JP2020046351A - Voltage input circuit and electric power measurer - Google Patents

Abstract

To provide a voltage input circuit with which it is possible to raise the degree of design freedom for the capacitance value of a capacitor.SOLUTION: A voltage input circuit 80 comprises an op-amp 811, an input unit 800 for supplying an input signal to an inverted input terminal of the op-amp 811, and a feedback unit 810 for feeding the output signal of the op-amp 811 back to the inverted input terminal of the op-amp 811. The input unit 800 includes n resistors (n≥2) that are connected in series, n-1 resistors that are connected between the connecting point of said resistors and a reference potential, n capacitors that are connected in series, and n-1 capacitors that are connected between the connecting point of said capacitors and the reference potential, the connecting point of resistors and the connecting point of capacitors being unconnected. The feedback unit 810 includes an RC parallel circuit.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a voltage input circuit and a power meter.

  As a power measuring device, one having a configuration shown in FIG. 7 is generally known (for example, see Patent Document 1). 7, the power measuring device 100 includes a voltage input circuit 10, a current input circuit 20, an arithmetic unit 30, a display unit 40, a memory 50, an operation unit 60, and a CPU 70.

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

  The current input circuit 20 amplifies the voltage applied to the shunt resistor 21 by the amplifier circuit 22 and converts the voltage to a digital signal by the A / D converter 23.

  The calculation unit 30 calculates a voltage value, a current value, a power value, and the like 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 a memory. 50. The display unit 40 displays the calculation result of the calculation unit 30. The operation unit 60 is, for example, a button, a key, an external keyboard, a mouse, or the like, and sets measurement conditions and the like. The CPU 70 is connected to the functional units 10 to 60 of the power measuring device 1 by a bus, controls the functional units 10 to 60, and controls the entire power measuring device 1.

JP 2009-288218 A

  FIG. 8 is a circuit diagram showing an example of a conventional voltage input circuit 10. In order to obtain good frequency characteristics, it is necessary to adjust the time constants of the respective RC parallel circuits to the same value in the voltage dividing circuit 11. That is, the time constant of the parallel circuit of the resistor 121 and the capacitor 131, the time constant of the parallel circuit of the resistor 122 and the capacitor 132, the time constant of the parallel circuit of the resistor 123 and the capacitor 133, and the time constant of the parallel circuit of the resistor 124 and the capacitor 134. The time constant must be the same value. Therefore, when using a resistor with a large resistance value, it is necessary to use a capacitor with a small capacitance value. Conversely, when using a resistor with a small resistance value, it is necessary to use a capacitor with a large capacitance value. The restrictions on selecting parts were great. In addition, a capacitor having a small capacitance generally has a large tolerance, and even when the tolerance is adjusted by a variable capacitor (trimmer capacitor) or the like, the influence of the adjustment sensitivity and the capacitance value fluctuation becomes large.

  Thus, the present disclosure is to provide a voltage input circuit and a power measuring device that can increase the degree of freedom in setting the capacitance value of a capacitor.

A voltage input circuit according to some embodiments includes a voltage dividing circuit, the voltage dividing circuit includes an operational amplifier, an input unit that supplies an input signal to an inverting input terminal of the operational amplifier, and an output signal of the operational amplifier. A feedback unit that feeds back to an inverting input terminal of the operational amplifier, wherein the input unit is connected between n (n ≧ 2) resistors connected in series, and a connection point between the resistors and a reference potential. N-1 resistors, n capacitors connected in series, and n-1 capacitors connected between a connection point between the capacitors and the reference potential. And the connection point between the capacitors are not connected, and the feedback unit has an RC parallel circuit.
As described above, by separating the resistor and the capacitor of the input section, the degree of freedom in setting the capacitance value of the capacitor can be increased.

The n is 2. The input unit includes a resistor T-type circuit in which a first resistor, a second resistor, and a third resistor are connected in a T shape, and a first capacitor, a second capacitor, and a third capacitor that are connected to each other by T. And a capacitor T-type circuit connected in a U-shape.
Thus, by setting n = 2, a voltage input circuit having a simple configuration can be realized.

In one embodiment, the input unit has a first switching unit, and a connection point between the first resistor and the first capacitor is connected to a + terminal of the voltage input circuit, and the first switching unit A connection point between the second resistor and the second capacitor is connected to a negative terminal of the voltage input circuit or connected to an inverting input terminal of the operational amplifier, and a connection point between the third resistance and the third capacitor is , Connected to an inverting input terminal of the operational amplifier, the-terminal may have the reference potential.
Thus, the range can be switched by having the first switching unit.

In one embodiment, a monitoring circuit that monitors a voltage at a middle point of the resistor T-type circuit and a middle point of the capacitor T-type circuit may be provided.
Thus, the provision of the monitoring circuit makes it possible to detect the occurrence of an abnormality.

In one embodiment, the feedback unit includes a plurality of sets of RC parallel circuits and a second switching unit, and the second switching unit uses any one of the plurality of sets of RC parallel circuits. Whether the output signal of the operational amplifier is fed back may be switched.
Thus, the range can be switched by having the second switching unit.

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

  According to the present disclosure, it is possible to provide a voltage input circuit and a power measurement device that can increase the degree of freedom in setting the capacitance value of a capacitor.

FIG. 2 is a diagram illustrating a voltage input circuit according to one embodiment. FIG. 3 is a diagram illustrating a first modification of the voltage divider circuit illustrated in FIG. 1. FIG. 5 is a diagram illustrating a second modification of the voltage divider circuit illustrated in FIG. 1. FIG. 7 is a diagram illustrating a third modification of the voltage divider circuit illustrated in FIG. 1. FIG. 11 is a diagram illustrating a fourth modification of the voltage divider circuit illustrated in FIG. 1. FIG. 13 is a diagram illustrating a fifth modification of the voltage divider circuit illustrated in FIG. 1. FIG. 11 is a diagram illustrating an example of a conventional power measuring device. FIG. 9 is a diagram illustrating an example of a voltage input circuit in a conventional power measuring device.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a voltage input circuit according to an embodiment of the present invention. As shown in FIG. 1, the voltage input circuit 80 includes a voltage dividing circuit 81a, an amplifier circuit 12, and an A / D converter 13. The voltage dividing circuit 81a divides the input voltage of the voltage input circuit 80. The amplifier circuit 12 amplifies the voltage divided by the voltage dividing circuit 81a. The A / D converter 13 converts the voltage amplified by the amplifier circuit 12 from an analog signal to a digital signal. Note that the amplifier circuit 12 may not be provided, and in that case, the A / D converter 13 converts the voltage divided by the voltage dividing circuit 81a from an analog signal to a digital signal.

  The voltage dividing circuit 81a includes an operational amplifier 811, an input unit 800 that supplies an input signal to an inverting input terminal of the operational amplifier 811, and a feedback unit 810 that feeds back an output signal of the operational amplifier 811 to the inverting input terminal of the operational amplifier 811.

  The input unit 800 is connected in series with n (n ≧ 2) resistors connected in series, and n−1 resistors connected between a connection point between the resistors and a reference potential (ground). N capacitors, and n-1 capacitors connected between a connection point between the capacitors and a reference potential, and a connection point between the resistors and a connection point between the capacitors are not connected. is there. FIG. 1 shows a case where n = 1. That is, the input unit 800 connects a resistor 821, a resistor 822, and a resistor 823 in a T-shape (hereinafter, referred to as a “resistor T-type circuit”) and a capacitor 831, a capacitor 832, and a capacitor 833 to a T-circuit. A T-type circuit (hereinafter, referred to as a “capacitor T-type circuit”) connected in a V-shape, and a connection point P between resistors (middle point of a resistance T-type circuit) and a connection point between capacitors (capacitor T-type circuit) (Middle point of the circuit) Q is not connected.

  The connection point between the resistor 821 and the capacitor 831 is connected to the + terminal of the voltage input circuit 80. That is, the terminal of the resistor 821 that is not connected to the capacitor 831 is connected to the middle point P, and the terminal of the capacitor 831 that is not connected to the resistor 821 is connected to the middle point Q. The connection point between the resistor 822 and the capacitor 832 is connected to the negative terminal (ground) of the voltage input circuit 80. That is, the terminal of the resistor 822 not connected to the capacitor 832 is connected to the midpoint P, and the terminal of the capacitor 831 not connected to the resistor 821 is connected to the midpoint Q. The connection point between the resistor 823 and the capacitor 833 is connected to the inverting input terminal of the operational amplifier 811. That is, the terminal of the resistor 823 that is not connected to the capacitor 833 is connected to the middle point P, and the terminal of the capacitor 833 that is not connected to the resistor 823 is connected to the middle point Q.

  The feedback unit 810 has an RC parallel circuit of a resistor 824 and a capacitor 834. One ends of the resistor 824 and the capacitor 834 are connected to an inverting input terminal of the operational amplifier 811, and the other ends of the resistor 824 and the capacitor 834 are connected to an output terminal of the operational amplifier 811.

  FIG. 2 shows a voltage dividing circuit 81b which is a first modification of the voltage dividing circuit 81a. FIG. 2 shows a case where n = 2 in the input section 800 of the voltage dividing circuit 81b. That is, the input section 800 of the voltage dividing circuit 81b has the resistors 825 and 826 on the input side of the resistor T-type circuit and the capacitors 835 and 836 on the input side of the capacitor T-type circuit. The connection points P and P 'between the resistors are not connected to the connection points Q and Q' between the capacitors.

  FIG. 3 shows a voltage dividing circuit 81c which is a second modification of the voltage dividing circuit 81a. As shown in FIG. 3, the feedback section 810 of the voltage dividing circuit 81c includes a plurality of sets of RC parallel circuits and a switching section (switch) 841. The switching unit 841 switches which RC parallel circuit is used to feed back the output signal of the operational amplifier 811. The feedback unit 810 of the voltage dividing circuit 81c shows a case where the number of RC parallel circuits is two. The feedback unit 810 of the voltage dividing circuit 81c selects only the RC parallel circuit of the resistor 824 and the capacitor 834 or selects both the RC parallel circuit and the RC parallel circuit of the resistor 827 and the capacitor 837 by the switching unit 841. Switch.

  The feedback unit 810 of the voltage dividing circuit 81c can change the resistance value between the inverting input terminal and the output terminal of the operational amplifier 811 by the switching unit 841, so that the voltage dividing ratio of the input voltage of the voltage dividing circuit 81c is changed. can do. Specific examples of the partial pressure ratio will be described later.

  FIG. 4 shows a voltage dividing circuit 81d which is a third modification of the voltage dividing circuit 81a. As shown in FIG. 4, the input section 800 of the voltage dividing circuit 81d has a switching section (switch) 842. The switching unit 842 switches whether to connect the connection point of the resistor 822 and the capacitor 832 to the negative terminal (ground) or to the inverting input terminal of the operational amplifier 811.

  When the connection point of the resistor 822 and the capacitor 832 is connected to the ground, the voltage dividing circuit 81d divides the input voltage by the ratio between the resistance value of the resistor 821 and the combined resistance value of the resistors 822 and 823. The voltage is further divided by the ratio of the resistance values of the resistors 823 and 824. When the connection point between the resistor 822 and the capacitor 832 is connected to the inverting input terminal of the operational amplifier 811, the input voltage is equal to the combined resistance value of the resistor 821, the resistor 822, and the resistor 823, The voltage is divided by the ratio of the resistance values. Therefore, the partial pressure ratio can be changed by the switching unit 842. Specific examples of the partial pressure ratio will be described later.

  FIG. 5 shows a voltage dividing circuit 81e which is a fourth modification of the voltage dividing circuit 81a. Since the voltage division ratio changes by switching between the switching unit 841 and the switching unit 842, the range can be switched. For example, when the resistance of the resistor 821 is 9.9 MΩ, the resistance of the resistor 822 is 111.11 kΩ, the resistance of the resistor 823 is 1 MΩ, the resistance of the resistor 824 is 100 kΩ, and the resistance of the resistor 827 is 900 kΩ, the switching is performed. According to the switching of the unit 841 and the switching unit 842, the partial pressure ratio becomes as in the following (1) to (4).

(1) When the resistor 822 is connected to the ground by the switching unit 842 and the resistor 827 is short-circuited by the switching unit 841, in this case, the voltage at the middle point P is divided by the ratio of the resistance values of the resistors 823 and 824. Pressed. Since the resistance value of the resistor 821 is 9.9 MΩ and the combined resistance value of the resistors 822 and 823 is 100 kΩ, the voltage at the middle point P is 1/100 of the input voltage. The ratio between the resistance values of the resistor 823 and the resistor 824 is 1M: 100k = 10: 1. Therefore, the output voltage of the operational amplifier 811 is 1/1000 of the input voltage of the voltage dividing circuit 81e.

(2) The case where the resistor 822 is connected to the ground by the switching unit 842 and the resistor 827 is not short-circuited by the switching unit 841. In this case, the voltage at the middle point P is the resistance value of the resistor 823, the resistance 824, and the resistance. The voltage is divided at a ratio of 827 to the combined resistance value. The voltage at the midpoint P is 1/100 of the input voltage as described above. The ratio between the resistance of the resistor 823 and the combined resistance of the resistors 824 and 827 is 1M: (900k + 100k) = 1: 1. Therefore, the output voltage of the operational amplifier 811 is 1/100 of the input voltage of the voltage dividing circuit 81e.

(3) When the resistor 822 is connected to the inverting input terminal of the operational amplifier 811 by the switching unit 842, and the resistor 827 is short-circuited by the switching unit 841, in this case, the input voltage of the voltage dividing circuit 81e is reduced by the resistors 821 and 822. , And the ratio of the combined resistance value of the resistor 823 and the resistance value of the resistor 824. This ratio is (9.9M + 100k): 100k = 100: 1. Therefore, the output voltage of the operational amplifier 811 is 1/100 of the input voltage of the voltage dividing circuit 81e.

(4) When the resistor 822 is connected to the inverting input terminal of the operational amplifier 811 by the switching unit 842 and the resistor 827 is not short-circuited by the switching unit 841, in this case, the input voltage of the voltage dividing circuit 81e is The voltage is divided by the ratio of the combined resistance value of the resistors 822 and 823 to the combined resistance value of the resistors 824 and 827. This ratio is (9.9M + 100k) :( 900k + 100k) = 10: 1. Therefore, the output voltage of the operational amplifier 811 is 1/10 of the input voltage of the voltage dividing circuit 81e.

  The capacitance value of the capacitor of the feedback unit 810 is adjusted so that the time constant of the RC parallel circuit becomes a predetermined value. On the other hand, the capacitance value of the capacitor of the input unit 800 may be such that the shunt ratio at the midpoint P and the shunt ratio at the midpoint Q are the same. Since the ratio of the current flowing through the resistor 822 to the current flowing through the resistor 823 is 9: 1, the ratio between the capacitance of the capacitor 832 and the capacitance of the capacitor 833 may be 9: 1. For example, the capacitance value of the capacitor 832 is 297 pF, and the capacitance value of the capacitor 833 is 33 pF.

  FIG. 6 shows a voltage dividing circuit 81f which is a fifth modification of the voltage dividing circuit 81a. The voltage dividing circuit 81f includes a monitoring circuit 820. The monitoring circuit 820 is a circuit that constantly monitors the voltages at the midpoints P and Q. If the rate of change or the amount of change in the voltage at the midpoints P and Q exceeds the threshold, it can be determined that an abnormality has occurred. For example, as illustrated in FIG. 6, the monitoring circuit 820 includes a resistor 828, a resistor 829, a capacitor 838, a capacitor 839, and an operational amplifier 812. The voltage at the midpoints P and Q has a constant value without being affected by the range switching even when the switching units 841 and 842 shown in FIG. 5 are provided for the range switching. Therefore, the monitoring circuit 820 can appropriately detect occurrence of an abnormality.

  Thus, in the voltage dividing circuits 81a to 81f, the middle point P of the resistor T-type circuit and the middle point Q of the capacitor T-type circuit are not connected, and the input unit 800 separates the resistor and the capacitor. Therefore, when setting the capacitance value of the capacitor of the input section 800, there is no longer the restriction that the time constants of the respective RC parallel circuits are adjusted as in the related art, and the degree of freedom in setting the capacitance value of the capacitor can be increased. By increasing the degree of freedom in setting the capacitance value, it is not necessary to use a low-capacitance capacitor having a large tolerance of the capacitance value, and a capacitor having good characteristics can be selected. Further, the adjustment sensitivity by the trimmer capacitor can be reduced, and as a result, it is possible to reduce an error due to a deviation in setting of the capacitance value. In addition, mixing of patterns can be avoided by the separate design of the DC system and the AC system, and the characteristic verification becomes easy. Further, since the AC voltage dividing ratio is determined by the capacitance value, it is possible to flexibly cope with a change in the resistance value.

  Further, the voltage input circuit 10 of the power measuring device 100 shown in FIG. 7 can be replaced with the above-described voltage input circuit 80. As described above, a capacitor having good characteristics can be selected for the voltage input circuit 80, so that a power measuring device including the voltage input circuit 80 can measure a voltage with high accuracy.

  The embodiment of the present invention has been described with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes various modifications without departing from the spirit of the present invention. It is.

DESCRIPTION OF SYMBOLS 12 Amplification circuit 13 A / D converter 80 Voltage input circuit 81a, 81b, 81c, 81d, 81e Voltage divider circuit 800 Input section 810 Feedback section 820 Monitoring circuit 811,812 Operational amplifier 821,822,823,824,825,826, 827,828,829 Resistance 831,832,833,834,835,836,837,838,839 Capacitor 841,842 Switching unit

Claims (6)

A voltage input circuit having a voltage dividing circuit,
The voltage dividing circuit includes:
An operational amplifier,
An input unit for supplying an input signal to an inverting input terminal of the operational amplifier,
A feedback unit that feeds back an output signal of the operational amplifier to an inverting input terminal of the operational amplifier,
The input unit includes n (n ≧ 2) resistors connected in series, n−1 resistors connected between a connection point between the resistors and a reference potential, and n serially connected resistors And n-1 capacitors connected between a connection point between the capacitors and the reference potential, and a connection point between the resistors and a connection point between the capacitors are not connected. Yes,
The voltage input circuit, wherein the feedback unit has an RC parallel circuit. N is 2;
The input unit includes a resistor T-type circuit in which a first resistor, a second resistor, and a third resistor are connected in a T-shape, and a capacitor T-type in which a first capacitor, a second capacitor, and a third capacitor are connected in a T-shape. The voltage input circuit according to claim 1, further comprising a circuit. The input unit has a first switching unit,
A connection point between the first resistor and the first capacitor is connected to a + terminal of the voltage input circuit;
By the first switching unit, a connection point of the second resistor and the second capacitor is connected to a negative terminal of the voltage input circuit, or connected to an inverting input terminal of the operational amplifier,
A connection point between the third resistor and the third capacitor is connected to an inverting input terminal of the operational amplifier;
The voltage input circuit according to claim 2, wherein the-terminal has the reference potential.   The voltage input circuit according to claim 2, further comprising a monitoring circuit that monitors a voltage at a middle point of the resistor T-type circuit and a middle point of the capacitor T-type circuit. The feedback unit has a plurality of sets of RC parallel circuits and a second switching unit,
5. The apparatus according to claim 1, wherein the second switching unit switches which one of the plurality of sets of RC parallel circuits is used to feed back the output signal of the operational amplifier. The voltage input circuit according to claim 1. A power measuring device comprising the voltage input circuit according to claim 1.

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