JP2009168644A - Magnetic balance type current sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic balance type current sensor for preventing degradation of current detection accuracy, when a coil or a resistor is connected to a power supply terminal or a ground terminal. <P>SOLUTION: This magnetic balance type current sensor 100 comprises a sensor body section 20, a coil L<SB>1</SB>, a resistor R<SB>L2</SB>, and a capacitor C. The coil L<SB>1</SB>is disposed in a path for connecting the power supply terminal 12 to a sensor body section 20, the resistor R<SB>L2</SB>is disposed on a route for connecting the ground terminal 14 to the sensor body section 20, and the resistor R<SB>L2</SB>has the same direct current resistance as the direct current resistance component (resistance R<SB>L1</SB>) of the coil L<SB>1</SB>. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a single-power-supply voltage output type magnetic balance type current sensor that measures, for example, battery current and motor drive current of a hybrid car and an electric vehicle, and a large current flowing through a motor of a machine tool.

As illustrated in FIG. 8, the magnetic balance type current sensor includes a ring-shaped magnetic core 2 having a gap G (such as a permalloy core having a high magnetic permeability and a small residual magnetism), and a Hall element 3 ( An example of a magnetic detection element) and a negative feedback coil _LFB in which a winding is provided on the magnetic core 2. The magnetic core 2 is arranged so that the bus bar 1 through which the measured current I _in flows. Therefore, a first magnetic field is generated in the gap G by the current I _{in to} be measured, and this is applied to the magnetic sensitive surface of the Hall element 3. On the other hand, a current is supplied to the negative feedback coil _LFB so as to generate a second magnetic field that cancels (sets to zero) the first magnetic field applied to the magnetic sensitive surface of the Hall element 3. A current to be measured I _in is obtained from the supplied current.

As a known document related to a magnetic balance type current sensor, there is the following Patent Document 1.
JP 2002-228689 A

  In the case of single power supply driving, for example, two resistors are generally connected in series between a power supply terminal and a ground terminal, and the voltage at the connection point of these resistors is generally used as a reference voltage for a differential amplifier in the sensor. On the other hand, since various noises enter between the power supply and the current sensor, it is conceivable to connect the coil as a noise filter to one of the power supply terminal and the ground terminal in order to prevent destruction and malfunction of the current sensor. However, in the magnetic balance type current sensor, the supply current from the power supply varies greatly from 0 to several tens mA due to the measurement principle, and therefore the voltage drop due to the DC resistance component of the coil provided as a noise filter is the reference voltage. As a result, there is a problem that the accuracy of the current sensor deteriorates. In addition to noise countermeasures, there is a similar problem when a resistor is connected to either the power supply terminal or the ground terminal in order to prevent an inrush current when the power is turned on.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a magnetic balance type current sensor capable of preventing deterioration of current detection accuracy when a coil or a resistor is connected to a power supply terminal or a ground terminal. Is to provide.

The first aspect of the present invention is a magnetic balanced current sensor. This current sensor
A sensor body that outputs a voltage according to the current to be measured based on the principle of a magnetic balance type,
A coil provided in a path connecting one of the power supply terminal or the ground terminal and the sensor main body,
And a resistor having the same DC resistance as that of the coil provided in a path connecting the other of the power supply terminal or the ground terminal and the sensor main body.

The second aspect of the present invention is also a magnetic balance type current sensor. This current sensor
A sensor body that outputs a voltage according to the current to be measured based on the principle of a magnetic balance type,
A first coil provided in a path connecting one of a power supply terminal or a ground terminal and the sensor main body;
And a second coil having the same DC resistance component as the first coil, provided in a path connecting the other of the power supply terminal or the ground terminal and the sensor main body.

The third aspect of the present invention is also a magnetic balance type current sensor. This current sensor
A sensor body that outputs a voltage according to the current to be measured based on the principle of a magnetic balance type,
A first resistor provided in a path connecting one of a power supply terminal or a ground terminal and the sensor main body;
A second resistor having the same DC resistance as the first resistor, provided in a path connecting the other of the power supply terminal or the ground terminal and the sensor main body.

In the current sensor of each aspect, the sensor body is
A magnetic detection element in which a first magnetic field generated by the current to be measured is applied to a magnetosensitive surface;
A negative feedback differential amplifier to which an output voltage of the magnetic detection element is input;
A negative feedback coil that generates a second magnetic field that cancels out the first magnetic field applied to the magnetic sensing surface of the magnetic sensing element when an output current of the negative feedback differential amplifier flows;
A current-voltage converter that converts a current flowing through the negative feedback coil to generate a voltage to generate the second magnetic field;
It is preferable to have an output differential amplifier that amplifies the voltage output from the current-voltage converter.

  According to the present invention, a coil or a resistor is connected between the power supply terminal and the sensor main body and between the ground terminal and the sensor main body, and the coils or the resistors have the same DC resistance. The voltage drop caused by the coil or resistor on the power supply terminal side cancels out the voltage drop caused by the coil or resistor on the ground terminal side. Therefore, compared with the case where the coil or resistor is connected only between one of the power supply terminal and the sensor main body and between the ground terminal and the sensor main body, or the coil or the resistance is connected to both. As compared with the case where the coils or resistors do not have the same DC resistance, deterioration of current detection accuracy is prevented.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or equivalent component, member, etc. which are shown by each drawing, and the overlapping description is abbreviate | omitted suitably. In addition, the embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

(First embodiment)
Since the schematic configuration of the magnetic balanced current sensor according to the present embodiment is as illustrated in FIG. 8 described above, the details of the circuit configuration will be mainly described here. FIG. 1 is a circuit diagram of a magnetic balance type current sensor 100 according to a first embodiment of the present invention. The magnetic balance type current sensor 100 operates with a single power source (constant voltage source V _C , for example, 5 V).

Magnetic balance current sensor 100 includes a sensor body 20, a coil _{L 1,} a resistor _{R L2,} and a capacitor C. As will be described later, the sensor body 20 outputs a voltage V _O corresponding to the measured current I _in from the sensor output terminal 16 based on the principle of the magnetic balance type. The coil L ₁ is provided in a path connecting the power supply terminal 12 and the sensor main body 20, and the resistor R _L2 is provided in a path connecting the ground terminal 14 and the sensor main body 20. Coil L ₁ functions as a noise filter for removing noise to enter in a path leading from the constant voltage source V _C to the power supply terminal 12. The coil L ₁ in FIG. 1 is equivalently represented by the series connection of an ideal coil without DC resistance component and the resistance R _L1. The resistor R _L2 has the same DC resistance as the DC resistance component (resistor R _L1 ) of the coil L ₁ . Capacitor C is provided through a coil _{L 1} and a resistor _{R L2} between the power supply terminal 12 and the ground terminal 14.

Sensor body 20 includes a Hall element 3 as a magnetic detection element, a negative feedback differential amplifier 24, and a negative feedback coil L _FB, a detection resistor R _S as a current-voltage converter, a reference voltage source 25 And an output differential amplifier 28. The reference voltage source 25 includes a voltage dividing resistor R _Hi · R _Lo and a current buffer 26 (impedance converter).

The voltage _dividing resistor R _Hi · R _Lo is connected in series between the power supply terminal 12 and the ground terminal 14. Here, the coil L ₁ is provided in a path connecting the power supply terminal 12 voltage dividing resistors R _Hi, the resistor R _L2 is provided in the path connecting the ground terminal 14 and the resistor R _Lo . Since as described above the resistance _{R L2} have the same DC resistance and the DC resistance component of the coil _{L 1} (resistor _{R L1),} if the resistance value of the voltage dividing resistors _R Hi · _{R Lo} same, the power supply terminal 12 ground terminal 14 is constant (about 2.5 V) regardless of the amount of direct current flowing between the voltage _dividing resistor _RHi and _RLo . The voltage at the connection point of the voltage _dividing resistors R _Hi and R _Lo is output as a reference voltage V _ref (about 2.5 V) via the current buffer 26 (impedance converter).

In FIG. 1, the Hall element 3 is equivalently represented by a bridge connection of four resistors, and a constant Hall element drive current is allowed to flow between the terminals a and b so that the Hall element 3 is connected between the output terminals c and d. The voltage is proportional to the applied magnetic field (in other words, proportional to the measured current I _in ). The output terminals c and d of the Hall element 3 are connected to the input terminals of the negative feedback differential amplifier 24, respectively. A negative feedback coil _LFB and a detection resistor _RS are connected in series to a path connecting the output terminal of the negative feedback differential amplifier 24 and the output terminal of the reference voltage source 25. Both ends of the detection resistor _RS are connected to the input terminal of the output differential amplifier 28, and the output terminal of the output differential amplifier 28 is connected to the sensor output terminal 16 of the magnetic balanced current sensor 100. The detection resistor R _S is a very small resistor for converting the current supplied to the negative feedback coil L _FB into a voltage, and its resistance value is sufficiently smaller than the input impedance of the output differential amplifier 28.

The output voltage of the Hall element 3 is input to the negative feedback differential amplifier 24. The negative feedback differential amplifier 24 sucks or discharges current from the output terminal so that the potential difference between the terminals c and d is always zero, that is, the first magnetic field described above on the magnetic sensitive surface of the Hall element 3. The negative feedback current I _FB is supplied to the negative feedback coil L _FB so that the second magnetic field and the second magnetic field cancel each other. Here, for example, the number of turns of 4,000 turns of the negative feedback coil _{L FB,} if 200A to be measured current _{I in,} the negative feedback current from "the principle of equal ampere-turn" _I FB = 200 / 4,000 = 0.05 (A).

Negative feedback current I _FB is converted to a voltage V _S by the detection resistor R _S, the voltage V _S is output after being amplified by the output differential amplifier 28 from the sensor output terminal 16. The output differential amplifier 28 includes an operational amplifier 29 and resistors R _{3 to} R _6, and the resistance values of the resistors R _{3 to} R ₆ are R ₃ = R ₄ , R ₅ = R ₆ , and the output difference The amplification factor of the dynamic amplifier 28 is R ₅ / R ₃ . The amplification degree is, for example, near 1. The output voltage V _O of the output differential amplifier 28 (that is, the output voltage of the magnetic balance type current sensor 100) is V _O = − (R ₅ / R ₃ ) V _S + V _ref [V] (Formula 1) where V _ref Is about 2.5V
It becomes.

According to this embodiment, the coil L ₁ is provided in a path connecting the power supply terminal 12 and the sensor body 20, the resistor R _L2 is provided in a path connecting the ground terminal 14 and the sensor body 20, since the resistance _{R L2} have the same DC resistance and the DC resistance component of the coil _{L 1} (resistor _{R L1),} and the voltage drop becomes equal to the voltage drop due to the coil _{L 1} by the resistor _{R L2.} Therefore, even if the negative feedback current I _FB changes following the change _in the measured current I _in (that is, even if the amount of DC current flowing between the power supply terminal 12 and the ground terminal 14 changes), the voltage dividing resistor The voltage at the connection point of R _Hi and R _Lo is constant (about 2.5 V), and as a result, the reference voltage V _ref output from the reference voltage source 25 of the sensor body 20 is constant. In this respect, to be provided a resistor R _L2 to the power supply terminal 12 side by the ground terminal 14 side provided coil L ₁ as shown in FIG. 2 (Comparative Example), a direct current flowing between the power supply terminal 12 and the ground terminal 14 Depending on the amount of current, the voltage at the connection point of the voltage _dividing resistors R _Hi and R _Lo varies and the reference voltage V _ref varies. For this reason, the output voltage V _O of the output differential amplifier 28 (that is, the output voltage of the magnetic balance type current sensor) also fluctuates, leading to deterioration of current detection accuracy. This will be specifically examined below.

3, the case of FIG. 2 (Comparative Example) and the relationship between the measured current _{I in} and the sensor output _{V O} in (DC resistance component (resistance _{R L1} of the coil _{L 1)} 8ohms is), the ideal case (a coil It is the contrast figure which contrasted the same relationship in the DC resistance component (resistance R _L1 ) of L ₁ is 0). Here, the number of turns of the negative feedback coil _LFB is 4,000 turns. As shown in this figure, the output voltage V _O in the case of FIG. 2 (Comparative Example) according to the absolute value of the measured current I _in increases is smaller as compared with the ideal case. Specifically, when the measured current I _in is ± 200 A, the negative feedback current I _FB = ± 200 / 4,000 = ± 0.05 (A) from the “equal ampere-turn principle”, so FIG. ), The voltage drop due to the resistor R _L1 is 8Ω × | ± 0.05A | = 0.4V. Here, the current flowing through the resistor _{R L1} is a negative feedback current _{I FB} in the calculation of the voltage drop due to the resistance _{R L1} does not depend on the direction of the negative feedback current _{I FB} | is set to | ± 0.05 A. In addition, since operational amplifiers and the like are of a low current consumption type and the drive current of the Hall element is small, currents other than the negative feedback current _IFB are ignored (that is, direct current flowing between the power supply terminal 12 and the ground terminal 14). _Are all negative feedback current I _FB ). In this case, since the voltage drop due to the resistor R _L1 is 0.4 V as described above, the reference voltage V _ref is reduced by 0.2 V, and thus the sensor output V _O is also reduced by 0.2 V (see the above formula 1).

FIG. 4 shows the relationship between the measured current I _in and the error of the sensor output V _{O in} the case of FIG. 2 (comparative example) (the DC resistance component (resistance R _L1 ) of the coil L ₁ is 8Ω) and the ideal case. is a comparison view comparing the same relations in (direct current resistance component of the coil L ₁ (resistor R _L1) is 0). As shown in this figure, it can be seen that is the absolute value is larger the error of the output voltage in the case of FIG. 2 (Comparative Example) according to the absolute value of the measured current I _in is increased. Specifically, as described above, when the measured current I _in is 200 A, the sensor output V _O drops by 0.2 V. Therefore, if the full scale is 2 V, the error is −10%. Similarly, when the measured current I _in is −200 A, the error is 10%.

On the other hand, in the magnetic balance type current sensor 100 of the present embodiment, since the fluctuation of the reference voltage V _ref is suppressed by the resistance R _L2 described above, it is closer to an ideal case than the case of FIG. 2 (comparative example). Obviously, an output voltage is obtained and the error of the sensor output V _O is reduced.

In the present embodiment, the resistor R _L2 is provided in the path connecting the ground terminal 14 and the sensor main body 20, but instead of this, the same DC resistance component as the resistor R _L2 (that is, the coil L ₁ and case of providing the coil L ₂ having the same DC resistance component) can also achieve the same effect. Further, it is also possible when the positional relationship between the coil L ₁ and a resistor R _L2 Conversely the same effect.

(Second Embodiment)
FIG. 5 is a circuit diagram of a magnetic balanced current sensor 200 according to the second embodiment of the present invention. Magnetic balance type current sensor 200 of the present embodiment, as compared to the magnetic balance type current sensor 100 of the first embodiment, pure resistance in place of the coil _{L 1 R L1 (R L1 =} R L2) is It differs in that it is provided, and it matches in other points. Such a configuration can be said to be effective for preventing an inrush current when the power is turned on when the capacitor C has a large capacity such as several thousand μF. This embodiment can also achieve the same effects as those of the first embodiment.

(Third embodiment)
The magnetic balanced current sensor of the present embodiment has the same circuit configuration as the magnetic balanced current sensor of the first or second embodiment, but the configuration of the negative feedback coil _LFB is different. Will be described.

FIG. 6 is a schematic perspective view of a magnetic balanced current sensor 300 according to the third embodiment of the present invention. Magnetic balance current sensor 300 includes a Hall element 3, and a negative feedback coil _{L FB.} The Hall element 3 and the negative feedback coil _LFB are fixedly disposed on the wide main surface of the bus bar 7 and integrated with the bus bar 7. The bus bar 7 has a flat plate shape (for example, a copper plate), and is attached so as to form a path of the current to be measured via the attachment holes 42 and 44. Although not limited to this, the negative feedback coil _LFB is configured by providing a soft magnetic magnetic yoke (not shown) inside the bobbin 31 provided with the winding 32. Hereinafter, the shape of the magnetic balance type current sensor 300 will be described in detail with reference to FIG.

  FIG. 7 is an explanatory view of the shape of the magnetic balance type current sensor 300 shown in FIG. 6, in which (A) is a plan view, (B) is a front sectional view, and (C) is a right side view.

The negative feedback coil _LFB is fixed (for example, bonded) to the substantially longitudinal center of the bus bar 7, and its axial direction is substantially perpendicular to the longitudinal direction of the bus bar 7 and substantially parallel to the width direction. One end face of the negative feedback coil _LFB is located at the edge of the bus bar 7, and the other end face is located substantially at the center in the width direction of the bus bar 7. The Hall element 3 is fixed (for example, bonded) substantially at the center on the other end face. Sensitive surface of the Hall element 3 is opposed to the end surface of the negative feedback coil L _FB (i.e. magnetic yoke end face), a vertical substantially the width direction of the bus bar 7. Therefore, sensitive surface of the magnetic field (first magnetic field) and the Hall element 3 generated by the current flowing through the bus bar 7 becomes substantially perpendicular, also the magnetic field generated by the current flowing through the negative feedback coil L _FB (second magnetic field ) And the magnetic sensitive surface of the Hall element 3 are also substantially vertical. As in the first or second embodiment, a current is supplied to the negative feedback coil _LFB so that the output voltage of the Hall element 3 becomes zero. The magnetic field and the second magnetic field cancel each other. In other words, negative feedback coil L _FB generates a second magnetic field to cancel the first magnetic field applied to the sensitive surface of the Hall element. A current flowing through the bus bar 7 is detected based on a current flowing through the negative feedback coil _LFB in order to generate the second magnetic field.

  The magnetic balanced current sensor 300 according to the present embodiment can be said to be more advantageous for miniaturization and weight reduction than the magnetic balanced current sensors according to the first and second embodiments.

  The present invention has been described above by taking the embodiment as an example. However, it will be understood by those skilled in the art that various modifications can be made to each component of the embodiment within the scope of the claims. For example, although the Hall element is shown as the magnetic detection element in the embodiment, the magnetic detection element is not limited to this, and may be a magnetoresistance effect element or the like.

1 is a circuit diagram of a magnetic balanced current sensor according to a first embodiment of the present invention. Circuit diagram of magnetically balanced current sensor according to comparative example In the case of FIG. 2 (comparative example) (the DC resistance component (resistance R _L1 ) of the coil L ₁ is 8Ω), the relationship between the measured current I _in and the sensor output V _O , and the ideal case (DC of the coil L ₁ ) Comparison diagram comparing the same relationship in the case where the resistance component (resistance R _L1 ) is 0) In the case of FIG. 2 (comparative example) (the DC resistance component (resistance R _L1 ) of the coil L ₁ is 8Ω), the relationship between the error of the measured current I _in and the sensor output V _O and the ideal case (coil L ₁ Comparison diagram comparing the same relation in the case of the DC resistance component (resistance R _L1 ) is 0) Circuit diagram of magnetically balanced current sensor according to second embodiment of the present invention Schematic perspective view of a magnetic balanced current sensor according to a third embodiment of the present invention It is a shape explanatory view of the magnetic balance type current sensor shown in FIG. 6, (A) is a plan view, (B) is a front sectional view, (C) is a right side view. Schematic perspective view of basic configuration magnetic balanced current sensor

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bus bar 3 Hall element 12 Power supply terminal 14 Grounding terminal 16 Sensor output terminal 20 Sensor main body part 24 Negative feedback differential amplifier 25 Reference voltage source 28 Output differential amplifier L ₁ coil R _L2 resistance L _FB negative feedback coil _RS Detection resistor R _Hi / R _Lo voltage dividing resistor 100, 200, 300 Magnetic balance type current sensor

Claims (4)

A sensor body that outputs a voltage according to the current to be measured based on the principle of a magnetic balance type,
A coil provided in a path connecting one of the power supply terminal or the ground terminal and the sensor main body,
A magnetic balance type current sensor, comprising: a resistor having the same DC resistance as that of the coil provided in a path connecting the other of the power supply terminal or the ground terminal and the sensor main body. A sensor body that outputs a voltage according to the current to be measured based on the principle of a magnetic balance type,
A first coil provided in a path connecting one of a power supply terminal or a ground terminal and the sensor main body;
A magnetic balance type current sensor comprising: a second coil having a DC resistance component identical to that of the first coil, provided in a path connecting the other of the power supply terminal or the ground terminal and the sensor main body. A sensor body that outputs a voltage according to the current to be measured based on the principle of a magnetic balance type,
A first resistor provided in a path connecting one of a power supply terminal or a ground terminal and the sensor main body;
A magnetic balance type current sensor comprising: a second resistor having a DC resistance identical to the first resistor, provided in a path connecting the other of the power supply terminal or the ground terminal and the sensor main body. The current sensor according to any one of claims 1 to 3, wherein the sensor body is
A magnetic detection element in which a first magnetic field generated by the current to be measured is applied to a magnetosensitive surface;
A negative feedback differential amplifier to which an output voltage of the magnetic detection element is input;
A negative feedback coil that generates a second magnetic field that cancels out the first magnetic field applied to the magnetic sensing surface of the magnetic sensing element when an output current of the negative feedback differential amplifier flows;
A current-voltage converter that converts a current flowing through the negative feedback coil to generate a voltage to generate the second magnetic field;
A magnetic balance type current sensor comprising an output differential amplifier for amplifying a voltage output from the current-voltage converter.

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