Ac small signal sampling circuit without negative voltage based on operational amplifier

Abstract

The application relates to an AC small-signal sampling circuit without negative voltage based on an operational amplifier, which comprises an operational amplifier U1, a voltage transformer PT1 and resistors R1-R8 connected with the voltage transformer PT1. The utility model can save the cost of a DC-DC chip and its peripheral circuit required for generating negative voltage by collecting traditional AC signals, and greatly saves the space of a PCB board. In addition, since the input end of the operational amplifier is connected with the voltage transformer, front and back isolation is realized, the anti-interference ability to the outside world is greatly improved, the sampling value is very accurate, and the utility model is especially suitable for some places with high precision requirements, such as the sampling circuit of an FTU.

Description

Technical Field

[0001] This application relates to the field of AC signal sampling circuit technology, and in particular to an AC small-signal sampling circuit based on an operational amplifier that does not require negative voltage. Background Technology

[0002] Traditional methods for acquiring AC signals typically use only a single operational amplifier circuit, which requires a negative voltage. The DC-DC chip and its peripheral circuitry needed to generate this negative voltage are not only expensive but also occupy significant PCB space. Furthermore, a single operational amplifier circuit cannot effectively prevent external interference, leading to fluctuations in the sampled values ​​and resulting in measurement errors. Utility Model Content

[0003] The purpose of this application is to provide an AC small-signal sampling circuit based on an operational amplifier that does not require negative voltage, which is simple in structure, high in precision, low in manufacturing cost, and stable in signal transmission.

[0004] To achieve the above objectives, this utility model provides an AC small-signal sampling circuit based on an operational amplifier that does not require a negative voltage. The circuit includes an operational amplifier U1, a voltage transformer PT1, and resistors R1-R8. One end of resistor R1 is connected to pin 1 of the voltage transformer PT1, and the other end is connected to the inverting input terminal INA- of the operational amplifier U1. One end of resistor R2 is connected to pin 4 of the voltage transformer PT1, and the other end is connected to the non-inverting input terminal INA+ of the operational amplifier U1. One end of resistor R3 is connected to the output terminal OUTA of the operational amplifier U1, and the other end is connected to the inverting input terminal INA- of the operational amplifier U1. The resistors are connected as follows: one end of resistor R4 is connected to the non-inverting input terminal INA+ of operational amplifier U1, and the other end is connected to the output terminal OUTB of operational amplifier U1; one end of resistor R5 is connected to the non-inverting input terminal INB+ of operational amplifier U1, and the other end is connected to the +5V power supply; one end of resistor R6 is connected to the non-inverting input terminal INB+ of operational amplifier U1, and the other end is connected to the ground wire; one end of resistor R7 is connected to the external AC input signal, and the other end is connected to pin 2 of voltage transformer PT1; one end of resistor R8 is connected to pin 1 of voltage transformer PT1, and the other end is connected to pin 4 of voltage transformer PT1.

[0005] To facilitate the connection of the AC small signal sampling circuit with the FTU device, the voltage transformer PT1 is connected to the FTU through wires AC_L and AC_N, and the resistor R7 is set on the wire AC_L.

[0006] In order to effectively suppress external interference and ensure stable output of the subsequent stage, the input terminals 2 and 3 and the output terminals 1 and 4 of the voltage transformer PT1 are completely isolated.

[0007] To further ensure sampling accuracy, the operational amplifier U1 integrates operational amplifier A and operational amplifier B. Operational amplifier B, together with resistors R5 and R6, forms an offset circuit, whose output voltage VREF is the offset voltage, which serves as the reference voltage for the input pin of operational amplifier A.

[0008] In summary, this invention has the following advantages: It saves the cost of the DC-DC chip and its peripheral circuits required for generating negative voltage from traditional AC signals, and also significantly saves PCB board space. Furthermore, because the operational amplifier input is connected to the voltage transformer, true front-to-back isolation is achieved, greatly improving its anti-interference capability and making the sampled values ​​very accurate, especially suitable for applications with high precision requirements, such as FTU sampling circuits. Moreover, due to the presence of the offset voltage VREF, this circuit can sample not only AC signals but also DC signals containing negative values, such as the magnitude of the forward and reverse current of a motor. Additionally, the input INB- and output OUTB of the B operational amplifier are directly connected, forming a voltage follower. Regardless of the impedance change of the subsequent A operational amplifier, the output VREF of the B operational amplifier remains constant. Its output voltage approximates the input voltage, exhibiting high impedance to the preceding circuit and low impedance to the following circuit, effectively acting as a constant voltage source. Therefore, it provides "isolation" between the preceding and following circuits, ensuring the purity and stability of the signal during transmission. Attached Figure Description

[0009] Figure 1 This is the circuit schematic of the AC small-signal sampling circuit based on an operational amplifier that does not require negative voltage according to this utility model. Detailed Implementation

[0010] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more definite definition of the scope of protection of the present invention.

[0011] like Figure 1The circuit shown is an AC small-signal sampling circuit based on an operational amplifier that does not require a negative voltage. It includes an operational amplifier U1, a voltage transformer PT1, and resistors R1-R8. One end of resistor R1 is connected to pin 1 of the voltage transformer PT1, and the other end is connected to the inverting input terminal INA- of the operational amplifier U1. One end of resistor R2 is connected to pin 4 of the voltage transformer PT1, and the other end is connected to the non-inverting input terminal INA+ of the operational amplifier U1. One end of resistor R3 is connected to the output terminal OUTA of the operational amplifier U1, and the other end is connected to the inverting input terminal INA- of the operational amplifier U1. One end of resistor R4 is connected to the non-inverting input terminal INA+ of operational amplifier U1, and the other end is connected to the output terminal OUTB of operational amplifier U1. One end of resistor R5 is connected to the non-inverting input terminal INB+ of operational amplifier U1, and the other end is connected to the +5V power supply. One end of resistor R6 is connected to the non-inverting input terminal INB+ of operational amplifier U1, and the other end is connected to the ground wire. One end of resistor R7 is connected to the external input AC signal L, and the other end is connected to pin 2 of voltage transformer PT1. One end of resistor R8 is connected to pin 1 of voltage transformer PT1, and the other end is connected to pin 4 of voltage transformer PT1.

[0012] This application is mainly used for measuring small AC signals in an FTU. An AC signal output from the primary side enters the FTU through a cable, and then enters the voltage transformer PT1 through two wires, AC_L and AC_N. After passing through the output pin of the transformer, it enters the operational amplifier. After processing by the operational amplifier, the output VOUT is sent to the microcontroller for sampling.

[0013] The voltage transformer PT1 primarily performs preliminary sampling of externally input signals. Its input pins 2 and 3, and output pins 1 and 4, are completely isolated, effectively suppressing external interference and ensuring stable output from subsequent stages. Operational amplifier U1 integrates two operational amplifiers, A and B. First, operational amplifier B, along with resistors R5 and R6, forms an offset circuit. The 5V voltage is divided by resistors R5 and R6 and enters the INB+ input pin of operational amplifier B. Its output voltage VREF is the offset voltage, which also serves as the reference voltage for the input pin of operational amplifier A. During measurement, a small AC signal enters operational amplifier A through the INA- and INA+ terminals. Combined with the offset voltage of operational amplifier B, the original negative value is shifted to a positive value. In this way, the sampling chip or CPU can directly acquire the complete AC signal.

[0014] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape, principle and application direction of this application should be covered within the scope of protection of this application.

Claims

1. An AC small-signal sampling circuit based on an operational amplifier that does not require negative voltage, characterized in that: The system includes operational amplifier U1, voltage transformer PT1, and resistors R1-R7. One end of resistor R1 is connected to pin 1 of voltage transformer PT1, and the other end is connected to the inverting input terminal INA- of operational amplifier U1. One end of resistor R2 is connected to pin 4 of voltage transformer PT1, and the other end is connected to the non-inverting input terminal INA+ of operational amplifier U1. One end of resistor R3 is connected to the output terminal OUTA of operational amplifier U1, and the other end is connected to the inverting input terminal INA- of operational amplifier U1. One end of resistor R4 is connected to the output terminal OUTA of operational amplifier U1, and the other end is connected to the inverting input terminal INA- of operational amplifier U1. The non-inverting input terminal INA+ is connected to the other end, and the other end is connected to the output terminal OUTB of operational amplifier U1. One end of resistor R5 is connected to the non-inverting input terminal INB+ of operational amplifier U1, and the other end is connected to the +5V power supply. One end of resistor R6 is connected to the non-inverting input terminal INB+ of operational amplifier U1, and the other end is connected to the ground wire. One end of resistor R7 is connected to the external input AC signal, and the other end is connected to pin 2 of voltage transformer PT1. One end of resistor R8 is connected to pin 1 of voltage transformer PT1, and the other end is connected to pin 4 of voltage transformer PT1.

2. The AC small-signal sampling circuit based on an operational amplifier without the need for negative voltage as described in claim 1, characterized in that: The voltage transformer PT1 is connected to the FTU via wires AC_L and AC_N, and resistor R7 is set on wire AC_L.

3. The AC small-signal sampling circuit based on an operational amplifier without the need for negative voltage as described in claim 2, characterized in that: The input terminals 2 and 3, and the output terminals 1 and 4 of the voltage transformer PT1 are completely isolated.

4. The AC small-signal sampling circuit based on an operational amplifier without negative voltage according to any one of claims 1-3, characterized in that: The operational amplifier U1 integrates operational amplifier A and operational amplifier B. Operational amplifier B, together with resistors R5 and R6, forms an offset circuit. Its output voltage VREF is the offset voltage, which serves as the reference voltage for the input pin of operational amplifier A.

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