Current sensor device

Abstract

To provide an electric current sensor device that is hardly influenced by a temperature change and can perform current detection accurately.SOLUTION: In an electric current sensor device 10, a magnetic core 12 is annular, and a primary conductor 50 is inserted inside the magnetic core. A load 143 of a drive circuit 14 is a secondary conductor 151 that is wound around the magnetic core 12. A detection resistor 16 converts a current flowing in the secondary conductor 151 into a voltage and generates a detection voltage at one end of the detection resistor. A drive portion 141 switches the direction of the current flowing in the secondary conductor 151 on the basis of pulse signals. A detection portion 20 detects a current that has flowed in the primary conductor 50 on the basis of a duty ratio of the pulse signals. A pulse signal generation circuit 18 monitors the detection voltage generated at one end of the detection resistor 16 and inverts on / off of the pulse signals. A clock generation portion 201 of the detection portion 20 generates clock signals at a predetermined period. A counter 211 counts the duty ratio of the pulse signals using the clock signals.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a current sensor device, and particularly to a fluxgate type current sensor device.

Background Art

[0002] Patent Document 1 discloses an example of a fluxgate type current sensor.

[0003] As shown in FIG. 17, in the current sensor 90 described in Patent Document 1, the voltage generated at the center tap of the winding 903 wound around the magnetizable member 901 and the reference voltage are compared by a comparator 905. The comparison result of the comparator 905 is supplied to the flip-flop 907. The flip-flop 907 outputs a "1" signal or a "0" signal according to the output of the comparator 905. The "1" signal and the "0" signal are respectively input to the AND circuits 909 and 911, and the logical product with the clock signal Ck is obtained. The AND circuit 909 outputs the number of clock pulses corresponding to the duration of the "1" signal, and the AND circuit 911 outputs the number of clock pulses corresponding to the duration of the "0" signal. The outputs of the AND circuits 909 and 911 are input to the up-down counter 913, and its count value is incremented or decremented. The count value of the up-down counter 913 represents the difference between the duration of the "1" signal and the duration of the "0" signal for each period defined by consecutive "1" signals and "0" signals. This difference depends on the magnitude of the current flowing through the winding 920 wound around the magnetizable member 901. Therefore, the magnitude of the current flowing through the winding 920 can be known based on the count value of the up-down counter 907.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The current sensor 90 in Patent Document 1 determines the magnitude of the current flowing through the winding 920 based on the difference between the number of clock pulses corresponding to the duration of the "1" signal and the number of clock pulses corresponding to the duration of the "0" signal. However, this method may produce errors due to changes in the characteristics of the magnetizing member 901 caused by temperature changes. Specifically, the duration of the "1" signal and the duration of the "0" signal fluctuate under the influence of temperature changes. On the other hand, the clock signal Ck is substantially unaffected by temperature changes. As a result, the outputs of the AND circuits 909 and 911 are affected by temperature changes, and the magnitude of the detected current is affected by temperature changes.

[0006] The present invention aims to provide a current sensor device that is less susceptible to the effects of temperature changes and can accurately detect current. [Means for solving the problem]

[0007] The present invention provides a current sensor device for detecting the current flowing through a primary conductor, as a first current sensor device. It comprises a magnetic core, a drive circuit, a detection resistor, a pulse signal generation circuit, and a detection unit. The magnetic core is annular in shape, with the primary conductor passing through its interior. The aforementioned drive circuit includes a drive unit and a load, The load is a secondary conductor wound around the magnetic core, The aforementioned detection resistor is connected in series with the drive circuit, converts the current flowing through the secondary conductor into a voltage, and generates a detection voltage at one end thereof. The pulse signal generation circuit generates a pulse signal according to the detected voltage, The drive unit switches the direction of the current flowing through the secondary conductor based on the pulse signal, The detection unit detects the current flowing through the primary conductor based on the duty cycle of the pulse signal. The pulse signal generation circuit monitors the detection voltage generated at one end of the detection resistor and inverts the pulse signal between on and off states. The detection unit comprises a clock generation unit and a counter. The aforementioned clock generation unit generates a clock signal with a predetermined period, The counter counts the duty cycle of the pulse signal using the clock signal. We provide a current sensor device.

[0008] Furthermore, the present invention provides a second current sensor device, which is a first current sensor device, The aforementioned path switching circuit is an H-bridge circuit having four switches. We provide a current sensor device.

[0009] Furthermore, the present invention provides a third current sensor device, which is a first or second current sensor device, The pulse signal generation circuit compares the detected voltage with a predetermined threshold voltage and inverts the pulse signal's on and off state each time the detected voltage exceeds the predetermined threshold voltage. The predetermined threshold voltage is set in advance, taking into consideration the magnetic saturation of the magnetic core. We provide a current sensor device.

[0010] Furthermore, the present invention provides a fourth current sensor device which is any of the first to third current sensor devices, The aforementioned drive circuit further includes a chopper circuit as the load, The secondary conductor is connected to the drive unit via the chopper circuit. We provide a current sensor device.

[0011] Furthermore, the present invention provides a fifth current sensor device, which is any of the first to fourth current sensor devices, The current sensor device further comprises a temperature sensor and a correction value storage unit that stores temperature and correction value in association. The correction value is based on the sensitivity of the current sensor device and the temperature change of the offset output. The detection unit obtains a correction value corresponding to the detected temperature from the correction value storage unit according to the detected temperature detected by the temperature sensor, and corrects the detection of the current flowing through the primary conductor using the correction value. A current sensor device is provided.

[0012] Further, the present invention provides a sixth current sensor device, which is any one of the current sensor devices from the first to the fifth, The current sensor device further includes an overcurrent detection unit. The overcurrent detection unit monitors the frequency of the pulse signal and issues an overcurrent flag when the frequency exceeds a predetermined frequency. A current sensor device is provided.

[0013] Further, the present invention provides a seventh current sensor device, which is any one of the current sensor devices from the first to the sixth, The current sensor device further includes a self-diagnosis unit. The self-diagnosis unit has an additional conductor at least partially passed inside the magnetic core and a current supply unit for supplying current to the additional conductor during testing. A current sensor device is provided.

[0014] Further, the present invention provides an eighth current sensor device, which is any one of the current sensor devices from the first to the seventh, The detection resistor is selected from a plurality of pre-provided resistors according to the magnetic core. A current sensor device is provided.

[0015] Further, the present invention provides a ninth current sensor device, which is any one of the current sensor devices from the first to the eighth, The current sensor device further includes a shield case. The magnetic core is formed by winding a strip-shaped magnetic material. The magnetic body has two ends, The shield case is provided with an opening, Both ends of the secondary conductor are drawn out of the shield case through the opening and are connected to the drive circuit outside the shield case. When the shield case is equally divided into two regions, a first region close to the opening and a second region far from the opening, both ends of the magnetic body are located in the second region. A current sensor device is provided.

Effect of the Invention

[0016] The current sensor device of the present invention detects the current flowing through the primary conductor based on the duty ratio of the pulse signal. Even if the period of the pulse signal fluctuates due to temperature change, its duty ratio is hardly affected by the temperature change. Therefore, the duty ratio of the pulse signal accurately reflects the current flowing through the primary conductor. Thus, the current sensor device of the present invention is hardly affected by temperature change and can accurately detect current.

Brief Description of the Drawings

[0017] [Figure 1] It is a circuit block diagram showing a current sensor device according to an embodiment of the present invention. [Figure 2] It is a circuit block diagram showing the main part of the current sensor device in FIG. 1. For simplicity of explanation, the chopper circuit has been removed. [Figure 3] It is a graph showing the B-H curve of the magnetic core included in the main part of FIG. 2, and is a graph showing the B-H curve when no current is flowing through the primary conductor. [Figure 4] It is a graph showing the B-H curve of the magnetic core included in the main part of FIG. 2, and is a graph showing the B-H curve when an arbitrary current is flowing through the primary conductor. [Figure 5] It is a circuit block diagram showing the pulse signal generation circuit included in the main part of FIG. 2 and the first direction of the current flowing through the secondary conductor. [Figure 6]Figure 5 shows the BH curve of the magnetic core as seen from the secondary conductor, and a graph showing the changes in magnetic flux density B and magnetic field H caused by the current flowing through the secondary conductor in the pulse signal generation circuit. [Figure 7] Figure 2 is a circuit block diagram showing the pulse signal generation circuit included in the main part, and the second direction of current flowing through the secondary conductor. [Figure 8] Figure 7 shows the BH curve of the magnetic core as seen from the secondary conductor, and a graph illustrating the changes in magnetic flux density B and magnetic field H caused by the current flowing through the secondary conductor in the pulse signal generation circuit. [Figure 9] Figures 5 and 7 are time charts showing the time variation of the voltage at each part of the pulse signal generation circuit. [Figure 10] Figures (a), (b), (c), and (d) show the four states determined by the combination of the state of the chopper circuit and the state of the H-bridge circuit included in the current sensor device of Figure 1, along with the current flow in each state and the BH characteristics of the magnetic core as seen from the secondary conductor. [Figure 11] This is a time chart showing the time variation of the pulse signal VH supplied to the delay circuit in the current sensor device shown in Figure 1, and the time variation of the output voltage VCH of the 1 / n frequency divider supplied to the chopper circuit. The letters in parentheses correspond to Figures 10(a), 10(b), 10(c), and 10(d). [Figure 12] This graph shows the effect of temperature compensation in the detection unit included in the current sensor device shown in Figure 1. [Figure 13] This figure illustrates a method for measuring the over-input characteristics of the magnetic core included in the current sensor device shown in Figure 1. [Figure 14] This is a schematic diagram showing the first positional relationship between a pair of ends of a strip-shaped magnetic material that forms the magnetic core included in the current sensor device shown in Figure 1, and the opening of the shield case that houses the magnetic core. [Figure 15] This is a schematic diagram showing the second positional relationship between a pair of ends of a strip-shaped magnetic material that forms the magnetic core included in the current sensor device shown in Figure 1, and the opening of the shield case that houses the magnetic core. [Figure 16]This graph illustrates the allowable over-input characteristics of the magnetic core included in the current sensor device shown in Figure 1. [Figure 17] This is a circuit block diagram showing the current sensor disclosed in Patent Document 1. [Modes for carrying out the invention]

[0018] Referring to Figure 1, the current sensor device 10 according to one embodiment of the present invention comprises a magnetic core 12, a drive circuit 14, a detection resistor 16, a pulse signal generation circuit 18, and a detection unit 20.

[0019] Referring to Figure 2, the magnetic core 12 is annular. Preferably, the magnetic core 12 has high magnetic permeability. A primary conductor 50 is passed inside the magnetic core 12. The current sensor device 10 according to this embodiment is a current sensor device that detects the current flowing through this primary conductor 50.

[0020] As shown in Figure 1, the drive circuit 14 includes a drive unit 141 and a load 143. In this embodiment, the drive unit 141 is an H-bridge circuit 141 having four switches 145. In this embodiment, the load 143 includes a secondary conductor 151 and a chopper circuit 153. However, the chopper circuit 153 is not essential in this invention. Therefore, Figure 2 shows the drive circuit 14 with the chopper circuit 153 omitted. In the following description, the chopper circuit 153 will be omitted. The chopper circuit 153 will be described later with reference to Figures 10 and 11.

[0021] As shown in Figure 2, the secondary conductor 151 is wound around the magnetic core 12 and connected to the H-bridge circuit 141. The H-bridge circuit 141 is connected to a predetermined power supply. The H-bridge circuit 141 is a circuit that switches the direction of the current flowing through the secondary conductor 151 between a first direction and a second direction. The first direction and the second direction are opposite to each other.

[0022] As can be seen from Figure 1 or Figure 2, the drive circuit 14 in this embodiment energizes the magnetic core 12 using a single secondary conductor 151. Therefore, compared to known drive circuits that use a pair of secondary conductors, manufacturing variations are reduced and it is easier to achieve the desired characteristics.

[0023] As shown in Figure 2, the detection resistor 16 is connected in series with the drive unit 141. The detection resistor 16 may consist of a single resistor. However, it is preferable to have multiple resistors and to select one from among them according to the characteristics of the magnetic core 12. The detection resistor 16 converts the current flowing through the secondary conductor 151 into a voltage and generates detection voltages VRs at one end. More specifically, the detection resistor 16 generates detection voltages VRs at the connection point between the detection resistor 16 and the H-bridge circuit 141.

[0024] As shown in Figure 2, the pulse signal generation circuit 18 includes a comparator 181, a T flip-flop 183, and an inverter 185. A predetermined threshold voltage Vth (not shown) is input to the comparator 181. The predetermined threshold voltage Vth is preset considering the magnetic saturation of the magnetic core 12. In this embodiment, a T flip-flop 183 is used, but other means may be used.

[0025] As can be seen from Figure 2, the comparator 181 compares the detection voltages VRs generated at one end of the detection resistor 16 with a predetermined threshold voltage Vth. The comparator 181 changes its output voltage VC according to the comparison result. Specifically, it outputs an output voltage VC that turns on when the detection voltages VRs exceed the predetermined threshold voltage Vth, and turns off when they fall below it.

[0026] Each time the T flip-flop 183 detects a rising (or falling) edge of the output voltage VC from the comparator 181, it inverts the on and off state of its output pulse signal VH. The pulse signal VH is sent directly to the drive unit 141 as pulse signal VH1. The pulse signal VH is also inverted in the inverter 185 and sent to the drive unit 141 as pulse signal VH2. In this way, the pulse signal generation circuit 18 monitors the detected voltages VRs generated at one end of the detection resistor 16 and generates pulse signals VH (VH1, VH2) according to the detected voltages VRs. In other words, the pulse signal generation circuit 18 inverts the on and off state of the pulse signal VH each time the detected voltages VRs exceed the predetermined threshold voltage Vth, based on the comparison result between the detected voltages VRs and the predetermined threshold voltage Vth.

[0027] As can be seen from Figure 2, the pulse signal VH1 from the T flip-flop 183 controls switches SW2 and SW4 of the switches 145 that make up the drive unit 141. Specifically, pulse signal VH1 controls one of switches SW2 and SW4 to be turned on (or off) and the other to be turned off (or on). In addition, pulse signal VH2 from the inverter 185 controls switches SW1 and SW3 of the switches 145 that make up the drive unit 141. Specifically, pulse signal VH2 controls one of switches SW1 and SW3 to be turned on (or off) and the other to be turned off. Since pulse signal VH2 is the inverse of pulse signal VH1, switch SW1 is turned on or off simultaneously with switch SW4, and switch SW3 is turned on or off simultaneously with switch SW2. The drive unit 141 controls the direction of the current flowing through the secondary conductor 151 according to the on / off states of switches SW1, SW2, SW3, and SW4. In this way, the drive unit 141 of the drive circuit 14 switches the direction of the current flowing through the secondary conductor 151 based on the pulse signals VH1 and VH2 from the pulse signal generation circuit 18.

[0028] Here, we assume that in an ideal current sensor device 10, no current is flowing through the primary conductor 50. In this case, the drive circuit 14 and the pulse signal generation circuit 18 operate such that the duty cycle of the pulse signal VH is 50%. In other words, in an ideal current sensor device 10, when no current is flowing through the primary conductor 50, the drive circuit 14 and the pulse signal generation circuit 18 operate such that the off-period and on-period of the pulse signal VH are equal to each other.

[0029] Referring again to Figure 1, the detection unit 20 comprises a clock generation unit 201 and a counter 211. The clock generation unit 201 generates a clock signal with a predetermined period that is sufficiently short compared to the period of the pulse signal VH. In other words, the clock generation unit 201 generates a clock signal with a predetermined frequency that is sufficiently high compared to the frequency of the pulse signal VH.

[0030] Counter 211 uses the clock signal to count the duty cycle of the pulse signal VH. More specifically, counter 211 counts the clock pulses corresponding to the off-period and on-period of each cycle of the pulse signal VH.

[0031] As shown in Figure 1, the detection unit 20 further includes a duty cycle conversion unit 213, a temperature compensation circuit 22, a temperature sensor 24, a filter circuit 215, and a comparator 217. However, the temperature compensation circuit 22 and the temperature sensor 24 are not essential in this invention.

[0032] As can be seen from Figure 1, the duty cycle conversion unit 213 generates a duty cycle signal representing the duty cycle of the pulse signal VH based on the count value of the counter 211. This duty cycle signal changes depending on the current (detected current) flowing through the primary conductor 50.

[0033] The duty cycle signal from the duty cycle conversion unit 213 is input to the filter circuit 215 via the temperature compensation circuit 22. The temperature compensation circuit 22 and the temperature sensor 24 will be described later. The filter circuit 215 integrates the duty cycle signal. The integrated duty cycle signal is compared with a predetermined threshold (alert current) in the comparator 217. The comparator 217 outputs a detection signal indicating whether or not current has flowed through the primary conductor 50, depending on the comparison result. The comparator 217 can support thresholds for DC current, AC current, and overcurrent detection as predetermined thresholds. When the comparator 217 supports thresholds for DC current, AC current, and overcurrent detection, it outputs detection signals for DC current, AC current, and overcurrent detection to the corresponding output terminals.

[0034] As described above, the detection unit 20 detects the current flowing through the primary conductor 50 based on the duty cycle of the pulse signal VH. The duty cycle is less affected even when the period of the pulse signal VH is affected by temperature changes. Therefore, compared to the current sensor in Patent Document 1, which detects current based on the difference between the number of clock pulses corresponding to the on period of the pulse signal and the number of clock pulses corresponding to the off period, this unit can detect current with higher accuracy.

[0035] The operation of the drive circuit 14 and the pulse signal generation circuit 18 will be described in detail below. In Figure 5, the switch 145 of the drive unit 141 is configured using a pair of CMOS sensors.

[0036] Here, we assume that the magnetic core 12 has characteristics represented by a BH curve as shown in Figure 3. In this case, when current flows through the primary conductor 50 passing inside the magnetic core 12, the BH curve of the magnetic core 12 shifts towards the strong magnetic field side as shown in Figure 4. Under this influence, the duty cycle of the pulse signal VH generated by the pulse signal generation circuit 18 changes as follows. Note that when no current flows through the primary conductor 50, the duty cycle of the pulse signal VH is assumed to be 50%.

[0037] As shown in Figure 5, when switches QP1 and QN1 are ON and switches QP2 and QN2 are OFF, a current I1 in the first direction flows through the secondary conductor 151. At this time, the BH characteristics of the magnetic core 12 as seen from the secondary conductor 151 are as shown in Figure 6.

[0038] As shown in Figure 7, when switches QP1 and QN1 are off and switches QP2 and QN2 are on, a current I2 in the second direction flows through the secondary conductor 151. At this time, the BH characteristics of the magnetic core 12 as seen from the secondary conductor 151 are as shown in Figure 8.

[0039] As can be seen from Figure 9, when current flows through the secondary conductor 151, the detected voltage VRs rises in proportion to the magnitude of the current. When the detected voltage VRs exceeds a predetermined threshold voltage Vth, the output voltage VC of the comparator 181 changes from off to on. When the output voltage VC of the comparator 181 changes from off to on, the output voltage VH of the T flip-flop 183 changes from off to on or from on to off in accordance with its rising edge. When the output voltage VH of the T flip-flop 183 changes from off to on or from on to off, the direction of the current flowing through the secondary conductor 151 changes from the first direction (Figure 5) to the second direction (Figure 7) or from the second direction (Figure 7) to the first direction (Figure 5). At this time, the detected voltage VRs drops instantaneously. When the detected voltage VRs falls below the predetermined threshold voltage Vth, the output voltage VC of the comparator 181 changes from on to off. After that, the detected voltage VRs rises again. From here on, the drive circuit 14 and the pulse signal generation circuit 18 repeat the above operation.

[0040] As described above, the pulse signal generation circuit 18 generates a pulse signal VH with a period of one cycle consisting of a first period T1 corresponding to the time when current flows in the first direction and a second period T2 corresponding to the time when current flows in the second direction. The duty cycle of the pulse signal VH = T1 / (T1+T2) is proportional to the magnitude of the current flowing through the primary conductor 50. The current sensor device 10 of this embodiment detects the current flowing through the primary conductor 50 based on this duty cycle.

[0041] The pulse signal generation circuit 18 in this embodiment switches the pulse signal VH on and off before the detected voltages VRs saturate, using a predetermined threshold voltage Vth. This shortens the period of the pulse signal VH and increases the current detection speed of the current sensor device 10.

[0042] In the above explanation, when no current flows through the primary conductor 50, the duty cycle of the pulse signal VH is ideally 50%. However, due to variations in the on-resistance of SW1, SW2, SW3, and SW4, and the offset of the pulse signal generation circuit 18, the duty cycle of the pulse signal VH may not be 50%. The chopper circuit 153 (see Figure 1), in addition to the operation of the drive unit 141, reverses the direction of the current flowing through the secondary conductor 151. The polarity of the offset does not change even when the direction of the current flowing through the secondary conductor 151 is reversed by the chopper circuit 153. Therefore, by using the chopper circuit 153, it is possible to cancel out the effects caused by the duty cycle of the pulse signal VH not being 50%. Note that offset is an output other than 0 that is output when the output output from the circuit should ideally be 0. The operation of the chopper circuit 153 will be explained below.

[0043] As shown in Figure 1, the secondary conductor 151 is connected to the drive unit 141 via the chopper circuit 153. The chopper circuit 153 is composed of, for example, multiple switches (not shown).

[0044] As shown in Figure 1, the current sensor device 10 further includes a delay unit 191 and a 1 / n frequency divider 193. The delay unit 191 receives either a pulse signal VH1 from the T flip-flop 183 or a pulse signal VH2 from the inverter 185.

[0045] As can be seen from Figure 1, the delay unit 191 delays the pulse signal VH so that the current reversal occurs at the appropriate timing. The 1 / n frequency divider 193 divides the delayed pulse signal VHd from the delay unit 191 by 1 / n. For example, the 1 / n frequency divider 193 divides the delayed pulse signal VHd by 1 / 4. In other words, n in the 1 / n frequency divider 193 is, for example, 2 or 4. Figure 10 shows the operation of the chopper circuit 153 when n=4, i.e., when the delayed pulse signal VHd is divided by 1 / 4.

[0046] As can be seen from Figure 10, the chopper circuit 153 alternately switches between path 1 shown in Figures 10(a) and 10(b) and path 2 shown in Figures 10(c) and 10(d). Meanwhile, the H-bridge circuit 141 switches the direction of the current flowing through the H-bridge circuit 141 between the first direction shown in Figure 10(b) or Figure 10(d) and the second direction shown in Figure 10(a) or Figure 10(c), respectively, during the periods when the chopper circuit 153 is forming path 1 and during the periods when it is forming path 2.

[0047] As shown in Figure 11, the output signal VCH of the 1 / n frequency divider 193 (see Figure 1) repeatedly switches between on and off. During the period when the output signal VCH is off, path 1 (see Figure 10(a) or Figure 10(b)) is selected in the chopper circuit 153. During this time, the pulse signal VH supplied to the H-bridge circuit 141 changes between on, off, on, and off. Also, during the period when the output signal VCH of the 1 / n frequency divider 193 is on, path 2 (see Figure 10(c) or Figure 10(d)) is selected in the chopper circuit 153. During this time, the pulse signal VH supplied to the H-bridge circuit 141 changes between on, off, on, and off.

[0048] As can be seen from Figure 11, the pulse signal VH immediately after the path is changed in the chopper circuit 153 has an extremely narrow pulse width due to transient phenomena. This pulse does not reflect the current flowing through the primary conductor 50. Therefore, after the path is changed in the chopper circuit 153, the first period of the pulse signal VH is ignored by the detection unit 20.

[0049] As can be seen from Figures 10 and 11, the on-period T1 and off-period T2 of the pulse signal VH in path 1 correspond to the periods when current flows in the second and first directions, respectively, through the secondary conductor 151. On the other hand, the on-period T1' and off-period T2' of the pulse signal VH in path 2 correspond to the periods when current flows in the first and second directions, respectively, through the secondary conductor 151. Thus, the direction of the current flowing through the secondary conductor 151 is opposite in the on-period T1 and on-period T1', and the direction of the current flowing through the secondary conductor 151 is opposite in the off-period T2 and off-period T2'. Therefore, by calculating the difference between the duty cycles of the on-period T1 and off-period T2 and the duty cycles of the on-period T1' and off-period T2', the effects of on-resistance variations between SW1, SW2, SW3, and SW4 and the offset of the pulse signal generation circuit 18 can be canceled out. In this way, the detection unit 20 can accurately detect the current flowing through the primary conductor 50 based on the duty cycle of the pulse signal VH.

[0050] Referring again to Figure 1, the temperature compensation circuit 22 and temperature sensor 24 will be described. The temperature sensor 24 detects the temperature of the current sensor device 10, preferably the temperature around the magnetic core 12, and outputs a temperature detection signal to the temperature compensation circuit 22. The temperature compensation circuit 22 includes a compensation value storage unit (not shown). The compensation value storage unit stores the temperature and the compensation value in association. The compensation value is based on the sensitivity of the current sensor device 10 and the temperature change of the offset output. The compensation value is obtained in advance by measuring the temperature characteristics of the current sensor, etc.

[0051] The temperature compensation circuit 22 reads a correction value corresponding to the detected temperature from the correction value storage unit based on the temperature detection signal from the temperature sensor 24, and uses this correction value to correct the duty cycle obtained by the duty cycle conversion unit 213. This ensures that the duty cycle is appropriately corrected according to the temperature at which the current sensor device 10 is in use. As a result, the accuracy of the current detection judgment performed in the subsequent stage is improved. In this way, the detection unit 20 obtains a correction value corresponding to the detected temperature from the correction value storage unit according to the detected temperature detected by the temperature sensor 24, and uses this correction value to correct the detection of the current flowing through the primary conductor 50.

[0052] As can be seen from Figure 12, when a constant current (4.5 mA) flowing through the primary conductor 50 is detected by the current sensor device 10, the detected current value will change depending on the temperature if temperature compensation is not performed. On the other hand, when temperature compensation is performed, the current value detected by the current sensor device 10 will be an almost constant value, independent of the temperature. Therefore, the current sensor device 10 of this embodiment can perform highly accurate current detection over a wide temperature range by suppressing the effects of temperature changes by using a duty cycle and by actively performing temperature compensation.

[0053] As shown in Figure 1, the current sensor device 10 of this embodiment further includes a self-diagnosis unit 28. The self-diagnosis unit 28 includes an additional conductor 281 and a self-test drive circuit (current supply unit) 283. The additional conductor 281 is at least partially routed inside the magnetic core 12. In this embodiment, the additional conductor 281 is a coil wound around the magnetic core 12. The self-test drive circuit 283 supplies current to the additional conductor 281 during testing.

[0054] As can be seen from Figure 1, when performing a test, an external command to execute the test is given to the self-test drive circuit 283, which then supplies a predetermined DC or AC test current to the additional conductor 281. By monitoring the output terminal of the current sensor device 10, it is possible to determine whether the test current is being detected appropriately. As the test current, the current sensor device 10 can use detectable DC current, detectable AC current, and overcurrent.

[0055] As shown in Figure 1, the current sensor device 10 of this embodiment further includes an overcurrent detection unit 30. The overcurrent detection unit 30 includes an overcurrent comparator 301, a frequency comparator 303, and an OR (logical disjunction) circuit 305.

[0056] The overcurrent comparator 301 compares the current value indicated by the duty cycle signal from the temperature compensation circuit 22 with a preset overcurrent threshold. When the current value indicated by the duty cycle signal exceeds the overcurrent threshold, the overcurrent comparator 301 outputs an overcurrent detection signal.

[0057] The frequency comparator 303 receives a preset frequency threshold Fth as input. The frequency comparator 303 determines the frequency of the pulse signal VH from the count value of the counter 211 and compares it with the frequency threshold Fth. If the frequency of the pulse signal VH exceeds the frequency Fth, the frequency comparator 303 outputs an overcurrent detection signal.

[0058] The overcurrent detection signals from the overcurrent comparator 301 and the overcurrent detection signals from the frequency comparator 303 are input to the OR circuit 305, which outputs either of the overcurrent detection signals to the outside as an overcurrent flag indicating overcurrent.

[0059] The reason why the current sensor device 10 of this embodiment includes a frequency comparator 303 in addition to the overcurrent comparator 301 in the overcurrent detection unit 30 is as follows.

[0060] The current sensor device 10 according to this embodiment employs a fluxgate method. In the fluxgate current sensor device 10, if a current significantly exceeding the expected current to be detected flows through the primary conductor 50, the frequency of the pulse signal VH increases significantly. As a result, the current sensor device 10 becomes unable to detect the current flowing through the primary conductor 50 based on the duty cycle of the pulse signal VH. The overcurrent detection unit 30 detects that a current so large that current detection based on the duty cycle of the pulse signal VH is not possible has flowed through the primary conductor 50. In this way, the overcurrent detection unit 30 monitors the frequency of the pulse signal and issues an overcurrent flag when that frequency exceeds a predetermined frequency.

[0061] Referring to Figures 13 to 15, the magnetic core 12 is housed in the shield case 32. Thus, in this embodiment, the current sensor device 10 further comprises the shield case 32. In this embodiment, the secondary conductor 151 (see Figure 1) is wound around the magnetic core 12 and is housed together with the magnetic core 12 in the shield case 32. The magnetic core 12, the secondary conductor 151, and the shield case 32 constitute the sensor unit 40.

[0062] As shown in Figures 13 to 15, the shield case 32 is provided with an opening 321. This is to allow both ends of the secondary conductor 151 wound around the magnetic core 12 to be brought out to the outside. Both ends of the secondary conductor 151 are brought out of the shield case 32 through the opening 321 and connected to the drive circuit 14 outside the shield case 32. In the current sensor device 10 according to this embodiment, both ends of the additional conductor 281 are also brought out of the shield case 32 through the opening 321. Then, both ends of the additional conductor 281 are connected to the self-test drive circuit 283 outside the shield case 32.

[0063] As can be seen from Figures 14 and 15, in this embodiment, the magnetic core 12 is formed by winding a strip of magnetic material. Therefore, the magnetic core 12 has a pair of ends 121.

[0064] As shown in Figures 14 and 15, the two ends 121 of the magnetic core 12 are positioned close together so as not to overlap. In Figure 14, the ends 121 of the magnetic core 12 are oriented in the opposite direction to the opening 321 of the shield case 32. On the other hand, in Figure 15, the ends 121 of the magnetic core 12 are oriented in the same direction as the shield case 32. Thus, there can be various positional relationships between the ends 121 of the magnetic core 12 and the shield case 32. The inventor's experiments have shown that the positional relationship between the ends 121 of the magnetic core 12 and the shield case 32 affects the characteristics of the sensor unit 40.

[0065] In the current sensor device 10 shown in Figure 1, the sensor unit 40 must have a predetermined over-input characteristic. When the sensor unit 40 and the primary conductor 50 are arranged as shown in Figure 13, and a predetermined overcurrent (e.g., 30A at 100ms) is instantaneously applied to the primary conductor 50, the duty cycle of the current sensor device 10 shows the response shown in Figure 16. The reference center line in Figure 16 (the thin line in Figure 16) indicates a duty cycle of 50%. The duty cycle changes significantly at the moment current is flowing, but it may shift slightly from 50% even when the current is turned off. This amount of shift is called the over-input characteristic, and a smaller amount indicates a smaller error. For example, as shown in Figure 16, the duty cycle 2 seconds after the current is turned off must be 0.6mA or less in terms of current. This amount of shift is called the over-input characteristic, and a smaller amount indicates a smaller error.

[0066] According to the inventor's experiments, the defect rate of the sensor unit 40 with the configuration shown in Figure 14 is low with respect to over-input characteristics. In contrast, the defect rate of the sensor unit 40 with the configuration shown in Figure 15 is high with respect to over-input characteristics. Therefore, it is preferable that the magnetic core 12 is housed in the shield case 32 such that its end 121 faces away from the opening 321 of the shield case 32. However, the orientation of the end 121 of the magnetic core 12 and the orientation of the opening 321 of the shield case 32 do not need to be directly opposite. Specifically, if the shield case 32 is divided equally into two regions, a first region close to the opening 321 and a second region far from the opening 321, the end 121 of the magnetic core 12 should both be located in the second region. Preferably, the end 121 should be located within a 45-degree range centered on the direction directly opposite to the opening 321.

[0067] Although the present invention has been described above with reference to embodiments, the present invention is not limited to the embodiments described above, and various modifications and changes are possible without departing from the spirit of the present invention. [Explanation of Symbols]

[0068] 10 Current sensor device 12 magnetic cores 121 End 14. Drive Circuit 141 Drive Unit (H-Bridge Circuit) 143 load 145 switches 151 Secondary conductor 153 Chopper Circuit 16 detection resistor 18. Pulse signal generation circuit 181 Comparator 183 T Flip-Flop 185,187 Inverter 191 Delay Element 193 1 / n frequency divider 20 Detection unit 201 Clock generation unit 211 counter 213 Duty Shift Conversion Unit 215 Filter Circuit 217 Comparator 22 Temperature compensation circuit 24 Temperature Sensors 28 Self-Diagnosis Department 281 Additional Conductors 283 Self-test drive circuit 30 Overcurrent detection unit 301 Overcurrent comparator 303 Frequency comparator 305 OR circuit (Logical OR circuit) 32 Shield Cases 321 Aperture 40 Sensor section 50 Primary conductor

Claims

[Claim 1] A current sensor device for detecting the current flowing through a primary conductor, It comprises a magnetic core, a drive circuit, a detection resistor, a pulse signal generation circuit, and a detection unit. The magnetic core is annular in shape, with the primary conductor passing through its interior. The aforementioned drive circuit includes a drive unit and a load, The load is a secondary conductor wound around the magnetic core, The aforementioned detection resistor is connected in series with the drive circuit, converts the current flowing through the secondary conductor into a voltage, and generates a detection voltage at one end thereof. The pulse signal generation circuit generates a pulse signal according to the detected voltage, The drive unit switches the direction of the current flowing through the secondary conductor based on the pulse signal, The detection unit detects the current flowing through the primary conductor based on the duty cycle of the pulse signal. The pulse signal generation circuit monitors the detection voltage generated at one end of the detection resistor and inverts the pulse signal between on and off states. The detection unit comprises a clock generation unit and a counter. The aforementioned clock generation unit generates a clock signal with a predetermined period, The counter counts the duty cycle of the pulse signal using the clock signal. The current sensor device further comprises a shielded case. The magnetic core is formed by winding a strip of magnetic material, The aforementioned shield case is provided with an opening, Both ends of the secondary conductor are led out of the shield case through the opening and connected to the drive circuit outside the shield case. The magnetic material has two ends, When the shield case is divided equally into two regions, a first region close to the opening and a second region far from the opening, the ends of the magnetic material are both located in the second region. Current sensor device.

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