JP6728777B2 - Current detector - Google Patents

Description

The present invention relates to a current detection device that utilizes the non-linear characteristic of a high-permeability material used for leakage detection and the like.

As this type of current detection device, devices having various configurations have been proposed and implemented, but a flux gate type current sensor is known as a device that is structurally simple and capable of detecting a minute current. (See, for example, Patent Documents 1 and 2).
The conventional example described in Patent Document 1 has the configuration shown in FIG. That is, the cores 101 and 102, which are made of a soft magnetic material and have the same shape and the same size and are formed in an annular shape, the exciting coil 103 wound the same number of times as the cores 101 and 102, and the cores 101 and 102 are collectively covered. And the detection coil 104 wound around.

An AC power supply (not shown) is connected to the exciting coil 103, and a detection circuit (not shown) is connected to the detection coil 104. Then, a conductor 105 to be measured, which is an object for measuring a current, is inserted through the centers of both cores 101 and 102.
The exciting coil 103 is wound around the cores 101 and 102 so that the magnetic fields generated in the cores 101 and 102 when they are energized have opposite phases and cancel each other out.

Then, when the exciting current iex is passed through the exciting coil 103, the change over time of the magnetic flux density B generated in each of the cores 101 and 102 is as shown in FIG. The magnetic characteristics of the soft magnetic cores 101 and 102 have a linear relationship between the magnetic field density H and the magnetic flux density B when the magnetic field size H is within a predetermined range. However, when the magnitude H of the magnetic field exceeds a predetermined value, there is a magnetic saturation state in which the magnetic flux density B does not change. Therefore, when the exciting current iex is passed through the exciting coil 103, the magnetic flux density B is generated in each core 101 and 102. The magnetic flux density B to be changed changes into a vertically symmetrical trapezoidal wave shape as shown by the solid line, and is 180° out of phase with each other.

Now, assuming that the direct current value I is flowing downward in the conductor 105 to be measured as indicated by the arrow, the magnetic flux density corresponding to this direct current component is superimposed, and as a result, the magnetic flux density B is shown in FIG. As shown by the broken line, of the trapezoidal waves, the upper trapezoidal wave has its width enlarged, while the lower trapezoidal wave has its width reduced.
Here, a change in the magnetic flux density B generated in the cores 101 and 102 is expressed by a sine wave (corresponding to electromotive force) as shown in FIG. In FIG. 24C, a sine wave (electromotive force) having a frequency f, which is 180° out of phase as shown by the solid line in FIG. 24B, appears in correspondence with the trapezoidal wave shown by the solid line. Are offset by 180° and thus cancel each other out. On the other hand, corresponding to the trapezoidal wave shown by the broken line in FIG. 24(b), the second harmonic of the frequency 2f doubled as shown by the broken line appears in FIG. 24(c). Since the phases of the second harmonics are not shifted by 180°, when they are superposed on each other, a sine wave signal as shown in the lowermost stage of FIG.

The detection signal captured by the detection coil 104 corresponds to the direct current value I flowing through the measured wire 105, and the current value I can be detected by processing this.
In Patent Document 2, an annular magnetic core, an exciting coil wound on the magnetic core, an auxiliary exciting coil wound on the magnetic core, and an AC exciting voltage is applied to the exciting coil. A second excitation circuit that applies a pulsed voltage that generates a magnetic field in the same direction as the magnetic field generated by the excitation coil to the auxiliary excitation coil in synchronization with the first excitation circuit and the rise and fall of the excitation voltage. And a current sensor having a current/voltage conversion circuit for converting the current flowing in the excitation coil into a voltage and a detection means for detecting the timing at which the AC magnetic field of the magnetic core is saturated in the positive and negative directions, respectively. .. The detection means of the current sensor includes a comparator connected to the output side of the current/voltage conversion circuit, a low-pass filter supplied with the output of the comparator, and an amplifier for amplifying the output of the low-pass filter. ing.

JP-A-2000-162244 JP, 2011-17618, A

However, in the conventional example described in Patent Document 1, since the two cores 101 and 102 are used, it is actually difficult to completely match the magnetic characteristics of the cores 101 and 102. Due to the difference in magnetic characteristics, the voltage due to the exciting current iex is generated without being completely canceled. This deteriorates the S/N ratio of the detection voltage corresponding to the second harmonic component, and there is an unsolved problem that it is difficult to detect a minute current.

Further, the second harmonic corresponding to the current value I output from the detection coil 104 has a trapezoidal wave shape that is distorted when the current value I becomes too large. The relationship is no longer proportional. As a result, the detection range of the current value I is limited, and there is an unsolved problem that a wide range of current cannot be detected.
In the conventional example described in Patent Document 2, although the current detection is realized by one magnetic core, the magnetic core is excited by the oscillation circuit, and immediately after the exciting current is converted into the voltage, the binary value is obtained by the comparator. Due to this configuration, noise is superimposed on the measured current when a noisy load such as an inverter is connected, and noise superimposed on the excitation current also causes the comparator to malfunction, making it impossible to accurately measure current. There are challenges.

Further, in the conventional examples described in Patent Documents 1 and 2, since the current detection is performed based on the output current change due to the detected current, the magnetic core detects the current that keeps in the saturated state. There is an unsolved problem that cannot be done.
Therefore, the present invention has been made by paying attention to the unsolved problem of the above-mentioned conventional example, and an object thereof is to provide a current detection device capable of detecting the detected current over a wide range with high accuracy. ..

In order to achieve the above object, a current detection device according to an aspect of the present invention is an excitation device that is wound so as to be electrically insulated and magnetically coupled to a magnetic core that surrounds a conductive wire into which a detected current can flow. A coil, an exciting unit that applies a rectangular wave voltage with a constant frequency to make the magnetic core in a saturated state or a state in the vicinity thereof, and an exciting current that flows in the exciting coil are converted into a voltage. Based on the output current-voltage conversion unit, the filter unit that removes the noise component superimposed on the voltage output from this current-voltage conversion unit, and the timing at which the magnitude of the output voltage output from this filter unit changes Output from the current-voltage conversion unit, and a binarization unit that converts the rectangular-wave voltage into a rectangular-wave voltage, a first current detection unit that detects the inflow of the detected current based on the rectangular-wave voltage output from the binarization unit, A full-wave rectified value forming unit that outputs a full-wave rectified value of the voltage, and a second current detection unit that detects the inflow of the detected current based on the full-wave rectified value of the full-wave rectified value forming unit. There is.

According to one aspect of the present invention, the current detection device can be configured by using one magnetic core, the S/N ratio does not decrease due to the difference in material characteristics of the magnetic core, and a small current to an excessive current can be prevented. It is possible to detect a wide range of detection current with high accuracy.

It is a block diagram which shows 1st Embodiment of the electric current detection apparatus which is 1 aspect of this invention. It is a circuit diagram which shows an example of the excitation part applicable to 1st Embodiment. FIG. 6 is a characteristic diagram showing a relationship between a magnetic field strength and a magnetic flux density of the magnetic core and a characteristic diagram showing an inductance characteristic of the magnetic core. It is a schematic diagram which shows the output voltage waveform of an exciting circuit, and the current waveform of an exciting coil. It is a circuit diagram which shows the specific structure of the current-voltage conversion part applicable to 1st Embodiment. It is a circuit diagram which shows the specific structure of the filter part applicable to 1st Embodiment. It is a circuit diagram which shows the specific structure of the binarization part applicable to 1st Embodiment. It is a circuit diagram which shows the specific structure of the 1st electric current detection part applicable to 1st Embodiment. It is a block diagram which shows 2nd Embodiment of the electric current detection apparatus which is 1 aspect of this invention. It is a block diagram which shows the specific structure of the 1st electric current detection part applicable to 2nd Embodiment. It is a block diagram which shows the specific structure of the full-wave rectification value formation part which can be applied to 2nd Embodiment. It is a circuit diagram which shows the specific structure of the 2nd electric current detection part applicable to 2nd Embodiment. It is a circuit diagram which shows the specific structure of the logical sum circuit applicable to 2nd Embodiment. It is a block diagram which shows 3rd Embodiment of the electric current detection apparatus which is 1 aspect of this invention. It is a circuit diagram which shows the concrete structure of the exciting part applicable to 3rd Embodiment. It is a circuit diagram which shows the concrete structure of the temperature correction|amendment part applicable to 3rd Embodiment. It is a figure which shows the relationship between the output voltage of the oscillation circuit at the time of a current detection, and the current detection voltage of a current detection circuit. It is a figure which shows the relationship between the output voltage of an oscillation circuit and the current detection voltage of a current detection circuit when an ambient temperature change occurs. It is a figure which shows the relationship between the output voltage of an oscillation circuit and the current detection voltage of a current detection circuit when the ambient temperature change countermeasure is taken. It is a circuit diagram which shows the concrete structure of the exciting part applicable to 4th Embodiment of the electric current detection apparatus which is 1 aspect of this invention. It is a block diagram which shows 5th Embodiment of the electric current detection apparatus which is 1 aspect of this invention. It is a circuit diagram which shows the concrete structure of the temperature correction|amendment part applicable to 5th Embodiment. It is another circuit diagram which shows the specific structure of the temperature correction|amendment part applicable to 5th Embodiment. It is explanatory drawing which shows a prior art example, (a) A block diagram of a sensor part, (b) is a figure which shows the magnetic flux density of each magnetic core when exciting current is supplied to an exciting coil, (c) is each magnetic core It is the figure which expressed the magnetic flux density of with the sine wave.

Next, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar reference numerals are given to the same or similar parts.
Further, the embodiments described below exemplify an apparatus and a method for embodying the technical idea of the present invention, and the technical idea of the present invention is the material, shape, structure, The layout is not specified as below. Various changes can be added to the technical idea of the present invention within the technical scope defined by the claims described in the claims.

First, a first embodiment of the present invention will be described.
As shown in FIG. 1, the current detection device 1 according to one embodiment of the present invention has a ring-shaped magnetic core 3 around a conducting wire 2 into which a minute detection current (for example, several tens mA to several hundreds mA) can flow. It is arranged. That is, the conductor wire 2 is inserted into the magnetic core 3.
An exciting coil 4 is wound around the magnetic core 3 in a predetermined number of turns so as to be electrically insulated and magnetically coupled. An exciting circuit 5 as an exciting unit is connected to one end of the exciting coil 4, and a rectangular wave voltage Va is applied from the exciting circuit 5 to the exciting coil 4 to make the magnetic core 3 in a saturated state or a state in the vicinity thereof. To supply the exciting current.

As shown in FIG. 2, the exciting circuit 5 has a structure of an astable multivibrator and applies a rectangular wave voltage Va of a predetermined frequency to the exciting coil 4 to supply an exciting current. That is, the excitation circuit 5 includes the operational amplifier 5a that operates as a comparator. A feedback resistor 5b is connected between the output side and the inverting input side of the operational amplifier 5a. The voltage dividing resistors 5c and 5d are connected in series between the output side of the operational amplifier 5a and the ground, and the connection point of these voltage dividing resistors 5c and 5d is connected to the non-inverting input side of the operational amplifier 5a. Further, a capacitor 5e is connected between the inverting input side of the operational amplifier 5a and the ground.

In this excitation circuit 5, when the resistance value of the feedback resistor 5b is R ₁ , the resistance value of the voltage dividing resistor 5c is R ₂ , the resistance value of the voltage dividing resistor 5d is R _3, and the capacitance value of the capacitor 5e is C _1. , And outputs a rectangular wave voltage Va having a frequency f _V represented by the following equation (1).
f _V =1/(2·C ₁ ·R ₁ ·ln(1+2·R ₃ /R ₂ )) …………(1)
Here, when the operational amplifier 5a cannot sufficiently supply the exciting current to the exciting coil 4, it is possible to increase the exciting current by connecting a current booster (not shown) to the output side of the operational amplifier 5a as necessary. ..

As shown in FIG. 3A, the magnetic core 3 has a BH characteristic showing the relationship between the magnetic flux density B having a large squareness ratio and the magnetic field strength H, and shows the non-linear characteristic of a high magnetic permeability material. Have. The inductance of the magnetic core 3 having the B-H characteristic rapidly disappears near the saturation current as shown in FIG. When an arbitrary current C is applied to the conductor 2 penetrating the magnetic core 3, the B-H characteristic of FIG. 3A shows that the strength of the magnetic field shifts in the H direction according to the current C and the inductance disappears. Changes.

The pulsed rectangular wave voltage Va shown in FIG. 4A is applied to the exciting coil 4 by using the magnetic core 3 having the B-H characteristic shown in FIG. 3, and the magnetic core 3 is excited with a current sufficiently saturated. The current flowing through the exciting coil 4 in such a case can be schematically represented as shown in FIG.
That is, when a pulsed rectangular wave voltage Va is applied to the exciting coil 4, a current initially determined by the inductance of the magnetic core 3 flows and the inductance of the magnetic core 3 saturates (point F in FIG. 4B). An exciting current Iex determined by the resistance of the exciting coil 4 flows.

When an arbitrary detection current I flows into the conductor 2 penetrating the magnetic core 3, the timing at which the inductance disappears changes according to the current C, as shown in FIG. Therefore, in the exciting current shown in FIG. 4B, the timing at which the inductance disappears changes from point F to point H. That is, the duty ratio of the current flowing through the exciting coil 4 changes.
Therefore, by detecting the change in the duty ratio of the exciting current Iex of the exciting coil 4 due to the disappearance of the inductance, the detected current C flowing into the conductor 2 can be detected.

Therefore, at the other end of the exciting coil 4, a current-voltage conversion circuit 6 as a current-voltage conversion unit for converting the excitation current into a voltage, and a filter circuit 7 as a filter unit for removing unnecessary noise components from the converted voltage. , A binarization circuit 8 as a binarization unit for generating a pulsed rectangular wave voltage at the timing when the inductance of the voltage proportional to the exciting current disappears based on the filter output, and the duty ratio of the rectangular wave voltage are detected. The 1st electric current detection circuit 9 as a 1st electric current detection part is connected.

As shown in FIG. 5, the current-voltage conversion circuit 6 is composed of a shunt resistor 6a connected between the exciting coil 4 and the ground, and the exciting voltage Vb is output from the exciting coil 4 side of the shunt resistor 6a. It
When the resistance value of the shunt resistor 6a is R _SH , this excitation voltage Vb is represented by the product of the resistance value R _SH and the excitation current Iex as in the following equation (2).
Vb=Iex·R _SH ………… (2)

The filter circuit 7 is designed according to the frequency of the noise component to be removed, but can be configured by a low pass filter as an example.
As shown in FIG. 6, the filter circuit 7 is composed of a positive feedback type secondary low-pass filter 7a. In the low-pass filter 7a, the excitation voltage Vb output from the current-voltage conversion circuit 6 is input to the non-inverting input side via the resistors 7b and 7c, and the output side and the inverting input side are directly connected. The operational amplifier 7d, the resistor 7c, the capacitor 7e connected between the non-inverting input side connection point of the operational amplifier 7d and the ground, and the connection point between the resistors 7b and 7c and the inverting input side of the operational amplifier 7d. And a capacitor 7f.

The cut-off frequency fc of the filter circuit 7 is expressed by the following equation (3) when the resistance values of the resistors 7b and 7c are the same resistance value Rf and the capacitances of the capacitors 7e and 7f are the same Cf.
fc=1/(2・π・Rf・Cf) …………(3)
Here, by setting the resistance value Rf and the capacitance Cf according to the lower limit frequency of the noise component to be removed, it is possible to reliably remove the high frequency noise component. Moreover, since a second-order low-pass filter is applied, a sharp cutoff characteristic can be obtained.

As shown in FIG. 7, the binarization circuit 8 is composed of a comparator with hysteresis 8a. This hysteresis-equipped comparator 8a has an operational amplifier 8b to which the filter output Vf output from the filter circuit 7 is input on the inverting input side, and resistors 8c and 8d connected between the output side of the operational amplifier 8b and ground. The connection point of 8c and 8d is connected to the non-inverting input side of the operational amplifier 8b.

When the rectangular wave voltage output from the comparator with hysteresis 8a is Vc and the resistance values of the resistors 8c and 8d are R _8c and R _8d , the hysteresis width Vhy of the comparator 8a with hysteresis is expressed by the following formula (4). It is represented by.
Vhy=Vc·(R _8c +R _8d )/R _8c …………(4)
In this way, by configuring the binarization circuit 8 with the comparator with hysteresis 8a, even if noise remains in the filter output output from the filter circuit 7, the influence of noise within the range of the hysteresis width Vhy. It is possible to output the rectangular wave voltage Vc from which is removed.

As shown in FIG. 8, the first current detection circuit 9 receives a rectangular wave voltage Vc output from the binarization circuit 8, integrates it and smoothes it, and a low pass filter 9a. And an absolute value circuit 9b for converting the output of 9a into an absolute value and outputting the measured voltage Vd corresponding to the measured current value.
As described above, according to the first embodiment, the rectangular wave voltage Va having a predetermined frequency is applied from the exciting circuit 5 serving as the exciting unit to the exciting coil 4 wound around the magnetic core 3 so that the magnetic core 3 is in the saturated state or An exciting current Iex for supplying a state in the vicinity thereof is supplied. The duty ratio of the exciting current Iex is changed by changing the timing of disappearance of the inductance as shown in FIG. 4 by the detection current flowing into the conducting wire 2 passing through the magnetic core 3 by the exciting current Iex.

The exciting current Iex is converted into a voltage by the current-voltage conversion circuit 6, and the converted voltage is supplied to the filter circuit 7 to remove a high frequency noise component superimposed on the voltage input by the filter circuit 7. Then, the binarizing circuit 8 binarizes the rectangular wave voltage Vc. By supplying this rectangular wave voltage Vc to the first current detection circuit 9, a DC voltage representing the current value of the measured current according to the duty ratio of the rectangular wave voltage Vc is output.

As described above, in the first embodiment, the exciting current Iex flowing through the exciting coil 4 is converted into a voltage by the current-voltage converting circuit 6, and the converted voltage is supplied to the filter circuit 7 so that a noise component superimposed on the voltage is generated. Is removed and then converted into a rectangular wave voltage Vc by the binarization circuit 8, and the converted rectangular wave voltage Vc is formed by the first current detection circuit 9 to form a voltage representing a duty ratio according to the measured current of the rectangular wave voltage Vc. To do. Therefore, even if a high-frequency noise is superposed on the exciting current Iex flowing through the exciting coil 4 due to the presence of a load such as an inverter circuit that is a high-frequency noise source in the vicinity of the magnetic core 3, the filter circuit 7 does not operate. Since the noise removal is surely performed and then converted into the rectangular wave voltage Vc by the binarization circuit 8, it is possible to reliably prevent the noise component from affecting the rectangular wave voltage Vc.
Moreover, as described above, by configuring the binarization circuit 8 with the comparator with hysteresis 8a, even if a noise component remains in the filter output output from the filter circuit 7, the effect of the noise component is ensured by the hysteresis function. Then, the rectangular wave voltage Vc removed can be formed.

As described above, according to the first embodiment, by applying the rectangular wave voltage Va to the exciting coil 4, the exciting current that causes the duty ratio change in the exciting coil 4 due to the disappearance of the inductance according to the measured current. Iex is supplied, and the change in the duty ratio of the exciting current Iex is controlled by a simple configuration in which the current-voltage conversion circuit 6, the filter circuit 7, the binarization circuit 8 and the first current detection circuit 9 are provided. It is possible to reliably detect a minute detection current flowing into the conductive wire 2 penetrating 3 and to reduce the cost. At this time, since only one magnetic core 3 needs to be provided, it is not necessary to provide two magnetic cores as in the conventional example described in Patent Document 1, and the S/N ratio varies depending on the material characteristics of the magnetic core. It is possible to detect a minute detection current with high accuracy without decreasing. Further, since the current detecting device can be configured with one magnetic core and one exciting coil, the size and cost can be reduced. Furthermore, since no magnetic sensor or the like is used, it is possible to provide a robust current detection device that is less affected by ambient environmental conditions.

Further, the excitation current Iex of the excitation coil 4 is excited by the binarization circuit 8 necessary for detecting the detection current C flowing into the conductor 2 by detecting the change in the duty ratio due to the disappearance of the inductance. When a rectangular wave voltage is generated from the voltage, the signal from which unnecessary noise components are removed by the filter circuit 7 is binarized.
For this reason, when the output voltage of the current-voltage conversion circuit is directly supplied to the comparator as in the conventional example described in Patent Document 2, the comparator malfunctions due to high frequency noise. The high-frequency noise can be removed by supplying the output voltage of the voltage conversion circuit 6 to the filter circuit 7. Therefore, it is possible to reliably prevent a malfunction and perform highly accurate current detection.

Moreover, by configuring the frequency of the rectangular wave voltage applied to the exciting coil 4 to be selectable, it is possible to select the frequency according to the detected current, and it is possible to detect the current in a wide current range. In this case, the oscillation frequency can be selected by selecting the capacitance of the capacitor by connecting a capacitor having a different capacitance in parallel with the capacitor 5e forming the excitation circuit 5 shown in FIG. 2 by a switch. Instead of changing the capacitance of the capacitor, at least one of the voltage dividing resistors 5c and 5d may be connected in parallel with a resistor having a different resistance value by a switch, and the capacitance of the capacitor may be changed. Both the resistance value of the resistor and the resistance value of the resistor may be changed.
In addition, in the said 1st Embodiment, although the case where the oscillation circuit which comprises an astable multivibrator was applied as the excitation circuit 5 was demonstrated, it is not limited to this, A rectangular wave voltage is applied to the excitation coil 4. Any oscillation circuit can be applied as long as it can be applied.

Next, a second embodiment of the current detection device 1 according to one aspect of the present invention will be described with reference to FIGS. 9 to 13.
In the second embodiment, when an excessive current flows into the conducting wire 2, a circuit configuration for detecting the excessive current is added.
That is, in the second embodiment, the first current detection circuit 9 in the first embodiment described above supplies the measured voltage Vd output from the absolute value circuit 9b to the comparison circuit 9c as shown in FIG. The current detection threshold value Vref1 is compared with the current detection threshold value Vref1, and when the measured voltage Vd is equal to or higher than the current detection threshold value Vref1, the high level current detection signal Sa is output.

Further, as shown in FIG. 9, the current detection device 1 includes an excessive current detection unit 10 to which the exciting voltage Vb output from the current-voltage conversion circuit 6 is input. The overcurrent detection unit 10 receives a full-wave rectified value forming circuit 11 that forms a full-wave rectified value obtained by full-wave rectifying the excitation voltage Vb, and a full-wave rectified value output from the full-wave rectified value forming circuit 11. And a second current detection circuit 12 as a second current detection unit that detects an excessive current.

As shown in FIG. 11, the full-wave rectified value forming circuit 11 receives an exciting voltage Vb output from the current-voltage converting circuit 6 and converts the exciting voltage Vb into an absolute value circuit 11a and an absolute value circuit 11a. The absolute value voltage output from the value circuit 11a is integrated, averaged, and output as the full-wave rectified voltage Ve.
As shown in FIG. 12, the second current detection circuit 12 includes a comparator 12a to which the full-wave rectified voltage Ve output from the integration circuit 11b of the full-wave rectified value forming circuit 11 is input. The comparator 12a is composed of, for example, an operational amplifier, the full-wave rectified voltage Ve output from the full-wave rectified value forming circuit 11 is input to the non-inverting input side, and is divided by the voltage dividing resistors 12b and 12c on the inverting input side. When the full-wave rectified voltage Ve becomes equal to or higher than the excessive current threshold value Vref2, the excessive current threshold value Vref2 is input and the high level excessive current detection signal Sb is output.

Then, the current detection signal Sa output from the first current detection circuit 9 and the excessive current detection signal Sb output from the second current detection circuit 12 are supplied to the OR circuit 13. As shown in FIG. 13, the OR circuit 13 includes a diode 13a to which the current detection signal Sa output from the first current detection circuit 9 is input and an overcurrent detection signal output from the second current detection circuit 12. It has a diode 13b to which Sb is input. The cathodes of both diodes 13a and 13b are connected to each other, a resistor 13c is connected between the connection point and the ground, and the terminal voltage of this resistor 13c is output as a current detection signal Sc.

According to the second embodiment, the first current detection circuit 9 outputs the measured voltage Vd according to the detection current flowing into the conductor 2 from the absolute value circuit 9b, as in the first embodiment described above. When the measured voltage Vd becomes equal to or higher than the current detection threshold Vref1, the comparison circuit 9c outputs a high-level current detection signal Sa, which is output as the current detection signal Sc through the OR circuit 13. The current detection signal Sc can detect that a detection current of a set value (for example, 20 mA) or more flows into the conductor 2.

In the state where the first current detection circuit 9 is detecting the current based on the duty ratio due to the abrupt change of the excitation current Iex, the excitation voltage Vb output from the current-voltage conversion circuit 6 is the full-wave rectified value forming circuit 11. Will also be supplied. In this state, as shown in FIG. 4, the exciting current Iex has a waveform in which the duty ratio changes in accordance with the measured current value and changes in positive and negative pulses and repeats. Therefore, the absolute value of the full-wave rectified value forming circuit 11 is increased. Since the total value of the pulse widths for one cycle when the value circuit 11a makes the absolute value becomes a constant value regardless of the change of the duty ratio, when the integrating circuit 11b integrates and averages, the positive pulse The value is approximately half the peak value. When the full-wave rectified voltage Ve output from the integrating circuit 11b is supplied to the second current detection circuit 12 and compared with the overcurrent threshold Vref2 by the comparator 12a, Ve<Vref2, and the output of the comparator 12a is Keep low level.

However, in the first current detection circuit 9, the detected current is detected by the change in the duty ratio of the exciting current due to the change between the saturation state and the disappearance state of the inductance of the magnetic core 3. As described above, when an excessive current (for example, 3 A or more) flows in, the magnetic core 3 is saturated regardless of the application of the rectangular wave voltage, and the exciting current does not change, and the current in the first current detection circuit 9 does not occur. It cannot be detected.

When an excessive current flows into this conductor, the exciting current Iex has a positive value or a negative value proportional to the excessive current, and the exciting voltage Vb output from the current-voltage conversion circuit 6 also has a positive value or a negative value.
Therefore, when the absolute value circuit 11a of the full-wave rectified value forming circuit 11 converts the absolute value and the integrating circuit 11b integrates the integrated value, the integrated output voltage of the integrating circuit 11b increases with the passage of time. Since the integrated output voltage is supplied to the comparator 12a that constitutes the second current detection circuit 12, the high-level excessive current detection signal Sb is output from the comparator 12a when the integrated output voltage becomes equal to or higher than the excessive current threshold Vref2. Is output. Since the excessive current detection signal Sb is supplied to the OR circuit 13, the OR circuit 13 outputs the high level current detection signal Sc.

As described above, according to the second embodiment, when the detected current flowing into the conductor 2 is in the minute current range, the duty of the exciting current Iex flowing through the exciting coil 4 in the absolute value circuit 9b of the first current detecting circuit 9 is increased. A current detection signal Sa that becomes high level is output via the OR circuit 13 when a current detection process according to the ratio is performed and a detected current equal to or higher than the current detection threshold is detected.
On the other hand, when the detected current flowing into the conductor 2 is an excessive current, the excessive current detection signal Sb which becomes high level when the excessive current of the excessive current threshold Vref2 or more is detected by the second current detection circuit 12 is the OR circuit 13 Is output via.

Therefore, according to the second embodiment, by adding the full-wave rectified value forming circuit 11, the second current detection circuit 12, and the OR circuit 13 to the configuration of the above-described first embodiment, the excess current from the minute current region is increased. It is possible to detect a wide range of current up to the current region.
Moreover, a comparator is arranged on the output side of the first current detection circuit 9 and the second current detection circuit 12 so that a high-level current detection signal is output when a detection current of a set current value or more flows in. Therefore, current detection can be accurately performed with a simple configuration.

In the second embodiment, the case where the first current detection circuit 9 and the second current detection circuit 12 are provided with comparators and the outputs of these comparators are supplied to the OR circuit 13 has been described. However, the measured voltage Vd of the absolute value circuit 9b of the first current detection circuit 9 and the full-wave rectified voltage Ve of the full-wave rectified value forming circuit 11 of the overcurrent detection unit 10 are A/D converted. The detected current value may be displayed by inputting it to an arithmetic processing unit such as a microcomputer.

Next, a third embodiment of the present invention will be described with reference to FIGS.
In the third embodiment, fluctuations in measured values due to the influence of the surrounding environment on the first current detection circuit 9 are suppressed.
That is, in the third embodiment, as shown in FIG. 14, the voltage limiting circuit 15 as a voltage limiting unit is connected to the output side of the exciting circuit 5, and the first current detecting circuit 9 changes the measured value due to the temperature change. A first correction circuit 9d is provided as a temperature correction unit for correcting the temperature.

As shown in FIG. 15, the voltage limiting circuit 15 is connected between the output side of the operational amplifier 5a of the exciting circuit 5 of the first embodiment and the ground. The voltage limiting circuit 15 is composed of a first constant voltage diode 16 and a second constant voltage diode 17 each having a Zener diode whose anodes are connected to each other so that the energization directions are opposite to each other. Here, in the first constant voltage diode 16 and the second constant voltage diode 17, the anode of the first constant voltage diode 16 is connected to the anode of the second constant voltage diode 17. The cathode of the first constant voltage diode 16 is connected to the output side of the operational amplifier 5a, and the cathode of the second constant voltage diode 17 is connected to the ground.

The voltage limiting circuit 15 includes a positive/negative limiter circuit that limits the amplitude of the positive-side voltage and the negative-side voltage of the positive/negative rectangular wave voltage Va output from the operational amplifier 5a to the amplitude range between the positive-side limit voltage and the negative-side limit voltage. I am configuring. The positive limit voltage and the negative limit voltage are the rectangular wave voltage Va output from the output terminal to when the rectangular wave voltage has an amplitude change due to a change in the ambient temperature of the exciting circuit 5. Is set to a value that does not affect the.

Further, the first correction circuit 9d is connected between the low-pass filter 9a and the absolute value circuit 9b of the first current detection circuit 9 as shown in FIG. The first correction circuit 9d is connected between the operational amplifier 9f to which the filter output of the low-pass filter 9a is supplied to the inverting input side via the resistor 9e, and the output side and the inverting input side of the operational amplifier 9f. An inverting amplifier including a feedback resistor 9g, a resistor 9h connected between the non-inverting input side of the operational amplifier 9f and the ground to avoid the influence of a bias current, and a thermistor 9i connected in parallel with the resistor 9e as a temperature compensation unit. Is composed of.

Here, in the thermistor 9i, the first constant voltage diode 16 and the second constant voltage diode 17 forming the voltage limiting circuit 15 provided in the above-described excitation circuit 5 have positive temperature characteristics, so that the first constant voltage diode In order to compensate the positive temperature characteristics of 16 and the second constant voltage diode 17, a negative characteristic, that is, a characteristic in which the resistance value decreases as the temperature rises is set. Therefore, in the first correction circuit 9d, since the thermistor 9i is connected in parallel with the resistor 9e, the resistance of the thermistor 9i decreases due to the rise in temperature, and the combined resistance Rs of the resistor 9e and the thermistor 9i decreases, The increase in the amplification factor compensates for the decrease in the measured voltage Vd, which is the amplified output.

According to the third embodiment, similarly to the second embodiment described above, the first current detection circuit 9 detects the detection current in the minute current region, and the second current detection circuit 12 detects the detection current in the excessive current region. Can be detected.
By the way, the excitation circuit 5 has a temperature-dependent characteristic, and the rectangular wave voltage Va is compared with the voltage decrease width on the positive side as shown by the dotted line in FIG. There may occur a case where the voltage decrease width on the negative side becomes large. In this way, when the voltage decrease width is different on the positive side and the negative side of the rectangular wave voltage Va, a measurement current is generated in the conductor 2 when averaged by the low-pass filter 9a of the first current detection circuit 9. A filter output Vf larger than 0, which is the same as that in the case of By inverting and amplifying this filter output Vf by the first correction circuit 9d, as shown in FIG. 18B, a minute detection current C is generated in the conductor 2 shown in FIG. A measurement voltage Vd equivalent to the measurement voltage Vd shown in b) will be output, resulting in erroneous detection due to a change in ambient temperature.

However, in the present embodiment, the voltage limiting circuit 15 is connected between the output terminal of the operational amplifier 5a of the exciting circuit 5 and the ground. The voltage limiting circuit 15 limits the positive-side voltage and the negative-side voltage of the rectangular wave voltage Va of the exciting circuit 5 so as to exclude the fluctuation range due to the temperature change. Therefore, as shown in FIG. 18A, even if the rectangular wave voltage Va output from the operational amplifier 5a changes in amplitude due to a change in ambient temperature, the amplitude fluctuation does not affect the rectangular wave voltage Va. The voltage will be limited.

As described above, by limiting the positive and negative limit voltages of the voltage limiting circuit 15 to be small, the voltage fluctuation (amplitude fluctuation) due to the change of the ambient temperature can be removed, but the voltage limiting circuit 15 has a small limiting voltage. If too much, the change amount of the filter output of the low-pass filter 9a of the first current detection circuit 9 due to the change of the duty ratio of the exciting voltage Vb due to the minute current flowing through the conductor 2 becomes small, so that the current detection accuracy deteriorates. become.

For this reason, it is preferable to set the limit voltage of the voltage limiter circuit 15 to a voltage that is not affected by the maximum voltage fluctuation width within the range of the ambient temperature to be used.
However, since the first constant voltage diode 16 and the second constant voltage diode 17 themselves, which are Zener diodes forming the voltage limiting circuit 15, also have a temperature-dependent characteristic in which the forward voltage rises as the temperature rises, As the ambient temperature rises, the limit voltage also rises, and the voltage fluctuation due to the rise in ambient temperature affects the rectangular wave voltage Va. This variation of the rectangular wave voltage Va appears as a variation of the measured voltage Vd in the first current detection circuit 9, and causes a false detection.

On the other hand, in the present embodiment, a thermistor 9i having a negative resistance characteristic that the resistance value decreases with increasing temperature is inserted in parallel with the resistor 9e in the first correction circuit 9d of the first current detection circuit 9. Has been done. Since the resistance value of the thermistor 9i decreases in accordance with the increase in ambient temperature, the combined resistance Rs of the resistance value R5 of the resistance 9e and the resistance value Rt of the thermistor 9i decreases. When the resistance value of the resistor 9h is R6, the amplification factor −R6/Rs of the operational amplifier 9f increases.
Therefore, the first correction circuit 9d compensates for the decrease in the measured voltage Vd output from the first correction circuit 9d due to the temperature dependence of the first constant voltage diode 16 and the second constant voltage diode 17 that form the voltage limiting circuit 15. Therefore, the accurate measurement voltage Vd can be obtained as shown in FIG.

In the third embodiment, the case where the inverting amplifier is applied as the first correction circuit 9d and the measured voltage Vd decreases as the duty ratio of the rectangular wave voltage Va output from the excitation circuit 5 increases. Although described above, the present invention is not limited to this, and by connecting a similar inverting amplifier to the output side of the inverting amplifier, the measured voltage Vd that increases with an increase in the duty ratio of the rectangular wave voltage Va of the exciting circuit 5 is obtained. Can be obtained. Further, by configuring the first correction circuit 9d with a non-inverting amplifier, it is possible to obtain the measured voltage Vd that increases as the duty ratio of the rectangular wave voltage Va of the excitation circuit 5 increases.
Further, in the third embodiment described above, the case where the anodes of the first constant voltage diode 16 and the second constant voltage diode 17 are connected to each other as the voltage limiting circuit 15 has been described, but the present invention is not limited to this. You may make it connect mutually.

Next, a fourth embodiment of the present invention will be described with reference to FIG.
In the fourth embodiment, the variation of the rectangular wave voltage generated in the exciting circuit 5 due to the influence of the surrounding environment is suppressed.
That is, in the fourth embodiment, as shown in FIG. 20, the excitation circuit 5 of the first embodiment is further provided with a current amplification circuit 5f as a current amplification unit. The current amplifier circuit 5f is provided on the output side of the operational amplifier 5a, amplifies the output of the operational amplifier 5a, and outputs it as a rectangular wave voltage Va. That is, the output of the oscillating circuit 5osc including the operational amplifier 5a, the feedback resistor 5b, the voltage dividing resistors 5c and 5d, and the capacitor 5e is amplified by the current amplifying circuit 5f.

The current amplification circuit 5f is composed of an n-channel MOSFET 51 and a p-channel MOSFET 52 which are connected in series and connected between a power supply and a ground, and the source of the n-channel MOSFET 51 and the source of the p-channel MOSFET 52 are connected. The output side of the operational amplifier 5a is connected to the gate of the n-channel MOSFET 51 and the gate of the p-channel MOSFET 52. The connection point between the n-channel MOSFET 51 and the p-channel MOSFET 52 is connected to one end of the exciting coil 4.
The rectangular wave voltage Va output from the current amplification unit 5f is the same as the oscillation frequency f of the output of the oscillation circuit 5osc expressed by the above formula (1), and the current amplification unit 5f has the same oscillation frequency. Then, the rectangular wave voltage Va capable of supplying a larger exciting current to the exciting coil 4 can be output.

According to the fourth embodiment, the rectangular wave voltage output from the operational amplifier 5a is input to the current amplification circuit 5f, is supplied to the gates of the n-channel MOSFET 51 and the p-channel MOSFET 52, and is supplied in accordance with the positive and negative rectangular wave voltages. The channel MOSFET 51 and the p-channel MOSFET 52 are alternately turned on and off, and a pulse voltage that switches between positive and negative depending on the on/off operation is supplied to one end of the exciting coil 4 as a rectangular wave voltage Va.

Thus, in the exciting circuit 5, the output of the oscillating circuit 5osc is used as the gate signal of the n-channel MOSFET 51 and the p-channel MOSFET 52, and the output of the current amplifying circuit 5f is supplied to the exciting coil 4 as the rectangular wave voltage Va. Therefore, even if a voltage variation or the like occurs in the output of the oscillation circuit 5osc due to a change in the temperature environment or the like, the output of the oscillation circuit 5osc is rectangular after the influence of the voltage variation or the like is removed by the current amplification circuit 5f. The wave voltage Va is supplied to the exciting coil 4. Therefore, by providing the current amplification circuit 5f, unstable factors such as voltage fluctuation due to temperature can be reduced, that is, the influence of the surrounding environment can be avoided and more accurate current measurement can be performed. ..

Further, by providing the current amplification circuit 5f, it is possible to perform adjustment so that a desired exciting current can be obtained, so that restrictions on the exciting current can be reduced. Therefore, the degree of freedom in selecting the number of turns of the magnetic core 3 can be increased.
In addition, in the said 4th Embodiment, although the case where the current amplifier circuit 5f was comprised using the n channel MOSFET51 and the p channel MOSFET52 was demonstrated, it is not restricted to this. For example, the current amplifier circuit 5f can be configured using bipolar transistors.
Further, in the fourth embodiment, the case where the current amplifier circuit 5f is further provided in the first embodiment has been described, but in the second embodiment and the third embodiment, the current amplifier circuit 5f is provided. It is also possible to provide.

Next, a fifth embodiment of the present invention will be described with reference to FIGS.
In the fifth embodiment, in the fourth embodiment, the variation of the rectangular wave voltage Vc output from the binarization circuit 8 due to the influence of the surrounding environment is suppressed.
In the fifth embodiment, as shown in FIG. 21, the first current detection circuit 9 outputs the output of the low pass filter 9a due to the influence of the surrounding environment between the low pass filter 9a and the absolute value circuit 9b. The second correction circuit 9j is provided to correct the change in the rectangular wave voltage Vc.
As shown in FIG. 22, the second correction circuit 9j includes voltage dividing resistors 61 and 62, a diode 63 provided between the voltage dividing resistor 61 and the voltage dividing resistor 62, and a differential circuit 64. ..
The diode 63 is composed of, for example, a Zener diode, the anode of the diode 63 is connected to the high potential side voltage dividing resistor 61, and the cathode is connected to the voltage dividing resistor 62.

The differential circuit 64 includes a voltage dividing resistors 65 and 66 provided between the output side of the low pass filter 9a and the ground, and an operational amplifier 67 whose connection point between the voltage dividing resistors 65 and 66 is input to the non-inverting input side. And resistors 68 and 69 connected in series between the output side of the operational amplifier 67 and the connection point of the diode 63 and the resistor 62. The connection point of the resistors 68 and 69 is connected to the inverting input side of the operational amplifier 67.
That is, the second correction circuit 9j uses the differential circuit 64 to obtain the difference between the rectangular wave voltage Vc that is the output of the low-pass filter 9a and the variation of the output characteristic of the diode 63 due to the change in the surrounding environment. , The rectangular wave voltage Vc is removed of the fluctuation component due to the change of the surrounding environment, and this is output to the absolute value circuit 9b.

In the fifth embodiment, similarly to the above-described fourth embodiment, it is possible to suppress the variation of the rectangular wave voltage Va even when the ambient temperature changes. Furthermore, in the fifth embodiment, the second correction circuit 9j is provided on the output side of the low-pass filter 9a of the first current detection circuit 9 to suppress the change in the rectangular wave voltage Vc due to the change in the ambient environment. It is possible to detect a minute current without being affected by, that is, it is possible to perform highly accurate current measurement.
Further, the second correction circuit 9j can be realized with a simple configuration including the resistors 65, 66, 68 and 69, the differential circuit 64 including the operational amplifier 67, the resistors 61 and 62, and the diode 63.

In the fifth embodiment, as shown in FIG. 22, the case where the diode 63 is used to correct the rectangular wave voltage Vc has been described. However, the present invention is not limited to this, and as shown in FIG. 23, for example. Alternatively, the thermistor 70 may be used to correct the rectangular wave voltage Vc. That is, in FIG. 22, in place of the voltage dividing resistor 61, the diode 63 and the voltage dividing resistor 62 connected in series, the thermistor 70 is set to the high potential side, and the thermistor 70 and the resistor 71 connected in series are connected to the power source and the ground. The connection point between the thermistor 70 and the resistor 71 is connected to one end of the resistor 68 of the differential circuit 64.

Even in the case of the configuration shown in FIG. 23, it is possible to obtain the same operational effect as the second correction circuit 9j using the diode 63.
In addition, in the said 1st-5th embodiment, although the case where the filter circuit 7 connected to the output side of the current-voltage conversion circuit 6 was comprised by the secondary low pass filter was demonstrated, it is not limited to this. However, it may be configured by a first-order low-pass filter or a band-pass filter that passes only necessary signal components.

Further, in the above-described first to fifth embodiments, the case has been described in which one conductor wire 2 is inserted into the magnetic core 3 to detect the current flowing through the conductor wire 2, but the present invention is not limited to this. It is also possible to detect a minute difference current by inserting two conductor wires that generate a minute difference current in the magnetic core 3.
Although the present invention has been described with reference to the specific embodiments, the present invention is not limited to these descriptions. Various embodiments of the invention, as well as various modifications of the disclosed embodiments, will be apparent to persons skilled in the art upon reference to the description of the invention. Therefore, the scope of the claims should be understood to cover these modifications and embodiments included in the scope and gist of the present invention.

DESCRIPTION OF SYMBOLS 1... Current detection device, 2... Conductive wire, 3... Magnetic core, 4... Excitation coil, 5... Excitation circuit, 6... Current-voltage conversion circuit, 7... Filter circuit, 8... Binarization circuit, 9... First current Detection circuit, 10... Excess current detection unit, 11... Full-wave rectified value forming circuit, 12... Second current detection circuit, 15... Voltage limiting circuit

Claims (16)

An exciting coil wound so as to be electrically insulated and magnetically coupled to a magnetic core surrounding a conducting wire into which a detection current can flow,
An exciting unit that supplies an exciting current to the exciting coil by applying a rectangular wave voltage having a constant frequency to bring the magnetic core into a saturated state or a state in the vicinity thereof,
An exciting current flowing through the exciting coil, a current-voltage converter that converts the voltage into a voltage and outputs the voltage,
A filter unit that removes a noise component superimposed on the voltage output from the current-voltage conversion unit;
A binarization unit that converts the output voltage output from the filter unit into a rectangular wave voltage based on the timing at which the magnitude of the output voltage changes;
A first current detection unit that detects an inflow of the detection current based on a rectangular wave voltage output from the binarization unit;
A full-wave rectified value forming unit that outputs a full-wave rectified value of the voltage output from the current-voltage conversion unit,
A current detection device comprising: a second current detection unit that detects the inflow of the detected current based on the full-wave rectified value of the full-wave rectified value forming unit. The current detection device according to claim 1 , wherein the filter unit includes a low-pass filter that blocks noise frequency components. The current sensing device according to claim 1 or 2 , wherein the exciting unit includes an oscillating circuit that generates the rectangular wave voltage. The current detecting device according to claim 3 , wherein the exciting unit includes a voltage limiting unit that limits the amplitude of the rectangular wave voltage generated in the oscillation circuit. The current detection device according to claim 4 , wherein the voltage limiting unit is composed of a constant voltage diode connected between the output side of the oscillation circuit and the ground. The current amplification unit that amplifies the excitation current supplied to the excitation coil by inputting the rectangular wave voltage output from the excitation unit, is included in any one of claims 1 to 5. The current detection device described in. The current detection device according to claim 6 , wherein the current amplification unit includes a switching element. The current detection device according to claim 7 , wherein the switching element is a MOSFET. The current - voltage converter, the current sensing device according to any one of claims 1 8, characterized in that it is constituted by a shunt resistor. The binarization unit, a current sensing device according to any one of claims 1 to 9, characterized in that it is constituted by a comparator threshold voltage is input. The current detection unit according to any one of claims 1 to 10 , wherein the first current detection unit detects a duty ratio of the rectangular wave voltage and outputs a detection signal corresponding to the detected current. apparatus. The said 1st electric current detection part is equipped with the temperature correction|amendment part which temperature-corrects the rectangular wave voltage output from the said binarization part, The any one of Claim 1 to 11 characterized by the above-mentioned. Current sensing device. The current detection device according to claim 12 , wherein the temperature correction unit includes a thermistor whose resistance value changes according to ambient temperature. The current detection device according to claim 12 , wherein the temperature correction unit includes a diode and a differential circuit. 14. The current detection device according to claim 13 , wherein the temperature correction unit includes an inverting amplifier including the thermistor. The current detection device according to claim 13 , wherein the temperature correction unit includes the thermistor and a differential circuit.

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