one end of the detection resistor R4, the negative end RCD- is connected to the other end of the detection resistor R4, and are jointly connected to the reference voltage source, a two-stage RC low-pass filter is provided in series between the positive end RCD+ of the induction coil of the leakage transformer CT1 and the non-inverting input end of the operational amplifier U1, wherein the first-stage filter uses the reference voltage source as a reference plane, and the second-stage filter uses GND as a reference plane, a high-pass filter is provided between the reference voltage source and the inverting input end of the operational amplifier U1, and a low-pass RC filter circuit is provided between the output end of the operational amplifier U1 and the IO port of the single-chip microcomputer.

2. The AC residual current detection circuit according to claim 1, characterized in that: The primary filter includes a resistor R1 and a capacitor C1, one end of the resistor R1 is connected to the positive end RCD+ of the induction coil of the leakage transformer CT1, the other end of the resistor R1 is connected to one end of the capacitor C1, and the other end of the capacitor C1 is connected to the reference voltage source.

3. The AC residual current detection circuit according to claim 2, characterized in that: The secondary filter includes a resistor R2 and a capacitor C2, one end of the resistor R2 is connected to the common end of the resistor R1 and the capacitor C1, the other end of the resistor R2 is connected to one end of the capacitor C2, and the other end of the capacitor C2 is grounded.

4. The AC residual current detection circuit according to claim 1, characterized in that: The high-pass filter includes a resistor R3 and a capacitor C3, one end of the resistor R3 is connected to the inverting input terminal of the operational amplifier U1, the other end of the resistor R3 is connected to one end of the capacitor C3, and the other end of the capacitor C3 is connected to the reference voltage source.

5. The AC residual current detection circuit according to claim 1, characterized in that: The low-pass RC filter circuit includes a resistor R6 and a capacitor C4. One end of the resistor R6 is connected to the output end of the operational amplifier U1, and the other end of the resistor R6 is respectively connected to the IO port of the microcontroller and one end of the capacitor C4. The other end of the capacitor C4 is grounded.

6. The AC residual current detection circuit according to claim 5, characterized in that: A resistor R7 is provided between the common end of the resistor R6 and the capacitor C4 and the IO port of the single chip microcomputer.

7. The AC residual current detection circuit according to claim 1, characterized in that: A resistor R5 is provided between the inverting input terminal and the output terminal of the operational amplifier U1.