JPH0812211B2 - 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) An AC effective value-DC conversion circuit is a circuit that obtains an AC effective value and converts it to DC based on this effective value.

In such a conversion circuit, according to the definition formula of the effective value,
To average and square the input signal squared,
There is a square circuit that squares an input signal, an averaging circuit that averages by integrating the output of the square circuit, and a square root circuit that squares the output of the averaging circuit. Conventionally, each of these circuits is provided. It is known that this is incorporated into a monolithic IC (Practical Electronic Handbook (4) Showa
No. 421 and No. 4, published by CQ Publishing Co., Ltd., 5th edition, November 1, 58
(See page 22).

However, the AC rms-conversion circuit is monaural
The one incorporated in the IC has a problem that not only the circuit configuration is very complicated because the square root circuit is necessary, but also the cost thereof is high.

And, despite the problem of high cost, there is another problem of poor reliability.

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.

In the proposed circuit, although the circuit configuration is simple, there is a problem in that the accuracy of the RMS value conversion is inferior, and it is not possible to use it when performing highly accurate RMS value 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-mentioned object, the present invention inputs an input unit to which a rectified voltage to be converted into an effective value is applied, an output unit to output a squared current, and a negative feedback voltage. A square wave circuit having a negative feedback input section, an input section to which a squared current is given from an output section of the square circuit, and an output section for outputting an effective value voltage of the rectified voltage, and the square circuit An averaging circuit that averages the rectified voltage based on a current and outputs the rectified voltage as an effective value voltage, wherein the squaring circuit converts a rectified voltage given to an input portion thereof into a current proportional to the rectified voltage value. A first converting means for converting and a current obtained by inputting an averaged voltage from the averaging circuit provided to a negative feedback input section thereof as a negative feedback voltage and dividing the rectified voltage between the negative feedback voltage and the rectified voltage. Second conversion means for converting to Then adds each current from the two conversion means, and is configured as comprising the addition means for outputting the added current as the square of the current.

According to this configuration, the rectified voltage applied to the input section of the squaring circuit is converted into a current proportional thereto by the first converting means of the squaring circuit.

Further, the output of the averaging circuit is given to the negative feedback input section of the squaring circuit as a negative feedback voltage. The negative feedback voltage applied to the negative feedback input of the squaring circuit is converted by the second means into a current divided between the negative feedback voltage and the rectified voltage.

Then, the respective currents are added by the adding means of the squaring circuit, so that the squaring current is output from the squaring circuit.

Then, this squared current is expressed by a formula in which the negative feedback voltage is used as the denominator and the square value of the rectified voltage value is used as the numerator. When this squared current is input to the averaging circuit, the averaging circuit eventually outputs the effective value voltage of the rectified voltage according to the theoretical formula.

Therefore, according to the present invention, since the square circuit and the averaging circuit are simply combined and the output voltage of the averaging circuit is negatively fed back to the square circuit without using the square root circuit, the circuit configuration is simple. , It is possible to obtain a circuit that is cheaper in cost than the one configured with a monolithic IC.

Further, since the RMS value conversion according to the theoretical formula is performed, it is possible not only to perform the AC RMS value-DC conversion that is more reliable than that of the pseudo RMS value conversion method, Considering the cost of a monolithic IC, it is highly reliable.

(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 AC voltage (e ₀ ), OU
T is an output terminal for the RMS 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 rectified voltage (e ₁ ) that should be converted into an effective value.

2 includes an input unit 21 to which a rectified voltage (e ₁ ) to be converted into an effective value from the full-wave rectifier circuit 1 is applied, an output unit 22 that outputs a squared current (i), and a negative feedback voltage (V ₀ ) Is inputted to the square feedback circuit 23.

3 is the squared current (i) from the output section 22 of the squaring circuit 2.
An input unit 31 which is supplied, and an output unit 32 for outputting the effective value voltage of the rectified voltage _{(e 1) (V 0)} , also outputs the effective value voltage (V ₀₎ as a negative feedback voltage (V ₀₎ Is an averaging circuit having an output unit 33 for And 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 ).

Squaring circuit 2, a first conversion means for converting the rectified voltage given to the input unit 21 of it (e ₁₎ to the first current (i ₁₎ which is proportional to the rectifier voltage (e _1), a resistor R4 I have it. The resistor R4 is connected between the input section 21 and the output section 22 of the squaring circuit 2.

The square circuit 2 also inputs the negative feedback voltage (V ₀ ) from the negative feedback output section 33 of the averaging circuit 2 provided to the negative feedback input section 23 thereof, and outputs the rectified voltage (e ₁ ) to this As second conversion means for dividing the voltage between the negative feedback voltage (V ₀ ) and the second and third currents (i ₂ , i ₃ ), the resistors R1, R2, R3, R5, R6 and the diode D1, With D2.

The resistors R1, R2 and R3 are the input section 21 and the negative feedback input section of the squaring circuit 2.
23 and 23 are connected in series with each other. The resistor R5 and the diode D1, and the resistor R6 and the diode D2 are connected in series so as to form a first series circuit and a second series circuit, respectively. The first series circuit includes resistors R1 and R2.
Is connected between the connection point 24 and the output section 22, and the second series circuit is connected between the connection point 25 of the resistors R2 and R3 and the output section 22.

The squaring circuit 2 further adds the respective currents (i ₁ , i ₂ , i ₃ ) from the conversion means, and adds the summed current (i = i ₁ + i ₂ + i ₃ ) to the squared current (i ) Is added, and the addition means is a resistor.
One end of R4 and the cathodes of the diodes D1 and D2 are connected in common, and the common connection point 26 is provided.

The averaging circuit 3 includes an operational amplifier AMP and its operational amplifier A.
A smoothing capacitor C and an amplification degree determining resistor R7 are connected in parallel between the inverting input terminal (-) and the output terminal of MP. Further, the non-inverted input terminal (+) of the operational amplifier AMP is grounded. The output terminal of the operational amplifier AMP is connected to the output units 32 and 33 of the averaging circuit 3.

Next, the operation and action will be described with reference to the time chart of 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, and FIG. 2 (a2) shows the waveform of the rectified voltage flowing through the resistor R4 of the squaring circuit 2. 2 shows the waveform of a current (i ₁ ), FIG. 2 (b 1) shows the waveform of a voltage (e ₂ ) appearing at the connection point 24, and FIG. 2 (b 2) shows a second current (i ₂ ) flowing through the resistor R 5. 2) (c1) shows the waveform of the voltage (e ₃ ) appearing at the connection point 25, and FIG. 2 (c2) shows the resistance R6.
2 shows the waveform of the third current (i ₃ ) flowing through the wire, and FIG. 2 (d) shows the waveform of the squared current (i) appearing at the connection point 26.

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.

Since the input part 31 of the averaging circuit 3 is imaginary earth, the first current (i ₁ ) flowing through the resistor R4 of the squaring circuit 2
Becomes i = e ₁ / R ₄ .

Here, i ₁ is the current value of the first 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 . Also,
The symbol “/” is a division symbol (÷) (hereinafter the same).

The waveform of the first current (i ₁ ) is as shown in FIG. 2 (a2).

On the other hand, the negative feedback voltage (V ₀ ) and the rectified voltage (e ₁ ) given to the negative feedback input section 23 of the squaring circuit 2 are connected at the connection point (24).
In the case of, the voltage is divided by low resistance R1, R2, R3, so the connection point
The voltage (e ₂ ) at 24 is as shown in FIG. 2 (b1).

That is, this voltage (e ₂ ) has a negative potential as indicated by hatching. Therefore, the second current (i ₂ ) flowing through the resistor R5 becomes as shown in FIG. 2 (b2) by the diode D1.

Similarly, the voltage (e ₃ ) at the connection point 25 is shown in FIG.
As shown in 1). Therefore, the third current (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 26, the added current (i) (squared current i) is the second current.
As shown in FIG. In the waveform of the squared current (i), the second current (i ₂ ) is applied between aa and the third current is applied between bb.
It corresponds to the current (i ₃ ), respectively.

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 Can be more closely approximated to the square of the rectified voltage (V ₀ ). Further, the waveform of the squared current (i) in FIG. 2 (d) is a two-point broken line, but if the connecting points 24, 25, etc. are increased, the broken line can be brought closer to the square curve. Of course you can.

Assuming that the AC input signal is e ₀ , the output signal of the full-wave rectifier circuit 1 is e ₁ , and the amplitudes of these signals are a ₀ , then e ₀ = a ₀ · sinωt (1) e ₁ = a ₀ · sinωt (0 ≦ ωt ≦ π) or e ₁ = −a ₀ · sinωt (π ≦ ωt ≦ 2π) Therefore, e ₀ ² = e ₁ ² (2) Next, the averaging circuit 3 includes the operational amplifier AMP, Since it is an integrating circuit including the capacitor C and the resistor R ₇ , the integrated output V ₀ of the averaging circuit 3 is averaged by the integrating action of the capacitor C when the current i flows through the resistor R 7. This is equal to the state where the output current i of the squaring circuit 2 is in the middle of the peak value and the bottom value, in this case, a constant current is charged by Iave (see FIG. 2 (d)). Therefore, V ₀ = −k ₁ ⋅Iave = −R 7 ⋅Iave (k ₁ : constant) (3) On the other hand, the current i of the output unit 22 of the squaring circuit 2 is, needless to say, the full-wave AC input signal e ₀ . This is a square-approximate current obtained by combining the rectified output e ₁ and the current value based on the output V ₀ that is negatively fed back from the averaging circuit 3,
When the waveform always satisfies the relationship shown in FIG. 2 (d), this current i is a signal having twice the frequency of the input signal e _{0 and having} a frequency twice the frequency of the input signal e _0. Since the phase is shifted by 90 ° with respect to, it can be regarded as a cosine waveform. Thus, i = Iave-Iave · cos2ωt = Iave · (1-cos2ωt) = 2 · Iave · sin 2 ωt (4) (4) equation, is deformed (3) from the relationship of the expression, further as follows .

i = 2 (−V ₀ / k ₁ ) · sin ² ωt (4) ′ Now, the output current i of the squaring circuit 2 is always squared as shown in the equation (4) [or (4) ′ equation]. In order to be obtained as a product, a break point a in FIG.
It is necessary to satisfy the condition that b is always the same phase (constant phase).

To this end, the signal e ₀ (or e ₁ ) input to the squaring circuit 2 and the voltage V ₀ that is negatively fed back are in a proportional relationship (otherwise, the expression (4) will not hold). ). That is, it is necessary that the relational expression of a ₀ = k ₂ · V ₀ (a ₀ : amplitude of input signal e ₀ , k ₂ : constant) (5) always holds. Then, if the relation of the equation (5) is established, a ₀ = k ₂ · V ₀
The following theoretical analysis may be carried out on the premise of.

Therefore, it will be verified whether or not the relation of the expression (5) is established.

Now, assuming that a ₀ = k ₂ · V ₀ holds, e ₀
If (or e ₁ ) doubles, its amplitude a ₀ naturally doubles. Therefore, from the relation of the equation (5), V ₀ is also doubled, and the element currents i ₁ , i ₂ , i ₃ are also doubled. As a result, i
Also doubles, and the output V ₀ also doubles. In other words, assuming that a ₀ = k ₂ · V ₀ holds in the negative feedback loop,
Since no contradiction occurs, it can be said that the assumption of this equation (5) is valid.

Therefore, the following equation can be derived from the relations of the equations (1) to (5). That is, sin ² ωt = e ₀ ² / a ₀ ² from the equation (1) (6) Therefore, from the relationship of the equations (4) ′ and (6), i = 2 · (−V ₀ / k ₁ ) · ( e ₀ ² / a ₀ ² ) (7) Substituting the expression (5) into the expression (7), i = 2 · (−V ₀ / k ₁ ) · {e ₀ ² / (k ₂ V ₀ ) ² } = − {2 / (k ₁ k ₂ ² )} (e ₀ ² / V ₀ ) (8) Here, in expression (8), − {2 / (k ₁ k ₂ ² )} = k
In other words, i = k · e ₀ ² / V ₀ (9) Next, the value of the output voltage V ₀ of the averaging circuit 3 will be specifically examined.

As described above, if the relational expression of the equation (5) is satisfied in the circuit shown in FIG. 1, the relation of the expression (9) is satisfied, so that when the cycle of the input signal e ₀ is T, Iave = (1 / T) ∫idt = (1 / T) ∫ (k · e ₀ ² / V ₀ ) dt (10). And since there is a relation of the formula (3), the formula (10) is as follows.

That is, the specific value of the output voltage V ₀ of the averaging circuit 3 is
Although it is given by the equation (11), this value of V ₀ is an effective value voltage exactly as defined by the AC effective value.

Thus, in the present invention, the output voltage V ₀ of the averaging circuit 3
It can be seen that by negatively feeding back the square root circuit 2 to the square circuit 2, the same effect as that obtained by performing the square root processing can be obtained without the purpose of providing the square root circuit.

In this embodiment, since the circuit and the element for limiting the frequency characteristic are not used, the frequency characteristic is good. Also,
The time constant is determined by the capacitance value of the capacitor C of the averaging circuit 3 and the resistor R7, but the time constant can be shortened to such an extent that the ripple component of the AC voltage (e ₀ ) is not affected by the time constant. Therefore, it becomes more responsive.

Furthermore, since the rms value conversion is performed according to the rms theoretical formula, the effect of distorted waves 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.

[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 time chart used for explaining the operation of the circuit of FIG. 1 ... Full wave rectification circuit, 2 ... Squaring circuit, 3 ... Averaging 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, an output section to output a squared current, and a negative feedback input section to which a negative feedback voltage is input, the squaring circuit. The circuit has an input section to which a squared current from the output section of the circuit is given, and an output section that outputs an effective value voltage of the rectified voltage, and averages the rectified voltage based on the squared current to obtain an effective value voltage. Averaging circuit for outputting as, the squaring circuit converts the rectified voltage applied to the input part thereof into a current proportional to the rectified voltage value, and a negative feedback input part thereof. A second converting means for inputting the averaged voltage from the averaging circuit given as a negative feedback voltage and converting the rectified voltage into a current divided between the rectified voltage and the negative feedback voltage; When each current of is added The AC effective value, characterized in that it comprises an adding means for outputting the added current as the square of the current - direct current conversion circuit.