A current detection circuit

Abstract

The utility model relates to a kind of current detection circuit, including including sampling circuit, operational amplifier circuit, the operational amplifier circuit includes input resistance R2, operational amplifier U1A, filter circuit, output resistance R4, the filter circuit includes filter resistance R3, filter capacitor C1, the resistance R2 one end connects sampling input end, the other end connects the negative pole of operational amplifier U1A, the output resistance R4 one end connects the operational amplifier U1A and is outputted, the other end as the total output end of the current detection circuit, the filter circuit is connected to the negative pole and operational amplifier output end of operational amplifier U1A in parallel. The circuit uses single operational amplifier, simplifies circuit structure, significantly reduces cost, saves the limited space of circuit board, and circuit protection is better, efficacy is remarkable, is suitable for the current detection of large-scale electrical appliance.

Description

Technical Field

[0001] This utility model relates to the field of current and voltage detection technology, and specifically to a current detection circuit. Background Technology

[0002] Remote monitoring of aerator pumps in large-scale fishponds is achieved through a communication module connected to a server. The system transmits the collected operating current and voltage data of the aerator pumps to the server in real time. By analyzing the current and voltage, faults are identified or protection mechanisms are activated. Users can remotely view the operating status information of the aerator pumps, including voltage and current, and can also remotely monitor and operate them. In the event of various faults or power outages, timely feedback can be provided to the user. Typically, fishponds cover tens or hundreds of acres, requiring a large number of aerator pumps. Therefore, a controller that can control more aerator pumps is more competitive.

[0003] For one control circuit, at least four currents need to be detected, including three-phase current and zero-sequence current. Each current detection circuit requires a current transformer, sampling current, signal conditioning circuit, protection circuit, etc., necessitating a large number of electronic components. For example, Figure 1 This diagram illustrates a conventional AC current detection circuit. The current induced by the AC transformer CT1 is sampled as a voltage by resistor R6. This voltage is then converted from negative to positive by a precision absolute voltage circuit composed of operational amplifiers U3A and U3B, and diodes D1 and D3. Finally, it is filtered into DC by a low-pass filter composed of R2 and C1, and then fed into the AD detection port of the MCU / DSP. R5 and D2 are used for input port protection and to prevent the input voltage from exceeding VREF, which could affect the accuracy of the ADC. This circuit has the following drawbacks:

[0004] 1) The op-amp requires dual power supply, which requires an additional circuit for a negative power supply and increases costs.

[0005] 2) Precision absolute circuits require two operational amplifiers and at least seven components, including resistors, diodes, and capacitors.

[0006] 3) The current is measured using the average value method, and the effective value is calculated by converting the effective value and average value of the sinusoidal signal, rather than by actually calculating the true effective value through integration. When there are harmonics in the mains power, there will be a relatively large deviation from the reading of the true effective value meter. Utility Model Content

[0007] In view of this, a current detection circuit with simplified circuit structure, good efficiency and low cost is provided.

[0008] A current detection circuit includes a sampling circuit and an operational amplifier circuit. The operational amplifier circuit includes an input resistor R2, an operational amplifier U1A, a filter circuit, and an output resistor R4. The filter circuit includes a filter resistor R3 and a filter capacitor C1. One end of the resistor R2 is connected to the sampling input terminal, and the other end is connected to the negative terminal of the operational amplifier U1A. One end of the output resistor R4 is connected to the operational amplifier output terminal of the operational amplifier U1A, and the other end serves as the total output terminal of the current detection circuit. The filter circuit is connected in parallel to the negative terminal of the operational amplifier U1A and the operational amplifier output terminal.

[0009] Preferably, the positive terminal of the operational amplifier U1A is connected to at least one signal conditioning circuit. Each signal conditioning circuit includes a voltage divider resistor R5, a resistor R6, and a filter capacitor C3. The resistor R6 and the filter capacitor C3 are connected in parallel and then in series with the voltage divider resistor R5. One end of the voltage divider resistor R5 is connected to the positive terminal of the operational amplifier U1A, and the other end is connected to the parallel circuit of the resistor R6 and the filter capacitor C3. The other end of the parallel circuit is grounded.

[0010] Preferably, the current detection circuit includes an AC transformer CT1 for sensing the current to be measured, and the sampling circuit includes a sampling resistor R1. One end of the sampling resistor R1 is connected to the inflow end (1) of the AC transformer CT1 and the input resistor R2, and the other end is grounded at the outflow end (2) of the AC transformer CT1.

[0011] Preferably, a branch of the output terminal of the output resistor R4 is connected to a capacitor C2, with one end of the capacitor C2 connected between the output terminal of the output resistor R4 and the total output terminal, and the other end grounded.

[0012] Preferably, the operational amplifier U1A is an LM224 operational amplifier and is powered by a 5V voltage. Its full-amplitude output voltage is 3.6V, which is lower than the MCU power supply voltage.

[0013] Preferably, the input resistor R2 and the output resistor R4 have the same or similar resistance values, and the filter resistor R3 has a resistance value that is ten times or more than that of the input resistor R2.

[0014] Preferably, the positive voltage input at the non-inverting input of the operational amplifier U1A raises the AC signal to above 0V, to half of the MCU's operating voltage, which is 3.3V. The MCU samples n points at equal intervals within one 20ms cycle of the mains power to calculate the true RMS value of the current.

[0015] Preferably, when the rated AC signal output by the operational amplifier U1A is 1.76V peak-to-peak, the voltage signal input to the MCU is an AC signal with a peak value of 1.76V superimposed on a DC level of 1.62V. At this time, the minimum input voltage of the MCU is 0.74V and the maximum input voltage is 2.50V.

[0016] Preferably, the resistance value of the voltage divider resistor R5 is the same as or close to the resistance value of the filter resistor R3, and the resistance value of the filter voltage divider resistor R5 is twenty times or more than that of the resistor R6.

[0017] Furthermore, the AC transformer CT1 is used to sense the current to be measured in the oxygenation pump.

[0018] The above-described current detection circuit has at least the following advantages:

[0019] It has the following advantages:

[0020] 1) It adopts an operational amplifier that can be powered by a single power supply, which saves one op-amp compared to the traditional circuit, simplifies the circuit structure, and reduces the circuit cost. It is especially useful for remote monitoring of aerator pumps in large-scale fish ponds. Large fish ponds also use a large number of aerator pumps, which can significantly reduce costs.

[0021] 2) Only AC signal amplification is needed, without the need for complex absolute value circuits. Complex calculations are implemented by software algorithms, and the signal conditioning circuits for each channel are fewer than those of traditional absolute value circuits.

[0022] 3) Due to the limitations of the casing size and cost, every inch of space on the PCB board is precious. After the improvement, each component occupies less than 1 / 4 of the panel space before the improvement.

[0023] 4) The operational amplifier can be powered by 5V, and its full-amplitude output voltage will not exceed the MCU supply voltage. This not only saves one protection diode, but also provides better input protection than the improved diode-based input protection, resulting in better circuit efficiency. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a traditional mains current detection circuit.

[0025] Figure 2 This is a schematic diagram of a current detection circuit provided in an embodiment of the present invention. Detailed Implementation

[0026] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present utility model. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present utility model without creative effort are within the protection scope of the present utility model.

[0027] Please see Figure 2 This illustration shows a current detection circuit provided by an embodiment of the present invention, including a sampling circuit and an operational amplifier circuit. The operational amplifier circuit includes an input resistor R2, an operational amplifier U1A, a filter circuit, and an output resistor R4. The filter circuit includes a filter resistor R3 and a filter capacitor C1. One end of the resistor R2 is connected to the sampling input terminal, and the other end is connected to the negative terminal of the operational amplifier U1A. One end of the output resistor R4 is connected to the operational amplifier output terminal of the operational amplifier U1A, and the other end serves as the total output terminal of the current detection circuit. The filter circuit is connected in parallel to the negative terminal of the operational amplifier U1A and the operational amplifier output terminal.

[0028] As shown in the figure, preferably, the positive terminal of the operational amplifier U1A is connected to at least one signal conditioning circuit. Each signal conditioning circuit includes a voltage divider resistor R5, a resistor R6, and a filter capacitor C3. The resistor R6 and the filter capacitor C3 are connected in parallel and then connected in series with the voltage divider resistor R5. One end of the voltage divider resistor R5 is connected to the positive terminal of the operational amplifier U1A, and the other end is connected to the parallel circuit of the resistor R6 and the filter capacitor C3. The other end of the parallel circuit is grounded.

[0029] Preferably, the current detection circuit includes an AC transformer CT1 for sensing the current to be measured. The sampling circuit includes a sampling resistor R1, one end of which is connected to both the inflow terminal (1) and the input resistor R2 of the AC transformer CT1, and the other end is grounded simultaneously with the outflow terminal (2) of the AC transformer CT1. Further, the AC transformer CT1 is used to sense the current to be measured from the aerator pump. Since there are usually multiple aerator pumps in a fishpond, the battery monitoring and control of each aerator pump requires the detection of at least four currents, including three-phase current and zero-sequence current. The current detection circuit described above in this embodiment can be used for the detection of each current.

[0030] Preferably, a branch of the output terminal of the output resistor R4 is connected to a capacitor C2, with one end of the capacitor C2 connected between the output terminal of the output resistor R4 and the total output terminal, and the other end grounded.

[0031] Preferably, the operational amplifier U1A is an LM224 operational amplifier powered by 5V, and its full-amplitude output voltage is 3.6V, which is lower than the MCU power supply voltage. More preferably, the positive voltage input to the non-inverting input of the operational amplifier U1A boosts the AC signal to above 0V, to half of the MCU's operating voltage. The MCU's operating voltage is 3.3V. Within one 20ms cycle of the mains power, the MCU samples n points at equal intervals to calculate the true RMS value of the current.

[0032] Preferably, the input resistor R2 and the output resistor R4 have the same or similar resistance values, and the filter resistor R3 has a resistance value that is ten times or more than that of the input resistor R2. More preferably, when the rated AC signal output by the operational amplifier U1A is 1.76V peak-to-peak, the voltage signal input to the MCU is an AC signal with a peak value of 1.76V superimposed on a DC level of 1.62V. At this time, the minimum input voltage of the MCU is 0.74V, and the maximum input voltage is 2.50V.

[0033] Preferably, the resistance value of the voltage divider resistor R5 is the same as or close to the resistance value of the filter resistor R3, and the resistance value of the filter voltage divider resistor R5 is twenty times or more than that of the resistor R6.

[0034] The above-described current detection circuit has at least the following advantages:

[0035] 1) It adopts an operational amplifier U1A that can be powered by a single power supply, which saves one op-amp compared with the traditional circuit and simplifies the circuit structure;

[0036] 2) Only AC signal amplification is needed, without the need for complex absolute value circuits. Complex calculations are implemented by software algorithms, and the signal conditioning circuits for each channel are fewer than those of traditional absolute value circuits.

[0037] 3) Due to the limitations of the casing size and cost, every inch of space on the PCB board is precious. After the improvement, each component occupies less than 1 / 4 of the panel space before the improvement.

[0038] 4) The LM224 op-amp is powered by 5V, and its full-amplitude output voltage is 5V-1.4V=3.6V, which will not exceed the MCU supply voltage of 3.3V+0.3V. This not only saves one protection diode, but also provides better input protection than the improved diode-based input protection.

[0039] It should be noted that this utility model is not limited to the above-described embodiments. Based on the inventive spirit of this utility model, those skilled in the art can make other changes, and these changes made based on the inventive spirit of this utility model should be included within the scope of protection claimed by this utility model.

Claims

1. A current detection circuit, comprising a sampling circuit and an operational amplifier circuit, characterized in that, The operational amplifier circuit includes an input resistor R2, an operational amplifier U1A, a filter circuit, and an output resistor R4. The filter circuit includes a filter resistor R3 and a filter capacitor C1. One end of the resistor R2 is connected to the sampling input terminal, and the other end is connected to the negative terminal of the operational amplifier U1A. One end of the output resistor R4 is connected to the operational amplifier output terminal of the operational amplifier U1A, and the other end serves as the total output terminal of the current detection circuit. The filter circuit is connected in parallel to the negative terminal of the operational amplifier U1A and the operational amplifier output terminal.

2. The current detection circuit as described in claim 1, characterized in that, The positive terminal of the operational amplifier U1A is connected to at least one signal conditioning circuit. Each signal conditioning circuit includes a voltage divider resistor R5, a resistor R6, and a filter capacitor C3. The resistor R6 and the filter capacitor C3 are connected in parallel and then in series with the voltage divider resistor R5. One end of the voltage divider resistor R5 is connected to the MCU power supply terminal, and the other end is connected to the parallel circuit of the resistor R6 and the filter capacitor C3. The other end of the parallel circuit is grounded.

3. The current detection circuit as described in claim 1, characterized in that, The current detection circuit is provided with an AC transformer CT1 for sensing the current to be measured. The sampling circuit includes a sampling resistor R1. One end of the sampling resistor R1 is connected to the inflow end (1) of the AC transformer CT1 and the input resistor R2 at the same time, and the other end is grounded at the outflow end (2) of the AC transformer CT1 at the same time.

4. The current detection circuit as described in claim 1, characterized in that, The output terminal of the output resistor R4 is connected to a branch of capacitor C2. One end of capacitor C2 is connected between the output terminal of the output resistor R4 and the total output terminal, and the other end is grounded for filtering.

5. The current detection circuit as described in claim 1, characterized in that, The operational amplifier U1A uses an LM224 op-amp and is powered by 5V. Its full-amplitude output voltage is 3.6V, which is lower than the MCU power supply voltage.

6. The current detection circuit as described in claim 1, characterized in that, The input resistor R2 and the output resistor R4 have the same or similar resistance values, and the filter resistor R3 has a resistance value that is ten times or more than that of the input resistor R2.

7. The current detection circuit as described in claim 1, characterized in that, The positive voltage input to the non-inverting input of the operational amplifier U1A raises the AC signal to above 0V, up to half of the MCU's operating voltage, which is 3.3V. Within one 20ms cycle of the mains power, the MCU samples n points at equal intervals to calculate the true RMS value of the current.

8. The current detection circuit as described in claim 1, characterized in that, When the rated AC signal output by the operational amplifier U1A is 1.76V peak-to-peak, the voltage signal input to the MCU is an AC signal with a peak value of 1.76V superimposed on a DC level of 1.62V. At this time, the minimum input voltage of the MCU is 0.74V and the maximum input voltage is 2.50V.

9. The current detection circuit as described in claim 2, characterized in that, The resistance value of the voltage divider resistor R5 is the same as or close to the resistance value of the filter resistor R3, and the resistance value of the voltage divider resistor R5 is twenty times or more than that of the resistor R6.

10. The current detection circuit as described in claim 3, characterized in that, The AC transformer CT1 is used to sense the current to be measured in the oxygenation pump.

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