JP2023146957A - Electric current sensor device - Google Patents

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

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

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

As shown in FIG. 17, the current sensor 90 described in Patent Document 1 uses a comparator 905 to compare the voltage generated at the center tap of a winding 903 wound around a magnetizable member 901 with a reference voltage. The comparison result of comparator 905 is supplied to flip-flop 907. Flip-flop 907 outputs a “1” signal or a “0” signal depending on the output of comparator 905. The "1" signal and the "0" signal are input to AND circuits 909 and 911, respectively, and the logical product with the clock signal Ck is calculated. AND circuit 909 outputs a number of clock pulses corresponding to the duration of the "1" signal, and 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 to increase or decrease the count value. 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 successive "1" 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.

US Patent No. 4,899,103

The current sensor 90 of Patent Document 1 detects 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. I am looking for the size of However, this method may cause errors due to changes in the characteristics of the magnetizable member 901 due to temperature changes. Specifically, the duration of the "1" signal and the duration of the "0" signal vary 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 the temperature change, and the magnitude of the detected current is affected by the temperature change.

SUMMARY OF THE INVENTION An object of the present invention is to provide a current sensor device that is less susceptible to temperature changes and can accurately detect current.

The present invention is a current sensor device that detects a current flowing through a primary conductor as a first current sensor device, comprising:
It includes a magnetic core, a drive circuit, a detection resistor, a pulse signal generation circuit, and a detection section.
The magnetic core has an annular shape, and the primary conductor is passed through the inside of the magnetic core.
The drive circuit has a drive section and a load,
The load is a secondary conductor wound around the magnetic core,
The detection resistor is connected in series to the drive circuit, converts the current flowing through the secondary conductor into 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 ratio of the pulse signal,
The pulse signal generation circuit monitors the detection voltage generated at the one end of the detection resistor and inverts the pulse signal between on and off,
The detection unit includes a clock generation unit and a counter,
The clock generation unit generates a clock signal with a predetermined period,
The counter provides a current sensor device that counts the duty ratio of the pulse signal using the clock signal.

Further, the present invention provides a first current sensor device as a second current sensor device, comprising:
The path switching circuit provides a current sensor device that is an H-bridge circuit with four switches.

Further, the present invention provides a first or second current sensor device as a third current sensor device, comprising:
The pulse signal generation circuit compares the detected voltage with a predetermined threshold voltage and inverts the pulse signal between on and off each time the detected voltage exceeds the predetermined threshold voltage,
The present invention provides a current sensor device in which the predetermined threshold voltage is predetermined in consideration of magnetic saturation of the magnetic core.

Further, the present invention provides, as the fourth current sensor device, any one of the first to third current sensor devices,
The drive circuit further includes a chopper circuit as the load,
The secondary conductor provides a current sensor device connected to the drive section via the chopper circuit.

Further, the present invention provides any one of the first to fourth current sensor devices as a fifth current sensor device,
The current sensor device further includes a temperature sensor and a correction value storage unit that stores temperature and correction values in association with each other,
The correction value is based on a temperature change in 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 detects the current flowing through the primary conductor using the correction value. A current sensor device for correcting is provided.

Further, the present invention provides any one of the first to fifth current sensor devices as a sixth current sensor device,
The current sensor device further includes an overcurrent detection section,
The overcurrent detection section provides a current sensor device that monitors the frequency of the pulse signal and issues an overcurrent flag when the frequency exceeds a predetermined frequency.

Further, the present invention provides any one of the first to sixth current sensor devices as a seventh current sensor device,
The current sensor device further includes a self-diagnosis section,
The self-diagnosis section provides a current sensor device having an additional conductor passed at least partially inside the magnetic core, and a current supply section supplying current to the additional conductor during a test. .

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

Further, the present invention provides any one of the first to eighth current sensor devices as a ninth current sensor device,
The current sensor device further includes a shield case,
The magnetic core is formed by winding a band-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 from 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, the ends of the magnetic body are both located in the second region. A current sensor device is provided.

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 changes due to temperature changes, its 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.

1 is a circuit block section showing a current sensor device according to an embodiment of the present invention. 2 is a circuit block diagram showing main parts of the current sensor device of FIG. 1. FIG. The chopper circuit has been removed to simplify the explanation. 3 is a graph showing the BH curve of the magnetic core included in the main part of FIG. 2, and is a graph showing the BH curve when no current flows through the primary conductor. 3 is a graph showing a BH curve of a magnetic core included in the main part of FIG. 2, and is a graph showing a BH curve when an arbitrary current is flowing through a primary conductor. 3 is a circuit block diagram showing a pulse signal generation circuit included in the main part of FIG. 2 and a first direction of current flowing through a secondary conductor. FIG. 6 is a graph showing a BH curve of the magnetic core seen from the 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. 5. FIG. 3 is a circuit block diagram showing a pulse signal generation circuit included in the main part of FIG. 2 and a second direction of current flowing through a secondary conductor. FIG. 8 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 a current flowing through the secondary conductor in the pulse signal generation circuit of FIG. 7. 8 is a time chart showing temporal changes in voltages at various parts in the pulse signal generation circuit shown in FIGS. 5 and 7. FIG. (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 FIG. , and the BH characteristics of the magnetic core as seen from the secondary conductor. 2 is a time chart showing temporal changes in a pulse signal VH supplied to a delay device included in the current sensor device of FIG. 1 and temporal changes in an output voltage VCH of a 1/n frequency divider supplied to a chopper circuit. The alphabets in parentheses correspond to FIGS. 10(a), 10(b), 10(c), and 10(d). 2 is a graph showing the effect of temperature correction in the detection section included in the current sensor device of FIG. 1. FIG. FIG. 2 is a diagram for explaining a method of measuring over-input characteristics of a magnetic core included in the current sensor device of FIG. 1. FIG. FIG. 2 is a schematic diagram showing a first positional relationship between a pair of ends of a strip-shaped magnetic material forming a magnetic core included in the current sensor device of FIG. 1 and an opening of a shield case that accommodates the magnetic core. FIG. 2 is a schematic diagram showing a second positional relationship between a pair of ends of a strip-shaped magnetic material forming a magnetic core included in the current sensor device of FIG. 1 and an opening of a shield case that accommodates the magnetic core. 2 is a graph for explaining the over-input characteristics allowed in the magnetic core included in the current sensor device of FIG. 1. FIG. 1 is a circuit block diagram showing a current sensor disclosed in Patent Document 1. FIG.

Referring to FIG. 1, a current sensor device 10 according to an 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 section 20. .

Referring to FIG. 2, the magnetic core 12 is annular. Preferably, the magnetic core 12 has high magnetic permeability. A primary conductor 50 is passed 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.

As shown in FIG. 1, the drive circuit 14 includes a drive section 141 and a load 143. In this embodiment, the drive section 141 is an H-bridge circuit 141 having four switches 145. Further, in this embodiment, the load 143 includes a secondary conductor 151 and a chopper circuit 153. However, in the present invention, the chopper circuit 153 is not essential. Therefore, FIG. 2 shows the drive circuit 14 in which the chopper circuit 153 is omitted. In the following description, it is assumed that the chopper circuit 153 is omitted. The chopper circuit 153 will be described later with reference to FIGS. 10 and 11.

As shown in FIG. 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 source. 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 directions opposite to each other.

As understood from FIG. 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 are fewer manufacturing variations and it is easier to achieve desired characteristics.

As shown in FIG. 2, the detection resistor 16 is connected in series to the drive section 141. Detection resistor 16 may be composed of a single resistor. However, it is preferable to prepare a plurality of resistors and to select one of the resistors 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 a detection voltage VRs at one end thereof. 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.

As shown in FIG. 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 set in advance in consideration of magnetic saturation of the magnetic core 12. Although the T flip-flop 183 is used in this embodiment, other means may be used.

As understood from FIG. 2, the comparator 181 compares the detection voltage VRs generated at one end of the detection resistor 16 with a predetermined threshold voltage Vth. Comparator 181 changes its output voltage VC according to the comparison result. Specifically, the output voltage VC is turned on when the detection voltage VRs exceeds a predetermined threshold voltage Vth, and turned off when the detection voltage VRs is below a predetermined threshold voltage Vth.

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 states of the pulse signal VH that is its output. The pulse signal VH is sent as is to the drive section 141 as the pulse signal VH1. Furthermore, the pulse signal VH is inverted by the inverter 185 and sent to the drive section 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) according to the detection voltage VRs. In other words, the pulse signal generation circuit 18 inverts the pulse signal VH between on and off every time the detection voltage VRs exceeds the predetermined threshold voltage Vth, based on the comparison result between the detection voltage VRs and the predetermined threshold voltage Vth.

As understood from FIG. 2, the pulse signal VH1 from the T flip-flop 183 controls the switch SW2 and the switch SW4 among the switches 145 that constitute the drive section 141. Specifically, the pulse signal VH1 controls to turn on (or turn off) one of the switches SW2 and SW4 and turn off (or turn on) the other. Further, the pulse signal VH2 from the inverter 185 controls the switch SW1 and the switch SW3 among the switches 145 that constitute the drive section 141. Specifically, the pulse signal VH2 controls one of the switch SW1 and the switch SW3 to be turned on (or off) and the other to be turned off. Note that since the pulse signal VH2 is an inversion of the pulse signal VH1, the switch SW1 is turned on or off at the same time as the switch SW4, and the switch SW3 is turned on or off at the same time as the switch SW2. The drive unit 141 controls the direction of the current flowing through the secondary conductor 151 according to whether switches SW1, SW2, SW3, and SW4 are turned on or off. In this way, the drive section 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.

Here, assume that in the 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 the ideal current sensor device 10, the drive circuit 14 and the pulse signal generation circuit 18 operate so that the off period and on period of the pulse signal VH are equal to each other when no current flows through the primary conductor 50. works.

Referring to FIG. 1 again, the detection section 20 includes a clock generation section 201 and a counter 211. Clock generation section 201 generates a clock signal with a predetermined cycle that is sufficiently shorter than the cycle of pulse signal VH. In other words, the clock generation unit 201 generates a clock signal with a predetermined frequency that is sufficiently higher than the frequency of the pulse signal VH.

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

As shown in FIG. 1, the detection section 20 further includes a duty conversion section 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.

As understood from FIG. 1, the duty converter 213 generates a duty ratio signal representing 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 flowing through the primary conductor 50 (current to be detected).

The duty ratio signal from the duty converter 213 is input to the filter circuit 215 via the temperature correction circuit 22. The temperature correction circuit 22 and temperature sensor 24 will be described later. Filter circuit 215 integrates the duty ratio signal. The integrated duty ratio signal is compared with a predetermined threshold (alert current) in a comparator 217. Comparator 217 outputs a detection signal indicating whether or not current flows through primary conductor 50, depending on the comparison result. The comparator 217 can correspond to thresholds for direct current, alternating current, and overcurrent detection as predetermined thresholds. When the comparator 217 corresponds to the threshold values for direct current, alternating current, and overcurrent detection, the comparator 217 outputs the detection signals for direct current, alternating current, and overcurrent detection as detection signals to the respective corresponding output terminals. Output to.

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 not easily affected even if the cycle of the pulse signal VH is affected by temperature changes. Therefore, compared to 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 of the pulse signal and the number of clock pulses corresponding to the off period of the pulse signal, current detection is performed with higher accuracy. be able to.

The operations of the drive circuit 14 and pulse signal generation circuit 18 will be described in detail below. Note that in FIG. 5, the switch 145 of the drive unit 141 is configured using a pair of CMOS.

Here, it is assumed that the magnetic core 12 has characteristics expressed by a BH curve as shown in FIG. In this case, when a current flows through the primary conductor 50 passing inside the magnetic core 12, the BH curve of the magnetic core 12 shifts toward the strong magnetic field side, as shown in FIG. Under this influence, the duty ratio of the pulse signal VH generated by the pulse signal generation circuit 18 changes as follows. It is assumed that when no current flows through the primary conductor 50, the duty ratio of the pulse signal VH is 50%.

As shown in FIG. 5, when the switch QP1 and the switch QN1 are on and the switch QP2 and the switch QN2 are off, a current I1 in the first direction flows through the secondary conductor 151. At this time, the BH characteristic of the magnetic core 12 viewed from the secondary conductor 151 is as shown in FIG.

As shown in FIG. 7, when the switch QP1 and the switch QN1 are off and the switch QP2 and the switch QN2 are on, a current I2 in the second direction flows through the secondary conductor 151. At this time, the BH characteristic of the magnetic core 12 viewed from the secondary conductor 151 is as shown in FIG.

As understood from FIG. 9, when a current flows through the secondary conductor 151, the detection voltage VRs increases depending on the magnitude of the current. When the detection voltage VRs exceeds the 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 its rise. 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). (FIG. 7) to the first direction (FIG. 5). At this time, the detection voltage VRs drops instantaneously. When the detection voltage VRs becomes equal to or lower than the predetermined threshold voltage Vth, the output voltage VC of the comparator 181 changes from on to off. After that, the detection voltage VRs rises again. Thereafter, the drive circuit 14 and the pulse signal generation circuit 18 repeat the operations described above.

As described above, the pulse signal generation circuit 18 divides the first period T1 corresponding to the time period in which the current flows in the first direction and the second period T2 corresponding to the time period in which the current flows in the second direction into one cycle. A pulse signal VH is generated. The duty ratio=T1/(T1+T2) of the pulse signal VH is proportional to the magnitude of the current flowing through the primary conductor 50. Current sensor device 10 of this embodiment detects the current flowing through primary conductor 50 based on this duty ratio.

The pulse signal generation circuit 18 of this embodiment uses a predetermined threshold voltage Vth to switch the pulse signal VH between on and off before the detection voltage VRs is saturated. Thereby, the period of the pulse signal VH can be shortened and the current detection speed of the current sensor device 10 can be increased.

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 generation circuit 18, the duty ratio of the pulse signal VH may not be 50%. In addition to the operation of the drive unit 141, the chopper circuit 153 (see FIG. 1) reverses the direction of the current flowing through the secondary conductor 151. The polarity of the offset does not change even if 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 offset the influence caused by the fact that the duty ratio of the pulse signal VH is not 50%. Note that an offset is an output other than 0 that is output when the output from the circuit or the like should ideally be 0. The operation of the chopper circuit 153 will be explained below.

As shown in FIG. 1, it is connected to the drive unit 141 via a secondary conductor 151 and a chopper circuit 153. The chopper circuit 153 is composed of, for example, a plurality of switches (not shown).

As shown in FIG. 1, the current sensor device 10 further includes a delay device 191 and a 1/n frequency divider 193. The pulse signal VH1 from the T flip-flop 183 or the pulse signal VH2 from the inverter 185 is input to the delay device 191.

As understood from FIG. 1, the delay device 191 delays the pulse signal VH so that the current is reversed at an appropriate timing. The 1/n frequency divider 193 divides the delayed pulse signal VHd from the delay device 191 by 1/n. For example, the 1/n frequency divider 193 divides the delayed pulse signal VHd into 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, that is, when the frequency of the delayed pulse signal VHd is divided by 1/4.

As understood from FIG. 10, the chopper circuit 153 connects path 1 shown in FIGS. 10(a) and 10(b) and path 2 shown in FIGS. 10(c) and 10(d). , alternately switch. On the other hand, the H-bridge circuit 141 changes the direction of the current flowing through the H-bridge circuit 141 during the period when the chopper circuit 153 forms the path 1 and during the period when the chopper circuit 153 forms the path 2, as shown in FIG. 10(b). ) or the first direction shown in FIG. 10(d) and the second direction shown in FIG. 10(a) or FIG. 10(c).

As shown in FIG. 11, the output signal VCH of the 1/n frequency divider 193 (see FIG. 1) repeats on and off. While the output signal VCH is off, the chopper circuit 153 selects path 1 (see FIG. 10(a) or FIG. 10(b)). During this time, the pulse signal VH supplied to the H-bridge circuit 141 changes from on to off to on to off. Further, while the output signal VCH of the 1/n frequency divider 193 is on, the chopper circuit 153 selects path 2 (see FIG. 10(c) or FIG. 10(d)). During this time, the pulse signal VH supplied to the H-bridge circuit 141 changes from on to off to on to off.

As understood from FIG. 11, the pulse signal VH immediately after the route is changed in the chopper circuit 153 has an extremely narrow pulse width due to a transient phenomenon. This pulse does not reflect the current flowing through the primary conductor 50. Therefore, after the route is changed in the chopper circuit 153, the first cycle of the pulse signal VH is ignored in the detection unit 20.

As understood from FIGS. 10 and 11, the on-period T1 and off-period T2 of the pulse signal VH in path 1 are the periods in which the current in the second direction and the first direction flow in the secondary conductor 151, respectively. handle. On the other hand, the on period T1' and the off period T2' of the pulse signal VH in path 2 correspond to the periods in which the currents in the first direction and the second direction flow through the secondary conductor 151, respectively. In this way, the direction of the current flowing through the secondary conductor 151 is opposite between the on period T1 and the on period T1', and the direction of the current flowing through the secondary conductor 151 is opposite between the off period T2 and the off period T2'. The direction is opposite. Therefore, by finding the difference between the duty ratio of the on period T1 and the off period T2 and the duty ratio of the on period T1' and the off period T2', it is possible to reduce the on-resistance variation among SW1, SW2, SW3, and SW4, and to generate a pulse signal. The effect of the offset of 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 ratio of the pulse signal VH.

Referring again to FIG. 1, the temperature correction 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 correction circuit 22. The temperature correction circuit 22 includes a correction value storage section (not shown). The correction value storage unit stores temperature and correction values in association with each other. The correction value is based on the sensitivity of the current sensor device 10 and the temperature change in the offset output. The correction value is obtained by measuring the temperature characteristics and the like of the current sensor in advance.

The temperature correction circuit 22 reads a correction value corresponding to the detected temperature from the correction value storage section based on the temperature detection signal from the temperature sensor 24, and uses the correction value to correct the duty ratio determined by the duty conversion section 213. do. Thereby, the duty ratio is appropriately corrected depending on the temperature when the current sensor device 10 is used. As a result, the accuracy of current detection and judgment performed at a later 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 detects the current flowing through the primary conductor 50 using the correction value. to correct.

As can be understood from FIG. 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 unless temperature correction is performed. It depends and changes. On the other hand, when temperature correction is performed, the current value detected by the current sensor device 10 becomes a substantially constant value regardless of temperature. Therefore, the current sensor device 10 of the present embodiment suppresses the influence of temperature changes by using the duty ratio, and also actively performs temperature correction, thereby achieving high accuracy over a wide temperature range. Can perform current detection.

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

As can be understood from FIG. 1, when performing a test, when an instruction to perform a test is given to the self-test drive circuit 283 from the outside, the self-test drive circuit 283 causes the additional conductor 281 to perform a predetermined DC or AC test. Supply current. By monitoring the output terminal of the current sensor device 10, it is possible to know whether the test current is being detected appropriately. As the test current, a direct current that can be detected by the current sensor device 10, an alternating current that can be detected, and an overcurrent can be used.

As shown in FIG. 1, the current sensor device 10 of this embodiment further includes an overcurrent detection section 30. The overcurrent detection section 30 includes an overcurrent comparator 301, a frequency comparator 303, and an OR (logical sum) circuit 305.

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. Overcurrent comparator 301 outputs an overcurrent detection signal when the current value indicated by the duty ratio signal exceeds the overcurrent threshold.

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

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, and the OR circuit 305 detects either overcurrent detection as an overcurrent flag indicating an overcurrent. Output the signal to the outside.

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

The current sensor device 10 according to this embodiment employs a flux gate method. In the fluxgate type current sensor device 10, when a current that greatly exceeds 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 cannot detect the current flowing through the primary conductor 50 based on the duty ratio of the pulse signal VH. The overcurrent detection section 30 detects that a current so large that current detection based on the duty ratio of the pulse signal VH cannot be performed has flowed through the primary conductor 50. In this way, the overcurrent detector 30 monitors the frequency of the pulse signal and issues an overcurrent flag when the frequency exceeds a predetermined frequency.

Referring to FIGS. 13 to 15, the magnetic core 12 is housed in a shield case 32. As shown in FIG. Thus, in this embodiment, current sensor device 10 further includes shield case 32. In this embodiment, the secondary conductor 151 (see FIG. 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 section 40.

As shown in FIGS. 13 to 15, the shield case 32 is provided with an opening 321. As shown in FIGS. This is to draw out both ends of the secondary conductor 151 wound around the magnetic core 12 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 from the shield case 32 through the opening 321 of the shield case 32. Both ends of the additional conductor 281 are connected to a self-test drive circuit 283 outside the shield case 32.

As understood from FIGS. 14 and 15, in this embodiment, the magnetic core 12 is formed by winding a strip-shaped magnetic material. Therefore, the magnetic core 12 has a pair of ends 121.

As shown in FIGS. 14 and 15, the two ends 121 of the magnetic core 12 are arranged close to each other so as not to overlap each other. In FIG. 14, the end portion 121 of the magnetic core 12 is oriented in a direction opposite to the direction of the opening 321 of the shield case 32. On the other hand, in FIG. 15, the end portion 121 of the magnetic core 12 is oriented in the same direction as the shield case 32. In this way, there may be various positional relationships between the end portion 121 of the magnetic core 12 and the shield case 32. According to the inventor's experiments, it was found that the positional relationship between the end portion 121 of the magnetic core 12 and the shield case 32 affects the characteristics of the sensor section 40.

In the current sensor device 10 of FIG. 1, the sensor section 40 needs to have predetermined over-input characteristics. When the sensor unit 40 and the primary conductor 50 are arranged as shown in FIG. 13 and a predetermined overcurrent (for example, 30 A for 100 ms) is instantaneously passed through the primary conductor 50, the duty ratio of the current sensor device 10 shows the response shown in FIG. 16. . The reference center line in FIG. 16 (thin line in FIG. 16) indicates a duty ratio of 50%. The duty ratio changes greatly at the moment when the current is flowing, but it may shift slightly from 50% even when the current is turned off. This amount of shift is called an overinput characteristic, and the smaller the amount, the smaller the error. For example, as shown in FIG. 16, the over-input characteristic requires that the duty ratio 2 seconds after the current is turned off is 0.6 mA or less in terms of current. This amount of shift is called an overinput characteristic, and the smaller the amount, the smaller the error.

According to the inventor's experiments, the defective product rate of the sensor unit 40 having the configuration shown in FIG. 14 is low regarding excessive input characteristics. On the other hand, the sensor unit 40 having the configuration shown in FIG. 15 has a high defect rate regarding excessive input characteristics. Therefore, it is preferable that the magnetic core 12 be housed in the shield case 32 such that the end 121 thereof faces the opposite side of the opening 321 of the shield case 32. However, the orientation of the end portion 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, when 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, the end portion 121 of the magnetic core 12 is located in the second region. That's fine. Preferably, the end portion 121 may be located within a range of 45 degrees centered on the direction directly opposite to the opening 321.

Although the present invention has been described above with reference to embodiments, the present invention is not limited to the above-described embodiments, and various modifications and changes can be made without departing from the gist of the present invention. It is.

10 Current sensor device 12 Magnetic core 121 End portion 14 Drive circuit 141 Drive unit (H bridge circuit)
143 Load 145 Switch 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 device 193 1/n frequency divider 20 Detection section 201 Clock generation section 211 Counter 213 Duty conversion unit 215 Filter circuit 217 Comparator 22 Temperature correction circuit 24 Temperature sensor 28 Self-diagnosis unit 281 Additional conductor 283 Self-test drive circuit 30 Overcurrent detection unit 301 Overcurrent comparator 303 Frequency comparator 305 OR circuit (logical sum circuit) )
32 Shield case 321 Opening 40 Sensor section 50 Primary conductor

Claims (9)

A current sensor device that detects a current flowing through a primary conductor,
It includes a magnetic core, a drive circuit, a detection resistor, a pulse signal generation circuit, and a detection section.
The magnetic core has an annular shape, and the primary conductor is passed through the inside of the magnetic core.
The drive circuit has a drive section and a load,
The load is a secondary conductor wound around the magnetic core,
The detection resistor is connected in series to the drive circuit, converts the current flowing through the secondary conductor into 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 ratio of the pulse signal,
The pulse signal generation circuit monitors the detection voltage generated at the one end of the detection resistor and inverts the pulse signal between on and off,
The detection unit includes a clock generation unit and a counter,
The clock generation unit generates a clock signal with a predetermined period,
The counter is a current sensor device that counts the duty ratio of the pulse signal using the clock signal. The current sensor device according to claim 1,
In the current sensor device, the driving section is an H-bridge circuit having four switches. The current sensor device according to claim 1 or 2,
The pulse signal generation circuit compares the detected voltage with a predetermined threshold voltage and inverts the pulse signal between on and off each time the detected voltage exceeds the predetermined threshold voltage,
In the current sensor device, the predetermined threshold voltage is predetermined in consideration of magnetic saturation of the magnetic core. The current sensor device according to any one of claims 1 to 3,
The drive circuit further includes a chopper circuit as the load,
In the current sensor device, the secondary conductor is connected to the drive section via the chopper circuit. The 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 temperature and correction values in association with each other,
The correction value is based on a temperature change in 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 detects the current flowing through the primary conductor using the correction value. Current sensor device for correction. The current sensor device according to any one of claims 1 to 5,
The current sensor device further includes an overcurrent detection section,
The overcurrent detection unit is a current sensor device that monitors the frequency of the pulse signal and issues an overcurrent flag when the frequency exceeds a predetermined frequency. The current sensor device according to any one of claims 1 to 6,
The current sensor device further includes a self-diagnosis section,
The self-diagnosis unit includes an additional conductor that is passed at least partially inside the magnetic core, and a current supply unit that supplies current to the additional conductor during a test. The current sensor device according to any one of claims 1 to 7,
In the current sensor device, the detection resistor is selected from a plurality of resistors provided in advance according to the magnetic core. The 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 band-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 from 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, the ends of the magnetic body are both located in the second region. Current sensor device.

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