JPH06160442A - Current detecting device - Google Patents

Abstract

PURPOSE:To correct the temperature characteristic of a current detection circuit by connecting in series a diode with a load resistor between the output and earth of a diode bridge. CONSTITUTION:A diode bridge 9 rectifies an AC current proportional to a current 7a to be measured by means of a current transformer 8 and a forward voltage drop 12b through a load resistor 10 and diode 13. By passing the dropped output voltage 12b through a low-pass filter 11 having different charging and discharging time constants, an output voltage which is nearly proportional to the effective value of the current 7a is obtained. Since the diode 13 has a negative temperature characteristic which reduces the voltage drop 12b when the temperature rises, the temperature characteristic of current detection circuit can be corrected by offsetting the positive temperature characteristic of the transformer 8 by using the diode 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detecting device for detecting an alternating current by insulating it.

[0002]

2. Description of the Related Art A conventional current detecting device of this type
A description will be given with reference to the drawings. FIG. 2 shows a conventional current detecting device, which is composed of a current transformer 2, a diode bridge 3, and a load resistor 4 of the current transformer 2, and its output voltage 6 is a low-pass having a peak-hold type time constant. It is connected to the filter 5.

The operation of the current detecting device configured as described above will be described. The alternating current 1b proportional to the measured current 1a detected by the current transformer 2 is rectified by the diode bridge 3 and converted into a voltage by the load resistor 4. The voltage 6 allows the low-pass filter 5 having a different charge / discharge time constant to obtain an output voltage substantially proportional to the effective value of the measured current 1a.

[0004]

However, in the above configuration, the temperature characteristic of the current transformer 2 is as shown in FIG.
As shown in (a), there is a positive temperature characteristic that the current transformer output current 1b rises as the ambient temperature rises. Therefore, the temperature characteristic of the current detection circuit has a negative temperature characteristic as shown in FIG. 3 (b). Therefore, there is a problem that an error occurs in the detected current value depending on the ambient temperature.

The present invention is intended to solve the above-mentioned problems of the conventional example, and an object thereof is to correct the temperature characteristic of the current detection circuit.

[0006]

In order to solve the above-mentioned problems, the present invention comprises a diode connected in series with a load resistance between the output of a diode bridge and ground.

[0007]

According to the present invention, by connecting the diode in series with the load resistance, the positive temperature characteristic of the current transformer can be corrected by the negative temperature characteristic of the diode.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A current detection circuit according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a current detecting device according to an embodiment of the present invention, in which a current transformer 8, a diode bridge 9, a load resistor 10 of the current lance 8 and a diode 13 connected in series thereto constitute a front stage. There is.
The output is connected to a low pass filter 11 having a peak hold type time constant.

The operation of the current detecting device configured as described above will be described. The alternating current 7b proportional to the measured current 7a detected by the current transformer 8 is rectified by the diode bridge 9 and converted into a voltage by the load resistor 10 and the diode forward voltage drop 12b. With the voltage 12a, an output voltage that is substantially proportional to the effective value of the measured current 7a can be obtained by a low-pass filter having a different charge / discharge time constant.

Here, the temperature characteristic of the forward voltage drop of the diode 13 will be described. The characteristics of the diode 13 are shown in FIG.
As shown in (c), there is a negative temperature characteristic in which the forward voltage drop 12b decreases as the temperature rises, so the positive temperature characteristic of the current transformer 8 and the negative temperature characteristic of the diode 13 are canceled out, and this current detection circuit The temperature characteristics of are improved.

[0012]

As is apparent from the above description, the present invention can correct the temperature characteristic of the current detecting device by providing a diode in series with the output of the diode bridge and the load resistance.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a current detection device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional current detection circuit.

3A is a temperature characteristic diagram of a current transformer, FIG. 3B is a temperature characteristic diagram of a current detection circuit, and FIG. 3C is a temperature characteristic diagram of a forward voltage drop of a diode.

[Explanation of symbols]

 8 Current transformer 9 Diode bridge 13 Diode 10 Load resistance

Claims (1)

[Claims] 1. A current detecting device comprising a current transformer, a diode, a resistor and a capacitor, wherein the diode is connected in series with a load resistor of the current transformer.