JPH06186253A - Current detector - Google Patents

Abstract

PURPOSE:To provide a current detector wherein the value of the temperature fluctuation of an offset voltage and a magnetic-flux sensitivity is small. CONSTITUTION:A magnetic gap 1a is formed in the magnetic path of a ring- shaped core 1 composed of a soft magnetic material, a magnetism-sensing element (a Hall element) 3 is inserted into the magnetic gap, and an electric current flowing in a coil 2 wound on the ring-shaped core is detected by the output voltage of the Hall element. At this time, the magnetism-sensing element (the Hall element) 3 is driven at a constant voltage, a thermosensitive resistance RT21 and a fixed resistance R3 are connected in series across the ground-side terminal of an initial-stage amplification circuit 101 for the output voltage of the magnetism-sensing element and the ground side, an offset-voltage adjusting circuit in which a variable resistance has been inserted in series with a positive voltage and a negative voltage is formed, and a thermosensitive resistance RT22 is connected to a feedback resistance across the output terminal and the input terminal of the amplification circuit 101.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is obtained by a magnetic sensing element in which a current to be detected is passed through a coil wound around a magnetic core or a through coil and inserted into an air gap provided in a magnetic path of the magnetic core. The present invention relates to a current detector that amplifies a detected signal and detects a current flowing through a coil.

[0002]

2. Description of the Related Art The principle of construction of a current detector is shown in FIG. A coil 2 for passing a detected current is wound around a magnetic core 1 made of a soft magnetic material, and a magnetic sensitive element is provided in a magnetic gap 1a formed in a part of a magnetic path of the magnetic core 1. 3 and an amplifier circuit 4 for amplifying the detection signal from the magnetic sensitive element 3.
And constitute a current detector. In the amplifier circuit 4, a residual voltage adjusting resistor for adjusting a residual voltage included in a voltage amplifier, the magnetic sensitive element 3 and a detection signal from the magnetic sensitive element, and an amplifier for adjusting an amplification degree of the detection signal. Degree adjustment resistor, etc. are connected. FIG. 3 shows a specific example of an amplifier circuit in a conventional current detector. In the amplifier circuit of the conventional current detector shown in FIG. 3, the two input terminals of the voltage amplifier 101 are connected to the two output terminals of the magnetic sensitive element 3 through resistors R ₁₁ and R _12, and the input of the voltage amplifier is connected. To adjust the drift voltage to the side ground terminal, a first power supply terminal T ₁₁ for applying a voltage (+ V) for adjusting to a positive potential and a voltage (−V) for adjusting to a negative potential are applied. The residual voltage adjusting variable resistors VR ₁₁ and VR ₂₁ are connected in series with the second power supply terminal T _21, and the output at the middle point is the resistance R between the input side terminal of the voltage amplifier 101 and the ground line. ₂₁ and a resistor R ₃₁ are connected in series and connected to the middle point thereof, and a resistor R ₄₁ is provided between the connection point of the variable resistors VR ₁₁ and VR ₂₁ for drift voltage adjustment and the connection point of the resistors R ₂₁ and R _31. Voltage amplifier 10 on the amplification side
1 is connected in series between the output terminal of No. 1 and the ground terminal T ₃₁ , and a resistor R ₁₃ is feedback-connected between the intermediate connection point of the amplification degree adjusting variable resistors VR ₄₂ and VR ₄₃ and the input terminal of the voltage amplifier 101. Constitutes an amplifier circuit. Meanwhile, the magnetic sensing element 3 is connected between the collector terminal and the ground terminal T ₃₁ of the PNP transistor 102 and drive terminal, resistor R ₅₁ connected in series between the power supply terminal T ₁₁ of the positive potential ground terminal T ₃₁ and It is driven by a constant current circuit which is connected from the voltage dividing point of R ₇₁ to the base terminal of the transistor 102, and a resistor R ₆₁ is connected between the first power supply terminal T ₁₁ and the emitter terminal of the transistor 102. The output voltage V ₀₁ of this amplifier circuit is represented by the following formula ₁ when the output voltages of the output terminals of the magnetic sensing element 3 are V ₁ and V ₂ .

[0003]

[Equation 1]

The detection signals from the magnetic sensing element 3 are VR ₄₂ and V
The amplification degree is adjusted by R ₄₃ , and the residual voltage of the current detector is adjusted by VR ₁₁ and VR ₂₁ .

[0005]

However, the conventional current detection / amplification circuit has the following temperature characteristics. Since the internal resistance of the magnetic sensing element 3 has a positive or negative temperature characteristic, the in-phase potential of each of the output voltages V ₁ and V ₂ changes depending on the temperature, and the influence thereof affects the output voltage V ₀₁ of the amplifier circuit. Appears as a change. Since the detection signal (V ₁ -V ₂ ) from the magnetic sensing element 3 has a negative temperature characteristic, its influence is the output voltage V of the amplifier circuit.
Appears as a negative temperature characteristic in ₀₁ . Therefore, when the operating temperature range becomes wide, there is a problem in that the two temperature characteristics cause a large variation in the output voltage of the current detector, thus deteriorating the accuracy of the current detector. Particularly, for the purpose of detecting a direct current in the purpose of using this type of current detector, a current detector in which both the temperature characteristics of the offset voltage of the amplifier circuit and the temperature characteristics of the magnetic flux sensitivity are stable is required. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems in the prior art and provide a current detector that operates in a wide temperature range and can detect with high accuracy.

[0006]

According to the present invention, a coil is wound, or the coil is penetrated, and the coil is disposed in the magnetic gap of an annular magnetic core partly formed with a magnetic gap. In a current detector including a magnetic sensitive element and an amplifier circuit that amplifies a detection signal of the magnetic sensitive element, a constant voltage drive is used as a driving method of the magnetic sensitive element, and a temperature sensitive resistor is provided in an amplification degree adjusting circuit of the amplifier circuit. Is connected to compensate the negative temperature characteristic as an amplifier circuit with a positive temperature characteristic for amplifying the detection signal of the magnetic sensitive element, and by inserting and connecting a temperature sensitive resistor to the residual voltage adjustment circuit, the ambient temperature changes. In contrast, the current detector has a small change in output voltage.

That is, according to the present invention, a coil is wound, or a magnetic core made of an annular soft magnetic material in which a magnetic gap is formed in a part of a magnetic path penetrating the coil, and the inside of the magnetic gap. And a constant voltage power supply circuit for supplying the magnetic sensitive element to the magnetic sensitive element, and an amplifier circuit for amplifying the detected signal of the magnetic sensitive element. The amplifier circuit amplifies the detected signal from the magnetic sensitive element. It is composed of a first voltage amplifier circuit and a second voltage amplifier section that determines the output voltage value by receiving the output signal of the first voltage amplifier circuit, and the sense that a ground side terminal and a ground line are connected via a resistor. A first voltage amplification circuit consisting of a temperature resistance,
A current detector comprising a feedback resistor connected between an output terminal and an input terminal of an output circuit, and an amplifier circuit in which a temperature-sensitive resistor is connected to the feedback resistor.

[0008]

The gallium arsenide (GaAs) hall element, which has a good Hall voltage temperature coefficient and high product sensitivity, is used as the hall element used in this type of current detector. GaAs
When the Hall element is driven by a constant current, the value of the temperature coefficient of magnetic flux sensitivity is smaller than when it is driven by a constant voltage, but the offset voltage when the magnetic flux is zero is a temperature coefficient compared with when it is driven by a constant voltage. Is large and becomes a value more than twice. An object of the present invention is to reduce the temperature coefficient of magnetic flux sensitivity and the value of drift to 1/2 or less as compared with the case of constant current driving of a conventional GaAs Hall element.
The temperature drift of the offset voltage during constant current driving when the magnetic flux of the GaAs Hall element is zero is 0.4 to 0.6% / ° C, the temperature drift of the magnetic flux sensitivity is 0.1% / ° C, and the constant voltage is constant. The offset voltage during driving is 0.2 to 0.3% / ° C, and the temperature drift of magnetic flux sensitivity is 0.2 to 0.3% / ° C. That is, the value of the temperature drift of the offset voltage during constant current driving is larger than the value of the temperature drift of the magnetic flux sensitivity. When the practical temperature range is 50 ° C, the absolute value of the temperature drift is 20% due to the change in offset voltage with temperature.
~ 30% will change. Therefore, in the current detector of the present invention, a constant voltage drive circuit with a small temperature change of the offset voltage is used for the drive circuit of the Hall element, and the ground terminal of the amplifier circuit is used to correct the temperature change of the offset voltage and the magnetic flux sensitivity. A temperature-sensitive resistor for adjusting the offset voltage is used between the output side and the ground side, and a temperature-sensitive resistor is used as a feedback resistor from the output side of the amplifier circuit that determines the amplification degree of the amplifier circuit to the input terminal. The temperature-sensitive resistance is connected by connecting a positive resistance temperature coefficient posistor having a low resistance value and a metal film resistance in series so as to have a positive temperature coefficient when the Hall element has a negative temperature coefficient. .

[0009]

FIG. 1 shows an embodiment of the present invention. Magnetic sensitive element 3
The driving terminals are directly connected to a positive voltage power source terminal T ₁ and a negative voltage power source terminal T _{2 each} having a small internal resistance of the power source without a resistor to form a constant voltage drive. Two output terminals of the magnetic sensitive element 3 are connected to two input terminals of a voltage amplifier 101 for amplifying the detected voltage detected by the magnetic sensitive element via a resistor R _{1, respectively,} and a positive voltage is applied to adjust the residual voltage. the residual voltage adjusting variable resistor VR ₁ and VR ₂ between the power supply terminal T ₁ and the power supply terminal T ₂ of the order to apply a negative voltage to be connected in series, the input terminal on the ground side of the voltage amplifier 101 The temperature-sensitive resistor RT ₂₁ is connected to the terminal side of the amplifier 101 and the resistor R ₃ is connected to the ground side
Are connected in series, a resistor R ₄ is inserted and connected between the midpoints of VR ₁ and VR _{2 and} the midpoints of R ₂ and R ₃ , and the output terminal of the voltage amplifier 101 is connected to the input terminal of the voltage amplifier 103 of the next stage. A part of the output voltage is fed back from the output terminal of the voltage amplifier 101 to the input side by using the temperature sensitive resistor RT ₂₂ as a feedback resistor. On the output side of the voltage amplifier 103, a variable resistor VR ₃ for adjusting the amplification degree is provided.
And VR ₄ are connected in series between the output terminal of the voltage amplifier 103 and the ground terminal T ₃ , and the connection point of the amplification degree adjusting variable resistors VR ₃ and VR ₄ is connected to the input terminal of the voltage amplifier 103. . The output voltage V ₀ of this amplifier circuit is expressed by the following equation 2 when the output voltages of the output terminals of the magnetic sensing element 3 are V ₁ and V ₂ .

[0010]

[Equation 2]

Since the detection signal (V ₁ -V ₂ ) from the magnetic sensing element 3 has a temperature characteristic, temperature sensing resistors RT ₂₁ and RT ₂₂ are used in the voltage amplifying circuit shown in FIG. RT ₂₁ prevents temperature drift due to temperature change,
The value of the temperature-sensitive resistor RT ₂₂ is set to T ₂₂ so that the expression of Formula 3 is satisfied.

[0012]

[Equation 3]

ΔRT ₂₂ in the equation 3 is the temperature sensitive resistance RT ₂₂
Is the amount of change in resistance with respect to a temperature change of 1 ° C. In the case of the above setting, the decrease in the signal output due to the negative temperature characteristic of the detection signal (V ₁ -V ₂ ) from the magnetic sensing element 3 increases the amplification degree due to temperature due to the resistance increase due to the temperature of the temperature sensitive resistor RT _22. Therefore, a stable output of the current detector can be obtained. Further, the value of the temperature drift of the magnetic sensitive element 3 is reduced by driving the magnetic sensitive element 3 at a constant voltage, and the common mode potential of the input terminal portion of the voltage amplifier 101 is incorporated by incorporating the temperature sensitive resistor RT _21. Can be stabilized, so that the influence on the output of the current detector due to the variation of the common-mode potential can be eliminated. FIG. 2 shows another embodiment according to the present invention. The amplifying circuit is the same as the conventional amplifying circuit shown in FIG. 3 and the output circuit, but the temperature sensing resistor RT ₂₁ for correcting the temperature drift of the output voltage and the temperature sensing resistor RT for compensating the temperature fluctuation of the amplification degree. _{Use 22} . The output voltage V ₀ is expressed by the equation (2), and if the temperature-sensitive resistance value is set to satisfy the condition expressed by the equation (3), the change in the amplification degree due to the temperature change can be prevented. According to the embodiment of the present invention, a current detector having an offset voltage of ± 1% or less and a magnetic flux sensitivity change of ± 1% or less when the operating temperature changes by 50 ° C. can be obtained. In comparison with the above, a current detector having characteristics of drift and temperature fluctuation of magnetic flux sensitivity of 1/2 to 1/5 can be obtained.

[0014]

As described above, according to the present invention, it is possible to provide a current detector which is less affected by temperature fluctuations and which can obtain a stable output.

[Brief description of drawings]

FIG. 1 is an amplifier circuit diagram of a current detector showing an embodiment of the present invention.

FIG. 2 is an amplifier circuit diagram of a current detector according to another embodiment of the present invention.

FIG. 3 is an amplifier circuit diagram of a conventional current detector.

FIG. 4 is a principle diagram showing the principle of a current detector.

[Explanation of symbols]

1 magnetic core 1a magnetic gap 2 coil 3 magnetically sensitive element 4 amplifying circuit 101, 103 the voltage amplifier 102 transistor _{R 1, R 3, R 4} , R 11, R 13, R 21, R 31, R 41,
R _51, R _61, R ₇₁ resistors RT _21, RT ₂₂ temperature sensitive resistor _{VR 1, VR 2, VR 3} , VR 4, VR 11, VR 21, V
R ₄₂ , VR ₄₃ variable resistance

Claims (1)

[Claims] 1. A magnetic core made of an annular soft magnetic material in which a coil is wound or a magnetic gap is formed in a part of a magnetic path that penetrates the coil, and the magnetic core is disposed in the magnetic gap. A magnetic sensitive element, a constant voltage power supply circuit for supplying the magnetic sensitive element, and an amplifier circuit for amplifying a detection signal of the magnetic sensitive element,
The amplifier circuit includes a first voltage amplifier circuit that amplifies a detection signal from the magnetic sensitive element, and a second voltage amplifier unit that receives an output signal of the first voltage amplifier circuit and determines an output voltage value, and is grounded. A first voltage amplifier circuit consisting of a temperature-sensitive resistor connected via a resistor between the side terminal and the ground wire, and an amplifier that connects the temperature-sensitive resistor to the feedback resistor connected between the output terminal and the input terminal of the output circuit. A current detector characterized by comprising a circuit.