Isolation detection circuit

Abstract

The utility model discloses an isolation detection circuit, including difference circuit and bias circuit, the first input of difference circuit is connected with the first end of the equipment of waiting for detecting, and the second input of difference circuit is connected with the second end of the equipment of waiting for detecting, and the output of difference circuit is as voltage detection end, the first input of difference circuit is connected with the first end of bias circuit, and the second input of difference circuit is connected with the second end of bias circuit. In the signal of being detected and the detection output signal not common, need to do to the safety regulation isolation detection, and the voltage of the both ends of the equipment of waiting for detecting is detected through difference circuit, and the bias circuit is set up simultaneously and generates two -way bias current and is added to the two input of difference circuit respectively, and the current of difference circuit input end is increased, and the drive current in the specification range of the operational amplifier internal triode of difference circuit is ensured, and the isolation high accuracy detection is realized.

Description

Technical Field

[0001] This utility model relates to the field of voltage detection technology, and in particular to isolation detection circuits. Background Technology

[0002] In electronic devices, differential circuits are commonly used to detect battery voltage. However, to meet safety isolation requirements, the resistance at the input of the differential circuit is relatively large. Therefore, if the battery voltage is low, the input of the differential circuit will receive a weak current signal, affecting the accuracy of the battery voltage detection. Utility Model Content

[0003] This invention provides an isolation detection circuit to solve the problem of poor accuracy when detecting voltage.

[0004] According to one aspect of the present invention, an isolation detection circuit is provided, including a differential circuit and a bias circuit;

[0005] The first input terminal of the differential circuit is connected to the first terminal of the device under test, the second input terminal of the differential circuit is connected to the second terminal of the device under test, and the output terminal of the differential circuit serves as a voltage detection terminal.

[0006] The first terminal of the bias circuit is connected to the first input terminal of the differential circuit, and the second terminal of the bias circuit is connected to the second input terminal of the differential circuit.

[0007] The voltage detection terminal and the device under test are not grounded together.

[0008] Optionally, the differential circuit includes a first input branch, a second input branch, and an amplifier;

[0009] The first end of the first input branch is connected to the first end of the device under test, and the second end of the first input branch is connected to the first input end of the amplifier.

[0010] The first end of the second input branch is connected to the second end of the device under test, the second end of the second input branch is connected to the second input end of the amplifier, and the output end of the amplifier serves as the voltage detection end.

[0011] The first terminal of the bias circuit is connected to the third terminal of the first input branch, and the second terminal of the bias circuit is connected to the third terminal of the second input branch.

[0012] Optionally, the first input branch includes a third resistor and a fourth resistor, and the second input branch includes a fifth resistor and a sixth resistor;

[0013] The first end of the third resistor is connected to the first end of the device under test, the second end of the third resistor is connected to the first end of the fourth resistor, the second end of the fourth resistor is connected to the first input end of the amplifier, and the second end of the third resistor is also connected to the first end of the bias circuit.

[0014] The first end of the fifth resistor is connected to the second end of the device under test, the second end of the fifth resistor is connected to the first end of the sixth resistor, the second end of the sixth resistor is connected to the second input end of the amplifier, and the second end of the fifth resistor is also connected to the second end of the bias circuit.

[0015] Optionally, the resistance value of the third resistor is equal to the resistance value of the fifth resistor, and the resistance value of the fourth resistor is equal to the resistance value of the sixth resistor.

[0016] Optionally, the differential circuit further includes a first capacitor, with a first terminal connected to the output terminal of the amplifier and a second terminal connected to ground.

[0017] Optionally, the bias circuit includes a seventh resistor, an eighth resistor, and a voltage source;

[0018] The first end of the seventh resistor is connected to the first terminal of the voltage source, the second end of the seventh resistor is connected to the third end of the first input branch, the first end of the eighth resistor is connected to the first terminal of the voltage source, the second end of the eighth resistor is connected to the third end of the second input branch, and the second terminal of the voltage source is connected to the ground terminal.

[0019] Optionally, the resistance value of the seventh resistor is equal to the resistance value of the eighth resistor.

[0020] Optionally, the power supply voltage of the voltage source is the same as the power supply voltage of the amplifier.

[0021] Optionally, the resistance value of the seventh resistor is less than the resistance value of the third resistor, and the resistance value of the eighth resistor is less than the resistance value of the fifth resistor.

[0022] Optionally, the resistance values ​​of the third resistor and the fifth resistor are both in the range of 1M ohms to 10M ohms;

[0023] The resistance values ​​of the seventh resistor and the eighth resistor are both between 10K ohms and 100K ohms.

[0024] The technical solution of this utility model embodiment requires safety-compliant isolation detection when the detected signal and the detection output signal are not grounded, that is, when the detected signal and the voltage detection terminal are not grounded. The voltage of the detected signal is detected by a differential circuit, and at the same time, a bias circuit is set to generate two bias currents that are superimposed on the two input terminals of the differential circuit, increasing the current at the input terminal of the differential circuit. This ensures that the transistor inside the operational amplifier of the differential circuit receives the drive current within the specified range, thereby avoiding the inaccurate detection due to the small signal current at the input terminal of the differential circuit, and achieving isolated high-precision detection.

[0025] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this utility model, nor is it intended to limit the scope of this utility model. Other features of this utility model will become readily apparent from the following description. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A schematic diagram of an isolation detection circuit provided in an embodiment of this utility model;

[0028] Figure 2 This is a schematic diagram of another isolation detection circuit provided in an embodiment of the present invention. Detailed Implementation

[0029] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention 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 invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0030] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this utility model are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the utility model described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0031] Figure 1 This is a schematic diagram of an isolation detection circuit provided in an embodiment of the present invention, with reference to... Figure 1 The isolation detection circuit includes: a differential circuit 10 and a bias circuit 11;

[0032] The first input terminal of the differential circuit 10 is connected to the first terminal BAT+ of the device under test, the second input terminal of the differential circuit 10 is connected to the second terminal BAT- of the device under test, and the output terminal of the differential circuit 10 serves as the voltage detection terminal Ubat.

[0033] The first terminal of the bias circuit 11 is connected to the first input terminal of the differential circuit 10, and the second terminal of the bias circuit 11 is connected to the second input terminal of the differential circuit 10.

[0034] Among them, the voltage detection terminal Ubat is not grounded with the device under test.

[0035] Optionally, the device under test can be a battery. In this embodiment and the following embodiments, the device under test is a battery. When the detected signal and the detection terminal are not "grounded", there is usually an extremely high voltage difference between them. If safety isolation is not performed, once the detected signal is connected to the detection terminal, the huge voltage difference will generate an extremely high current that will destroy the device. Therefore, for the case where the detected signal and the detection terminal are not "grounded", a very high insulation impedance needs to be set between the detected signal and the detection terminal to achieve safety isolation detection. To meet the safety isolation standard, the network between the two ends of the battery and the detection terminal needs to have sufficient creepage distance and a sufficiently small current. Therefore, the resistance value of the resistor on the input side of the differential circuit 10 needs to be very large, reaching the megaohm level. Since the battery voltage is relatively low, after adding a large resistor for isolation, the drive current is too low, resulting in a large accuracy deviation.

[0036] To address the aforementioned issues, a bias circuit 11 is configured to output a bias current to the input of the differential circuit 10, ensuring that the input of the differential circuit 10 can obtain a drive current within the specified range. This ensures distortion-free detection of small signals, meeting safety isolation requirements while achieving high-precision detection.

[0037] The technical solution of this utility model embodiment detects the detected signal, such as the voltage across the battery terminals, using a differential circuit. Simultaneously, a bias circuit generates two bias currents that are superimposed on the two input terminals of the differential circuit, increasing the current at the input terminals of the differential circuit. This ensures that the transistors inside the operational amplifier of the differential circuit receive the drive current within the specified range. By adding a bias circuit after reducing the detected signal, it can ensure that the small signal is amplified and detected without distortion, achieving isolated high-precision detection and optimizing the problem of low accuracy.

[0038] Figure 2 This is a schematic diagram of another isolation detection circuit provided in this utility model embodiment, referred to... Figure 2 The differential circuit 10 includes a first input branch 101, a second input branch 102, an amplifier 103, a first resistor R1, and a second resistor R2.

[0039] The first end of the first input branch 101 is connected to the first end BAT+ of the device under test, and the second end of the first input branch 101 is connected to the first input end of the amplifier 103.

[0040] The first end of the second input branch 102 is connected to the second end BAT- of the device under test, the second end of the second input branch 102 is connected to the second input end of the amplifier 103, and the output end of the amplifier 103 serves as the voltage detection end Ubat.

[0041] The first end of the first resistor R1 is connected to the second input terminal of the amplifier 103, and the second end of the first resistor R1 is connected to the output terminal of the amplifier 103.

[0042] The first end of the second resistor R2 is connected to the first input terminal of the amplifier 103, and the second end of the second resistor R2 is connected to the ground terminal GND.

[0043] The first end of the bias circuit 11 is connected to the third end of the first input branch 101, and the second end of the bias circuit 11 is connected to the third end of the second input branch 102.

[0044] The differential circuit 10 is connected to the first terminal BAT+ of the device under test (DUT) via the first input branch 101 and to the second terminal BAT- via the second input branch 102. The amplifier 103 in the differential circuit 10 calculates the voltage difference between the first terminal BAT+ and the second terminal BAT- of the DUT, multiplies it by a fixed factor for amplification, and finally outputs the amplified signal. The output voltage is proportional to the voltage difference between the first terminal BAT+ and the second terminal BAT- of the DUT. Therefore, the voltage between the first terminal BAT+ and the second terminal BAT- of the DUT can be obtained from the voltage output by the differential circuit 10. The first input terminal of the amplifier 103 can be a non-inverting input terminal, and the second input terminal can be an inverting input terminal.

[0045] At least one resistor may be included between the first end of the first input branch 101 and the third end of the first input branch 101. When two or more resistors are included, the resistors are connected in series. At least one resistor may be included between the first end of the second input branch 102 and the third end of the second input branch 102. When two or more resistors are included, the resistors are connected in series.

[0046] Preferably, the number of resistors connected to the first and third terminals of the first input branch 101 is the same as the number of resistors connected to the first and third terminals of the second input branch 102. Setting the same number and value of resistors in both input branches of the differential circuit is to construct a symmetrical circuit structure. This symmetry enables efficient common-mode rejection, stable DC operating point, low temperature drift, and high circuit performance. Furthermore, different numbers of resistors would result in different creepage distances and safety clearances for the two branches when fabricating resistors on the printed circuit board (PCB), making it difficult to meet uniform standards when complying with safety regulations. Therefore, the number of resistors between the first and third terminals of each input branch is the same, and the number of resistors between the third and second terminals is also the same.

[0047] The first input branch 101 may include at least two resistors connected in series. The second input branch 102 includes the same number of resistors as the first input branch 101. Taking the first input branch 101 as an example, the first terminal of the first resistor in the first input branch 101 serves as the first terminal of the first input branch 101, and the second terminal of the first resistor is connected to other resistors. The second terminal of the last resistor in the first input branch 101 serves as the second terminal of the first input branch 101. The first terminal of the last resistor in the first input branch 101 is connected to the previous resistor. The common terminal of any two resistors in the first input branch 101 can serve as the third terminal of the first input branch 101. The second input branch 102 follows the same principle. The third terminal of the first input branch 101 is connected to the first terminal of the bias circuit 11, and the third terminal of the second input branch 102 is connected to the second terminal of the bias circuit 11. The first power supply terminal U+ of the amplifier 103 is connected to a first voltage, and the second power supply terminal U- is connected to a second voltage.

[0048] Continue to refer to Figure 2 Optionally, the first input branch 101 includes a third resistor R3 and a fourth resistor R4, and the second input branch 102 includes a fifth resistor R5 and a sixth resistor R6.

[0049] The first end of the third resistor R3 is connected to the first end BAT+ of the device under test as the first end of the first input branch 101. The second end of the third resistor R3 is connected to the first end of the fourth resistor R4. The second end of the fourth resistor R4 is connected to the first input end of the first input branch 102 as the second end of the amplifier 103. The second end of the third resistor R3 is also connected to the first end of the bias circuit 11 as the third end of the first input branch 101.

[0050] The first end of the fifth resistor R5 is connected to the second terminal BAT- of the device under test as the first end of the second input branch 102. The second end of the fifth resistor R5 is connected to the first end of the sixth resistor R6. The second end of the sixth resistor R6 is connected to the second input terminal of the amplifier 103 as the second end of the second input branch 102. The second end of the fifth resistor R5 is also connected to the second terminal of the bias circuit 11 as the third end of the second input branch 102.

[0051] In this embodiment, the current input to amplifier 103 is reduced to meet the safety isolation requirements by using the third resistor R3 and the fifth resistor R5. Simultaneously, the third resistor R3 and the fifth resistor R5 facilitate the subsequent construction of equations based on the voltage at the third terminal of the first input branch 101 and the third terminal of the second input branch 102, as shown in equations (1) and (2) below. The fourth resistor R4 and the sixth resistor R6 facilitate the subsequent construction of equations using the second and third terminals of the first input branch 101 and the second and third terminals of the second input branch 102, as shown in equations (5) and (6) below. These four equations facilitate the determination of the relationship between the voltage at the voltage detection terminal Ubat and the voltage at the first terminal BAT+ and the second terminal BAT- of the device under test, thereby enabling the determination of the voltage of the device under test based on the voltage detection terminal Ubat.

[0052] The resistance of the first resistor R1 is equal to the resistance of the second resistor R2, the resistance of the third resistor R3 is equal to the resistance of the fifth resistor R5, and the resistance of the fourth resistor R4 is equal to the resistance of the sixth resistor R6.

[0053] Continue to refer to Figure 2 The differential circuit 10 also includes a first capacitor C1. The first end of the first capacitor C1 is connected to the output terminal of the amplifier 103, and the second end of the first capacitor C1 is connected to the ground terminal GND. The first capacitor C1 is used to filter the voltage output from the output terminal of the amplifier 103.

[0054] Continue to refer to Figure 2 The bias circuit 11 includes a seventh resistor R7, an eighth resistor R8, and a voltage source 111.

[0055] The first terminal of the seventh resistor R7 is connected to the first terminal of the voltage source 111. The second terminal of the seventh resistor R7 is connected to the third terminal of the first input branch 101, specifically the second terminal of the third resistor R3. The first terminal of the eighth resistor R8 is connected to the first terminal of the voltage source 111. The second terminal of the eighth resistor R8 is connected to the third terminal of the second input branch 102, specifically the second terminal of the fifth resistor R5. The second terminal of the voltage source 111 is connected to the ground terminal GND.

[0056] The resistance of the seventh resistor R7 is equal to the resistance of the eighth resistor R8.

[0057] The supply voltage of voltage source 111 is the same as the supply voltage of amplifier 103 to reduce circuit cost. The voltage supplied by voltage source 111 to the seventh resistor R7 and the eighth resistor R8 can be 5V or 3.3V. The resistance values ​​of the seventh resistor R7 and the eighth resistor R8 can be adjusted according to the voltage of the voltage source to output the voltage within the operating range of amplifier 103.

[0058] Too large or too small a bias current is unacceptable. Too large a bias current can easily lead to saturation distortion after the superimposed detection voltage signal, while too small a bias current will cause cutoff distortion, both affecting detection accuracy and batch consistency. When the voltage supplied by the voltage source is different, the magnitude of the bias current can be changed by adjusting the values ​​of the seventh resistor R7 and the eighth resistor R8 to ensure that the bias current meets the operational amplifier specifications.

[0059] Optionally, the resistance of the seventh resistor R7 is less than that of the third resistor R3, and the resistance of the eighth resistor R8 is less than that of the fifth resistor R5. The resistance values ​​of the third resistor R3 and the fifth resistor R5 are both between 1M ohms and 10M ohms; the resistance values ​​of the seventh resistor R7 and the eighth resistor R8 are both between 10K ohms and 100K ohms.

[0060] To meet safety isolation requirements, the current between the pre- and post-isolation stages must reach the μA level. This satisfies the safety isolation requirements of both industrial and medical standards. Therefore, the resistance values ​​of the third resistor R3 and the fifth resistor R5 need to be relatively large, such as reaching the megaohm level. Amplifier 103 includes transistors. To ensure the amplifier operates in the amplification region, the base current input to the transistors is typically in the mA level. Therefore, the resistance values ​​of the seventh resistor R7, the eighth resistor R8, the fourth resistor R4, and the sixth resistor R6 must be smaller than those of the third resistor R3 and the fifth resistor R5. This ensures that the current input to amplifier 103 allows it to operate in the amplification region. Furthermore, the resistance values ​​of the seventh resistor R7 and the eighth resistor R8 can be set to the kiloohm level, such as 10K ohms or 100K ohms.

[0061] According to Holkieff's current law, the following equation holds:

[0062] (1)

[0063] (2)

[0064] in, The voltage at the first terminal BAT+ of the device under test. The voltage at the second terminal BAT- of the device under test. The potential of the third terminal V10 of the first input branch 101 is... The potential of the third terminal V20 of the second input branch 102 is... The potential of the second terminal V30 of the first input branch 101 is... The potential of the second terminal V40 of the second input branch 102 is... Let R3 be the resistance value of the third resistor. This is the resistance value of the fourth resistor, R4. Let R5 be the resistance value of the fifth resistor. This is the resistance value of the sixth resistor, R6. Let R7 be the resistance value of the seventh resistor. This is the resistance value of the eighth resistor, R8.

[0065] because , , , Subtracting the two equations, we get:

[0066] (3)

[0067] (4)

[0068] Based on the potential of the second terminal of the first input branch 101 and the potential of the second terminal of the second input branch 102 Combining Kirchhoff's current law, we have the following equation:

[0069] (5)

[0070] (6)

[0071] in, Let R1 be the resistance value of the first resistor. Let R2 be the resistance value of the second resistor. This is the potential of the voltage detection terminal Ubat.

[0072] because , , Subtracting equation (5) from equation (6) yields:

[0073] (7)

[0074] Substituting equation (7) into equation (4), we get:

[0075] (8)

[0076] (9)

[0077] According to equation (9), the potential of the voltage detection terminal Ubat is... The voltage difference between the first terminal BAT+ and the second terminal BAT- of the device under test can be obtained. That is, the voltage of the battery is obtained.

[0078] Based on the virtual short and virtual open characteristics of the amplifier, it can be known that According to equations (1), (2), (5), and (6), there are a total of 6 unknowns in the four formulas, namely: , , , , , Since there are six unknowns in the four equations that cannot be solved individually, we can set special conditions: the resistance of the first resistor R1 is equal to that of the second resistor R2, the resistance of the third resistor R3 is equal to that of the fifth resistor R5, the resistance of the fourth resistor R4 is equal to that of the sixth resistor R6, and the resistance of the seventh resistor R7 is equal to that of the eighth resistor R8. This allows us to extract the potential of the voltage detection terminal Ubat using the four formulas. The voltage difference between the first terminal BAT+ and the second terminal BAT- of the device under test ( The relationship between the voltages of the two terminals is then determined based on the potential of the voltage detection terminal Ubat. Obtain the voltage of the device under test.

[0079] In this embodiment, by setting the seventh resistor R7, the eighth resistor R8 and the voltage source 111, the current in the input amplifier 103 is increased, thereby making the small noise negligible, improving the detection accuracy of the battery, controlling the detection voltage deviation within 0.5%, and the circuit structure is simple and low cost.

[0080] According to another aspect of the present invention, an isolation detection system is also provided, including a device to be tested and an isolation detection circuit as described in any of the above embodiments. The beneficial effects of the isolation detection system are the same as those of the isolation detection circuit, and will not be repeated here.

[0081] It should be understood that the various forms of the process shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this utility model can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this utility model can be achieved, and this is not limited herein.

[0082] The specific embodiments described above do not constitute a limitation on the scope of protection of this utility model. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this utility model should be included within the scope of protection of this utility model.

Claims

1. An isolation detection circuit, characterized in that, Includes differential circuits and bias circuits; The first input terminal of the differential circuit is connected to the first terminal of the device under test, the second input terminal of the differential circuit is connected to the second terminal of the device under test, and the output terminal of the differential circuit serves as a voltage detection terminal. The first terminal of the bias circuit is connected to the first input terminal of the differential circuit, and the second terminal of the bias circuit is connected to the second input terminal of the differential circuit. The voltage detection terminal and the device under test are not grounded together.

2. The isolation detection circuit according to claim 1, characterized in that, The differential circuit includes a first input branch, a second input branch, and an amplifier; The first end of the first input branch is connected to the first end of the device under test, and the second end of the first input branch is connected to the first input end of the amplifier. The first end of the second input branch is connected to the second end of the device under test, the second end of the second input branch is connected to the second input end of the amplifier, and the output end of the amplifier serves as the voltage detection end. The first terminal of the bias circuit is connected to the third terminal of the first input branch, and the second terminal of the bias circuit is connected to the third terminal of the second input branch.

3. The isolation detection circuit according to claim 2, characterized in that, The first input branch includes a third resistor and a fourth resistor, and the second input branch includes a fifth resistor and a sixth resistor; The first end of the third resistor is connected to the first end of the device under test, the second end of the third resistor is connected to the first end of the fourth resistor, the second end of the fourth resistor is connected to the first input end of the amplifier, and the second end of the third resistor is also connected to the first end of the bias circuit. The first end of the fifth resistor is connected to the second end of the device under test, the second end of the fifth resistor is connected to the first end of the sixth resistor, the second end of the sixth resistor is connected to the second input end of the amplifier, and the second end of the fifth resistor is also connected to the second end of the bias circuit.

4. The isolation detection circuit according to claim 3, characterized in that, The resistance value of the third resistor is equal to the resistance value of the fifth resistor, and the resistance value of the fourth resistor is equal to the resistance value of the sixth resistor.

5. The isolation detection circuit according to claim 2, characterized in that, The differential circuit further includes a first capacitor, the first end of which is connected to the output terminal of the amplifier, and the second end of which is connected to the ground terminal.

6. The isolation detection circuit according to claim 3, characterized in that, The bias circuit includes a seventh resistor, an eighth resistor, and a voltage source; The first end of the seventh resistor is connected to the first terminal of the voltage source, the second end of the seventh resistor is connected to the third end of the first input branch, the first end of the eighth resistor is connected to the first terminal of the voltage source, the second end of the eighth resistor is connected to the third end of the second input branch, and the second terminal of the voltage source is connected to the ground terminal.

7. The isolation detection circuit according to claim 6, characterized in that, The resistance value of the seventh resistor is equal to the resistance value of the eighth resistor.

8. The isolation detection circuit according to claim 6, characterized in that, The power supply voltage of the voltage source is the same as the power supply voltage of the amplifier.

9. The isolation detection circuit according to claim 6, characterized in that, The resistance value of the seventh resistor is less than that of the third resistor, and the resistance value of the eighth resistor is less than that of the fifth resistor.

10. The isolation detection circuit according to claim 6, characterized in that, The resistance values ​​of the third resistor and the fifth resistor are both between 1 MΩ and 10 MΩ. The resistance values ​​of the seventh resistor and the eighth resistor are both between 10K ohms and 100K ohms.

Images