CN204347110U - A kind of alternating current sample circuit - Google Patents

Abstract

An AC sampling circuit, the inverting input terminal of the op amp U1A is connected to the zero line AC-N of the sampled AC through the resistor R1, one of the positive phase input terminals is connected to the live line AC-L of the sampled AC through the resistor R2, and the other is connected to the live line AC-L of the sampled AC through the resistor R1 The resistor R3 is grounded, and the resistor R4 is connected between the inverting input terminal and the output terminal of the operational amplifier U1A to form a positive half-wave detection circuit. The output terminal of the operational amplifier U1A is used as the output terminal of the positive half-wave detection circuit; The phase input terminal is connected to the live line AC-L through the resistor R8, the positive phase input terminal is connected to the neutral line AC-N through the resistor R9, and the other is grounded through the resistor R11, and the resistor R10 is connected across the inverting input terminal and the output terminal of the operational amplifier U1B Between them, a negative half-wave detection circuit is formed, and the output terminal of the operational amplifier U1B is used as the output terminal of the negative half-wave detection circuit; the output terminal of the positive half-wave detection circuit is connected with the output terminal of the negative half-wave detection circuit, and their contacts are used as The output terminal of the AC sampling circuit.

Description

An alternating current sampling circuit

technical field

The invention relates to an alternating current sampling circuit.

Background technique

The application of alternating current is very extensive, and the accuracy of sampling the alternating current is very important for the alternating current electric equipment. the

The usual AC sampling method is to use a diode to rectify the AC, and then filter it through a capacitor to process the AC into a DC. The condition of the AC can be obtained by detecting the condition of the DC. There are following deficiencies in this existing alternating current sampling circuit:

1. The diode has a threshold voltage. When the sampled AC voltage is lower than the threshold voltage, the diode rectifier circuit cannot work normally, and the AC cannot be sampled;

2. There is a nonlinear error in the diode, which will cause inaccurate sampling;

3. Diodes have poor temperature characteristics and are easily affected by ambient temperature, which can easily lead to inaccurate detection.

Contents of the invention

Aiming at the above-mentioned technical problems existing in the prior art, the present invention provides an alternating current sampling circuit, which is accurate in sampling and does not have a threshold voltage, and can sample low-voltage alternating current.

In order to achieve the above object, the present invention provides the following technical solutions.

An alternating current sampling circuit, including operational amplifier U1A, operational amplifier U1B, resistors R1, R2, R3, R4, R8, R9, R10 and R11, the inverting input terminal of operational amplifier U1A is connected to the neutral line of the sampled alternating current via resistor R1 AC-N, the non-inverting input terminal is connected to the live wire AC-L of the sampled AC through the resistor R2, and the other is grounded through the resistor R3, and the resistor R4 is connected between the inverting input terminal and the output terminal of the operational amplifier U1A to form Positive half-wave detection circuit, the output terminal of the operational amplifier U1A is used as the output terminal of the positive half-wave detection circuit; the inverting input terminal of the operational amplifier U1B is connected to the live wire AC-L of the sampled alternating current through the resistor R8, and the positive phase input terminal is routed through the resistor R9 is connected to the zero line AC-N of the sampled alternating current, and the other is grounded through resistor R11. Resistor R10 is connected between the inverting input terminal and output terminal of op amp U1B to form a negative half-wave detection circuit. The op amp U1B The output end is used as the output end of the negative half-wave detection circuit; the output end of the positive half-wave detection circuit is connected with the output end of the negative half-wave detection circuit, and their contacts are used as the output end of the AC sampling circuit.

Among them, resistors R6 and R7 are also included. One end of resistor R6 is connected to positive bias power supply +Vref, the other end is connected to live wire AC-L, one end of resistor R7 is connected to positive bias power supply +Vref, and the other end is connected to neutral wire AC-N to form a DC bias circuit.

Among them, resistors R5 and R12 are also included, and the resistors R5 and R12 are connected in series between the output terminal of the positive half-wave detection circuit and the output terminal of the negative half-wave detection circuit, and the contact point of the resistors R5 and R12 is used as the output of the AC sampling circuit end.

Among them, a filter capacitor C2 is also included, one end of which is connected to the output end of the AC sampling circuit, and the other end is grounded.

Wherein, the resistance values of the resistors R1 and R2 are equal, the resistance values of the resistors R3 and R4 are equal, the resistance values of the resistors R8 and R9 are equal, and the resistance values of the resistors R10 and R11 are equal.

The beneficial effects created by the present invention are: use the positive half-wave detection circuit and the negative half-wave detection circuit mainly composed of operational amplifiers to replace diodes to rectify the positive half-wave and negative half-wave of alternating current respectively, and the linearity and temperature of the operational amplifiers The characteristics are relatively good, it is not easily affected by the ambient temperature, and there is no nonlinear error, so the AC sampling circuit created by the present invention is accurate in sampling, and because there is no threshold voltage in the operational amplifier, even low-voltage AC can be sampled .

Description of drawings

Fig. 1 is the circuit schematic diagram of the alternating current sampling circuit created by the present invention.

Fig. 2 is a waveform diagram of one cycle of the sampled alternating current.

FIG. 3 is a waveform diagram of one cycle of the output of the positive half-wave detection circuit.

FIG. 4 is a waveform diagram of one cycle of the output of the negative half-wave detection circuit.

Fig. 5 is a waveform diagram of one cycle of the output of the alternating current sampling circuit created by the present invention.

Detailed ways

The invention will be described in detail below in conjunction with specific embodiments.

As shown in Figure 1, the AC sampling circuit of this embodiment includes operational amplifier U1A, operational amplifier U1B, resistors R1~R12, capacitors C1 and C2, and the inverting input terminal of operational amplifier U1A is connected to the neutral line of the sampled AC power via resistor R1 AC-N, the non-inverting input terminal is connected to the live wire AC-L of the sampled AC through the resistor R2, and the other is grounded through the resistor R3, and the resistor R4 is connected between the inverting input terminal and the output terminal of the operational amplifier U1A to form Positive half-wave detection circuit, the output terminal of the operational amplifier U1A is used as the output terminal of the positive half-wave detection circuit; the inverting input terminal of the operational amplifier U1B is connected to the live wire AC-L of the sampled alternating current through the resistor R8, and the positive phase input terminal is routed through the resistor R9 is connected to the zero line AC-N of the sampled alternating current, and the other is grounded through resistor R11. Resistor R10 is connected between the inverting input terminal and output terminal of op amp U1B to form a negative half-wave detection circuit. The op amp U1B The output terminal is used as the output terminal of the negative half-wave detection circuit; the resistors R5 and R12 are connected in series between the output terminal of the positive half-wave detection circuit and the output terminal of the negative half-wave detection circuit, and the contact point of the resistors R5 and R12 is used as the AC sampling output of the circuit. One end of the capacitor C2 is connected to the output end of the alternating current sampling circuit, and the other end is grounded, which serves to filter the output of the alternating current sampling circuit in this embodiment. In this embodiment, the resistance values of the resistors R1 and R2 are equal, the resistance values of the resistors R3 and R4 are equal, the resistance values of the resistors R8 and R9 are equal, and the resistance values of the resistors R10 and R11 are equal.

One end of the resistor R6 is connected to the positive bias power supply +Vref, the other end is connected to the live wire AC-L, one end of the resistor R7 is connected to the positive bias power supply +Vref, and the other end is connected to the neutral line AC-N to form a DC bias circuit. Set the power supply +Vref to +5V voltage power supply. The function of the DC bias circuit is to increase the voltage of the AC input to the AC sampling circuit in this embodiment as a whole, so as to prevent crossover distortion of the full-wave rectified waveform.

The waveform of one cycle of the sampled AC is shown in Figure 2, combined with Figure 1, where U1 is the level of the neutral line AC-N, U2 is the level of the live line AC-L, when the sampled AC is a positive half-wave , first superimposed with the positive bias power supply +Vref (resistors R6 and R7 will produce a little voltage drop), and then sent out in two ways, and one way is sent to the positive half-wave detection circuit, which is proportionally amplified by the positive half-wave detection circuit, and the operational amplifier U1A The output voltage Uo1 at the output end of the circuit is known from the calculation formula Uo1=R1/R4(U2-U1). Since U2-U1>0 at this time, Uo1 is positive, that is to say, the positive half wave of the sampled AC is replaced by the positive half wave The detection circuit amplifies the output according to a certain ratio. The other channel is sent to the negative half-wave detection circuit, which is proportionally amplified by the negative half-wave detection circuit, and the output terminal of the operational amplifier U1B outputs the voltage Uo2. According to the calculation formula, Uo2=R8/R10(U1-U2), because at this time U2- U1>0, and the operating power supply of the operational amplifier is a single power supply, so Uo2=0.

When the sampled AC is a negative half-wave, it is firstly superimposed with the positive bias power supply +Vref (resistors R6 and R7 will produce a little voltage drop), and then sent out in two ways, one of which is sent to the positive half-wave detection circuit. The wave detection circuit is proportionally amplified, and the output voltage Uo1 of the output terminal of the operational amplifier U1A is known from the calculation formula Uo1=R1/R4(U2-U1). Since U2-U1<0 at this time, and the operating power supply of the operational amplifier is a single power supply, So Uo1=0. The other channel is sent to the negative half-wave detection circuit, which is proportionally amplified by the negative half-wave detection circuit, and the output terminal of the operational amplifier U1B outputs the voltage Uo2. According to the calculation formula, Uo2=R8/R10(U1-U2), because at this time U2- U1<0, Uo2 is positive, that is to say, the negative half wave of the sampled alternating current is amplified by the negative half wave detection circuit according to a certain ratio and then output.

The output waveforms of one cycle of the positive half-wave detection circuit and the negative half-wave detection circuit are shown in Figure 3 and Figure 4, respectively. Waveform Uo, the waveform of one cycle of Uo is shown in Figure 5. The condition of the sampled alternating current can be known from Uo.

Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention, rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art Personnel should understand that the technical solution of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solution of the present invention.

Claims (5)

1. An alternating current sampling circuit is characterized in that it comprises operational amplifier U1A, operational amplifier U1B, resistors R1, R2, R3, R4, R8, R9, R10 and R11, and the inverting input terminal of operational amplifier U1A is connected via resistor R1 The neutral line AC-N of the sampled alternating current, one of the positive phase input terminals is connected to the live line AC-L of the sampled alternating current through the resistor R2, the other is grounded through the resistor R3, and the resistor R4 is connected across the inverting input terminal of the operational amplifier U1A and Between the output terminals, a positive half-wave detection circuit is formed, and the output terminal of the operational amplifier U1A is used as the output terminal of the positive half-wave detection circuit; the inverting input terminal of the operational amplifier U1B is connected to the live wire AC-L of the sampled alternating current through the resistor R8, and the positive One of the phase input terminals is connected to the neutral line AC-N of the sampled AC through resistor R9, and the other is grounded through resistor R11. Resistor R10 is connected between the inverting input terminal and output terminal of operational amplifier U1B to form a negative half-wave detection In the circuit, the output terminal of the operational amplifier U1B is used as the output terminal of the negative half-wave detection circuit; the output terminal of the positive half-wave detection circuit is connected with the output terminal of the negative half-wave detection circuit, and their contacts are used as the output terminal of the AC sampling circuit. 2. The AC sampling circuit according to claim 1, further comprising resistors R6 and R7, one end of the resistor R6 is connected to the positive bias power supply +Vref, the other end is connected to the live line AC-L, and one end of the resistor R7 is connected to the positive bias power supply Power supply +Vref, the other end is connected to the neutral line AC-N to form a DC bias circuit. 3. The AC sampling circuit according to claim 1, further comprising resistors R5 and R12, the resistors R5 and R12 are connected in series between the output end of the positive half-wave detection circuit and the output end of the negative half-wave detection circuit Between, the junction of resistors R5 and R12 is used as the output terminal of the alternating current sampling circuit. 4. The alternating current sampling circuit according to claim 1, further comprising a filter capacitor C2, one end of which is connected to the output end of the alternating current sampling circuit, and the other end is grounded. 5. The alternating current sampling circuit according to claim 1, characterized in that, the resistance values of resistors R1 and R2 are equal, the resistance values of resistors R3 and R4 are equal, the resistance values of resistors R8 and R9 are equal, and the resistance values of resistors R10 and R11 are equal. The values are equal.