JPH0674975A - Current detecting circuit - Google Patents

Abstract

PURPOSE:To accurately measure electric current, even when ambient temperature changes, by providing a temperature gradient setting section where the connection point of two resistors having the same resistance value but a different temperature coefficient is connected to an operational amplifier. CONSTITUTION:A temperature gradient setting section 4 comprises the first and second resistors 4a and 4b having an identical resistance value but a different temperature coefficient, and an operational amplifier 4c. The resistors 4a and 4b are connected in series between a power supply and the ground, and constitute a divided circuit for power supply voltage. In addition, a point P for the division, or the contact point of the resistors 4a and 4b is connected to one of the input terminals of the amplifier 4c. Also, the state of output voltage from a Hall element 20 in this constitution does not change, relative to the output voltage at normal temperature, even when ambient temperature rises or drops, thereby providing high measurement accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit portion of a current detecting device for detecting a magnetic flux density generated on the outer periphery of a conductor by a Hall element and measuring the amount of current in the conductor in an electrically non-contact state. It is a thing.

[0002]

2. Description of the Related Art FIG. 3 shows temperature-output characteristics of a Hall element. Generally, the output of the Hall element is the ambient temperature as shown by the output voltage Tx and the output voltage Ty at different ambient temperatures in the figure. Has a characteristic that the zero point at which the output voltage becomes zero moves and the slope of the output voltage (that is, the sensitivity to the magnetic flux density) also changes.

Therefore, in the current detecting circuit 90 combined with the conventional Hall element 20, as shown in FIG. 4, an offset adjusting section 91 for correcting the movement of the zero point and a predetermined temperature, for example, 25. A sensitivity adjusting unit 92 is provided to adjust the output voltage to an appropriate gradient at room temperature of ° C, and is designed so that a large error does not occur in normal measurement.

[0004]

However, the above-described conventional current detection circuit 90 has the characteristic that the slope of the output voltage changes with the change of the ambient temperature, that is, the characteristic that the sensitivity changes with the ambient temperature. As shown in FIG. 5, the slope of the output voltages Tx and Ty so as to rotate around the zero point with respect to the output voltage T ₂₅ at room temperature as shown in FIG. Changes, and accurate measurement cannot be expected, which causes a problem of poor versatility, and it has been a problem to solve this problem.

[0005]

As a concrete means for solving the above-mentioned conventional problems, the present invention is a circuit for measuring the amount of current by the output of a Hall element, which is a sensitivity adjusting section and an offset adjusting section. In the current detection circuit provided with, two resistors having the same resistance value and different temperature coefficients are connected in series between the power supply and the ground, and the two resistances are provided in the current detection circuit. By providing a current detection circuit characterized by being provided with a temperature gradient setting unit configured by connecting a connection point of a device and one input of an operational amplifier, the sensitivity change due to temperature is also corrected to solve the problem. It is a solution.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described in detail based on an embodiment shown in the drawings. Reference numeral 1 in FIG. 1 is a current detection circuit shown in the main part, and this current detection circuit 1 measures the current value by the output of the Hall element 20. Therefore, as described in the conventional example, The offset adjusting unit 2 and the sensitivity adjusting unit 3 for correcting the characteristics of the Hall element 20 are provided in the same manner as in the conventional example.

In addition to the above, according to the present invention, the current detecting circuit 1 is provided with a temperature inclination setting section 4, and the Hall element 2 is changed by the temperature inclination setting section 4 due to a change in ambient temperature.
It is supposed that the fluctuation of the sensitivity that occurs at 0 is corrected, and that the measurement error due to the change of the ambient temperature does not occur, and the measurement accuracy can be improved.

In this embodiment, the temperature gradient setting section 4 is composed of a first resistor 4a, a second resistor 4b, and an operational amplifier 4c such as an operational amplifier. Resistor 4a and second resistor 4
b is connected in series between the power supply and the ground to form a division circuit for the power supply voltage, and the division is performed at the point P, that is, the first resistor 4a and the second resistor 4b.
Is connected to one input terminal of the operational amplifier 4c.

Here, the results of experiments conducted by the inventor of the present invention will be described. The temperature coefficient of the slope of the output voltage of the Hall element 20 is about 600 ppm. To correct this, the temperature slope is corrected. The first resistor 4 as the setting unit 4
a and the second resistor 4b have the same resistance value (50 kΩ in the case of this embodiment), and the first resistor 4a
Give a temperature coefficient of 800ppm to the second resistor 4a
The purpose was achieved by giving a temperature coefficient of 00 ppm and connecting it to the non-inverting input of the operational amplifier 4c which constitutes the offset adjusting section 2.

FIG. 2 shows the state of the output voltage from the Hall element 20 in the above-mentioned configuration, and when the ambient temperature rises and falls with respect to the output voltage T _{25 at} room temperature. The output voltage Tx, Ty does not change in inclination (sensitivity). For example, even when used in a bad environmental condition such as for vehicle use, the conventional example (see also FIG. 5 of the conventional example is also referred to. ), It is possible to guarantee a high measurement accuracy.

[0011]

As described above, according to the present invention, two resistors having the same resistance value and different temperature coefficients are connected in series between the power source and the ground, and the two resistors of the two resistors are connected. By using the current detection circuit provided with the temperature gradient setting unit formed by connecting the connection point and one input of the operational amplifier, the temperature coefficient of the Hall element caused by the change of the ambient temperature is compensated, and for example, for a vehicle. Even when it is used under adverse environmental conditions, the measurement accuracy is remarkably increased, and it is extremely effective in improving the versatility of this type of current detection circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a current detection circuit according to the present invention.

FIG. 2 is a graph showing an output state of the same embodiment.

FIG. 3 is a graph showing the output of a Hall element.

FIG. 4 is a circuit diagram showing a conventional example.

FIG. 5 is a graph showing an output state of a conventional example.

[Explanation of symbols]

1 ... Current detection circuit 2 ... Offset adjustment unit 3 ... Sensitivity adjustment unit 4 ... Temperature gradient setting unit 4a ... First resistor, 4b ... Second resistor, 4c ...
… Operational amplifier 20… Hall element P… Connection point

Claims (1)

[Claims] 1. A circuit for measuring the amount of current by the output of a hall element, wherein the current detection circuit comprises a sensitivity adjustment section and an offset adjustment section, and the current detection circuit has the same resistance value. Further, a temperature gradient setting unit is provided in which two resistors having different temperature coefficients are connected in series between a power source and a ground, and a connection point of the two resistors and one input of an operational amplifier are connected. A current detection circuit characterized by being provided.