A variant differential AC voltage sampling circuit

Abstract

The present invention discloses a modified differential AC voltage sampling circuit, which includes an AC power supply. The N line of the AC power supply is grounded through a Y capacitor C1. The AC power supply is successively connected with an AC voltage dividing circuit, a differential operational amplifier circuit, a rectifying circuit and a sampling signal filtering circuit. Through the modified differential sampling and rectifying filtering of the AC voltage, the present invention eliminates the sampling error caused by the insertion of the Y capacitor in the circuit, and also eliminates the influence of temperature on the sampling accuracy of the AC voltage. In addition, the use of high-voltage rectifying devices and high-voltage filtering capacitors is avoided, improving the reliability of the circuit, and having good use value and application prospects.

Description

Technical Field

[0001] The present invention relates to an AC voltage sampling control circuit in the field of power supplies, and particularly to a variant differential AC voltage sampling circuit. Background Art

[0002] AC power supplies are widely used, and AC voltage sampling is an essential circuit in power voltage detection and control.

[0003] There are various existing AC voltage sampling circuits. There is a way as shown in the specification Figure 1 where first, it passes through diode rectification and capacitor filtering, and then obtains the required AC voltage sampling signal through resistor voltage division; there is also a way as shown in the specification Figure 3 where first, it passes through resistor voltage division, and then through diode rectification and capacitor filtering.

[0004] However, these sampling methods all have two common problems:

[0005] (1) To meet the EMC requirements, a Y capacitor C1 must be inserted into the electrical equipment circuit. Once the common-mode filter C1 is inserted into the AC line or DC line, the AC rectification circuit is equivalent to a voltage-doubling rectification circuit, and the AC voltage sampling signal voltage will vary with the size of C1. Especially in the case of light load and no load in the AC rectification circuit, the sampling error is even greater. The specification Figure 2 simulated the Figure 1 existing AC voltage sampling circuit as shown. Vsense is the AC voltage sampling signal before inserting C1 at normal temperature, Vsense_Y is the AC voltage sampling signal after inserting C1 into the circuit at normal temperature, and Vsense_T is the AC voltage sampling signal before inserting C1 at high temperature. In the appendix Figure 2 , Vsense is 3V, while Vsense_Y has risen to 4.7V. Vsense_T is slightly lower than Vsense, and Figure 2 in the appendix, Vsense_T and Vsense slightly overlap. It can be found that although the temperature has a relatively small impact on the AC voltage sampling accuracy error in the existing AC voltage sampling circuit as shown in the appendix Figure 1 , the insertion of C1 seriously affects the AC voltage sampling accuracy error;

[0006] (2) The changes in ambient temperature and operating temperature will affect the forward voltage drop of the rectifier diode. Therefore, the AC voltage sampling signal voltage will vary with temperature. The appendix Figure 4 simulated the appendix Figure 3The existing AC voltage sampling circuit shown, Vsense is the AC voltage sampling signal before inserting C1 at normal temperature, Vsense_Y is the AC voltage sampling signal after inserting C1 in the circuit at normal temperature, and Vsense_T is the AC voltage sampling signal before inserting C1 at high temperature. Attached Figure 4 Among them, Vsense is 3V, while Vsense_Y has risen to 4.7V, and Vsense_T has dropped to 2.5V. It can be found that attached Figure 3 In the existing AC voltage sampling circuit shown, not only the insertion of C1 seriously affects the AC voltage sampling accuracy error, but also the temperature has a relatively serious impact on the AC voltage sampling accuracy error..

[0007] In summary, the existing AC voltage sampling circuits have the technical problem of large sampling accuracy errors due to their respective circuit characteristics. Summary of the Invention

[0008] The object of the present invention is to provide a variant differential AC voltage sampling circuit that can effectively avoid the technical problems of seriously affecting the sampling accuracy due to the insertion of C1 and temperature changes.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows: A variant differential AC voltage sampling circuit includes an AC power supply, the N line of the AC power supply is grounded through a Y capacitor C1, and the AC power supply is sequentially connected with an AC voltage dividing circuit, a differential operational amplifier circuit, a rectifying circuit, and a sampling signal filtering circuit;

[0010] The AC voltage dividing circuit is used to divide the AC power supply into an AC signal voltage with the required amplitude and transmit it to the differential operational amplifier circuit;

[0011] The differential operational amplifier circuit is used to convert the AC signal voltage into a unipolar signal voltage and transmit it to the rectifying circuit. The unipolar signal voltage is a low-impedance positive and negative half-wave bun-shaped wave signal;

[0012] The rectifying circuit is used to rectify the unipolar signal voltage into a pulsating DC signal and transmit it to the sampling signal filtering circuit;

[0013] The sampling signal filtering circuit is used to output an AC voltage sampling signal according to the pulsating DC signal.

[0014] Preferably: The AC voltage dividing circuit is a resistor voltage dividing circuit or a voltage dividing circuit composed of a capacitor and a resistor.

[0015] Preferably, the AC voltage dividing circuit includes resistors R1 - R8. The L line of the AC power supply is connected to the ground terminal of C1 through resistors R1 - R4, and the N line of the AC power supply is connected to the ground terminal of C1 through R5 - R8, and the resistance values of R1 - R8 satisfy: R1 + R2 + R3 = R5 + R6 + R7, and R4 = R8.

[0016] Preferably, the differential operational amplifier circuit includes two operational amplifiers AMP1 and AMP2, and resistors R9 - R16;

[0017] One of the positive input terminals of AMP1 is divided into two paths. One path is connected between R3 and R4 through R11, and the other path is connected to the ground terminal of C1 through R15. One of the negative input terminals of AMP1 is divided into two paths. One path is connected between R7 and R8 through R9, and the other path is connected to R10;

[0018] One of the positive input terminals of AMP2 is divided into two paths. One path is connected between R7 and R8 through R14, and the other path is connected to the ground terminal of C1 through R16. One of the negative input terminals of AMP1 is divided into two paths. One path is connected between R3 and R4 through R12, and the other path is connected to R13; and the resistance values of R9 - R16 are the same.

[0019] Preferably, the rectifier circuit includes diodes D1 and D2. The positive electrode of D1 is connected to the output terminal of AMP1, and the negative electrode is connected to R10. The positive electrode of D2 is connected to the output terminal of AMP2, and the negative electrode is connected to R13, and the negative electrodes of D1 and D2 are connected together.

[0020] Preferably, the sampling signal filtering circuit includes R17, R18 and capacitor C2. The negative electrodes of D1 and D2 are connected to the ground terminal of C1 through R17 and R18, and C2 is connected in parallel with R18. The voltage across C2 is the AC voltage sampling signal.

[0021] The input terminal of the AC voltage dividing circuit is connected to the AC power supply, and the output terminal is connected to the input terminal of the differential operational amplifier circuit. It can be composed of a resistor network or a resistor - capacitor network. The purpose is to divide the AC power supply into an AC signal voltage with the required amplitude and transmit it to the subsequent differential operational amplifier circuit.

[0022] The differential operational amplifier circuit is composed of operational amplifiers and resistors and capacitors. The AC signal voltage obtained by dividing the voltage of the AC voltage dividing circuit is converted into a low - impedance, single - polarity, positive and negative half - wave bread - shaped wave signal through the impedance transformation of resistors, capacitors and operational amplifiers, and is transmitted to the subsequent rectifier circuit.

[0023] The rectifier circuit is composed of semiconductor devices with unidirectional conduction characteristics, rectifying the signal output by the differential operational amplifier circuit into a pulsating DC signal and transmitting it to the sampling signal filtering circuit.

[0024] The sampling signal filtering circuit consists of a resistor-capacitor network, which obtains a smooth DC signal with good linearity corresponding to the AC voltage amplitude by resistive voltage division and RC filtering of the pulsating DC signal output by the rectifier circuit.

[0025] The core of the present invention is to perform differential detection on the AC source voltage using a differential operational amplifier circuit and lossless rectification by a diode to obtain a smooth DC signal with good linearity corresponding to the AC voltage amplitude.

[0026] Compared with the prior art, the advantages of the present invention are as follows: (1) eliminating the sampling error caused by the insertion of Y capacitors in the circuit; (2) eliminating the influence of temperature on the sampling accuracy of AC voltage; (3) avoiding the use of high-voltage rectifying devices and high-voltage filtering capacitors, and improving the reliability of the circuit. Description of the Drawings

[0027] Figure 1 is the circuit schematic diagram of the conventional AC voltage sampling circuit with rectification first and then voltage division;

[0028] Figure 2 is Figure 1 the sampling voltage error simulation diagram of

[0029] Figure 3 is the circuit schematic diagram of the conventional AC voltage sampling circuit with voltage division first and then rectification;

[0030] Figure 4 is Figure 3 the sampling voltage error simulation diagram of

[0031] Figure 5 is the circuit block diagram of the present invention;

[0032] Figure 6 is the circuit schematic diagram of the present invention;

[0033] Figure 7 is Figure 6 the sampling voltage error simulation diagram of

[0034] In the figure: 110, AC voltage division circuit; 120, differential operational amplifier circuit; 130, rectifier circuit; 140, sampling signal filtering circuit. Detailed Embodiments

[0035] The present invention will be further described below with reference to the accompanying drawings.

[0036] Embodiment 1: Refer to Figure 5 , a variant differential AC voltage sampling circuit, including an AC power supply, the N line of the AC power supply is grounded through a Y capacitor C1, and the AC power supply is sequentially connected with an AC voltage division circuit 110, a differential operational amplifier circuit 120, a rectifier circuit 130, and a sampling signal filtering circuit 140;

[0037] The AC voltage dividing circuit 110 is used to divide the AC power supply into an AC signal voltage with a required amplitude and transmit it to the differential operational amplifier circuit 120;

[0038] The differential operational amplifier circuit 120 is used to convert the AC signal voltage into a unipolar signal voltage and transmit it to the rectifier circuit 130. The unipolar signal voltage is a flat-top wave signal with low impedance positive and negative half-waves;

[0039] The rectifier circuit 130 is used to rectify the unipolar signal voltage into a pulsating DC signal and transmit it to the sampling signal filtering circuit 140;

[0040] The sampling signal filtering circuit 140 is used to output an AC voltage sampling signal according to the pulsating DC signal.

[0041] The AC voltage dividing circuit 110 is a resistor voltage dividing circuit or a voltage dividing circuit composed of a capacitor and a resistor.

[0042] Embodiment 2: Refer to Figure 6 and Figure 7 , based on Embodiment 1, we give a specific circuit structure. Among them, the AC voltage dividing circuit 110 includes resistors R1-R8. The L line of the AC power supply is connected to the grounding end of C1 through resistors R1-R4, and the N line of the AC power supply is connected to the grounding end of C1 through R5-R8. The resistance values of R1-R8 satisfy: R1+R2+R3 = R5+R6+R7, and R4 = R8.

[0043] The differential operational amplifier circuit 120 includes two operational amplifiers AMP1 and AMP2, and resistors R9-R16;

[0044] Among them, the positive input terminal of AMP1 is divided into two paths. One path is connected between R3 and R4 through R11, and the other path is connected to the grounding end of C1 through R15. The negative input terminal of AMP1 is divided into two paths. One path is connected between R7 and R8 through R9, and the other path is connected to R10;

[0045] The positive input terminal of AMP2 is divided into two paths. One path is connected between R7 and R8 through R14, and the other path is connected to the grounding end of C1 through R16. The negative input terminal of AMP1 is divided into two paths. One path is connected between R3 and R4 through R12, and the other path is connected to R13; and the resistance values of R9-R16 are the same.

[0046] The rectifier circuit 130 includes diodes D1 and D2; the positive electrode of D1 is connected to the output terminal of AMP1, and the negative electrode is connected to R10; the positive electrode of D2 is connected to the output terminal of AMP2, and the negative electrode is connected to R13, and the negative electrodes of D1 and D2 are connected together.

[0047] The sampling signal filtering circuit 140 includes R17, R18 and capacitor C2. The cathodes of D1 and D2 are connected to the grounded end of C1 via R17 and R18. C2 is in parallel with R18, and the voltage across C2 is the AC voltage sampling signal.

[0048] In this embodiment:

[0049] Regarding the AC voltage dividing circuit 110: Actually, resistors R1 - R4 form the L-phase voltage dividing network, and resistors R5 - R8 form the N-phase voltage dividing network. The voltage dividing reference point is the common mode ground of the AC power supply, which is also the reference ground of the subsequent circuit. R1 + R2 + R3 = R5 + R6 + R7, R4 = R8, and the voltage V R4 across R4 and the voltage V R8 across R8 are the common mode sampling voltages of the L-phase and N-phase with respect to the reference ground of the subsequent circuit, and they are AC sine wave voltages. The calculation formulas are as follows:

[0050] V R4 =-V R8 =Vac÷(R1 + R2 + R3 + R4 + R5 + R6 + R7 + R8)×R4

[0051] When Vac = 220V, R1 + R2 + R3 = R5 + R6 + R7 = 3MΩ, and R4 = R8 = 47KΩ:

[0052]

[0053] where Vac is the input voltage of the AC power supply.

[0054] Regarding the differential operational amplifier circuit 120: Actually, resistors R11 and R15 form the in-phase input voltage dividing resistor network of operational amplifier AMP1, and resistors R9 and R10 form the anti-phase input resistor network of operational amplifier AMP1; resistors R14 and R16 form the in-phase input voltage dividing resistor network of operational amplifier AMP2, and resistors R12 and R13 form the anti-phase input resistor network of operational amplifier AMP2. R9 = R10 = R11 = R12 = R13 = R14 = R15 = R16. According to the virtual short principle of the operational amplifier, the output voltage of the differential operational amplifier circuit 120 is exactly equal to its input voltage Vout. Therefore, in combination with the circuit diagram of the present invention, in this embodiment, Vout = V R4 =V R8 =4.798V pk V pkThe peak voltage, and this voltage is a unipolar signal voltage, and the waveform is a bun-shaped wave signal with low impedance positive and negative half-waves. Since the input side of the differential operational amplifier circuit 120 is the common-mode voltage of the AC power supply with respect to the operational amplifier reference ground, and the operational amplifier circuit operates in a differential amplification mode, even if a Y-capacitor is inserted in the line, it will not be equivalent to a voltage-doubling rectified voltage on the input side of the operational amplifier circuit, and it will not affect the true value sampling of the AC voltage. In other words, the variant differential AC voltage sampling circuit can effectively avoid the influence of the insertion of the Y-capacitor on the sampling accuracy error.

[0055] Regarding the rectifier circuit 130: In this embodiment, the diode D1 is the rectifying device of the operational amplifier AMP1, and the diode D2 is the rectifying device of the operational amplifier AMP2. The output voltage of this rectifier circuit 130 is also Vout = V R4 = V R8 = 4.798V pk Moreover, this voltage is a DC voltage containing twice the AC ripple, and its rectification and filtering coefficient K≈0.758. Since the inverting input resistors R10 and R13 of the differential operational amplifier circuit 120 are both connected to the output terminal of the rectifier circuit 130, the output voltage of the rectifier circuit 130 is not affected by the forward voltage drop of the rectifying diode. In other words, the temperature stability of the output voltage of the rectifier circuit 130 is very good.

[0056] Regarding the sampling signal filtering circuit 140: The required sampling voltage ratio is obtained by dividing the voltage through the resistors R17 and R18. At the same time, the resistors R17, R18, and the capacitor C2 together achieve the filtering effect of twice the AC ripple. The larger the capacitance of the capacitor C2, the smaller the AC ripple of the AC voltage sampling signal output by the sampling signal filtering circuit 140, but the detection speed will become slower; the smaller the capacitor, the larger the AC ripple of the AC voltage sampling signal, but the detection speed will become faster. The RC time constant can be appropriately adjusted according to the AC power supply frequency.

[0057] Based on the design of the present invention, actually the AC voltage sampling signal has nothing to do with temperature and whether C1 is inserted. Therefore, in order to distinguish it from Figure 2 、 Figure 4 Vsense, Vsense_Y, and Vsense_T in. We set the AC voltage sampling signal output by the sampling signal filtering circuit 140 as Vs, and the calculation method is:

[0058] Vs = V R4 ÷(R17 + R18)×R17×K

[0059] When R17 = 10KΩ, R18 = 47KΩ, and the RC filtering coefficient K = 0.758:

[0060] Vs = 4.798÷(10 + 47)×47×0.758 = 3V。

[0061] To verify that in the present invention, regardless of the insertion of the Y capacitor C1, it has no influence on the sampling accuracy of the AC voltage, we Figure 6 conducted simulations, three times respectively:

[0062] First time: When at room temperature, C1 was not inserted, and the AC voltage sampling signal was obtained;

[0063] Second time: When at room temperature, C1 was inserted into the circuit, and the AC voltage sampling signal was obtained;

[0064] Third time: When at high temperature, C1 was not inserted, and the AC voltage sampling signal was obtained;

[0065] The simulation diagrams of the sampling voltage errors obtained three times are all Figure 7 as shown. It can be seen that the three AC voltage sampling signals are exactly the same and overlap.

[0066] In summary, the variant differential AC sampling circuit provided by the present invention includes an AC voltage divider circuit, a differential operational amplifier circuit 120, a rectifier circuit 130, and a sampling signal filtering circuit 140. Based on the conventional AC voltage sampling circuit, the present invention eliminates the sampling error caused by the insertion of the Y capacitor in the circuit through variant differential sampling and rectification filtering of the AC voltage, and also eliminates the influence of temperature on the sampling accuracy of the AC voltage. At the same time, it avoids the use of high-voltage rectifying devices and high-voltage filtering capacitors, improves the circuit reliability, and has good use value and application prospects.

[0067] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A variant differential AC voltage sampling circuit for eliminating sampling errors caused by the insertion of Y capacitors in a circuit. It includes an AC power supply, and the N wire of the AC power supply is grounded through a Y capacitor C1. It is characterized in that: The AC power supply is sequentially connected with an AC voltage dividing circuit, a differential operational amplifier circuit, a rectifying circuit, and a sampling signal filtering circuit; The AC voltage dividing circuit is used to divide the AC power supply into an AC signal voltage with a required amplitude and transmit it to the differential operational amplifier circuit; The differential operational amplifier circuit is used to convert the AC signal voltage into a unipolar signal voltage and transmit it to the rectifying circuit. The unipolar signal voltage is a flat-topped wave signal with low impedance for positive and negative half-cycles; The rectifying circuit is used to rectify the unipolar signal voltage into a pulsating DC signal and transmit it to the sampling signal filtering circuit; The sampling signal filtering circuit is used to output an AC voltage sampling signal according to the pulsating DC signal; The AC voltage dividing circuit is a resistor voltage dividing circuit; The AC voltage dividing circuit includes resistors R1 - R8. Among them, the L line of the AC power supply is connected to the grounding end of C1 through resistors R1 - R4, and the N line of the AC power supply is connected to the grounding end of C1 through R5 - R8. And the resistance values of R1 - R8 satisfy: R1 + R2 + R3 = R5 + R6 + R7, R4 = R8; The differential operational amplifier circuit includes two operational amplifiers AMP1, AMP2, and resistors R9 - R16; Among them, the positive input terminal of AMP1 is divided into two paths. One path is connected between R3 and R4 through R11, and the other path is connected to the grounding end of C1 through R15; the negative input terminal of AMP1 is divided into two paths. One path is connected between R7 and R8 through R9, and the other path is connected to R10; The positive input terminal of AMP2 is divided into two paths. One path is connected between R7 and R8 through R14, and the other path is connected to the grounding end of C1 through R16; the negative input terminal of AMP1 is divided into two paths. One path is connected between R3 and R4 through R12, and the other path is connected to R13; and the resistance values of R9 - R16 are the same; The rectifying circuit includes diodes D1, D2; the positive electrode of D1 is connected to the output terminal of AMP1, and the negative electrode is connected to R10; the positive electrode of D2 is connected to the output terminal of AMP2, and the negative electrode is connected to R13, and the negative electrodes of D1 and D2 are connected together; The sampling signal filtering circuit includes R17, R18, and capacitor C2. The negative electrodes of D1 and D2 are connected to the grounding end of C1 through R17 and R18, and C2 is connected in parallel with R18. The voltage across C2 is the AC voltage sampling signal.

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