JPH09329628A - Hall element type current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a current detection output stabilized against temperature fluctuation by absorbing fluctuation in the output voltage and the imbalance voltage of a Hall element by correction of the reference voltage being applied to a differential amplifier circuit and the reference voltage for a window comparator. SOLUTION: Output voltage from a Hall element 1 is taken out through a differential amplifier circuit comprising an operational amplifier OP1 and passed through a window comparator comprising operational amplifiers OP3, 4 to produce a binarized detection output. On the other hand, the output voltage from the Hall element 1 is divided by resistors RA, RB to produce an intermediate voltage which is then employed as a reference voltage for producing a doubled voltage through an operational amplifier OP5 and operational resistors RC, RD. The doubled voltage is employed for setting the reference voltage of the differential amplifier circuit, the threshold level of the window comparator and the reference voltage of resistors R5-R7 for setting the width of the window thus absorbing fluctuation in the output voltage and the imbalance voltage of the Hall element 1 due to temperature fluctuation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Hall element type current detector for detecting a current to be detected by utilizing a magnetic-electric conversion function of a Hall element, and particularly to stable binarization while reducing current consumption. The present invention relates to a current detector that obtains an output.

[0002]

2. Description of the Related Art A Hall element having a magnetic-electrical conversion function is used as a current detecting element requiring electrical insulation, and has a higher voltage than a measuring circuit, and a line current of various electric equipment and communication equipment. In order to detect the voltage, the strength of the magnetic field generated by the line current is converted into a voltage through the coil and extracted as a current detection signal. Further, in the binarization detection of the line current, the current detection signal is compared with a reference level (threshold value) by a comparator and is taken out as an ON / OFF signal indicating whether or not the current detection signal exceeds the reference level.

FIG. 2 shows a basic voltage detection circuit for a Hall element. A voltage is applied between the input side terminal pair 2 and 3 of the Hall element 1 to cause an appropriate bias current to flow in the Hall element 1. Then, the Hall element 1 generates a voltage between the output terminal pairs 4 and 5 according to the strength of the magnetic field acting from the outside through the space. As a method of supplying a bias current to the Hall element 1,
There is a method of constant voltage driving by a constant voltage power source 6 as shown in FIG. 7A or a constant current driving by a constant current power source 7 as shown in FIG. The temperature characteristics of the Hall output voltage and the unbalanced voltage according to the above two driving methods are as shown in FIGS. 3A and 3B, and the constant voltage drive is more suitable for the output voltage and the unbalanced voltage with respect to the temperature change. It has excellent stability.

FIG. 4 shows a circuit example of a Hall element type current detector driven by a constant voltage. The output voltage from the output side terminal pairs 4 and 5 of the Hall element 1 is taken out by a differential amplifier circuit composed of an operational amplifier (operational amplifier) OP1 and operational resistors R1 to R4. An operational amplifier OP configured as a voltage follower circuit is connected to the input side terminal pairs 2 and 3 of the Hall element 1.
A constant voltage corresponding to the reference voltage Vref1 is applied from 2. This voltage is also used as the reference voltage of the differential amplifier circuit.

The operational amplifiers OP3 and OP4 are configured as window comparators and determine whether the output voltage of the operational amplifier OP1 is within the window width (VH-VL) set by the threshold voltages VL and VH. Take out as digitized output. The threshold voltages VL and VH are the reference voltage Vref2.
Is divided by resistors R5, R6, and R7 for voltage division.

[0006]

FIG. 5 shows the Hall element 1.
The change in internal resistance with respect to the input side terminal pairs 2 and 3 due to temperature is shown, and the internal resistance greatly changes due to temperature change.
Therefore, in the constant voltage driving by the operational amplifier OP2, when the ambient temperature of the Hall element 1 rises, the input side terminal pair 2, 3
The current between them increases, and the current consumption of the circuit (the bias current of the Hall element occupies most) increases. For example, the Hall element 1 has an internal resistance of about 350 at a temperature of 25 ° C.
When the reference voltage Vref1 is 1.6 V, the Hall element current is about 5 mA. Under this condition, the temperature is 60 ℃
Rises, the internal resistance decreases to about 170Ω, the Hall element current increases to about 9 mA, and the current consumption increases to about double.

As a circuit for suppressing the increase in current consumption due to the above temperature rise, as shown in FIG. 6, the input terminal pair 2 and 3 of the Hall element 1 is supplied with a constant voltage source from a constant voltage source which becomes a constant voltage VC to a current limiting resistor R0. A method of supplying a bias current through For example, if the resistance value of the resistor R0 is 820Ω, the Hall element current at a temperature of 60 ° C. can be suppressed to about 5 mA.

However, in the constant voltage driving through the current limiting resistor R0, the applied voltage between the input side terminal pair 2 and 3 changes due to the change of the internal resistance of the Hall element 1 due to the temperature change,
This phenomenon has characteristics close to current drive, the output voltage and unbalanced voltage of the Hall element 1 become close to the characteristics of constant current drive shown in FIG. 3, and the Hall output voltage and unbalanced voltage rise in a low temperature range with respect to room temperature. However, it decreases in the high temperature range.

Therefore, even if the magnetic field strength is the same, the output voltage and the unbalanced voltage of the operational amplifier OP1 change due to the temperature change, and the output voltage fluctuation of the operational amplifier OP1 constitutes the operational amplifiers OP3 and OP4. An erroneous binarization detection output is obtained for a fixed threshold value and window width of the window comparator. The same inconvenience also occurs when the binarization circuit is replaced with a window comparator and replaced with a comparator for detecting whether or not the Hall element output voltage is higher than one threshold voltage. Further, there is a similar inconvenience when the binarization circuit by the comparator is omitted and the output of the differential amplifier circuit is used as the analog current detection signal.

An object of the present invention is to provide a Hall element type current detector which can obtain a stable current detection output against temperature changes while suppressing current consumption of the Hall element.

It is another object of the present invention to provide a Hall element type current detector which obtains a stable binarized current detection output against temperature changes while suppressing current consumption of the Hall element.

[0012]

According to the present invention, in order to suppress current consumption, a bias current of a Hall element is supplied from a constant voltage source through a current limiting resistor, and in the case of this bias current supply system, the Hall element due to temperature change is supplied. The output of the output voltage and the unbalanced voltage are absorbed by the correction of the reference voltage given to the differential amplifier circuit, and by the correction of the reference voltage of the window comparator etc. And is characterized by the following configuration.

That is, the present invention is a Hall element type current detector for supplying a bias current to an input side terminal pair of a Hall element and extracting an output voltage of an output side terminal pair from a differential amplifier circuit. A bias current supply circuit that supplies a bias current to the Hall element through a limiting resistor, an intermediate voltage detection circuit that obtains an intermediate voltage between both ends of the output-side terminal pair of the Hall element, and the intermediate voltage with the intermediate voltage as a reference voltage. A constant voltage generating circuit that generates a constant voltage of the same ratio as the above, and uses this voltage as a reference voltage of the differential amplifier circuit.

Further, a comparator for comparing the output voltage of the differential amplifier circuit with a threshold value to obtain a binarized current detection output is provided, and the comparator divides the output voltage of the constant voltage generating circuit and outputs the binary voltage. It is characterized in that the threshold voltage is set.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit configuration showing an embodiment of the present invention, and portions equivalent to those in FIG. 4 or 6 are designated by the same reference numerals. In order to suppress the current consumption, the hall element 1 is controlled from the constant voltage VC to the current limiting resistor R0 in the same manner as in FIG.
A bias current supply circuit that supplies a bias current by applying a voltage between the pair of input side terminals 2 and 3 via.

The voltage dividing resistors RA and RB are made to have the same resistance value and are connected in series, and the output side terminal pair 4 of the Hall element 1 is connected.
An intermediate voltage detection circuit connected between 5 and obtaining an intermediate voltage of the output voltage of the Hall element 1. The intermediate voltage may be a 1: N intermediate voltage in which the resistors RA and RB are changed to different ratios.

The operational amplifier OP5 includes resistors RA and R for voltage division.
The intermediate voltage generated by B is used as a reference voltage, and the constant voltage generating circuit obtains a non-inverted voltage output twice as high as the intermediate voltage by the operation resistors RC and RD which have the same resistance value. In the differential amplifier circuit composed of the operational amplifier OP1 and the operational resistors R1 to R4, one end of the operational resistor R4 is connected to the inverting input terminal (-) of the operational amplifier OP5, and the same reference voltage (intermediate voltage) as that of the operational amplifier OP5. To be The operational amplifier OP5
It is also possible to divide the output of 1 to 1/2 and use it as the reference voltage of the differential amplifier circuit.

The output voltage of the operational amplifier OP5 (twice the intermediate voltage) is the threshold values VH and V of the window comparator.
It is set to the reference voltage applied to the voltage dividing resistors R5 to R7 for setting L and the window width.

In the above configuration, the voltage dividing resistors RA and R
The voltage at the point b, which is the connection point of B, is half the voltage at the point a of the Hall element 1, and the point c is the inverting input terminal of the operational amplifier OP5 (the reference of the differential amplifier circuit composed of the operational amplifier OP1 and the like). Voltage). The voltage at point c becomes the reference voltage applied to the voltage dividing resistors R5 to R7. D
It becomes 1/2 of the voltage at the point.

Therefore, when the temperature of the Hall element 1 becomes lower than the standard temperature and the Hall output voltage between the output side terminal pairs 4 and 5 increases, the internal resistance between the input side terminal pairs 2 and 3 also increases, b The voltage at the point also rises. As a result, the reference voltage (point c) of the differential amplifier circuit rises at the same ratio, and the output voltage of the operational amplifier OP2 (point d) rises at a double rate. As a result, as the output voltage of the Hall element 1 increases due to the temperature decrease, the threshold value of the window comparator and the window width also increase at the same rate. Further, as the unbalanced voltage of the Hall element increases, the reference voltage (point c) of the differential amplifier circuit increases at the same rate. Therefore,
It is possible to obtain a stable binarized output even when the Hall output voltage and the unbalanced voltage increase due to the temperature decrease.

On the contrary, when the temperature of the Hall element 1 rises above the standard temperature, the Hall output voltage between the output side terminal pair 4 and 5 decreases, but the reference voltage of the differential amplifier circuit (point c).
Also drops at the same ratio, and the output voltage (point d) of the operational amplifier OP2 also drops at a double ratio, so that a stable binarized output can be obtained. In the embodiment, the case where the binarized output is obtained using the window comparator is shown. However, the same operational effect can be obtained by using the configuration in which the comparator having one threshold value is used to obtain the binarized output. it can.

Further, even when the current detection is detected as an analog signal, that is, when the operational amplifier OP5 is used only as a reference voltage setting device of the differential amplifier circuit, the analog detection signal stabilized against temperature changes. Can be obtained. Furthermore, when this analog detection signal is converted into a digital signal by an A / D converter, the A / D
The reference voltage signal of the converter is generated or corrected by the output of the operational amplifier OP5, and the digital detection signal stabilized with respect to the temperature change can be obtained.

[0023]

As described above, according to the present invention, the intermediate voltage of the output voltage of the Hall element is detected, and the constant voltage generating circuit using this intermediate voltage as the reference voltage obtains the output voltage of the same ratio to obtain the differential voltage. Since it is used as the reference voltage of the amplifier circuit, in order to prevent the current consumption of the Hall element from increasing due to the temperature rise, the Hall sensor due to the temperature change is used while the current detector is configured to supply the bias current to the element through the current limiting resistor R0. A stable current detection output can be obtained even when the output voltage of the device and the unbalanced voltage change.

Further, when a binarized output is obtained by a comparator such as a window comparator, the threshold value of the comparator is divided by the output of the constant voltage generating circuit so that it is stabilized against temperature changes. A digitized current detection output can be obtained. Further, in the circuit configuration, since the bias current is supplied to the Hall element via the current limiting resistor R0, the operational amplifier OP2 having a relatively large output current in FIG. 4 is not necessary, and instead of this, the output current A small operational amplifier OP5 can be used, and there is no restriction on selection of the operational amplifier to be used.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention.

FIG. 2 is a basic circuit diagram of a Hall element type current detector.

[Fig. 3] Output voltage / unbalanced voltage characteristics depending on the temperature of the Hall element.

FIG. 4 is a circuit example of a conventional Hall element type current detector.

FIG. 5 is an internal resistance characteristic according to the temperature of the Hall element.

FIG. 6 is a circuit example of another conventional Hall element type current detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Hall element 2, 3 ... Input side terminal pair 4, 5 ... Output side terminal pair OP1-OP5 ... Operational amplifier R1-R7 ... Resistance RA-RD ... Resistance

Claims (2)

[Claims] 1. A Hall element type current detector for supplying a bias current to an input side terminal pair of a Hall element and extracting an output voltage of an output side terminal pair from a differential amplifier circuit, wherein: A bias current supply circuit that supplies a bias current to the Hall element, an intermediate voltage detection circuit that obtains an intermediate voltage of the voltages across the output-side terminal pair of the Hall element, and the same ratio as the intermediate voltage with the intermediate voltage as a reference voltage. A Hall element type current detector, comprising: a constant voltage generating circuit that generates a constant voltage and uses this voltage as a reference voltage of the differential amplifier circuit. 2. A comparator is provided for comparing the output voltage of the differential amplifier circuit with a threshold value to obtain a binary current detection output, and the comparator divides the output voltage of the constant voltage generating circuit to divide the output voltage. The Hall element type current detector according to claim 1, characterized in that the threshold voltage is set.