JP2016223994A - Current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current sensor equipped with a configuration with which it is possible to reduce the circuit scale and current consumption of an arithmetic circuit.SOLUTION: A magnetic field generation unit 120 generates a bias magnetic field Bb in the vertical direction to a current magnetic field Bi that occurs due to that a current I under measurement flows to a bus bar 200. A sensor element 130 outputs a sinusoidal signal that includes a sinθ component with regard to an angle θ that is formed by the bias magnetic field Bb and a composite magnetic field Bs composed by the current magnetic field Bi and the bias magnetic field Bb. Meanwhile, a signal processing unit 180, having a memory 186 in which a conversion map for converting the sinθ component into a tanθ component that corresponds to the sinθ component is stored, converts the sinusoidal signal into a digital signal and inputs it, as well as converts the sinθ component into a tanθ component on the basis of the conversion map and acquires a signal that includes the tanθ component as a sensor signal.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a current sensor that detects a current flowing in a current path to be measured.

  Conventionally, for example, Patent Document 1 proposes a current sensor configured to detect a current flowing in a current path to be measured. Specifically, the current sensor is configured to include a bias magnet, a magnetic sensor, and an arithmetic circuit.

  The bias magnet generates a bias magnetic field in a direction perpendicular to a current magnetic field generated when the current to be measured flows through the current path to be measured. The magnetic sensor outputs a signal including sin θ and a signal including cos θ according to an angle θ formed by a bias magnetic field and a first magnetic field composed of a first bias magnetic field. The arithmetic circuit inputs a signal including sin θ and a signal including cos θ from the magnetic sensor, and calculates sin θ / cos θ to output a signal corresponding to tan θ proportional to the current as a sensor signal.

JP 2013-64663 A

  However, in the above conventional technique, since the arithmetic circuit performs digital signal processing on both the signal including sin θ and the signal including cos θ from the magnetic sensor, an A / D conversion circuit corresponding to each signal is required. Further, it is necessary to increase the A / D conversion speed in order to increase the response to current. Along with this, there is a problem that the scale of the A / D conversion circuit is increased and the current consumption is also increased.

  In view of the above points, an object of the present invention is to provide a current sensor having a configuration capable of reducing the circuit scale and current consumption of an arithmetic circuit.

  In order to achieve the above object, according to the first aspect of the present invention, a bias magnetic field (Bb) is generated in a direction perpendicular to the current magnetic field (Bi) generated when the current to be measured flows through the current path to be measured (200) The magnetic field generation part (120) to be made is provided.

  Moreover, it has several magnetoresistive elements (131-134), and the resistance value of several magnetoresistive elements (131-134) when several magnetoresistive elements (131-134) receive the influence of an external magnetic field. Output a sinusoidal signal including a sin θ component for an angle θ formed by a bias magnetic field (Bb) and a combined magnetic field (Bs) composed of a current magnetic field (Bi) and a bias magnetic field (Bb). The sensor element (130) to be provided is provided.

  Furthermore, a memory (186) storing a conversion map for converting the sin θ component into a tan θ component corresponding to the sin θ component is input, and the sine wave signal is converted into a digital signal and inputted, and based on the conversion map. And a signal processing unit (180) for converting a sin θ component into a tan θ component and acquiring a signal including the tan θ component as a sensor signal.

  According to this, since the signal processing unit (180) has a conversion map for converting the sin θ component into the tan θ component in advance, the signal processing unit (180) receives a cosine wave signal including cos θ from the sensor element (130). There is no need to enter. That is, an A / D conversion circuit that converts the cosine wave signal into a digital signal in the signal processing unit (180) can be eliminated. Therefore, the circuit scale and current consumption occupied by the A / D conversion circuit in the signal processing unit (180) can be reduced.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

It is a mimetic diagram when the current sensor concerning one embodiment of the present invention is attached to a bus bar. It is sectional drawing of the current sensor shown in FIG. It is a circuit diagram of the current sensor shown in FIG. It is the figure which showed the conversion map. It is the figure which showed how to make the conversion map. It is a figure for demonstrating the case where the error of the component of tan (theta) is not contained in the predetermined | prescribed error tolerance | permissible_range. It is a figure for demonstrating the case where the error of the component of tan (theta) is contained in the predetermined | prescribed error tolerance | permissible_range.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The current sensor according to the present embodiment detects, for example, a current to be measured flowing in a bus bar connected to an in-vehicle battery or the like.

  As shown in FIGS. 1 and 2, the current sensor 100 includes a substrate 110, a magnetic field generation unit 120, a sensor element 130, a circuit chip 140, leads 150, and a mold resin 160.

  The magnetic field generator 120 generates a bias magnetic field Bb in a direction perpendicular to the current magnetic field Bi generated by the current I to be measured flowing through the bus bar 200 that is the detection target. The magnetic field generator 120 is installed on the one surface 111 of the substrate 110. The magnetic field generator 120 serves to apply the bias magnetic field Bb to the sensor element 130. The magnetic field generator 120 is configured as a plate-like bias magnet, for example.

  The sensor element 130 is a plate-shaped chip component having a plurality of magnetoresistive elements whose resistance values change when affected by an external magnetic field. As shown in FIG. 2, the sensor element 130 is disposed on the magnetic field generator 120.

  The circuit chip 140 includes a signal processing circuit for performing a preset operation on the signal input from the sensor element 130. The circuit chip 140 is installed on the one surface 111 of the substrate 110.

  The lead 150 is a connection component for electrically connecting the outside and the current sensor 100. In the present embodiment, the plurality of leads 150 are arranged in a direction perpendicular to the longitudinal direction of the leads 150. Each lead 150 is electrically connected to the circuit chip 140 via a wire (not shown).

  The mold resin 160 is a sealing member that seals a part of the substrate 110, the magnetic field generation unit 120, the sensor element 130, the circuit chip 140, and the lead 150. Specifically, the mold resin 160 seals each component so that a portion of the lead 150 opposite to the substrate 110, that is, a portion of the outer lead is exposed. Thereby, the current sensor 100 is formed as a mold IC. As a material of the mold resin 160, for example, an epoxy resin is employed.

  The current sensor 100 having the above configuration is assembled to the bus bar 200 as shown in FIG. Specifically, the current sensor 100 is assembled to the bus bar 200 so that the direction of current flowing through the bus bar 200, that is, the longitudinal direction of the bus bar 200 and the bias magnetic field Bb are parallel to each other. In other words, the current sensor 100 is assembled to the bus bar 200 so that the current magnetic field Bi generated by the measured current I flowing in the bus bar 200 and the bias magnetic field Bb are perpendicular to each other. A combined magnetic field Bs composed of a bias magnetic field Bb and a current magnetic field Bi is applied to the sensor element 130.

  Next, the circuit configuration of the sensor element 130 and the circuit chip 140 in the current sensor 100 will be described. As shown in FIG. 3, the sensor element 130 is configured such that the four magnetoresistive elements 131 to 134 form a bridge circuit.

  Although not shown, each of the magnetoresistive elements 131 to 134 is configured as a GMR element in which a pin magnetic layer, a nonmagnetic layer, a free magnetic layer, and an upper electrode are sequentially formed on the lower electrode. The pinned magnetic layer is a ferromagnetic metal layer whose magnetization direction is fixed. The nonmagnetic layer is a layer for allowing a current to flow from the free magnetic layer to the pinned magnetic layer. The free magnetic layer is a ferromagnetic metal layer whose magnetization direction changes under the influence of an external magnetic field. In each of the magnetoresistive elements 131 to 134, the magnetization directions of the pinned magnetic layers are parallel to each other.

  The sensor element 130 is installed on the magnetic field generator 120 so that the magnetization directions of the magnetoresistive elements 131 to 134 are perpendicular to the bias magnetic field Bb. Therefore, as shown in FIG. 1, when the angle formed by the bias magnetic field Bb and the combined magnetic field Bs is θ, the voltage at each midpoint of each half bridge output from the sensor element 130 is a sine value, that is, sin θ. Including sine wave signal. Therefore, the sensor element 130 determines whether the bias magnetic field Bb and the combined magnetic field Bs are based on a change in the resistance value of the magnetoresistive elements 131 to 134 when the magnetoresistive elements 131 to 134 are affected by an external magnetic field. A sine wave signal including a sin θ component is output for the formed angle θ.

  Here, when the sine wave signal is Vsin, the sine wave signal is expressed by Vsin = A (t) · sin θ + Voff (t). Since heat is generated in the bus bar 200 when the current I to be measured flows through the bus bar 200, the sin θ component includes an amplitude component (A (t)) and an offset component (Voff (t)) depending on temperature. include. The amplitude component corresponds to the sensitivity of the sensor element 130.

  The circuit chip 140 includes a temperature sensor 170 and a signal processing unit 180. The temperature sensor 170 detects a temperature caused by heat generated by the current I to be measured flowing through the bus bar 200. That is, the temperature sensor 170 detects the temperature of the signal processing unit 180. Then, the temperature sensor 170 outputs a temperature signal including temperature information to the second A / D conversion unit 182. The temperature sensor 170 includes, for example, a thermistor formed on a substrate constituting the circuit chip 140, a temperature detection circuit such as a diode, an estimation circuit that estimates the temperature from the output of the sensor element 130, and the like.

  The signal processing unit 180 is a digital circuit having a function of converting a sin θ component included in a sine wave signal into a tan θ component corresponding to the sin θ component. The signal processing unit 180 includes a first A / D conversion unit 181, a second A / D conversion unit 182, an amplitude calculation unit 183, an offset calculation unit 184, a temperature correction unit 185, a memory 186, a calculation unit 187, and a D / D A conversion unit 188 is included.

  The first A / D conversion unit 181 is a circuit unit that receives a sine wave signal from the sensor element 130 and converts it into a digital signal. The second A / D conversion unit 182 is a circuit unit that receives a temperature signal from the temperature sensor 170 and converts it into a digital signal.

  The amplitude calculation unit 183 includes a multiplication circuit 183a and an addition / subtraction circuit 183b. The multiplication circuit 183a multiplies the temperature indicated by the temperature information of the temperature signal by the data (1TAMP) stored in the memory 186. The addition / subtraction circuit 183b adds / subtracts the calculation result of the multiplication circuit 183a and the data (AMP) stored in the memory 186. Thereby, the amplitude calculation unit 183 acquires a parameter (A_T) for canceling the temperature-dependent amplitude.

  The offset calculation unit 184 includes a multiplication circuit 184a and an addition / subtraction circuit 184b. The multiplication circuit 184a multiplies the temperature indicated by the temperature information of the temperature signal by the data (TOF) stored in the memory 186. The addition / subtraction circuit 184b adds / subtracts the calculation result of the multiplication circuit 184a and the data (OFF) stored in the memory 186. Thereby, the offset calculation unit 184 acquires a parameter (Voff_T) for canceling the temperature-dependent offset.

  The temperature correction unit 185 includes an addition / subtraction circuit 185a and a multiplication circuit 185b. The addition / subtraction circuit 185a eliminates the offset component depending on the temperature included in the sine wave signal by adding or subtracting the parameter obtained by the offset calculation unit 184 to the sine wave signal converted into the digital signal. Further, the multiplication circuit 185b multiplies the parameter obtained by the amplitude calculator 183, thereby eliminating the amplitude component depending on the temperature included in the sine wave signal. Accordingly, the temperature correction unit 185 acquires a sine wave signal including a sin θ component that does not depend on the temperature. That is, the temperature correction unit 185 obtains Vsin = sin θ.

  Note that the circuit configuration may be such that the amplitude component is corrected first with respect to the sine wave signal by connecting the multiplication circuit 185 b to the first A / D conversion unit 181.

  The memory 186 is a storage unit that stores data used by the amplitude calculation unit 183 and the offset calculation unit 184 and a conversion map used by the calculation unit 187.

  The conversion map is data for converting a sin θ component into a tan θ component corresponding to the sin θ component. As shown in FIG. 4, in the conversion map, the horizontal axis corresponds to the component of sin θ, and the vertical axis corresponds to the component of tan θ. Based on this conversion map, the sin θ component is converted into a tan θ component.

  Specifically, the conversion map includes a plurality of division points, one or a plurality of functions, and a plurality of constants. The plurality of division points are parameters for dividing the maximum value and the minimum value of the sin θ component into a plurality of sections. In FIG. 4, since the interval between the maximum value and the minimum value of the sin θ component is divided into nine sections, eight division points are set.

  In addition, when dividing between the maximum value and the minimum value of the component of sin θ into two sections, the dividing point is a dividing point corresponding to the maximum value of the component of sin θ and a dividing point corresponding to the minimum value of the component of sin θ. And a dividing point between the maximum value and the minimum value of the component of sin θ.

The function is an Nth order function that connects adjacent dividing points among a plurality of dividing points. For example, in the case of a quadratic function, the function is expressed as y = a · x ² + b · x + c. y corresponds to the component of tan θ, and x corresponds to the component of sin θ. The function may be common to all the sections, or may be different for each section.

  The constant is set for the function for each of the plurality of sections so that the functions are smoothly connected in adjacent sections among the plurality of sections. In the case of the above quadratic function, a is set from a1 to a9 corresponding to each section. Also, b is set from b1 to b9 corresponding to each section. Similarly, c is set from c1 to c9 corresponding to each section. If the function becomes a cubic function, a constant corresponding to the cubic function is prepared.

  Here, the memory 186 is configured to be rewritable. For this reason, the plurality of division points are stored in the memory 186 so as to be rewritable. For example, each division point can be finely adjusted later according to the installation state of the current sensor 100 in a state where the initial value is stored at the time of manufacturing the current sensor 100.

  This is because when the current sensor 100 is assembled to the bus bar 200, a slight shift may occur in the conversion map depending on the positional relationship between the current sensor 100 and the bus bar 200, and the like. For this reason, the division point can be rewritten to correct this slight shift. Thus, it is preferable that the current sensor 100 is shipped in a state where the dividing points are finely adjusted.

  The calculation unit 187 is a circuit unit that converts a sin θ component into a tan θ component based on a conversion map for a sine wave signal that has been corrected for temperature characteristics based on temperature information. That is, the calculation unit 187 converts the sin θ component into the tan θ component by using, as a function, the constant of the interval corresponding to the sin θ component among the plurality of intervals. Thereby, the calculating part 187 acquires the signal containing the component of tan (theta) as a sensor signal. In addition, the calculation unit 187 outputs the sensor signal to the D / A conversion unit 188.

  The D / A conversion unit 188 is a circuit unit that converts a sensor signal as a digital signal that has been subjected to arithmetic processing by the arithmetic unit 187 into an analog signal. The output of the D / A converter 188 is output to the external device as the sensor output of the current sensor 100. The above is the configuration of the current sensor 100 according to the present embodiment.

  Next, how to create a conversion map will be described. As shown in FIG. 5, first, the sensor element 130 is prepared and the measured current I is swept from the minimum value to the maximum value. Thereby, the data of sin θ is acquired. Then, eight division points are set for the acquired sin θ data and written to the memory 186. Thereby, the component of sin θ is divided into nine sections.

  Subsequently, an Nth order function and a constant are derived in each section using the least square method (interpolation function calculation). In addition, the function and constant are written into the memory 186 to create a temporary conversion map. Then, the measured current I is swept from the minimum value to the maximum value. As a result, tan θ data is acquired using a temporary conversion map.

  Thereafter, it is determined whether or not the error of the tan θ component obtained by the temporary conversion map is uniform. That is, it is determined whether or not the error of the component of tan θ is included within a predetermined error allowable range. For example, as shown in FIG. 6, the error of the tan θ component is included in a predetermined error allowable range in a certain section, while the error exceeds the error allowable range in another section. As described above, when the error of the component of tan θ is not uniform, the process returns to the step of writing the dividing point in the memory 186.

  Then, a dividing point different from the previously written dividing point is written in the memory 186. Subsequently, the current to be measured I is swept from the minimum value to the maximum value, and tan θ data is acquired using a temporary conversion map. Again, it is determined whether or not the error of the tan θ component obtained by the provisional conversion map is uniform. If the error is included in the predetermined error allowable range in all the sections as shown in FIG. Is completed.

  When the error of the tan θ component is not included in the predetermined error allowable range, the division point is written, the interpolation function is calculated, the current sweep, and the tan θ data until the error of the tan θ component is included in the predetermined error allowable range. Repeat acquisition and error determination. 6 and 7, the range of the current I to be measured and the error range are the same.

  The conversion map created as described above is written in the memory 186 of each current sensor 100 as a conversion map common to a plurality of current sensors 100 manufactured. Each current sensor 100 is shipped.

  The current sensor 100 operates as follows. First, when the current I to be measured flows through the bus bar 200, the sensor element 130 outputs a sine wave signal including a sin θ component. Further, the temperature sensor 170 outputs a temperature signal.

  The signal processing unit 180 uses the temperature information included in the temperature signal and the data in the memory 186 to set parameters (A_T, Voff_T) for canceling the temperature-dependent amplitude and offset by the amplitude calculation unit 183 and the offset calculation unit 184. get.

  Then, the signal processing unit 180 corrects the temperature characteristic of the sine wave signal by the temperature correction unit 185 using the parameters (A_T, Voff_T) for canceling the amplitude and the offset. As a result, the signal processing unit 180 acquires a sin θ component that does not depend on the temperature. In addition, the signal processing unit 180 converts the sin θ component into the tan θ component using the conversion map in the calculation unit 187. The component of tan θ is proportional to the magnitude of the current I to be measured. The signal processing unit 180 outputs a sensor signal including the tan θ component.

  The D / A converter 188 converts the sensor signal into a digital signal and outputs it as a sensor output to an external device. The external device controls the measured current I flowing through the bus bar 200 based on the sensor signal.

  As described above, in the current sensor 100 of the present embodiment, only the sine wave signal including the sin θ component is acquired in the sensor element 130, and the signal processor 180 uses the conversion map to convert the tan θ component from the sin θ component. It is characterized by acquiring. As described above, since the signal processing unit 180 obtains the tan θ component only from the sin θ component using the conversion map stored in advance, the current sensor 100 does not need an A / D conversion unit related to the cosine wave signal including cos θ. Therefore, the circuit scale and current consumption occupied by the A / D conversion circuit in the signal processing unit 180 can be reduced.

  Further, since the signal processing unit 180 performs temperature correction of the sine wave signal by the temperature correction unit 185 before converting the sin θ component into the tan θ component based on the conversion map, the temperature characteristics are considered in the conversion map. There is no need to do. That is, since a plurality of variations of conversion maps are not required for each temperature, there is an advantage that the signal processing unit 180 only needs to have one conversion map that does not depend on temperature.

  As for the correspondence between the description of the present embodiment and the description of the claims, the bus bar 200 corresponds to the “current path to be measured” in the claims.

(Other embodiments)
The configuration of the current sensor 100 shown in each of the above embodiments is an example, and the present invention is not limited to the configuration shown above, and other configurations that can realize the present invention can be used. As for the arrangement relationship between the magnetic field generator 120 and the sensor element 130, as long as the relationship between the magnetization direction of the pinned magnetic layer of each of the magnetoresistive elements 131 to 134 and the direction of the bias magnetic field Bb can be maintained as described above, any arrangement is possible. The relationship may be good. Moreover, although each magnetoresistive element 131-134 of the sensor element 130 was comprised as a GMR element, you may be comprised as a TMR element.

  In the above embodiment, the temperature correction unit 185 performs temperature correction of the sine wave signal, but this is an example of signal processing. Therefore, the current sensor 100 may be configured not to perform temperature correction of the sine wave signal.

  In the above embodiment, the interval between the maximum value and the minimum value of the sin θ component is divided into a plurality of sections by dividing points. However, if possible, the interval between the maximum value and the minimum value of the sin θ component is 1. You may approximate with two functions.

  In the above embodiment, the data of the division points stored in the memory 186 can be rewritten, but this is an example. For example, the data of the dividing points stored in the memory 186 may not be rewritable.

  Furthermore, in the above-described embodiment, the current sensor 100 is configured to measure the current I to be measured flowing through the bus bar 200 connected to the vehicle battery or the like, but this is an example of the application of the current sensor 100. Therefore, the measurement target is not limited to the vehicle bus bar 200, and the current sensor 100 may be applied to wiring used for other purposes.

DESCRIPTION OF SYMBOLS 120 Magnetic field generation part 130 Sensor element 131-134 Magnetoresistive element 180 Signal processing part 186 Memory 200 Bus bar (measurement current path)
Bi current magnetic field Bb bias magnetic field Bs synthetic magnetic field

Claims (4)

A magnetic field generator (120) for generating a bias magnetic field (Bb) in a direction perpendicular to a current magnetic field (Bi) generated by the current to be measured flowing through the current to be measured (200);
Resistance values of the plurality of magnetoresistive elements (131 to 134) when the plurality of magnetoresistive elements (131 to 134) are affected by an external magnetic field. A sinusoidal wave including a sin θ component with respect to an angle θ formed by the bias magnetic field (Bb) and a combined magnetic field (Bs) composed of the current magnetic field (Bi) and the bias magnetic field (Bb). A sensor element (130) for outputting a signal;
A memory (186) that stores a conversion map for converting the sin θ component into a tan θ component corresponding to the sin θ component, converts the sine wave signal into a digital signal, and inputs the digital signal to the conversion map. A signal processor (180) that converts the sin θ component into the tan θ component based on the signal and acquires a signal including the tan θ component as a sensor signal;
A current sensor comprising:   The signal processing unit (180) acquires temperature information caused by heat generated by the current to be measured flowing through the current to be measured (200), and based on the conversion map, the component of the sin θ is obtained as the tan θ. 2. The current sensor according to claim 1, wherein a temperature characteristic is corrected for the sine wave signal based on the temperature information before conversion into the component. The transformation map includes a plurality of division points that divide between a maximum value and a minimum value of the sin θ component into a plurality of sections, and a function for connecting adjacent division points among the plurality of division points, A constant set for the function for each of the plurality of sections so that the functions are smoothly connected in adjacent sections among the plurality of sections,
The signal processing unit (180) converts the sin θ component to the tan θ component by using a constant of the interval corresponding to the sin θ component of the plurality of intervals for the function. Item 3. The current sensor according to Item 1 or 2.   The current sensor according to claim 3, wherein the plurality of division points are stored in the memory (186) so as to be rewritable.

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