JP2012037508A - Current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure an orientation of a current to be detected without using a Hall element while reducing an error caused by an element arrangement accuracy at the time of sensor assembly.
The current sensor includes a magnetic core 1 for passing a magnetic flux generated by a current I to be detected, a resonance circuit including a winding Lo wound around the magnetic core 1, and a predetermined frequency for the resonance circuit. And an output that outputs an electrical signal corresponding to the direction of the detected current based on a change in the characteristics of the resonant circuit that changes in accordance with the direction of the detected current. A circuit 11 and a magnetic field bias unit (bias winding 2 and constant current power supply 3) for applying a magnetic field bias to the magnetic core 1 are provided.
[Selection] Figure 1

Description

  The present invention relates to a current sensor.

  In a magnetic proportional type current sensor, a magnetic core serving as a magnetic path of a circulating magnetic flux generated by a detected current is provided, and a Hall element is disposed in the gap of the magnetic core. The level of the electric signal output from the Hall element changes according to the strength and direction of the circulating magnetic flux due to the detected current. For this reason, the electric signal output from the Hall element is amplified by the amplifier circuit and output as the current value of the detected current (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 63-61961

  In such a current sensor, an error occurs in the detected current value due to variations in the hall element characteristics, the arrangement position of the hall element, and the like. For this reason, by adjusting circuit constants (such as resistance values of resistance elements in the amplifier circuit) at the time of manufacturing the current sensor, the amplification degree of the amplifier circuit is corrected for each individual current sensor, and such errors are reduced. Yes.

  The present invention has been made in view of the above-described problems, and an object thereof is to reduce errors caused by element arrangement accuracy during sensor assembly.

  In order to solve the above problems, the present invention is configured as follows.

  The current sensor according to the present invention applies a magnetic core for passing a magnetic flux by a detected current, a resonance circuit including a winding wound around the magnetic core, and a signal having a predetermined frequency to the resonance circuit. And an output circuit that is connected to the resonance circuit and outputs an electrical signal corresponding to the direction of the detected current based on a change in characteristics of the resonance circuit that changes according to the direction of the detected current.

  As a result, since no Hall element is used, errors due to element placement accuracy during sensor assembly can be reduced, and the direction of the detected current can be measured without using the Hall element. it can.

  In addition to the above current sensor, the current sensor according to the present invention may be as follows. In this case, the current sensor further includes a magnetic field bias unit that applies a magnetic field bias to the magnetic core.

  Thereby, since the inductance of the winding increases or decreases according to the direction of the detected current, an electric signal corresponding to the direction of the detected current is output based on the characteristic change of the resonance circuit.

  In addition to the above current sensor, the current sensor according to the present invention may be as follows. In this case, the magnetic field bias unit is a bias winding wound around the magnetic core and a power source or a permanent magnet that conducts a constant current to the bias winding. The magnetic field bias magnetically saturates the magnetic core. Let the area reach.

  In addition, a current sensor according to the present invention includes a magnetic core for passing a magnetic flux by a detected current, a resonance circuit including a winding wound around the magnetic core, and a signal having a predetermined frequency with respect to the resonance circuit. Is disposed in the gap between the magnetic core and an output circuit that outputs an electric signal having a magnitude corresponding to a change in characteristics of the resonant circuit according to the magnitude of the detected current. A Hall element and a polarity inversion circuit that inverts the output polarity of the output circuit in accordance with the direction of the current to be detected based on the output voltage of the Hall element.

  According to the present invention, it is possible to reduce errors due to the arrangement accuracy of elements during sensor assembly.

1 is a circuit diagram showing a configuration of a current sensor according to Embodiment 1 of the present invention. FIG. 2 is a diagram illustrating the inductance characteristics of the winding Lo in FIG. FIG. 3 is a diagram for explaining the characteristics of the output voltage Vout of the current sensor shown in FIG. FIG. 4 is a circuit diagram showing a configuration of a current sensor according to Embodiment 2 of the present invention. FIG. 5 is a circuit diagram showing a configuration of a current sensor according to Embodiment 3 of the present invention. FIG. 6 is a diagram for explaining the characteristics of the latch-type Hall element. FIG. 7 is a circuit diagram showing an equivalent circuit of the output circuit and the polarity inverting circuit in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.

  1 is a circuit diagram showing a configuration of a current sensor according to Embodiment 1 of the present invention.

  In FIG. 1, a magnetic core 1 is a magnetic core that serves as a magnetic path of a circulating magnetic flux due to a detected current I. For the magnetic core 1, a ferrite core, an electromagnetic steel plate core, or the like is used. In this embodiment, the magnetic core 1 is a ring-shaped core.

  The winding 2 is a bias winding wound around the magnetic core 1. The constant current power source 3 causes the winding 2 to conduct a constant current. By the constant current power source 3 so that the ampere turn (the product of the number of turns of the winding 2 and the current value by the constant current power source 3) is about half of the rated current (maximum current to be measured) by the detected current I. A current value is determined.

  The winding 2 and the constant current power source 3 constitute a magnetic field bias unit. The magnetic field bias unit applies a magnetic field bias to the magnetic core 1. The magnetic field bias causes the magnetic core 1 to reach the magnetic saturation region.

  The winding Lo is wound around the magnetic core 1 and functions as an inductor. A capacitor Co and a resistor Ro are connected in series to the winding Lo, and a series resonance circuit is formed by the winding Lo, the capacitor Co, and the resistor Ro. An oscillator 4 is connected to the series resonance circuit. The oscillator 4 outputs an electrical signal having a predetermined oscillation frequency fosc. The oscillation frequency fosc is a frequency in the vicinity of the resonance frequency fo of the series resonance circuit when the detected current I is zero. Even if the resonance frequency increases or decreases due to an inductance change due to the detected current I, the oscillation frequency fosc The frequency does not match the resonance frequency.

  The rectifier circuit 5 includes a diode D and a capacitor C, and rectifies and smoothes the voltage across the capacitor Co.

  The amplifier circuit 6 is a circuit that amplifies the output voltage of the rectifier circuit 5. In this embodiment, the amplifier circuit 6 is a differential amplifier circuit. In this amplifier circuit 6, the positive output terminal of the rectifier circuit 5 is connected to the positive input terminal of the operational amplifier OP via the resistor R1, and the negative output terminal of the rectifier circuit 5 is connected to the negative input terminal of the operational amplifier OP. The resistor R2 is connected, the negative input terminal of the operational amplifier OP is connected to the ground via the resistor R4, one end of the resistor R3 is connected to the positive input terminal of the operational amplifier OP, and the other end of the resistor R3. Is connected to the output terminal of the operational amplifier OP.

  The rectifier circuit 5 and the amplifier circuit 6 constitute an output circuit 11. The output circuit 11 is connected to the above-described resonance circuit, and outputs an electric signal (output voltage Vout) corresponding to the direction of the detected current I based on the characteristic change of the resonance circuit that changes according to the direction of the detected current I. Output.

  Next, the operation of the current sensor will be described.

  When a predetermined current is conducted to the winding 2 by the constant current power source 3, the magnetic field in the magnetic core 1 reaches the magnetic saturation region. Therefore, due to the DC superimposition characteristics, the inductance of the winding Lo is lower than when there is no current from the constant current power source 3. The inductance at this time is Lb. FIG. 2 is a diagram illustrating the inductance characteristics of the winding Lo in FIG.

  When the detected current I is zero, it is the inductance Lb of the winding Lo, and a current having an amplitude corresponding to the impedance of the series resonance circuit at that time is conducted to the winding Lo, the capacitor Co, and the resistor Ro. . Then, the voltage across the capacitor Co due to this current is rectified and smoothed by the rectifier circuit 5, and the rectified and smoothed DC voltage is amplified by the amplifier circuit 6 to become the output voltage Vout. The output voltage Vout when the detected current I is zero is Vb. FIG. 3 is a diagram for explaining the characteristics of the output voltage Vout of the current sensor shown in FIG.

  Next, when the current value of the detected current I is positive (that is, the detected current I is conducted in the direction I + in FIG. 1), the magnetic flux generated by the detected current I in the magnetic core 1 is a constant current. Since the magnetic field in the magnetic core 1 is strengthened, the inductance of the winding Lo is decreased from Lb as shown in FIG. For this reason, the impedance of the series resonant circuit is lowered, and the amplitude of the current that is conducted through the series resonant circuit is increased, so that the output voltage Vout of the current sensor increases from Vb as shown in FIG.

  On the other hand, when the current value of the detected current I is negative (that is, the detected current I is conducted in the direction of I− in FIG. 1, the magnetic flux generated by the detected current I is constant current in the magnetic core 1. Since the magnetic field in the magnetic core 1 is weakened, the inductance of the winding Lo increases from Lb as shown in FIG. For this reason, since the impedance of the series resonance circuit increases and the amplitude of the current conducted through the series resonance circuit decreases, the output voltage Vout of the current sensor decreases from Vb as shown in FIG.

  Therefore, the direction of the detected current I is specified by comparing the output voltages Vout and Vb. That is, if the output voltage Vout is larger than Vb, the direction of the detected current I is the direction of I + in FIG. 1, and if the output voltage Vout is smaller than Vb, the direction of the detected current I is I− in FIG. Direction. Further, the magnitude of the detected current I is also specified from the difference between the output voltages Vout and Vb.

  As described above, the current sensor according to the first embodiment includes the magnetic core 1 for passing the magnetic flux generated by the detected current I, and the resonance circuit including the winding Lo wound around the magnetic core 1. An oscillator 4 that applies a signal having a predetermined frequency fosc to the resonance circuit, and the direction of the detected current based on a characteristic change of the resonance circuit that is connected to the resonance circuit and changes according to the direction of the detected current. And an output circuit 11 for outputting a corresponding electrical signal.

  As a result, the Hall element is not used, and the detection accuracy is almost determined by the Q characteristics of the resonance circuit, so that errors due to the element placement accuracy during sensor assembly can be reduced, and the Hall element is used. The direction of the detected current I and the like can be measured without doing so.

  The current sensor according to the first embodiment further includes a magnetic field bias unit (bias winding 2 and constant current power supply 3) that applies a magnetic field bias to the magnetic core 1.

  As a result, the inductance of the winding Lo increases or decreases in accordance with the direction of the detected current I, so that an electrical signal corresponding to the direction of the detected current I is output based on the change in the characteristics of the resonance circuit.

Embodiment 2. FIG.

  In the second embodiment of the present invention, a permanent magnet is used as a magnetic field bias unit that applies a magnetic field bias to the magnetic core 1.

  FIG. 4 is a circuit diagram showing a configuration of a current sensor according to Embodiment 2 of the present invention. As shown in FIG. 4, in the current sensor according to the second embodiment, instead of the magnetic core 1, the winding 2 and the constant current circuit 3 in FIG. And a permanent magnet 16 connected to the.

  The permanent magnet 16 constitutes a magnetic field bias unit. The magnetic field bias unit applies a magnetic field bias to the magnetic core 15. The magnetic field bias causes the magnetic core 15 to reach the magnetic saturation region.

  Since the other components in FIG. 4 are the same as those in the first embodiment, the description thereof is omitted. The current sensor according to the second embodiment operates in the same manner as the current sensor according to the first embodiment, and detects the current value of the detected current I.

  As described above, in the second embodiment, the permanent magnet 16 is provided as the magnetic field bias unit. As a result, the inductance of the winding Lo increases or decreases in accordance with the direction of the detected current I, so that an electrical signal corresponding to the direction of the detected current I is output based on the change in the characteristics of the resonance circuit.

Embodiment 3 FIG.

  FIG. 5 is a circuit diagram showing a configuration of a current sensor according to Embodiment 3 of the present invention.

  In FIG. 5, the magnetic core 21 is the same core as the magnetic core 1 but has a gap. A Hall element 22 is installed in the gap of the magnetic core 21. The hall element 22 is a latch type hall element. FIG. 6 is a diagram for explaining the characteristics of the latch-type Hall element. As shown in FIG. 6, the magnetic field strength-output voltage characteristic of the latch-type Hall element is a hysteresis characteristic.

  The series resonance circuit including the winding Lo, the capacitor Co, and the resistor Ro is the same as that in the first embodiment. Further, in the third embodiment, the rectifier circuit 5a is connected to the resonance circuit instead of the rectifier circuit 5. The rectifier circuit 5a is a voltage doubler rectifier circuit composed of diodes D and D1 and capacitors C and C1.

  The amplifier circuit 23 is a circuit that amplifies the output voltage of the rectifier circuit 5a. In the third embodiment, the amplifier circuit 23 operates as an inverting amplifier circuit or a non-inverting amplifier circuit depending on the state of the polarity inverting circuit 24. In the amplifier circuit 23, the positive output terminal of the rectifier circuit 5a is connected to the positive input terminal of the operational amplifier OP1 via resistors R11 and R12, and is connected to the negative input terminal of the operational amplifier OP1 via resistors R13 and R14. It is connected. One end of the resistor R15 is connected to the negative input terminal of the operational amplifier OP1, and the other end of the resistor R15 is connected to the output terminal of the operational amplifier OP1.

  The rectifier circuit 5a and the amplifier circuit 23 constitute an output circuit 41. The output circuit 41 is connected to the above-described resonance circuit, and outputs an electric signal (output voltage Vout) having a magnitude corresponding to the characteristic change of the resonance circuit according to the magnitude of the detected current I.

  The polarity inversion circuit 24 inverts the output polarity of the output circuit 41 in accordance with the direction of the detected current I based on the output voltage of the Hall element 22. In the third embodiment, the polarity inversion circuit 24 inverts the polarity of the output voltage Vout by operating the amplifier circuit 23 as either an inverting amplifier circuit or a non-inverting amplifier circuit.

  The polarity inverting circuit 24 has open collector (or open drain) comparators OP2 and OP3. The comparators OP2 and OP3 are realized by operational amplifiers, for example. The positive input terminal of the comparator OP2 and the negative input terminal of the comparator OP3 are connected to each other, and a reference voltage Vref is applied to the connection point between them by the DC power supply 31. The reference voltage Vref is an intermediate voltage between the two output voltages VH and VL of the Hall element 22, as shown in FIG. The negative input terminal of the comparator OP2 and the positive input terminal of the comparator OP3 are connected to each other, and the output voltage Vs of the Hall element 22 is applied to the connection point between them. The output terminal of the comparator OP2 is connected to the connection point between the resistors R11 and R12, and the output terminal of the comparator OP3 is connected to the connection point between the resistors R13 and R14.

  Next, the operation of the current sensor according to the third embodiment will be described.

  In the current sensor according to the third embodiment, the inductance of the winding Lo changes according to the magnitude of the detected current I, and the output voltage of the rectifier circuit 5a changes according to the change. Therefore, the absolute value of the output voltage Vout of the amplifier circuit 23 changes according to the magnitude of the detected current I.

  On the other hand, when the current value of the detected current I is positive (that is, when the detected current I is conducted in the direction of I + in FIG. 5), the output voltage Vs of the Hall element 22 becomes VL, and the comparator OP3 The output voltage is fixed to zero, the output voltage of the open collector type comparator OP2 becomes indefinite, and is determined by the amplifier circuit 23.

  On the other hand, when the current value of the detected current I is negative (that is, when the detected current I is conducted in the direction I- in FIG. 5), the output voltage Vs of the Hall element 22 becomes VH, and the comparator OP2 The output voltage of the open-collector type comparator OP3 becomes indefinite and is determined by the amplifier circuit 23.

  FIG. 7 is a circuit diagram showing an equivalent circuit of the output circuit 41 and the polarity inversion circuit 24 in FIG. FIG. 7A is a circuit diagram showing an equivalent circuit of the output circuit 41 and the polarity inversion circuit 24 when the current value of the detected current I is positive. FIG. 7B is a circuit diagram showing an equivalent circuit of the output circuit 41 and the polarity inversion circuit 24 when the current value of the detected current I is negative.

  As shown in FIG. 7A, when the current value of the current I to be detected is positive, the voltage at the connection point between the resistor R13 and the resistor R14 is zero. It operates as an amplifier circuit, and the polarity of the output voltage Vout is not inverted (that is, the output voltage Vout becomes positive).

  On the other hand, as shown in FIG. 7B, when the current value of the detected current I is negative, the voltage at the connection point between the resistor R11 and the resistor R12 is set to zero. It operates as an inverting amplifier circuit, and the polarity of the output voltage Vout is inverted (that is, the output voltage Vout becomes negative).

  As described above, according to the third embodiment, the output circuit 41 outputs an electric signal having a magnitude corresponding to the characteristic change of the resonance circuit according to the magnitude of the detected current I, and polarity inversion. The circuit 24 inverts the output polarity of the output circuit 41 according to the direction of the detected current I based on the output voltage of the Hall element 22.

  Thereby, although the Hall element 22 is used, the Hall element 22 is only used for detecting the direction of the detected current I and is not directly used for measuring the magnitude of the detected current I. The placement accuracy of the Hall elements 22 during sensor assembly has little effect on the measurement accuracy of the current sensor.

  Each embodiment described above is a preferred example of the present invention, but the present invention is not limited to these, and various modifications and changes can be made without departing from the scope of the present invention. It is.

  For example, in the first, second, and third embodiments, the resonance circuit including the winding Lo may be a parallel resonance circuit with a capacitor.

  Further, the rectifier circuit 5a in the third embodiment may be the rectifier circuit 5, and the rectifier circuit 5 in the first and second embodiments may be the rectifier circuit 5a.

  The present invention is applicable to, for example, an insulation type current sensor.

1, 15, 21 Magnetic core 2 windings (an example of a bias winding, a part of an example of a magnetic field bias unit)
3. Constant current power supply (part of an example of magnetic field bias unit)
4 Oscillator 11, 41 Output circuit 16 Permanent magnet (an example of a magnetic field bias unit)
22 Hall element 24 Polarity inversion circuit Co capacitor (part of an example of resonance circuit)
Lo winding (part of an example of resonant circuit)
Ro resistance (part of an example of a resonant circuit)

Claims (4)

A magnetic core for passing magnetic flux due to the detected current;
A resonant circuit including a winding wound around the magnetic core;
An oscillator that applies a signal of a predetermined frequency to the resonant circuit;
An output circuit connected to the resonant circuit and outputting an electrical signal corresponding to the direction of the detected current based on a characteristic change of the resonant circuit that changes according to the direction of the detected current;
A current sensor comprising:   The current sensor according to claim 1, further comprising a magnetic field bias unit that applies a magnetic field bias to the magnetic core. The magnetic field bias unit is a bias winding wound around a magnetic core and a power source that conducts a constant current to the bias winding, or a permanent magnet,
The magnetic field bias causes the magnetic core to reach a magnetic saturation region;
The current sensor according to claim 2. A magnetic core for passing magnetic flux due to the detected current;
A resonant circuit including a winding wound around the magnetic core;
An oscillator that applies a signal of a predetermined frequency to the resonant circuit;
An output circuit connected to the resonance circuit and outputting an electric signal having a magnitude corresponding to a characteristic change of the resonance circuit according to the magnitude of the detected current;
A hall element disposed in a gap of the magnetic core;
A polarity inversion circuit for inverting the output polarity of the output circuit according to the direction of the detected current based on the output voltage of the Hall element;
A current sensor comprising:

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