JPS5823009B2 - signal isolation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal isolation circuit for electrically insulating and extracting DC signals.

An object of the present invention is to realize a signal isolation circuit that is not affected by noise contained in an input DC signal and has a simple overall configuration.

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

In the figure, T is a winding n1. n3 and n
The transformer AO configured by applying No. 3 is a device for passing a reference alternating current Is through the winding n2, and a triangular wave signal generator, for example, is used for this purpose.

AMP is an amplifier that AC amplifies the signal generated in the winding n', cojl and C0P2 are comparators that take the output signal of the amplifier AMP as one input, and the other input terminals have reference voltages +△1 and -△, respectively. 2 is applied.

GA is a gate circuit which receives the output signals of comparators C0P1 and C0P2 as input.

RO is a resistor connected in series with the winding n2, and a voltage corresponding to the reference alternating signal flowing through the winding n2 is generated across the resistor.

SW is a switch driven by the output of the gate circuit GA, and SH is a sample-and-hold circuit, which here includes a switch SW and is composed of a capacitor CO and an amplifier A2.

FIG. 2 is a diagram showing the relationship between ampere turns AT and magnetic flux Φ in the transformer T.

Since the transformer used in the present invention has a saturable iron core, it has a characteristic that the magnetic flux Φ is saturated at a certain ampere turn A10 or more as shown in the figure.

The operation of the apparatus having such a configuration will now be explained with reference to FIG.

Now, in the block diagram of FIG. 1, the windings n of the transformer T,
While applying the input DC current Ix to the winding n2, the third
A reference triangular wave signal as shown by IS in Figure A is given.

Then, the magnitude of this reference triangular wave signal is adjusted so that the resulting ampere turn n2Is is sufficiently larger than the ampere turn ATO that saturates the iron core of the transformer T. Specifically, n2s is about 5 to 10 times larger than ATO. If it is selected to have a large value, positive and negative differential pulses as shown in the opening of FIG. 3 are generated in the winding n3 at the time when Is and IX intersect in FIG. 3A.

This is because in the transformer T, its iron core is saturated with positive or negative polarity except for a short time before and after Is and IX intersect, and in this state there is no change in magnetic flux, so a signal is sent to winding n3. does not occur, but at the point where Is and IX intersect, the ampere turn nII due to the human-powered DC signal IX, and the ampere turn n2I due to the reference triangular wave signal Is.
The sum n□■X1n2■s with s becomes 0, and the polarity of saturation of the iron core is reversed.

Therefore, at this point, the saturation state of the iron core is released, and a differential pulse dΦ/dt of magnetic flux is generated in the winding n3.

The amplifier AMP AC amplifies the differential pulse generated in the winding n3, and then applies the output to the comparators C0P1 and C0P2.

The comparators C0P1 and C0P2 output, for example, a Vine Bell signal when the level of the AC amplified differential pulse exceeds the reference voltage +△1 or part 2. A pulse signal as shown is obtained.

The switch SW is driven for a short time by the pulse signal shown in FIG. 3C output from the gate circuit GA, samples the voltage across the resistor RO at that time, and
This is held in capacitor CO.

Therefore, as shown in FIG. 3, from the output terminal of the sample and hold circuit SH, the magnitude EO is
An analog signal corresponding to x and electrically isolated from this input DC signal can be obtained.

In this embodiment, a case has been described in which a triangular wave signal is used as the reference alternating current given to the winding n2, but a ramp signal or a sine wave signal may be used.

Further, although the point in time when IX and Is intersect is detected by the signal generated in the winding n3, other magnetic flux change detecting means, such as a Hall element, may be used in place of n3.

In addition, the transformer T can be constructed by making the cross-sectional area of a part of the magnetic circuit (iron core) smaller than the cross-sectional area of other parts, or by making a part of the magnetic circuit a material that is easily subject to magnetic saturation. It may also be made to have saturation characteristics.

As explained above, according to the present invention, the transformer is in a saturated state for most of the period except for a short period when the reference alternating signal Is and the input DC signal Ix intersect. Even if IX contains noise, the switch SW will not be driven. Therefore, a signal isolation circuit with a simple overall configuration that is not affected by noise can be realized.

[Brief explanation of the drawing]

FIG. 1 is a configuration block diagram showing one embodiment of the present invention, and FIG.
The figure is a diagram showing the relationship between ampere turns and magnetic flux of the transformer used in the present invention, and FIG. 3 is an operating waveform diagram for explaining the operation of the apparatus shown in FIG. 1.

Claims (1)

[Claims] 1. A transformer in which at least two or more windings are provided on a saturable iron core, a magnetic flux change detection means for detecting a change in magnetic flux in the saturable iron core, and one winding of the transformer. a reference alternating signal generator that provides a reference alternating signal that changes with time; and a sample that receives a signal corresponding to the reference alternating signal as an input and samples and holds the reference alternating signal at the time when the output signal is obtained from the magnetic flux change detecting means. and a hold circuit, the signal isolation circuit is configured to apply a human-powered DC signal to another winding of the transformer and obtain an analog signal corresponding to the input DC signal from the output side of the sample-and-hold circuit. . 2. The signal isolation circuit according to claim 1, wherein changes in magnetic flux within the saturable iron core are obtained from windings applied to the saturable iron core. 3. The signal isolation circuit according to claim 1, wherein the magnitude of the reference alternating signal is selected such that the ampere turns resulting from the reference alternating signal are at least five times larger than the ampere turns that saturate the iron core of the transformer.