JPWO2013105451A1 - Current sensor - Google Patents

Abstract

To provide a current sensor capable of accurately adjusting offset and sensitivity at a time. A magnetoelectric conversion circuit (11) that converts a magnetic field into a voltage and outputs the voltage from an output terminal, a buffer amplification circuit (12) connected to the output terminal of the magnetoelectric conversion circuit, and an adjustment circuit (13) that adjusts the output of the buffer amplification circuit The adjustment circuit includes a first adjustment unit (131) that outputs the adjusted voltage from the output terminal, a second adjustment unit (133) that can adjust the amplification factor of the buffer amplification circuit, and a first adjustment unit. A buffer circuit (132) provided between the output terminal of the adjustment unit and the second adjustment unit, and the offset of the output of the buffer amplifier circuit is adjusted by the voltage output from the first adjustment unit. Features.

Description

  The present invention relates to a current sensor capable of measuring a current to be measured without contact.

  In fields such as motor drive technology in electric vehicles and hybrid cars, a relatively large current is handled, and therefore, a current sensor capable of measuring a large current in a non-contact manner is required for these applications. As such a current sensor, there has been proposed a system that detects a change in a magnetic field caused by a current to be measured using a magnetic detection element.

  In a current sensor using a magnetic detection element, the sensitivity of the magnetic detection element varies from element to element. Therefore, gain (sensitivity) adjustment and offset (when the measured current is 0 A) are obtained in order to obtain a desired sensor output corresponding to the measured current. The deviation of the sensor output from the reference value) must be adjusted. For example, Patent Document 1 proposes a current sensor that simplifies the adjustment by eliminating the change in the drive current of the magnetic detection element due to the sensitivity adjustment and preventing the change in the offset voltage.

JP 2010-127636 A

  The current sensor described in Patent Document 1 is adjusted through a step of adjusting a resistance for offset adjustment while measuring a sensor output and a step of adjusting a resistance for sensitivity adjustment while measuring a sensor output. That is, in the adjustment of the current sensor, it is necessary to perform the step of changing the adjustment resistance in accordance with the measured value of the sensor output at least twice. As described above, the current sensor described in Patent Document 1 has a problem in that the adjustment resistance value cannot be adjusted at a time, so that adjustment takes time. In addition, in this current sensor, since the resistance value is adjusted while measuring the sensor output, there is a problem that a resistor capable of gradually changing the resistance value must be used.

  This invention is made | formed in view of this point, and it aims at providing the current sensor which can adjust an offset and a sensitivity precisely at once.

  The current sensor of the present invention includes a magnetoelectric conversion circuit that converts a magnetic field into a voltage and outputs the voltage from an output end, a buffer amplification circuit connected to the output end of the magnetoelectric conversion circuit, and an adjustment that adjusts an output of the buffer amplification circuit A first adjustment unit that outputs the adjusted voltage from an output terminal, a second adjustment unit that can adjust an amplification factor of the buffer amplification circuit, and a first adjustment unit. And a buffer circuit provided between the output terminal and the second adjustment unit, and an offset of an output of the buffer amplifier circuit is adjusted by a voltage output from the first adjustment unit. .

  According to this configuration, the buffer circuit is provided between the first adjustment unit for adjusting the offset of the output of the buffer amplification circuit and the second adjustment unit for adjusting the amplification factor of the buffer amplification circuit. The offset adjustment process performed by the output adjustment of the first adjustment unit is not affected by the sensitivity adjustment process performed by the second adjustment unit. As a result, the offset and sensitivity can be accurately adjusted at a time. In addition, it is not necessary to provide a dedicated terminal for adjusting the offset in the buffer amplifier circuit. In addition, since the constant balance in the buffer amplifier circuit is not lost, it is possible to prevent deterioration of the amplifier circuit characteristics such as temperature characteristics.

  In the current sensor of the present invention, the buffer amplifier circuit is an operational amplifier including a first input terminal connected to the magnetoelectric conversion circuit, a second input terminal connected to the adjustment circuit, and an output terminal. Preferably, the second adjustment unit includes a third adjustment resistor and a fourth adjustment resistor connected in series to the buffer circuit, and the buffer amplifier circuit and the fourth adjustment resistor are connected in parallel. . According to this configuration, the magnetoelectric conversion circuit is not affected by the state on the output end side of the buffer amplifier circuit with a simple circuit configuration. Further, the magnetoelectric conversion circuit is not affected by the state on the adjustment circuit side.

  In the current sensor of the present invention, the first adjustment unit includes a first adjustment resistor and a second adjustment resistor connected in series between a voltage source and a ground, and the first adjustment resistor and the second adjustment resistor. It is preferable that the connection point of the resistor is connected to the input terminal of the buffer circuit.

  In the current sensor of the present invention, the magnetoelectric conversion circuit includes a bridge circuit having a magnetosensitive element whose electrical characteristics change in accordance with a magnetic field, and an input terminal connected to the bridge circuit, to the magnetic field measured by the bridge circuit. An amplifying circuit for generating a current in response, a coil having one end connected to the output end of the amplifying circuit, a current-voltage conversion circuit connected to the other end of the coil and generating a voltage corresponding to the current flowing through the coil; The amplifier circuit preferably controls the current flowing through the coil so as to generate a magnetic field that cancels the magnetic field applied to the magnetosensitive element. According to this configuration, the magnetoelectric conversion circuit has a low impedance output, but since the buffer amplifier circuit is provided between the magnetoelectric conversion circuit and the adjustment circuit, it is possible to prevent the current measurement accuracy from being deteriorated due to the adjustment circuit. In addition, since the buffer amplifier circuit is provided between the magnetoelectric conversion circuit and the adjustment circuit, the current flowing through the coil is not affected by the circuit subsequent to the current-voltage conversion circuit. Thereby, when the induced magnetic field due to the current to be measured is small, a minute coil current can be converted into a current voltage with high accuracy.

  In the current sensor of the present invention, the magnetosensitive element may be a magnetoresistive element.

  In the current sensor of the present invention, the buffer circuit is preferably an operational amplifier.

  An adjustment method for a current sensor according to the present invention includes a magnetoelectric conversion circuit that converts a magnetic field into a voltage and outputs the voltage from an output end, an adjustment circuit for adjusting the voltage at the output end of the magnetoelectric conversion circuit, and the magnetoelectric conversion circuit A buffer amplifier circuit connected to the output terminal, and the adjustment circuit includes: a first adjustment unit that outputs the adjusted voltage from the output terminal; an output terminal of the first adjustment unit; and a second adjustment unit. A buffer circuit provided between the input terminal and the voltage value at the output terminal of the buffer amplifier circuit in two states where the current values of the current under measurement flowing through the current path to be measured are different. And a step of simultaneously adjusting the outputs of the first adjustment unit and the second adjustment unit based on the measured two voltage values of the output terminal of the buffer amplifier circuit. .

  According to the present invention, it is possible to provide a current sensor capable of accurately adjusting offset and sensitivity at a time.

It is a schematic diagram which shows the structure outline of the current sensor which concerns on this Embodiment. It is a circuit diagram which shows the structural example of the current sensor which concerns on this Embodiment. It is a circuit diagram which shows the structural example of the adjustment resistance of the current sensor which concerns on this Embodiment.

  In the current sensor capable of adjusting the offset and the sensitivity, the offset adjustment process and the sensitivity adjustment process need to be performed separately because one adjustment process affects the other adjustment process. . The inventor pays attention to this point and devise the connection relationship between the offset adjustment unit for offset adjustment and the sensitivity adjustment unit for sensitivity adjustment, so that one adjustment step does not affect the other adjustment step. Thus, the present invention has been completed.

  That is, the gist of the present invention is a buffer circuit that converts impedance between the offset adjustment unit and the sensitivity adjustment unit so that the output of the offset adjustment unit is not affected by the circuit state of the sensitivity adjustment unit. A buffer circuit). Thereby, since the output of the offset adjustment unit is not affected by the circuit state of the sensitivity adjustment unit, the offset and sensitivity can be accurately adjusted at a time by eliminating the influence of the sensitivity adjustment step from the offset adjustment step. Hereinafter, the current sensor of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing a configuration example of a magnetic balanced current sensor according to the present embodiment. FIG. 2 is a circuit diagram showing a configuration example of the current sensor according to the present embodiment. As shown in FIG. 1, the current sensor 1 according to the present embodiment is disposed in the vicinity of a conductor (current path) 2 through which a current I to be measured flows. As shown in FIGS. 1 and 2, the current sensor 1 includes a magnetoelectric conversion circuit 11 that converts an induced magnetic field A generated by the current I to be measured into electric power, and a buffer circuit (buffer amplification circuit) 12 that is connected to the magnetoelectric conversion circuit 11. And an adjustment circuit 13 connected to the buffer circuit 12 and used for adjusting the offset and sensitivity.

  The magnetoelectric conversion circuit 11 includes a bridge circuit 111, a differential / current amplifier (voltage / current conversion circuit) 112, a feedback coil 113, and an I / V amplifier (amplification circuit, current / voltage conversion circuit) 114.

  In the magnetoelectric conversion circuit 11, the bridge circuit 111 includes four magnetoresistive elements M <b> 1 to M <b> 4 so that the induced magnetic field A caused by the current I to be measured can be detected. The magnetoresistive elements M1 to M4 are GMR (Giant Magneto Resistance) elements, TMR (Tunnel Magneto Resistance) elements, and the like whose resistance value changes when an external magnetic field is applied. The bridge circuit 111 including the magnetoresistive elements M1 to M4 can realize the magnetic balance type current sensor 1 that can detect the induced magnetic field A caused by the current I to be measured with high sensitivity.

In the bridge circuit 111, a power supply (voltage source) that supplies a power supply voltage _Vdd is connected to a connection point between the magnetoresistive effect elements M1 and M3. In addition, a ground for applying a ground voltage GND (0 V) is connected to a connection point between the magnetoresistive elements M2 and M4. The first output Out1 of the bridge circuit 111 is extracted from the connection point of the magnetoresistive elements M1 and M2, and the second output Out2 of the bridge circuit 111 is extracted from the connection point of the magnetoresistive elements M3 and M4. The voltage difference between these two outputs is configured to correspond to the magnetic field applied to the bridge circuit 111. The bridge circuit 111 may include a fixed resistance element whose resistance value does not change due to an external magnetic field.

  A differential / current amplifier (amplifier circuit) 112 that amplifies the voltage difference between the first output Out1 and the second output Out2 of the bridge circuit 111 to generate a current is connected to the subsequent stage of the bridge circuit 111. That is, the differential / current amplifier 112 generates a current corresponding to the magnetic field applied to the bridge circuit 111 from the voltage difference between the first output Out1 and the second output Out2 of the bridge circuit 111.

  A feedback coil 113 is connected to the subsequent stage of the differential / current amplifier 112. The feedback coil 113 is configured by, for example, a spiral planar conductive pattern. When a current (feedback current) from the differential / current amplifier 112 flows through the conductive pattern, a reverse canceling magnetic field B corresponding to the induced magnetic field A caused by the current I to be measured can be generated. However, the shape of the feedback coil 111 is not particularly limited.

The feedback coil 113 is connected to an I / V amplifier (current / voltage conversion circuit) 114 that converts a feedback current into a voltage. The I / V amplifier 114 includes an operational amplifier 114 a having two input ends and one output end, and one of the input ends is connected to the feedback coil 113. The other input terminal of the operational amplifier 114a is connected to a connection point between two resistance elements 115a and 115b having the same resistance value connected at one end. The resistance values of the resistance elements 115a and 115b may be different. The other end of the resistor element 115a is connected to a power supply that supplies a power supply voltage _Vdd, and the other end of the resistor element 115b is connected to a ground that supplies a ground voltage GND (0V). As a result, a reference voltage corresponding to 1/2 of the power supply voltage V _dd is applied to the other input terminal of the operational amplifier 114a. The output terminal of the operational amplifier 114a is connected to the other input terminal of the operational amplifier 114a through the resistance element 114b. The output of the operational amplifier 114a becomes the output of the I / V amplifier 114.

  In the magnetoelectric conversion circuit 11, when the bridge circuit 111 receives the induced magnetic field A due to the current I to be measured, a voltage difference is generated between the first output Out1 and the second output Out2. At this time, the differential current amplifier 112 generates a current corresponding to the voltage difference and passes it through the feedback coil 113. When a current flows through the feedback coil 113, a cancel magnetic field B is generated around the feedback coil 113 so as to cancel the induced magnetic field A caused by the current I to be measured. The current flowing through the feedback coil 113 is converted into a voltage by the I / V amplifier 114. The voltage output from the I / V amplifier 114 in an equilibrium state in which the induced magnetic field A and the canceling magnetic field B are canceled out has a magnitude corresponding to the measured current I.

  The output terminal of the I / V amplifier 114, that is, the output terminal of the magnetoelectric conversion circuit 11 is connected to the input terminal of the buffer circuit (buffer amplifier circuit) 12. The buffer circuit 12 is composed of an operational amplifier having two input terminals and one output terminal, and the output terminal of the I / V amplifier 114 is connected to one input terminal thereof.

  The other input end and output end of the buffer circuit 12 are connected to an adjustment circuit 13 for adjusting the offset (the amount of deviation from the reference value of the sensor output when the current to be measured is 0 A) and sensitivity in the current sensor 1. Has been. Thereby, the output voltage of the magnetoelectric conversion circuit 11 applied to one input terminal can be adjusted by the adjustment circuit 13 connected to the other input terminal and the output terminal, and can be output from the output terminal.

  The impedance between the two input terminals of the buffer circuit 12 is so high that the circuit connected to one input terminal does not interfere with the circuit connected to the other input terminal. That is, the buffer circuit 12 is configured to have a high impedance input so that the voltage at the output terminal of the magnetoelectric conversion circuit 11 is not affected by the adjustment state of the adjustment circuit 13. In other words, the magnetoelectric conversion circuit 11 and the adjustment circuit 13 are separated by the buffer circuit 12.

  Further, in the buffer circuit 12, the impedance between the input end and the output end is so high that the circuit connected to the output end does not interfere with the circuit connected to the input end. That is, the buffer circuit 12 is configured to have a high impedance so that the voltage at the output terminal of the magnetoelectric conversion circuit 11 is not affected by the voltage at the output terminal of the buffer circuit 12. The voltage at the output terminal of the buffer circuit 12 does not affect the voltage at one input terminal connected to the magnetoelectric conversion circuit 11. As a result, the output voltage of the magnetoelectric conversion circuit 11 is not affected by the circuit connected to the subsequent stage of the buffer circuit 12. As a result, it is possible to prevent the output voltage of the magnetoelectric conversion circuit 11 from fluctuating due to the influence of the circuit connected to the subsequent stage of the buffer circuit 12 and degrading the current measurement accuracy.

  The adjustment circuit 13 includes an offset adjustment unit (first adjustment unit) 131 for offset adjustment, a buffer circuit (buffer circuit) 132 connected to the offset adjustment unit 131, and a sensitivity adjustment unit (first adjustment unit) connected to the buffer circuit 132. 2 adjustment unit) 133.

  The offset adjustment unit 131 includes an adjustment resistor 131a in which two resistor elements are connected in parallel and an adjustment resistor 131b in which two resistor elements are connected in parallel. One end of the adjustment resistor 131 a and one end of the adjustment resistor 131 b are connected, and this connection point is connected to the buffer circuit 132 at the subsequent stage as an output end of the offset adjustment unit 131. A power supply is connected to the other end of the adjustment resistor 131a, and a ground is connected to the other end of the adjustment resistor 131b. As a result, the buffer circuit 132 is supplied with a voltage determined by the resistance values of the adjustment resistors 131a and 131b.

  In the offset adjustment unit 131, one of the two resistance elements constituting the adjustment resistors 131a and 131b is configured to be added at the time of correction. Thereby, the offset of the current sensor 1 can be adjusted by adding a resistance element and adjusting the combined resistance value of the adjustment resistors 131a and 131b. In the case of this configuration, the correction can be made simply by adding a resistance element. The adjustment resistors 131a and 131b may be configured so that the resistance elements can be exchanged. The configuration of the adjustment resistors 131a and 131b is not limited to the configuration in which two resistance elements are connected in parallel, and can be changed as appropriate. The adjustment resistors 131a and 131b may be realized by a single resistance element.

  The buffer circuit 132 is configured by an operational amplifier having two input ends and one output end, and the output end of the offset adjustment unit 131 is connected to one input end thereof. The output terminal of the buffer circuit 132 is connected to the other input terminal. Thus, a voltage follower circuit that outputs a voltage corresponding to the output voltage of the offset adjustment unit 131 is configured.

  The input terminal of the sensitivity adjustment unit 133 is connected to the output terminal of the buffer circuit 132. In the buffer circuit 132, the impedance between the input terminal and the output terminal is high enough to prevent the circuit connected to the input terminal from interfering with the circuit connected to the input terminal. The buffer circuit 132 is configured to perform impedance conversion so that the voltage at the output end of the offset adjustment unit 131 is not affected by the current at the input end of the sensitivity adjustment unit 133. The current at the output terminal connected to the sensitivity adjustment unit 133 does not affect the voltage at one input terminal connected to the offset adjustment unit 131.

  Thus, the output of the offset adjustment unit 131 is not affected by the circuit state of the sensitivity adjustment unit 133. In other words, the offset adjustment unit 131 and the sensitivity adjustment unit 133 are separated by the buffer circuit 132. As a result, the offset adjustment unit 131 and the sensitivity adjustment unit 133 can be optimized simultaneously, and the offset and sensitivity can be adjusted with high accuracy at a time. Note that the optimization of the offset adjustment unit 131 and the sensitivity adjustment unit 133 need not be strictly the same. For example, it includes a case where the adjustment between the offset adjustment unit 131 and the sensitivity adjustment unit 133 is performed continuously without a measurement step in between.

  The sensitivity adjustment unit 133 includes an adjustment resistor 133a in which two resistance elements are connected in parallel and an adjustment resistor 133b in which two resistance elements are connected in parallel. One end of the adjustment resistor 133 a and one end of the adjustment resistor 133 b are connected, and this connection point is connected to the other input end of the buffer circuit 12. The output terminal of the buffer circuit 132 is connected to the other end of the adjustment resistor 133a. The output terminal of the buffer circuit 12 is connected to the other end of the adjustment resistor 133b.

  In the sensitivity adjustment unit 133, one of the two resistance elements constituting the adjustment resistors 133a and 133b is configured to be added at the time of correction. Thus, a resistance element is added to adjust the combined resistance value of the adjustment resistors 133a and 133b, and the sensitivity of the current sensor 1 can be adjusted. In the case of this configuration, it can be easily corrected by adding a resistance element once. The adjustment resistors 131a and 131b may be configured so that the resistance elements can be exchanged. Further, the configuration of the adjustment resistors 133a and 133b is not limited to the configuration in which two resistance elements are connected in parallel, and can be changed as appropriate. The adjustment resistors 133a and 133b may be realized by a single resistance element.

  As described above, the connection point of the adjustment resistors 133a and 133b is connected to the other input end of the buffer circuit 12, and the output end of the buffer circuit 12 is connected to the other end of the adjustment resistor 133b. Thereby, the buffer circuit 12 can adjust the output of the magnetoelectric conversion circuit 11 by the adjustment circuit 13, and can output from the output terminal. The output of the buffer circuit 12 becomes the output of the current sensor 1.

Next, offset adjustment and sensitivity adjustment in the current sensor 1 will be described. In the current sensor 1 configured as described above, the voltage value V _IV at the output terminal of the I / V amplifier 114 is expressed by the following formula (1). In Expression (1), V _ref represents the voltage value (= V _dd / 2) of the reference voltage applied to the other input terminal of the operational amplifier 114a, R _s represents the resistance value of the resistance element 114b, and I _coil represents feedback. The current value of the feedback current flowing through the coil 113 is shown.

The voltage value _Vout at the output terminal of the buffer circuit 12 is expressed by the following equation (2). In the formula _{(2), V ofs} represents the voltage value of the output terminal of the buffer circuit 132, _{R a} represents a resistance value of the adjusting resistor 133a of the sensitivity adjustment unit 133, _{R b} is the adjustment resistor 133b of the sensitivity adjustment unit 133 Indicates the resistance value.

The voltage value V _ofs at the output terminal of the buffer circuit 132 is expressed by the following equation (3). In Expression (3), R _c represents the resistance value of the adjustment resistor 131 a of the offset adjustment unit 131, and R _d represents the resistance value of the adjustment resistor 131 _b of the offset adjustment unit 131.

From the expressions (1) to (3), the voltage value _Vout at the output terminal of the buffer circuit 12 is expressed by the following expression (4).

As shown in Expression (4), the voltage value V _out of the output terminal of the buffer circuit 12 is the resistance value R _{a of} the adjustment resistor 133 a of the sensitivity adjustment unit 133, the resistance value R _b of the adjustment resistor 133 _b , and the offset adjustment unit 131. resistance _{R c} of the adjusting resistors 131a, represented by the resistance value _{R d} of the adjustment resistor 131b. For this reason, by measuring the output voltage values _{Vout in} a plurality of different states, the resistance values of the adjustment resistors 131a, 131b, 133a, and 133b can be determined so as to match the intended sensitivity characteristics and offset characteristics.

An example of a more specific adjustment method will be described. First, as shown in the following formula (5), the resistance value R _a1 of the adjustment resistor 133a of the sensitivity adjustment unit 133 in the initial state is set equal to the resistance value R _b1 of the adjustment resistor 133b of the sensitivity adjustment unit 133 in the initial state. To do.

At this time, the voltage value V _ofs at the output terminal of the buffer circuit 132 is expressed by the following equation (6).

The feedback current flowing through the feedback coil 113 is composed of a current generated by sensing an induced magnetic field and an offset current. Therefore, the current value I _coil is the sum of the current value I _sens by sensing and the offset current value I _ofs as shown in the following formula (7).

Further, the target sensitivity G _set (mV / A) at the time of 100 A measurement (current value of the current to be measured is 100 A) is set. G _set is represented by the following formula (8). G _set represents the ratio of the output voltage value of the current sensor 1 to the current value of the current to be measured. In Expression (8), I _sens (100) indicates a current value generated by sensing when the current to be measured is 100 A, and R _a2 indicates the resistance value of the adjustment resistor 133a of the sensitivity adjustment unit 133 after adjustment (achieves the target sensitivity). indicates the resistance value of the adjusting resistor 133a) _{for, R b2} represents the resistance of the adjusting resistors 133b of the sensitivity adjustment unit 133 after adjustment (the resistance value of the adjusting resistor 133b for achieving the target speed).

Next, in the initial state described above, the output voltage value _Vout when the measured current is 0 A and 100 A is measured. The output voltage value V _out (0) when the measured current is 0 A and the output voltage value V _out (100) when the measured current is 100 A are expressed by the following equations (9) and (10), respectively. The

From formulas (9) and (10), I _ofs and I _sens (100) are obtained as shown in the following formulas (11) and (12), respectively.

From Expression (8), the ratio of R _a2 and R _b2 for achieving the target sensitivity is expressed as the following Expression (13). Therefore, the relationship between R _a2 and R _b2 for achieving the target sensitivity can be determined from the above equation (12) and the following equation (13).

On the other hand, when adjusting the current sensor 1 so that the offset is zero, that is, when adjusting the current sensor 1 so that V _out (0) is an ideal output Vdd / 2 in the zero magnetic field, the output voltage value The following equation (14) holds for V _out (0). In Expression (14), R _c2 indicates the resistance value of the adjustment resistor 131a of the offset adjustment unit 131 after adjustment (resistance value of the adjustment resistor 131a for achieving the target offset), and R _d2 indicates the offset adjustment after adjustment. The resistance value of the adjustment resistor 131b of the part 131 (resistance value of the adjustment resistor 131b for achieving a target offset) is shown.

From Expression (14), R _c2 and R _d2 for achieving the target offset are expressed as the following Expression (15). Therefore, the relationship between R _c2 and R _d2 for achieving the target offset can be determined from the above equation (11) and the following equation (15).

Thereafter, resistance elements constituting the adjustment resistors 131a, 131b, 133a, and 133b are added so as to realize the relationship between the resistance values (R _a2 , R _b2 , R _c2 , and R _d2 ) calculated as described above. Thereby, the sensitivity characteristic and the offset characteristic of the current sensor 1 are adjusted, and the intended offset characteristic and sensitivity characteristic can be realized.

  As described above, the current sensor 1 according to the present embodiment uses the buffer circuit 132 that performs impedance conversion so that the voltage at the output terminal of the offset adjustment unit 131 is not affected by the current at the input terminal of the sensitivity adjustment unit 133. Yes. More specifically, a buffer circuit 132 having a high impedance between the input and output terminals is provided between the adjustment resistors 131a and 131b constituting the offset adjustment unit 131 and the adjustment resistors 133a and 133b constituting the sensitivity adjustment unit 133. Provided. For this reason, the offset adjustment process performed by the output adjustment of the offset adjustment unit 131 is not affected by the sensitivity adjustment process performed by the output adjustment of the sensitivity adjustment unit 133. As a result, the offset and sensitivity can be accurately adjusted at a time.

Since the current sensor 1 according to the present embodiment includes the buffer circuit 12 between the magnetoelectric conversion circuit 11 and the adjustment circuit 13, the current-voltage conversion reference voltage _Vref is maintained at _Vdd / 2. Can do. Therefore, the maximum value of the coil current determined by the potential difference between V _dd or GND and V _ref and the coil resistance can be set to the maximum value (current value corresponding to V _dd / 2) on the circuit configuration. Thereby, even when the induced magnetic field due to the current to be measured is large, the magnetic field received by the magnetoresistive element can be reduced by flowing a large current through the coil. As a result, hysteresis of the magnetoresistive effect element due to a large induction magnetic field can be prevented, and deterioration of current accuracy of the current sensor 1 using the magnetoresistive effect element can be prevented.

  Next, a configuration example of the adjustment resistors 133a and 133b will be described with reference to FIG. FIG. 3 is a circuit diagram illustrating a configuration example of the adjustment resistors 133a and 133b. The configuration example of the adjustment resistors 131a and 131b is the same as the configuration example of the adjustment resistors 133a and 133b, and the configuration shown in FIG. 3 can be applied.

  FIG. 3A shows an example in which the adjustment resistor 133a is configured by a single resistance element, and the adjustment resistor 133b is configured by two resistance elements connected in parallel. In this case, the resistance value of the adjustment resistor 133b can be adjusted more finely than the adjustment resistor 133a. The adjustment resistor 133b may be configured by a single resistance element, and the adjustment resistor 133a may be configured by two resistance elements connected in parallel. FIG. 3B shows an example in which the adjustment resistors 133a and 133b are each composed of two resistance elements connected in parallel. In this case, both the resistance values of the adjustment resistors 133a and 133b can be finely adjusted.

  FIG. 3C shows an example in which the adjustment resistors 133a and 133b are each composed of three resistance elements connected in parallel. In this case, the resistance values of the adjustment resistors 133a and 133b can be adjusted more finely. Note that the number of resistance elements constituting the adjustment resistors 133a and 133b may be four or more. By increasing the number of resistance elements connected in parallel, the resistance values of the adjustment resistors 133a and 133b can be adjusted more finely. FIG. 3D shows an example in which the adjustment resistors 133a and 133b are each composed of two resistance elements connected in parallel and one resistance element connected in series. In this case, the resistance values of the adjustment resistors 133a and 133b can be finely adjusted by adding or changing the resistance elements connected in parallel.

  As described above, the current sensor 1 according to the present embodiment adjusts the resistance values of the adjustment resistors 131a, 131b, 133a, and 133b by the combination of the resistance elements that constitute the adjustment resistors 131a, 131b, 133a, and 133b. Can be adjusted. For this reason, in the current sensor 1 of the present embodiment, it is not necessary to use a resistor whose resistance value gradually changes. For example, it is not affected by vibrations or changes with time, such as volume resistance. Further, it is not necessary to use an expensive apparatus for correction, such as laser trimming. For this reason, stable correction can be realized at low cost.

  In addition, this invention is not limited to the said embodiment, A various change can be implemented. For example, as an adjustment resistor for adjusting the offset and sensitivity, a resistor formed as an IC may be used so that resistors connected in parallel can be switched by a switch. Further, an integrated circuit can be used as the operational amplifier constituting the current sensor. In this respect, the current sensor 1 according to the embodiment having four operational amplifiers is preferable in that it can be realized by using one IC package including two or four operational amplifiers. Moreover, in the said embodiment, although the sensitivity is adjusted on the basis of the case where a to-be-measured electric current is 100 A, the electric current value used as a reference | standard can be set arbitrarily.

  Further, the connection relationship, size, and the like of each element in the above embodiment can be changed without changing the gist of the invention. In addition, the structures, methods, and the like described in the above embodiments can be combined as appropriate. In addition, the present invention can be implemented with appropriate modifications without departing from the scope of the present invention.

  The current sensor of the present invention can be used, for example, to detect the magnitude of a current for driving a motor of an electric vehicle or a hybrid car.

  This application is based on Japanese Patent Application No. 2012-4016 for which it applied on January 12, 2012. All this content is included here.

An adjustment method for a current sensor according to the present invention includes a magnetoelectric conversion circuit that converts a magnetic field into a voltage and outputs the voltage from an output end, an adjustment circuit for adjusting the voltage at the output end of the magnetoelectric conversion circuit, and the magnetoelectric conversion circuit A buffer amplifier circuit connected to the output terminal, wherein the adjustment circuit outputs a regulated voltage from the output terminal, and a second regulator unit capable of adjusting an amplification factor of the buffer amplifier circuit And a buffer circuit provided between the output end of the first adjustment unit and the input end of the second adjustment unit, and the current value of the current to be measured flowing through the current path to be measured is different. The step of measuring the voltage value of the output terminal of the buffer amplifier circuit for the two states, and the first adjusting unit and the second adjusting unit based on the measured two voltage values of the output terminal of the buffer amplifier circuit And a step of simultaneously adjusting the output of

In the sensitivity adjustment unit 133, one of the two resistance elements constituting the adjustment resistors 133a and 133b is configured to be added at the time of correction. Thus, a resistance element is added to adjust the combined resistance value of the adjustment resistors 133a and 133b, and the sensitivity of the current sensor 1 can be adjusted. In the case of this configuration, it can be easily corrected by adding a resistance element once. The adjustment resistors 133a and 133b may be configured so that the resistance elements can be exchanged. Further, the configuration of the adjustment resistors 133a and 133b is not limited to the configuration in which two resistance elements are connected in parallel, and can be changed as appropriate. The adjustment resistors 133a and 133b may be realized by a single resistance element.

In addition, this invention is not limited to the said embodiment, A various change can be implemented. For example, as an adjustment resistor for adjusting the offset and the sensitivity, a resistor formed as an IC so that a resistor connected in parallel can be switched by a switch may be used. Further, an integrated circuit can be used as the operational amplifier constituting the current sensor. In this respect, the current sensor 1 according to the embodiment having four operational amplifiers is preferable in that it can be realized using two IC packages including two operational amplifiers or one IC package including four operational amplifiers. Moreover, in the said embodiment, although the sensitivity is adjusted on the basis of the case where a to-be-measured electric current is 100 A, the electric current value used as a reference | standard can be set arbitrarily.

Claims (7)

A magnetoelectric conversion circuit that converts a magnetic field into a voltage and outputs the voltage from an output end, a buffer amplification circuit connected to the output end of the magnetoelectric conversion circuit, and an adjustment circuit that adjusts the output of the buffer amplification circuit,
The adjustment circuit includes a first adjustment unit that outputs an adjusted voltage from an output end, a second adjustment unit that can adjust an amplification factor of the buffer amplifier circuit, an output end of the first adjustment unit, and the second adjustment unit. A buffer circuit provided between the adjustment unit and
The current sensor, wherein an offset of an output of the buffer amplifier circuit is adjusted by a voltage output from the first adjustment unit. The buffer amplifier circuit is an operational amplifier including a first input terminal connected to the magnetoelectric conversion circuit, a second input terminal connected to the adjustment circuit, and an output terminal,
The second adjustment unit has a third adjustment resistor and a fourth adjustment resistor connected in series to the buffer circuit, and the buffer amplifier circuit and the fourth adjustment resistor are connected in parallel. The current sensor according to claim 1.   The first adjustment unit includes a first adjustment resistor and a second adjustment resistor connected in series between a voltage source and a ground, and a connection point between the first adjustment resistor and the second adjustment resistor is the buffer. The current sensor according to claim 1, wherein the current sensor is connected to an input terminal of the circuit. The magnetoelectric conversion circuit includes a bridge circuit having a magnetosensitive element whose electrical characteristics change according to a magnetic field, and an amplifier whose input end is connected to the bridge circuit and generates a current according to the magnetic field measured by the bridge circuit. A circuit, a coil having one end connected to the output end of the amplifier circuit, and a current-voltage conversion circuit that is connected to the other end of the coil and generates a voltage corresponding to the current flowing through the coil.
The current sensor according to claim 1, wherein the amplifier circuit controls a current flowing through the coil so as to generate a magnetic field that cancels a magnetic field applied to the magnetosensitive element.   The current sensor according to claim 4, wherein the magnetosensitive element is a magnetoresistive effect element.   The current sensor according to claim 1, wherein the buffer circuit is an operational amplifier. A magnetoelectric conversion circuit that converts a magnetic field into a voltage and outputs the voltage from an output end; an adjustment circuit for adjusting a voltage at the output end of the magnetoelectric conversion circuit; and a buffer amplifier circuit connected to the output end of the magnetoelectric conversion circuit; With
The adjustment circuit includes a first adjustment unit that outputs an adjusted voltage from an output end, and a buffer circuit provided between the output end of the first adjustment unit and the input end of the second adjustment unit. Prepared,
Measuring the voltage value of the output terminal of the buffer amplifier circuit for two states in which the current value of the current to be measured flowing through the current path to be measured is different;
A step of simultaneously adjusting the outputs of the first adjustment unit and the second adjustment unit based on the measured two voltage values of the output terminal of the buffer amplifier circuit; Adjustment method.

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