JP7181742B2 - Current input circuit and power measuring instrument - Google Patents

Description

The present disclosure relates to current input circuits and power meters.

2. Description of the Related Art As a power measuring instrument, one having a configuration shown in FIG. 2 is generally known (see, for example, Patent Document 1). In FIG. 2, the power measuring instrument 1 includes a voltage input circuit 10, a current input circuit 20, a computing section 30, a display section 40, a memory 50, an operating section 60, and a CPU .

The voltage input circuit 10 divides the input voltage by the voltage divider circuit 11 , amplifies it by the amplifier circuit 12 , and converts it into a digital signal by the A/D converter 13 .
output to

The current input circuit 20 amplifies the voltage across the shunt resistor 21 with the amplifier circuit 22 and converts it into a digital signal with the A/D converter 23 .

The calculation unit 30 calculates a voltage value, a current value, a power value, etc. from the voltage signal input from the A/D converter 13 and the current signal input from the A/D converter 23, and stores the calculation result in memory. 50. The display unit 40 displays the computation results of the computation unit 30 . The operation unit 60 includes, for example, buttons, keys, an external keyboard and mouse, etc., and measurement conditions and the like are set. The CPU 70 is connected to the functional units 10 to 60 of the power measuring device 1 via a bus, controls the functional units 10 to 60, and controls the power measuring device 1 as a whole.

JP 2009-288218 A

In the current input circuit 20 shown in FIG. 2, the circuit pattern in the current input circuit 20 is connected from the point P, which is the connection point between the ± terminals (L terminals) on the current output side and the shunt resistor 21, to the grounded housing 100. through which current flows by multiple paths. As a result, a voltage is generated by the current and the impedance of the circuit pattern, and an extra potential difference is generated between the input and output terminals of the amplifier circuit 22, causing an error in measuring the current flowing through the shunt resistor 21.

Accordingly, an object of the present disclosure is to provide a current input circuit and a power measuring instrument capable of reducing current measurement errors.

A current input circuit according to some embodiments includes an A terminal for inputting a current and ± terminals for outputting a current, a shunt resistor connected between the A terminal and the ± terminals, and a voltage across the shunt resistor. and a post-processing circuit for converting the voltage amplified by the amplifier circuit from an analog signal to a digital signal, the post-processing circuit having a resistor and indicating a reference potential of the amplifier circuit The first pattern is connected via the resistor to a second pattern indicating a reference potential of the post-processing circuit, the second pattern is connected to the ± terminals , and the post-processing circuit is amplified by the amplifier circuit. It has an operational amplifier that outputs a differential component between the voltage obtained and the reference potential of the amplifier circuit, and converts the output signal of the operational amplifier from an analog signal to a digital signal.
In this manner, the reference potential of the amplifier circuit and the reference potential of the post-processing circuit are separated, and the first pattern indicating the reference potential of the amplifier circuit is connected to the second pattern indicating the reference potential of the post-processing circuit through the resistor. On the other hand, by connecting the second pattern to the ± terminals, the common mode current flowing through the amplifier circuit can be reduced, so that the error in current measurement can be reduced.
Further, by extracting the differential component with the reference potential of the amplifier circuit after the voltage applied to the shunt resistor is amplified by the amplifier circuit, it is possible to further reduce the error in the current measurement.

In one embodiment, a power supply circuit for supplying voltage to the amplification circuit and the post-processing circuit may be provided, the amplification circuit having an inductor, the inductor being connected to the power supply circuit.
With such a configuration, it is possible to insulate the amplifier circuit from the power supply circuit and reduce the common mode current.

In one embodiment, the first pattern may be arranged to surround the amplifier circuit, and the second pattern may be arranged to surround the post-processing circuit.
According to such a configuration, noise can be reduced by the shield effect.

A power meter according to some embodiments comprises the current input circuit.
According to such a configuration, current can be measured with high accuracy.

According to the present disclosure, it is possible to provide a current input circuit and a power measuring instrument capable of reducing current measurement errors.

FIG. 2 illustrates a current input circuit according to one embodiment; It is a figure which shows an example of the conventional power measuring device.

EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing this invention is demonstrated, referring drawings.

FIG. 1 is a diagram showing a current input circuit according to one embodiment of the invention. As shown in FIG. 1, the current input circuit 200 includes an A terminal for inputting current, ± terminals for outputting current, a shunt resistor 210, an amplifier circuit 220, a post-processing circuit 230, and a power supply circuit 240. .

One end of the shunt resistor 210 is connected to the A terminal of the current input circuit 200, the other end of the shunt resistor 210 is connected to ± terminals of the current input circuit 200, and the shunt resistor 210 converts the current signal into a voltage signal.

The amplifier circuit 220 amplifies the voltage applied to the shunt resistor 210 by the operational amplifiers 221 and 222 . The amplifier circuit 220 is not limited to the configuration shown in FIG. 1, and any conventional amplifier circuit can be used. For example, although two stages of operational amplifiers are used in FIG. may

A first plane pattern 250 indicating the reference potential of the amplifier circuit 220 is arranged so as to surround the amplifier circuit 220 . In FIG. 1, the first plane pattern 250 is shaded in order to distinguish the first plane pattern 250 from the second plane pattern 260. As shown in FIG. In addition, the symbol of an inverted triangle that means connection to the first plane pattern 250 is also hatched. The first plane pattern 250 is connected through resistors 234 and 235 to a second plane pattern 260 indicating the reference potential of the post-processing circuit 230 .

One end of the resistor 223 is connected to the output terminal of the operational amplifier 222 and the post-processing circuit 230 , and the other end of the resistor 223 is connected to the resistor 224 . One end of the resistor 224 is connected to the resistor 223 and the other end of the resistor 224 is connected to the plane pattern 250 .

The post-processing circuit 230 has an A/D converter 236, which converts the voltage amplified by the amplifier circuit 220 from an analog signal to a digital signal.

A second plane pattern 260 indicating the reference potential of post-processing circuit 230 is arranged to surround post-processing circuit 230 . Also, the second plane pattern 260 is connected to ± terminals of the current input circuit 200 . A non-hatched inverted triangle symbol means connection to the second plane pattern 260 . The symbol of an inverted triangle placed near the ± terminals means that the ± terminals and the second plane pattern 260 are connected.

The post-processing circuit 230 may have an operational amplifier (differential amplifier) 231 in front of the A/D converter 236 as shown in FIG. In that case, the operational amplifier 231 outputs the differential component between the voltage amplified by the amplifier circuit 220 and the reference potential of the amplifier circuit 220, and removes the common-mode component. Then, the A/D converter 236 converts the output signal of the operational amplifier 231 from an analog signal to a digital signal.

One end of the resistor 232 is connected to the output terminal of the operational amplifier 222 and the other end of the resistor 232 is connected to the first input terminal of the operational amplifier 231 . One end of the resistor 234 is connected to the first plane pattern 250 and the other end of the resistor 234 is connected to the second input terminal of the operational amplifier 231 . One end of the resistor 233 is connected to the first input terminal of the operational amplifier 231 and the other end of the resistor 233 is connected to the output terminal of the operational amplifier 231 . One end of the resistor 235 is connected to the second input terminal of the operational amplifier 231 and the other end of the resistor 235 is connected to the second plane pattern 260 . The resistance values of the resistors 232 and 234 are the same, and the resistance values of the resistors 233 and 235 are also the same. The resistors 232, 233, 234, 235 and the operational amplifier 231 constitute a differential amplifier circuit. The differential amplifier circuit amplifies the differential component of the input signal by (resistance values of resistors 233 and 235)/(resistance values of resistors 232 and 234) and outputs the result.

The power supply circuit 240 generates a DC voltage by DC/DC conversion and supplies power to the amplifier circuit 220 and the post-processing circuit 230 . In FIG. 1, only wiring for power supply to the operational amplifier 222 is shown, and other wiring is omitted. The + terminal of the power supply circuit 240 is connected to the second plane pattern 260 through the capacitor 241 , and the - terminal of the power supply circuit 240 is directly connected to the second plane pattern 260 .

One end of the inductor 225 is connected to the power supply circuit 240 and the other end of the inductor 225 is connected to power supply terminals of the operational amplifiers 221 and 222 . Inductor 225 is, for example, a choke coil. This makes it possible to insulate the amplifier circuit 220 from the power supply circuit 240 and reduce the common mode current. Incidentally, as a power supply for the amplifier circuit 220, an insulated power supply (for example, an insulated DC/DC converter) may be separately provided to increase the impedance to the power supply.

The second plane pattern 260 is connected to ± terminals (L terminals) of the current input circuit 200 . Also, the second plane pattern 260 is connected to the grounded housing 100 via a capacitor 261 . In the current input circuit 200, the current flows from the connection point P between the ± terminals and the shunt resistor 210 to the housing 100 through the path 1 passing through the second plane pattern 260, or through the first plane pattern 250, the resistors 234 and 235, and the Current flows through the path 2 passing through the second plane pattern 260 . By increasing the resistance values of the resistors 234 and 235, the common mode current flowing through the path 2 can be made extremely small. That is, in the conventional current input circuit 20 shown in FIG. 2, the common mode current flowing inside the amplifier circuit 22 is large, but in the current input circuit 200 according to the present invention, the common mode current flowing inside the amplifier circuit 220 is can be made very small. Therefore, according to the present invention, it is possible to reduce errors in current measurement.

Further, the current input circuit 200 may be provided with an operational amplifier 231 to amplify the differential component between the output voltage of the operational amplifier 222 and the reference potential of the amplifier circuit 220 . It should be noted that the amplification here includes 1-fold. Since the resistance value of the shunt resistor 210 is small, the voltage applied to the shunt resistor 210 is also small. can be removed. Therefore, it is possible to further reduce the current measurement error.

Also, the current input circuit 20 of the power measuring instrument 1 shown in FIG. 2 can be replaced with the current input circuit 200 described above. That is, the power measuring instrument according to the present invention includes a voltage input circuit 10, a current input circuit 200, an arithmetic unit 30, a display unit 40, a memory 50, an operation unit 60, and a CPU70. A power measuring device that includes the current input circuit 200 can measure current with high accuracy.

Although the embodiments of the present invention have been described above with reference to the drawings, the specific configuration is not limited to these embodiments, and various modifications are possible without departing from the scope of the present invention. be

100 housing 200 current input circuit 210 shunt resistor 220 amplifier circuit 221, 222, 231 operational amplifier 223, 224, 232, 233, 234, 235 resistor 225 inductor 226, 241, 261 capacitor 230 post-processing circuit 236 A/D converter 240 power supply Circuit 250 First plane pattern 260 Second plane pattern

Claims (4)

A terminal for inputting current and ± terminals for outputting current,
a shunt resistor connected between the A terminal and the ± terminal;
an amplifier circuit that amplifies the voltage applied to the shunt resistor;
a post-processing circuit that converts the voltage amplified by the amplifier circuit from an analog signal to a digital signal,
The post-processing circuit has a resistor, a first pattern indicating a reference potential of the amplifier circuit is connected to a second pattern indicating a reference potential of the post-processing circuit via the resistor, and the second pattern is connected to the connected to the ± terminals ,
The post-processing circuit has an operational amplifier that outputs a differential component between the voltage amplified by the amplifier circuit and a reference potential of the amplifier circuit, and converts the output signal of the operational amplifier from an analog signal to a digital signal. A current input circuit characterized by: A power supply circuit that supplies voltage to the amplifier circuit and the post-processing circuit,
2. The current input circuit according to claim 1 , wherein said amplifier circuit has an inductor, said inductor being connected to said power supply circuit. 3. The current input circuit according to claim 1, wherein said first pattern is arranged so as to surround said amplifier circuit, and said second pattern is arranged so as to surround said post-processing circuit. A power measuring instrument comprising the current input circuit according to any one of claims 1 to 3 .

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