An ac constant current source circuit based on a floating ground connection load

Abstract

This invention discloses an AC constant current source circuit based on a floating ground connected load, comprising: an AC signal generation circuit, a power input filter circuit, a voltage-to-current conversion circuit, and a load floating ground circuit. A direct digital frequency synthesizer (DDS) chip is used to generate a frequency-adjustable AC signal, and the amplitude is adjustable by adjusting the amplification factor through a programmable differential amplifier. The filter circuit removes DC bias and high-frequency noise from the signal. An operational amplifier is used to build a voltage-to-current conversion circuit to achieve constant current. The output terminal adopts a symmetrical design to achieve a floating ground connection to the load, reducing common-mode interference from ground, improving the output impedance of the circuit, and enhancing the circuit's load-carrying capacity. This invention's voltage-controlled AC constant current source circuit is simple to implement, has stable output, and high current accuracy. Furthermore, the microprocessor allows for adjustment of the current amplitude and frequency, meeting the constant current source requirements under different slurry flotation conditions.

Description

Technical Field

[0001] This invention relates to an AC constant current source circuit based on a floating ground connected load. Background Technology

[0002] Foam flotation of slurry is currently the most widely used mineral processing method in industrial settings. The detection of the slurry level not only affects the overall flotation efficiency of the system, but more importantly, it directly impacts the quality of the flotation product. Instability and low accuracy of the constant current source are significant factors leading to inaccurate slurry level detection. Therefore, the performance indicators of the pressure-controlled AC constant current source are the cornerstone of the slurry level measurement system, playing a crucial role in ensuring accurate measurement of the entire system.

[0003] Figure 2 A current source circuit according to the prior art includes two operational amplifiers A21 and A22, resistors R21, R23 and R25, feedback resistors R22, R24 and R26, and load R2L. Its working principle is as follows: The input voltage Vin2 of the circuit is applied to the left end of resistor R25 through two stages of negative feedback A21 and A22, and the right end of R25 is fed back to the inverting terminal of A21 through R26. Under the conditions that R23 / R24=R22 / (R25+R26) and R21=R22=R23=R24, the voltage applied across R25 is equal in magnitude and opposite in direction to the input voltage. The circuit achieves constant output current by keeping the input voltage and the resistance value of R25 constant. However, after the load R2L is connected, the output current does not flow entirely through the load. The presence of feedback resistor R26 will cause current shunting, resulting in unstable output and increased reactive power consumption of the circuit. In addition, one end of the load R2L is grounded, which will introduce common-mode interference and cause great interference to subsequent sampling. It is not suitable for industrial sites of slurry flotation.

[0004] Figure 3 Another constant current source circuit in the prior art includes an operational amplifier A31 and resistors R31, R32, R33, and R34. Its working principle is as follows: positive and negative feedback are introduced. When R31 / R34 = R32 / R33, the output current I = -Vin3 / R34, ensuring a constant input voltage. The output is controlled by adjusting the resistance of R34. However, this structure causes a portion of the output current to be fed back to the positive and negative inputs of the operational amplifier, resulting in power loss. Furthermore, a larger R32 reduces the circuit's speed and accuracy, placing high demands on the operational amplifier. Under conditions requiring high output amplitude and frequency, the constant current effect is poor, and distortion is severe.

[0005] Therefore, it is necessary to design a new AC constant current source circuit. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an AC constant current source circuit based on a floating ground connected load, which has stable current output and high accuracy.

[0007] The technical solution of the invention is as follows:

[0008] An AC constant current source circuit based on a floating ground connected load includes a voltage-to-current conversion circuit and a load floating ground circuit.

[0009] The voltage-to-current conversion circuit includes a cascaded two-stage negative feedback amplifier circuit; the two-stage negative feedback amplifier circuit is an amplifier circuit based on operational amplifier A42 and operational amplifier A43;

[0010] The floating load circuit includes an amplifier circuit based on op-amp A45 and a voltage follower based on op-amp A44 connected together.

[0011] The load R4L is connected between the output of the piezo-current converter circuit and the output of the operational amplifier A45.

[0012] In voltage-to-current conversion circuits:

[0013] The voltage signal Vin4 is connected to the inverting input terminal of the operational amplifier A42 via resistor R42, and the non-inverting input terminal of the operational amplifier A42 is grounded via resistor R43; a resistor R44 is connected across the inverting input terminal and the output terminal of the operational amplifier A42.

[0014] A resistor R45 is connected between the output terminal of op-amp A42 and the inverting input terminal of op-amp A43; the non-inverting input terminal of op-amp A43 is grounded through a resistor R52; a resistor R46 is connected between the inverting input terminal and the output terminal of op-amp A43; the output terminal of op-amp A43 is connected to the first terminal of the load resistor R4L through a resistor R47; the second terminal of the load resistor R4L is connected to the output terminal of op-amp A45 in the load floating ground circuit.

[0015] In a floating load circuit:

[0016] The output terminal of op-amp A45 is connected to the second terminal of the load resistor R4L; a resistor R51 is connected across the output terminal and the inverting input terminal of op-amp A45; the non-inverting input terminal of op-amp A45 is grounded through a resistor R50; the inverting input terminal of op-amp A45 is connected to the output terminal of op-amp A44 through a resistor R49; the output terminal and the inverting input terminal of op-amp A44 are shorted to form a voltage follower; the non-inverting input terminal of op-amp A44 is connected to the first terminal of the load resistor R4L; the output terminal of op-amp A44 is connected to the inverting input terminal of op-amp A42 through a resistor R48.

[0017] By selecting resistors R42 = R44 = R45 = R46, the output current, which is also the load current, is obtained.

[0018] R47 has a value ranging from 500R to 5K.

[0019] It also includes a microprocessor, an AC signal generation circuit, a programmable differential amplifier circuit, and a power input filter circuit, used to generate the voltage signal Vin4;

[0020] The AC signal generation circuit is implemented using a DDS (Digital Signal Generator), and the microcontroller controls the DDS output via SPI serial communication.

[0021] The system generates AC signals of different frequencies; a programmable differential amplifier circuit is used to adjust the amplitude of the AC signals. The AC signal generation circuit is implemented using a DDS (Digital Subsystem Digital Signal Generator), and the microcontroller controls the DDS to output AC signals of different frequencies via SPI serial communication.

[0022] The programmable differential amplifier circuit communicates serially with the microprocessor via SPI. By adjusting its voltage amplification factor, the voltage-to-current conversion circuit obtains input signals of different amplitudes, thereby enabling the voltage-to-current conversion circuit to output current excitations of different amplitudes.

[0023] The power input filter uses a multi-stage LC low-pass filter to remove high-frequency noise and introduces a DC blocking capacitor (C44) to remove DC bias.

[0024] A voltage follower (A44) is introduced into the outermost feedback loop of the voltage-to-current conversion circuit, which improves the speed of the circuit, increases the output impedance of the constant current source, and utilizes the characteristic that the input impedance of the operational amplifier approaches infinity to reduce the current in the feedback loop and the reactive power consumption of the feedback resistor (R48), thereby improving the accuracy of the constant current source.

[0025] The resistors used in the voltage-to-current conversion circuit are high-precision resistors with low temperature drift and 0.1%. At the same time, in order to reduce the influence of the load impedance on the output of the constant current source, resistors R48, R44, R45, and R46 are impedance matched according to Formula 2. A small capacitor (pF level) is connected in parallel in the operational amplifier feedback loop for phase compensation and suppression of high-frequency noise.

[0026] The symmetrical floating ground design introduces a unity-gain negative feedback (A45) at the output of the operational amplifier (A44) to the side of the load (R4L) that was originally grounded, thus achieving a floating ground connection to the load. According to Formula 2, the output impedance of the circuit is twice that when the load is grounded, avoiding electromagnetic interference from common ground and providing higher current accuracy and load-carrying capacity.

[0027] The technical solution implemented by this invention can be divided into four parts according to the workflow: AC signal generation circuit, power input filtering circuit, voltage-current conversion circuit, and load floating ground circuit.

[0028] Step 1: AC signal generation circuit. The DDS chip (Direct Digital Synthesizer) is connected to the microprocessor and communicates via SPI. The frequency of the AC signal output by the DDS chip is controlled, and the signal is amplified by a programmable differential amplifier. The amplification factor is modified by the microprocessor according to the requirements of the working conditions, so that AC signals of different amplitudes and frequencies can be output.

[0029] Step 2: Power input filter circuit. After amplifying the AC signal, the signal is filtered by introducing an LC filter circuit to filter out high-frequency noise. The DC blocking capacitor C44 is connected to isolate the DC bias in the signal and is connected to one end of resistor R41. The other end of resistor R41 is connected to GND to form a high-pass filter to filter out low-frequency noise.

[0030] Step 3: Voltage-to-current conversion circuit. The filtered signal Vin4 is applied to the inverting input of operational amplifier A42 via R42. Operational amplifiers A42 and A43 form a two-stage negative feedback circuit, with a pF ceramic capacitor connected in parallel across the feedback resistor for phase compensation and suppression of high-frequency noise. One end of resistor R47 is connected to the output of A43, and the other end is connected to the non-inverting input of A44. The signal is fed back to the inverting input of operational amplifier A42 through voltage follower A44 and feedback resistor R48. Since the input impedance of operational amplifier A44 approaches infinity, the current through R47 is almost equal to the current through the load R4L. Based on the virtual short and virtual open circuit principle, the current through R4L is:

[0031]

[0032] Step 4: Floating load circuit. Connect one end of R49 to the output of operational amplifier A44 and the other end to the inverting input of operational amplifier A45. Together with R51, this forms a unity negative feedback amplifier circuit, ensuring that the voltages across the load R4L are equal in magnitude but opposite in direction, achieving a floating ground connection. C47 and R51 are connected in parallel to filter out noise. At this point, the circuit's output impedance is twice that when the load is grounded.

[0033]

[0034] More preferably, a bias resistor is connected in series at the non-inverting input of all operational amplifiers with negative feedback amplification to reduce the bias current of the operational amplifier.

[0035] More preferably, the resistors in the voltage-to-current conversion circuit are selected as precision resistors with low temperature drift and an accuracy of 0.1%, the operational amplifier is selected as an operational amplifier with a large gain-wideband product (GBP) and a high slew rate (SR), and the capacitors connected in parallel in the operational amplifier feedback loop are selected as ceramic capacitors of 10pF to 20pF.

[0036] More preferably, according to Formula 1, let R42 = R44 = R45 = R46, so that the output current of the constant current source depends only on the input voltage Vin4 and the resistor R47.

[0037] More preferably, impedance matching is performed on the constant current source circuit so that R44 / R48 = R45 / R46, ensuring that the output impedance of the constant current source circuit is as large as possible and reducing the impact of load changes on the constant current accuracy.

[0038] Through the above four steps, the voltage-controlled constant current source circuit can stably output a current signal with high accuracy and adjustable amplitude and frequency.

[0039] Beneficial effects:

[0040] This invention relates to an AC constant current source circuit based on a floating ground connected load, comprising: an AC signal generation circuit, a power input filter circuit, a voltage-to-current conversion circuit, and a load floating ground circuit. A direct digital frequency synthesizer (DDS) chip is used to generate a frequency-adjustable AC signal, and the amplitude is adjustable by adjusting the amplification factor through a programmable differential amplifier. The filter circuit removes DC bias and high-frequency noise from the signal. An operational amplifier is used to construct the voltage-to-current conversion circuit to achieve constant current. The output terminal adopts a symmetrical design to achieve a floating ground connection to the load, reducing common-mode interference from ground, improving the output impedance of the circuit, and enhancing the circuit's load-carrying capacity. This invention's voltage-controlled AC constant current source circuit is simple to implement, has stable output, and high current accuracy. Furthermore, the microprocessor allows for adjustment of the current amplitude and frequency, meeting the constant current source requirements under different slurry flotation conditions.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] 1. This invention can control the constant current source circuit to output current signals of different amplitudes and frequencies through a microprocessor without changing the hardware circuit structure.

[0043] 2. This invention introduces a voltage follower into the outermost feedback loop of the voltage-current conversion circuit, which improves the circuit speed, increases the output impedance of the constant current source, and improves the output accuracy of the constant current source.

[0044] 3. The present invention adds a unity negative feedback amplifier circuit to the output terminal of the outermost feedback loop voltage follower. Its output is connected to the end of the load R4L that was originally grounded, realizing the floating ground connection of the load. The output impedance is twice that when the load is grounded, and it prevents electromagnetic interference from the common ground, so that the constant current source has higher current accuracy and load-carrying capacity. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of an embodiment of the present invention.

[0046] Figure 2 This is a constant current source circuit based on existing technology.

[0047] Figure 3 This is another constant current source circuit in the existing technology.

[0048] Figure 4 This invention provides a precision voltage-controlled AC constant current source circuit suitable for mineral pulp flotation. Detailed Implementation

[0049] The present invention will now be described in detail with reference to the accompanying drawings and specific examples, so that those skilled in the art can better understand and use the present invention. However, the examples given are not intended to limit the present invention, and the scope of protection of the present invention is not limited to the specific embodiments given.

[0050] This invention provides a precision voltage-controlled AC constant current source circuit for mineral pulp flotation. Figure 1 The basic principle block diagram of this invention is as follows: The microprocessor controls the AC signal generation circuit and the programmable differential amplifier to output AC input signals of different frequencies and amplitudes. The power input filter circuit filters out noise and DC bias in the signal, and then the voltage-to-current conversion circuit outputs the required current signal at constant current. The load is connected to floating ground to increase the output impedance and improve the accuracy and stability of the current output.

[0051] Figure 4 This is a circuit diagram of a precision voltage-controlled AC constant current source according to an embodiment of the present invention. It specifically describes a Direct Digital Synthesizer (DDS) chip. A programmable differential amplifier is connected to a microprocessor via SPI to control the frequency and amplitude of the power input signal. An STM32 microprocessor inputs a frequency control word to the DDS chip AD9833 via SPI communication to achieve controllable input signal frequency. The amplification of the input signal is achieved by controlling the amplification factor of the programmable differential amplifier (a programmable differential amplifier is existing technology, or an inverting or non-inverting amplifier based on a combination of a multiplexer and an operational amplifier is used to adjust the amplification factor). The non-inverting input of operational amplifier A41 is connected to the output of the programmable differential amplifier, and the inverting input is connected to its output to form a voltage follower for isolation. Inductors L41, L42, L43 and C41, C42, C43 form a multi-stage low-pass filter to remove high-frequency noise. C44 is connected in series between L43 and R42 as a DC blocking capacitor to isolate DC bias, and together with R41, it forms a high-pass filter to remove low-frequency noise (common 50Hz power frequency interference), thus obtaining the input signal Vin4 of the voltage-to-current conversion circuit.

[0052] Resistor R42 is connected to the inverting input of operational amplifier A42. R44 and C45 are connected in parallel between the inverting input and the output of A42. R43 is connected in series at the non-inverting input of A42. One end of R45 is connected to the output of A42, and the other end is connected to the inverting input of A43. R46 and C46 are connected in parallel between the inverting input and the output of A43. R52 is connected in series at the non-inverting input of A43, thus forming a two-stage negative feedback amplifier. One end of resistor R47 is connected to the output of A43, and the other end is fed back to the inverting input of A42 through a voltage follower formed by A44 and feedback resistor R48. According to Formula 1, selecting resistors R42 = R44 = R45 = R46 yields the output current as shown in Formula 3.

[0053]

[0054] Resistor R47 must be a precision resistor with low temperature drift. According to Formula 3, its output current is only related to the input voltage Vin4 and resistor R47. Under the premise of keeping R47 unchanged, Vin4 can be adjusted to obtain constant current source outputs with different frequencies and amplitudes.

[0055] Resistor R49 is connected at one end to the output terminal of A44 and at the other end to the inverting input of A45. R51 and C47 are connected in parallel between the inverting and output terminals of A45, and R50 is connected in series at the non-inverting input of A45. This forms a unity negative feedback amplifier circuit, ensuring that the voltage on the right side of the load R4L is the same in magnitude but opposite in direction to the voltage on its left side, thus floating the load to ground. According to Equation 2, to ensure stable output of the constant current source and reduce the influence of load impedance, the output resistor Ro should be as large as possible to reduce the voltage drop across the load, making the voltage across resistor R47 approach the input voltage Vin4, thereby achieving precise constant current grounding.

[0056] More specifically, resistors R49 and R51 are precision resistors, and R49 = R51; resistors R43, R50, and R52 are used as operational amplifier bias resistors, and their size is equal to the parallel combination of the inverting input resistor and the feedback resistor.

[0057] More specifically, the voltage-to-current conversion circuit should select an operational amplifier with high voltage, low drift, large gain-bandwidth product, and high slew rate, and the resistor R47 should be of an appropriate value (generally 500R~5K).

[0058] The system design of this invention can meet the requirements of 0.1% constant current source output current accuracy in slurry flotation testing, with adjustable amplitude from 0.1mA to 20mA and adjustable frequency from 100Hz to 50kHz. The maximum amplitude and frequency are not limited to 20mA and 50kHz, and can be adjusted according to the needs of the on-site working conditions.

[0059] For the AC constant current source circuit proposed in this invention, the resistors are selected as low-temperature drift, high-precision surface-mount resistors with an accuracy of 0.1%, with R41=R42=R44=R45=R46=R48=R49=R51=10kΩ, the current sampling resistor R47=510Ω, the bias resistors R43=3.3kΩ and R50=R52=5kΩ, the compensation capacitors C45=C46=C47=2.5pF, the filter inductors L41=L42=L43=100nH, the filter capacitors C41=C42=C43=4.7pF, the DC blocking capacitor C44=4.7uf, and the operational amplifiers A41, A42, A43, A44, and A45 are selected as LTC6090.

[0060] The above embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. An AC constant current source circuit for floating ground based load, characterized by, Includes voltage-to-current conversion circuits and load floating ground circuits; The voltage-to-current conversion circuit includes a cascaded two-stage negative feedback amplifier circuit; the two-stage negative feedback amplifier circuit is an amplifier circuit based on operational amplifier A42 and operational amplifier A43; In the voltage-to-current conversion circuit, the filtered signal Vin4 is applied to the inverting input of operational amplifier A42 via R42. Operational amplifiers A42 and A43 form a two-stage negative feedback circuit, and a pF-level ceramic capacitor is connected in parallel with the feedback resistor for phase compensation and suppression of high-frequency noise. One end of resistor R47 is connected to the output terminal of A43, and the other end is connected to the non-inverting input of A44. The signal is fed back to the inverting input of operational amplifier A42 through voltage follower A44 and feedback resistor R48. The floating load circuit includes an amplifier circuit based on op-amp A45 and a voltage follower based on op-amp A44 connected together. The load R4L is connected between the output of the piezo-current converter circuit and the output of the operational amplifier A45. The load floating circuit connects one end of R49 to the output of operational amplifier A44 and the other end to the inverting input of operational amplifier A45. Together with R51, it forms a unity negative feedback amplifier circuit, making the voltage across the load R4L equal in magnitude and opposite in direction, thus achieving a floating connection. C47 and R51 are connected in parallel to filter out noise. In voltage-to-current conversion circuits: The voltage signal Vin4 is connected to the inverting input terminal of the operational amplifier A42 via resistor R42, and the non-inverting input terminal of the operational amplifier A42 is grounded via resistor R43; a resistor R44 is connected across the inverting input terminal and the output terminal of the operational amplifier A42. A resistor R45 is connected between the output terminal of op-amp A42 and the inverting input terminal of op-amp A43; the non-inverting input terminal of op-amp A43 is grounded through a resistor R52; a resistor R46 is connected between the inverting input terminal and the output terminal of op-amp A43; the output terminal of op-amp A43 is connected to the first terminal of the load resistor R4L through a resistor R47; the second terminal of the load resistor R4L is connected to the output terminal of op-amp A45 in the load floating ground circuit. In a floating load circuit: The output terminal of op-amp A45 is connected to the second terminal of the load resistor R4L; a resistor R51 is connected across the output terminal and the inverting input terminal of op-amp A45; the non-inverting input terminal of op-amp A45 is grounded through a resistor R50; the inverting input terminal of op-amp A45 is connected to the output terminal of op-amp A44 through a resistor R49; the output terminal and the inverting input terminal of op-amp A44 are shorted to form a voltage follower; the non-inverting input terminal of op-amp A44 is connected to the first terminal of the load resistor R4L; the output terminal of op-amp A44 is connected to the inverting input terminal of op-amp A42 through a resistor R48. Selecting the resistance R42=R44=R45=R46, the output current, i.e. the load current is ​ R47 has a value ranging from 500R to 5K; It also includes a microprocessor, an AC signal generation circuit, a programmable differential amplifier circuit, and a power input filter circuit, used to generate the voltage signal Vin4; The AC signal generation circuit is implemented through a DDS, and the microcontroller controls the DDS to output AC signals of different frequencies through SPI serial communication; the programmable differential amplifier circuit is used to adjust the amplitude of the AC signal.

Images