Electric 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 more particularly to a fluxgate type current sensor device. [Background technology]

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

[0003] As shown in FIG. 17 , a current sensor 90 described in Patent Document 1 uses a comparator 905 to compare a voltage generated at a center tap of a winding 903 wound around a magnetizable member 901 with a reference voltage. The comparison result of the comparator 905 is supplied to a flip-flop 907. The flip-flop 907 outputs a “1” signal or a “0” signal depending on the output of the comparator 905. The “1” signal and the “0” signal are input to AND circuits 909 and 911, respectively, which perform a logical AND with a clock signal Ck. The AND circuit 909 outputs a number of clock pulses corresponding to the duration of the “1” signal, and the AND circuit 911 outputs a number of clock pulses corresponding to the duration of the “0” signal. The outputs of the AND circuits 909 and 911 are input to an up-down counter 913, which increments or decrements its count value. The count value of up / down counter 913 represents the difference between the duration of a "1" signal and the duration of a "0" signal for each period defined by successive "1" and "0" signals. This difference depends on the magnitude of the current flowing through winding 920 wound around magnetizable member 901. Therefore, the magnitude of the current flowing through winding 920 can be determined based on the count value of up / down counter 907. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 4,899,103 Summary of the Invention [Problem 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 a "1" signal and the number of clock pulses corresponding to the duration of a "0" signal. However, this method may cause errors due to changes in the characteristics of the magnetizable member 901 caused by temperature changes. Specifically, the duration of the "1" signal and the duration of the "0" signal fluctuate due to 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 also affected by temperature changes.

[0006] An object of the present invention is to provide a current sensor device that is less susceptible to the influence of temperature changes and is capable of detecting current with high accuracy. [Means for solving the problem]

[0007] The present invention provides a first current sensor device that detects a current flowing through a primary conductor, The device includes a magnetic core, a drive circuit, a detection resistor, a pulse signal generation circuit, and a detection unit, The magnetic core is annular, and the primary conductor is passed through the magnetic core. the drive circuit includes a drive unit and a load; the load is a secondary conductor wound around the magnetic core, the 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 of the detection resistor; the pulse signal generating circuit generates a pulse signal in response to the detected voltage; the driving unit switches the direction of a current flowing through the secondary conductor based on the pulse signal, the detection unit detects a current flowing through the primary conductor based on a duty ratio of the pulse signal, the pulse signal generation circuit monitors a detection voltage generated at the one end of the detection resistor and inverts the on and off of the pulse signal; the detection unit includes a clock generation unit and a counter, the clock generating unit generates a clock signal with a predetermined cycle, The counter counts the duty ratio of the pulse signal using the clock signal. A current sensor device is provided.

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

[0009] Furthermore, the present invention provides a third current sensor device, which is the first or second current sensor device, the pulse signal generating circuit compares the detected voltage with a predetermined threshold voltage, and inverts the on and off states of the pulse signal every time the detected voltage exceeds the predetermined threshold voltage; The predetermined threshold voltage is determined in advance in consideration of the magnetic saturation of the magnetic core. A current sensor device is provided.

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

[0011] Furthermore, the present invention provides a fifth current sensor device, which is any one of the first to fourth current sensor devices, the current sensor device further includes a temperature sensor and a correction value storage unit that stores a temperature and a correction value in association with each other; the correction value is based on temperature changes of the sensitivity and offset output of the current sensor device; The detection unit obtains a correction value corresponding to the detected temperature from the correction value storage unit in accordance with 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] Furthermore, the present invention provides a sixth current sensor device, which is any one of the first to fifth current sensor devices, 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] Furthermore, the present invention provides a seventh current sensor device, which is any one of the first to sixth current sensor devices, The current sensor device further includes a self-diagnosis unit, The self-diagnosis unit includes an additional conductor that is at least partially passed through the magnetic core, and a current supply unit that supplies a current to the additional conductor during testing. A current sensor device is provided.

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

[0015] Furthermore, the present invention provides a ninth current sensor device, which is any one of the first to eighth current sensor devices, The current sensor device further includes a shield case, The magnetic core is formed by winding a strip-shaped magnetic body, The magnetic body has two ends, The shield case has an opening, both ends of the secondary conductor are drawn out of the shielding case through the opening and connected to the drive circuit outside the shielding case, When the shielding case is equally divided into two regions, a first region close to the opening and a second region far from the opening, the ends of the magnetic body are all located in the second region. A current sensor device is provided. [Effects 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 a pulse signal. Even if the period of the pulse signal fluctuates due to temperature changes, the duty ratio is hardly affected by temperature changes. Therefore, the duty ratio of the pulse signal accurately reflects the current flowing through the primary conductor. Therefore, the current sensor device of the present invention is less susceptible to temperature changes and can accurately detect current. [Brief explanation of the drawings]

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

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

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

[0020] As shown in FIG. 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 addition, in this embodiment, the load 143 includes a secondary conductor 151 and a chopper circuit 153. However, the chopper circuit 153 is not essential to the present invention. Therefore, FIG. 2 shows the drive circuit 14 without the chopper circuit 153. In the following description, the chopper circuit 153 will be omitted. The chopper circuit 153 will be described later with reference to FIGS. 10 and 11.

[0021] 2, the secondary conductor 151 is wound around the magnetic core 12 and connected to an 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 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] 1 or 2, the drive circuit 14 in this embodiment excites the magnetic core 12 using a single secondary conductor 151. Therefore, compared to known drive circuits that use a pair of secondary conductors, there is less manufacturing variation and it is easier to achieve desired characteristics.

[0023] As shown in FIG. 2, the detection resistor 16 is connected in series with the driver 141. The detection resistor 16 may be configured as a single resistor. However, it is preferable to provide a plurality of resistors and select one from among them depending on 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 a detection voltage VRs at one end of the voltage. More specifically, the detection resistor 16 generates the detection voltage VRs at the connection point between the detection resistor 16 and the H-bridge circuit 141.

[0024] 2, the pulse signal generating circuit 18 has 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 set in advance in consideration of the magnetic saturation of the magnetic core 12. In this embodiment, the T flip-flop 183 is used, but other means may also be used.

[0025] 2, the comparator 181 compares the detection voltage 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, the comparator 181 outputs an output voltage VC that is on when the detection voltage VRs exceeds the predetermined threshold voltage Vth and is off when the detection voltage VRs falls below the predetermined threshold voltage Vth.

[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 / off state of the pulse signal VH, which is its output. The pulse signal VH is sent directly to the drive unit 141 as the pulse signal VH1. The pulse signal VH is also inverted by the inverter 185 and sent to the drive unit 141 as the pulse signal VH2. In this way, the pulse signal generation circuit 18 monitors the detection voltage VRs generated at one end of the detection resistor 16 and generates the pulse signal VH (VH1, VH2) in accordance with the detection voltage VRs. In other words, based on the comparison result between the detection voltage VRs and a predetermined threshold voltage Vth, the pulse signal generation circuit 18 inverts the on / off state of the pulse signal VH each time the detection voltage VRs exceeds the predetermined threshold voltage Vth.

[0027] As can be seen from FIG. 2 , the pulse signal VH1 from the T flip-flop 183 controls the switches SW2 and SW4 of the switches 145 that constitute the driver 141. Specifically, the pulse signal VH1 controls one of the switches SW2 and SW4 to turn on (or off) and the other to turn off (or on). Furthermore, the pulse signal VH2 from the inverter 185 controls the switches SW1 and SW3 of the switches 145 that constitute the driver 141. Specifically, the pulse signal VH2 controls one of the switches SW1 and SW3 to turn on (or off) and the other to turn off. Note that the pulse signal VH2 is an inversion of the pulse signal VH1, so the switch SW1 and the switch SW4 are turned on or off simultaneously, and the switch SW3 is turned on or off simultaneously with the switch SW2. The driver 141 controls the direction of the current flowing through the secondary conductor 151 depending on whether the switches SW1, SW2, SW3, and SW4 are turned on or off. 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, assume that in an ideal current sensor device 10, no current flows through the primary conductor 50. In this case, the drive circuit 14 and the pulse signal generation circuit 18 operate so that the duty ratio of the pulse signal VH is 50%. In other words, in an ideal current sensor device 10, when no current flows through the primary conductor 50, the drive circuit 14 and the pulse signal generation circuit 18 operate so that the off period and the on period of the pulse signal VH are equal to each other.

[0029] 1 again, the detection unit 20 includes a clock generation unit 201 and a counter 211. The clock generation unit 201 generates a clock signal having a predetermined cycle that is sufficiently shorter than the cycle of the pulse signal VH. In other words, the clock generation unit 201 generates a clock signal having a predetermined frequency that is sufficiently higher than the frequency of the pulse signal VH.

[0030] The counter 211 counts the duty ratio of the pulse signal VH using a clock signal. Specifically, the counter 211 counts the clock pulses corresponding to the OFF period and the ON period in each cycle of the pulse signal VH.

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

[0032] 1, the duty conversion unit 213 generates a duty ratio signal that indicates the duty ratio of the pulse signal VH based on the count value of the counter 211. This duty ratio signal changes depending on the current (current to be detected) flowing through the primary conductor 50.

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

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

[0035] The following provides a detailed explanation of the operations of the drive circuit 14 and the pulse signal generation circuit 18. In Fig. 5, the switch 145 of the drive unit 141 is configured using a pair of CMOS.

[0036] Here, it is assumed that the magnetic core 12 has characteristics represented by a BH curve as shown in Figure 3. In this case, when a current flows through the primary conductor 50 that passes inside the magnetic core 12, the BH curve of the magnetic core 12 shifts toward the strong magnetic field side as shown in Figure 4. As a result, the duty ratio of the pulse signal VH generated by the pulse signal generating circuit 18 changes as follows: When no current flows through the primary conductor 50, the duty ratio of the pulse signal VH is assumed to be 50%.

[0037] 5, when the switches QP1 and QN1 are turned on and the switches QP2 and QN2 are turned off, a current I1 flows in a first direction through the secondary conductor 151. At this time, the BH characteristics of the magnetic core 12 as viewed from the secondary conductor 151 are as shown in FIG.

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

[0039] As can be seen from FIG. 9, when a current flows through the secondary conductor 151, the detection voltage VRs rises in accordance with the magnitude of the current. When the detection 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 response to the 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 (FIG. 5) to the second direction (FIG. 7) or from the second direction (FIG. 7) to the first direction (FIG. 5). At this time, the detection voltage VRs drops instantaneously. When the detection voltage VRs falls below the predetermined threshold voltage Vth, the output voltage VC of the comparator 181 changes from ON to OFF. Thereafter, the detection voltage VRs rises again. Thereafter, the drive circuit 14 and the pulse signal generation circuit 18 repeat the above-described operations.

[0040] In this way, the pulse signal generating circuit 18 generates a pulse signal VH whose cycle is made up of a first period T1 corresponding to the time during which current flows in the first direction and a second period T2 corresponding to the time during which current flows in the second direction. The duty ratio 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 ratio.

[0041] The pulse signal generating circuit 18 of the present embodiment uses a predetermined threshold voltage Vth to switch the pulse signal VH on and off before the detection voltage VRs becomes saturated, thereby shortening the period of the pulse signal VH and increasing the current detection speed of the current sensor device 10.

[0042] In the above description, when no current flows through the primary conductor 50, the duty ratio 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 generating circuit 18, the duty ratio of the pulse signal VH may not be 50%. In addition to the operation of the driver 141, the chopper circuit 153 (see FIG. 1) reverses the direction of the current flowing through the secondary conductor 151. Even if the chopper circuit 153 reverses the direction of the current flowing through the secondary conductor 151, the polarity of the offset does not change. Therefore, by using the chopper circuit 153, it is possible to offset the effect of the duty ratio of the pulse signal VH not being 50%. Note that the offset is an output other than 0 that is output when the output from that circuit or the like should ideally be 0. The operation of the chopper circuit 153 will now be described.

[0043] 1, the secondary conductor 151 is connected to the driving unit 141 via a chopper circuit 153. The chopper circuit 153 is made up of, for example, a plurality of switches (not shown).

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

[0045] As can be seen from FIG. 1, the delay circuit 191 delays the pulse signal VH so that the current reversal occurs at an appropriate timing. The 1 / n frequency divider 193 divides the frequency of the delayed pulse signal VHd from the delay circuit 191 by 1 / n. For example, the 1 / n frequency divider 193 divides the frequency of 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. FIG. 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 Fig. 10, the chopper circuit 153 alternately switches between path 1 shown in Fig. 10(a) and Fig. 10(b) and path 2 shown in Fig. 10(c) and Fig. 10(d). Meanwhile, the H-bridge circuit 141 switches the direction of the current flowing through the H-bridge circuit 141 between a first direction shown in Fig. 10(b) or Fig. 10(d) and a second direction shown in Fig. 10(a) or Fig. 10(c) during each of the periods when the chopper circuit 153 forms path 1 and the period when the chopper circuit 153 forms path 2.

[0047] As shown in FIG. 11, the output signal VCH of the 1 / n frequency divider 193 (see FIG. 1) repeatedly turns on and off. While the output signal VCH is off, path 1 (see FIG. 10(a) or FIG. 10(b)) is selected in the chopper circuit 153. During this period, the pulse signal VH supplied to the H-bridge circuit 141 changes from on to off, on to off, and so on. Furthermore, while the output signal VCH of the 1 / n frequency divider 193 is on, path 2 (see FIG. 10(c) or FIG. 10(d)) is selected in the chopper circuit 153. During this period, the pulse signal VH supplied to the H-bridge circuit 141 changes from on to off, on to off, and so on.

[0048] 11, the pulse signal VH has an extremely narrow pulse width due to a transient phenomenon immediately after the path is changed in the chopper circuit 153. 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] 10 and 11 , the on-period T1 and off-period T2 of the pulse signal VH for path 1 correspond to periods during which current flows in the second and first directions in the secondary conductor 151, respectively. On the other hand, the on-period T1' and off-period T2' of the pulse signal VH for path 2 correspond to periods during which current flows in the first and second directions in the secondary conductor 151, respectively. As described above, the direction of the current flowing in the secondary conductor 151 is opposite between the on-period T1 and the on-period T1', and the direction of the current flowing in the secondary conductor 151 is opposite between the off-period T2 and the off-period T2'. Therefore, by calculating the difference between the duty ratios of the on-period T1 and the off-period T2 and the duty ratios of the on-period T1' and the off-period T2', it is possible to offset the effects of variations in on-resistance among SW1, SW2, SW3, and SW4 and the offset of the pulse signal generation circuit 18. In this way, the detection unit 20 can accurately detect the current flowing through the primary conductor 50 based on the duty ratio of the pulse signal VH.

[0050] Referring again to FIG. 1, the temperature correction circuit 22 and the 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 correction circuit 22. The temperature correction circuit 22 includes a correction value storage unit (not shown). The correction value storage unit stores a correspondence between temperatures and correction values. The correction value is based on the temperature change of the sensitivity and offset output of the current sensor device 10. The correction value is obtained in advance by measuring the temperature characteristics of the current sensor, etc.

[0051] The temperature correction 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 the correction value to correct the duty ratio calculated by the duty conversion unit 213. This allows the duty ratio to be appropriately corrected depending on the temperature during use of the current sensor device 10. As a result, the accuracy of the current detection determination 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 in accordance with the detected temperature detected by the temperature sensor 24, and uses the correction value to correct the detection of the current flowing through the primary conductor 50.

[0052] As can be seen from Figure 12, when the current sensor device 10 detects a constant current (4.5 mA) flowing through the primary conductor 50, the detected current value varies depending on the temperature unless temperature compensation is performed. On the other hand, when temperature compensation is performed, the current value detected by the current sensor device 10 becomes a substantially constant value independent of the temperature. Therefore, the current sensor device 10 of this embodiment not only reduces the influence of temperature changes by using the duty ratio, but also actively performs temperature compensation, thereby enabling highly accurate current detection over a wide temperature range.

[0053] As shown in FIG. 1, the current sensor device 10 of this embodiment further includes a self-diagnosis unit 28. The self-diagnosis unit 28 has an additional conductor 281 and a self-test drive circuit (current supply unit) 283. The additional conductor 281 is at least partially passed 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 a current to the additional conductor 281 during testing.

[0054] 1, when a test is performed, an instruction to perform the test is externally given to the self-test drive circuit 283, and the self-test drive circuit 283 supplies a predetermined DC or AC test current to the additional conductor 281. Then, by monitoring the output terminal of the current sensor device 10, it is possible to know whether the test current is being properly detected. The test current may be a DC current detectable by the current sensor device 10, an AC current detectable by the current sensor device 10, or an overcurrent.

[0055] 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 sum) circuit 305.

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

[0057] A preset frequency threshold Fth is input to the frequency comparator 303. The frequency comparator 303 obtains the frequency of the pulse signal VH from the count value of the counter 211 and compares it with the frequency threshold Fth. When the frequency of the pulse signal VH exceeds the frequency Fth, the frequency comparator 303 outputs an overcurrent detection signal.

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

[0059] In the current sensor device 10 of this embodiment, the overcurrent detection unit 30 includes the frequency comparator 303 in addition to the overcurrent comparator 301 for the following reason.

[0060] The current sensor device 10 according to this embodiment employs a fluxgate system. In the fluxgate current sensor device 10, when 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 is unable to detect the current flowing through the primary conductor 50 based on the duty ratio of the pulse signal VH. The overcurrent detection unit 30 detects that a current so large that current detection based on the duty ratio of the pulse signal VH is no longer 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 the frequency exceeds a predetermined frequency.

[0061] 13 to 15, the magnetic core 12 is housed in a shield case 32. As described above, in this embodiment, the current sensor device 10 further includes a shield case 32. In this embodiment, the secondary conductor 151 (see FIG. 1) is wound around the magnetic core 12 and 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] 13 to 15 , the shield case 32 has an opening 321 for allowing both ends of the secondary conductor 151 wound around the magnetic core 12 to be drawn out to the outside. Both ends of the secondary conductor 151 are drawn out of the shield case 32 through the opening 321 of the shield case 32 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 drawn out of the shield case 32 through the opening 321 of the shield case 32. Both ends of the additional conductor 281 are then connected to the self-test drive circuit 283 outside the shield case 32.

[0063] 14 and 15, in this embodiment, the magnetic core 12 is formed by winding a strip-shaped magnetic body. Therefore, the magnetic core 12 has a pair of end portions 121.

[0064] 14 and 15, the two ends 121 of the magnetic core 12 are arranged close to each other so as not to overlap. In FIG. 14, the end 121 of the magnetic core 12 is oriented in the opposite direction to the opening 321 of the shield case 32. On the other hand, in FIG. 15, the end 121 of the magnetic core 12 is oriented in the same direction as the shield case 32. As described above, there are various possible positional relationships between the end 121 of the magnetic core 12 and the shield case 32. Furthermore, according to experiments conducted by the inventors, it has been found that the positional relationship between the end 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 of FIG. 1, the sensor unit 40 must have a predetermined over-input characteristic. When the sensor unit 40 and primary conductor 50 are arranged as shown in FIG. 13 and a predetermined over-current (e.g., 30 A for 100 ms) is instantaneously applied to the primary conductor 50, the duty ratio of the current sensor device 10 exhibits the response shown in FIG. 16. The reference center line (thin line in FIG. 16) in FIG. 16 indicates a duty ratio of 50%. The duty ratio changes significantly the moment the current is flowing, but it may also shift slightly from 50% even when the current is turned off. This shift is called the over-input characteristic, and the smaller the shift, the smaller the error. For example, as shown in FIG. 16, the duty ratio must be 0.6 mA or less in terms of current two seconds after the current is turned off. This shift is called the over-input characteristic, and the smaller the shift, the smaller the error.

[0066] According to experiments conducted by the inventors, the sensor unit 40 configured as shown in FIG. 14 has a low reject rate for over-input characteristics. In contrast, the sensor unit 40 configured as shown in FIG. 15 has a high reject rate for over-input characteristics. Therefore, it is preferable that the magnetic core 12 is housed in the shield case 32 so 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 exactly opposite. Specifically, if the shield case 32 is equally divided into two regions, a first region close to the opening 321 and a second region far from the opening 321, both of the end 121 of the magnetic core 12 need only be located in the second region. Preferably, the end 121 should be located within a 45-degree range centered on the direction exactly opposite the opening 321.

[0067] The present invention has been described above by presenting an embodiment thereof, but the present invention is not limited to the above-described embodiment, and various modifications and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0068] 10 Current sensor device 12 Magnetic core 121 End 14 Drive circuit 141 Drive unit (H-bridge circuit) 143 Load 145 Switch 151 Secondary Conductor 153 Chopper Circuit 16 Detector resistor 18 Pulse signal generation circuit 181 Comparator 183 T Flip-Flop 185,187 Inverter 191 Delay Device 193 1 / n frequency divider 20 Detector 201 Clock generation unit 211 Counter 213 Duty conversion unit 215 Filter Circuit 217 Comparator 22 Temperature compensation circuit 24 Temperature Sensor 28 Self-diagnosis section 281 Additional Conductors 283 Self-Test Drive Circuit 30 Overcurrent detection section 301 Overcurrent comparator 303 Frequency Comparator 305 OR circuit (logical sum circuit) 32 Shield case 321 Aperture 40 Sensor section 50 Primary conductor

Claims

1. A current sensor device for detecting a current flowing through a primary conductor, The device includes a magnetic core, a drive circuit, a detection resistor, a pulse signal generating circuit, and a detection unit. The magnetic core is annular, and the primary conductor is passed through the magnetic core. the drive circuit includes a drive unit and a load; the load is a secondary conductor wound around the magnetic core, the detection resistor is connected in series with the drive circuit, converts a current flowing through the secondary conductor into a voltage, and generates a detection voltage at one end of the detection resistor; the pulse signal generating circuit generates a pulse signal in response to the detected voltage; The driving unit switches a direction of a current flowing through the secondary conductor based on the pulse signal, The detection unit detects a current flowing through the primary conductor based on a duty ratio of the pulse signal, the pulse signal generating circuit monitors a detection voltage generated at the one end of the detection resistor and inverts the on and off of the pulse signal; the detection unit includes a clock generation unit and a counter, the clock generating unit generates a clock signal having a predetermined period; The counter counts the duty ratio of the pulse signal by using the clock signal. Current sensor device.

2. 2. The current sensor device according to claim 1, The driving section is an H-bridge circuit having four switches. Current sensor device.

3. 3. The current sensor device according to claim 1, the pulse signal generating circuit compares the detection voltage with a predetermined threshold voltage, and inverts the on and off state of the pulse signal every time the detection voltage exceeds the predetermined threshold voltage; The predetermined threshold voltage is determined in advance in consideration of the magnetic saturation of the magnetic core. Current sensor device.

4. A current sensor device according to any one of claims 1 to 3, The drive circuit further includes a chopper circuit as the load, The secondary conductor is connected to the drive unit via the chopper circuit. Current sensor device.

5. A current sensor device according to any one of claims 1 to 4, The current sensor device further includes a temperature sensor and a correction value storage unit that stores a temperature and a correction value in association with each other, the correction value is based on a temperature change of a sensitivity and an offset output of the current sensor device; The detection unit obtains a correction value corresponding to the detected temperature from the correction value storage unit in response 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. Current sensor device.

6. A current sensor device according to any one of claims 1 to 5, 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. Current sensor device.

7. A current sensor device according to any one of claims 1 to 6, The current sensor device further includes a self-diagnosis unit, The self-diagnosis unit includes an additional conductor that is at least partially passed inside the magnetic core, and a current supply unit that supplies a current to the additional conductor during testing. Current sensor device.

8. A current sensor device according to any one of claims 1 to 7, The detection resistor is selected from a plurality of resistors provided in advance according to the magnetic core. Current sensor device.

9. A current sensor device according to any one of claims 1 to 8, The current sensor device further includes a shield case, The magnetic core is formed by winding a strip-shaped magnetic body, The shield case has an opening, Both ends of the secondary conductor are led out of the shielding case through the opening and connected to the drive circuit outside the shielding case. Current sensor device.

10. A current sensor device as claimed in claim 9, The magnetic body has two ends, 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, the ends of the magnetic body are all located in the second region. Current sensor device.

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