JP2594806B2 - DC current detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a direct current detection for detecting a current flowing through a winding by exciting a magnetically sensitive element inserted in a magnetic gap in a closed magnetic circuit with a pulse voltage. About the vessel.

[Conventional technology]

Generally, a DC current detector is a magnetic core 4 around which a coil 5 for flowing a current to be detected is wound as shown in a schematic diagram of FIG.
A magnetic sensitive element 2 such as a Hall element or a magnetoresistive element for detecting the magnetic intensity is inserted into a magnetic gap 10 provided in a part of the closed magnetic circuit. In order to obtain a sensitivity output from the magnetically sensitive element 2, a detection circuit is used which amplifies the output by passing a DC current through a coil 5 wound around a magnetic core 4. In a conventional detection circuit of this type, as shown in FIG. 5, a direct current is applied to a magnetically sensitive element 2 from a drive circuit 1 to excite it, and a DC output from the magnetically sensitive element 2 is subjected to DC amplification by an amplifier circuit 3. I have.

[Problems to be solved by the invention]

However, in the detection circuit of the conventional DC current detector,
In order to increase the sensitivity, that is, the output voltage / current to be measured, the output of the magnetically sensitive element 2 is directly connected to the amplifier circuit 3 to increase the degree of amplification and improve the detection capability. However, there is a disadvantage that the offset temperature coefficient of the amplifier circuit 3 increases as the amplification degree increases and the temperature drift increases.

[Means for solving the problem]

The present invention eliminates the conventional drawbacks, and inserts a coil 5 for flowing a measured DC current into a magnetic gap 10 provided in a part of a closed magnetic circuit of a wound magnetic core 4 to oscillate from an oscillation circuit. The output from the magnetically sensitive element 2 excited by the pulse output from the drive circuit chopped by the frequency is AC-amplified, synchronously rectified in synchronization with the oscillation frequency, and the measured DC current is detected as a smoothed DC output. It is a DC current detector.

[Action]

Since the output from the magnetically sensitive element 2 excited by the pulse signal from the drive circuit driven by the oscillation frequency is an alternating current, the output can be obtained from an AC amplifying circuit with a small temperature drift from which the offset is removed.

〔Example〕

1 and 2 are a block diagram and a schematic circuit diagram of a detection circuit of an embodiment of a DC current detector according to the present invention, and FIG. 3 is a waveform diagram showing an output of each unit in FIG.

As shown in the figure, the pulse voltage cut by the chopper circuit 6 by the frequency oscillated by the oscillation circuit 8 excites the magnetically sensitive element 2 such as a Hall element. Therefore, the output from the magnetically sensitive element 2 for detecting the intensity of the magnetic field generated by the measured current is an alternating current chopped as shown by a curve A in FIG. When this is amplified by the AC amplifying circuit 3, the output is, as shown in FIG. 3B, a chopped pulse voltage of V _{B1 including} the output voltage V _{B2 in} which the offset voltage of the amplifying circuit 3 is amplified. Become. Synchronous rectifier circuit 7 for synchronizing this amplified output with the chopped oscillation frequency
The output from the synchronous rectifier circuit 7 obtained by applying a voltage from the oscillation circuit 8 to the rectified circuit becomes a pulse output voltage of V _B1 −V _B2 from which the offset voltage V _B2 is removed as shown in FIG. When this pulse output voltage is smoothed by the smoothing circuit 9, a DC output voltage of (V _B1 −V _B2 ) / 2 according to FIG. 3D is obtained. Therefore, the measured current flowing through the coil 5 is detected as the DC output of FIG. 3 (D).

〔The invention's effect〕

As described above, according to the present invention, the magnetically sensitive element 2
The offset voltage is removed by AC-amplifying a pulse signal that is output by applying a pulse voltage to the DC power supply, so that the amplification degree can be increased and a DC current detector with small temperature drift and high accuracy can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a detection circuit in an embodiment of a DC current detector according to the present invention, FIG. 2 is a schematic circuit diagram in FIG.
FIG. 3 is an output waveform diagram of each circuit in FIGS. 1 and 2, FIG. 4 is a schematic diagram of a detection portion of a generally used DC current detector, and FIG. 5 is used in a conventional DC current detector. It is a block diagram of a detection circuit. 1 ... Drive circuit, 2 ... Magnetic sensitive element, 3 ... Amplifier circuit, 4 ...
... magnetic core, 5 ... coil, 6 ... chopper circuit, 7 ... synchronous rectification circuit, 8 ... oscillation circuit, 9 ... smoothing circuit, 10 ... magnetic gap.

Claims (2)

(57) [Claims] An oscillation circuit includes a magnetic sensing element inserted into a magnetic gap provided in a part of a closed magnetic circuit of a magnetic core on which a coil for flowing a DC current to be measured is wound. DC current detector excited by a pulse output from the driving circuit 1 chopped by the oscillation frequency of the DC current. 2. The DC current as claimed in claim 1, wherein a pulse output from said magnetically sensitive element is AC-amplified and is DC-output by a synchronous rectifier circuit and a smoothing circuit synchronized with said oscillation frequency. Detector.