JP2001141756A - Current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make precisely measurable any directional current to be measured in a current sensor operated by the supply of a single power source. SOLUTION: When a current to be measured Iin is made to flow to an input coil 15, a magnetic flux is generate within a magnetic core 10, and a potential difference is caused between a pair of output terminals 14L and 14R provided on a Hall element 12. This potential difference is inputted to a pair of operational amplifiers 20 V and 20 W having a positive voltage Vcc received in the power source terminals. Since both the operational amplifiers 20 V and 20 W have reverse input polarities, only one operational amplifier 20 V takes this voltage potential as a positive input signal and outputs a positive voltage. The operational amplifier 20 V is operated so as to make a current flow to an output coil 21 V and a resistor 22 V so that the potential difference between both the input terminals is 0 V. The voltage Vout at one end of the resistor 22 to which this current Iout is carried is outputted from a sensor output terminal 23 V as a detection signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current sensor, and more particularly, to a current sensor which receives a single power supply and operates while a current to be measured and a power supply of the current sensor are electrically insulated. Here, the single power source has a positive and a negative output terminal, to which a load is connected, and one of the positive and negative output terminals is connected to the ground. Means to supply

[0002]

2. Description of the Related Art Generally, as shown in FIG. 3, an input coil 4 for supplying a current to be measured to a part of an annular magnetic core 3 having a gap 3a is wound around the current sensor. 3a, a Hall element 5 is arranged, and together with an amplifier circuit for amplifying the output of the Hall element 5,
These magnetic cores 3 are packaged. Note that such a current sensor is disclosed in Japanese Patent Application Laid-Open No. 8-262604.

FIG. 4 shows an amplifier circuit 6 of the conventional current sensor 1 which operates by receiving power from a single power supply (not shown). The amplifier circuit 6 captures the potential difference between the output voltage of the Hall element 5 and the internal reference voltage Vrf1 into an operational amplifier 7, amplifies the potential difference, and outputs the amplified voltage. Therefore, as shown in FIG. 5, when the current to be measured does not flow, the current sensor 1 outputs an offset voltage Voff (for example, 2.5 V) based on the internal reference voltage Vrf1.

The reason why the output signal is offset by the internal reference voltage Vrf1 as described above is as follows. That is, since the current sensor 1 receives only a positive voltage from a single power supply, for example, and only the positive voltage V + is applied to the power supply terminal of the operational amplifier 7 (see FIG. 4), the operational amplifier 7 receives only the positive voltage. Cannot output. For this reason,
If the output is set to 0 V when the measured current is not flowing without performing the offset, the current can be measured when the measured current flows in one direction. When flowing, the output of the operational amplifier 7 becomes 0
This is because V remains displayed and current measurement cannot be performed.

[0005]

When the above-described current sensor 1 is used, as shown in FIG. 4, a correction circuit 8 for canceling the offset voltage Voff is used.
Must be connected to the output side of the current sensor 1. The correction circuit 8 includes an operational amplifier 9 that operates by receiving a positive voltage V + and a negative voltage V- from two power supplies (not shown).
The offset voltage Voff is canceled by taking the external reference voltage Vrf2 having the same design magnitude as the offset voltage Voff into the operational amplifier 9.

However, considering that each circuit for generating both the internal and external reference voltages Vrf1 and Vrf2 is affected by temperature, it is difficult to completely match the external reference voltage Vrf2 with the offset voltage Voff. In addition, a problem arises in that the difference in potential is included in the detection result as an error, and accurate measurement cannot be performed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a current sensor capable of accurately measuring the current to be measured in any direction in a current sensor that operates by receiving a single power supply. With the goal.

[0008]

According to a first aspect of the present invention, there is provided a current sensor comprising: a magnetic core through which a magnetic flux based on a current to be measured passes; a magnetic detecting element disposed in an air gap of the magnetic core;
The output of the magnetic sensing element is connected to the input side, and includes a pair of operational amplifiers operated by a single power supply, and a pair of sensor output terminals respectively connected to the output side of each operational amplifier. It is characterized in that it is connected to the magnetic sensing element with the polarity reversed.

According to a second aspect of the present invention, there is provided a current sensor comprising: a magnetic core through which a magnetic flux based on a current to be measured passes; a magnetic detection element disposed in an air gap of the magnetic core; A pair of output terminals provided on the detection element are connected to each other, and one of the operational amplifiers operated by a single power supply, and the input polarity of the other operational amplifier are inverted, and + and-
Each output terminal of the magnetic detection element is connected to both input terminals, respectively, and the other operational amplifier that operates with a single power supply, and a pair of resistors respectively connected between the output terminal of each operational amplifier and the ground, It has a pair of sensor output terminals connected to the output terminal of each operational amplifier and the common connection part of each resistor.By the output current of each operational amplifier, a magnetic flux in a direction opposite to the magnetic flux based on the current to be measured is generated in the magnetic core. It is characterized in that one output wire is provided at each output terminal of each operational amplifier.

[0010] In the first and second aspects of the present invention, the magnetic core is a substance having a high magnetic permeability with respect to vacuum, for example, is formed in an annular shape, and a conductive wire can pass through the ring. In the present invention, it is particularly preferable to use a substance having a small hysteresis between the external magnetic field and the internal magnetic field.

[0011]

When the current to be measured flows, the magnetic sensing element gives a signal corresponding to the direction and magnitude of the current to be measured to both operational amplifiers. Here, since both operational amplifiers operate with a single power supply, they can output only a voltage of one polarity. However, since both operational amplifiers are connected to the magnetic sensing element with the input polarities reversed, when the current to be measured flows in one direction, the output signal of the magnetic sensing element is always one of the operational amplifiers. , And the output of the operational amplifier on the opposite side becomes 0V. In this way, depending on the direction in which the measured current flows,
A detection signal corresponding to the magnitude of the measured current is output from only one of the pair of sensor output terminals connected to the output side of each operational amplifier. When the measured current is not flowing, the outputs of both sensor output terminals are both 0V.

<Invention of Claim 2> When the current to be measured flows, a magnetic flux having a direction and magnitude corresponding to the current to be measured is generated in the magnetic core, and a potential difference corresponding to the magnetic flux is provided in the magnetic detecting element. It occurs between a pair of output terminals. Then, this potential difference is applied between both the + and-input terminals provided in both the operational amplifiers. Here, both the operational amplifiers are connected to the magnetic detection element with the input polarities reversed. The op amp receives a positive input signal and the other op amp receives a negative input signal. However, since both operational amplifiers operate with a single power supply, they can output only a voltage of one polarity. Therefore, one of the operational amplifiers amplifies and outputs the input signal, but the other operational amplifier does not perform the amplification operation, and the output is 0V.

When one of the operational amplifiers performs an amplifying operation, a magnetic flux in a direction opposite to the magnetic flux based on the current to be measured is generated in the magnetic core by the output current. Here, the operational amplifier is +
It has the property of operating so that the potential difference between both input terminals of-and-becomes 0V. Therefore, one of the operational amplifiers operates so that the magnetic flux based on the current to be measured is offset by the magnetic flux based on the output current of the operational amplifier, and the potential difference between the output terminals of the magnetic detection element is set to 0V. As a result, a current corresponding to the current to be measured flows through the resistor, and a voltage shifted from the ground by a voltage applied to the resistor becomes:
It is output from one sensor output terminal. At this time, since the output of the other operational amplifier is 0V, the output of the other sensor output terminal is 0V. Also, when the measured current flows in the opposite direction, the above one and the other are reversed,
Further, when the measured current is not flowing, the outputs of both sensor output terminals are both 0V.

[0014]

As described above, even if the current sensor according to the first and second aspects of the present invention operates by receiving a single power supply, an offset voltage is generated in the detection signal as in the prior art. Since there is no need, it is not necessary to provide a conventionally required correction circuit, whereby the error factor is suppressed, and the current to be measured in any direction can be accurately measured.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS <First Embodiment> A first embodiment of the present invention will be described below with reference to FIG. The current sensor according to the present embodiment includes, for example, a package including a magnetic core 10, an amplifier circuit 11, and the like, and is used by receiving power from a single external power supply (not shown). The magnetic core 10 has an annular shape, and an input coil 15 having a number of turns N1 is wound around a part thereof. Both ends of the electric wire constituting the input coil 15 are a pair of input terminals 16 of the current sensor.

Also, a part of the ring forming the magnetic core 10 includes:
A gap (see FIG. 1, reference numeral 10A) is formed, and a Hall element 12 as a magnetic detection element is interposed in the gap. As shown in FIG.
Two terminals are provided, and a power supply circuit for driving a Hall element (not shown) is connected to the power supply terminals 13 extending upward and downward in the figure. Then, a potential difference corresponding to the magnetic flux passing through the Hall element 12 is output between the pair of output terminals 14L and 14R extending in the left-right direction in FIG.
This is amplified by the amplifier circuit 11 described below. In this embodiment, it is assumed that when a magnetic flux is generated in the direction of arrow A in FIG. 1, the potential of the output terminal 14R disposed on the right side in FIG. 1 becomes higher than that of the output terminal 14L on the opposite side.

The amplifying circuit 11 of the present embodiment includes a pair of operational amplifiers 20 and 20.
Uses a single power supply, and both have a positive voltage Vcc
(For example, +15 V) is applied, while the-side power supply terminal is connected to the ground. Therefore, these two operational amplifiers 20 and 20 can output only a positive voltage.

The operational amplifiers 20, 20 are connected to the Hall element 12 with their input polarities reversed. Specifically, the + input terminal of the operational amplifier 20 shown in the upper part of FIG. 1 (hereinafter, appropriately referred to as “first operational amplifier 20V”) and the operational amplifier 2 shown in the lower part of FIG.
0 (hereinafter, appropriately referred to as “second operational amplifier 20W”) is connected in parallel to one output terminal 14R of the Hall element 12, while both operational amplifiers 20V,
The remaining 20 W input terminals are connected in parallel to the other output terminal 14 L of the Hall element 12.

An output coil 21 and a resistor 22 are connected in series to the output of each operational amplifier 20, and one end of the resistor 22 is connected to the ground. The sensor output terminals 23 are drawn out from the common connection between the output coil 21 and the resistor 22. Hereinafter, these 21-
In the case where 23 is distinguished by the one connected to the first or second operational amplifier, “V” is attached to the sign of the one connected to the first operational amplifier 20V (for example, “output coil 21V”), "W" is appended to the code of the one connected to the two operational amplifiers 20W (for example, "output coil 21W").

The output coils 21V and 21W are:
Both are wound around the magnetic core 10. Here, the winding direction of each output coil 21V, 21W is the same as that of each operational amplifier 20V,
Based on the output voltage of 20W, each output coil 21V, 2
It is set so that when a current flows to 1 W, a magnetic flux in the opposite direction to the magnetic flux generated by the input coil 15 is generated in the magnetic core 10. Therefore, the winding directions of the two output coils 21V and 21W are opposite to each other in response to the reversal of the input polarities of the two operational amplifiers 20V and 20W. The number of turns of both output coils 21V and 21W is N2.
It has become.

Next, the operation of this embodiment having the above configuration will be described. When the measured current Iin flows in the input coil 15 in, for example, the direction of arrow C, a magnetic flux is generated in the magnetic core 10 in, for example, the direction of arrow A. Then, the magnetic flux penetrates the Hall element 12, and a potential difference corresponding to the magnetic flux is generated between the pair of output terminals 14L and 14R provided in the Hall element 12, and this potential difference is generated by the first and second operational amplifiers 20V and 20V.
It is provided between the + and-input terminals provided for 20W.

Here, both operational amplifiers 20V and 20W are:
Since the input polarity is reversed and connected to the Hall element 12, one of the operational amplifiers captures the potential difference between the output terminals 14L and 14R of the Hall element 12 as a positive input signal, and the other operational amplifier Capture as a negative input signal. Specifically, in this embodiment, when a magnetic flux is generated in the direction of arrow A, both output terminals 14
The potential of the output terminal 14R on the right side of FIG. 1 is higher than the potential of the second input terminal L, 14R. A negative input signal is taken into the operational amplifier 20W.

Here, both operational amplifiers 20V and 20W are:
Since both receive only a positive voltage at the power supply terminal, the first operational amplifier 20V that has received the positive input signal amplifies this and outputs a positive voltage, but the second operational amplifier 20W that has received the negative input signal has The amplified negative voltage cannot be output, and as a result, 0 V is output.

When the first operational amplifier 20V outputs a positive voltage, the first operational amplifier 20V outputs a positive voltage based on the positive voltage.
The current Iout flows through the output coil 21V and the resistor 22V connected to the output side of FIG. 1, and a magnetic flux is generated in the magnetic core 10 in a direction opposite to the magnetic flux generated by the input coil 15 (in the direction of arrow B in FIG. 1). Here, generally, the operational amplifier has a property of operating such that the potential difference between both the positive and negative input terminals is set to 0V. Therefore, the first operational amplifier 20V cancels the magnetic flux generated by the input coil 15 generated in the magnetic core 10 by the magnetic flux generated by the output coil 21V, so that the potential difference between the output terminals 14L and 14R of the Hall element 12 becomes 0V. Works. That is, the current Iout (= N1 / N2) satisfying the law of equal ampere-turn with the current to be measured Iin.
* Iin) flows through the output coil 21V to cancel the magnetic flux in the magnetic core 10.

Then, the current Iout flows through the resistor 22V, and a voltage Vout (= N1 / N2 *) is applied to one end of the resistor 22V.
Iin * R; R is the resistance value of the resistor 22), which is output from one sensor output terminal 23V. At this time, since the second operational amplifier 20W is not operating, the output of the other sensor output terminal 23W becomes 0V.

When the measured current Iin flows in the opposite direction, the output of one sensor output terminal 23V becomes 0V and the output of the other sensor output terminal 23W corresponds to the measured current Iin by the same principle. Voltage Vout (= N1 / N2 * Ii
n * R). Therefore, a pair of sensor output terminals 2
The direction of the measured current Iin can be detected depending on which sensor output terminal of 3 V and 23 W outputs the detection signal. When the measured current Iin is not flowing, the outputs of both sensor output terminals 23V and 23W are both 0V.
Becomes

As described above, the current sensor according to the present embodiment operates by receiving a single power supply. However, since the offset voltage does not occur in the detection signal as in the prior art, the conventionally required correction circuit is used. This eliminates the need to provide a current source, thereby reducing the error factor and accurately measuring the current to be measured in any direction.

<Second Embodiment> This embodiment is shown in FIG. 2, and is different from the first embodiment only in the configuration of the amplifier circuit 30. That is, the amplifier circuit 30 includes an inverting amplifier circuit 32 using an operational amplifier 31 and a non-inverting amplifier circuit 34 using an operational amplifier 33 connected in parallel to one output terminal 14R of the Hall element 12. Each of the operational amplifiers 31 and 33 also receives the positive voltage Vcc from the single power supply at the + power supply terminal, and the − power supply terminal is connected to the ground. A pair of output terminals 23V and 23W are connected to the outputs of the operational amplifiers 31 and 33. The other output terminal 14L of the Hall element 12 is
Connected to ground. Note that the other configuration is the same as that of the first embodiment, and a duplicate description will be omitted.

In this embodiment, when the measured current Iin flows through the input coil 15, the Hall element 12 supplies a voltage signal corresponding to the measured current Iin to each of the operational amplifiers 31 and 33. At this time, when the measured current Iin flows in a predetermined direction and, for example, a positive voltage is applied to the input terminals of the operational amplifiers 31 and 33, the non-inverting amplifier circuit 34 amplifies the positive voltage and outputs one of the sensor output terminals. Although a positive voltage is output to 23W, the inverting amplifier circuit 32 cannot amplify the positive voltage and output a negative voltage, and the output of the other sensor output terminal 23V becomes 0V.

When the measured current Iin flows in the reverse direction, the output results of the non-inverting amplifier circuit 34 and the inverting amplifier circuit 32 are reversed. In this manner, the same effects as those of the first embodiment can be obtained by the present embodiment.

<Other Embodiments> The present invention is not limited to the above embodiments. For example, the following embodiments are also included in the technical scope of the present invention.
In addition to the following, various changes can be made without departing from the scope of the invention. (1) In the current sensor of the second embodiment, when the measured current flows in one direction and in the opposite direction,
Although the output signal of the Hall element 12 is amplified at the same amplification factor, it may be amplified at a different amplification factor. (2) In the first embodiment, for example, the number of turns of the output coils 21V and 21W may be different from each other so that the amplification factor differs depending on the direction in which the measured current Iin flows.

(3) Although the current sensor of the first embodiment employs a package structure, a magnetic core, an amplifier circuit, and the like may be separately arranged on a substrate without using a package.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a current sensor according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a current sensor according to a second embodiment of the present invention.

FIG. 3 is a side view of a known current sensor.

FIG. 4 is a circuit diagram of a conventional current sensor.

FIG. 5 is a graph showing a relationship between an input signal and an output signal of a conventional current sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Magnetic core 12 ... Hall element (magnetic detection element) 14L, 14R ... Output terminal 20, 31, 33 ... Operational amplifier 20V ... 1st operational amplifier 20W ... 2nd operational amplifier 21V, 21W ... Output coil (conductive wire) 22 ... Resistance 23 ... Sensor output terminal Iin: measured current

Claims (2)

[Claims] A magnetic core through which a magnetic flux based on a current to be measured passes; a magnetic detecting element disposed in an air gap of the magnetic core; an output of the magnetic detecting element is connected to an input side;
A pair of operational amplifiers operated by a single power supply; and a pair of sensor output terminals respectively connected to the output side of each of the operational amplifiers. The both operational amplifiers are connected to the magnetic detection element with their input polarities reversed. Current sensor characterized by the above-mentioned. 2. A magnetic core through which a magnetic flux based on a current to be measured penetrates; a magnetic detecting element disposed in an air gap of the magnetic core; and a pair of + and-input terminals, Output terminals are connected to each other, and one operational amplifier that operates with a single power supply;
Each output terminal of the magnetic detection element is connected to both input terminals of the other, and the other operational amplifier operated by a single power supply, and a pair of resistors respectively connected between the output terminal of each operational amplifier and ground. And a pair of sensor output terminals respectively connected to an output terminal of each of the operational amplifiers and a common connection portion of each of the resistors, and an output current of each of the operational amplifiers is used in the magnetic core based on the current to be measured. A current sensor comprising: a conducting wire configured to generate a magnetic flux in a direction opposite to a magnetic flux at an output terminal of each of the operational amplifiers.