A current power amplifier circuit structure

Abstract

This invention provides a current power amplifier circuit structure, comprising: a precision feedback circuit, the output of which includes a first branch node and a second branch node; a first operational amplifier, the positive terminal of which is connected to the first branch node, and the negative terminal of which is connected in series with a third resistor and then grounded; a precision sampling circuit, the input of which is connected to the second branch node; a power amplifier circuit, the input of which is connected to the output node of the operational amplifier, and the output of which is connected in series with the precision sampling circuit; a resistor, connected in series between the output terminals of the precision sampling circuit and the power amplifier circuit; and a multi-stage filter, one end of which is connected between the negative terminal of the first operational amplifier and the third resistor, and the other end of which is connected between the first operational amplifier and the power amplifier circuit. This invention converts a large current into a small secondary current output and controls the magnitude of the output current; simultaneously, it utilizes negative feedback characteristics to achieve high-precision output of the small current, solving the problem of potential DC current on the primary side of the transformer.

Description

Technical Field

[0001] This invention relates to the field of electrical energy metering technology, and in particular to a current amplifier circuit structure suitable for low current output from a standard power source. Background Technology

[0002] Electricity meter calibration devices include the standard source method and the standard meter method. The standard source method device can directly output accurate calibration power, i.e., accurate voltage, current, and phase angle. The output power setting is multiplied by the time measured by a high-accuracy timer within the device to obtain a standard energy value, which is used for error calculation of the tested electrical equipment. This principle device does not require a main standard and is essentially a "watt-second method" calibration device.

[0003] The standard meter method for electrical energy verification uses a configured main electrical energy standard to measure the standard electrical energy value, and the device's power output is the power required at the verification point. The electrical energy error of the tested electrical energy equipment is calculated based on the electrical energy value measured by the main standard, which is the standard electrical energy value. This principle of equipment requires the use of a main electrical energy standard.

[0004] Under current technology, a power amplifier circuit refers to an amplifier circuit whose output can drive a relatively heavy load (with a small resistance) and can provide a large power output.

[0005] However, the signal-to-noise ratio of the current output circuit of traditional power sources is low, and the accuracy and stability of low current output are poor. It is necessary to optimize the current amplifier circuit in the power source to improve the signal-to-noise ratio of low current output in order to meet the current output requirements under low current conditions. Summary of the Invention

[0006] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide a current power amplifier circuit structure to improve the accuracy and stability of the power source current output under low current conditions, and to use it as a standard power source to test and calibrate the metering characteristics of electricity meters under low current conditions.

[0007] To solve the above problems, the present invention provides a current power amplifier circuit structure, comprising:

[0008] A precision feedback circuit, the output of which includes a first branch node and a second branch node;

[0009] The first operational amplifier A1 has its positive input terminal connected to the first branch node, and its negative input terminal connected in series with the third resistor R3 and then grounded.

[0010] A precision sampling circuit, wherein the input terminal of the precision sampling circuit is connected to the second branch node;

[0011] A power amplifier circuit, the input of which is connected to the output node of the first operational amplifier A1, and the output of which is connected in series with the precision sampling circuit;

[0012] resistor R L It is connected in series between the output terminals of the precision sampling circuit and the power amplifier circuit.

[0013] A further improvement of the present invention is that the precision feedback circuit includes a first resistor R1 and a second resistor R2 connected in series, and the positive terminal of the first operational amplifier A1 is connected between the first resistor R1 and the second resistor R2.

[0014] A further improvement of the present invention is that the precision sampling circuit includes a second operational amplifier A2, a fourth resistor R4 and a zero flux transformer T2. The fourth resistor R4 is connected in parallel with the second operational amplifier A2 and then connected to the second resistor R2. The input coil of the zero flux transformer T2 is connected in series between the positive and negative terminals of the second operational amplifier A2.

[0015] A further improvement of the present invention is that: the power amplifier circuit is a transformer T1, one end of the input coil of the transformer T1 is connected to the output terminal of the first operational amplifier A1, the other end of the input coil of the transformer T1 is grounded, one end of the output coil of the transformer T1 is connected to one end of the output coil of the zero flux transformer T2, and the other end of the output coil of the transformer T1 is connected to the resistor R. L After being connected in series, it is connected to the other end of the output coil of the zero flux transformer T2.

[0016] A further improvement of the present invention is that it also includes:

[0017] A multi-stage filter, one end of which is connected between the negative terminal of the first operational amplifier A1 and the third resistor R3, and the other end of which is connected between the output terminal of the first operational amplifier A1 and the input terminal of the input coil of the power amplifier circuit.

[0018] A further improvement of the present invention is that the multi-stage filter includes a three-stage third-order Butterworth filter and a second-order active low-pass filter connected in series, and the input terminal of the three-stage third-order Butterworth filter is connected between the first operational amplifier A1 and the power amplifier circuit.

[0019] A further improvement of the present invention is that it also includes:

[0020] A linear power supply or battery used for power supply.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] The AC deep feedback circuit uses a passive transformer as the power amplification stage. By leveraging the transformer's high isolation impedance, low leakage, and low distributed parameter influence on the primary and secondary sides, leakage of the output current to the primary circuit is reduced, greatly improving the accuracy and stability of small currents. At the same time, the transformer's low-frequency resistance removes the low-frequency DC component in the output current, significantly improving the distortion and phase performance of the output current and enhancing the stability of the entire feedback loop.

[0023] The DC deep feedback circuit uses a high-precision operational amplifier with low offset, high gain, low temperature drift, and low noise to reduce the offset error of the filter and the error affected by ambient temperature, reduce the DC feedback error from the input to the output of the series multi-stage filter, and achieve the purpose of eliminating the DC component of the output voltage in the operational amplifier.

[0024] Using a linear power supply or battery power, the primary and secondary windings of the transformer are shielded when using a linear power supply, which reduces the distributed capacitance of the transformer secondary and the shield ground. In addition, using battery power further reduces leakage current. Attached Figure Description

[0025] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0026] Figure 1 This is a schematic diagram of a specific embodiment of the current amplifier circuit in this invention.

[0027] Figure 2 This is a schematic diagram of a specific embodiment of the AC feedback loop of the current amplifier in the present invention.

[0028] Figure 3 This is a schematic diagram of the DC feedback circuit of the current amplifier in an embodiment of the present invention;

[0029] Figure 4 This is a circuit diagram of a third-order Butterworth filter in an embodiment of the present invention;

[0030] Figure 5 This is a circuit diagram of a second-order low-pass filter in an embodiment of the present invention. Detailed Implementation

[0031] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] In the description of this invention, it should be noted that the terms "first," "second," "third," "fourth," etc., are used for descriptive purposes and should not be construed as indicating or implying relative importance.

[0033] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0034] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0035] like Figure 1-5 As shown, this embodiment of the invention provides a current power amplifier circuit structure, which includes a precision feedback circuit, a first operational amplifier A1, a precision sampling circuit, a power amplifier circuit, and a resistor R. L and multi-stage filters, where:

[0036] The output of the precision feedback circuit includes a first branch node and a second branch node;

[0037] The positive terminal of the first operational amplifier A1 is connected to the first branch node, and the negative terminal of the first operational amplifier A1 is connected in series with the third resistor R3 and then grounded.

[0038] The input terminal of the precision sampling circuit is connected to the second branch node;

[0039] The input terminal of the power amplifier circuit is connected to the output node of the operational amplifier, and the output terminal of the power amplifier circuit is connected in series with the precision sampling circuit.

[0040] resistor R L It is connected in series between the output terminals of the precision sampling circuit and the power amplifier circuit;

[0041] One end of the multi-stage filter is connected between the negative terminal of the first operational amplifier A1 and the third resistor R3, and the other end is connected between the output terminal of the first operational amplifier A1 and the input terminal of the input coil of the power amplifier circuit.

[0042] Specifically, in this embodiment, please refer to Figure 1 As shown, for the AC feedback loop, the AC component of the output voltage V0 is filtered out by a series multi-stage filter, therefore the AC part cannot be fed back to A1.

[0043] Therefore, based on the AC / DC dual-loop negative feedback circuit structure, the current amplifier circuit drives the transformer, and the transformer realizes power conversion, transforming the large current on the primary side into a small current output on the secondary side, wherein:

[0044] A single-loop negative feedback circuit serves as the precision control circuit for the output current. The precision control of the current output is achieved through a feedback control amplifier based on a zero-flux transformer. By controlling the negative feedback of the zero-flux transformer, the magnitude of the output current is controlled, while utilizing the characteristics of negative feedback to achieve high-precision output of small currents.

[0045] The negative feedback circuit of the other loop is a DC-DC de-circuit for the op-amp output. Since the transformer cannot carry DC, a DC-DC de-circuit feedback circuit is added to eliminate DC from the op-amp output, thereby solving the problem of DC on the primary side of the transformer. If the current amplifier uses a switching or linear amplifier, there will be leakage current, which will affect the accuracy of the current output. A linear power supply or a secondary isolation power supply, or a battery power supply solution can be used.

[0046] Specifically, please refer to Figure 1 As shown, in an embodiment of the present invention, the precision feedback circuit includes a first resistor R1 and a second resistor R2 connected in series, and the positive terminal of the operational amplifier A1 is connected between the first resistor R1 and the second resistor R2.

[0047] In this embodiment, the precision feedback circuit consists of two high-precision platinum resistors, a first resistor R1 and a second resistor R2. This scheme uses mutually matched precision platinum resistors with a temperature drift of 1ppm as the first resistor R1 and the second resistor R2 for precision feedback, solving the problem of the R1 / R2 ratio being affected by temperature and aging drift, thus improving the accuracy of the precision feedback loop. The operational amplifier circuit provides a sinusoidal current output with extremely low distortion. The power amplifier circuit improves the stability of the entire feedback loop. The precision sampling circuit improves the accuracy and stability of the entire sampling circuit, ultimately achieving accurate and stable small current output.

[0048] Specifically, please refer to Figure 1 As shown, the precision sampling circuit includes a second operational amplifier A2, a fourth resistor R4, and a zero flux transformer T2. The fourth resistor R4 is connected in parallel with the second operational amplifier A2 and then connected to the second resistor R2. The input coil of the zero flux transformer T2 is connected in series between the positive and negative terminals of the second operational amplifier A2.

[0049] Specifically, please refer to Figure 1As shown, in an embodiment of the present invention, the power amplifier circuit is a transformer T1. One end of the input coil of transformer T1 is connected to the output terminal of the first operational amplifier A1, and the other end of the input coil of transformer T1 is grounded. One end of the output coil of transformer T1 is connected to one end of the output coil of the zero flux transformer T2, and the other end of the output coil of transformer T1 is connected to the resistor R. L After being connected in series, it is connected to the other end of the output coil of the zero flux transformer T2.

[0050] Specifically, please refer to Figure 1 As shown, in an embodiment of the present invention, the multi-stage filter includes a third-order Butterworth filter and a second-order active low-pass filter connected in series. The input terminal of the third-order Butterworth filter is connected between the first operational amplifier A1 and the power amplifier circuit.

[0051] Please see Figure 2 As shown, the AC output feedback circuit includes: precision feedback, operational amplifier, precision sampling, power amplification, etc., and the input signal V... i and precision feedback signal V fi The common feedback control operational amplifier controls the power amplifier circuit, ultimately controlling the output current I. out .

[0052] Therefore, for an AC feedback loop, the AC output feedback stage includes: precision feedback, operational amplifier, precision sampling, power amplification, etc. The input signal and the precision feedback signal jointly control the operational amplifier, which in turn controls the power amplification circuit, ultimately controlling the output current.

[0053] Please see Figure 3 As shown, Figure 3 The diagram shows the equivalent circuit of the DC loop. For the DC feedback loop, the DC component of the output voltage V0, after being filtered by a series multi-stage filter to remove the AC component, is directly passed through V... f Feedback is sent to operational amplifier A1.

[0054] Therefore, for the DC feedback loop, the DC component of the output voltage after the AC component is filtered out by a series multi-stage filter is directly fed back to the operational amplifier. The circuit uses a three-stage third-order Butterworth filter and a two-order active filter in series as the AC removal circuit, that is, this loop only feeds back DC.

[0055] The filter capacitor uses a low-leakage CBB capacitor to reduce leakage current and ensure stable capacitance value. This solves the problem of poor accuracy and stability caused by leakage at low currents. The stable capacitance value also solves the problem that the capacitance value is affected by temperature and time, which leads to changes in filter parameters and thus cannot completely filter out the AC component in the DC feedback signal.

[0056] Meanwhile, the operational amplifier adopts ADI's high-precision integrated operational amplifier ADA4522-2, which has an input offset of less than 5uV, an open-loop gain of more than 130dB, a temperature drift of less than 22nV per degree, and a typical noise value of 117nV (0.1Hz-10Hz). By using a high-precision operational amplifier with low offset, high gain, low temperature drift, and low noise, the offset error of the filter and the error affected by the ambient temperature are reduced, and the DC feedback error from the input to the output of the series multi-stage filter is reduced, thereby eliminating the DC component of the output voltage in the operational amplifier.

[0057] Please see Figure 4 As shown, the circuit uses a three-stage third-order Butterworth filter and a two-order active filter connected in series as an AC rejection circuit, meaning that this loop only feeds back DC.

[0058] The filter capacitor uses a low-leakage CBB capacitor to reduce leakage current and ensure stable capacitance value. This solves the problem of poor accuracy and stability caused by leakage at low currents. The stable capacitance value also solves the problem that the capacitance value is affected by temperature and time, which leads to changes in filter parameters and thus cannot completely filter out the AC component in the DC feedback signal.

[0059] When conducting metering performance tests on electricity meters under low current conditions, a high-stability, high-accuracy power source is required to output stable and reliable voltage and current signals as test signals.

[0060] To improve the signal-to-noise ratio of the current signal under low-current conditions, the power source adopts the current amplifier circuit structure based on AC / DC dual-loop negative feedback circuit in this scheme to output a low-current signal. In the remaining design, the current transformer uses a 10ppm high-precision, high-bandwidth zero-flux current transformer, the resistor uses a 1ppm precision platinum resistor, the operational amplifier uses a low-offset, high-gain, and high-precision operational amplifier, and the op-amp uses a high-precision integrated op-amp from ADI, with an input offset of less than 5μV, an open-loop gain of greater than 130dB, a temperature drift of less than 22nV per degree, and a typical noise value of 117nV (0.1Hz-10Hz), ultimately achieving accurate and stable low-current output and eliminating the DC component in the op-amp.

[0061] Specifically, since solving the leakage problem in the power amplifier power supply system is the key to solving the leakage current, in the embodiments of the present invention, the current power amplifier circuit structure also includes a linear power supply or a battery.

[0062] This solution uses either a linear power supply or battery power. When using a linear power supply, the primary and secondary windings of the transformer are shielded, and the distributed capacitance of the transformer secondary and the shielding ground is reduced. If the transformer cannot solve the leakage problem, battery power can be used to further reduce leakage current. The layout and wiring of the circuit board and the whole machine are optimized to reduce the coupling capacitance between lines. For critical signal lines, special wires with good shielding effect and low coupling capacitance are used. Special terminals are used for terminal interfaces to reduce the coupling capacitance at the contact points. Critical circuits or signal processing parts are shielded with shielding covers.

[0063] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the scope of protection of this invention.

Claims

1. A current power amplifier circuit structure, characterized in that, include: A precision feedback circuit, the output of which includes a first branch node and a second branch node; The first operational amplifier A1 has its positive input terminal connected to the first branch node, and its negative input terminal connected in series with the third resistor R3 and then grounded. A precision sampling circuit, wherein the input terminal of the precision sampling circuit is connected to the second branch node; A power amplifier circuit, the input of which is connected to the output node of the first operational amplifier A1, and the output of which is connected in series with the precision sampling circuit; resistor R L It is connected in series between the output terminals of the precision sampling circuit and the power amplifier circuit; The precision feedback circuit includes a first resistor R1 and a second resistor R2 connected in series, and the positive terminal of the first operational amplifier A1 is connected between the first resistor R1 and the second resistor R2. The precision sampling circuit includes a second operational amplifier A2, a fourth resistor R4, and a zero flux transformer T2. The fourth resistor R4 is connected in parallel with the second operational amplifier A2 and then connected to the second resistor R2. The input coil of the zero flux transformer T2 is connected in series between the positive and negative terminals of the second operational amplifier A2.

2. The current amplifier circuit structure according to claim 1, characterized in that, The power amplifier circuit is a transformer T1. One end of the input coil of the transformer T1 is connected to the output terminal of the first operational amplifier A1, and the other end of the input coil of the transformer T1 is grounded. One end of the output coil of the transformer T1 is connected to one end of the output coil of the zero flux transformer T2, and the other end of the output coil of the transformer T1 is connected to the resistor R. L After being connected in series, it is connected to the other end of the output coil of the zero flux transformer T2.

3. The current amplifier circuit structure according to claim 1, characterized in that, Also includes: A multi-stage filter, one end of which is connected between the negative terminal of the first operational amplifier A1 and the third resistor R3, and the other end of which is connected between the output terminal of the first operational amplifier A1 and the input terminal of the input coil of the power amplifier circuit.

4. The current amplifier circuit structure according to claim 3, characterized in that, The multi-stage filter includes a three-stage third-order Butterworth filter and a second-order active low-pass filter connected in series. The input terminal of the three-stage third-order Butterworth filter is connected between the first operational amplifier A1 and the power amplifier circuit.

5. The current amplifier circuit structure according to claim 1, characterized in that, Also includes: A linear power supply or battery used for power supply.

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