High-precision current detection circuit

Abstract

The utility model discloses a high-precision current detection circuit, and belongs to the field of current detection. The circuit comprises a sampling resistor, a differential amplification circuit and a differential analog-to-digital converter, the two ends of the sampling resistor are connected between the in-phase input end (A1) and the inverted input end (A2) of the differential amplification circuit in parallel, meanwhile, the first end of the sampling resistor is used for inputting sampling current, and the second end of the sampling resistor is grounded; the output end of the differential amplification circuit is connected with the positive electrode input end (X1) of the differential analog-to-digital converter; and an in-phase bias input end (C1) of the differential amplification circuit and a cathode input end (X2) of the differential analog-to-digital converter are respectively connected with an external reference source with the same output voltage. According to the utility model, the precision of current detection is improved.

Description

Technical Field

[0001] The utility model belongs to the field of current detection. Specifically, the utility model relates to a high-precision current detection circuit. Background Art

[0002] In the prior art, in the commonly used post-stage detection circuit based on Hall current sensors, the conversion method from sampled current to voltage is basically the same, and all are converted through a fixed circuit; and the common post-stage scheme of the sampling circuit before was mainly designed by linear optocouplers. There is a linearity problem with linear optocouplers themselves. Although the design and manufacturing process of linear optocouplers have been improved currently, the linearity problem still exists. Especially for the full-scale measurement range, it is currently impossible to achieve a complete 1:1. And in this design scheme, through the optimization and innovation of the detection circuit, the linear optocoupler is removed in the design scheme, thus completely avoiding the linearity problem.

[0003] The comparative document (CN218003537U) relates to a power supply sampling circuit, a line controller and a multi-connected air conditioner system. The power supply sampling circuit includes a differential amplifier; a first power supply communication bus connected to the negative pole of the differential amplifier and a second power supply communication bus connected to the positive pole of the differential amplifier; a sampling resistor arranged between the first power supply communication bus and the second power supply communication bus; the differential amplifier outputs a sampling voltage, and the sampling voltage of each indoor unit is calculated according to the resistance value of the sampling resistor and the internal resistance of the power supply communication bus between the indoor unit and the line controller. Since the sampling voltage is related to the internal resistance of the power supply communication bus, it can be used to characterize the line energy consumption. This application determines the power supply sequence according to the line energy consumption, realizes the minimization of line loss, and improves the power supply efficiency. The sampling circuit in the above comparative document uses a bias voltage, and the bias voltage will affect the final current detection accuracy, and the comparative document does not overcome this problem. Summary of the Utility Model

[0004] The utility model aims to overcome the deficiencies of the prior art and provides a high-precision current detection circuit to achieve the purpose of improving the current detection accuracy.

[0005] To achieve the above purpose, the technical solution adopted by the utility model is as follows:

[0006] A high-precision current detection circuit, as Figure 1As shown, the circuit includes a sampling resistor, a differential amplifier circuit, and a differential analog-to-digital converter. Among them, both ends of the sampling resistor are connected in parallel between the non-inverting input terminal A1 and the inverting input terminal A2 of the differential amplifier circuit. At the same time, the first end of the sampling resistor is used to input the sampling current, and the second end is grounded; the output terminal of the differential amplifier circuit is connected to the positive input terminal X1 of the differential analog-to-digital converter; the non-inverting bias input terminal C1 of the differential amplifier circuit and the negative input terminal X2 of the differential analog-to-digital converter are respectively connected to an external reference source with the same output voltage.

[0007] Preferably, the differential amplifier circuit includes an operational amplifier, resistor R1, resistor R2, resistor R3, and resistor R4. Among them, resistor R1 is connected between the inverting input terminal A2 of the differential amplifier circuit and the inverting input terminal B2 of the operational amplifier; resistor R3 is connected between the non-inverting input terminal A1 of the differential amplifier circuit and the non-inverting input terminal B1 of the operational amplifier; resistor R4 is connected between the non-inverting bias input terminal C1 of the differential amplifier circuit and the non-inverting input terminal B1 of the operational amplifier; resistor R2 is connected between the inverting input terminal B2 of the operational amplifier and the output terminal of the operational amplifier; the output terminal of the operational amplifier serves as the output terminal of the differential amplifier circuit.

[0008] Preferably, the resistance value of resistor R1 is the same as that of resistor R3, and the resistance value of resistor R2 is the same as that of resistor R4.

[0009] Preferably, the resistance values of resistor R2 and resistor R1 are in proportion, and the resistance values of resistor R3 and resistor R4 are in proportion.

[0010] Preferably, the external reference source is a single-chip microcomputer, and the single-chip microcomputer is used to respectively output the same bias voltage to the non-inverting bias input terminal C1 of the differential amplifier circuit and the negative input terminal X2 of the differential analog-to-digital converter.

[0011] Preferably, the first end of the sampling resistor is connected to the output terminal of the Hall current sensor, and the Hall current sensor is used to output the sampling current to the sampling resistor.

[0012] The technical effects of the present invention are as follows:

[0013] 1. Through this technical solution, the sampling current of the Hall current sensor can be accurately converted, so that the digital control system can accurately obtain the actual total current of the current system;

[0014] 2. This technical solution realizes the positive and negative bidirectional current detection through a detection circuit under the condition of no negative power supply.

[0015] 3. The current detection accuracy of this technical solution does not depend on the accuracy and temperature stability of an external reference source;

[0016] 4. This technical solution can achieve low cost on the premise of meeting performance requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural diagram of a high-precision current detection circuit according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] The following will further describe in detail the specific embodiments of the present invention by describing the embodiments with reference to the drawings, aiming to help those skilled in the art have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention, and contribute to its implementation. It should be noted that the terms "first", "second", etc. used in this application are only for conveniently describing the technical solution to distinguish different components or terminals, and do not limit this application. To make the technical solution of the present invention clearer, the present invention will be explained and illustrated through the following embodiments.

[0019] A high-precision current detection circuit, as Figure 1 shown, the circuit includes a sampling resistor, a differential amplifier circuit, and a differential analog-to-digital converter (ADC). Among them, both ends of the sampling resistor are connected in parallel between the non-inverting input terminal A1 and the inverting input terminal A2 of the differential amplifier circuit. At the same time, the first end of the sampling resistor is used to input the sampling current, and the second end is grounded; the output terminal of the differential amplifier circuit is connected to the positive input terminal X1 of the differential analog-to-digital converter; the non-inverting bias input terminal C1 of the differential amplifier circuit and the negative input terminal X2 of the differential analog-to-digital converter are respectively connected to an external reference source with the same output voltage.

[0020] This application can be applied to various current detection fields. For example, for the detection of the bus current of an industrial energy storage BMS, a Hall current sensor can be connected to the industrial energy storage BMS bus. Then, the first end of the sampling resistor is connected to the output terminal of the Hall current sensor, and the Hall current sensor is used to output the sampling current to the sampling resistor. In actual implementation, other current sensors can also be used, and specific selection can be made flexibly according to the actual situation on site. After one end of the sampling resistor is connected to the sampling current output by the Hall current sensor, since its second end is grounded, a sampling voltage Vin is generated on the sampling resistor. This sampling voltage Vin is then amplified and biased by the subsequent differential amplifier circuit, and finally the amplified voltage signal is input to the differential analog-to-digital converter for conversion and then output to the digital control system, so as to achieve high-precision current detection. At the same time, the present invention does not limit the direction of the sampling current flowing into the sampling resistor, that is, this application realizes bidirectional current detection in both positive and negative directions under the condition of no negative power supply.

[0021] Specifically, the differential amplifier circuit includes an operational amplifier (AMP), a resistor R1, a resistor R2, a resistor R3, and a resistor R4, wherein the resistor R1 is connected between the inverting input terminal A2 of the differential amplifier circuit and the inverting input terminal B2 of the operational amplifier; the resistor R3 is connected between the non-inverting input terminal A1 of the differential amplifier circuit and the non-inverting input terminal B1 of the operational amplifier; the resistor R4 is connected between the non-inverting bias input terminal C1 of the differential amplifier circuit and the non-inverting input terminal B1 of the operational amplifier; the resistor R2 is connected between the inverting input terminal B2 of the operational amplifier and the output terminal of the operational amplifier; the output terminal of the operational amplifier serves as the output terminal of the differential amplifier circuit. In an optional embodiment of the present application, the model of the operational amplifier is LM324A.

[0022] In order to improve the detection accuracy, the present application utilizes the in-phase bias technology of the differential amplifier circuit. The bias voltage Vbias of the in-phase bias terminal C1 adopts an external reference source input. At the same time, the analog-to-digital converter of the differential amplifier circuit adopts a differential analog-to-digital converter. The negative input terminal X2 of the differential analog-to-digital converter is connected to the same external reference source as the in-phase bias terminal C1 of the differential amplifier circuit, so that the input levels of the in-phase bias terminal C1 of the differential amplifier circuit and the negative input terminal X2 of the differential analog-to-digital converter are unified, both of which are external reference sources. Therefore, when performing voltage amplification and sampling calculations, the external reference source can be cleverly offset, that is, the accuracy and temperature stability of the external reference source will not have a direct impact on the sampling results, thereby improving the sampling accuracy of the differential amplifier circuit.

[0023] In an optional embodiment of the present application, the external discrete circuit and operational amplifier in the above differential amplifier circuit can be replaced by an integrated differential amplifier to further improve the overall performance of the circuit. However, in order to reduce the device cost while meeting the performance requirements, the present application does not use an integrated differential amplifier. After actual testing and verification, it can also meet the measurement accuracy requirement of 0.2%.

[0024] In an optional embodiment of the present application, the external reference source can be made into a programmable form, so as to achieve compatibility of the subsequent circuit in different usage scenarios even if the sampling voltage Vin is different (the Hall current sensor has a different current measurement range). For example, the external reference source can be a single-chip microcomputer, which is used to output the same bias voltage Vbias to the in-phase bias input terminal C1 of the differential amplifier circuit and the negative input terminal X2 of the differential analog-to-digital converter, respectively, and the magnitude of the bias voltage Vbias can be controlled by the single-chip microcomputer programming.

[0025] To achieve high measurement accuracy, it is necessary to minimize error sources as much as possible, such as offset and gain errors, as well as noise, tolerance, and drift. These metrics are all crucial. For this purpose, in addition to selecting a high-precision operational amplifier, the selection of external components of the amplifier circuit is equally important. Especially for resistors, they should have matching ratios and cannot be selected arbitrarily; any deviation in these ratios will result in poor common-mode errors.

[0026] For common-mode errors, the common-mode rejection ratio (CMRR) of the differential amplifier circuit can be used for suppression. The resistance values of traditional resistors in actual use are not constant, and they are affected by mechanical loads and temperature. According to different requirements, resistors with different tolerances or matching resistor networks can be selected. Most of them are manufactured using thin-film technology and have ratio stability. Using these matching resistor networks can greatly improve the overall CMRR of the amplifier circuit. In addition, generally when the differential amplifier circuit is in use, the resistance value of resistor R1 is the same as that of resistor R3, and the resistance value of resistor R2 is the same as that of resistor R4, so as to ensure common-mode rejection. At this time, the output U of the differential amplifier circuit is: U = Vin * R2 / R1 + Vbias. Then, because the negative input terminal of the differential analog-to-digital converter is also the same bias voltage Vbias, the output of the differential analog-to-digital converter: U1 = X1 - X2 = U - Vbias = Vin * R2 / R1. Thus, in theoretical calculations, the external bias voltage Vbias can be eliminated, and the magnitude of the high-precision sampling current can be calculated.

[0027] Furthermore, in an alternative embodiment of the present application, the resistance values of resistor R2 and resistor R1 are in proportion, the resistance values of resistor R3 and resistor R4 are in proportion, and the proportionality size can be adjusted according to the current magnitude in different application scenarios, so as to achieve different proportional amplifications of the sampling voltage. For example, when the ratio of R2 to R1 is 1, the sampling result of the differential analog-to-digital converter is the product of the sampling current and the sampling resistor R5, that is, the sampling voltage Vin, and thus the magnitude of the sampling current can be calculated.

[0028] The above has made an exemplary description of the present utility model in conjunction with the accompanying drawings. Obviously, the specific implementation of the present utility model is not limited by the above methods. As long as various non-substantive improvements are made by adopting the method concept and technical solution of the present utility model; or without improvement, the above concept and technical solution of the present utility model are directly applied to other occasions, they are all within the protection scope of the present utility model.

Claims

1. A high-precision current detection circuit, characterized in that: The circuit includes a sampling resistor, a differential amplifier circuit, and a differential analog-to-digital converter. Among them, both ends of the sampling resistor are connected in parallel between the non-inverting input terminal (A1) and the inverting input terminal (A2) of the differential amplifier circuit. At the same time, the first end of the sampling resistor is used to input a sampling current, and the second end is grounded; the output terminal of the differential amplifier circuit is connected to the positive input terminal (X1) of the differential analog-to-digital converter; the non-inverting bias input terminal (C1) of the differential amplifier circuit and the negative input terminal (X2) of the differential analog-to-digital converter are respectively connected to an external reference source with the same output voltage.

2. The high-precision current detection circuit according to claim 1, wherein: The differential amplifier circuit includes an operational amplifier, resistor (R1), resistor (R2), resistor (R3), and resistor (R4). Among them, resistor (R1) is connected between the inverting input terminal (A2) of the differential amplifier circuit and the inverting input terminal (B2) of the operational amplifier; resistor (R3) is connected between the non-inverting input terminal (A1) of the differential amplifier circuit and the non-inverting input terminal (B1) of the operational amplifier; resistor (R4) is connected between the non-inverting bias input terminal (C1) of the differential amplifier circuit and the non-inverting input terminal (B1) of the operational amplifier; resistor (R2) is connected between the inverting input terminal (B2) of the operational amplifier and the output terminal of the operational amplifier; the output terminal of the operational amplifier serves as the output terminal of the differential amplifier circuit.

3. The high-precision current detection circuit according to claim 2, wherein: The resistance value of resistor (R1) is the same as that of resistor (R3), and the resistance value of resistor (R2) is the same as that of resistor (R4).

4. The high-precision current detection circuit according to claim 3, wherein: The resistance values of resistor (R2) and resistor (R1) are in proportion, and the resistance values of resistor (R3) and resistor (R4) are in proportion.

5. The high-precision current detection circuit according to claim 1, wherein: The external reference source is a single-chip microcomputer, and the single-chip microcomputer is used to respectively output the same bias voltage to the non-inverting bias input terminal (C1) of the differential amplifier circuit and the negative input terminal (X2) of the differential analog-to-digital converter.

6. A high-precision current detection circuit according to any one of claims 1-5, characterized in that: The first end of the sampling resistor is connected to the output terminal of the Hall current sensor, and the Hall current sensor is used to output a sampling current to the sampling resistor.

Images