Alternating current sampling circuit

Abstract

An alternating current sampling circuit comprises alternating current to be sampled, a current or voltage conversion circuit, a voltage lifting circuit and a voltage follower circuit, the voltage lifting circuit is composed of a magnetic bead, a second resistor, a third resistor and a first capacitor, one end of the magnetic bead is connected with a first output pin of the conversion circuit, and the other end of the magnetic bead is connected with one end of the second resistor. The other end of the second resistor is connected with direct current bias voltage through a third resistor and grounded through a first capacitor, the voltage follower circuit is composed of an operational amplifier, a second capacitor and a fourth resistor, and the other end of the second resistor is connected with a positive input pin of the operational amplifier. A reverse input pin of the operational amplifier is connected with an output pin of the operational amplifier, a voltage pin of the operational amplifier is connected with power supply voltage and is grounded through a second capacitor, a grounding pin of the operational amplifier is grounded, and an output pin of the operational amplifier is connected with a fourth resistor to adjust input impedance. And the output voltage is input into the analog-to-digital converter.

Description

Technical Field

[0001] The utility model relates to the technical field of power electronics, in particular to an AC sampling circuit. Background Art

[0002] At present, the AC sampling circuit generally needs to use two operational amplifiers in series to sample the AC power to be tested. For example, in the invention patent "AC Sampling Circuit" with authorization announcement number CN109061279B, the first operational amplifier is used to form a voltage follower to isolate the primary sampling value from the subsequent circuit, and then the second operational amplifier is used to form a voltage follower to raise the primary sampling value to above 0V. Finally, the output sampling signal can be output to the analog-to-digital converter inside the microcontroller for use. However, the AC sampling circuit of this invention patent uses two operational amplifiers, uses more electrical components, and the circuit is more complicated. The production cost is high, which is not conducive to cost control. Summary of the invention

[0003] In view of the above-mentioned problems, the utility model provides an AC sampling circuit, which can reduce the cost of the AC sampling circuit.

[0004] The technical solution of the utility model is: an AC sampling circuit, including AC power to be sampled, and also including a current or voltage conversion circuit, a voltage raising circuit, and a voltage following circuit. The voltage raising circuit is composed of a magnetic bead, a second resistor, a third resistor, and a first capacitor. One end of the magnetic bead is connected to the first output pin of the conversion circuit, and the other end of the magnetic bead is connected to one end of the second resistor. The other end of the second resistor is connected to a DC bias voltage and grounded through the first capacitor via the third resistor. The voltage following circuit is composed of an operational amplifier, a second capacitor, and a fourth resistor. The other end of the second resistor is connected to the positive input pin of the operational amplifier, the reverse input pin of the operational amplifier is connected to the output pin of the operational amplifier, the voltage pin of the operational amplifier is connected to the power supply voltage and grounded through the second capacitor, the ground pin of the operational amplifier is grounded, and the output pin of the operational amplifier is connected to the fourth resistor to adjust the input impedance for inputting the output voltage into an analog-to-digital converter.

[0005] Preferably, the current conversion circuit is composed of a current transformer CT1 and a first resistor, wherein two input pins of the current transformer CT1 are connected to the alternating current to be sampled, and the first resistor is connected between two output pins of the current transformer CT1.

[0006] Preferably, the voltage conversion circuit is composed of a voltage transformer PT1, a first resistor, and a fifth resistor. The first input pin of the voltage transformer PT1 is connected to the alternating current to be sampled via the fifth resistor, the second input pin of the voltage transformer PT1 is connected to the alternating current to be sampled, and the first resistor is connected between the two output pins of the voltage transformer PT1.

[0007] Preferably, the first resistor is a precision resistor with an accuracy of 0.1%.

[0008] Preferably, the DC bias voltage divided by the sum of the resistance values ​​of the second resistor and the third resistor is one order of magnitude greater than the input bias current of the operational amplifier and one order of magnitude smaller than the maximum output current of the current or voltage conversion circuit.

[0009] Preferably, the minimum output voltage is greater than 0.

[0010] The advantages of the utility model are as follows: by selecting appropriate second and third resistors, the utility model makes the DC bias voltage divided by the sum of the resistance values ​​of the second and third resistors one order of magnitude greater than the input bias current of the operational amplifier and one order of magnitude smaller than the maximum output current of the current transformer or the voltage transformer, thereby ensuring the sampling accuracy of the sampling circuit. At the same time, the minimum output voltage of the sampling circuit of the utility model is greater than 0, ensuring that the output voltage can be directly input to the analog-to-digital converter inside the single-chip microcomputer for use, simplifying the circuit structure, reducing the use of an operational amplifier and related circuit elements, and saving costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a diagram of an embodiment of the utility model;

[0012] Figure 2 Another embodiment of the present invention is shown in FIG. DETAILED DESCRIPTION Example 1

[0013] When the AC current to be sampled is AC current, refer to Figure 1, an AC sampling circuit, including a current conversion circuit, a voltage boost circuit, and a voltage follower circuit, wherein the current conversion circuit is composed of a current transformer CT1 and a first resistor R1, and is used to finally convert a wide range AC current signal of an AC current to be sampled into an AC low voltage signal, wherein the two input pins of the current transformer CT1, namely the first pin and the second pin, are connected to the AC current to be sampled, and the two output pins of the current transformer CT1, namely the third pin and the fourth pin, are connected to the first resistor R1, and the first resistor R1 is a precision resistor with an accuracy of 0.1%. In this embodiment, The current transformation ratio n:1 of the current transformer CT1 is 2000:1, the resistance of the first resistor R1 is 69.8Ω, and the voltage boosting circuit is composed of a magnetic bead E1, a second resistor R2, a third resistor R3, and a first capacitor C1. One end of the magnetic bead E1 is connected to the first output pin of the conversion circuit, and the other end of the magnetic bead E1 is connected to one end of the second resistor R2. The other end of the second resistor R2 is connected to the DC bias voltage DVCC1 through the third resistor R3 and is grounded through the first capacitor C1. In this embodiment, the resistance values ​​of the second resistor R2 and the third resistor R3 are both 1MΩ, the capacitance of the first capacitor C1 is 33nF, and the DC bias voltage DVCC1 is 3.3V. The voltage follower circuit is composed of an operational amplifier U1A, a second capacitor C2, and a fourth resistor R4. The other end of the second resistor R2 is connected to the positive input pin, i.e., pin 3, of the operational amplifier U1A. The reverse input pin, i.e., pin 2, of the operational amplifier U1A is connected to the output pin, i.e., pin 1, of the operational amplifier U1A. The voltage pin, i.e., pin 8, of the operational amplifier U1A is connected to the power supply voltage DVCC2 and is grounded via the second capacitor C2. The ground pin, i.e., pin 4, of the operational amplifier U1A is grounded. The output pin, i.e., pin 1, of the operational amplifier U1A is connected to the fourth resistor R4 to adjust the input impedance for inputting the output voltage into the analog-to-digital converter.

[0014] In this embodiment, the capacitance of the second capacitor C2 is 100 nF, and the resistance of the fourth resistor R4 is 100 Ω.

[0015] In this embodiment, the voltage across the first resistor R1 is for:

[0016] =i* / n

[0017] In the formula, is the voltage across the first resistor R1, i is the AC current value to be sampled, is the resistance of the first resistor R1, and n is the current transformation ratio of the current transformer CT1.

[0018] According to the operational amplifier virtual cut-off and the voltage division of the second resistor R2 and the third resistor R3, the voltage at the positive input terminal of the operational amplifier is for:

[0019]

[0020] In the formula, is the voltage at the positive input of the operational amplifier, is the resistance of the second resistor R2, DVCC1 is the DC bias voltage, is the resistance value of the third resistor R3, is the voltage across the first resistor R1, i is the AC current value to be sampled, is the resistance of the first resistor R1, and n is the current transformation ratio of the current transformer CT1.

[0021] According to the virtual short circuit of the operational amplifier, the output voltage of the sampling circuit for:

[0022]

[0023] Therefore, in order to ensure the sampling accuracy, the DC bias voltage is divided by the sum of the resistance values ​​of the second resistor and the third resistor, that is, DVCC1 / It should be one order of magnitude larger than the input bias current of the operational amplifier. The DC bias voltage is divided by the sum of the resistance values ​​of the second resistor and the third resistor, that is, DVCC1 / It should be one order of magnitude smaller than the maximum output current of the current conversion circuit, i.e., i / n, where i is the AC current value to be sampled and n is the current transformation ratio of the current transformer CT1. At the same time, in order to ensure that the output voltage of the sampling circuit Can be directly used as input to the analog-to-digital converter, and the output voltage of the sampling circuit should be ensured The minimum value of is greater than 0. Example 2

[0024] When the AC current to be sampled is AC voltage, see Figure 2, an AC sampling circuit, including a voltage conversion circuit, a voltage raising circuit, and a voltage following circuit, wherein the voltage conversion circuit is composed of a voltage transformer PT1, a first resistor R6, and a fifth resistor R5, and is used to finally convert a wide range AC voltage signal of an AC voltage input to be sampled into an AC small voltage signal, wherein the first input pin of the voltage transformer PT1, i.e., the first pin, is connected to the AC voltage to be sampled via the fifth resistor R5, and the second input pin of the voltage transformer PT1, i.e., the second pin, is connected to the AC voltage to be sampled, and the first resistor R6 is connected between the two output pins of the voltage transformer PT1, i.e., the third pin and the fourth pin, wherein the first resistor R6 is a precision resistor with an accuracy of 0.1%. In this embodiment, The voltage transformer PT1 is a current type voltage transformer, and its current transformation ratio m:1 is 1:1. The resistance of the first resistor R6 is 200Ω, and the resistance of the fifth resistor R5 is 153kΩ. The voltage boosting circuit is composed of a magnetic bead E2, a second resistor R7, a third resistor R8, and a first capacitor C3. One end of the magnetic bead E2 is connected to the first output pin of the conversion circuit, and the other end of the magnetic bead E2 is connected to one end of the second resistor R7. The other end of the second resistor R7 is connected to the DC bias voltage DVCC1 through the third resistor R8 and to the ground through the first capacitor C3. In this embodiment, the resistance of the second resistor R7 and the third resistor R8 are both 1MΩ, the capacitance of the first capacitor C3 is 33nF, and the DC bias voltage DVCC1 is 3.3V. The voltage follower circuit is composed of an operational amplifier U2A, a second capacitor C4, and a fourth resistor R9. The other end of the second resistor R7 is connected to the positive input pin of the operational amplifier U2A, that is, the third pin. The reverse input pin of the operational amplifier U2A, that is, the second pin, is connected to the output pin of the operational amplifier U2A, that is, the first pin. The voltage pin of the operational amplifier U2A, that is, the eighth pin, is connected to the power supply voltage DVCC2 and is grounded through the second capacitor C4. The ground pin of the operational amplifier U2A, that is, the fourth pin, is grounded. The output pin of the operational amplifier U2A, that is, the first pin, is connected to the fourth resistor R9 to adjust the input impedance and input the output voltage into the analog-to-digital converter. In this embodiment, the capacitance of the second capacitor C4 is 100nF, and the resistance of the fourth resistor R9 is 100Ω.

[0025] In this embodiment, the voltage across the first resistor R6 is for:

[0026]

[0027] In the formula, is the voltage across the first resistor R6, is the AC voltage value to be sampled, is the resistance value of the first resistor R6, is the resistance value of the fifth resistor R5, is the current transformation ratio of the current type voltage transformer.

[0028] According to the operational amplifier virtual cut-off and the voltage division of the second resistor R7 and the third resistor R8, the voltage at the positive input terminal of the operational amplifier is for:

[0029]

[0030] In the formula, is the voltage at the positive input of the operational amplifier, is the resistance of the second resistor R7, DVCC1 is the DC bias voltage, is the resistance value of the third resistor R8, is the voltage across the first resistor R6, is the AC voltage value to be sampled, is the resistance value of the first resistor R6, is the resistance value of the fifth resistor R5, is the current transformation ratio of the current type voltage transformer.

[0031] According to the virtual short circuit of the operational amplifier, the output voltage of the sampling circuit for:

[0032]

[0033] Therefore, in order to ensure the sampling accuracy, the DC bias voltage is divided by the sum of the resistance values ​​of the second resistor and the third resistor, that is, DVCC1 / It should be one order of magnitude larger than the input bias current of the operational amplifier. The DC bias voltage is divided by the sum of the resistance values ​​of the second resistor and the third resistor, that is, DVCC1 / The maximum output current of the voltage conversion circuit should be u / ( ) is one order of magnitude smaller, where u is the AC voltage value to be sampled, is the current transformation ratio of the voltage transformer PT1, is the resistance value of the fifth resistor R5. At the same time, in order to ensure that the output voltage of the sampling circuit Can be directly used as input to the analog-to-digital converter, and the output voltage of the sampling circuit should be ensured The minimum value of is greater than 0.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. An AC sampling circuit, characterized in that: It includes a current or voltage conversion circuit, a voltage boosting circuit, and a voltage following circuit. The voltage boosting circuit is composed of a magnetic bead, a second resistor, a third resistor, and a first capacitor. One end of the magnetic bead is connected to the first output pin of the conversion circuit, and the other end of the magnetic bead is connected to one end of the second resistor. The other end of the second resistor is connected to a DC bias voltage and to ground via the third resistor. The voltage following circuit is composed of an operational amplifier, a second capacitor, and a fourth resistor. The other end of the second resistor is connected to the positive input pin of the operational amplifier, and the reverse input pin of the operational amplifier is connected to the output pin of the operational amplifier. The voltage pin of the operational amplifier is connected to the power supply voltage and is grounded via the second capacitor. The ground pin of the operational amplifier is grounded, and the output pin of the operational amplifier is connected to the fourth resistor to adjust the input impedance for inputting the output voltage into an analog-to-digital converter.

2. The AC sampling circuit according to claim 1, characterized in that: The current conversion circuit is composed of a current transformer CT1 and a first resistor. Two input pins of the current transformer CT1 are connected to the AC current to be sampled, and the first resistor is connected between two output pins of the current transformer CT1.

3. The AC sampling circuit according to claim 1, characterized in that: The voltage conversion circuit is composed of a voltage transformer PT1, a first resistor, and a fifth resistor. The first input pin of the voltage transformer PT1 is connected to the AC power to be sampled via the fifth resistor, the second input pin of the voltage transformer PT1 is connected to the AC power to be sampled, and the first resistor is connected between the two output pins of the voltage transformer PT1.

4. An AC sampling circuit according to claim 2 or 3, characterized in that: The first resistor is a precision resistor with an accuracy of 0.1%.

5. The AC sampling circuit according to claim 1, characterized in that: The DC bias voltage divided by the sum of the resistance values ​​of the second resistor and the third resistor is one order of magnitude greater than the input bias current of the operational amplifier and one order of magnitude smaller than the maximum output current of the current or voltage conversion circuit.

6. The AC sampling circuit according to claim 1, characterized in that: The minimum output voltage is greater than 0.

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