Range switching circuit, current detection circuit and alternating current measuring instrument

Abstract

The invention provides a range switching circuit, a current detection circuit and an alternating current measuring instrument, and relates to the technical field of electric measuring instruments. The range switching circuit comprises a current input port which comprises a positive terminal and a negative terminal; the current and voltage conversion unit comprises a plurality of range gating branches, each range gating branch comprises a primary coil, a dotted terminal of the primary coil is electrically connected with the positive terminal, and a synonym terminal of the primary coil is electrically connected with the negative terminal; the bidirectional voltage limiting circuit is connected in parallel with the current input port and comprises a positive voltage limiting circuit and a negative voltage limiting circuit which are connected in parallel; the input negative electrode of the compensation unit is electrically connected with the dotted terminal of the primary coil, and the input positive electrode and the output end of the compensation unit are electrically connected with the synonym terminal of the primary coil. According to the invention, the amplitude of current impact on the sampling resistor can be obviously reduced, the damage caused by inconsistent measuring range is avoided, and the overall reliability of the alternating current measuring instrument is improved.

Description

Technical Field

[0001] The present application relates to the technical field of electrical measuring instruments, and in particular to a range switching circuit, a current detection circuit and an alternating current measuring instrument. Background Art

[0002] In the related technology, the multi-range AC current to voltage conversion circuit composed of an electromagnetic current transformer with multiple primary windings combined with a high-precision sampling resistor has the advantages of low equivalent input impedance, low power consumption, a small number of high-precision sampling resistors, and a high signal-to-noise ratio. It is widely used in the field of AC current measuring instruments.

[0003] AC current measuring instruments usually divide wide dynamic currents, such as currents from 1mA to 100A, into multiple different ranges. Measuring with different ranges can improve measurement accuracy. For ease of use, multi-range AC current measuring instruments generally have an automatic range switching function. In an automatic test and inspection system composed of a programmable signal source, a high-specification electricity meter, a computer, etc., when the system is in standby or a low-specification electricity meter to be tested is connected to the system, the output of the test signal source will be turned off or set to zero. At this time, the range of the electricity meter will default to the lowest range. If the electricity meter suddenly receives a large current signal during the inspection process, the sampling resistor will be subjected to an energy shock hundreds or even tens of thousands of times relative to the correct range, which can easily cause damage to the electricity meter. Summary of the invention

[0004] The present application aims to solve at least one of the technical problems existing in the prior art or related art.

[0005] To this end, a first aspect of the present application proposes a range switching circuit.

[0006] A second aspect of the present application provides a current detection circuit.

[0007] A third aspect of the present application provides an alternating current measuring instrument.

[0008] In view of this, the first aspect of the present application provides a range switching circuit, including: a current input port, the current input port includes a positive terminal and a negative terminal; a current-to-voltage conversion unit, the current-to-voltage conversion unit includes multiple range selection branches, each range selection branch includes a primary coil, the same-name end of the primary coil is electrically connected to the positive terminal, and the opposite-name end of the primary coil is electrically connected to the negative terminal; a bidirectional voltage limiting circuit, the bidirectional voltage limiting circuit is connected in parallel with the current input port, the bidirectional voltage limiting circuit includes a positive voltage limiting circuit and a negative voltage limiting circuit connected in parallel, and the bidirectional voltage limiting circuit is used to limit the voltage peak of the current input port to a target voltage value; a compensation unit, the input negative pole of the compensation unit is electrically connected to the same-name end of the primary coil, the input positive pole and the output end of the compensation unit are both electrically connected to the opposite-name end of the primary coil, and the compensation unit is used to reduce the input impedance of the range selection branch so that the input current of the primary coil and the input current of the compensation unit meet a preset proportional relationship.

[0009] In this technical solution, the range switching circuit is applied to a current detection circuit with multiple ranges and an AC measuring instrument. Exemplarily, the AC measuring instrument includes a voltmeter, an ammeter, a power meter, etc. This application refers to the above-mentioned electrical measuring instrument as an electrical meter.

[0010] The range switching circuit includes a current input port, which is used to connect the electrical signal to be measured. The current-voltage conversion unit converts the input electrical signal into a detection electrical signal, and measures the current value of the detection signal through a high-precision sampling resistor, and finally obtains the current value of the electrical signal to be detected at the current input port.

[0011] The current-to-voltage conversion unit includes a plurality of range selection branches, wherein each range selection branch corresponds to a current detection range, such as a 0.1A range, a 10A range or a 100A range.

[0012] For example, the current-voltage conversion unit includes a primary winding and a secondary winding, wherein the primary winding includes a plurality of sub-coils, and each sub-coil corresponds to a range selection branch. Exemplarily, assuming that the number of ranges is 4, corresponding to 0.1A range, 1A range, 10A range and 100A range, respectively, correspondingly, the number of range selection branches and sub-coils are both 4, respectively recorded as the first sub-coil, the second sub-coil, the third sub-coil and the fourth sub-coil.

[0013] Assuming that the number of turns of the secondary coil is 2000T, the 0.1A range corresponds to 1000T of the winding turns of the first sub-coil, the 1A range corresponds to 100T of the winding turns of the second sub-coil, the 10A range corresponds to 10T of the winding turns of the third sub-coil, and the 100A range corresponds to 1T of the winding turns of the fourth sub-coil.

[0014] Exemplarily, the range gating branch also includes a switch device, and each range gating branch is provided with a switch device. For example, there are 4 current ranges, namely 0.1A range, 1A range, 10A range and 100A range, then the number of range gating branches is also 4, and the 4 range gating branches correspond to 0.1A range, 1A range, 10A range and 100A range respectively. Taking the range of 0.1A as an example, at this time, the switch device connected in series with the 0.1A range gating branch is closed, and the switch devices of the 1A range gating branch, the 10A range gating branch and the 100A range gating branch are all disconnected. Taking the range of 1A of the electric meter as an example, at this time, the second switch connected in series with the second sub-coil is closed, and the switch devices connected in series with the 0.1A range gating branch, the third sub-coil and the fourth sub-coil are all disconnected.

[0015] Exemplarily, the switching device may be a relay.

[0016] The bidirectional voltage limiting circuit is connected in parallel with the current input port. The voltage peak of the signal to be measured input through the current input port will be limited to a safe target voltage value under the action of the bidirectional voltage limiting circuit. Therefore, even if the electricity meter has not switched to the correct range at this time, since the voltage peak of the input signal is limited, the current applied to the sampling resistor after passing through the current-voltage conversion unit will not exceed the designed safety range, thereby preventing the sampling resistor from being subjected to power shocks far greater than the safety threshold and preventing the problem of the sampling resistor changing value and being damaged.

[0017] On this basis, the range switching circuit of the present application is also provided with a compensation unit, which is electrically connected to the primary coil of the range gating branch. The compensation unit can reduce the equivalent input impedance of the range gating branch connected thereto. Since the voltage peak of the input signal has been limited to a relatively low level by the bidirectional voltage limiting circuit, the input impedance of the range gating branch is reduced by superimposing the effect of reducing the input impedance of the range gating branch, so that no matter what range the current value level of the input current is in, and what the range range of the range gating branch is, the impact on the sampling resistor can be controlled to a relatively low range.

[0018] Exemplarily, the compensation unit can be connected to one or several range-enabling branches among a plurality of range-enabling branches. When a range-enabling branch is selected, the switch device on the range-enabling branch is closed, and at this time, the primary coil of the range-enabling branch is equivalent to being directly connected to the current input port. When the equivalent input impedance of a range-enabling branch does not meet the high-precision detection requirements, a compensation unit can be set for the range-enabling branch. Since only one range-enabling branch will work at the same time, when the equivalent input impedance of multiple range-enabling branches does not meet the high-precision detection requirements, these range-enabling branches can reuse the compensation unit.

[0019] Exemplarily, the range selection branch that reduces the input impedance through the compensation unit is defined as the compensated range LC-B, and the primary winding of the current transformer in the current-voltage conversion unit corresponding to the compensated range LC-B is called the compensated winding RZ-B. The input end of the compensation unit receives the input current through the contacts of the switching device of the compensated range LC-B, and the output end of the compensation unit is connected to the compensated winding RZ-B, and ensures that the current flowing into the compensated winding RZ-B is equal to or proportional to the current input to the compensation unit, that is, the above-mentioned preset proportional relationship.

[0020] Exemplarily, the preset ratio relationship is 1: 1. Exemplarily, the preset ratio relationship is 1: M, where M is a real number greater than zero.

[0021] The present application sets up a bidirectional voltage limiting circuit and a compensation unit. The bidirectional voltage limiting circuit can reduce the peak voltage of the input current, and the compensation unit can reduce the input impedance of the range selection branch. Therefore, when the input current does not match the selection range, the amplitude of the current impact on the sampling resistor can be significantly reduced, thereby avoiding damage to the current detection circuit or the AC measuring instrument due to range mismatch, and improving the overall reliability of the AC measuring instrument.

[0022] In addition, the range switching circuit in the above technical solution provided by the present application may also have the following additional technical features:

[0023] In some technical solutions of the present application, optionally, the compensation unit includes: a first op amp, the inverting input terminal of the first op amp is electrically connected to the positive terminal, and to the same-name terminal of the primary coil; the non-phase input terminal of the first op amp is electrically connected to a common reference point; the output terminal of the first op amp is electrically connected to the opposite-name terminal of the primary coil; wherein the common reference point is electrically connected to the negative terminal.

[0024] In the technical solution, the compensation unit specifically includes a first op amp, the inverting input of the first op amp is electrically connected to the positive terminal, illustratively, the range selection branch includes a switch device, and the inverting input of the first op amp is connected to the positive terminal of the current input port through the contact of the switch device. The inverting input of the first op amp is simultaneously connected to the same-name terminal of the primary coil of the compensated range selection branch. The positive-phase input of the first op amp is connected to a common reference point, wherein the common reference point is electrically connected to the negative terminal of the current input port, and its position is equal to that of the negative terminal. The output of the first op amp is connected to the opposite-name terminal of the primary coil of the compensated range selection branch.

[0025] Exemplarily, the first operational amplifier may be formed by cascading a general operational amplifier and a current expander, wherein the current expander can provide a current gain greater than or equal to 1, or provide a voltage gain greater than or equal to 1.

[0026] By setting the first operational amplifier to compensate the range selection branch, the input impedance of the small-range range selection branch can be effectively reduced. Combined with the limiting effect of the bidirectional voltage limiting circuit on the voltage peak of the input current, when the input current does not match the range, the impact of the large input current on the precision sampling resistor can be significantly reduced, thereby avoiding damage to the precision sampling resistor and improving reliability.

[0027] In some technical solutions of the present application, optionally, the compensation unit includes: a second op amp, a non-phase input terminal of the second op amp is electrically connected to the positive terminal, an inverting input terminal of the second op amp is electrically connected to the opposite-name terminal of the primary coil, and an output terminal of the second op amp is electrically connected to the same-name terminal of the primary coil; a first resistor, a first end of the first resistor is electrically connected to a common reference point, and a second end of the first resistor is electrically connected to the non-phase input terminal of the second op amp; a second resistor, a first end of the second resistor is electrically connected to the common reference point, and a second end of the second resistor is electrically connected to the inverting input terminal of the second op amp.

[0028] In the technical solution, the compensation unit specifically includes a second op amp, the non-phase input terminal of the second op amp is electrically connected to the positive terminal, and illustratively, the range selection branch includes a switch device, and the inverting input terminal of the first op amp is connected to the positive terminal of the current input port through the contact of the switch device. The inverting input terminal of the first op amp is connected to the opposite-name terminal of the primary coil of the compensated range selection branch. The output terminal of the first op amp is connected to the same-name terminal of the primary coil of the compensated range selection branch.

[0029] The first resistor is an input resistor of the non-inverting input terminal of the second op amp, one end of the first resistor is connected to the common reference point, and the other end of the first resistor is connected to the non-inverting input terminal of the second op amp. Exemplarily, the first resistor is connected in parallel between the positive input terminal of the second op amp and the common reference point. The second resistor is an input resistor of the direction input terminal of the second op amp, one section of the second resistor is connected to the common reference point, and the other end of the second resistor is connected to the inverting input terminal of the second op amp.

[0030] Exemplarily, the second operational amplifier may be formed by cascading a general operational amplifier and a current expander, wherein the current expander can provide a current gain greater than or equal to 1, or provide a voltage gain greater than or equal to 1.

[0031] The embodiment of the present application provides another circuit design structure of the compensation unit, which can also reduce the input impedance of the small-range range selection branch. Combined with the limiting effect of the bidirectional voltage limiting circuit on the voltage peak of the input current, it can significantly reduce the impact of the large input current on the precision sampling resistor, avoid damage to the precision sampling resistor, and improve reliability.

[0032] In some technical solutions of the present application, optionally, the forward voltage limiting circuit includes: a first clamping diode, the anode of the first clamping diode is electrically connected to the positive terminal; a first voltage limiting diode, the anode of the first voltage limiting diode is electrically connected to the cathode of the first clamping diode, and the cathode of the first voltage limiting diode is electrically connected to a common reference point; the negative voltage limiting circuit includes: a second clamping diode, the cathode of the second clamping diode is electrically connected to the positive terminal; a second voltage limiting diode, the cathode of the second voltage limiting diode is electrically connected to the anode of the second clamping diode, and the anode of the second voltage limiting diode is electrically connected to the common reference point; wherein, the common reference point is electrically connected to the negative terminal.

[0033] In this technical solution, the voltage limiting circuit includes a voltage limiting diode and a clamping diode connected in series. Among them, the first clamping diode and the first voltage limiting diode are connected in series to form a forward voltage limiting circuit, the second clamping diode and the second voltage limiting diode are connected in series to form a reverse voltage limiting circuit, and the forward voltage limiting circuit and the reverse voltage limiting circuit are connected in reverse parallel.

[0034] The first clamping diode is a forward clamping diode, and the first voltage limiting diode is a first voltage limiting diode. The anode of the first clamping diode is electrically connected to the positive terminal of the current input port, the cathode of the first clamping diode is electrically connected to the anode of the first voltage limiting diode, and the cathode of the first voltage limiting diode is electrically connected to the common reference point. The second clamping diode is a negative clamping diode, and the second voltage limiting diode is a negative voltage limiting diode. The cathode of the second clamping diode is electrically connected to the positive terminal of the current input port, the anode of the second clamping diode is electrically connected to the cathode of the second voltage limiting diode, and the anode of the second voltage limiting diode is electrically connected to the common reference point.

[0035] The common end of the first clamping diode and the first voltage limiting diode is led out to form a positive voltage limiting power supply +Vc, and the common end of the second clamping diode and the second voltage limiting diode is led out to form a negative voltage limiting power supply -Vc.

[0036] Exemplarily, the first clamping diode and the second clamping diode may be two diodes in an independent package, or may be components inside a half-bridge or full-bridge rectifier package.

[0037] For example, taking the scenario where a current input port is connected to a high current of 100A as an example, the voltage peak of the high current input from the current input port can be limited to a voltage value of 2×Vd1 through a bidirectional voltage limiting circuit, wherein Vd1 is the voltage drop across the diodes when the first clamping diode, the second clamping diode, the first voltage limiting diode, and the second voltage limiting diode flow a current of 100A in the forward direction. For example, Vd1 is approximately 1V.

[0038] Among them, the first clamping diode and the second clamping diode are always in reverse bias, and the leakage current is very small, accounting for much less than 1% of the error level and can be ignored.

[0039] The bidirectional voltage limiting circuit of the present application can effectively limit the peak voltage of the current input port, can reduce the amplitude of the current impact on the high-precision sampling resistor in the multi-range current-voltage conversion unit, ensure that the sampling resistor is not damaged, and can effectively improve the overall reliability of the instrument. At the same time, the leakage current of the bidirectional voltage limiting circuit is negligible compared with the current to be measured, and will not affect the measurement accuracy.

[0040] In some technical solutions of the present application, optionally, the bidirectional voltage limiting circuit also includes: a third resistor, a first end of the third resistor is electrically connected to the positive electrode of the first voltage limiting diode, and a second end of the third resistor is connected to the positive power supply signal; wherein the positive power supply signal applies a first current signal to the first voltage limiting diode through the third resistor; a fourth resistor, a first end of the fourth resistor is electrically connected to the negative electrode of the second voltage limiting diode, and a second end of the fourth resistor is connected to the negative power supply signal; wherein the negative power supply signal applies a second current signal to the second voltage limiting diode through the fourth resistor.

[0041] In this technical solution, the bidirectional voltage limiting circuit includes a third resistor and a fourth resistor, wherein the third resistor is connected in parallel between the positive power supply signal +Vcc and the positive voltage limiting power supply +Vc formed by the common end of the first clamping diode and the first voltage limiting diode. Specifically, one end of the third resistor is connected to the positive electrode of the first voltage limiting diode, and the other end receives the positive power supply signal.

[0042] The fourth resistor is connected in parallel between the negative power supply signal -Vcc and the negative voltage limiting power supply -Vc formed by the common end of the second clamping diode and the second voltage limiting diode. Specifically, one end of the fourth resistor is connected to the cathode of the second voltage limiting diode, and the other end receives the negative power supply signal.

[0043] Exemplarily, the positive power supply signal +Vcc and the negative power supply signal -Vcc are provided by an external power supply, and the external power supply applies current to the first voltage limiting diode and the second voltage limiting diode through the third resistor and the fourth resistor, that is, the first current signal and the second current signal. By applying the first current signal and the second current signal, a bias voltage Vd2 is generated on the two voltage limiting diodes respectively. Wherein, Vd2 is the absolute value of the voltage drop generated across the first voltage limiting diode and the second voltage limiting diode when a current of 0.3A flows in the forward direction. Exemplarily, Vd2 is approximately 0.5V.

[0044] By applying current to the first voltage limiting diode and the second voltage limiting diode, the first clamping diode and the second clamping diode are always in a reverse biased state when the range switching circuit is working normally, thereby effectively reducing the leakage current of the first clamping diode and the second clamping diode, thereby not having a negative impact on the detection accuracy of the current detection circuit and the AC measuring instrument.

[0045] In a technical solution of the present application, optionally, the current value of the first current signal is less than or equal to 300 mA; the current value of the second current signal is less than or equal to 300 mA.

[0046] In this technical solution, the current passing through the third resistor and the second resistor, that is, the current value of the first current signal and the second current signal, is less than or equal to 300mA. Exemplarily, the current value of the first current signal and the second current signal ranges from 1mA to 20mA. Among them, when the current value of the first current signal and the second current signal is larger, the difference between the clamping voltage and the operating voltage can be reduced. When the current value of the first current signal and the second current signal is set to be less than 300mA, the performance of the external power supply, the power consumption of the third resistor and the fourth resistor, and the cost can be taken into account.

[0047] In some technical solutions of the present application, optionally, the bidirectional voltage limiting circuit also includes: a follower circuit, the input end of the follower circuit is electrically connected to the positive terminal; the output end of the follower circuit is electrically connected to the positive electrode of the first voltage limiting diode, and to the negative electrode of the second voltage limiting diode.

[0048] In this technical solution, another method for reducing the leakage current of a bidirectional voltage limiting circuit is provided. Specifically, the bidirectional voltage limiting circuit includes a follower circuit, the input end of the follower is electrically connected to the positive terminal of the current input port, and the output end of the follower circuit is interconnected with the positive electrode of the first voltage limiting diode and the negative electrode of the second voltage limiting diode. The follower circuit can apply current to the first voltage limiting diode and the second voltage limiting diode, thereby generating a bias voltage Vd2, wherein Vd2 is the absolute value of the voltage drop generated at both ends of the diode when a current of 0.3A flows in the forward direction of the first voltage limiting diode and the second voltage limiting diode. Exemplarily, Vd2 is about 0.5V. By applying current to the first voltage limiting diode and the second voltage limiting diode, the first clamping diode and the second clamping diode are always in a reverse biased state when the range switching circuit is working normally, thereby effectively reducing the leakage current of the first clamping diode and the second clamping diode, so as not to have a negative impact on the detection accuracy of the current detection circuit and the AC measuring instrument.

[0049] By setting up a follower circuit, the bidirectional protection will not shunt the input current, thereby preventing the bidirectional protection circuit from affecting the accuracy of current detection, that is, it will not have a negative impact on the detection accuracy of the current detection circuit using the protection circuit.

[0050] In some technical schemes of the present application, optionally, the follower circuit includes: a third op amp, the positive input terminal of the third op amp is electrically connected to the positive terminal; a fifth resistor, the fifth resistor is connected in series between the positive input terminal and the positive terminal of the third op amp; a first capacitor, the first end of the first capacitor is electrically connected to the positive input terminal of the third op amp, and the second end of the first capacitor is electrically connected to a common reference point; a second capacitor, the first end of the second capacitor is electrically connected to the output terminal of the third op amp, and the second end of the second capacitor is electrically connected to the inverting input terminal of the third op amp; a sixth resistor, the first end of the sixth resistor is electrically connected to the output terminal of the third op amp, and the second end of the sixth resistor forms the output terminal of the follower circuit; a seventh resistor, the first end of the seventh resistor is electrically connected to the inverting input terminal of the third op amp, and the second end of the seventh resistor is electrically connected to the second end of the sixth resistor.

[0051] In the technical scheme, a specific circuit structure of a follower circuit is proposed. Wherein, the follower circuit includes a third op amp, a fifth resistor, a sixth resistor, a seventh resistor, a first capacitor and a second capacitor. The positive input terminal of the third op amp is connected to the positive terminal of the current input port, one end of the fifth resistor is electrically connected to the positive input terminal of the third op amp, the other end of the fifth resistor is electrically connected to the positive terminal of the current input port, and the fifth resistor is the input resistor of the third op amp. The first capacitor is connected in parallel between the same-direction input terminal of the third op amp and a common reference point. The fifth resistor and the first capacitor are combined at the input terminal of the third op amp to form a low-pass filter, thereby effectively improving the resistance performance of the third op amp and the follower circuit to high-frequency interference.

[0052] The second capacitor is connected in parallel between the inverting input terminal and the output terminal of the third amplifier. The sixth resistor and the seventh resistor are connected in series and connected at both ends of the second capacitor. The common point between the sixth resistor and the seventh resistor forms the output terminal of the follower circuit. The sixth resistor, the seventh resistor and the second capacitor can form a phase compensation for the third amplifier. Since the third amplifier has a corresponding phase shift effect on a signal of a certain frequency, such a signal will be fed back to the input terminal to make the amplifier circuit unstable or even oscillate. By setting the second capacitor and the third resistor to form a phase compensation, the phase shift effect of the third amplifier can be offset.

[0053] In some technical solutions of the present application, optionally, the range switching circuit also includes a state output circuit, which includes: a rectifier bridge, a first AC input terminal of the rectifier bridge is electrically connected to the output terminal of the third op amp, and a second AC input terminal of the rectifier bridge is electrically connected to a common reference point; an eighth resistor, a first end of the eighth resistor is electrically connected to the positive DC output terminal of the rectifier bridge; a first light-emitting diode, a positive electrode of the first light-emitting diode is electrically connected to the second end of the eighth resistor; a first digital isolator, an input positive electrode of the first digital isolator is electrically connected to a negative electrode of the first light-emitting diode, an input negative electrode of the first digital isolator is electrically connected to a rectifier output negative electrode of the rectifier bridge, and an output terminal of the first digital isolator is used to output a state signal; wherein the state signal is used to indicate the working state of the bidirectional voltage limiting circuit.

[0054] In this technical solution, the range switching circuit includes a state output circuit, which can indicate the working state of the bidirectional voltage limiting circuit by changing the indication state, indicating whether there is a large forward current in the bidirectional voltage limiting circuit, specifically indicating the clamping diodes, including whether a large current flows through the first clamping diode and the second clamping diode.

[0055] Exemplarily, the state output circuit includes a rectifier bridge, an eighth resistor, a first light-emitting diode and a first digital isolator. The rectifier bridge can be formed by connecting four diodes. The rectifier bridge includes two AC input terminals, specifically a first AC input terminal and a second AC input terminal. The first AC input terminal is connected to the output terminal of the third op amp, and the second AC input terminal is connected to a common reference point. The DC output positive electrode of the rectifier bridge is connected to the positive electrode of the first light-emitting diode through the eighth resistor, and the DC output negative electrode of the rectifier bridge is connected to the input negative electrode of the first digital isolator, and the input positive electrode of the first digital isolator is connected to the negative electrode of the first light-emitting diode. The output terminal of the first digital isolator can output a state signal.

[0056] Exemplarily, when a large forward current passes through the clamping diodes, including the first clamping diode and the second clamping diode, in the bidirectional voltage limiting circuit, the points of the forward input terminal and the inverting input terminal of the third op amp are not equal. At this time, the third op amp enters the comparator state, and the voltage at the output terminal of the operational amplifier will be close to the power supply voltage, thereby generating a voltage difference with the common reference point. After being rectified by the rectifier bridge, this part of the voltage difference drives the first light-emitting diode to switch from the extinguished state to the power state, thereby indicating through light that the current working state of the bidirectional voltage limiting circuit is a state of passing a large current. At the same time, the output of the first digital isolator will change from the cut-off state to the on state, and the state change will be formed as a state signal. When the controller detects the state signal, it is determined that the current working state of the bidirectional voltage limiting circuit is a state of passing a large current.

[0057] In some technical solutions of the present application, optionally, the range switching circuit also includes a state output circuit, which includes: a ninth resistor, a first end of the ninth resistor is electrically connected to the cathode of the first clamping diode; a transistor, a base of the transistor is electrically connected to the second end of the ninth resistor, and an emitter of the transistor is electrically connected to the anode of the second clamping diode; a tenth resistor, a first end of the tenth resistor is electrically connected to the base of the transistor, and a second end of the tenth resistor is electrically connected to the emitter of the transistor; an eleventh resistor, a first end of the eleventh resistor is connected to a positive power supply signal; a second light-emitting diode, a positive electrode of the second light-emitting diode is electrically connected to the second end of the eleventh resistor; a second digital isolator, an input cathode of the second digital isolator is electrically connected to the collector of the transistor, an input cathode of the second digital isolator is electrically connected to the cathode of the second light-emitting diode, and an output end of the second digital isolator is used to output a state signal; wherein the state signal is used to indicate the working state of the bidirectional voltage limiting circuit.

[0058] In this technical solution, a circuit structure of another state output circuit is provided. Specifically, the range switching circuit includes a state output circuit, which can indicate the working state of the bidirectional voltage limiting circuit by changing the indication state, indicating whether there is a large forward current in the bidirectional voltage limiting circuit, specifically indicating the clamping diodes, including whether a large current flows through the first clamping diode and the second clamping diode.

[0059] Exemplarily, the state output circuit includes a transistor, and exemplary, the transistor is an NPN transistor. The base of the transistor is connected to the first end of the ninth resistor and the first end of the tenth resistor. The second end of the ninth resistor is connected to the positive voltage limiting power supply +Vc formed by the common end of the first clamping diode and the first voltage limiting diode. The emitter of the transistor is connected to the negative voltage limiting power supply -Vc formed by the common end of the second clamping diode and the second voltage limiting diode, and is connected to the second end of the tenth resistor. The collector of the transistor is electrically connected to the negative input electrode of the second digital isolator.

[0060] The first end of the eleventh resistor is connected to the positive power supply signal +Vcc, and illustratively, the positive power supply signal is provided by an external power supply. The second end of the eleventh resistor is connected to the positive electrode of the second light-emitting diode, and the negative electrode of the second light-emitting diode is electrically connected to the input positive electrode of the second digital isolator. The output end of the second digital isolator is used to output a status signal.

[0061] Among them, the resistance values ​​of the ninth resistor and the tenth resistor ensure that the transistor is in the cut-off state when the current detection circuit is working normally. When a large forward current passes through the clamping diodes in the bidirectional voltage limiting circuit, including the first clamping diode and the second clamping diode, the transistor is turned on, driving the second light-emitting diode to switch from the off state to the power state, thereby indicating through light that the current working state of the bidirectional voltage limiting circuit is a state of passing a large current. At the same time, the output of the second digital isolator will change from the cut-off state to the on state, and this state change will form a state signal. When the controller detects the state signal, it is determined that the current working state of the bidirectional voltage limiting circuit is a state of passing a large current.

[0062] In some technical solutions of the present application, optionally, the range switching circuit also includes: a signal selection circuit, the input end of the signal selection circuit is electrically connected to the positive terminal, the signal selection circuit is used to output a shunt signal, wherein the current value of the shunt signal is associated with the current value of the input current shunted by the bidirectional voltage limiting circuit to the current input port; a state identification circuit, the state identification circuit is electrically connected to the output end of the signal selection circuit, the state identification circuit is used to output a corresponding level signal based on a comparison result of the current value of the shunt signal with a preset threshold value; a state output circuit, the state output circuit is electrically connected to the state identification circuit, the state output circuit includes an indication component, and the indication component is used to switch the indication state according to the level signal.

[0063] In this technical solution, the range switching circuit includes a signal selection circuit, a state identification circuit and a state output circuit. Among them, the signal selection circuit can select a signal associated with the shunt of the bidirectional voltage limiting circuit, that is, the above-mentioned shunt signal, and the shunt signal is compared with a preset threshold in the state identification circuit, so as to identify whether there is a shunt state in the bidirectional voltage limiting circuit, and output a level signal as a result. Exemplarily, the level signal is a high level signal or a low level signal. The level signal can drive the indicating component in the state output circuit to change the indicating state, wherein the indicating component can be a light-emitting diode, and the indicating state includes a light-emitting state or an off state.

[0064] In some technical solutions of the present application, optionally, the range switching circuit further includes: a current limiting resistor, and each range selection branch is electrically connected to the positive terminal via a current limiting resistor.

[0065] In this technical solution, the current-voltage conversion unit includes a plurality of range selection branches, wherein each range selection branch corresponds to a current detection range, such as a 0.1A range, a 10A range or a 100A range.

[0066] For example, the current-voltage conversion unit includes a primary winding and a secondary winding, wherein the primary winding includes a plurality of sub-coils, and each sub-coil corresponds to a range selection branch. Exemplarily, assuming that the number of ranges is 4, corresponding to 0.1A range, 1A range, 10A range and 100A range, respectively, correspondingly, the number of range selection branches and sub-coils are both 4, respectively recorded as the first sub-coil, the second sub-coil, the third sub-coil and the fourth sub-coil.

[0067] Assuming that the number of turns of the secondary coil is 2000T, the 0.1A range corresponds to 1000T of the winding turns of the first sub-coil, the 1A range corresponds to 100T of the winding turns of the second sub-coil, the 10A range corresponds to 10T of the winding turns of the third sub-coil, and the 100A range corresponds to 1T of the winding turns of the fourth sub-coil.

[0068] A current limiting resistor is connected in series on each range selection branch. The current limiting resistor can be regarded as a "dummy load". The input impedance of each current range can be increased through the current limiting resistor, so that when the corresponding current range is at full-scale input current, the voltage peak value Vs of the current input port is always equal to or slightly less than the power supply voltage Vc of the voltage limiting power supply in the voltage limiting circuit, that is, less than the protection limit value (Vc+Vd) of the voltage limiting circuit, thereby improving the reliability and accuracy of the electricity meter.

[0069] In some technical solutions of the present application, optionally, multiple range selection branches include a first range selection branch, the current limiting resistor includes a first current limiting resistor, and the first range selection branch is electrically connected to the positive terminal through the first current limiting resistor; wherein the resistance value of the first current limiting resistor is equal to the quotient of the first voltage and the maximum range current value of the first range selection branch; and the first voltage is the turn-on voltage of the first voltage limiting diode and the second voltage limiting diode.

[0070] In this technical solution, under the premise of ensuring that the shunt ratio of the input current by the bidirectional voltage limiting circuit is less than the shunt target value, the blocking of the current limiting resistor in each range selection branch is increased to ensure that the leakage current of the bidirectional voltage limiting circuit within the peak voltage of 0.5V is negligible. Exemplarily, the above-mentioned current limiting resistor can be replaced by a wire as a low-cost solution.

[0071] Among them, one of the multiple range gating branches is defined as the first range gating branch, and a first current limiting resistor is provided in the first range gating branch. Let the maximum range current value of the first range gating branch be I, let the resistance value of the first current limiting resistor be R, let the forward conduction voltage of the voltage limiting diode, including the first voltage limiting diode and the second voltage limiting diode, be V. Then R=V÷I.

[0072] The second aspect of the present application provides a current detection circuit, which includes a range switching circuit as provided in any of the above technical solutions, and therefore also includes the same technical effects. To avoid repetition, they will not be described here.

[0073] The third aspect of the present application provides an AC current measuring instrument, which includes a range switching circuit as provided in any of the above technical solutions; and / or includes a current detection circuit as provided in any of the above technical solutions, and therefore also includes the same technical effects. To avoid repetition, they will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0075] Figure 1 A circuit diagram of a range switching circuit of some embodiments of the present application is shown;

[0076] Figure 2 A circuit diagram of a range switching circuit of some embodiments of the present application is shown;

[0077] Figure 3 A circuit diagram of a range switching circuit of some embodiments of the present application is shown;

[0078] Figure 4 A local current schematic diagram of a bidirectional voltage limiting circuit of some embodiments of the present application is shown;

[0079] Figure 5 A circuit diagram showing a follower circuit of some embodiments of the present application;

[0080] Figure 6 A circuit diagram of a follower circuit of some embodiments of the present application is shown;

[0081] Figure 7 A circuit diagram showing a state output circuit of some embodiments of the present application;

[0082] Figure 8 A circuit diagram showing a state output circuit of some embodiments of the present application;

[0083] Fig. 9 Circuit diagrams of a signal selection circuit, a state identification circuit, and a state output circuit according to some embodiments of the present application are shown.

[0084] Reference numerals:

[0085] 100 range switching circuit, 102 current input port, 104 current-voltage conversion unit, 1042 range selection branch, 1044 primary coil, 106 bidirectional voltage limiting circuit, 1062 positive voltage limiting circuit, 1064 negative voltage limiting circuit, 1066 follower circuit, 108 compensation unit, 110 state output circuit, 1102 rectifier bridge, 112 signal selection circuit, 114 state recognition circuit;

[0086] I+ positive terminal, I- negative terminal, A2 first op amp, GR common reference point, A3 second op amp, R301 first resistor, R302 second resistor, D1 first clamping diode, D3 first voltage limiting diode, D2 second clamping diode, D4 ​​second voltage limiting diode, R11 third resistor, R12 fourth resistor, A6 third op amp, R21 fifth resistor, C21 first capacitor, C22 second capacitor, R22 sixth resistor, R23 seventh resistor, R7 eighth resistor, LED7 first light-emitting diode, G07 first digital isolator, R81 ninth resistor, Q8 transistor, R82 tenth resistor, R83 eleventh resistor, LED8 second light-emitting diode, G08 second digital isolator, Rc current limiting resistor. DETAILED DESCRIPTION

[0087] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0088] In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present application is not limited to the specific embodiments disclosed below.

[0089] Refer to the following Figures 1 to 9 The invention describes a range switching circuit, a current detection circuit and an alternating current measuring instrument provided according to some embodiments of the present application.

[0090] In some embodiments of the present application, a range switching circuit is provided. Figure 1 The circuit diagram of the range switching circuit 100 of some embodiments of the present application is shown as follows: Figure 1As shown, the range switching circuit 100 includes: a current input port 102, the current input port 102 includes a positive terminal I+ and a negative terminal I-; a current-to-voltage conversion unit 104, the current-to-voltage conversion unit 104 includes a plurality of range selection branches 1042, each range selection branch 1042 includes a primary coil 1044, the same-name end of the primary coil 1044 is electrically connected to the positive terminal I+, and the opposite-name end of the primary coil 1044 is electrically connected to the negative terminal I-; a bidirectional voltage limiting circuit 106, the bidirectional voltage limiting circuit 106 is connected in parallel with the current input port 102, and the bidirectional voltage limiting circuit 106 is connected in parallel with the current input port 102. 06 includes a positive voltage limiting circuit 1062 and a negative voltage limiting circuit 1064 connected in parallel, and the bidirectional voltage limiting circuit 106 is used to limit the voltage peak of the current input port 102 to a target voltage value; a compensation unit 108, the input negative pole of the compensation unit 108 is electrically connected to the same-name end of the primary coil 1044, and the input positive pole and output end of the compensation unit 108 are both electrically connected to the opposite-name end of the primary coil 1044. The compensation unit 108 is used to reduce the input impedance of the range selection branch 1042 so that the input current of the primary coil 1044 and the input current of the compensation unit 108 meet a preset proportional relationship.

[0091] In this embodiment, the range switching circuit 100 is applied to a current detection circuit with multiple ranges and an AC measuring instrument. Exemplarily, the AC measuring instrument includes a voltmeter, an ammeter, a power meter, etc. This application refers to the above-mentioned electrical measuring instrument as an electrical meter.

[0092] The range switching circuit 100 includes a current input port 102, which is used to connect the electrical signal to be measured. The current-voltage conversion unit 104 converts the input electrical signal into a detection electrical signal, and measures the current value of the detection signal through a high-precision sampling resistor Rs, and finally obtains the current value of the electrical signal to be detected at the current input port 102.

[0093] The current-to-voltage conversion unit 104 includes a plurality of range selection branches 1042 , wherein each range selection branch 1042 corresponds to a current detection range, such as a 0.1A range, a 10A range, or a 100A range.

[0094] For example, the current-to-voltage conversion unit 104 includes a primary winding and a secondary winding, wherein the primary winding includes a plurality of sub-coils, and each sub-coil corresponds to a range selection branch 1042. Exemplarily, assuming that the number of ranges is 4, corresponding to 0.1A range, 1A range, 10A range, and 100A range, respectively, correspondingly, the number of range selection branches 1042 and sub-coils are both 4, respectively recorded as the first sub-coil, the second sub-coil, the third sub-coil, and the fourth sub-coil.

[0095] Assuming that the number of turns of the secondary coil is 2000T, the 0.1A range corresponds to 1000T of the winding turns of the first sub-coil, the 1A range corresponds to 100T of the winding turns of the second sub-coil, the 10A range corresponds to 10T of the winding turns of the third sub-coil, and the 100A range corresponds to 1T of the winding turns of the fourth sub-coil.

[0096] Exemplarily, the range selection branch 1042 also includes a switch device, and each range selection branch 1042 is provided with a switch device. For example, there are 4 current ranges, namely 0.1A range, 1A range, 10A range and 100A range, then the number of range selection branches 1042 is also 4, and the 4 range selection branches 1042 correspond to 0.1A range, 1A range, 10A range and 100A range respectively. Taking the range of 0.1A as an example, at this time, the switch device connected in series with the 0.1A range selection branch 1042 is closed, and the switch devices of the 1A range selection branch 1042, the 10A range selection branch 1042 and the 100A range selection branch 1042 are all disconnected. Taking the electricity meter in the 1A range as an example, at this time, the second switch connected in series with the second sub-coil is closed, and the switch elements connected in series with the 0.1A range selection branch 1042, the third sub-coil and the fourth sub-coil are all disconnected.

[0097] Exemplarily, the switching device may be a relay.

[0098] For ease of use and to prevent users from selecting the wrong range, high-specification electricity meters are usually designed with automatic range switching. This not only reduces the probability of large currents entering low current ranges, but also avoids the problem of measuring small currents with large current ranges, resulting in reduced measurement accuracy, thereby giving full play to their high-precision measurement capabilities.

[0099] In the actual use of the power meter, when setting up the measurement system or after stopping the measurement, the user usually turns off the output of the test signal source or sets the output signal of the test signal source to zero. At this time, the power meter will automatically stay at the lowest range, such as the 0.1A range.

[0100] For example, taking the 0.1A range corresponding to the 1000T winding as an example, if the signal source suddenly outputs a large current, such as 12A of current, since the electricity meter needs a certain reaction time to switch the range, before the electricity meter switches to the corresponding 10A range, the 12A current will pass through the 1000T winding, and the primary of the transformer has 12000AT, which is 100 times the correct range. At this time, the current on the secondary side will also increase to 100 times the correct range. Since the power is proportional to the square of the current, this will cause the sampling resistor Rs to be forced to withstand a power impact of 10,000 times the correct range, which can easily cause the sampling resistor Rs to change in value and cause damage to the electricity meter.

[0101] The simple way of limiting voltage by anti-parallel diodes also has the hidden danger of leakage current affecting the accuracy of the bidirectional voltage limiting circuit. The reason is that when the circuit is working normally, one of the anti-parallel diodes is always in a forward biased state. Under the forward bias voltage at both ends of the diode, the current Id passing through it is Iss×(e (Vd / VT) -1), where Iss is the reverse saturation current of the diode, which is about 1μA, e is a natural constant, Vd is the on-state voltage of the diode, VT is the thermal voltage, and VT = k×Ta / q, where q is the electron charge, k is the Boltzmann constant, and Ta is the absolute thermodynamic temperature. At room temperature of 20°C, the thermal voltage is approximately equal to 25mV. Under the action of a forward voltage of 100mV, the diode leakage current is about 53μA, and the leakage current approximately doubles for every 10°C increase in temperature. Such a leakage current has seriously affected the measurement accuracy.

[0102] In view of the above problems, the present application sets a bidirectional voltage limiting circuit 106 in parallel with the current input port 102, and the voltage peak of the signal to be measured input through the current input port 102 will be limited to a safe target voltage value under the action of the bidirectional voltage limiting circuit 106. Therefore, even if the electricity meter has not switched to the correct range at this time, since the voltage peak of the input signal is limited, the current applied to the sampling resistor after passing through the current-voltage conversion unit 104 will not exceed the safety range of the design, thereby preventing the sampling resistor from being subjected to a power shock far greater than the safety threshold, and preventing the problem of the sampling resistor changing value and being damaged.

[0103] On this basis, the range switching circuit 100 of the present application is further provided with a compensation unit 108, and the compensation unit 108 is electrically connected to the primary coil 1044 of the range gating branch 1042. The compensation unit 108 can reduce the equivalent input impedance of the range gating branch 1042 connected thereto. Since the voltage peak of the input signal has been limited to a relatively low level by the bidirectional voltage limiting circuit 106, the input impedance of the range gating branch 1042 is reduced by superimposing the effect of reducing the input impedance, so that no matter what range the current value level of the input current is in, and what the range range of the range gating branch 1042 is, the impact on the sampling resistor can be controlled to a relatively low range.

[0104] Exemplarily, the compensation unit 108 can be connected to one or more of the multiple range selection branches 1042. When a range selection branch 1042 is selected, the switch device on the range selection branch 1042 is closed, and at this time, the primary coil 1044 of the range selection branch 1042 is equivalent to being directly connected to the current input port 102. When the equivalent input impedance of a range selection branch 1042 does not meet the high-precision detection requirements, the compensation unit 108 can be set for the range selection branch 1042. Since only one range selection branch 1042 will work at the same time, when the equivalent input impedance of multiple range selection branches 1042 does not meet the high-precision detection requirements, these range selection branches 1042 can reuse the compensation unit 108.

[0105] Exemplarily, the range selection branch 1042 that reduces the input impedance through the compensation unit 108 is defined as the compensated range LC-B, and the primary winding of the current transformer in the current-to-voltage conversion unit 104 corresponding to the compensated range LC-B is called the compensated winding RZ-B. The input end of the compensation unit 108 receives the input current through the contacts of the switching device of the compensated range LC-B, and the output end of the compensation unit 108 is connected to the compensated winding RZ-B, and ensures that the current flowing into the compensated winding RZ-B is equal to or proportional to the current input to the compensation unit 108, which is the above-mentioned preset proportional relationship.

[0106] Exemplarily, the preset ratio relationship is 1: 1. Exemplarily, the preset ratio relationship is 1: M, where M is a real number greater than zero.

[0107] The present application sets a bidirectional voltage limiting circuit 106 and a compensation unit 108. The bidirectional voltage limiting circuit 106 can reduce the peak voltage of the input current, and the compensation unit 108 can reduce the input impedance of the range selection branch 1042. Therefore, when the input current does not match the selection range, the amplitude of the current impact on the sampling resistor can be significantly reduced, thereby avoiding damage to the current detection circuit or the AC measuring instrument due to range mismatch, and improving the overall reliability of the AC measuring instrument.

[0108] In some embodiments of the present application, optionally, Figure 2 A circuit diagram of a range switching circuit of some embodiments of the present application is shown, such as Figure 2 As shown, the compensation unit 108 includes: a first op amp A2, the inverting input terminal of the first op amp A2 is electrically connected to the positive terminal I+, and to the same-name terminal of the primary coil 1044; the non-phase input terminal of the first op amp A2 is electrically connected to the common reference point GR; the output terminal of the first op amp A2 is electrically connected to the opposite-name terminal of the primary coil 1044; wherein the common reference point GR is electrically connected to the negative terminal I-.

[0109] In this embodiment, the compensation unit 108 specifically includes a first amplifier A2, the inverting input terminal of the first amplifier A2 is electrically connected to the positive terminal I+, and illustratively, the range selection branch 1042 includes a switch device, and the inverting input terminal of the first amplifier A2 is connected to the positive terminal I+ of the current input port 102 through the contact of the switch device. The inverting input terminal of the first amplifier A2 is also connected to the same-name terminal of the primary coil 1044 of the compensated range selection branch 1042. The positive-phase input terminal of the first amplifier A2 is connected to a common reference point GR, wherein the common reference point GR is electrically connected to the negative terminal I- of the current input port 102, and its point position is equal to the point position of the negative terminal I-. The output terminal of the first amplifier A2 is connected to the opposite-name terminal of the primary coil 1044 of the compensated range selection branch 1042.

[0110] Exemplarily, the first operational amplifier A2 may be formed by cascading a general operational amplifier and a current expander, wherein the current expander can provide a current gain greater than or equal to 1, or provide a voltage gain greater than or equal to 1.

[0111] By setting the first operational amplifier A2 to compensate the range selection branch 1042, the input impedance of the small-range range selection branch 1042 can be effectively reduced. Combined with the limiting effect of the bidirectional voltage limiting circuit 106 on the voltage peak of the input current, when the input current does not match the range, the impact of the large input current on the precision sampling resistor can be significantly reduced, thereby avoiding damage to the precision sampling resistor and improving reliability.

[0112] In some embodiments of the present application, optionally, Figure 3 A circuit diagram of a range switching circuit of some embodiments of the present application is shown, such as Figure 3 As shown, the compensation unit 108 includes: a second operational amplifier A3, a non-phase input terminal of the second operational amplifier A3 is electrically connected to the positive terminal I+, an inverting input terminal of the second operational amplifier A3 is electrically connected to the opposite-name terminal of the primary coil 1044, and an output terminal of the second operational amplifier A3 is electrically connected to the same-name terminal of the primary coil 1044; a first resistor R301, a first end of the first resistor R301 is electrically connected to the common reference point GR, and a second end of the first resistor R301 is electrically connected to the non-phase input terminal of the second operational amplifier A3; a second resistor R302, a first end of the second resistor R302 is electrically connected to the common reference point GR, and a second end of the second resistor R302 is electrically connected to the inverting input terminal of the second operational amplifier A3.

[0113] In this embodiment, the compensation unit 108 specifically includes a second op amp A3, the non-inverting input terminal of the second op amp A3 is electrically connected to the positive terminal I+, and illustratively, the range selection branch 1042 includes a switch device, and the inverting input terminal of the first op amp A2 is connected to the positive terminal I+ of the current input port 102 through the contact of the switch device. The inverting input terminal of the first op amp A2 is connected to the opposite-name terminal of the primary coil 1044 of the compensated range selection branch 1042. The output terminal of the first op amp A2 is connected to the same-name terminal of the primary coil 1044 of the compensated range selection branch 1042.

[0114] The first resistor R301 is an input resistor of the non-inverting input terminal of the second amplifier A3, one end of the first resistor R301 is connected to the common reference point GR, and the other end of the first resistor R301 is connected to the non-inverting input terminal of the second amplifier A3. Exemplarily, the first resistor R301 is connected in parallel between the positive input terminal of the second amplifier A3 and the common reference point GR. The second resistor R302 is an input resistor of the direction input terminal of the second amplifier A3, one section of the second resistor R302 is connected to the common reference point GR, and the other end of the second resistor R302 is connected to the inverting input terminal of the second amplifier A3.

[0115] Exemplarily, the second operational amplifier A3 may be formed by cascading a general operational amplifier and a current expander, wherein the current expander can provide a current gain greater than or equal to 1, or provide a voltage gain greater than or equal to 1.

[0116] The embodiment of the present application provides another circuit design structure of the compensation unit 108, which can also reduce the input impedance of the small-range range selection branch 1042. Combined with the limiting effect of the bidirectional voltage limiting circuit 106 on the voltage peak of the input current, it can significantly reduce the impact of the large input current on the precision sampling resistor, avoid damage to the precision sampling resistor, and improve reliability.

[0117] In some embodiments of the present application, optionally, Figure 1 As shown, the forward voltage limiting circuit 1062 includes: a first clamping diode D1, the anode of the first clamping diode D1 is electrically connected to the positive terminal I+; a first voltage limiting diode D3, the anode of the first voltage limiting diode is electrically connected to the cathode of the first clamping diode D1, and the cathode of the first voltage limiting diode D3 is electrically connected to the common reference point GR; the negative voltage limiting circuit 1064 includes: a second clamping diode D2, the cathode of the second clamping diode D2 is electrically connected to the positive terminal I+; a second voltage limiting diode D4, the cathode of the second voltage limiting diode D4 is electrically connected to the anode of the second clamping diode D2, and the anode of the second voltage limiting diode D4 is electrically connected to the common reference point GR; wherein, the common reference point GR is electrically connected to the negative terminal I-.

[0118] In this embodiment, the voltage limiting circuit includes a voltage limiting diode and a clamping diode connected in series. The first clamping diode D1 and the first voltage limiting diode D3 are connected in series to form a forward voltage limiting circuit 1062, the second clamping diode D2 and the second voltage limiting diode D4 are connected in series to form a reverse voltage limiting circuit, and the forward voltage limiting circuit 1062 and the reverse voltage limiting circuit are connected in reverse parallel.

[0119] The first clamping diode D1 is a forward clamping diode, and the first voltage limiting diode D3 is a first voltage limiting diode. The anode of the first clamping diode D1 is electrically connected to the positive terminal I+ of the current input port 102, the cathode of the first clamping diode D1 is electrically connected to the anode of the first voltage limiting diode D3, and the cathode of the first voltage limiting diode D3 is electrically connected to the common reference point GR. The second clamping diode D2 is a negative clamping diode, and the second voltage limiting diode D4 is a negative voltage limiting diode. The cathode of the second clamping diode D2 is electrically connected to the positive terminal I+ of the current input port 102, the anode of the second clamping diode D2 is electrically connected to the cathode of the second voltage limiting diode D4, and the anode of the second voltage limiting diode D4 is electrically connected to the common reference point GR.

[0120] The common end of the first clamping diode D1 and the first voltage limiting diode D3 is led out to form a positive voltage limiting power supply +Vc, and the common end of the second clamping diode D2 and the second voltage limiting diode D4 is led out to form a negative voltage limiting power supply -Vc.

[0121] Exemplarily, the first clamping diode D1 and the second clamping diode D2 may be two diodes in an independent package, or may be components inside a half-bridge or full-bridge rectifier package.

[0122] For example, taking the scenario where the current input port 102 is connected to a high current of 100A as an example, the voltage peak of the high current input from the current input port 102 can be limited to a voltage value of 2×Vd1 through the bidirectional voltage limiting circuit 106, where Vd1 is the voltage drop across the first clamping diode D1, the second clamping diode D2, the first voltage limiting diode D3, and the second voltage limiting diode D4 when a current of 100A flows in the forward direction. For example, Vd1 is about 1V.

[0123] Among them, the first clamping diode D1 and the second clamping diode D2 are always in reverse bias, and the leakage current is very small, accounting for much less than 1% of the error level and can be ignored.

[0124] The bidirectional voltage limiting circuit 106 of the present application can effectively limit the peak voltage of the current input port 102, can reduce the amplitude of the current impact on the high-precision sampling resistor in the multi-range current-voltage conversion unit 104, ensure that the sampling resistor is not damaged, and can effectively improve the overall reliability of the instrument. At the same time, the leakage current of the bidirectional voltage limiting circuit 106 is negligible compared with the current to be measured, and will not affect the measurement accuracy.

[0125] In some embodiments of the present application, optionally, Figure 4 A partial current schematic diagram of a bidirectional voltage limiting circuit of some embodiments of the present application is shown, such as Figure 1 and Figure 4 As shown, the bidirectional voltage limiting circuit 106 also includes: a third resistor R11, a first end of the third resistor R11 is electrically connected to the positive electrode of the first voltage limiting diode D3, and a second end of the third resistor R11 is connected to the positive power supply signal; wherein the positive power supply signal applies a first current signal to the first voltage limiting diode D3 through the third resistor R11; a fourth resistor R12, a first end of the fourth resistor R12 is electrically connected to the negative electrode of the second voltage limiting diode D4, and a second end of the fourth resistor R12 is connected to the negative power supply signal; wherein the negative power supply signal applies a second current signal to the second voltage limiting diode D4 through the fourth resistor R12.

[0126] In this embodiment, the bidirectional voltage limiting circuit 106 includes a third resistor R11 and a fourth resistor R12, wherein the third resistor R11 is connected in parallel between the positive power supply signal +Vcc and the positive voltage limiting power supply +Vc formed by the common end of the first clamping diode D1 and the first voltage limiting diode D3. Specifically, one end of the third resistor R11 is connected to the positive electrode of the first voltage limiting diode D3, and the other end receives the positive power supply signal.

[0127] The fourth resistor R12 is connected in parallel between the negative power supply signal -Vcc and the negative voltage limiting power supply -Vc formed by the common end of the second clamping diode D2 and the second voltage limiting diode D4. Specifically, one end of the fourth resistor R12 is connected to the cathode of the second voltage limiting diode D4, and the other end receives the negative power supply signal.

[0128] Exemplarily, the positive power supply signal +Vcc and the negative power supply signal -Vcc are provided by an external power supply, and the external power supply applies current, i.e., the first current signal and the second current signal, to the first voltage limiting diode D3 and the second voltage limiting diode D4 through the third resistor R11 and the fourth resistor R12. By applying the first current signal and the second current signal, a bias voltage Vd2 is generated on the two voltage limiting diodes, respectively. Wherein, Vd2 is the absolute value of the voltage drop generated across the first voltage limiting diode D3 and the second voltage limiting diode D4 when a current of 0.3A flows in the forward direction. Exemplarily, Vd2 is approximately 0.5V.

[0129] By applying current to the first voltage limiting diode D3 and the second voltage limiting diode D4, when the range switching circuit 100 is working normally, the first clamping diode D1 and the second clamping diode D2 are always in a reverse biased state, thereby effectively reducing the leakage current of the first clamping diode D1 and the second clamping diode D2, thereby not having a negative impact on the detection accuracy of the current detection circuit and the AC measuring instrument.

[0130] In an embodiment of the present application, optionally, the current value of the first current signal is less than or equal to 300 mA; the current value of the second current signal is less than or equal to 300 mA.

[0131] In this embodiment, the current passing through the third resistor R11 and the second resistor R302, that is, the current value of the first current signal and the second current signal, is less than or equal to 300mA. Exemplarily, the current value of the first current signal and the second current signal ranges from 1mA to 20mA. Among them, when the current value of the first current signal and the second current signal is larger, the difference between the clamping voltage and the operating voltage can be reduced. When the current value of the first current signal and the second current signal is set to be less than 300mA, the performance of the external power supply, the power consumption of the third resistor R11 and the fourth resistor R12, and the cost can be taken into account.

[0132] In some embodiments of the present application, optionally, Figure 5 A circuit diagram of a follower circuit of some embodiments of the present application is shown, such as Figure 1 and Figure 5 As shown, the bidirectional voltage limiting circuit 106 also includes: a follower circuit 1066, the input end of the follower circuit 1066 is electrically connected to the positive terminal I+; the output end of the follower circuit 1066 is electrically connected to the positive electrode of the first voltage limiting diode D3, and is electrically connected to the negative electrode of the second voltage limiting diode D4.

[0133] In this embodiment, another method for reducing the leakage current of the bidirectional voltage limiting circuit 106 is provided. Specifically, the bidirectional voltage limiting circuit 106 includes a follower circuit 1066, the input end of the follower is electrically connected to the positive terminal I+ of the current input port 102, and the output end of the follower circuit 1066 is interconnected with the positive electrode of the first voltage limiting diode D3 and the negative electrode of the second voltage limiting diode D4. Through the follower circuit 1066, current can be applied to the first voltage limiting diode D3 and the second voltage limiting diode D4, thereby generating a bias voltage Vd2, wherein Vd2 is the absolute value of the voltage drop generated across the diodes when a current of 0.3A flows in the forward direction of the first voltage limiting diode D3 and the second voltage limiting diode D4. Exemplarily, Vd2 is approximately 0.5V. By applying current to the first voltage limiting diode D3 and the second voltage limiting diode D4, when the range switching circuit 100 is working normally, the first clamping diode D1 and the second clamping diode D2 are always in a reverse biased state, thereby effectively reducing the leakage current of the first clamping diode D1 and the second clamping diode D2, thereby not having a negative impact on the detection accuracy of the current detection circuit and the AC measuring instrument.

[0134] By setting the follower circuit 1066, the bidirectional protection will not shunt the input current, thereby preventing the bidirectional protection circuit from affecting the accuracy of current detection, that is, it will not have a negative impact on the detection accuracy of the current detection circuit using the protection circuit.

[0135] In some embodiments of the present application, optionally, Figure 6 A circuit diagram of a follower circuit of some embodiments of the present application is shown, such as Figure 6 As shown, the follower circuit 1066 includes: a third operational amplifier A6, the positive input terminal of the third operational amplifier A6 is electrically connected to the positive terminal I+; a fifth resistor R21, the fifth resistor R21 is connected in series between the positive input terminal of the third operational amplifier A6 and the positive terminal I+; a first capacitor C21, the first end of the first capacitor C21 is electrically connected to the positive input terminal of the third operational amplifier A6, and the second end of the first capacitor C21 is electrically connected to the common reference point GR; a second capacitor C22, the first end of the second capacitor C22 is electrically connected to the first capacitor C21, and the second end of the first capacitor C21 is electrically connected to the common reference point GR; The output end of the third operational amplifier A6 is electrically connected, and the second end of the second capacitor C22 is electrically connected to the inverting input end of the third operational amplifier A6; the sixth resistor R22, the first end of the sixth resistor R22 is electrically connected to the output end of the third operational amplifier A6, and the second end of the sixth resistor R22 forms the output end of the follower circuit 1066; the seventh resistor R23, the first end of the seventh resistor R23 is electrically connected to the inverting input end of the third operational amplifier A6, and the second end of the seventh resistor R23 is electrically connected to the second end of the sixth resistor R22.

[0136] In this embodiment, a specific circuit structure of a follower circuit 1066 is proposed. Wherein, the follower circuit 1066 includes a third amplifier A6, a fifth resistor R21, a sixth resistor R22, a seventh resistor R23, a first capacitor C21 and a second capacitor C22. The positive input terminal of the third amplifier A6 is connected to the positive terminal I+ of the current input port 102, one end of the fifth resistor R21 is electrically connected to the positive input terminal of the third amplifier A6, the other end of the fifth resistor R21 is electrically connected to the positive terminal I+ of the current input port 102, and the fifth resistor R21 is the input resistance of the third amplifier A6. The first capacitor C21 is connected in parallel between the same direction input terminal of the third amplifier A6 and the common reference point GR. The fifth resistor R21 and the first capacitor C21 are combined at the input terminal of the third amplifier A6 to form a low-pass filter, thereby effectively improving the resistance performance of the third amplifier A6 and the follower circuit to high-frequency interference.

[0137] The second capacitor C22 is connected in parallel between the inverting input terminal and the output terminal of the third amplifier A6. The sixth resistor R22 and the seventh resistor R23 are connected in series and connected at the two ends of the second capacitor C22. Wherein, the common point between the sixth resistor R22 and the seventh resistor R23 forms the output terminal of the follower circuit 1066. The sixth resistor R22, the seventh resistor R23 and the second capacitor C22 can form the phase compensation of the third amplifier A6. Wherein, because the third amplifier A6 has a corresponding phase shift effect on the signal of a certain frequency, such a signal is fed back to the input terminal to make the amplifier circuit unstable or even oscillate, and the phase shift effect of the third amplifier A6 can be offset by arranging the second capacitor C22 and the third resistor R11 to form phase compensation.

[0138] In some embodiments of the present application, optionally, Figure 7 A circuit diagram of a state output circuit of some embodiments of the present application is shown, such as Figure 1 , Figure 6 and Figure 7As shown, the range switching circuit 100 also includes a state output circuit 110, which includes: a rectifier bridge 1102, a first AC input terminal of the rectifier bridge 1102 is electrically connected to the output terminal of the third operational amplifier A6, and a second AC input terminal of the rectifier bridge 1102 is electrically connected to the common reference point GR; an eighth resistor R7, a first end of the eighth resistor R7 is electrically connected to the DC output positive electrode of the rectifier bridge 1102; a first light-emitting diode LED7, a positive electrode of the first light-emitting diode LED7 is electrically connected to the second end of the eighth resistor R7; a first digital isolator G07, an input positive electrode of the first digital isolator G07 is electrically connected to the cathode of the first light-emitting diode LED7, an input cathode of the first digital isolator G07 is electrically connected to the rectifier output cathode of the rectifier bridge 1102, and an output terminal of the first digital isolator G07 is used to output a state signal; wherein the state signal is used to indicate the working state of the bidirectional voltage limiting circuit 106.

[0139] In this embodiment, the range switching circuit 100 includes a state output circuit 110, which can indicate the working state of the bidirectional voltage limiting circuit 106 by changing the indication state, indicating whether there is a large forward current in the bidirectional voltage limiting circuit 106, specifically indicating whether a large current flows through the clamping diodes, including the first clamping diode D1 and the second clamping diode D2.

[0140] Exemplarily, the state output circuit 110 includes a rectifier bridge 1102, an eighth resistor R7, a first light-emitting diode LED7 and a first digital isolator G07. The rectifier bridge 1102 can be formed by connecting four diodes. The rectifier bridge 1102 includes two AC input terminals, specifically a first AC input terminal and a second AC input terminal. The first AC input terminal is connected to the output terminal of the third op amp A6, and the second AC input terminal is connected to the common reference point GR. The DC output positive electrode of the rectifier bridge 1102 is connected to the positive electrode of the first light-emitting diode LED7 through the eighth resistor R7, and the DC output negative electrode of the rectifier bridge 1102 is connected to the input negative electrode of the first digital isolator G07, and the input positive electrode of the first digital isolator G07 is connected to the negative electrode of the first light-emitting diode LED7. The output terminal of the first digital isolator G07 can output a state signal.

[0141] Exemplarily, when a large forward current passes through the clamping diodes in the bidirectional voltage limiting circuit 106, including the first clamping diode D1 and the second clamping diode D2, the points of the forward input terminal and the inverting input terminal of the third op amp A6 are not equal. At this time, the third op amp A6 enters the comparator state, and the voltage at the output terminal of the operational amplifier will be close to the power supply voltage, thereby generating a voltage difference with the common reference point GR. After being rectified by the rectifier bridge 1102, this part of the voltage difference drives the first light-emitting diode LED7 to switch from the off state to the power state, thereby indicating that the current working state of the bidirectional voltage limiting circuit 106 is a state of passing a large current by emitting light. At the same time, the output of the first digital isolator G07 will change from the cut-off state to the on state, and this state change will form a state signal. When the controller detects the state signal, it is determined that the current working state of the bidirectional voltage limiting circuit 106 is a state of passing a large current.

[0142] In some embodiments of the present application, optionally, Figure 8 A circuit diagram of a state output circuit of some embodiments of the present application is shown, such as Figure 1 and Figure 8 As shown, the range switching circuit 100 also includes a state output circuit 110, which includes: a ninth resistor R81, a first end of the ninth resistor R81 is electrically connected to the cathode of the first clamping diode D1; a transistor Q8, a base of the transistor Q8 is electrically connected to the second end of the ninth resistor R81, and an emitter of the transistor Q8 is electrically connected to the anode of the second clamping diode D2; a tenth resistor R82, a first end of the tenth resistor R82 is electrically connected to the base of the transistor Q8, and a second end of the tenth resistor R82 is electrically connected to the emitter of the transistor Q8; an eleventh resistor R83, the first end of the eleventh resistor R83 is connected to the positive power supply signal; the second light-emitting diode LED8, the positive electrode of the second light-emitting diode LED8 is electrically connected to the second end of the eleventh resistor R83; the second digital isolator G08, the input negative electrode of the second digital isolator G08 is electrically connected to the collector of the transistor Q8, the input positive electrode of the second digital isolator G08 is electrically connected to the negative electrode of the second light-emitting diode LED8, and the output end of the second digital isolator G08 is used to output a status signal; wherein, the status signal is used to indicate the working status of the bidirectional voltage limiting circuit 106.

[0143] In this embodiment, another circuit structure of a state output circuit 110 is provided. Specifically, the range switching circuit 100 includes a state output circuit 110. The state output circuit 110 can indicate the working state of the bidirectional voltage limiting circuit 106 by changing the indication state, indicating whether there is a large forward current in the bidirectional voltage limiting circuit 106, specifically indicating whether a large current flows through the clamping diodes, including the first clamping diode D1 and the second clamping diode D2.

[0144] Exemplarily, the state output circuit 110 includes a transistor Q8, and exemplary, the transistor Q8 is an NPN transistor Q8. The base of the transistor Q8 is connected to the first end of the ninth resistor R81, and is also connected to the first end of the tenth resistor R82. The second end of the ninth resistor R81 is connected to the positive voltage limiting power supply +Vc formed by the common end of the first clamping diode D1 and the first voltage limiting diode D3. The emitter of the transistor Q8 is connected to the negative voltage limiting power supply -Vc formed by the common end of the second clamping diode D2 and the second voltage limiting diode D4, and is also connected to the second end of the tenth resistor R82. The collector of the transistor Q8 is electrically connected to the negative input electrode of the second digital isolator G08.

[0145] The first end of the eleventh resistor R83 is connected to the positive power supply signal +Vcc, and illustratively, the positive power supply signal is provided by an external power supply. The second end of the eleventh resistor R83 is connected to the positive electrode of the second light-emitting diode LED8, and the cathode of the second light-emitting diode LED8 is electrically connected to the input positive electrode of the second digital isolator G08. The output end of the second digital isolator G08 is used to output a state signal.

[0146] Among them, the resistance values ​​of the ninth resistor R81 and the tenth resistor R82 ensure that the transistor Q8 is in the cut-off state when the current detection circuit is working normally. When a large forward current passes through the clamping diodes in the bidirectional voltage limiting circuit 106, including the first clamping diode D1 and the second clamping diode D2, the transistor Q8 is turned on, driving the second light-emitting diode LED8 to switch from the off state to the power state, thereby indicating through light that the current working state of the bidirectional voltage limiting circuit 106 is a state of passing a large current. At the same time, the output of the second digital isolator G08 will change from the cut-off state to the on state, and the state change will be formed as a state signal. When the controller detects the state signal, it is determined that the current working state of the bidirectional voltage limiting circuit 106 is a state of passing a large current.

[0147] In some embodiments of the present application, optionally, Fig. 9 The circuit diagrams of the signal selection circuit, the state identification circuit and the state output circuit of some embodiments of the present application are shown as follows: Figure 1 and Fig. 9As shown, the range switching circuit 100 also includes: a signal selection circuit 112, the input end of the signal selection circuit 112 is electrically connected to the positive terminal I+, and the signal selection circuit 112 is used to output a shunt signal, wherein the current value of the shunt signal is associated with the current value of the input current shunted by the bidirectional voltage limiting circuit 106 to the current input port 102; a state identification circuit 114, the state identification circuit 114 is electrically connected to the output end of the signal selection circuit 112, and the state identification circuit 114 is used to output a corresponding level signal according to a comparison result between the current value of the shunt signal and a preset threshold value; a state output circuit 110, the state output circuit 110 is electrically connected to the state identification circuit 114, and the state output circuit 110 includes an indication component, and the indication component is used to switch the indication state according to the level signal.

[0148] In this embodiment, the range switching circuit 100 includes a signal selection circuit 112, a state identification circuit 114 and a state output circuit 110. The signal selection circuit 112 can select a signal associated with the shunting of the bidirectional voltage limiting circuit 106, that is, the above-mentioned shunting signal, and the shunting signal is compared with a preset threshold in the state identification circuit 114, so as to identify whether there is a shunting state in the bidirectional voltage limiting circuit 106, and output a resulting level signal. Exemplarily, the level signal is a high level signal or a low level signal. The level signal can drive the indicating component in the state output circuit 110 to change the indicating state, wherein the indicating component can be a light emitting diode, and the indicating state includes a light emitting state or an off state.

[0149] For example, Fig. 9 As shown, the signal selection circuit 112 includes an operational amplifier A91, a non-inverting input terminal of the operational amplifier A91 is electrically connected to the positive terminal I+, and an inverting input terminal of the operational amplifier A91 is electrically connected to the output terminal of the operational amplifier A91.

[0150] The state identification circuit 114 includes an amplifier A92 and an amplifier A93, and also includes a resistor R91, a resistor R92, a resistor R93 and a resistor R94. The resistor R91 is connected in series with the resistor R92, and the output end of the amplifier A91 is electrically connected to the resistor R91, and is connected to the negative terminal I- through the resistor R91 and the resistor R92. The positive input end of the amplifier A92 is connected to the signal -Vc, the negative input end of the amplifier A92 is electrically connected to the common end of the resistor R91 and the resistor R92, and the output end of the amplifier A92 is connected to the first end of the resistor R93.

[0151] The non-inverting input terminal of the amplifier A93 is electrically connected to the inverting input terminal of the amplifier A92, and the inverting input terminal of the amplifier A93 is connected to the signal +Vc. The output terminal of the amplifier A93 is connected to the first terminal of the resistor R94. The second terminal of the resistor R94 is connected to the second terminal of the resistor R93.

[0152] The state output circuit 110 includes a digital isolator G09 and a light emitting diode LED9. The positive electrode of the light emitting diode is electrically connected to the common end of the resistor R94 and the resistor R93, the negative electrode of the light emitting diode LED9 is electrically connected to the positive input of the digital isolator G09, and the negative input of the digital isolator is connected to the external power supply signal -Vcc.

[0153] In some embodiments of the present application, optionally, Figure 1 As shown, the range switching circuit 100 also includes: a current limiting resistor Rc, and each range selection branch 1042 is electrically connected to the positive terminal I+ through a current limiting resistor Rc.

[0154] In this embodiment, the current-to-voltage conversion unit 104 includes a plurality of range selection branches 1042 , wherein each range selection branch 1042 corresponds to a current detection range, such as a 0.1A range, a 10A range, or a 100A range.

[0155] For example, the current-to-voltage conversion unit 104 includes a primary winding and a secondary winding, wherein the primary winding includes a plurality of sub-coils, and each sub-coil corresponds to a range selection branch 1042. Exemplarily, assuming that the number of ranges is 4, corresponding to 0.1A range, 1A range, 10A range, and 100A range, respectively, correspondingly, the number of range selection branches 1042 and sub-coils are both 4, respectively recorded as the first sub-coil, the second sub-coil, the third sub-coil, and the fourth sub-coil.

[0156] Assuming that the number of turns of the secondary coil is 2000T, the 0.1A range corresponds to 1000T of the winding turns of the first sub-coil, the 1A range corresponds to 100T of the winding turns of the second sub-coil, the 10A range corresponds to 10T of the winding turns of the third sub-coil, and the 100A range corresponds to 1T of the winding turns of the fourth sub-coil.

[0157] A current limiting resistor Rc is connected in series on each range selection branch 1042. The current limiting resistor Rc can be regarded as a "dummy load". The input impedance of each current range can be increased by the current limiting resistor Rc, so that when the corresponding current range is at full-scale input current, the voltage peak value Vs of the current input port 102 is always equal to or slightly less than the power supply voltage Vc of the voltage limiting power supply in the voltage limiting circuit, that is, less than the protection limit value (Vc+Vd) of the voltage limiting circuit, thereby improving the reliability and accuracy of the electricity meter.

[0158] In some embodiments of the present application, optionally, Figure 1As shown, the multiple range selection branches 1042 include a first range selection branch 1042, the current limiting resistor Rc includes a first current limiting resistor, and the first range selection branch 1042 is electrically connected to the positive terminal I+ through the first current limiting resistor; wherein the resistance value of the first current limiting resistor is equal to the quotient of the first voltage and the maximum range current value of the first range selection branch 1042; the first voltage is the turn-on voltage of the first voltage limiting diode D3 and the second voltage limiting diode D4.

[0159] In this embodiment, under the premise of ensuring that the shunting ratio of the input current by the bidirectional voltage limiting circuit 106 is less than the shunting target value, the blocking of the current limiting resistor Rc in each range selection branch 1042 is increased to ensure that the leakage current of the bidirectional voltage limiting circuit 106 within the peak voltage of 0.5V is negligible. Exemplarily, the above-mentioned current limiting resistor Rc can be replaced by a wire as a low-cost solution.

[0160] Among them, one range selection branch 1042 among the multiple range selection branches 1042 is defined as the first range selection branch 1042, and a first current limiting resistor is provided in the first range selection branch 1042. Assume that the maximum range current value of the first range selection branch 1042 is I, the resistance value of the first current limiting resistor is R, and the forward conduction voltage of the voltage limiting diode, including the first voltage limiting diode D3 and the second voltage limiting diode D4, is V. Then R=V÷I.

[0161] The second aspect of the present application provides a current detection circuit, which includes a range switching circuit as provided in any of the above embodiments, which can significantly reduce the amplitude of the current impact on the high-precision sampling resistor and can control the current impact within 4 times the normal current peak value, thereby significantly improving the overall reliability of the instrument.

[0162] At the same time, the compensation unit is used to reduce the input impedance of the small current range. The design of the bidirectional voltage limiting circuit is simple and low-cost, and the small current range is fully protected. Moreover, the bidirectional voltage limiting circuit basically does not shunt the input current, so it will not have a negative impact on the detection accuracy, and can ensure the detection accuracy of the current detection circuit.

[0163] The third aspect of the present application provides an AC current measuring instrument, which includes a range switching circuit as provided in any of the above embodiments; and / or includes a current detection circuit as provided in any of the above embodiments, and therefore also includes the same technical effects, which will not be repeated here to avoid repetition.

[0164] In the description of this application, the term "plurality" refers to two or more than two. Unless otherwise clearly defined, the terms "upper" and "lower" indicate positions or positional relationships based on the positions or positional relationships described in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on this application. The terms "connect", "install", "fixed", etc. should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0165] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "specific embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0166] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A range switching circuit, characterized in that: include: A current input port, the current input port comprising a positive terminal and a negative terminal; A current-to-voltage conversion unit, the current-to-voltage conversion unit comprising a plurality of range gating branches, each of the range gating branches comprising a primary coil, a like-name end of the primary coil being electrically connected to the positive terminal, and an opposite-name end of the primary coil being electrically connected to the negative terminal; a bidirectional voltage limiting circuit, the bidirectional voltage limiting circuit being connected in parallel with the current input port, the bidirectional voltage limiting circuit comprising a positive voltage limiting circuit and a negative voltage limiting circuit connected in parallel, the bidirectional voltage limiting circuit being used to limit a voltage peak value of the current input port to a target voltage value; A compensation unit, wherein the input negative pole of the compensation unit is electrically connected to the same-name end of the primary coil, the input positive pole and the output end of the compensation unit are both electrically connected to the opposite-name end of the primary coil, and the compensation unit is used to reduce the input impedance of the range selection branch so that the input current of the primary coil and the input current of the compensation unit meet a preset proportional relationship.

2. The range switching circuit according to claim 1, characterized in that: The compensation unit comprises: A first operational amplifier, wherein an inverting input terminal of the first operational amplifier is electrically connected to the positive terminal and to the same-name terminal of the primary coil; a non-inverting input terminal of the first operational amplifier is electrically connected to a common reference point; and an output terminal of the first operational amplifier is electrically connected to the opposite-name terminal of the primary coil; Wherein, the common reference point is electrically connected to the negative terminal.

3. The range switching circuit according to claim 2, characterized in that: The compensation unit comprises: A second operational amplifier, wherein a non-phase input terminal of the second operational amplifier is electrically connected to the positive terminal, an inverting input terminal of the second operational amplifier is electrically connected to the opposite-name terminal of the primary coil, and an output terminal of the second operational amplifier is electrically connected to the same-name terminal of the primary coil; a first resistor, wherein a first end of the first resistor is electrically connected to the common reference point, and a second end of the first resistor is electrically connected to a non-inverting input terminal of the second operational amplifier; A second resistor, wherein a first end of the second resistor is electrically connected to the common reference point, and a second end of the second resistor is electrically connected to the inverting input terminal of the second operational amplifier.

4. The range switching circuit according to claim 1, characterized in that: The forward voltage limiting circuit comprises: a first clamping diode, wherein an anode of the first clamping diode is electrically connected to the anode terminal; a first voltage limiting diode, wherein an anode of the first voltage limiting diode is electrically connected to a cathode of the first clamping diode, and a cathode of the first voltage limiting diode is electrically connected to a common reference point; The negative voltage limiting circuit comprises: a second clamping diode, wherein a cathode of the second clamping diode is electrically connected to the anode terminal; a second voltage limiting diode, wherein a cathode of the second voltage limiting diode is electrically connected to an anode of the second clamping diode, and an anode of the second voltage limiting diode is electrically connected to the common reference point; Wherein, the common reference point is electrically connected to the negative terminal.

5. The range switching circuit according to claim 4, characterized in that: The bidirectional voltage limiting circuit also includes: a third resistor, wherein a first end of the third resistor is electrically connected to the anode of the first voltage limiting diode, and a second end of the third resistor is connected to a positive power supply signal; wherein the positive power supply signal applies a first current signal to the first voltage limiting diode through the third resistor; A fourth resistor, wherein a first end of the fourth resistor is electrically connected to the cathode of the second voltage limiting diode, and a second end of the fourth resistor is connected to a negative power supply signal; wherein the negative power supply signal applies a second current signal to the second voltage limiting diode through the fourth resistor.

6. The range switching circuit according to claim 5, characterized in that: The current value of the first current signal is less than or equal to 300 mA; the current value of the second current signal is less than or equal to 300 mA.

7. The range switching circuit according to claim 4, characterized in that: The bidirectional voltage limiting circuit also includes: A follower circuit, wherein the input end of the follower circuit is electrically connected to the positive terminal; the output end of the follower circuit is electrically connected to the positive electrode of the first voltage limiting diode, and is electrically connected to the negative electrode of the second voltage limiting diode.

8. The range switching circuit according to claim 7, characterized in that: The follower circuit comprises: A third operational amplifier, wherein a positive input terminal of the third operational amplifier is electrically connected to the positive terminal; a fifth resistor, the fifth resistor being connected in series between the positive input terminal of the third operational amplifier and the positive terminal; a first capacitor, wherein a first end of the first capacitor is electrically connected to a positive input end of the third operational amplifier, and a second end of the first capacitor is electrically connected to the common reference point; A second capacitor, wherein a first end of the second capacitor is electrically connected to the output end of the third operational amplifier, and a second end of the second capacitor is electrically connected to the inverting input end of the third operational amplifier; a sixth resistor, wherein a first end of the sixth resistor is electrically connected to the output end of the third operational amplifier, and a second end of the sixth resistor is formed as the output end of the follower circuit; A seventh resistor, wherein a first end of the seventh resistor is electrically connected to the inverting input end of the third operational amplifier, and a second end of the seventh resistor is electrically connected to the second end of the sixth resistor.

9. The range switching circuit according to claim 8, characterized in that: The range switching circuit also includes a state output circuit, and the state output circuit includes: A rectifier bridge, wherein a first AC input terminal of the rectifier bridge is electrically connected to an output terminal of the third operational amplifier, and a second AC input terminal of the rectifier bridge is electrically connected to the common reference point; an eighth resistor, a first end of the eighth resistor being electrically connected to the DC output positive electrode of the rectifier bridge; a first light emitting diode, wherein an anode of the first light emitting diode is electrically connected to a second end of the eighth resistor; A first digital isolator, wherein the input positive electrode of the first digital isolator is electrically connected to the cathode of the first light-emitting diode, the input negative electrode of the first digital isolator is electrically connected to the rectifier output negative electrode of the rectifier bridge, and the output end of the first digital isolator is used to output a state signal; wherein the state signal is used to indicate the working state of the bidirectional voltage limiting circuit.

10. The range switching circuit according to any one of claims 5 to 8, characterized in that: The range switching circuit also includes a state output circuit, and the state output circuit includes: a ninth resistor, wherein a first end of the ninth resistor is electrically connected to a cathode of the first clamping diode; a transistor, wherein the base of the transistor is electrically connected to the second end of the ninth resistor, and the emitter of the transistor is electrically connected to the anode of the second clamping diode; a tenth resistor, wherein a first end of the tenth resistor is electrically connected to the base of the transistor, and a second end of the tenth resistor is electrically connected to the emitter of the transistor; an eleventh resistor, a first end of the eleventh resistor being connected to a positive power supply signal; a second light emitting diode, wherein the anode of the second light emitting diode is electrically connected to the second end of the eleventh resistor; A second digital isolator, wherein the negative input electrode of the second digital isolator is electrically connected to the collector of the transistor, the positive input electrode of the second digital isolator is electrically connected to the cathode of the second light-emitting diode, and the output end of the second digital isolator is used to output a status signal; wherein the status signal is used to indicate the working status of the bidirectional voltage limiting circuit.

11. The range switching circuit according to any one of claims 4 to 8, characterized in that: Also includes: a signal selection circuit, wherein an input end of the signal selection circuit is electrically connected to the positive terminal, and the signal selection circuit is used to output a shunt signal, wherein a current value of the shunt signal is associated with a current value of an input current of the current input port shunted by the bidirectional voltage limiting circuit; A state identification circuit, the state identification circuit is electrically connected to the output end of the signal selection circuit, and the state identification circuit is used to output a corresponding level signal according to a comparison result between the current value of the shunt signal and a preset threshold value; A state output circuit is electrically connected to the state identification circuit, and the state output circuit includes an indication component, and the indication component is used to switch the indication state according to the level signal.

12. The range switching circuit according to any one of claims 4 to 9, characterized in that: Also includes: Current limiting resistor, each of the range selection branches is electrically connected to the positive terminal through a current limiting resistor.

13. The range switching circuit according to claim 12, characterized in that: The plurality of range gating branches include a first range gating branch, the current limiting resistor includes a first current limiting resistor, and the first range gating branch is electrically connected to the positive terminal through the first current limiting resistor; The resistance value of the first current limiting resistor is equal to the quotient of the first voltage and the maximum range current value of the first range selection branch; the first voltage is the conduction voltage of the first voltage limiting diode and the second voltage limiting diode.

14. A current detection circuit, characterized in that: include: A range switching circuit as claimed in any one of claims 1 to 13.

15. An alternating current measuring instrument, characterized in that: include: The range switching circuit according to any one of claims 1 to 13; and / or The current sensing circuit as claimed in claim 14.

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