JPH03170073A - Hall element current detecting device - Google Patents

Abstract

PURPOSE:To enable accurate current detection by setting the correction coefficient of a 2nd-stage offset reference voltage generation part according to temperature different from the temperature in initial setting. CONSTITUTION:An offset reference voltage is so adjusted by an offset reference voltage setting part 6 so that when no current flows through a body to be detected, a voltage variation detecting circuit generates no output at the temperature in the initial setting. Consequently, the voltage variation detecting circuit can detects voltage variation at a bias current input terminal according to the temperature in the initial setting. The output of this voltage detecting circuit is used to generate the 2nd-stage offset reference voltage of a 2nd-stage amplifying circuit. Namely, a 2nd-stage offset reference voltage generation part 8 multiplies the output of the voltage variation detecting circuit by the correction coefficient to generate a 2nd-stage offset reference voltage.

Description

[Detailed Description of the Invention] A. Industrial Application Field The present invention amplifies the detection output of a Hall element current detector,
The present invention relates to a Hall element current detection device that outputs a current detection signal, and particularly to one that compensates for fluctuations in the current detection signal due to temperature changes.

B. Summary of the Invention The Hall element current detection device of the present invention uses a voltage change detection circuit to determine the deviation between the voltage at the bias current input terminal of the Hall element current detector and an offset reference voltage, and outputs a predetermined value to the output of the voltage change detection circuit. The current detection signal is corrected by multiplying it by a correction coefficient and using the resulting voltage as the second-stage offset reference voltage of the second-stage amplifier circuit.

By setting the offset reference voltage of the voltage change detection circuit under the initial setting temperature and setting the correction coefficient under a temperature different from that temperature, the second stage has the same temperature characteristics as the DC offset. This generates an offset reference voltage, thereby making it possible to compensate for temperature characteristics.

C. 2. Description of the Related Art In general, magnetic sensors that detect current include a Hall element current detection device.

FIG. 3 shows the configuration of the Hall element current detection device. This detection device consists of a magnetic circuit consisting of a Hall element 1 and a ferrite core 2, and a magnetic flux density measuring circuit 3. By detecting the magnetic flux density in the magnetic gap of the ferrite core 2, the target current is detected.

In this current detection device, a DC offset occurs in the current detection signal or the gain changes due to the temperature characteristics of the Hall element.

For example, when using a current detection device with a DC offset like this in an inverter's current control circuit,
It is known that a torque ripple in the output frequency occurs because a DC current component is superimposed on the output current (D. vol. 107, No. 2, p. 183, 1983).

For this reason, conventionally, when controlling a motor using an inverter, the output of a current detector is read when the motor is stopped and no current is flowing, and the offset is adjusted based on this result.

D. Problems to be Solved by the Invention However, this method has a problem in that errors occur when the offset changes due to temperature changes.

Offset notes in current detection devices are caused by mechanical misalignment of terminals attached to semiconductors, so the temperature characteristics vary depending on the individual sensor.

Therefore, it has been extremely difficult to compensate for variations in offset due to temperature changes.

SUMMARY OF THE INVENTION In view of these problems, it is an object of the present invention to provide a Hall element current detection device that can easily and accurately compensate for offset fluctuations due to temperature changes.

E. SUMMARY OF THE INVENTION The voltage at the bias current input of a Hall element current detector varies with temperature changes. This is due to variations in the bias current from the constant current source due to temperature changes and variations in the internal resistance of the Hall element current detector.

The present invention detects this voltage change at the bias current input terminal and adjusts the offset based on the detection result. As a means for this purpose, the Hall element current detection device according to the present invention includes the following: We are prepared.

■ A voltage change detection circuit that detects the voltage at the bias current input terminal of the Hall element current detector, integrates the deviation between this detected value and the offset reference voltage, and outputs it as a changed voltage.

(2) An offset setting section for setting the offset reference voltage of the voltage change detection circuit so that the voltage change detection circuit has no output when the object to be detected has no current at the above temperature.

(2) A second-stage offset generation circuit that multiplies the output of the voltage change detection circuit by a predetermined correction coefficient and then outputs the result as a second-stage offset reference voltage to the second-stage amplifier circuit.

(2) A correction coefficient setting section for setting the correction coefficient so that the second stage amplifier circuit has no output when the detected object has no current at a temperature different from the above temperature.

In this device, a voltage change detection circuit detects a voltage change at the bias current input end by taking the deviation between the voltage at the bias current input end and an offset reference voltage.

This offset reference voltage is determined by the offset FIi voltage setting section under the temperature at which the detected object is set at the initial setting, that is, at the temperature at which the first stage offset reference voltage and the gain of the second stage amplifier circuit are set. The voltage change detection circuit is adjusted so that there is no output when there is no current. Thereby, the voltage change detection circuit can detect a voltage change at the bias current input terminal with reference to the temperature at the time of initial setting.

The output of this voltage change detection circuit is the second output of the second stage amplifier circuit.
Used to generate a stage offset reference voltage. That is, the second stage offset reference voltage generation section generates the second stage offset reference voltage by multiplying the output of the voltage change detection circuit by the correction coefficient.

Here, the correction coefficients are set as follows. First, at the time of initial setting, the second stage amplifier circuit has no output. If the device is placed at a temperature different from the initial setting, for example by using a constant temperature bath, the second stage amplifier circuit will generate an output corresponding to the DC offset. The voltage at the bias current input terminal is proportional to this DC offset.

Therefore, in this state, by adjusting the correction coefficient and setting the second stage offset voltage so that the second stage amplifier circuit has no output, it becomes possible to compensate for the DC offset at any temperature.

F. Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a Hall element current detection device according to an embodiment of the present invention.

The constant current circuit 4 generates a constant current to be supplied to the Hall element 2, and includes a Zener diode D and a resistor R. , R, and a transistor Tr.

The first stage amplifier circuit 5 amplifies the output of the Hall element 2, and includes an amplifier OP and resistors R, .about.R, which determine the gain thereof.

The first stage offset setting circuit 6 sets the offset reference voltage VOF+ of the first stage amplifier circuit 5, and includes a variable resistor VR to which voltages E and -E are applied to both ends, and a resistor R. It consists of By adjusting the variable resistor VR, it is possible to generate voltages ranging from positive to negative.

The second stage amplifier circuit 7 is for amplifying the output of the first stage amplifier circuit 5, and is composed of an amplifier OP, a variable resistor VR, and a resistor R7, and is configured to adjust the gain by the variable resistor VR. It has become.

The second stage offset generation circuit 8 generates an offset reference voltage (2) of the second stage amplifier circuit 7 from the voltage VfN at the constant current input terminal of the Hall element 2. F! It is intended to generate. This circuit 8 includes an amplifier OP, a resistor Rs+R. and a low-pass filter circuit consisting of a capacitor C, and an amplifier OP.
4 and capacitor C! , C, and a resistance circuit consisting of a resistor R1G and a variable resistor VR. The output terminal CP is for outputting the output voltage of the inverting circuit to the outside.

Filter 9 is for output short circuit protection, and resistor RIl
+Rl1 and a capacitor C4. The output terminal O is
This is for outputting the output voltage of the second stage amplifier circuit 7 to the outside via the filter 9.

Next, the operation of this device will be explained.

FIG. 2 shows the change in bias voltage (7) of the Hall element 2 with temperature.

As shown in FIG. 2(a), the rate of change in internal resistance of the Hall element 2 due to temperature is, for example, about 0.3%/°C in the case of a GaAs Hall element. As shown in FIG. 2(b), if the rate of change of the constant current circuit 4 is approximately 0.06%/''C, the rate of change of the voltage vT at the bias current input terminal of the Hall element 2 is As shown in (C) in Figure 2, 0
．． It is about 36%/℃. Therefore, by detecting the voltage vT, the temperature of the Hall element 2 can be detected.

When the temperature is low, adjust the variable resistor VR, and output terminal C? Assume that the voltage VCP is O. Thereby, the voltage VCP indicates the amount of change in temperature based on the temperature at the time of adjustment.

Next, when the Hall element 2 is heated to a high temperature, a DC offset appears at the output terminal O due to the temperature change. Variable resistance VR. Adjust the second stage offset reference voltage V. (2) By adjusting the output voltage V of output terminal 0. lJ. Let r be O.

At this time, the second stage offset reference voltage V is set so that the temperature characteristic of the DC offset is positive or negative. ■Ha-V. It can be adjusted within the range of P<Vo■<V cp').

The second stage offset reference voltage V adjusted in this way
. (2) changes with the same temperature characteristics as the DC offset, so it is possible to compensate for the DC offset regardless of the temperature.

Next, the adjustment procedure for this device will be explained.

First, the ferrite core I (see FIG. 3) is demagnetized and left for about 30 minutes to release the heat generated during magnetic sentry, and the CT section (ferrite core 1 and Hall element 2) is returned to room temperature. next,
The CT section is placed in a magnetic box to reduce the effects of earth's magnetic field.

After turning on the power, the variable resistor VR is adjusted to set the voltage vcp of the output terminal CP to O. Further, the variable resistor VR is adjusted to set the first stage offset reference voltage Vor+, and the voltage V at the output terminal O is set. Let ur be O.

Next, after passing the current to be detected, variable resistor VR,
Adjust the gain.

Thereafter, the CT section is placed in a constant temperature bath and brought to a high temperature, for example, about 60°C. Then, the CT section is placed in a magnetic box and demagnetized. Furthermore, the voltage V is obtained by adjusting the variable resistor VR. Set Uf to O.

Then, check the gain, and if the specified accuracy is obtained,
Finish the adjustment.

G. Effects of the Invention As explained above, according to the present invention, the offset reference voltage of the voltage change detection circuit is set based on the temperature at the time of initial setting, and the offset reference voltage of the voltage change detection circuit is set based on the temperature different from the above temperature.
By setting the correction coefficient of the stage offset reference voltage generator, the second stage offset reference voltage generator having the same temperature characteristics as the DC offset
A stage offset reference voltage can be obtained.

Therefore, DC offset can be compensated for regardless of temperature changes, and accurate current detection becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a rate of change in voltage at a bias current input terminal, and FIG. 3 is an explanatory diagram of a Hall element current detection device. 2... Hall element, 4... Constant current circuit, 5... First stage amplifier circuit, 6... First stage offset setting circuit, 7
. . . 2nd stage amplifier circuit, 8 . . . 2nd stage offset generation circuit. Figure 2: Bias current λ cloudy declaration pressure Figure 3: Hole element current, detection thorn placement 1

Claims (1)

[Claims] (1) A Hall element current detector that operates with a constant current biased and detects the current to be detected, and amplifies and outputs the deviation between the output of this Hall element current detector and a first offset reference voltage. First-stage offset setting for setting the first-stage offset reference voltage so that the first-stage amplifier circuit and the first-stage amplifier circuit have no output when the detected object has no current at a certain temperature. and amplify the output of the first stage amplifier circuit,
a second stage amplifier circuit that outputs the current detection signal to the outside;
In the device comprising a gain setting unit for setting the output gain of the second stage amplifier circuit under the above-mentioned temperature, detecting the voltage at the bias current input terminal of the Hall element current detector; There is a voltage change detection circuit that integrates the deviation between this detected value and the offset reference voltage and outputs it as a changed voltage, and when the detected object has no current at the above temperature, this voltage change detection circuit outputs no output. An offset setting section for setting the offset reference voltage of the voltage change detection circuit, and a second stage offset for the second stage amplifier circuit after multiplying the output of the voltage change detection circuit by a predetermined correction coefficient. A second stage offset generation circuit outputs as a reference voltage, and when the detected object has no current at a temperature different from the above temperature,
A Hall element current detection device comprising: a correction coefficient setting section for setting the correction coefficient so that the second stage amplifier circuit has no output.