JPH0785093B2 - 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 one that consists of an averaging circuit that averages the squared circuit output by integrating it, and a square root circuit that squares the output of the averaging circuit. Conventionally, it is known that these circuits are incorporated into 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, the time constant 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) The present invention is intended to achieve the above object. A square circuit having an input section to which a rectified voltage to be converted into an effective value is applied and an output section in which a squared current appears, and an operational amplifier, and one input terminal of the operational amplifier is connected to the output section of the squaring circuit. An output obtained by inverting and amplifying the output of the operational amplifier is applied to the other input terminal, and the rectified voltage is averaged as an effective value voltage based on the squared current from the output section of the squaring circuit. An averaging circuit for outputting, and an inverting amplifier circuit for inverting and amplifying the effective value voltage output from the averaging circuit and supplying the inverted value to the other input terminal of the operational amplifier, wherein the squaring circuit has an input section thereof. A main path between the output section and the output section, and a sub path between the output section and the voltage dividing point for dividing the voltage difference between the rectified voltage applied to the input section and the potential of the ground section. And in front of the main road A main current according to the voltage difference between the rectified voltage and the output of the inverting amplifier circuit appearing in the output section due to an imaginary short circuit at both input terminals of the operational amplifier and the impedance value in the main path flows, and the sub path Means that a sub-current corresponding to the voltage difference between the divided voltage at the voltage dividing point and the output of the inverting amplifier circuit and the impedance value in the sub-path flows. A directional element is provided so as to conduct when the voltage is lower than the output of the inverting amplifier circuit to allow the sub-current to flow, and the output portion of the squaring circuit adds the main current and the sub-current. Both impedance values are set so that the current has a squared current waveform obtained by approximating the rectified voltage waveform with a square.

According to this configuration, since both input terminals of the operational amplifier of the averaging circuit are imaginary short-circuited, the voltage of one input terminal is the voltage of the other input terminal, that is, the inverted amplified output of the inverting amplifier circuit. Therefore, a current (main current) corresponding to the difference between the rectified voltage applied to the input part of the squaring circuit and the voltage at one input terminal of the operational amplifier and the resistance value in the main path is the main path. Flows in. In addition, since the directional element is provided in the sub-path, if the voltage of the output section is higher or lower than the voltage at the low voltage point, one input terminal of the operational amplifier is in the sub-path. A sub-current corresponding to the difference between the voltage at the low voltage and the voltage at the low voltage point and its resistance value flows. 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. This squared current is, after all, proportional to the square of the rectified voltage and inversely proportional to the inverted amplified output. Therefore, when this squared current is input to the averaging circuit, the output of the squaring circuit is changed. The voltage is a voltage corresponding to the theoretical formula of the effective value.

Therefore, according to the present invention, since the simple circuit configuration is simply a combination of a square circuit and an averaging circuit without using a square root circuit, the cost is lower than that of a monolithic IC. The 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 negatively returned to the squaring circuit, the averaging circuit can be designed without considering the influence of the impedance of the squaring circuit. There is also an effect that the design becomes extremely easy.

(Description of Embodiments) FIG. 1 is a circuit diagram 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 ). 1 is
It 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 negative 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. The squaring circuit 2 has an input unit 21 to which the rectified voltage (e ₁ ) from the full-wave rectifying circuit 1 is applied and an output unit 22 that outputs a squaring current (i). The squaring circuit 2 also includes a main path A (including a resistor R4) through which a main current (i ₁ ) flows between its input 21 and output 22 and a voltage point 23 lower than the rectified voltage (e ₁ ). , 24 and the output section 22 are provided with two auxiliary paths B and C through which the auxiliary currents (i ₂ , i ₃ ) respectively flow. The low voltage points 23 and 24 are connected to the resistors R1 and R2, respectively.
And a connection point between the resistors R2 and 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.
And an output section 32, 33 for outputting the effective value voltage (V ₀ ) of the rectified voltage (e ₁ ), and an inverting amplification output (−
V ₀₀ ) and an input section 34 to which the averaging circuit is provided. This averaging circuit 3 includes an operational amplifier AMP1, a smoothing capacitor C and an amplification degree determining resistor R7 connected in parallel with each other between the inverting input terminal (−) and the output terminal of the operational amplifier AMP1. I have it. This averaging circuit 3
Is configured to average the rectified voltage (e ₁ ) based on the squared current (i) and output it as an effective value voltage (V ₀ ).

4 is an input unit 41 connected to the output unit 33 of the averaging circuit 3,
Similarly, an inverting amplifier circuit having an output section 42 connected to the input section 34 of the averaging circuit 3,
Is a resistor R8 whose one end is connected to its input section 41, an operational amplifier AMP2 whose other end is connected to an inverting input terminal (-), and an inverting input terminal (-) of this operational amplifier AMP2.
And a resistor R9 connected between the output terminal and the output terminal.
The output terminal of this operational amplifier AMP2 is connected to its output terminal 42.

Next, the operation and action will be described with reference to the waveform chart of FIG. FIG. 2 (a1) shows the waveform of the rectified voltage (e ₁ ) given from the full-wave rectifier circuit 1 to the input section 21 of the squaring circuit 2.
Figure (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, and Figure 2 (b1) shows the waveform of the voltage (e ₂ ) appearing at the connection point 23. 2 (b2) shows the waveform of the sub-current (i ₂ ) flowing through the resistor R5 in the sub path B, and FIG. 2 (c1) shows the waveform of the voltage (e ₃ ) appearing at the connection point 24.
Figure 2 (c2) shows the auxiliary current (i ₃ ) flowing through the resistor R6 in the auxiliary path C.
2 (d) shows the waveform of the squared current (i) appearing at the connection point 22. In each figure, −V ₀₀ indicates the output of the inverting amplifier circuit 4.

A rectified voltage (e ₁ ) having a waveform as shown in FIG. 2 (a1) is applied to the input section 21 of the squaring circuit 2. Input part of averaging circuit 3
31 is an imaginary short, so the squaring circuit 2
The main current (i ₁ ) flowing through the resistor R4 has a value corresponding to the voltage difference between the rectified voltage (e ₀ ) and the inverted amplified output (−V ₀₀ ). If this value is expressed by an equation, i ₁ = (e ₁ −V ₀₀ ) / R ₄ . 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 ) applied to the input section 21 of the squaring circuit 2 is divided by the resistors R1, R2, and R3 at the connection points 23 and 24, so the voltage at the connection point 23. (E ₂ )
Becomes as shown in FIG. 2 (b1). That is, this voltage (e ₂ ) has a positive potential as indicated by hatching. Therefore, the auxiliary current (i ₂ ) flowing through the resistor R5 is caused by the diode D1 conducting when the negative voltage (e ₂ ) is lower than the inverting amplification output (−V ₀₀ ).
As shown in 2). Similarly, the voltage at node 24 (e
₃ ) becomes as shown in FIG. 2 (c1), so that the subcurrent (i ₃ ) flowing through the resistor R6 becomes as shown in FIG. 2 (c2) by the diode D2.

Since these respective currents (i ₁ , i ₂ , i ₃ ) are added at the connection point 22, the added current (squared current) (i) is shown in FIG.
As shown in. 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 A value that is inversely proportional to the inverted amplification output (-V ₀₀ ), that is, the following equation (1)
Given in.

i = (k ₁ · e ₀ ² ) / V ₀₀ = (k ₁ · e ₀ ² ) / (k ₂ · V ₀ ) ... (1) where V ₀₀ = k ₂ · V ₀ , i is the square Current value of the digitized current (i), k ₁ and k ₂ are constants, e ₀ is the voltage value of the rectified voltage (e ₀ ), V ₀ is the output value of the averaging circuit 2, and −V ₀₀ is the inverted amplification output value. Become.

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, the averaging current (I ave) flows through the resistor R7, so that the effective value voltage (V ₀ ) becomes a value represented by the following equation (2).

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

Therefore, the effective voltage (V ₀ ) is expressed by the following equation (3).

Since this formula matches the theoretical formula of the effective value, it can be seen that the effective voltage (V ₀ ) which is the output of the averaging circuit 3 is the 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 the denial wave is extremely small compared to the pseudo rms 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 negative voltage in the embodiment,
A positive voltage may be used, and in this case, the polarities of the diodes D1 and D2 may be reversed.

[Brief description of drawings]

The drawings relate to an embodiment of the present invention. FIG. 1 is a circuit diagram of this embodiment, and FIG. 2 is a current for explaining the operation of the circuit of FIG.
It is a wave form diagram of a voltage. 1 is a full-wave rectifier circuit, 2 is a square circuit, 3 is an averaging circuit, and 4 is an inverting amplifier circuit.

Claims (1)

[Claims] 1. A squaring circuit having an input section to which a rectified voltage to be converted into an effective value is applied and an output section in which a squared current appears, and an operational amplifier, wherein one input terminal of the operational amplifier is the squaring circuit. The output of the operational amplifier is inverted and amplified, and the other input terminal is connected to the output of the output of the square amplifier, and the rectified voltage is averaged based on the squared current from the output of the squaring circuit. And an inverting amplifier circuit that outputs as an effective value voltage, and an inverting amplifier circuit that inverts and amplifies the effective value voltage output from the averaging circuit and applies the inverted value to the other input terminal of the operational amplifier. , A main path between the input section and the output section, and a sub path between the output section and the voltage dividing point for dividing the voltage difference between the rectified voltage applied to the input section and the potential of the ground section. Each with a road and in front In the main path, a rectified voltage and a main current corresponding to an impedance value in the main path and a voltage difference between the inverting amplifier circuit output appearing in the output section due to an imaginary short circuit at both input terminals of the operational amplifier, In addition, a sub-current corresponding to a voltage difference between the divided voltage at the voltage dividing point and the output of the inverting amplifier circuit and an impedance value in the sub-path flows in the sub-path. Is provided with a directional element in a direction in which it conducts when the divided voltage is lower than the output of the inverting amplifier circuit so that the sub-current flows, and the main current and An AC effective value-DC conversion circuit, wherein both impedance values are set so that an added current with a sub-current has a squared current waveform obtained by approximating the rectified voltage waveform with a square.