JP2003035730A - Current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely and accurately execute temperature compensation of offset of a current detector over a wide temperature range. SOLUTION: The current detector measures a current by using a magnetoelectric transducer. The detector comprises a Hall element for detecting the current to regulate the offset of the transducer or an amplifier for amplifying an output of the transducer to cancel the offset, and, in addition, a Hall element for the temperature compensation. In this case, the offset voltage of the Hall element for the selected temperature compensation is subtracted from the offset voltage of the selected Hall element for detecting the current so that the offset may not change even when the temperature changes.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detector, and more particularly to a current detector which applies a magnetoelectric conversion element and exhibits good temperature characteristics.

[0002]

[Field of Industrial Application] A current detector to which a magnetoelectric conversion element is applied is also called DCCT (direct current transformer) and has a very wide range of application fields. As one example, the current flowing through the motor is detected, and the detected value is used to control the current of the motor. The current detector is also used for electric furnaces, power supply devices, and the like for similar purposes. In order to always perform accurate control in any field of application, a detector whose output is not influenced by the environment is required, and the current detector according to the present invention is used as a device that meets such a demand. To be done.

[0003]

2. Description of the Related Art At present, approximately two types of current detectors are used in current detectors that use magnetoelectric conversion elements. One of them is to feed back the output of a magnetoelectric conversion element (for example, a Hall element) to form a minor loop, and to send a control current that cancels the magnetic field due to the detected current to the magnetoelectric conversion element, There is a magnetic balance type current detector that detects the amount of detection.The other is an open loop type current detector that detects the magnetic field due to the current to be detected by a magnetoelectric conversion element and amplifies the detected current to obtain the amount of detection. There is.

The present invention is particularly effective in the latter open loop type current detector. This latter open loop type current detector is greatly influenced by the temperature characteristics of the offset voltage and the temperature characteristics of the output of the magnetoelectric conversion element and cannot be said to have good temperature characteristics.

That is, in the conventional open loop type current detector, the DC (direct current) for offset adjustment is set in the amplifier.
The offset is adjusted (for example, canceled) in the amplifier by applying the bias. In a conventional current detector having such an offset adjustment circuit, as shown in FIG. 3, a primary winding 2 is mounted on a magnetic core 1 of a magnetic circuit, and a magnetic-electric conversion element 4, for example, in a gap 3 of the magnetic core 1, A Hall element is attached, an amplifier 5 is connected to the output side of the Hall element, a gain adjusting circuit 6 is connected in parallel between both ends of the amplifier 5, that is, between its input and output terminals, and feedback is performed. An offset adjusting circuit 7 is connected to the input side of 5 to apply a DC bias.

It can be said that this method is stable and effective if the ambient temperature does not change. However, it is no exaggeration to say that the ambient temperature is constantly changing under normal use conditions. Further, the offset voltage of the Hall element also changes due to temperature change. Therefore, at a certain temperature, the offset voltage canceled by the above means reappears as the temperature changes.

In order to compensate for this characteristic, conventionally, a method of temperature compensation using the temperature characteristic of the semiconductor device, a method of temperature compensation using a temperature detecting element such as a thermistor, etc. have been adopted. It was

[0008]

However, the temperature characteristic of the offset voltage of the Hall element is not constant, and it has been impossible to obtain a remarkable offset temperature compensation effect by the method described above.

An object of the present invention is to reliably and accurately perform such temperature compensation of the offset of the current detector over a wide temperature range.

[0010]

According to the present invention, there is provided a current detector for measuring a current using a magnetoelectric conversion element, the magnetoelectric conversion element being provided in a magnetic core gap of a current detection magnetic circuit, and the magnetoelectric conversion element. It is characterized by comprising a summing amplifier for amplifying the output of the element and a temperature compensating magnetoelectric conversion element for adjusting and canceling the offset of the magnetoelectric conversion element.

The both magnetoelectric conversion elements are Hall elements.

In the present invention, when the Hall element for current detection and the Hall element for temperature compensation are combined, the selected Hall element for temperature compensation is selected from the offset voltage of the selected Hall element for current detection. It is characterized by subtracting the offset voltage of the element and selecting one that does not change even when the temperature changes.

[0013]

[Operation] The temperature change of the offset of the Hall element is not constant, but by using a selected element to some extent, the offset can be canceled very well in a wide temperature range. By making the selection criteria strict, it is possible to cancel the offset to almost zero in a wide temperature range. As described above, the offset can be canceled in a wide temperature range without any practical problem even with the more relaxed selection criteria.

In the present invention, means for compensating the offset temperature characteristic of the temperature compensating Hall element is provided. Further, it is provided with a means for changing the output gain of the temperature compensating Hall element. Further, it is provided with means for performing temperature compensation and gain change of the summing amplifier.

The present invention will be described with reference to the drawings. As shown in FIG. 1, in the current detector of the present invention, the output voltage output from the Hall element for current detection is amplified by the amplifier at the next stage and used as the detection voltage. This detection voltage outputs an offset voltage even if the primary current is 0A. In order to cancel this offset voltage, another Hall element is further provided, and in particular, it is used as a compensation Hall element.

That is, in the current detector of the present invention, as shown in FIG. 1, the primary winding 12 is mounted on the magnetic core 11 of the magnetic circuit, and the gap 13 of the magnetic core 11 has a magnetoelectric conversion element 14, for example, a hole. The element is attached, the amplifier 15 is connected to the output side through the resistor 20, and the gain adjusting circuit 16 is connected in parallel between both ends of the amplifier 15, that is, between the input and output terminals to perform feedback, Further, as an offset adjustment circuit on the input side of the amplifier 15, a magnetoelectric conversion element for temperature compensation, for example, a Hall element.
Connect a series circuit of 17, inverter 18 and resistor 19.

The output voltage of the Hall element 17 for temperature compensation is independent of the primary current of the Hall element 14 for current detection. The polarity of the output of the Hall element 17 for temperature compensation is inverted by the polarity inverter 20, and the signal amplifier for current detection.
Applied to 15. At this time, the variable resistor 19 allows the gain of the signal from the Hall element 17 for temperature compensation to be changed independently. The amplifier 15 for signal amplification is called a PTC to perform temperature compensation of gain between both ends of the amplifier 15, and a resistance element 16 having a positive temperature coefficient whose resistance value increases as the temperature rises is connected.

The temperature coefficient of the Hall element is not constant in the following points. 1) Temperature coefficient 2) Initial value of offset voltage (eg offset voltage at 25 ° C) 3) Sign of temperature coefficient

Therefore, when the current detecting Hall element and the compensating Hall element used in the current detector are combined, the temperature compensating Hall element has a temperature coefficient and an offset voltage which are different from those of the current detecting Hall element. It is not possible to apply those having significantly different initial values of, and those having different signs of temperature coefficients. In order to avoid this, it is necessary to select both Hall elements in advance. That is, it is necessary to subtract the offset voltage of the selected Hall element for temperature compensation from the offset voltage of the selected Hall element for current detection so that the offset voltage does not change even if the temperature changes.

Even if the Hall element is selected, the sign of the temperature coefficient is positive or negative, and therefore does not vary other than that. In addition, since the initial value of the offset voltage and the sign of the temperature coefficient have various values, it is often very difficult to select those having the same value in practice.

Table 1 shows the values of the offset voltage at 25 ° C. and 85 ° C. of the actual randomly selected Hall element.

[0022]

Here, it is assumed that two kinds of samples having the same sign slope are selected and one sample is used for current detection.
The other sample was used for temperature compensation and the temperature ranged from 25 ° C to 85 ° C.
When the temperature changes to ℃, verify the actual change in the offset value. Sample 2 is used as a Hall element for current detection,
Sample 4 is used as the Hall element for temperature compensation. The gain of the amplifier when using the Hall element of this sample was 66 times.

In order to cancel the offset voltage of sample 2 at 25 ° C., the offset voltage of sample 4 can be canceled by multiplying the offset voltage of sample 4 at 25 ° C. by a gain as follows. 2.23 / 1.65 = 1.36 (1) When the ambient temperature rises to 85 ° C, the offset voltage becomes the following formula. 2.20-1.58 (mV) x (2.23 / 1.65) = 64.6 (μV) (2) Since the gain of the amplifier is 66 times, the voltage of this offset is given by the following equation. 64.6 (μV) × 66 = 4.26 (mV) (3)

As a reference value for selection as described above, there is no practical problem in a wide range. Therefore, it was confirmed that the selection work did not become a major obstacle in manufacturing the product.

[0026]

FIG. 2 shows an example of a concrete circuit of the current detector of the present invention. That is, in the current detector of the present invention, as shown in FIG. 2, the primary winding 22 is mounted on the magnetic core 21 of the magnetic circuit to form the magnetic core 21.
A magnetic-electric conversion element 24, for example, a Hall element is mounted in the space 23 of the amplifier, and an amplifier 25 is connected to the output side thereof. A part of the series circuit of the device 30 is connected in parallel to perform feedback, and further, to the input side of the amplifier 25,
Magnetoelectric conversion element for temperature compensation as an offset adjustment circuit,
For example, a series circuit of the hall element 27, a polarity inverter 28 and a variable resistor 29 connected in parallel is connected.

The output of the Hall element 27 for compensation is inverted in polarity by the polarity inverter 28 and the signal amplifier 25 for current detection.
Applied to. At this time, a variable resistor 29 is connected in parallel between both ends of the inverter 28, so that the gain of the signal of the Hall element 27 for compensation can be independently changed.

The magnetoelectric conversion element 24 is a Hall element for detecting current, and the magnetoelectric conversion element 27 is a Hall element for temperature compensation. The output of the magnetoelectric conversion element 24 is input to the summing amplifier 25 and amplified. The polarity of the output of the magnetoelectric conversion element 27 is inverted by the polarity inverter 28 with respect to the magnetoelectric conversion element 24 and is input to the addition amplifier 25 and amplified.

The output of the polarity inverter 28 is its gain adjuster 29.
Is adjusted so that the offset of the magnetoelectric conversion element 24 is exactly canceled, and is input to the summing amplifier 25. At this time, since the output of the magnetoelectric conversion element 24 and the output of the inverting amplifier 28 have different signs, they are subtracted. The gain of summing amplifier 25 is determined by its gain adjuster 30. The output voltage of the Hall element 24 decreases as the temperature rises. Therefore, the summing amplifier 25
The other element that determines the gain of PTC is called PTC, and a positive temperature coefficient resistor 26 whose resistance value increases as the temperature rises is connected across the summing amplifier 25.

The above-mentioned gain adjuster 30 is a variable resistor,
It is connected between the output side of the summing amplifier 25 and the ground point. Further, the resistor 26 is connected between the input side of the width device 25 and the output tap of the gain adjuster 30. By configuring in this way,
It was confirmed that the current detector of this example also had no effect on its gain.

[0031]

As is apparent from the above description, according to the present invention, it is possible to construct a current detector having a very excellent offset temperature characteristic with a simple circuit and a simple manufacturing process. Therefore, a small and inexpensive current detector can be realized.

[Brief description of drawings]

FIG. 1 is a schematic circuit diagram showing a configuration of a current detector of the present invention.

FIG. 2 is a circuit diagram showing a preferred configuration of the current detector of the present invention.

FIG. 3 is a schematic circuit diagram showing a configuration of a conventional current detector.

[Explanation of symbols]

1, 11, 21 Magnetic core of magnetic circuit 2, 12, 22 Primary winding 3, 13, 23 voids 4,14,24 Magnetoelectric conversion element for current detection (Hall element) 5,15,25 summing amplifier 6, 16, 26 gain adjuster 7 Offset adjustment circuit 17, 27 Magnetoelectric conversion element for temperature compensation (Hall element) 18, 28 Polarity reverser 19, 29 Gain adjuster 20 resistance 30 gain adjuster

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2G017 AA02 AB05 AD53 BA10                 2G025 AA08 AA17 AB02                 2G035 AA03 AA05 AA12 AC01 AC02                       AD20 AD22 AD66

Claims (6)

[Claims] 1. A current detector for measuring a current using a magnetoelectric conversion element, wherein a current-detecting magnetoelectric conversion element provided in a magnetic core gap of a current detection magnetic circuit and an output of the magnetoelectric conversion element are amplified. And a temperature compensating magnetoelectric conversion element for adjusting and canceling the offset of the magnetoelectric conversion element. 2. The current detector according to claim 1, wherein the both magnetoelectric conversion elements are Hall elements. 3. When the Hall element for current detection and the Hall element for temperature compensation are combined, the offset voltage of the selected Hall element for temperature compensation is offset from the offset voltage of the selected Hall element for current detection. 3. The current detector according to claim 2, wherein the voltage is subtracted and a voltage is selected so that the offset voltage does not change even when the temperature changes. 4. The current detector according to claim 1, further comprising means (17, 18, 19) for compensating the offset temperature characteristic of the Hall element for temperature compensation. 5. The current detector according to claim 1, further comprising means (19) for changing the gain of the output of the temperature compensating Hall element. 6. Current amplifier according to claim 1, characterized in that it comprises means (26, 30) for temperature compensation and gain variation of the summing amplifier.