current sensor

Abstract

A current sensor for detecting a target current using a shunt resistor (4) includes a resistance value correction circuit (17, 53, 75, 86, 96) having a correction resistor (5), a signal application unit (6, 52) that applies an alternating current signal to a series circuit of the shunt resistor and the correction resistor, a first voltage detection unit (7) that detects a terminal voltage of the shunt resistor, a second voltage detection unit (8) that detects a terminal voltage of the correction resistor, and a correction unit (16) that calculates a resistance value of the shunt resistor based on a first voltage detection value of the first voltage detection unit and a second voltage detection value of the second voltage detection unit, and corrects a resistance value for current detection based on the calculated resistance value of the shunt resistor.

Description

TECHNICAL FIELD

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

[0002] As disclosed in Patent Documents 1 and 2, in conceivable current sensors, a terminal voltage of a shunt resistor provided in series in a path through which a detection target current flows is measured, and a current detection resistance value corresponding to a resistance value of the shunt resistor is calculated based on the measured voltage to calculate the current as the detection target. In this case, since the resistance value of the shunt resistor can change due to deterioration over time or the like, it can be necessary to correct the current detection resistance value for calculating the current at all times. In the following description, the conceivable current sensor disclosed in Patent Document 1 will be referred to as a first conceivable technology, and the conceivable current sensor disclosed in Patent Document 2 will be referred to as a second conceivable technology.

[0003] In the first conceivable technology, the current detection resistance value is corrected as follows. That is, the first conceivable technology provides a sub-resistor provided so that the detection target current flows in the sub-resistor similarly to the shunt resistor in a normal state, and a correction resistor provided so that the detection target current does not flow in the correction resistor at normal times. According to the above configuration, similarly to the shunt resistor, the sub-resistor deteriorates over time, but the correction resistor hardly deteriorates over time. In the first conceivable technology, the degrees of deterioration of the sub-resistor and the shunt resistor are obtained by comparing the resistance values of the sub-resistor and the correction resistor at the time of correction, and the current detection resistance value is corrected based on the degrees of deterioration.

[0004] In the second conceivable technology, the current detection resistance value is corrected as follows. That is, the second conceivable technology has a configuration in which a plurality of shunt resistors are provided and a correction current passes through an interconnection node of the plurality of shunt resistors, or an input terminal is provided in a central portion of the shunt resistor and a correction current passes through the input terminal. In the second conceivable technology, a terminal voltage of each resistor when the correction current passes therethrough is measured, and respective resistance values are calculated based on the measurement results to correct the current detection resistance value.

[0005] PRIOR ART DOCUMENTS

[0006] [PATENT DOCUMENTS]

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

[0008] Patent Document 2: U.S. Patent No. 10,473,724 SUMMARY

[0009] In the first conceivable technique, the shunt resistor is not used for direct correction, and it is assumed that the sub-resistor deteriorates in the same manner as the shunt resistor, and then the resistance value for current detection corresponding to the resistance value of the shunt resistor is indirectly corrected using the sub-resistor. Therefore, in the first conceivable technique, if the above assumption is not satisfied, the resistance value for current detection cannot be corrected with high accuracy, and as a result, the current detection accuracy can be reduced.

[0010] In the second conceivable technique, there is a difficulty in that the configuration becomes complicated because a plurality of shunt resistors need to be provided or an input terminal is provided in the central portion of the shunt resistor. Further, in the second conceivable technique, it is difficult to sufficiently improve the accuracy of correction because the accuracy of correction of the resistance value for current detection depends largely on the accuracy of the correction current.

[0011] The present disclosure was made in view of the above circumstances, and an object thereof is to provide a current sensor capable of accurately correcting a resistance value for current detection without causing a complicated configuration.

[0012] A current sensor detects a detection target current based on a terminal voltage of a shunt resistor provided in series in a path through which the detection target current flows and a resistance value for current detection corresponding to a resistance value of the shunt resistor. The current sensor includes a resistance value correction circuit for correcting the resistance value for current detection. The resistance value correction circuit includes a correction resistor, a signal application unit, a first voltage detection unit, a second 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 detection target current flows, and has a higher resistance accuracy than the shunt resistor.

[0013] The signal application unit applies an AC signal to a series circuit of the shunt resistor and the correction resistor. The first voltage detection unit detects a terminal voltage of the shunt resistor when the AC signal is applied to the series circuit. The second voltage detection unit detects a terminal voltage of the correction resistor when the AC signal is applied to the series circuit. The correction unit calculates a resistance value of the shunt resistor based on a first voltage detection value of the terminal voltage detection value detected by the first voltage detection unit and a second voltage detection value of the terminal voltage detection value detected by the second voltage detection unit, and corrects the resistance value for current detection based on a calculated resistance value of the calculated resistance value of the shunt resistor.

[0014] According to such a configuration, it is possible to directly correct the detection resistor value by using the shunt resistor without indirectly correcting the detection resistor value by using the sub resistor as in the first conceivable technique. In addition, according to the above-described configuration, unlike the second conceivable technique, it is not necessary to provide a plurality of shunt resistors, nor is it necessary to provide the input terminal at the center of the shunt resistor, but it is only necessary to provide one shunt resistor, and thus the configuration of the entire current sensor is not complicated.

[0015] Further, according to the above-described configuration, the calculation accuracy of the calculated resistance value and the correction accuracy of the detection resistor value depend to a large extent on the accuracy of the resistance value of the correction resistor and the detection accuracy of the first voltage detection value and the second voltage detection value. In this case, since the correction resistor has a higher resistance accuracy than the shunt resistor, the correction accuracy of the detection resistor value is sufficiently improved. Thus, according to the above-described configuration, it is possible to obtain the excellent effect that it is possible to correct the detection resistor value with high accuracy without complicating the configuration of the entire current sensor. BRIEF DESCRIPTION OF DRAWINGS

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

[0017] Figure 1 is a diagram schematically showing a configuration of a current sensor according to a first embodiment;

[0018] Figure 2 is a diagram showing a specific first configuration example of a signal application unit according to the first embodiment;

[0019] Figure 3 is a diagram showing a specific second configuration example of a signal application unit according to the first embodiment;

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

[0021] Figure 5 is a diagram showing a specific fourth configuration example of a signal application unit according to the first embodiment;

[0022] Figure 6 is a diagram showing a specific configuration example of each synchronous detection circuit according to the first embodiment;

[0023] Figure 7 is a diagram schematically showing a configuration of a current sensor according to a second embodiment;

[0024] Figure 8 is a diagram showing a specific first configuration example of a signal application unit according to the second embodiment;

[0025] Figure 9 is a diagram showing a specific second configuration example of a signal application unit according to the second embodiment;

[0026] Figure 10 is a diagram schematically showing a configuration of a current sensor according to the third embodiment;

[0027] Figure 11 is a diagram schematically showing a configuration of a current sensor switched to a first connection state according to the third embodiment;

[0028] Figure 12 is a diagram schematically showing a configuration of a current sensor switched to a second connection state according to the third embodiment;

[0029] Figure 13 is a diagram schematically showing a configuration of a current sensor switched to a third connection state according to the third embodiment;

[0030] Figure 14 is a diagram schematically showing a configuration of a current sensor according to the fourth embodiment; and

[0031] Figure 15 is a diagram schematically showing a configuration of a current sensor according to the fifth embodiment. DETAILED DESCRIPTION

[0032] Hereinafter, a plurality of embodiments will be described with reference to the drawings. In each of the embodiments, substantially the same components are denoted by the same reference numerals and description thereof will be omitted.

[0033] (First Embodiment)

[0034] Reference will be made to Figures 1 to 6 A first embodiment of the present disclosure will be described.

[0035] (Overall Configuration)

[0036] Figure 1 The current sensor 1 of the present embodiment shown is mounted on a vehicle such as an automobile, and detects a detection target current that is a current flowing through a measurement target 2. The measurement target 2 can be a battery such as a main engine battery that supplies electric power to a drive unit for driving the vehicle, an auxiliary battery that supplies electric power to an auxiliary device of the vehicle, a DC / DC converter, or the like. The DC / DC converter supplies electric power to an electric motor that generates a driving force for driving the vehicle, and constitutes the above-described drive unit together with the electric motor.

[0037] In this case, the load 3 is connected in series to the measurement target 2, and the loop circuit is constituted by the measurement target 2, the load 3, a switch (not shown), and the like. When the measurement target 2 is the above-described battery, the load 3 can be, for example, the above-described motor, the above-described DC / DC converter, an electric compressor, or the like. In addition, when the measurement target 2 is the above-described DC / DC converter, the load 3 can be, for example, the above-described motor or the like.

[0038] The current sensor 1 includes a shunt resistor 4, a correction resistor 5, a signal application unit 6, a first voltage detection unit 7, a second voltage detection unit 8, and a control unit 9. One terminal of the shunt resistor 4 is connected to the high-potential side terminal of the measurement target 2 through the load 3, and the other terminal is connected to the ground as a reference potential of the circuit and the low-potential side terminal of the measurement target 2. That is, the shunt resistor 4 is provided in series with a path through which the detection target current flows. The current sensor 1 detects the detection target current using the terminal voltage of the shunt resistor 4 thus provided and a detection resistance value corresponding to the resistance value of the shunt resistor 4.

[0039] One terminal of the correction resistor 5 is connected to the signal application unit 6, and the other terminal is connected to the one terminal of the shunt resistor 4. That is, the correction resistor 5 is connected in series with the shunt resistor 4 in a path different from the path through which the detection target current flows. In this case, since the detection target current is a relatively large current, the resistance value of the shunt resistor 4 is a relatively small value, for example, on the order of μΩ.

[0040] On the other hand, since the relatively large detection target current does not flow through the correction resistor 5, its resistance value is relatively large, for example, on the order of mΩ. In general, it can be difficult to accurately form a resistor having a small resistance value, but it can be relatively easy to accurately form a resistor having a large resistance value. Therefore, in the present embodiment, the resistance accuracy of the correction resistor 5 is sufficiently higher than the resistance accuracy of the shunt resistor 4.

[0041] The signal application unit 6 applies a pulse wave or a sinusoidal AC signal to the series circuit of the shunt resistor 4 and the correction resistor 5 at a correction time when the detection resistance value described later is corrected. In other words, the signal application unit 6 applies the same AC signal to the shunt resistor 4 and the correction resistor 5 at the time of correction. In this case, the signal application unit 6 is configured as a current source for supplying an alternating current from, for example, a power supply line 10 supplied with a power supply voltage VDD of +5 V to the series circuit. The first voltage detection unit 7 detects the terminal voltage of the shunt resistor 4 at the time of application of the AC signal 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 FIG. 10, the A / D converter is abbreviated as ADC. Figure 1

[0042] ​In order to detect the terminal voltage of the shunt resistor 4, the first A / D converter 11 performs an A / D conversion operation as follows. That is, the first A / D converter 11 inputs a signal of each terminal of the shunt resistor 4, and outputs a voltage difference of each terminal of the shunt resistor 4, that is, a digital signal corresponding to the voltage between the terminals of the shunt resistor 4, by performing an A / D conversion on each signal. The digital signal thus output from the first A / D converter 11 is a signal corresponding to the signal of the terminal of the shunt resistor 4.

[0043] The first synchronous detection circuit 12 inputs the digital signal output from the first A / D converter 11, and 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 correction 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 output a signal representing a detection value of the terminal voltage as a first voltage detection value to the control unit 9.

[0044] When the series circuit of the shunt resistor 4 and the correction resistor 5 is not applied with the AC signal, that is, in the normal state, the first voltage detection unit 7 detects the terminal voltage of the shunt resistor 4 as follows. That is, in the normal state, the first A / D converter 11 performs an A / D conversion operation in the same manner as in the correction, in this case, the digital signal output from the first A / D converter 11 is output to the control unit 9 without being input to the first synchronous detection circuit 12. That is, in the normal state, the first voltage detection unit 7 detects the terminal voltage of the shunt resistor 4 based on the output signal of the first A / D converter 11, and outputs a signal representing a detection value of the terminal voltage as a first voltage detection value to the control unit 9.

[0045] The second voltage detection unit 8 detects the terminal voltage of the correction resistor 5 when the series circuit of the shunt resistor 4 and the correction resistor 5 is applied with the AC signal, 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. That is, the second A / D converter 13 inputs a signal of each terminal of the correction resistor 5, and outputs a voltage difference of each terminal of the correction resistor 5, that is, a digital signal corresponding to the voltage between the terminals of the correction resistor 5, by performing an A / D conversion on each signal. The digital signal thus output from the second A / D converter 13 is a signal corresponding to the signal of the terminal of the correction resistor 5.

[0046] The second synchronous detection circuit 14 inputs the digital signal output from the second A / D converter 13, and synchronously detects the signal 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. In this way, 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 output a signal representing a detection value of the terminal voltage as a second voltage detection value to the control unit 9.

[0047] The control unit 9 is configured, together with the first voltage detection unit 7 and the second voltage detection unit 8, as a semiconductor integrated circuit such as the same ASIC. The ASIC is an abbreviation of Application Specific Integrated Circuit. The control unit 9 includes functional blocks such as a current detection unit 15 and a correction unit 16. Each of these functional blocks is implemented by hardware. The control unit 9 can be configured as a semiconductor integrated circuit different from the first voltage detection unit 7 and the second voltage detection unit 8. For example, the control unit 9 can be configured by a microcomputer including a CPU, a RAM, a ROM, and the like. In this case, each of the above-mentioned functional blocks is implemented by executing a computer program stored in the ROM or the like by the CPU of the control unit 9 to provide processing corresponding to the computer program, that is, by software. Alternatively, in this case, at least part of the functional blocks of the parking lot server apparatus can be implemented in hardware.

[0048] The current detection unit 15 detects a detection target current using a signal corresponding to the terminal voltage of the shunt resistor 4 output from the first voltage detection unit 7 at normal times and a detection resistance value corresponding to the resistance value of the shunt resistor 4. The detection resistance value is set based on the initial resistance value of the shunt resistor 4 actually used, and is stored in advance in a memory provided in the control unit 9. Here, since the detection target current is a relatively large current flowing in the shunt resistor 4, the resistance value changes from the initial value due to deterioration or the like over time.

[0049] Therefore, the above-mentioned detection resistance value is corrected at any time by the operation of the correction unit 16. At the time of 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 above correction resistor value is an initial resistance value of the correction resistor 5 actually used, and is stored in advance in a memory provided in the control unit 9. Since the detection target current does not flow in the correction resistor 5 in the normal state, the resistance value hardly changes from the initial value due to aging deterioration or the like. As described above, in the above configuration, the resistance value correction circuit 17 for correcting the detection resistance value is configured by the correction resistor 5, the signal application unit 6, the first voltage detection unit 7, the second voltage detection unit 8, and the correction unit 16.

[0051] <Detail Configuration of Signal Application Unit>

[0052] The detail configuration of the signal application unit 6 includes, for example Figure 2 a first configuration example shown in Figure 3 a second configuration example shown in Figure 4 a third configuration example shown in Figure 5 a fourth configuration example shown in

[0053] [1] First Configuration Example

[0054] As shown in Figure 2 , the signal application unit 6a of the first configuration example includes a transistor 21, a signal generation unit 22, an OP amplifier 23, and the like. The transistor 21 is, for example, an N-channel MOSFET, whose drain is connected to the power supply line 10 through the correction resistor 5, and whose source is connected to the ground through the shunt resistor 4. The signal generation unit 22 generates and outputs a pulse wave signal or a sine wave signal whose frequency is the same as that of the alternating current applied to the series circuit of the shunt resistor 4 and the correction resistor 5.

[0055] The output signal of the signal generation unit 22 is supplied to the non-inverting input terminal of the OP amplifier 23. The inverting input terminal of the OP amplifier 23 is connected to the drain of the transistor 21, and its output terminal is connected to the gate of the transistor 21. According to the above configuration, the transistor 21 is driven by the OP amplifier 23 so that the AC signal which is the 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 6a of the first configuration example is configured to be driven by an amplifier. In this case, the correction resistor 5 also functions as a current source for the signal application unit 6a.

[0056] [2] Second Configuration Example

[0057] As shown in Figure 3 , the signal application unit 6b of the second configuration example is different from Figure 2The signal applying unit 6a of the first configuration example shown is different in that a resistor 24 is added. In this case, the drain of the transistor 21 is connected to the power supply line 10 via the resistor 24, and its source is connected to the ground via the correction resistor 5 and the shunt resistor 4.

[0058] Even with the above configuration, as in the first configuration example, transistor 21 is driven by OP amplifier 23, so that an AC signal, which is an alternating current, is applied to the series circuit of shunt resistor 4 and correction resistor. As described above, signal application unit 6b of the second configuration example has an amplifier drive configuration similar to that of signal application unit 6a of the first configuration example. In this case, resistor 24 and transistor 21, which are provided separately from correction resistor 5, serve as the current source of signal application unit 6b.

[0059] [3] Third configuration example

[0060] like Figure 4 As shown, the signal applying unit 6c of the third configuration example is Figure 2 The signal application unit 6a of the first configuration example shown is different in that a buffer 25 is provided instead of the OP amplifier 23. In this case, the output signal of the signal generation unit 22 is supplied 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, so 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 of the third configuration example has a buffer drive configuration.

[0061] [4] Fourth configuration example

[0062] like Figure 5 As shown, the signal applying unit 6d of the fourth configuration example is Figure 3 The signal application unit 6b of the second configuration example shown is different in that a buffer 25 is provided instead of the OP amplifier 23. In this case, the output signal of the signal generation unit 22 is supplied 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, so 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 of the fourth configuration example has a buffer drive configuration.

[0063] [5] Characteristics of each configuration example

[0064] In the first configuration example and the third configuration example, since the correction resistor 5 is arranged close to the power supply line 10, and the shunt resistor 4 is arranged close to the 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 configuration example and the third configuration example, although it is likely that detection errors of the terminal voltages of the shunt resistor 4 and the correction resistor 5 occur, compared to the second configuration example and the fourth configuration example, the correction resistor 5 commonly provides the current source to the application units 6a and 6c, so that as an advantage, the number of elements can be suppressed to a small number.

[0065] In the second configuration example and the fourth configuration example, since in order to configure the current sources of the signal application units 6b and 6d, a resistor 24 different from the correction resistor 5 needs to be provided, as a disadvantage, the number of elements increases compared to the first configuration example and the third configuration example. However, in the second configuration example and the fourth configuration example, since both the correction resistor 5 and the shunt resistor 4 are arranged near the 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 configuration example and the fourth configuration example, there is an advantage that detection errors of the terminal voltages of the shunt resistor 4 and the correction resistor 5 can be suppressed to be smaller than those of the first configuration example and the third configuration example.

[0066] According to the first configuration example and the second configuration example of the amplifier drive configuration, the drain voltage of the transistor 21 is controlled to be constant by the operation of the OP amplifier 23, so that the first configuration example and the second configuration example have an advantage compared to the third configuration example and the fourth configuration example of the buffer drive configuration, so that the precision of the AC current applied to the series circuit of the shunt resistor 4 and the correction resistor 5 can be improved. On the other hand, compared to the first configuration example and the second configuration example, according to the third configuration example and the fourth configuration example, by using the buffer 25 instead of the OP amplifier 23, there is an advantage that the circuit scale can be suppressed to a smaller size.

[0067] <Specific configuration of each synchronization detection circuit>

[0068] The specific configuration of the first synchronization detection circuit 12 and the second synchronization detection circuit 14 includes, for example Figure 6 the configuration shown. In this case, an alternating current signal of the AC current applied to the series circuit of the shunt resistor 4 and the correction resistor 5 by the signal application unit 6 is defined as "Io x 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 Rl. Here, ω is an angular frequency, and t is time.

[0069] As Figure 6As shown, the first synchronous 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, the digital signal output from the first A / D converter 11 is input to each of the input terminals of the multipliers 31 and 32 of the first synchronous detection circuit 12. This digital signal is a signal corresponding to the terminal voltage of the shunt resistor 4 at the time of correction, and is defined as

[0070] A cosine wave signal of "cos(ωt)" is input to the other input terminal of the multiplier 31. A sine wave signal of "-sin(ωt)" is input to the other input terminal of the multiplier 32. As a result, in each of the output signals of the multipliers 31 and 32, a signal having an angular frequency ω is extracted as a direct current component. The output signals of the multipliers 31 and 32 are input to the LPFs 33 and 34, respectively.

[0071] The output signal I2 of the LPF 33 is a low-frequency signal proportional to the in-phase component of the input signal, and the output signal Q2 of the LPF 34 is a low-frequency signal proportional to the quadrature-phase component of the input signal. The arithmetic unit 35 calculates the square root of the sum of the squares of the signals I2 and Q2, and outputs a signal representing the calculation result. The output signal of the arithmetic unit 35 is expressed as "R2 x Io". The output signal of the arithmetic unit 35 becomes the output signal of the first synchronous detection circuit 12, and is supplied to the correction unit 16 of the control unit 9.

[0072] 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, the digital signal output from the second A / D converter 13 is input to each of the input terminals of the 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 at the time of correction, and is defined as

[0073] A cosine wave signal of "cos(ωt)" is input to the other input terminal of the multiplier 36. A sine wave signal of "-sin(ωt)" is input to the other input terminal of the multiplier 37. As a result, in each of the output signals of the multipliers 36 and 37, a signal having an angular frequency ω is extracted as a direct current component. The output signals of the multipliers 36 and 37 are input to the LPFs 38 and 39, respectively.

[0074] The output signal I1 of the LPF 38 is a low-frequency signal proportional to the in-phase component of the input signal, and the output signal Q1 of the LPF 39 is a low-frequency signal proportional to the quadrature-phase component of the input signal. The arithmetic unit 40 calculates the square root of the sum of the squares of the signals I1 and Q1, and outputs a signal representing the calculation result. The output signal of the arithmetic unit 40 is expressed as "R1 x Io". The output signal of the arithmetic unit 40 becomes the output signal of the second synchronous detection circuit 14, and is supplied to the correction unit 16 of the control unit 9.

[0075] The correction unit 16 obtains a value "R2 / R1" by dividing the output signal "R2 / Io" of the first synchronous detection circuit 12 by the output signal "R1 / Io" of the second synchronous detection circuit 14. Here, the resistance value R1 of the correction resistor 5 is a known value and is stored in advance in a memory of the control unit 9 or the like. Therefore, the correction unit 16 multiplies the value "R2 / R1" obtained as described above by the resistance value R1 stored in advance, so that the resistance value R2 of the shunt resistor 4 at the current time, that is, the resistance value at the current time, can be calculated.

[0076] The above-described embodiment provides the following effects.

[0077] The current sensor 1 according to the present embodiment detects a detection target current based on a terminal voltage of a shunt resistor 4 provided in series in a path through which the detection target current flows and a resistance value for current detection corresponding to a resistance value of the shunt resistor 4. The current sensor includes a resistance value correction circuit 17 for correcting the resistance value for current detection. 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 detection target current flows, and has a higher resistance accuracy than the shunt resistor 4.

[0078] The signal application unit 6 applies an AC signal to a series circuit of the shunt resistor 4 and the correction resistor 5. The first voltage detection unit 7 detects a terminal voltage of the shunt resistor 4 when the AC signal is applied to the series circuit. The second voltage detection unit 8 detects a terminal voltage of the correction resistor 5 when the AC signal is applied to the series circuit. The correction unit 16 calculates a resistance value of the shunt resistor 4 based on a first voltage detection value that is a terminal voltage detection value of the first voltage detection unit 7 and a second voltage detection value that is a terminal voltage detection value of the second voltage detection unit 8, and corrects the resistance value for current detection based on a calculated resistance value that is the calculated resistance value of the shunt resistor 4.

[0079] According to such a configuration, it is possible to directly correct the detection resistance value by using the shunt resistor 4 without indirectly correcting the detection resistance value by using a sub resistor as in the first conceivable technique. Furthermore, according to the above-described configuration, unlike the second conceivable technique, it is not necessary to provide a plurality of shunt resistors, nor is it necessary to provide the input terminal in the center of the shunt resistor, and only one shunt resistor 4 needs to be provided, so that the configuration of the entire current sensor 1 is not complicated.

[0080] Furthermore, according to the above-described configuration, the calculation accuracy of the calculated resistance value and the correction accuracy of the detection resistance value depend to a large extent on the accuracy of the resistance value of the correction resistor 5 and the detection accuracy of the first voltage detection value and the second voltage detection value. 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. Therefore, according to the above-described embodiment, it is possible to obtain the excellent effect of being able to correct the detection resistance value with high accuracy without complicating the configuration of the entire current sensor 1.

[0081] In this case, the first voltage detection unit 7 includes a first synchronous detection circuit 12 that inputs a signal of the terminal of the shunt resistor 4 and synchronously detects the signal at the same frequency as the AC signal to extract and output the signal, and 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. Furthermore, in this case, the second voltage detection unit 8 includes a second synchronous detection circuit 14 that inputs a signal of the terminal of the correction resistor 5 and synchronously detects the signal at the same frequency as the AC signal to extract and output the signal, and 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.

[0082] According to such a configuration, the terminal voltages of the shunt resistor 4 and the correction resistor 5 are detected based on signals extracted by synchronous detection at the same frequency as the frequency of the AC signal applied to the shunt resistor 4 and the correction resistor 5. Therefore, according to the present embodiment, the detection accuracy of the detection value of each of the first voltage detection value and the second voltage detection value is limited to be reduced due to the influence of noise such as offset on the circuit side and thermoelectric electromotive force, and thus, it is possible to further improve the accuracy of the correction of the detection resistance value.

[0083] The signal application unit 6 applies a pulse wave or a sinusoidal AC signal to the series circuit of the shunt resistor 4 and the correction resistor 5. When the signal application unit 6 applies a sinusoidal wave AC signal, the configuration for generating the AC signal, specifically, the configuration of the signal generation unit 22 is complicated, but the signal includes only a frequency component desired to be an AC signal. Therefore, it is possible to suppress a detection error of the first voltage detection value and the second voltage detection value to a low level, in other words, it is possible to improve the accuracy of correction of the resistance value for detection. On the other hand, in the case where the signal application unit 6 applies a pulse wave AC signal, since the AC signal includes a harmonic component, it is possible that an error occurs in the detection value of each of the first voltage detection value and the second voltage detection value. However, it is possible to simplify the configuration for generating the AC signal, specifically, it is possible to simplify the configuration of the signal generation unit 22.

[0084] (Second Embodiment)

[0085] Reference Figures 7 to 9 A second embodiment of the present disclosure will be described.

[0086] (Overall Configuration)

[0087] As Figure 7 illustrated, the current sensor 51 of the present embodiment is different from the current sensor 1 of the first embodiment illustrated in Figure 1 in that a signal application unit 52 is arranged instead of the signal application unit 6.

[0088] Like the signal application unit 6, the signal application unit 52 applies a pulse wave signal or a sinusoidal wave AC signal to the series circuit of the shunt resistor 4 and the correction resistor 5 at the time of correction. In this case, the signal application unit 52 is configured as a voltage source that supplies an AC voltage to the series circuit of the shunt resistor 4 and the correction resistor 5. As described above, in the above configuration, the resistance value correction circuit 53 for correcting the resistance value for detection is configured by the correction resistor 5, the signal application unit 52, the first voltage detection unit 7, the second voltage detection unit 8, and the correction unit 16.

[0089] (Detailed Configuration of Signal Application Unit)

[0090] A specific example of the signal application unit 52 includes a first configuration example illustrated in Figure 8 , a second configuration example illustrated in Figure 9 , and the like.

[0091] [1] First Configuration Example

[0092] As Figure 8As shown, the signal applying unit 52a of the first configuration example includes a transistor 61, a signal generating unit 62, an OP amplifier 63, etc. The transistor 61 is, for example, an N-channel MOSFET, a drain of which is connected to a power supply line 64 supplied with a power supply voltage VDD such as +5V, and a source of which is connected to the ground via the correction resistor 5 and the shunt resistor 4.

[0093] The signal generating unit 62 generates and outputs a pulse wave signal or a sine wave signal having the same frequency as the AC voltage applied to the series circuit of the shunt resistor 4 and the correction resistor 5. The output signal of the signal generating unit 62 is supplied to the non-inverting input terminal of the OP amplifier 63. The inverting input terminal of the OP amplifier 63 is connected to the source of the transistor 61, and its output terminal is connected to the gate of the transistor 61. According to the above configuration, the transistor 61 is driven by the OP amplifier 63 so that the AC signal, which is an AC voltage, is applied to the series circuit of the shunt resistor 4 and the correction resistor 5. As described above, the signal applying unit 52a of the first configuration example is configured to be driven by an amplifier.

[0094] [2] Second configuration example

[0095] like Figure 9 As shown, the signal applying unit 52b of the second configuration example is Figure 8 The signal application unit 52a of the first configuration example shown is different in that a buffer 65 is provided instead of the OP amplifier 63. In this case, the output signal of the signal generation unit 62 is supplied to the input terminal of the buffer 65. The output terminal of the buffer 65 is connected to the gate of the transistor 61. According to the above configuration, the transistor 61 is driven by the buffer 65 so that an AC signal, which is an AC voltage, is applied to the series circuit of the shunt resistor 4 and the correction resistor 5. As described above, the signal application unit 52b of the second configuration example has a buffer drive configuration.

[0096] [3] Characteristics of each configuration example

[0097] According to the first configuration example of the amplifier drive configuration, the source voltage of the transistor 61 is controlled to be constant by the operation of the OP amplifier 63, so that the first configuration example has an advantage over the second configuration example of the buffer drive configuration, making it possible to improve the accuracy of the AC current voltage applied to the series circuit of the shunt resistor 4 and the correction resistor 5. On the other hand, according to the second configuration example, compared with the first configuration example, by using the buffer 65 instead of the OP amplifier 63, there is an advantage in being able to suppress the circuit scale to a smaller size.

[0098] As described above, the current sensor 51 of the present embodiment includes a resistance value correction circuit 53 capable of performing the same operation as the resistance value correction circuit 17 of the first embodiment, in addition to the feature that the AC signal applied to the series circuit of the shunt resistor 4 and the correction resistor 5 is changed from an AC current to an AC voltage at the time of correction in the first embodiment. Therefore, in the present embodiment, it is also possible to correct the resistance value for detection in the same manner as the first embodiment, and the same effects as the first embodiment can be obtained.

[0099] (Third Embodiment)

[0100] Reference Figures 10 to 13 A third embodiment of the present disclosure is described.

[0101] As Figure 10 illustrated, the current sensor 71 of the present embodiment adds a switching unit 72 to the current sensor 1 of the first embodiment illustrated in Figure 1 , and has a control unit 73 instead of the control unit 9, which are different from the first embodiment. The switching unit 72 includes, for example, a multiplexer or the like, and switches the connection state between each terminal of the shunt resistor 4 and the correction resistor 5 and each input terminal of the first voltage detection unit 7 and the second voltage detection unit 8. The operation of the switching unit 72 is controlled by the control unit 73.

[0102] Specifically, the switching unit 72 switches to three connection states including a first connection state as illustrated in Figure 11 , a second connection state as illustrated in Figure 12 , and a third connection state as illustrated in Figure 13 . As illustrated in Figure 11 , in the first connection state, each terminal of the shunt resistor 4 is connected to each input terminal of the first voltage detection unit 7, and each terminal of the correction resistor 5 is connected to each input terminal of the second voltage detection unit 8. That is, the first connection state is the same connection state as the current sensor 1 of the first embodiment which does not have the switching unit 72.

[0103] As illustrated in Figure 12 , in the second connection state, each terminal of the correction resistor 5 is connected to each input terminal of the first voltage detection unit 7, and each terminal of the correction resistor 5 is connected to each input terminal of the second voltage detection unit 8. As illustrated in Figure 13 , in the third connection state, each terminal of the correction resistor 5 is connected to each input terminal of the first voltage detection unit 7, and each terminal of the shunt resistor 4 is connected to each input terminal of the second voltage detection unit 8.

[0104] The control unit 73 is different from the control unit 9 in that a function block of the gain error reduction unit 74 is added. In the above configuration, the resistance value correction circuit 75 that corrects the resistance value of the detection resistance value is configured by the correction resistor 5, the signal application unit 6, the first voltage detection unit 7, the second voltage detection unit 8, the correction unit 16, and the gain error reduction unit 74. The gain error reduction unit 74 reduces the gain error of the first A / D converter 11 of the first voltage detection unit 7 and the second A / D converter 13 of the second voltage detection unit 8.

[0105] The gain error reduction unit 74 switches the connection state of the switching unit 72 to the first connection state when the operation of reducing the gain error is not performed, that is, at normal time or at correction of the detection resistance value. Then, the gain error reduction unit 74 reduces the gain error of the first A / D converter 11 and the second A / D converter 13 by switching the connection state of the switching unit 72 to the second connection state or the third connection state.

[0106] That is, in the second connection state, both the first voltage detection unit 7 and the second voltage detection unit 8 can detect the terminal voltage of the correction resistor 5. Then, signals representing these detection values are supplied to the gain error reduction unit 74. Therefore, in the second connection state, the gain error reduction unit 74 reduces the gain error of the first A / D converter 11 and the second A / D converter 13 based on the detection value of the terminal voltage of the correction resistor 5 detected by the first voltage detection unit 7 and the detection value of the terminal voltage of the correction resistor 5 detected by the second voltage detection unit 8. In this case, the gain error reduction unit 74 can perform correction, for example, such that the gains of the first A / D converter 11 and the second A / D converter 13 are the same.

[0107] In the first connection state, the first voltage detection unit 7 can detect the terminal voltage of the shunt resistor 4, and the second voltage detection unit 8 can detect the terminal voltage of the correction resistor 5. In the third connection state, the first voltage detection unit 7 can detect the terminal voltage of the correction resistor 5, and the second voltage detection unit 8 can detect the terminal voltage of the shunt resistor 4, which are opposite to the first connection state. Then, signals representing these detection values are supplied to the gain error reduction unit 74.

[0108] Accordingly, the gain error reduction unit 74 reduces the gain error of the first A / D converter 11 and the second A / D converter 13 based on the detected value of the terminal voltage of the shunt resistor 4 detected by the first voltage detection unit 7 in the first connection state and the detected value of the terminal voltage of the shunt resistor 4 detected by the second voltage detection unit 8 in the third connection state. Further, the gain error reduction unit 74 reduces the gain error of the first A / D converter 11 and the second A / D converter 13 based on the detected value of the terminal voltage of the correction resistor 5 detected by the second voltage detection unit 8 in the first connection state and the detected value of the terminal voltage of the correction resistor 5 detected by the first voltage detection unit 7 in the third connection state. In these cases, the gain error reduction unit 74 can reduce the gain error by, for example, averaging the two detected values to cancel out each gain error.

[0109] As described above, the resistance value correction circuit 75 of the current sensor 71 of the present embodiment includes the gain error reduction unit 74 for reducing each gain error of the first A / D converter 11 of the first voltage detection unit 7 and the second A / D converter 13 of the second voltage detection unit 8. According to such a configuration, the gain error of the first A / D converter 11 and the second A / D converter 13 can be reduced to a very small value, such as 0.1%. Accordingly, according to the present embodiment, the detection accuracy of the first voltage detection unit 7 on the terminal voltage of the shunt resistor 4 and the detection accuracy of the second voltage detection unit 8 on the terminal voltage of the correction resistor 5 are further improved, and as a result, the accuracy of the correction of the detected resistance value is further improved.

[0110] (Fourth Embodiment)

[0111] The fourth embodiment will be described below with reference to Figure 14 the drawings.

[0112] As Figure 14 shown, the current sensor 81 of the present embodiment differs from the current sensor 1 of the first embodiment shown in Figure 1 in that a temperature sensor 82 is added, and the current sensor 81 has a control unit 83 instead of the control unit 9. The temperature sensor 82 is disposed in the vicinity of the shunt resistor 4 and outputs a first temperature detection signal according to the temperature of the shunt resistor 4. The control unit 83 differs from the control unit 9 in that functional blocks such as a first temperature detection unit 84 and a current value correction unit 85 are added.

[0113] In the above configuration, the resistance value correction circuit 86 that corrects the resistance value of the detection resistance value is provided by the correction resistor 5, the signal application unit 6, the first voltage detection unit 7, the second voltage detection unit 8, the correction unit 16, the first temperature detection unit 84, and the current value correction circuit 85. The first temperature detection unit 84 detects the temperature of the shunt resistor 4 based on the temperature detection signal output from the temperature sensor 82. The current value correction circuit 85 cooperates with the correction unit 16 to perform the following operation. That is, the current value correction circuit 85 corrects the detection resistance value based on the calculated resistance value and the temperature detection value of the first temperature detection unit 84 as the first temperature detection value. Specifically, the current value correction circuit 85 corrects the detection resistance value based on the calculated resistance value after grasping the temperature of the shunt resistor 4 based on the first temperature detection value, and finally corrects the detection value of the detection target current. In this way, the current value correction circuit 85 corrects the detection value of the detection target current based on the first temperature detection value.

[0114] As described above, the resistance value correction circuit 86 of the current sensor 81 of the present embodiment includes the current value correction circuit 85 that corrects the detection resistance value, and finally corrects the detection value of the detection target current based on the first temperature detection value as the detected temperature of the first temperature detection unit 84 in cooperation with the first temperature detection unit 84 that detects the temperature of the shunt resistor 4. According to such a configuration, it is possible to correct the detection resistance value with high precision and correct the detection target current with high precision, taking into account the temperature characteristics of the resistance value of the shunt resistor 4.

[0115] (Fifth Embodiment)

[0116] The fifth embodiment will be described below with reference to Figure 15 the drawings.

[0117] As Figure 15 shown, the current sensor 91 of the present embodiment differs from the current sensor 81 of the fourth embodiment shown in Figure 14 in that a temperature sensor 92 is added, and the current sensor 91 has a control unit 93 instead of the control unit 83. The temperature sensor 92 is provided in the vicinity of the correction resistor 5 and outputs a second temperature detection signal corresponding to the temperature of the correction resistor 5. The control unit 93 differs from the control unit 83 in that a function block of a second temperature detection unit 94 is added, and a current value correction circuit 95 is provided instead of the current value correction circuit 85.

[0118] In the above configuration, the resistance value correction circuit 96 that corrects the resistance value of the detection resistance value is configured by the correction resistor 5, the signal application unit 6, the first voltage detection unit 7, the second voltage detection unit 8, the correction unit 16, the first temperature detection unit 84, the second temperature detection unit 94, and the current value correction unit 95. The second temperature detection unit 94 detects the temperature of the correction resistor 5 based on the second temperature detection signal output from the temperature sensor 92. In addition to the same operation as the current value correction unit 85, the current value correction unit 95 cooperates with the correction unit 16 to perform the following operation. That is, the current value correction unit 95 corrects the correction resistor value based on the second temperature detection value that is the detected temperature of the second temperature detection unit 94, and calculates the calculation resistance value using the corrected correction resistor value. In other words, the current value correction unit 95 corrects the calculated resistance value based on the second temperature detection value. Then, the current value correction unit 95 corrects the detection resistance value based on the corrected calculation resistance value and the first temperature detection value, and finally corrects the detection value of the detection target current. As described above, the current value correction unit 95 corrects the detection value of the detection target current based on the first temperature detection value and the second temperature detection value.

[0119] As described above, the resistance value correction circuit 96 of the current sensor 91 of the present embodiment has the first temperature detection unit 84 that detects the temperature of the shunt resistor 4, and the second temperature detection unit 94 that detects the temperature of the correction resistor 5, and the current value correction unit 95. In this case, the current value correction unit 95 corrects the detection resistance value based on the first temperature detection value that is the temperature detection value of the first temperature detection unit 84 and the second temperature detection value that is the temperature detection value of the second temperature detection unit 94, and further corrects the detection value of the detection target current. According to such a configuration, not only the temperature characteristics of the resistance value of the shunt resistor 4 are considered, but also the temperature characteristics of the resistance value of the correction resistor 5 are considered, and the detection resistance value is corrected with high precision, and finally the detection target current is detected with high precision.

[0120] (Other Embodiments)

[0121] The present disclosure is not limited to the embodiments that have been described above and shown in the drawings, but can be freely modified, combined, or extended without departing from the spirit of the present disclosure.

[0122] The numerical values and the like shown in the above embodiments are examples, and are not limited to those examples.

[0123] The specific configuration of the signal application units 6 and 52 can not be limited to the configuration described in each of the above embodiments, and can be any configuration as long as the feature applies the AC signal to the series circuit of the shunt resistor 4 and the correction resistor 5.

[0124] The specific configuration of the first synchronous detection circuit 12 can not be limited to the configuration described in each of the above-described embodiments, and can be any configuration as long as the signal of the terminal of the feature input shunt resistor 4 is input 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 of the terminal of the correction resistor can be input, and synchronous detection is performed at the same frequency as the frequency of the AC signal to extract and output the signal.

[0125] Although the present disclosure has been described in accordance with the embodiments, it is understood that the present disclosure is not limited to the above-described embodiments or configurations. The present disclosure incorporates various modifications and changes within the equivalent range. Furthermore, various combinations and forms, and further, other combinations and forms including only one element or more or less than these elements are also within the spirit and scope of the present disclosure.

Claims

1. A current sensor for detecting a detection target current based on a terminal voltage of a shunt resistor (4) arranged in series in a path through which the detection target current flows and a current detection resistance value corresponding to the resistance value of the shunt resistor, the current sensor comprising: A resistance value correction circuit (17, 53, 75, 86, 96) for correcting the current detection resistance value, wherein: The resistance value correction circuit includes: a correction resistor (5) connected in series with the shunt resistor in a path different from the path through which the detection target current flows and having a higher resistance accuracy than the shunt resistor; a signal applying unit (6, 52) that applies an AC signal to a series circuit of the shunt resistor and the correction resistor; a first voltage detection unit (7) that detects the terminal voltage of the shunt resistor when the AC signal is applied to the series circuit; a second voltage detection unit (8) that detects a terminal voltage of the correction resistor when the AC signal is applied to the series circuit; and A correction unit (16) calculates the resistance value of the shunt resistor based on a first voltage detection value and a second voltage detection value, and corrects the current detection resistance value based on the calculated resistance value, wherein the first voltage detection value is a detection value of the terminal voltage detected by the first voltage detection unit, the second voltage detection value is a detection value of the terminal voltage detected by the second voltage detection unit, and the calculated resistance value is a calculated resistance value of the shunt resistor.

2. The current sensor according to claim 1, wherein: The first voltage detection unit includes a first synchronous detection circuit (12) that inputs a signal from a terminal of the shunt resistor and synchronously detects the signal at the same frequency as the AC signal to extract and output the signal; the first voltage detection unit being configured to detect the terminal voltage of the shunt resistor based on an output signal of the first synchronous detection circuit; The second voltage detection unit includes a second synchronous detection circuit (14) that inputs a signal of a terminal of the correction resistor and synchronously detects the signal at the same frequency as the AC signal to extract and output the signal; as well as The second voltage detection unit is configured to detect the terminal voltage of the correction resistor based on an output signal of the second synchronous detection circuit.

3. The current sensor according to claim 1, wherein: The first voltage detection unit includes a first A / D converter (11) that performs an A / D conversion operation to detect the terminal voltage of the shunt resistor and the terminal voltage of the correction resistor; The second voltage detection unit includes a second A / D converter (13) that performs an A / D conversion operation to detect the terminal voltage of the shunt resistor and the terminal voltage of the correction resistor; and The resistance value correction circuit (75) further includes: a switching unit (72) that switches a connection state so that each of the first A / D converter and the second A / D converter is connected to each of the shunt resistor and the correction resistor, respectively; and A gain error reducing unit (74) reduces the gain error of the first A / D converter and the second A / D converter by switching the connection state of the switching unit.

4. The current sensor according to claim 1, wherein: The resistance value correction circuit (86, 96) further includes: a first temperature detection unit (84) that detects the temperature of the shunt resistor; and A current value correction unit (85, 95) corrects the detection value of the detection target current based on a first temperature detection value that is the temperature detected by the first temperature detection unit.

5. The current sensor according to claim 4, wherein: The resistance value correction circuit (96) further includes a second temperature detection unit (94) for detecting the temperature of the correction resistor; and The current value correction unit (95) corrects the detection value of the detection target current based on the first temperature detection value and a second temperature detection value which is the temperature detected by the second temperature detection unit.

6. The current sensor according to any one of claims 1 to 4, wherein: The signal applying unit applies the AC signal having a pulse wave or a sine wave to the series circuit.

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