current sensor

Abstract

A current sensor for detecting a target current using a shunt resistor (4) includes a resistance correction circuit (17, 63) and a power supply circuit (10). The resistance correction circuit (17, 63) includes: a correction resistor (5); a signal application unit (6, 62) for applying an AC signal to a series circuit of the shunt resistor and the correction resistor; a voltage detection unit (20) for detecting the terminal voltages of the shunt resistor and the correction resistor; and a correction unit (16) for calculating the resistance value of the shunt resistor and correcting the detection resistance value. The power supply circuit (10) includes: a first power generation unit (18) for generating a first power supply for the signal application unit from an externally supplied input power supply; and a second power generation unit (19) for generating a second power supply for the voltage detection unit.

Description

Technical Field

[0001] This disclosure relates to a current sensor that detects a target current by using the terminal voltage of a shunt resistor connected in series in the path through which the target current flows and a current detection resistance value corresponding to the resistance value of the shunt resistor. Background Technology

[0002] As disclosed in Patent Documents 1 and 2, in a conceivable current sensor, the terminal voltage of a shunt resistor connected in series with the path through which the target current flows is measured, and the current to be detected is calculated based on the measured voltage and the resistance value for current detection corresponding to the resistance value of the shunt resistor. In this case, since the resistance value of the shunt resistor may change due to deterioration over time, it may be necessary to constantly calibrate the resistance value for current detection used to calculate the current. In the following description, the conceivable current sensor disclosed in Patent Document 1 will be referred to as the first conceivable technology, and the conceivable current sensor disclosed in Patent Document 2 will be referred to as the second conceivable technology.

[0003] In a first contemplated technique, the resistance value for current detection is calibrated as follows: The first contemplated technique provides: a sub-resistor configured such that the target current flows through it, similar to a shunt resistor in its normal state; and a calibration resistor configured such that the target current does not flow through it during normal operation. According to this configuration, similar to the shunt resistor, the sub-resistor deteriorates over time, but the calibration resistor deteriorates almost entirely. In the first contemplated technique, the degree of deterioration of the sub-resistor and the shunt resistor is obtained by comparing their resistance values ​​during calibration, and the resistance value for current detection is calibrated based on this degree of deterioration.

[0004] In a second conceivable technique, the correction current detection resistor value is adjusted as follows. Specifically, the second conceivable technique has the following configuration: multiple shunt resistors are provided, and the correction current passes through the interconnection nodes of the multiple shunt resistors; or an input terminal is located in the central portion of the shunt resistors, and the correction current passes through the input terminal. In the second conceivable technique, the terminal voltage of each resistor is measured when the correction current passes through, and the individual resistance value is calculated based on the measurement results to correct the current detection resistor value.

[0005] Existing technical documents

[0006] [Patent Literature]

[0007] Patent Document 1: US Patent No. 8,779,777

[0008] Patent Document 2: US Patent No. 10,473,724 Summary of the Invention

[0009] In the first conceivable technique, the shunt resistor is not used for direct calibration, and it is assumed that the sub-resistor deteriorates in the same way as the shunt resistor. The sub-resistor is then used to indirectly calibrate the current-sensing resistor value corresponding to the shunt resistor value. Therefore, in the first conceivable technique, if the above assumptions are not met, the current-sensing resistor value cannot be calibrated with high accuracy, and as a result, the current-sensing accuracy may be reduced.

[0010] In the second contemplated technique, the configuration becomes complex due to the need to set multiple shunt resistors or to place the input terminal in the central part of the shunt resistors. Furthermore, in the second contemplated technique, it is difficult to sufficiently improve the calibration accuracy, since the accuracy of the calibration of the current sensing resistor value largely depends on the accuracy of the calibration current. Moreover, in both the first and second contemplated techniques, to improve the calibration accuracy of the sensing resistor value, it is necessary to increase the current flowing during calibration; however, when the current flowing during calibration increases, difficulties such as increased heat generation and increased power consumption may occur.

[0011] This disclosure is made in view of the above circumstances, and the purpose of this disclosure is to provide a current sensor that can accurately correct the resistance value for detection and suppress power consumption without making the configuration complex.

[0012] The current sensor detects the target current using the terminal voltage of a shunt resistor connected in series in the path through which the target current flows, and the current-detecting resistance value corresponding to the resistance value of the shunt resistor. The current sensor includes a resistance value correction circuit for correcting the detection resistance value and a power supply circuit for supplying power to the resistance value correction circuit. The resistance value correction circuit includes a correction resistor, a signal application unit, a voltage detection unit, and a correction unit. The correction resistor is connected in series with the shunt resistor in a path different from the path through which the target current flows. The signal application unit applies an AC signal to the series circuit of the shunt resistor and the correction resistor. The voltage detection unit detects the terminal voltage of the shunt resistor and the correction resistor when the AC signal is applied to the series circuit. The correction unit calculates the resistance value of the shunt resistor based on each detected terminal voltage value detected by the voltage detection unit, and corrects the detection resistance value based on the calculated resistance value for the shunt resistor.

[0013] With this resistor value correction circuit configuration, the detection resistance value can be directly corrected using a shunt resistor, unlike the first contemplated technique which indirectly corrects the detection resistance value using a sub-resistor. As a result, the accuracy of the detection resistance value correction is improved. Furthermore, unlike the second contemplated technique, this configuration eliminates the need for multiple shunt resistors and a central input terminal; only a single shunt resistor is required, thus simplifying the overall current sensor configuration.

[0014] In the resistor value correction circuit with the above configuration, the higher the level of the AC signal applied to the series circuit of the shunt resistor and the correction resistor, the higher the detection accuracy of the voltage at each terminal detected by the voltage detection unit, and ultimately improves the correction accuracy of the detection resistor value. In this case, the power supply circuit is configured to include: a first power supply generation unit that generates a first power supply with a low voltage relative to the input power supply by stepping down the input power supply provided from the outside; and a second power supply generation unit for generating a second power supply different from the first power supply, such that the power supply circuit provides the first power supply to the signal application unit and provides the second power supply to the voltage detection unit.

[0015] As described above, in this configuration, since the signal application unit operates by receiving power from a first power supply generated by stepping down the input power supply, it is possible to increase the output current while simultaneously reducing the power supply voltage. That is, it is possible to increase the level of the AC signal applied to the series circuit of the shunt resistor and the correction resistor. Therefore, according to this configuration, it is possible to achieve excellent results by enabling high-precision correction of the detection resistor value and suppressing power consumption to a low level without complicating the overall configuration of the current sensor. Attached Figure Description

[0016] The above and other objects, features, and advantages of this disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. In the drawings:

[0017] Figure 1 This is a schematic diagram illustrating the configuration of the current sensor according to the first embodiment;

[0018] Figure 2 This is an illustration used to explain a first power supply method for supplying input power to a power supply circuit according to a first embodiment;

[0019] Figure 3 This is an illustration used to explain a second power supply method for supplying input power to a power supply circuit according to the first embodiment;

[0020] Figure 4 This is an illustration showing a specific first configuration example of the signal application unit according to the first embodiment;

[0021] Figure 5 This is an illustration showing a specific second configuration example of the signal application unit according to the first embodiment;

[0022] Figure 6 This is an illustration showing a specific third configuration example of the signal application unit according to the first embodiment;

[0023] Figure 7 This is an illustration showing a specific fourth configuration example of the signal application unit according to the first embodiment;

[0024] Figure 8 This is a specific configuration example of each synchronization detection circuit according to the first embodiment;

[0025] Figure 9 This is a diagram illustrating a specific first configuration example of the power supply circuit according to the first embodiment;

[0026] Figure 10 This is a diagram illustrating a specific second configuration example of the power supply circuit according to the first embodiment;

[0027] Figure 11 This is a diagram illustrating a specific third configuration example of the power supply circuit according to the first embodiment;

[0028] Figure 12 This is a schematic diagram illustrating the configuration of a current sensor according to the second embodiment;

[0029] Figure 13 This is an illustration showing a specific first configuration example of the signal application unit according to the second embodiment; and

[0030] Figure 14 This is an illustration showing a specific second configuration example of the signal application unit according to the second embodiment. Detailed Implementation

[0031] Hereinafter, several embodiments will be described with reference to the accompanying drawings. In each embodiment, substantially the same components will be labeled with the same reference numerals and their descriptions will be omitted.

[0032] (First Embodiment)

[0033] refer to Figures 1 to 11 A first embodiment of this disclosure is described.

[0034] (Overall Configuration)

[0035] Figure 1The current sensor 1 shown in this embodiment is installed on a vehicle, such as an automobile, and detects a target current as the current flowing through a measurement target 2. The measurement target 2 may be a battery such as a main engine battery that supplies power to a drive unit used to drive the vehicle, an auxiliary battery that supplies power to auxiliary equipment of the vehicle, a DC / DC converter, etc. The DC / DC converter supplies power to an electric motor that generates driving force for driving the vehicle, and together with the electric motor, constitutes the aforementioned drive unit.

[0036] In this configuration, load 3 is connected in series with the measurement target 2, and the loop circuit is configured with the measurement target 2, load 3, and a switch (not shown). When the measurement target 2 is the aforementioned battery, load 3 can be, for example, the aforementioned electric motor, the aforementioned DC / DC converter, or an electric compressor. Furthermore, when the measurement target 2 is the aforementioned DC / DC converter, load 3 can be, for example, the aforementioned electric motor.

[0037] The current sensor 1 includes a shunt resistor 4, a calibration resistor 5, a signal application unit 6, a first voltage detection unit 7, a second voltage detection unit 8, a control unit 9, and a power supply circuit 10. One terminal of the shunt resistor 4 is connected to the high-potential side terminal of the measurement target 2 via a load 3, and the other terminal is connected to ground (serving as a reference potential for the circuit) and the low-potential side terminal of the measurement target 2. That is, the shunt resistor 4 is connected in series with the path through which the target current flows. The current sensor 1 uses the terminal voltage of the shunt resistor 4, configured in this way, and the detection resistance value corresponding to the resistance value of the shunt resistor 4 to detect the target current.

[0038] One terminal of the calibration resistor 5 is connected to the signal application unit 6, and the other terminal is connected to the same terminal of the shunt resistor 4. That is, the calibration resistor 5 and the shunt resistor 4 are connected in series in a path different from the path through which the target current flows. In this case, since the target current is relatively large, the resistance value of the shunt resistor 4 is relatively small, for example, on the order of μΩ.

[0039] On the other hand, since the relatively large target current does not flow through the calibration resistor 5, its resistance value is relatively large, for example, on the order of mΩ. Typically, it may be difficult to accurately form a resistor with a small resistance value, but it may be relatively easy to accurately form a resistor with a large resistance value. Therefore, in this embodiment, the resistance accuracy of the calibration resistor 5 is sufficiently higher than that of the shunt resistor 4.

[0040] During the calibration time when calibrating the detection resistor value (described later), the signal application unit 6 applies a pulse wave or sinusoidal AC signal to the series circuit of the shunt resistor 4 and the calibration resistor 5. In other words, the signal application unit 6 applies the same AC signal to the shunt resistor 4 and the calibration resistor 5 during calibration. In this case, the signal application unit 6 is configured as a current source that operates by being powered by a first power supply P1, which has a power supply voltage VDD generated by the power supply circuit 10, for example, approximately +1V. The signal application unit 6 supplies alternating current from the power supply line L1, which is supplied with the first power supply P1, to the series circuit.

[0041] The first voltage detection unit 7 detects the terminal voltage of the shunt resistor 4 when an AC signal is applied to the series circuit of the shunt resistor 4 and the correction resistor 5, and includes a first A / D converter 11 and a first synchronous detection circuit 12. In situations such as... Figure 1 In the accompanying diagram, the A / D converter is abbreviated as ADC. To detect the terminal voltage of the shunt resistor 4, the first A / D converter 11 performs the following A / D conversion operation: The first A / D converter 11 inputs the signal from each terminal of the shunt resistor 4, and by performing A / D conversion on each signal, outputs the voltage difference between each terminal of the shunt resistor 4, i.e., the digital signal corresponding to the voltage between the terminals of the shunt resistor 4. Thus, the digital signal output from the first A / D converter 11 is the signal corresponding to the signal at the terminals of the shunt resistor 4.

[0042] The first synchronous detection circuit 12 takes into account the digital signal output from the first A / D converter 11, synchronously detects the signal at the same frequency as the AC signal in the signal application unit 6, and extracts the signal. Then, the first synchronous detection circuit 12 outputs the extracted signal to the control unit 9. The output signal of the first synchronous detection circuit 12 is a signal corresponding to the terminal voltage of the shunt resistor 4. Thus, during the calibration period, the first voltage detection unit 7 is configured to detect the terminal voltage of the shunt resistor 4 based on the output signal of the first synchronous detection circuit 12, and outputs a signal representing the detected value of the terminal voltage as a first voltage detection value to the control unit 9.

[0043] When no AC signal is applied to the series circuit of shunt resistor 4 and correction resistor 5, i.e., in the normal state, the first voltage detection unit 7 detects the terminal voltage of shunt resistor 4 as follows: That is, in the normal state, the first A / D converter 11 performs A / D conversion operation in the same manner as during correction. In this case, the digital signal output from the first A / D converter 11 is output to the control unit 9 and is not input to the first synchronous detection circuit 12. In other words, in the normal state, the first voltage detection unit 7 detects the terminal voltage of shunt resistor 4 based on the output signal of the first A / D converter 11 and outputs a signal representing the detected value of the terminal voltage as the first voltage detection value to the control unit 9.

[0044] The second voltage detection unit 8 detects the terminal voltage of the correction resistor 5 when an AC signal is applied to the series circuit of the shunt resistor 4 and the correction resistor 5, and includes a second A / D converter 13 and a second synchronous detection circuit 14. The second A / D converter 13 performs an A / D conversion operation to detect the terminal voltage of the correction resistor 5 as follows: The second A / D converter 13 inputs a signal to each terminal of the correction resistor 5, and by performing an A / D conversion on each signal, outputs the voltage difference between each terminal of the correction resistor 5, i.e., a digital signal corresponding to the voltage between the terminals of the correction resistor 5. Thus, the digital signal output from the second A / D converter 13 is a signal corresponding to the signal at the terminals of the correction resistor 5.

[0045] The second synchronous detection circuit 14 takes into account the digital signal output from the second A / D converter 13, detects the signal synchronously at the same frequency as the AC signal in the signal application unit 6, and extracts the signal. Then, the second synchronous detection circuit 14 outputs the extracted signal to the control unit 9. The output signal of the second synchronous detection circuit 14 is a signal corresponding to the terminal voltage of the correction resistor 5. Thus, during the correction period, the second voltage detection unit 8 is configured to detect the terminal voltage of the correction resistor 5 based on the output signal of the second synchronous detection circuit 14, and outputs a signal representing the detected value of the terminal voltage as a second voltage detection value to the control unit 9.

[0046] As described above, in this embodiment, the first voltage detection unit 7 and the second voltage detection unit 8 detect the terminal voltages of the shunt resistor 4 and the correction resistor 5 when an AC signal is applied to the series circuit of the shunt resistor 4 and the correction resistor 5, and function as voltage detection unit 20. In this case, the first A / D converter 11 and the first synchronous detection circuit 12 constituting the first voltage detection unit 7, and the second A / D converter 13 and the second synchronous detection circuit 14 constituting the second voltage detection unit 8 are adapted to operate by receiving power from the second power supply P2 generated by the power supply circuit 10.

[0047] The control unit 9, together with the voltage detection unit 20, is configured as a semiconductor integrated circuit such as an ASIC. ASIC is short for Application-Specific Integrated Circuit. The control unit 9 includes functional blocks such as the current detection unit 15 and the correction unit 16. Each of these functional blocks is implemented in hardware. The control unit 9 can be configured as a semiconductor integrated circuit separate from the voltage detection unit 20. For example, the control unit 9 can be configured as a microcomputer including a CPU, RAM, ROM, etc. In this case, each of the aforementioned functional blocks is implemented by the CPU of the control unit 9 executing a computer program stored in the ROM, etc., to provide processing corresponding to the computer program; that is, by software implementation. Alternatively, in this case, at least some of the functional blocks of the parking lot server device can be implemented in hardware.

[0048] The current detection unit 15 uses a signal corresponding to the terminal voltage of the shunt resistor 4 output from the first voltage detection unit 7 during normal operation and a detection resistance value corresponding to the resistance value of the shunt resistor 4 to detect the target current. The detection resistance value is set based on the initial resistance value of the shunt resistor 4 actually used and is pre-stored in a memory set in the control unit 9. Here, since the target current, which is a relatively large current, flows in the shunt resistor 4, the resistance value changes from the initial value due to deterioration over time, etc.

[0049] Therefore, the aforementioned detection resistance value is constantly corrected through the operation of the correction unit 16. During correction, the correction unit 16 calculates the resistance value of the shunt resistor 4 based on the corrected resistance value corresponding to the resistance value of the correction resistor 5, a signal representing the first voltage detection value output from the first voltage detection unit 7, and a signal representing the second voltage detection value output from the second voltage detection unit 8. The correction unit 16 corrects the detection resistance value based on the calculated resistance value, which is the calculated resistance value of the shunt resistor 4. For example, the correction unit 16 can correct the detection resistance value to match the calculated resistance value.

[0050] The aforementioned calibration resistor value is the initial resistance value of the calibration resistor 5 actually used, and it is pre-stored in the memory set in the control unit 9. Since the target current does not flow in the calibration resistor 5 under normal conditions, the resistance value hardly changes from its initial value due to aging or deterioration. As described above, in the above configuration, the resistance value calibration circuit 17 for calibrating the detection resistance value is configured with the calibration resistor 5, the signal application unit 6, the first voltage detection unit 7, the second voltage detection unit 8, and the calibration unit 16.

[0051] The power supply circuit 10 provides power to the resistance value correction circuit 17 and includes a first power generation unit 18 and a second power generation unit 19. The first power generation unit 18 generates a first power supply P1 with a low voltage relative to the externally supplied input power supply Pin by stepping down the input power supply Pin. The second power generation unit 19 uses the input power supply Pin to generate a second power supply P2 different from the first power supply P1. The power supply circuit 10 provides the first power supply P1 and the second power supply P2 to the resistance value correction circuit 17. Specifically, the power supply circuit 10 provides the first power supply P1 to the signal application unit 6 and the second power supply P2 to the first voltage detection unit 7 and the second voltage detection unit 8, which serve as the voltage detection unit 20.

[0052] In the above configuration, the power supply method for the input power pin of the power supply circuit 10 is specifically assumed to be one of the following two methods. In the following description, it is assumed that the measurement target 2 is the main battery B1, which is a high-voltage battery of approximately several hundred volts that provides power to the drive unit used to drive the vehicle. For example... Figure 2 As shown, in the first power supply method, the input power Pin is provided from the auxiliary battery B2, which is, for example, a low-voltage battery of about 12V that provides power to the vehicle's auxiliary equipment. Furthermore, as... Figure 3 As shown, in the second power supply method, the input power Pin is provided from the main battery B1.

[0053] <Specific configuration of the signal application unit>

[0054] The specific configuration of the signal application unit 6 includes, for example: Figure 4 The first configuration example shown Figure 5 The second configuration example shown Figure 6 The third configuration example shown Figure 7 The fourth configuration example shown, etc.

[0055] [1] First configuration example

[0056] like Figure 4 As shown, the signal application unit 6a in the first configuration example includes a transistor 21, a signal generation unit 22, an op-amp 23, etc. The transistor 21 is, for example, an N-channel MOSFET, whose drain is connected to the power supply line L1 via a correction resistor 5, and whose source is connected to ground via a shunt resistor 4. The signal generation unit 22 generates and outputs a pulse wave signal or a sine wave signal with the same frequency as the alternating current applied to the series circuit of the shunt resistor 4 and the correction resistor 5.

[0057] The output signal of signal generation unit 22 is provided to the non-inverting input terminal of OP amplifier 23. The inverting input terminal of OP amplifier 23 is connected to the drain of transistor 21, and its output terminal is connected to the gate of transistor 21. According to the above configuration, transistor 21 is driven by OP amplifier 23, such that an AC signal of alternating current is applied to the series circuit of shunt resistor 4 and correction resistor 5. As described above, the signal application unit 6a of the first configuration example is configured to be driven by an amplifier. In this case, correction resistor 5 also serves as a current source for signal application unit 6a.

[0058] [2] Second configuration example

[0059] like Figure 5 As shown, the signal application unit 6b in the second configuration example and Figure 4 The signal application unit 6a shown in the first configuration example differs from the one shown in that a resistor 24 is added. In this case, the drain of transistor 21 is connected to the power line L1 via resistor 24, and its source is connected to ground via correction resistor 5 and shunt resistor 4.

[0060] Even with the above configuration, as in the first configuration example, transistor 21 is driven by OP amplifier 23, such that an AC signal, which is alternating current, is applied to the series circuit of shunt resistor 4 and correction resistor. As described above, the signal application unit 6b in the second configuration example has an amplifier drive configuration similar to that of the signal application unit 6a in the first configuration example. In this case, resistor 24 and transistor 21, which are disposed separately from correction resistor 5, serve as the current source for signal application unit 6b.

[0061] [3] Third configuration example

[0062] like Figure 6 As shown, the signal application unit 6c in the third configuration example and Figure 4 The signal application unit 6a shown in the first configuration example differs from the one shown in that a buffer 25 is arranged instead of an op-amp 23. In this case, the output signal of the signal generation unit 22 is provided to the input terminal of the buffer 25. The output terminal of the buffer 25 is connected to the gate of the transistor 21. According to the above configuration, the transistor 21 is driven by the buffer 25, such that an AC signal, which is an alternating current, is applied to the series circuit of the shunt resistor 4 and the correction resistor 5. As described above, the signal application unit 6c in the third configuration example has a buffer-driven configuration.

[0063] [4] Fourth configuration example

[0064] like Figure 7 As shown, the signal application unit 6d in the fourth configuration example and Figure 5The signal application unit 6b shown in the second configuration example differs in that a buffer 25 is arranged instead of an op-amp 23. In this case, the output signal of the signal generation unit 22 is provided to the input terminal of the buffer 25. The output terminal of the buffer 25 is connected to the gate of the transistor 21. According to the above configuration, the transistor 21 is driven by the buffer 25, such that an AC signal, which is an alternating current, is applied to the series circuit of the shunt resistor 4 and the correction resistor 5. As described above, the signal application unit 6d in the fourth configuration example has a buffer-driven configuration.

[0065] [5] Features of each configuration example

[0066] In the first and third configuration examples, since the correction resistor 5 is arranged close to the power line L1 and the shunt resistor 4 is arranged close to ground, the first voltage detection unit 7 and the second voltage detection unit 8 detect voltages at significantly different potentials from each other. Therefore, according to the first and third configuration examples, although detection errors in the terminal voltages of the shunt resistor 4 and the correction resistor 5 are likely to occur compared to the second and fourth configuration examples, the correction resistor 5 provides a common current source for the application units 6a and 6c, which, as an advantage, allows the number of components to be kept to a small number.

[0067] In the second and fourth configuration examples, because a resistor 24 different from the correction resistor 5 is required to configure the current source of the signal application units 6b and 6d, the number of components increases compared to the first and third configuration examples. However, in the second and fourth configuration examples, since both the correction resistor 5 and the shunt resistor 4 are arranged near ground, the first voltage detection unit 7 and the second voltage detection unit 8 detect voltages at similar potentials to each other. Therefore, according to the second and fourth configuration examples, there is an advantage in being able to suppress the detection error of the terminal voltages of the shunt resistor 4 and the correction resistor 5 to a level smaller than that of the first and third configuration examples.

[0068] According to the first and second configuration examples of the amplifier drive configuration, the drain voltage of transistor 21 is controlled to be constant by the operation of OP amplifier 23. This gives the first and second configuration examples an advantage over the third and fourth configuration examples of the buffer drive configuration, allowing for improved accuracy of the AC current applied to the series circuit of shunt resistor 4 and correction resistor 5. On the other hand, compared to the first and second configuration examples, the third and fourth configuration examples, by using buffer 25 instead of OP amplifier 23, have the advantage of reducing the circuit size to a smaller dimension.

[0069] <Specific configuration of each synchronization detection circuit>

[0070] The specific configurations of the first synchronization detection circuit 12 and the second synchronization detection circuit 14 include, for example: Figure 8 The configuration shown is as follows. In this case, the alternating current signal, which is the AC current applied by the signal application unit 6 to the series circuit of the shunt resistor 4 and the correction resistor 5, is defined as "Io×cos(ωt)", and the resistance value of the shunt resistor 4 is defined as R2, and the resistance value of the correction resistor 5 is defined as R1. Here, ω is the angular frequency, and t is time.

[0071] like Figure 8 As shown, the first synchronization detection circuit 12 includes multipliers 31 and 32, low-pass filters 33 and 34, and an arithmetic unit 35. In this specification, the low-pass filter can be abbreviated as LPF. During the correction time when an AC signal is applied to the series circuit of the shunt resistor 4 and the correction resistor 5, a digital signal output from the first A / D converter 11 is input to each input terminal of the multipliers 31 and 32 of the first synchronization detection circuit 12. This digital signal is a signal corresponding to the terminal voltage of the shunt resistor 4 during correction, and is defined as...

[0072] The cosine wave signal “cos(ωt)” is input to another input terminal of multiplier 31. The sine wave signal “-sin(ωt)” is input to another input terminal of multiplier 32. As a result, in each output signal of multipliers 31 and 32, the signal with angular frequency ω is extracted as a DC component. The output signals of multipliers 31 and 32 are input to LPFs 33 and 34, respectively.

[0073] The output signal I2 of LPF 33 is a low-frequency signal proportional to the in-phase component of the input signal, and the output signal Q2 of LPF 34 is a low-frequency signal proportional to the quadrature-phase component of the input signal. Arithmetic unit 35 calculates the square root of the sum of the squares of signals I2 and Q2, and outputs a signal representing the calculation result. The output signal of arithmetic unit 35 is expressed as "R2 × Io". The output signal of arithmetic unit 35 becomes the output signal of the first synchronization detection circuit 12 and is provided to the correction unit 16 of control unit 9.

[0074] The second synchronous detection circuit 14 includes multipliers 36 and 37, low-pass filters 38 and 39, and an arithmetic unit 40. During the correction time when an AC signal is applied to the series circuit of the shunt resistor 4 and the correction resistor 5, a digital signal output from the second A / D converter 13 is input to each input terminal of multipliers 36 and 37 of the second synchronous detection circuit 14. This digital signal is a signal corresponding to the terminal voltage of the correction resistor 5 during correction, and is defined as follows:

[0075] The cosine wave signal “cos(ωt)” is input to another input terminal of multiplier 36. The sine wave signal “-sin(ωt)” is input to another input terminal of multiplier 37. As a result, in each output signal of multipliers 36 and 37, the signal with angular frequency ω is extracted as a DC component. The output signals of multipliers 36 and 37 are input to LPFs 38 and 39, respectively.

[0076] The output signal I1 of LPF 38 is a low-frequency signal proportional to the in-phase component of the input signal, and the output signal Q1 of LPF 39 is a low-frequency signal proportional to the quadrature-phase component of the input signal. Arithmetic unit 40 calculates the square root of the sum of the squares of signals I1 and Q1 and outputs a signal representing the calculation result. The output signal of arithmetic unit 40 is expressed as "R1×Io". The output signal of arithmetic unit 40 becomes the output signal of the second synchronization detection circuit 14 and is provided to the correction unit 16 of control unit 9.

[0077] The correction unit 16 obtains the value "R2 / R1" by dividing the output signal "R2 / Io" of the first synchronization detection circuit 12 by the output signal "R1 / Io" of the second synchronization detection circuit 14. Here, the resistance value R1 of the correction resistor 5 is a known value and is stored in advance in the memory of the control unit 9, etc. Therefore, the correction unit 16 multiplies the value "R2 / R1" obtained as described above by the pre-stored resistance value R1, so that the resistance value R2 of the shunt resistor 4 at the current time can be calculated, that is, the resistance value is calculated.

[0078] <Specific configuration of the power supply circuit>

[0079] Specific examples of the power supply circuit 10 include, for example Figure 9 The first configuration example shown Figure 10 The second configuration example shown Figure 11 The third configuration example shown, etc.

[0080] [1] First configuration example

[0081] like Figure 9 As shown, the first power generation unit 18a of the power supply circuit 10a in the first configuration example includes a non-isolated switching power supply 51 whose input and output sides are not isolated from each other, and a low-dropout linear regulator 52. In this specification and in other documents such as... Figure 9 In the attached diagram, the low dropout linear regulator can be abbreviated as LDO.

[0082] The switching power supply 51 acts as a buck converter, taking input power supply pin as input and generating and outputting power prepared by stepping down the input power supply pin. The LDO 52 takes the power output from the switching power supply 51 as input, steps down the power supply, and generates and outputs a stable power supply. In the above configuration, the power output from the LDO 52 corresponds to the first power supply P1 and is provided to the signal application unit 6. As described above, the first power supply generation unit 18a includes the LDO 52 and generates the first power supply P1, the voltage value of which is stabilized by the LDO 52.

[0083] The second power generation unit 19a of the power supply circuit 10a is configured to include an LDO 53. The LDO 53 receives an input power supply pin, steps down the input power supply pin, and generates and outputs a stable power supply. In the above configuration, the power output from the LDO 53 corresponds to the second power supply P2 and is provided to the voltage detection unit 20, namely the first voltage detection unit 7 and the second voltage detection unit 8. As described above, the second power generation unit 19a includes an LDO 53 and generates the second power supply P2, the voltage value of which is stabilized by the LDO 53.

[0084] [2] Second configuration example

[0085] like Figure 10 As shown, in the second configuration example, the first power generation unit 18b of the power circuit 10b is connected to... Figure 9 The first power generation unit 18a shown in the first configuration example differs from the first power generation unit 18a in that an isolated power supply 54 is used instead of a switching power supply 51. The isolated power supply 54 has a configuration including insulating elements such as a transformer and is an isolated-type switching power supply with its input and output sides insulated from each other. The isolated power supply 54 acts as a buck converter, taking input power supply pin as input and generating and outputting power prepared by stepping down the input power supply pin. In this case, the LDO 52 takes the power output from the isolated power supply 54 as input, steps down the power supply, and generates and outputs a first power supply P1 as a stable power supply.

[0086] The second power generation unit 19b of the power circuit 10b and Figure 9 The second power generation unit 19a in the first configuration example shown differs from the second power generation unit 19a in that an isolated power supply 55 is added. The isolated power supply 55 has a configuration including insulating elements such as a transformer and is an isolated-type switching power supply with its input and output sides insulated from each other. The isolated power supply 55 acts as a buck converter, taking input power supply pin as input and generating and outputting power prepared by stepping down the input power supply pin. In this case, the LDO 53 takes the power output from the isolated power supply 55 as input, steps down the power supply, and generates and outputs a second power supply P2 as a stable power supply.

[0087] [3] Third configuration example

[0088] like Figure 11 As shown, in the third configuration example, the first power generation unit 18c of the power circuit 10c is connected to... Figure 9 The first power generation unit 18a shown in the first configuration example differs from the first power generation unit 18a in that it includes an insulating unit 56 with insulating elements such as a transformer. In this case, the switching power supply 51 receives the input power supply pin via the insulating unit 56 and generates and outputs power by stepping down the input power supply pin.

[0089] The second power generation unit 19c of the power supply circuit 10c and Figure 9 The second power generation unit 19a in the first configuration example shown differs from the second power generation unit 19a in that an insulation unit 56 is added. The insulation unit 56 is shared by both the first power generation unit 18c and the second power generation unit 19c. Therefore, the insulation unit 56 needs to have a larger capacity than the transformers provided in the isolated power supplies 54 and 55 in the second configuration example. In this case, the LDO 53 receives the input power supply Pin via the insulation unit 56, steps down the input power supply Pin, and generates and outputs a second power supply P2 as a stable power supply.

[0090] [4] Features of each configuration example

[0091] Although the first configuration example is only applicable to systems where insulation is not required in the power supply circuit 10, it has the advantage of keeping the configuration size small because it does not include a transformer, which is a relatively large component compared to the second and third configuration examples. On the other hand, the second and third configuration examples have the advantage that, although their sizes are larger than the first configuration example due to the inclusion of a transformer, they are suitable for systems where insulation is required in the power supply circuit 10.

[0092] The above embodiments provide the following effects.

[0093] According to this embodiment, the current sensor 1 detects the target current using the terminal voltage of a shunt resistor 4 connected in series in the path through which the target current flows and the current detection resistance value corresponding to the resistance value of the shunt resistor 4. The current sensor 1 includes a resistance value correction circuit 17 for correcting the detection resistance value and a power supply circuit 10 for supplying power to the resistance value correction circuit 17. The resistance value correction circuit 17 includes a correction resistor 5, a signal application unit 6, a first voltage detection unit 7, a second voltage detection unit 8, and a correction unit 16. The correction resistor 5 is connected in series with the shunt resistor in a path different from the path through which the target current flows, and its resistance accuracy is higher than that of the shunt resistor 4.

[0094] Signal application unit 6 applies an AC signal to the series circuit of shunt resistor 4 and correction resistor 5. First voltage detection unit 7 detects the terminal voltage of shunt resistor 4 when the AC signal is applied to the series circuit. Second voltage detection unit 8 detects the terminal voltage of correction resistor 5 when the AC signal is applied to the series circuit. Correction unit 16 calculates the resistance value of shunt resistor 4 based on a first voltage detection value (which is the terminal voltage detection value of first voltage detection unit 7) and a second voltage detection value (which is the terminal voltage detection value of second voltage detection unit 8), and corrects the detected resistance value based on the calculated resistance value of shunt resistor 4.

[0095] According to the resistance value correction circuit 17 with such a configuration, the detection resistance value is directly corrected by using the shunt resistor 4, without the need for indirect correction of the detection resistance value using a sub-resistor as in the first contemplated technique. As a result, the accuracy of the detection resistance value correction is improved. Furthermore, according to the above configuration, unlike the second contemplated technique, it is not necessary to provide multiple shunt resistors, nor is it necessary to provide an input terminal in the center of the shunt resistors; only one shunt resistor 4 is needed, making the overall configuration of the current sensor 1 less complex. Moreover, according to the above configuration, the calculation accuracy of the calculated resistance value and the correction accuracy of the detection resistance value largely depend on the accuracy of the resistance value of the correction resistor 5 and the detection accuracy of the first and second voltage detection values. In this case, since the correction resistor 5 has a higher resistance accuracy than the shunt resistor 4, the correction accuracy of the detection resistance value is sufficiently improved.

[0096] In the above configuration, since the power consumption cannot be increased unnecessarily, resistors with relatively small resistance values ​​can be used as shunt resistor 4 and correction resistor 5. Therefore, in the above configuration, in order to improve the detection accuracy of each terminal voltage detected by the first voltage detection unit 7 and the second voltage detection unit 8, and ultimately improve the correction accuracy of the detection resistor value, it is necessary to increase the level of the AC signal applied to the series circuit of shunt resistor 4 and correction resistor 5, that is, to increase the output current of signal application unit 6.

[0097] To increase the output current of the signal application unit 6, a power supply circuit 10 is required to carry a sufficiently large current. However, simply using a configuration for carrying a large current in the power supply circuit 10 can significantly increase power consumption. Therefore, the power supply circuit 10 of this embodiment includes: a first power generation unit 18 that generates a first power supply P1 with a low voltage relative to the input power supply Pin by stepping down the input power supply Pin provided from an external source; and a second power generation unit 19 that generates a second power supply P2 different from the first power supply P1. The power supply circuit 10 provides the first power supply P1 to the signal application unit 6 and the second power supply P2 to the first voltage detection unit 7 and the second voltage detection unit 8, which serve as voltage detection units 20.

[0098] As described above, in this embodiment, since the signal application unit 6 operates by receiving power from the first power supply P1 generated by stepping down the input power supply Pin, the power supply voltage VDD is set to a low voltage, for example, approximately +1V. On the other hand, it is possible to set the output current to a large current, for example, approximately 1A, that is, to increase the level of the AC signal applied to the series circuit of the shunt resistor 4 and the correction resistor 5. Therefore, according to the above embodiment, it is possible to obtain the excellent effect of not complicating the configuration of the entire current sensor 1, being able to accurately correct the detection resistance value, and suppressing power consumption to a low level.

[0099] According to the configuration of this embodiment described above, compared to the comparative example where the input power supply pin itself is provided to the signal application unit 6, there are the following advantages. Specifically, assuming that the power supplied from the power supply pin to the signal application unit 6 is equal in both the configuration of this embodiment and the configuration of the comparative example, in the configuration of the comparative example, it is necessary to increase the current output from the power supply pin to increase the current supplied to the signal application unit 6. Therefore, high voltage and high current may occur in this part, and a large amount of heat may be generated. On the other hand, in the configuration of this embodiment, the current supplied from the power supply pin to the power circuit 10 is limited to a small value, and the current supplied from the power circuit 10 to the signal application unit 6 is set to a large current. Therefore, in this embodiment, it is possible to suppress heat generation to a small value and power consumption to a low level compared to the configuration of the comparative example.

[0100] The first power generation unit 18 can be configured to include a switching power supply 51 or an isolated power supply 54, which is an isolated type switching power supply. Generally, a switching power supply can be more efficient than a linear regulator. Therefore, according to such a configuration, the power loss in the configuration used to generate the first power supply P1 is limited compared to a configuration that generates the first power supply P1 by using only a linear regulator or the like without using a switching power supply. As a result, the overall power consumption of the current sensor 1 can be further reduced.

[0101] The first power generation unit 18 includes an LDO 52, and generates a first power supply P1 whose voltage value is stabilized by the LDO 52. With this configuration, even if noise is superimposed on the input power supply pin, the switching power supply 51, the power output from the isolated power supply 54, etc., the first power supply P1 is a power supply with reduced noise. Therefore, with the above configuration, the influence of noise on the operation of the signal application unit 6 supplied with the first power supply P1 is prevented, specifically from affecting the accuracy of the AC signal applied to the series circuit of the shunt resistor 4 and the correction resistor 5. As a result, the accuracy of the correction of the detection resistor value can be well maintained.

[0102] The second power generation unit 19 includes an LDO 53 and generates a second power supply P2 whose voltage value is stabilized by the LDO 53. With this configuration, even if noise is superimposed on the input power supply pin, the power output from the isolated power supply 55, etc., the second power supply P2 is a power supply with reduced noise. Therefore, with the above configuration, it is possible to prevent noise from affecting the operation of the first voltage detection unit 7 and the second voltage detection unit 8, which are supplied with the second power supply P2, specifically, the detection accuracy of the voltage at each terminal of the shunt resistor 4 and the correction resistor 5. As a result, the accuracy of the correction of the detection resistor value can be well maintained.

[0103] (Second Embodiment)

[0104] refer to Figures 12 to 14 A second embodiment of this disclosure is described.

[0105] (Overall Configuration)

[0106] like Figure 12 As shown, the current sensor 61 in this embodiment and Figure 1 The current sensor 1 shown in the first embodiment is different in that a signal application unit 62 is arranged instead of a signal application unit 6.

[0107] Similar to signal application unit 6, signal application unit 62 applies a pulse wave signal or a sinusoidal AC signal to the series circuit of shunt resistor 4 and correction resistor 5 during calibration. In this case, signal application unit 62 is configured as a voltage source to provide AC voltage to the series circuit of shunt resistor 4 and correction resistor 5. As described above, in the above configuration, a resistance value correction circuit 63 for calibrating the resistance value for detection is configured by correction resistor 5, signal application unit 62, first voltage detection unit 7, second voltage detection unit 8, and correction unit 16. In this case, power supply circuit 10 provides first power supply P1 and second power supply P2 to resistance value correction circuit 63. Specifically, power supply circuit 10 provides first power supply P1 to signal application unit 62 and second power supply P2 to first voltage detection unit 7 and second voltage detection unit 8, which serve as voltage detection unit 20.

[0108] <Specific configuration of the signal application unit>

[0109] Specific examples of signal application unit 62 include Figure 13 The first configuration example shown Figure 14 The second configuration example shown, etc.

[0110] [1] First configuration example

[0111] like Figure 13 As shown, the signal application unit 62a of the first configuration example includes a transistor 71, a signal generation unit 72, an OP amplifier 73, etc. The transistor 71 is, for example, an N-channel MOSFET, whose drain is connected to the power supply line L1, and whose source is connected to ground through a correction resistor 5 and a shunt resistor 4.

[0112] Signal generation unit 72 generates and outputs a pulse wave signal or a sine wave signal with the same frequency as the AC voltage applied to the series circuit of shunt resistor 4 and correction resistor 5. The output signal of signal generation unit 72 is provided to the non-inverting input terminal of OP amplifier 73. The inverting input terminal of OP amplifier 73 is connected to the source of transistor 71, and its output terminal is connected to the gate of transistor 71. According to the above configuration, transistor 71 is driven by OP amplifier 73, such that an AC signal, which is an AC voltage, is applied to the series circuit of shunt resistor 4 and correction resistor 5. As described above, the signal application unit 62a of the first configuration example is configured to be driven by an amplifier.

[0113] [2] Second configuration example

[0114] like Figure 14 As shown, the signal application unit 62b in the second configuration example and Figure 13The signal application unit 62a shown in the first configuration example differs in that a buffer 75 is arranged instead of an op-amp 73. In this case, the output signal of the signal generation unit 72 is provided to the input terminal of the buffer 75. The output terminal of the buffer 75 is connected to the gate of the transistor 71. According to the above configuration, the transistor 71 is driven by the buffer 75, such that an AC signal of alternating current voltage is applied to the series circuit of the shunt resistor 4 and the correction resistor 5. As described above, the signal application unit 62b of the second configuration example has a buffer-driven configuration.

[0115] [3] Features of each configuration example

[0116] According to the first configuration example of the amplifier drive configuration, the source voltage of transistor 71 is controlled to be constant by the operation of OP amplifier 73, making the first configuration example advantageous compared to the second configuration example of the buffer drive configuration, thereby improving the accuracy of the AC current voltage applied to the series circuit of shunt resistor 4 and correction resistor 5. On the other hand, compared to the first configuration example, according to the second configuration example, by using buffer 75 instead of OP amplifier 73, there is an advantage in being able to suppress the circuit size to a smaller size.

[0117] As described above, in the current sensor 61 of this embodiment, the AC signal applied to the series circuit of the shunt resistor 4 and the correction resistor 5 during the correction time changes from AC current to AC voltage. The current sensor 61 includes a resistance value correction circuit 63 capable of performing the same operation as the resistance value correction circuit 17 of the first embodiment, and a power supply circuit 10 for providing power to the resistance value correction circuit 63. Therefore, in this embodiment, the detection resistance value can also be corrected in the same manner as in the first embodiment, and the same effect as in the first embodiment can be obtained.

[0118] (Other embodiments)

[0119] This disclosure is not limited to the embodiments described above and shown in the accompanying drawings, but can be freely modified, combined or extended without departing from the spirit of this disclosure.

[0120] The numerical values ​​shown in the above embodiments are examples, and are not limited to those examples.

[0121] The specific configurations of the resistance correction circuits 17 and 63 are not limited to those described in the above embodiments, and can be appropriately changed as long as they can achieve the same function as these configurations.

[0122] The specific configuration of signal application units 6 and 62 is not limited to the configuration described in each of the above embodiments, and can be any configuration as long as the feature applies an AC signal to the series circuit of shunt resistor 4 and correction resistor 5.

[0123] The specific configuration of the first synchronous detection circuit 12 is not limited to the configuration described in each of the above embodiments, and can be any configuration, as long as the signal at the terminal of the input shunt resistor 4 is used and synchronous detection is performed at the same frequency as the AC signal to extract and output the signal. The specific configuration of the second synchronous detection circuit 14 can be such that the signal at the terminal of the correction resistor can be used and synchronous detection is performed at the same frequency as the AC signal to extract and output the signal.

[0124] The specific configuration of the first power generation unit 18 is not limited to the configuration described in each of the above embodiments, and any configuration can be used, as long as it can generate a first power supply P1 with a low voltage relative to the input power supply Pin by stepping down the input power supply Pin provided from the outside. In addition, the specific configuration of the second power generation unit 19 is not limited to the configuration described in each of the above embodiments, and it can also be a configuration that can generate a second power supply P2 that is different from the first power supply P1.

[0125] For example, when signal application units 6 and 62 are configured to operate without being affected by noise, LDO 52 may not be required for the first power generation units 18a, 18b, and 18c. Even with this modified configuration, when signal application units 6a and 6b are driven by amplifiers as the specific configuration of signal application unit 6, or signal application unit 62a is driven by amplifiers as the specific configuration of signal application unit 62, noise reduction is achieved through the operation of OP amplifiers 23 and 73, thereby preventing noise from affecting the operation of signal application units 6 and 62.

[0126] Although this disclosure has been described with reference to examples, it should be understood that this disclosure is not limited to those examples or structures. This disclosure incorporates various modifications and variations within the equivalent scope. Furthermore, various combinations and forms, as well as other combinations and forms that include only one element or more or fewer of those elements, are also within the spirit and scope of this disclosure.

Claims

1. A current sensor for detecting the target current using a terminal voltage of a shunt resistor (4) connected in series in the path through which the target current flows and a current-detecting resistance value corresponding to the resistance value of the shunt resistor, the current sensor comprising: A resistance value correction circuit (17, 63) for calibrating the resistance value used for current detection; as well as A power supply circuit (10) that provides power to the resistance correction circuit, wherein: The resistance correction circuit includes: The calibration resistor (5) is connected in series with the shunt resistor in a path different from the path through which the target current flows; The signal application unit (6, 62) applies an AC signal to the series circuit of the shunt resistor and the correction resistor; Voltage detection unit (20) detects the terminal voltage of the shunt resistor and the terminal voltage of the correction resistor when the AC signal is applied to the series circuit; and The correction unit (16) calculates the resistance value of the shunt resistor based on each detected value of the terminal voltage of the shunt resistor and the terminal voltage of the correction resistor detected by the voltage detection unit, and corrects the current detection resistance value based on the calculated resistance value, wherein the calculated resistance value is the calculated resistance value of the shunt resistor; The power supply circuit includes: A first power generation unit (18) generates a first power supply with a low voltage relative to an externally supplied input power supply by stepping down the input power supply; and The second power generation unit (19) generates a second power source different from the first power source; and The power supply circuit is configured to provide the first power supply to the signal application unit and the second power supply to the voltage detection unit.

2. The current sensor according to claim 1, wherein: The first power generation unit includes switching power supplies (51, 54).

3. The current sensor according to claim 2, wherein: The switching power supply (54) is configured as an insulated power supply with the input side and the output side insulated from each other.

4. The current sensor according to claim 1, wherein: The input power is provided by the main battery (B1), which provides power to the drive unit used to drive the vehicle.

5. The current sensor according to claim 1, wherein: The input power is provided by the auxiliary battery (B2), which provides power to the vehicle's auxiliary equipment.

6. The current sensor according to any one of claims 1 to 5, wherein: The second power generation unit includes a linear regulator (53) with a low voltage drop, and generates the second power through the linear regulator.

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