JPH0785092B2 - AC effective value-DC conversion circuit - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an AC effective value-DC conversion circuit.

(Prior art and its problems) With the AC effective value-DC conversion circuit, the effective value of AC is obtained,
It is a circuit that converts to DC based on this effective value. Such a conversion circuit includes a squaring circuit that squares an input signal,
There is an averaging circuit that averages the squared circuit output by integrating it, and a square rooting circuit that squares the output of the averaging circuit. Conventionally, it is known that each of these circuits is incorporated in a monolithic IC. (See Practical Electronic Handbook (4), pages 421 and 422, published by CQ Publishing Co., Ltd., 5th edition, November 1, 1983).

However, in the case where the AC RMS value-DC conversion circuit is incorporated in the monolithic IC, the circuit configuration is very complicated because the square root circuit is required, and the cost thereof is high. was there. And, although there is a problem that the cost is high, there is another problem that the reliability is not good.

Also proposed is a system in which a rectifier and a time constant circuit composed of a capacitor and a resistor are combined, a specific number of the time constant circuit is set to a specific value, and pseudo effective value conversion is performed. Although the circuit of this proposal has a simple circuit configuration, it has a problem that the accuracy of effective value conversion is poor.
It could not be adopted when it is desired to perform highly accurate RMS conversion.

(Object of the Invention) The present invention aims to solve the above problems.

(Structure and Effect of the Invention) In order to achieve the above object, the present invention includes a squaring circuit having an output section in which a squared current appears and a negative feedback input section to which a negative feedback voltage is applied, and an operational amplifier, One of the input terminals of the operational amplifier is connected to the output section of the squaring circuit, and the other input terminal is supplied with a rectified voltage to be converted into an effective value. An averaging circuit that averages and outputs the difference between the voltage and the rectified voltage; and based on the averaged output voltage output from the averaging circuit and the voltage of the output section of the squaring circuit, the effective rectified voltage. A differential amplifier circuit that outputs a value and negatively feeds back this output to the negative feedback input section of the square circuit as a negative feedback voltage, wherein the square circuit is between the one input terminal and the ground section. To the main road A sub path between the voltage dividing point for dividing the difference voltage between the rectified voltage appearing at the input terminal and the negative feedback voltage appearing at the negative feedback input section and the ground section, and In the main path, there is a main current corresponding to the voltage difference between the rectified voltage appearing at one input terminal due to an imaginary short circuit at both input terminals of the operational amplifier and the potential of the ground section and the impedance value in the nuclear main path. flow,
A subcurrent according to a voltage difference between the divided voltage and the potential of the ground portion and an impedance value in the subpath flows in the subpath, and the subcurrent flows in the subpath. A directional element is provided in a direction in which a sub-current flows when the piezo voltage is in a first state in which the voltage is higher than the ground potential or in a second state in which the voltage is low, and the one input terminal is provided in the one input terminal. The added current obtained by adding the main current and the sub current is the first
In the above state, the current flows from one input terminal of the averaging circuit into the one input terminal in the second state, and the main current is adjusted so that the added current becomes a squared current that approximates the rectified voltage waveform. The impedance value of each of the road and the sub road is set.

Alternatively, the present invention comprises a squaring circuit having an output section in which a squared current appears and a negative feedback input section to which a negative feedback voltage is applied, and an operational amplifier, wherein one input terminal of the operational amplifier is the squaring circuit. A rectified voltage to be converted to an effective value is applied to the other input terminal of the output circuit, and the difference between the output voltage of the squaring circuit and the rectified voltage is averaged and output. Based on the averaged output voltage output from the averaging circuit and the voltage of the output section of the squaring circuit, and outputs the effective value of the rectified voltage, and this output of the squaring circuit. A differential amplifier circuit that negatively feeds back as a negative feedback voltage to a negative feedback input portion, wherein the square circuit forms a main path between the one input terminal and the negative feedback input portion, and the one input Rectified voltage appearing at the terminal There is a sub path between the voltage dividing point for dividing the voltage difference from the potential of the ground section and the negative feedback input section, and the main path has one input due to an imaginary short circuit at both input terminals of the operational amplifier. A main current according to the voltage difference between the rectified voltage appearing at the terminal and the negative feedback voltage and the impedance value in the main path flows, and the divided voltage and the potential of the negative feedback voltage flow in the sub path. A sub-current according to the voltage difference between the sub-path and the impedance value in the sub-path, and when the divided voltage is in the first state higher than the negative feedback voltage in the sub-path. Alternatively, a directional element is provided in a direction in which the sub-current flows in a conductive state when the second state is low, and an addition current obtained by adding the main current and the sub-current is provided to the one input terminal. In the state of 1, it is one of the input terminals of the averaging circuit Inflow In the second state, while flowing into the one input terminal, impedance values in the main path and the sub path are set such that the added current becomes a squared current that approximates the rectified voltage waveform. .

According to this configuration, since both input terminals of the operational amplifier of the averaging circuit are imaginary short-circuited, the rectified voltage applied to one input terminal side is the voltage of the other input terminal. Therefore, a current (main current) corresponding to the voltage difference between the output side of the squaring circuit and the grounding section or the voltage difference between the rectified voltage and the negative feedback voltage and the resistance value in the main path thereof is the main current. Flowing in the street. Further, since the directional element is provided in the sub path thereof, when the divided voltage is larger or smaller than the ground potential or the divided voltage is larger or smaller than the negative feedback voltage, An auxiliary current corresponding to the voltage difference and the resistance value in the auxiliary path flows in the auxiliary path. Since the main current and the auxiliary current are added in the squaring circuit, a squaring current appears at the output of the squaring circuit. Since this squared current is, after all, proportional to the square of the rectified voltage and inversely proportional to the output of the differential amplifier circuit, this squared current is input to the averaging circuit and averaged, and The voltage differentiated by the differential amplifier circuit becomes a voltage corresponding to the theoretical formula of the effective value.

Therefore, according to the present invention, since the circuit configuration is simple, that is, only the square circuit, the averaging circuit, and the differential amplifier circuit are combined, without using a square root circuit, it is more preferable than that configured by a monolithic IC. An inexpensive circuit can be obtained. Further, since the RMS value conversion is performed according to the theoretical formula, not only the AC RMS value-DC conversion that is more reliable than the pseudo RMS value conversion method can be performed, but also the monolithic IC. Even if it is configured as described above, it will be excellent in reliability in consideration of its cost.

Further, according to the present invention, since the output of the averaging circuit is not directly negatively fed back to the squaring circuit, the averaging circuit can be designed without considering the influence of the impedance of the squaring circuit. Therefore, there is also an effect that the circuit design becomes extremely easy.

(Description of Embodiments) FIG. 1 is a circuit diagram of Embodiment 1 of an AC effective value-DC conversion circuit of the present invention. In FIG. 1, IN is an input terminal for an AC voltage (e ₀ ), and OUT is an output terminal for an effective value voltage (V ₀ ). Reference numeral ₁ is a full-wave rectifier circuit that full-wave rectifies the AC voltage (e ₀ ) from the input terminal IN and outputs it as a positive rectified voltage (e ₁ ) that should be converted into an effective value.

Reference numeral 2 is a square circuit composed of resistors R1 to R6 and diodes D1 and D2. This squaring circuit 2 has a squaring current (i)
Has a negative feedback input section 22 to which a negative feedback voltage (V ₀ ) is applied. The squaring circuit 2 also includes a main path A (including a resistor R4) through which a main current (i ₁ ) flows between its output section 21 and a ground section 23, and a voltage point 24 lower than the rectified voltage (e ₁ ). , 25 and the grounding portion 23, respectively, a subcurrent (i
₂ and i ₃ ) have two sub paths B and C. The low voltage points 24 and 25 are the connection points of the resistors R1 and R2,
It is a connection point between the resistor R2 and the resistor R3. A resistor R5 and a diode D1, and a resistor R6 and a diode D2 are provided in each of the sub paths B and C. Since the diodes D1 and D2 function as directional elements, any elements having this function may be transistors or the like.

3 is a squared current (i) with respect to the output section 22 of the squaring circuit 2.
An input section 31 that gives a rectified voltage (e ₁ ) from the full-wave rectifier circuit 1, an output section 33 that outputs an averaged output voltage (V ₀₀ ), and an imaginary short circuit in the input section 31. Output unit that outputs the rectified voltage (e ₁ ) of
34 is an averaging circuit having. This averaging circuit 3
The operational amplifier AMP includes a smoothing capacitor C and an amplification degree determining resistor R7 that are connected in parallel between the inverting input terminal (-) and the output terminal of the operational amplifier AMP.

4 is one input terminal (-) 41 to the output section 33 of the averaging circuit 3.
Is also connected, and the other input terminal (+) 42 is also connected to the output section 34 of the averaging circuit 3.

Next, the operation and action of the first embodiment will be described with reference to the waveform chart of FIG. 2 (a1) shows the waveform of the rectified voltage (e ₁ ) given from the full-wave rectifier circuit 1 to the non-inverted input terminal (+) of the operational amplifier AMP of the averaging circuit 2, and FIG. 2 (a2) shows The waveform of the main current (i ₁ ) flowing through the resistor R4 in the main path A of the squaring circuit 2 is shown, FIG. 2 (b1) shows the waveform of the voltage (e ₂ ) appearing at the connection point 24, and FIG. b2) is resistance R5 in secondary path B
2 (c 1) shows the waveform of the sub-current (i ₂ ) flowing through the circuit, and FIG. 2 (c 1) shows the waveform of the voltage (e ₃ ) appearing at the connection point 25.
2) shows the waveform of the sub-current (i ₃ ) flowing through the resistor R6 in the sub path C, and FIG. 2 (d) shows the waveform of the squared current (i) appearing at the connection point 21. In each figure, 0 indicates the ground potential of the ground section 23.

A rectified voltage (e ₁ ) having a waveform as shown in FIG. 2 (a1) is applied to the non-inverting input terminal (+) of the operational amplifier AMP. The input / output terminals (+) and (-) of the operational amplifier AMP for inverting and inverting are imaginary short circuit, so the resistance R4 of the squaring circuit 2
The main current (i ₁ ) flowing through the circuit has a value corresponding to the voltage difference between the rectified voltage (e ₀ ) and the potential 0 of the ground portion 23. If this value is expressed by a formula, i ₁ = e ₁ / R ₄ is obtained. Here, i ₁ is the current value of the main current (i ₁ ), e ₁ is the voltage value of the rectified voltage (e ₁ ), and R ₄ is the resistance value of the resistor R ₄ . The symbol "/" is a division symbol (÷) (hereinafter the same). The waveform of the main current (i ₁ ) is as shown in Fig. 2 (a2).

On the other hand, the rectified voltage (e ₁ ) that appears at the output 21 of the squaring circuit 2
Is the resistance R1, R2, R3 at the connection points 24, 25 in relation to the output (V ₀ ) of the differential amplifier circuit 4 applied to the negative feedback input section 22.
Since it is divided by and, the voltage at its connection point 24 (e ₂ )
Becomes as shown in FIG. 2 (b1). That is, this voltage (e ₂ ) has a negative potential as indicated by hatching. Therefore, the auxiliary current (i ₂ ) flowing through the resistor R5 is
When the voltage (e ₂ ) is higher than 0, the diode D1 becomes conductive, as shown in FIG. 2 (b2). Similarly, the voltage (e ₃ ) at the connection point 25 becomes as shown in FIG. 2 (c1), and therefore the auxiliary current (i ₃ ) flowing through the resistor R6 is as shown in FIG. 2 (c2) by the diode D2. Become.

Since the addition of these respective currents (i ₁ , i ₂ , i ₃ ) is the squared current (i) appearing in the output section 21, the added current (squared current) (i) is shown in FIG. 2 (d). As shown. In the waveform of the squared current (i), the sub-current (i ₂ ) corresponds to aa and the sub-current (i ₃ ) corresponds to bb.

The magnitude of each current (i ₁ , i ₂ , i ₃ ) is determined by the resistance value of each resistor R4, R5, R6, but if each resistance value is appropriately selected, the squared current (i) waveform Is the square of the rectified voltage (V ₀ ),
It is possible to make it more approximate. Also, FIG. 2 (d)
The waveform of the squared current (i) of was a two-point broken line,
Of course, if the number of connection points 23, 24, etc. is increased, the polygonal line can be brought closer to the square curve.

Therefore, since the square of the AC voltage (e ₀ ) given to the full-wave rectifier circuit 1 is the square of the rectified voltage (e ₁ ), the squared current (i) is proportional to the square of the AC voltage (e ₀ ), and The value is inversely proportional to the differential amplification output (V ₀ ), that is, given by the following equation (1).

i = (k ₁ · e ₀ ² ) / V ₀ (1) where i is the current value of the squared current (i), k ₁ is a constant, and e ₀
Is the voltage value of the rectified voltage (e ₀ ), and V ₀ is the output value of the differential amplifier circuit 4.

This squared current (i) is averaged by the averaging circuit 3 to become an averaged current (I ave) as shown in FIG. 2 (d). In the averaging circuit 3, this averaging current (I ave) flows through the resistor R7, so that the averaging voltage (V ₀₀ ) has a value represented by the following equation (2).

_{V 00 = e 1 + R 7} · I ave = e 1 + (k 1 · R 7) · {1 / (T ·
V ₀ )} · ∫e ₀ ² dt ……… (2) where R ₇ is the resistance value of resistor R ₇ and I ave is the averaged current (I a
current value of ve), the voltage value of e ₀ AC voltage (e _0), V ₀ is the voltage value of the grandfather high voltage (V _0), T is the half cycle of the AC voltage (e _0).

Since the differential amplifier circuit 4 takes the differential between the rectified voltage (e ₁ ) and the averaged output (V ₀₀ ), if k ₂ is a constant, the effective value voltage (V ₀ ) is It will be indicated by (3).

V ₀ = k ₂ (e ₁ −V ₀₀ ) = {− (k ₁ · k ₂ · R ₇ ) / (T ·
V ₀ )} · ∫e ₁₂ dt (3) Therefore, if V ₀ is placed on the right side, Since this formula (4) matches the theoretical formula of the effective value,
It can be seen that the effective voltage (V ₀ ) output from the averaging circuit 3 is an effective value.

In this embodiment, since the circuit and the element for limiting the frequency characteristic are not used, the frequency characteristic is good. The time constant is determined by the capacitance value of the capacitor C of the averaging circuit 3 and the resistance value of the resistor R7. However, the time constant is set to such an extent that the ripple component of the AC voltage (e ₀ ) is not affected by the time constant. Since it can be shortened, it is more responsive. Furthermore, since the RMS value conversion is performed according to the RMS theoretical formula, the effect of distorted waves is much smaller than that of the pseudo RMS value conversion method, and RMS value conversion with excellent reliability must be performed. You can

Further, although the squaring circuit 2 of the embodiment is a diode approximation, the squaring circuit 2 is not limited to this and may be, for example, a squaring circuit using transistors.

Further, although the rectified voltage (e ₁ ) is a positive voltage in the embodiment, it may be a negative voltage. In this case, the polar directions of the diodes D1 and D2 may be reversed.

FIG. 3 is a circuit diagram of the second embodiment of the present invention, and the portions corresponding to those in FIG. 1 are designated by the same reference numerals. The feature of the second embodiment is that the negative feedback input section 22 is connected to the resistor R4 and each cathode side of the diodes D1 and D2.
4 is grounded to the grounding part 23. The operation is basically the same as that of FIG. 3 as shown in the waveform diagram of FIG. 4, except that the low voltage point 2
The voltage of 4,25 is the rectified voltage (e ₁ ) and the ground potential of the ground part 23 is 0.
And the main current (i) ₁ and the sub-currents (i ₂ , i ₃ ) in the main path A and the sub paths B, C are determined by the voltage difference (e) between the low voltage points 24, 25. ₂ , e ₃ ) and the negative feedback voltage (V ₀ ). Since the other points are the same as those in the first embodiment, detailed description thereof will be omitted.

[Brief description of drawings]

1 is a circuit diagram of the first embodiment, FIG. 2 is a current-voltage waveform diagram for explaining the operation of the circuit of FIG. 1, and FIG. 3 is a circuit diagram of the second embodiment. Circuit diagram, Figure 4 is the third
FIG. 7 is a current-voltage waveform diagram for explaining the operation of the circuit in the figure. 1 is a full-wave rectifier circuit, 2 is a square circuit, 3 is an averaging circuit, 4
Is a differential amplifier circuit.

Claims (2)

[Claims] 1. A squaring circuit having an output section where a squared current appears and a negative feedback input section to which a negative feedback voltage is applied, and an operational amplifier, one input terminal of which is the output of the squaring circuit. A rectified voltage to be converted into an effective value is applied to the other input terminal, and the difference between the voltage at the output of the squaring circuit and the rectified voltage is averaged and output. An averaging circuit, based on the averaged output voltage output from the averaging circuit and the voltage of the output section of the squaring circuit, outputs the effective value of the rectified voltage, and outputs this output to the negative of the squaring circuit. The feedback input section includes a differential amplifier circuit that negatively feeds back as a negative feedback voltage, wherein the squaring circuit forms a main path between the one input terminal and a ground section, and a rectification that appears at the one input terminal. Voltage and the negative feedback input There is a sub path between the voltage dividing point for dividing a voltage difference between the negative feedback voltage from the differential amplifier circuit and the grounding section, and the main path has an imaginary voltage at both input terminals of the operational amplifier. A main current flows according to the voltage difference between the rectified voltage appearing at one input terminal due to a short circuit and the potential of the ground portion and the impedance value in the main path,
A subcurrent according to a voltage difference between the divided voltage and the potential of the ground portion and an impedance value in the subpath flows through the subpath, and the subcurrent flows through the subpath. A directional element is provided in a direction in which a sub-current flows when the piezo voltage is in a first state in which the voltage is higher than the ground potential or in a second state in which the voltage is low, and the one input terminal is provided in the one input terminal. The added current obtained by adding the main current and the sub current is the first
In this state, the current flows from one input terminal of the averaging circuit to the one input terminal in the second state, and the main current is adjusted so that the added current becomes a squared current that approximates the rectified voltage waveform. An AC effective value-DC conversion circuit, characterized in that impedance values are set for each of the road and the sub road. 2. A squaring circuit having an output section where a squared current appears and a negative feedback input section to which a negative feedback voltage is applied, and an operational amplifier, one input terminal of which is an output of the squaring circuit. A rectified voltage to be converted into an effective value is applied to the other input terminal, and the difference between the voltage at the output of the squaring circuit and the rectified voltage is averaged and output. An averaging circuit, based on the averaged output voltage output from the averaging circuit and the voltage of the output section of the squaring circuit, outputs the effective value of the rectified voltage, and outputs this output to the negative of the squaring circuit. A differential amplifier circuit that negatively feeds back as a negative feedback voltage to a feedback input section, wherein the square circuit forms a main path between the one input terminal and the negative feedback input section, and the one input terminal. Rectified voltage appearing on the ground and the ground There is a sub path between the voltage dividing point for dividing the voltage difference from the potential of the operational amplifier and the negative feedback input section, and the main path appears at one input terminal due to an imaginary short circuit at both input terminals of the operational amplifier. A main current corresponding to the voltage difference between the rectified voltage and the negative feedback voltage and the impedance value in the main path flows, and the auxiliary path has a voltage between the divided voltage and the potential of the negative feedback voltage. A sub-current flows according to the voltage difference and the impedance value in the sub-path, and the sub-voltage is in the first state higher or lower than the negative feedback voltage in the sub-path. In the state 2, the directional element is provided in a direction in which it conducts and a subcurrent flows, and an added current obtained by adding the main current and the subcurrent to the one input terminal is the first state. In case of, it flows from one input terminal of the averaging circuit. In the second state, the impedance values in the main path and the sub path are set such that the added current flows into the one input terminal and the added current becomes a squared current that approximates the rectified voltage waveform. An AC effective value-DC conversion circuit characterized by: