JPS6046386B2 - current detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current detector with good linearity that allows a current detection coil to detect a current in a circuit under test regardless of the DC potential of the current detection coil.

Conventional current detectors equally divide the potential applied to both ends of the shunt to be measured using two multipliers, one of which is connected to the ground.
There is a method of detection using a differential amplifier, but this method has the disadvantage of impairing sensitivity when the potential of the shunt to be measured is high.

As a countermeasure to this problem, there is a current detector that utilizes a magnetoresistive element, but it has the drawback that the current in the circuit under test is not proportional to the sensor output voltage. FIG. 1 shows a circuit diagram of a conventional embodiment.

Here, 1 and 1' are terminals connected to the circuit under test, 2 is a coil that generates a magnetic field proportional to the current flowing from terminals 1 and 1', 3 and 3' are semiconductor magnetoresistive elements, and 4 and 4' is a resistor, and 3, 3' and 4, 4' form a bridge circuit. Further, 6 is a differential amplifier with high input impedance, 7 is its output, and 8 is a terminal for supplying DC voltage to the bridge circuit and the differential amplifier. When current flows through the coil 2, the magnetic field generated by the coil 2 is applied to the semiconductor magnetoresistive element 3',
Its resistance value changes, generating a voltage between bridge outputs a and a'. This voltage is amplified by a differential amplifier 6. R is the resistance value when the magnetic field applied to the semiconductor magnetoresistive element 3' is zero. , if the resistance value when the magnetic field is B is RB, then RB
/Ro is not proportional to the magnetic field until the magnetic field is equalized, as shown in the characteristic diagram of the magnetic field and resistance value of the element in FIG. Therefore, when the current flowing out from the circuit under test is small, the magnetic field applied to the semiconductor magnetoresistive element is low, and the bridge output voltage is not proportional to the current in the circuit under test. This fact does not pose much of a problem when used as a digital sensor that detects simple changes in current value, but it is a fatal drawback when used as a sensor that detects the current value of the circuit under test as an analog quantity. In order to eliminate this drawback, the present invention applies a bias magnetic field to each of the two series semiconductor magnetoresistive elements of the bridge circuit, and also applies a magnetic field generated by the current of the circuit under test.
The bias magnetic field is applied additively to one semiconductor magnetoresistive element and destructively to the other semiconductor magnetoresistive element, so that the bridge circuit output voltage is proportional to the current of the circuit under test. It is in the current detector.

The drawings will be explained below.

FIG. 2 is a circuit diagram of an embodiment of the current detector according to the present invention, in which 1, 1'' are terminals connected to the measuring circuit, 2, 2
″ is a coil.

The magnetic field generated by the coils 2, 2'' is configured to be applied to one of the semiconductor magnetoresistive elements 3, 3'' in an additive manner to the magnetic field produced by the magnets 5, 5'', and to the other in a destructive manner.4, 4 '' is a resistor, 5 and 5'' are electromagnets or magnets, 6 is a differential amplifier with high input impedance, 7 is its output, and 8 is a DC voltage supply terminal.

3.3" is the magnitude of the magnetic field generated by the 5.5" electromagnet or magnet that is applied to the semiconductor magnetoresistive element, and is the value in the region where the resistance change is proportional to the magnetic field B (from the equation in Figure 3) (value of) Next, the bridge output voltage is shown based on FIG.

The resistance values of the semiconductor magnetoresistive elements 3, 3'' and the resistors 4, 4'' in FIG.
1, R2, R3, and R4V. The input impedance of the differential amplifier 6 is a larger value than Rl, R2, R3, and R4 described above. At this time, the bridge output voltage E. (The voltage between A and a″ in Figure 2) can be expressed by the following formula. Here, R3=
If R4 is the resistance value when only the magnetic field generated by the magnet is applied to the semiconductor magnetoresistive element, then the resistance value when the magnetic field generated by the coil is applied additively and subtractively is as shown in the following formula. It is.

Here, B is the magnetic flux density generated by the circuit, and S is the proportionality coefficient.

From the above, equation (1) becomes as follows.

In equation (4), since B is proportional to the current of the circuit under test, it can be seen that the bridge output voltage is proportional to the current of the circuit under test.

As described above, by applying the present invention, it is possible to construct a current detector in which the sensor output voltage is proportional to the current of the circuit to be measured, and the current can be detected regardless of the DC potential of the circuit to be measured.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of a conventional nonlinear current detector, FIG. 2 is a circuit diagram of an embodiment of the present invention, and FIG. 3 is a diagram of magnetic field-resistance characteristics of a semiconductor magnetoresistive element. In the figure, 1,1''...terminal connected to the circuit under test, 2,2''...coil, 3,3''...semiconductor magnetoresistive element, 4,4''...resistance, 5, 5''... Electromagnet or magnet, 6... Differential amplifier, 7... Output terminal thereof, 8... DC voltage supply terminal.

Claims (1)

[Claims] 1. A magnetic field forming unit that applies a bias magnetic field to two coils that generate a magnetic field proportional to the current of the circuit under test, two series semiconductor magnetoresistive elements whose resistance value changes depending on the magnitude of the applied magnetic field, and two series resistors. and a bridge circuit that extracts an output voltage from between the connection point of the two series semiconductor magnetoresistive elements and the connection point of the two series resistors, and for one of the semiconductor magnetoresistive elements. generates a voltage proportional to the current of the circuit under test at the bridge output by applying the magnetic field generated by the current detection coil and the bias magnetic field additively and destructively to the other semiconductor magnetoresistive element. current detector.