Shunt

Abstract

The present invention relates to a shunt, which includes first and second constant current diodes (D1, D4), first and second voltage stabilizing diodes (D2, D3), and first and second operational amplifiers (A1, A2). The first constant current diode (D1), the first voltage stabilizing diode (D2), the second voltage stabilizing diode (D3), and the second constant current diode (D4) are connected in sequence. The present invention can change the output impedance of a high internal resistance source in a high-precision measurement system to transform it into a low internal resistance output.

Description

Technical Field

[0001] The present invention relates to a shunt. Background Art

[0002] During the use of a shunt, a voltage measurement circuit needs to be connected in parallel to the shunt. Therefore, the impedance caused by the load effect will inevitably be introduced, resulting in measurement errors. According to the corresponding resistance value of the shunt, the output resistance of a shunt with a nominal current of 100 A is 8 mΩ. As the resistance value of the shunt increases, the rated current will decrease accordingly. In the measurement of small currents below 10 mA, the load effect is more obvious. Therefore, in the design of a shunt with a nominal current of 1 mA, the influence of the load effect should be considered especially.

[0003] The working circuit models of shunts are mainly divided into two categories, namely ideal shunts and accurate AC / DC shunts. Specifically, in the case of no load, the ideal shunt circuit model is as Figure 2 shown. Wherein, sh is the abbreviation of shunt, ld is the wire load, and in is the abbreviation of input. The transfer function of the shunt can be expressed as:

[0004]

[0005] Since ωL and ωC are relatively small compared with R, for most R and C, and ωRC after squaring also has a relatively small influence, the above formula can be transformed into:

[0006] Z = R + jω(L - R 2 C) = R + jω(L eq );

[0007] The equivalent inductance of the AC / DC shunt in this formula is L eq = L - R 2 C. In practical applications, the inductance of the AC / DC shunt is reflected in the phase error. Then, according to the above formula, the AC / DC difference and angular error can be expressed by the following formula:

[0008]

[0009]

[0010] During the actual measurement process, the inductance, wire resistance and load impedance of the output wire of the AC / DC shunt are closely related to the AC / DC difference and angular difference performance of the shunt. Then, based on this, the accurate AC / DC shunt model (including load) is as Figure 3 shown. This model uses the same operation method as the model Figure 2 shown. Then, the equivalent inductance of the AC / DC shunt model can be expressed as:

[0011]

[0012] It can be seen that to simplify the accurate model of the shunt into a simple model, it is necessary to make R in much larger than R and R ld , and to make R ld less than R, or to make C i less than C s . For a small current shunt, especially a shunt below 10 mA, when the measured current is small, the resistance value of the sampling resistor is often large. Therefore, when measuring the output voltage of the shunt with an AC voltmeter, due to the limited input impedance of the voltmeter, the measurement error caused by the input impedance of the voltmeter will be amplified. Summary of the Invention

[0013] The purpose of the present invention is to provide a shunt.

[0014] To achieve the above invention purpose, the present invention provides a shunt, including first and second constant current diodes, first and second zener diodes, and first and second operational amplifiers. The first constant current diode, the first zener diode, the second zener diode, and the second constant current diode are connected in sequence.

[0015] According to one aspect of the present invention, the cathode of the first constant current diode is connected to the cathode of the first zener diode, the anode of the first zener diode is connected to the cathode of the second zener diode, and the anode of the second zener diode is connected to the anode of the second constant current diode.

[0016] According to one aspect of the present invention, it further includes first and second triodes;

[0017] The first triode is an NPN type triode, the base is connected to the line where the first constant current diode and the first zener diode are connected, the collector is connected to the positive power supply line, and the emitter is connected to the positive power supply of the second operational amplifier;

[0018] The second triode is a PNP type triode, the base is connected to the line where the second zener diode and the second constant current diode are connected, the collector is connected to the negative power supply line, and the emitter is connected to the negative power supply of the second operational amplifier.

[0019] According to one aspect of the present invention, the anode of the first constant current diode and the positive power supply of the first operational amplifier are both connected to the positive power supply line;

[0020] The cathode of the second constant current diode and the negative power supply of the first operational amplifier are both connected to the negative power supply line.

[0021] According to one aspect of the present invention, the non-inverting input terminal of the first operational amplifier is connected to an input signal, and the inverting input terminal is connected to the output terminal;

[0022] The output terminal of the first operational amplifier is connected to the line where the first and second zener diodes are connected;

[0023] The non-inverting input terminal of the second operational amplifier is connected to an input signal, and the inverting input terminal is connected to the output terminal.

[0024] According to one aspect of the present invention, it further includes a resistor, one end of which is connected to the input signal line and the other end is grounded.

[0025] According to one aspect of the present invention, the first and second operational amplifiers are non-inverting proportional amplifiers with a feedback gain of 1.

[0026] According to the concept of the present invention, the existing precision AC-DC shunt is improved, and an active bipolar buffer amplifier is additionally equipped to change the output impedance of a high internal resistance source in a high-precision measurement system, so that it is transformed into a low internal resistance output. For the measurement of the shunt, the output impedance of a 1 mA shunt can be reduced, thereby reducing the influence of the load effect on the measurement error and realizing power amplification to improve the measurement system accuracy and system stability.

[0027] According to one solution of the present invention, a circuit topology of a composite operational amplifier is adopted to increase the open-loop gain of the operational amplifier, thereby reducing the static error caused by the open-loop gain.

[0028] According to one solution of the present invention, a bootstrap circuit topology is adopted, so that the median voltage of the input terminal of the second-stage operational amplifier is always consistent with the input terminal of the first-stage operational amplifier, making the difference between the input voltage and the reference voltage approximately equal to zero, so that the common-mode voltage and harmonic distortion will not cause a change in the offset voltage.

[0029] According to one solution of the present invention, devices with a smaller input capacitance are used. Specifically, operational amplifiers with a smaller input capacitance are selected, and the input capacitance of the operational amplifier needs to be less than 20 pF. And the PCB layout is reasonably designed, such as Figure 4 shown, so that the PCB traces are as short as possible to reduce the trace inductance. At the same time, an electric field wall (i.e., Figure 4 the equipotential ring in) is added to the main PCB circuit, which can reduce the electric field and capacitance, and make the electric field of each part of the circuit consistent, thereby reducing the parasitic capacitance between the circuit and the space. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematically shows the circuit schematic diagram of the shunt of an embodiment of the present invention;

[0031] Figure 2Schematic representation of the ideal shunt (no load) model diagram;

[0032] Figure 3 Schematic representation of the precise AC / DC shunt (with load) model diagram;

[0033] Figure 4 Schematic representation of the PCB layout design diagram. Detailed implementation manners

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0035] When describing the embodiments of the present invention, the orientation or positional relationships expressed by the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" are based on the orientation or positional relationships shown in the relevant accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting the present invention.

[0036] The present invention will be described in detail below in conjunction with the accompanying drawings and specific implementation manners. The implementation manners cannot be elaborated one by one here, but the implementation manners of the present invention are not limited to the following implementation manners.

[0037] See Figure 1 , the active dual-stage buffered precision AC / DC shunt of the present invention can be applied to the research on key technologies of wide-range electric power standards and value transfer, as well as the derivative technologies of precision AC / DC conversion shunt products, and is used for precision AC / DC current measurement to calibrate AC / DC current sources / meters, precision AC / DC I / V converters, sensors, current transformers, DC shunts, etc.

[0038] The shunt of the present invention includes first and second constant current diodes D1, D4, first and second zener diodes D2, D3, and first and second operational amplifiers A1, A2. Among them, the first constant current diode D1, the first zener diode D2, the second zener diode D3, and the second constant current diode D4 are connected in sequence. Specifically, the cathode of the first constant current diode D1 is connected to the cathode of the first zener diode D2, the anode of the first zener diode D2 is connected to the cathode of the second zener diode D3, and the anode of the second zener diode D3 is connected to the anode of the second constant current diode D4. The anode of the first constant current diode D1 and the positive power supply terminal of the first operational amplifier A1 are both connected to the positive power line. The cathode of the second constant current diode D4 and the negative power supply terminal of the first operational amplifier A1 are both connected to the negative power line. Among them, the positive power line and the negative power line can form a power supply rail of ±15V, and the first constant current diode D1, the first zener diode D2, the second zener diode D3, and the second constant current diode D4 can constitute a positive and negative constant voltage source circuit.

[0039] In the present invention, considering that the driving ability of the circuit is limited, first and second triodes Q1, Q2 are also provided in the shunt for power amplification, so as to provide positive and negative voltage sources for the second operational amplifier A2. Among them, the first triode Q1 is an NPN-type triode, the base is connected to the line connecting the first constant current diode D1 and the first zener diode D2, the collector is connected to the positive power line, and the emitter is connected to the positive power supply terminal of the second operational amplifier A2; the second triode Q2 is a PNP-type triode, the base is connected to the line connecting the second zener diode D3 and the second constant current diode D4, the collector is connected to the negative power line, and the emitter is connected to the negative power supply terminal of the second operational amplifier A2.

[0040] In the present invention, the non-inverting input terminal of the first operational amplifier A1 is connected to the input signal, and the inverting input terminal is connected to the output terminal. The output terminal of the first operational amplifier A1 is connected to the line connecting the first and second zener diodes D2, D3. The non-inverting input terminal of the second operational amplifier A2 is connected to the input signal, and the inverting input terminal is connected to the output terminal. Among them, the first and second operational amplifiers A1, A2 are non-inverting proportional amplifiers, and the feedback gain is 1.

[0041] The shunt of the present invention further includes a resistor R1 for impedance matching. One end of the resistor R1 is connected to the input signal line, and the other end is grounded. The setting of the resistor R1 can make the output terminal maintain zero potential when there is no signal input. And, since the bias current of the operational amplifier input terminal is related to the magnitude of the differential mode signal, after adding this resistor, the input impedance of the operational amplifier can be kept flat within the entire amplitude and frequency band range.

[0042] In summary, the shunt (or buffer amplifier) of the present invention adopts a two-stage voltage follower and is cascaded using the topology of a bootstrap circuit, which can improve the AC / DC difference and phase difference between the input signal and the output signal of the precision AC / DC shunt. The input impedance is greater than 10 MΩ, the input capacitance is less than 20 pF, the AC / DC difference between input and output @100 kHz is less than 100 μV, the phase difference between input and output @100 kHz is less than 50 μrad, and the input offset voltage is less than 100 μV.

[0043] The above description is only one embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A shunt, characterized in that, It includes a first and a second constant current diode (D1, D4), a first and a second voltage stabilizing diode (D2, D3), and a first and a second operational amplifier (A1, A2). The first constant current diode (D1), the first voltage stabilizing diode (D2), the second voltage stabilizing diode (D3), and the second constant current diode (D4) are connected in sequence; It further includes a first and a second triode (Q1, Q2); The first triode (Q1) is an NPN type triode, with its base connected to the line connecting the first constant current diode (D1) and the first voltage stabilizing diode (D2), its collector connected to the positive power supply line, and its emitter connected to the positive power supply terminal of the second operational amplifier (A2); The second triode (Q2) is a PNP type triode, with its base connected to the line connecting the second voltage stabilizing diode (D3) and the second constant current diode (D4), its collector connected to the negative power supply line, and its emitter connected to the negative power supply terminal of the second operational amplifier (A2); The anode of the first constant current diode (D1) and the positive power supply terminal of the first operational amplifier (A1) are both connected to the positive power supply line; The cathode of the second constant current diode (D4) and the negative power supply terminal of the first operational amplifier (A1) are both connected to the negative power supply line; The non-inverting input terminal of the first operational amplifier (A1) is connected to the input signal, and the inverting input terminal is connected to the output terminal; The output terminal of the first operational amplifier (A1) is connected to the line connecting the first and the second voltage stabilizing diodes (D2, D3); The non-inverting input terminal of the second operational amplifier (A2) is connected to the input signal, and the inverting input terminal is connected to the output terminal An active bipolar buffer amplifier is additionally equipped to change the output impedance of a high internal resistance source in a high-precision measurement system and transform it into a low internal resistance output.

2. The diverter according to claim 1, wherein The cathode of the first constant current diode (D1) is connected to the cathode of the first voltage stabilizing diode (D2), the anode of the first voltage stabilizing diode (D2) is connected to the cathode of the second voltage stabilizing diode (D3), and the anode of the second voltage stabilizing diode (D3) is connected to the anode of the second constant current diode (D4).

3. The diverter according to claim 1, characterized in that It further includes a resistor (R1), with one end of the resistor (R1) connected to the input signal line and the other end grounded.

4. The diverter according to claim 1, characterized in that, The first and the second operational amplifiers (A1, A2) are non-inverting proportional amplifiers with a feedback gain of 1.

Images