A high-precision voltage-regulated constant current source system suitable for strong inductive loads

Abstract

The invention discloses a high-precision voltage-regulating constant-current source system suitable for a strong inductive load, comprising an MCU, an AD / DA module, a switching power supply, a constant-current source circuit, a compensation capacitor C, and a feedback voltage-dividing resistor; the MCU is connected to the DA module to generate a reference voltage signal; the DA module is connected to the constant-current source circuit to convert the reference voltage signal into a current signal through the constant-current source circuit; a high-precision sampling resistor is provided in the constant-current source circuit, the high-precision sampling resistor is connected to the AD module, and the current signal is converted into a measurement voltage signal through the high-precision sampling resistor and then sent to the AD module for analog-to-digital conversion; the compensation capacitor C is respectively connected to the switching power supply, the constant-current source circuit, and the feedback voltage-dividing resistor to compensate for the phase of a loop formed by the switching power supply, the constant-current source circuit, and the feedback voltage-dividing resistor; the switching power supply is connected to the feedback voltage-dividing resistor, the switching power supply is connected to the constant-current source circuit, and the switching circuit maintains a constant source voltage of an adjustment tube in the constant-current source circuit through the feedback voltage-dividing resistor.

Description

Technical Field

[0001] The invention belongs to the technical field of direct current motor drivers, and in particular relates to a high-precision voltage-regulated constant current source system suitable for strong inductive loads. Background Art

[0002] In the field of industrial control, the accuracy and stability of the constant current source are the key to the performance of the measurement system. In the future, high-performance programmable constant current sources will have more and more extensive applications. The research mainly focuses on the wide-range, high-precision constant current sources on the market, which are expensive, large in size, and have high power consumption. Most of them are not suitable for strong inductive loads and cannot meet the requirements of driving motor coils. Therefore, based on the circuit of the basic constant current source, through continuous improvement and improvement, a programmable current source with high accuracy and wide dynamic range is further designed for strong inductive loads such as industrial excitation coils. In the test system, current-type op amps are mostly used to output a given current. Although the accuracy can reach uA or even nA level, its dynamic adjustment range is too narrow and generally does not exceed 100mA. In addition, in order to ensure the accuracy and stability of the output current, the circuit is generally equipped with a large area of ​​radiator and a large area of ​​PCB board, which is not suitable for portable devices such as embedded systems. For excitation coils and inductive loads, the current dynamic range generally exceeds 2.5A, the output voltage exceeds 50V and the stability is at the 10-3 level to be competitive. In addition, most of the precision constant current sources on the market cannot perfectly adapt to inductive loads. When carrying inductive loads, their accuracy level cannot reach their precision. Strong inductive loads will cause system instability due to current hysteresis. The reason is that there is also hysteresis in the voltage at the reverse input terminal of the op amp, which increases the high-frequency phase shift of the feedback loop and causes self-oscillation. Prior art, such as the patent document with application number CN201810941862.2, discloses a bipolar high-precision constant current drive system and method suitable for inductive loads, which provides a solution. However, it is based on the combination of precision error op amp amplifier and power op amp amplifier for negative feedback amplification, and the structure is relatively complex. In terms of high dynamic range technology, the circuit power consumption is too large and the power density is low.

[0003] In view of the above technical problems, it is necessary to improve them. Summary of the invention

[0004] Based on the above-mentioned deficiencies in the prior art, the present invention provides a high-precision voltage-regulated constant current source system suitable for strong inductive loads.

[0005] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0006] A high-precision voltage-regulated constant current source system suitable for strong inductive loads comprises an MCU, an AD / DA module, a switching power supply, a constant current source circuit, a compensation capacitor C, and a feedback voltage-dividing resistor; the MCU is connected to the DA module to generate a reference voltage signal; the DA module is connected to the constant current source circuit to convert the reference voltage signal into a current signal through the constant current source circuit; the constant current source circuit has a high-precision sampling resistor, the high-precision sampling resistor is connected to the AD module, and is used to convert the current signal into a measurement voltage signal through the high-precision sampling resistor and then send it to the AD module for analog-to-digital conversion; the compensation capacitor C is respectively connected to the switching power supply, the constant current source circuit, and the feedback voltage-dividing resistor to compensate for the phase of a loop composed of the switching power supply, the constant current source circuit, and the feedback voltage-dividing resistor; the switching power supply is connected to the feedback voltage-dividing resistor, the switching power supply is connected to the constant current source circuit, and the switching circuit maintains a constant source voltage of an adjustment tube in the constant current source circuit through the feedback voltage-dividing resistor.

[0007] As a preferred solution, the feedback voltage divider resistor includes R FB1 , R FB2 .

[0008] As a preferred solution, the constant current source circuit includes a resistor R1 and a filter capacitor C1. The resistor R1, the filter capacitor C1 and the compensation capacitor C cooperate to perform frequency network compensation for a strong inductive load.

[0009] As a preferred solution, the AD / DA module includes an ADC chip and a DAC chip.

[0010] As a preferred solution, the constant current source system also includes a PC, the MCU communicates with the PC to perform timed serial port transmission and reception, receives PC program-controlled current data and sends sampled current data, interacts with the ADC chip and the DAC chip in the program, and displays the actual program-controlled output current and the preset value through the OLED.

[0011] As a preferred solution, the constant current source system is connected in series with an external load via a feedback voltage divider resistor, and the external load is an inductive load, including: an excitation coil, a linear motor, and a voice coil motor.

[0012] As a preferred solution, the constant current source system further includes a calibration module for reducing offset voltage, wherein the calibration module for reducing offset voltage includes a sliding resistor W1 and an integral modulation, wherein the integral modulation includes an integral link composed of a resistor R17 and a capacitor C29.

[0013] As a preferred solution, the high-precision sampling resistor is a high-precision low-temperature drift resistor, including a sampling resistor R21 and a sampling resistor R22, and the roots of the sampling resistor R21 and the sampling resistor R22 are sampling points.

[0014] As a preferred solution, the constant current source system further includes a linear power supply and an electrical isolation module, and the linear power supply is used to provide power for the MCU, the electrical isolation module, the AD / DA module, and the operational amplifier in the constant current source circuit.

[0015] As a preferred solution, the ground wires of each module of the constant current source system are designed to be separated, and the common ground is at the root of the power supply.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The present invention aims at the problem that the constant current source circuit has high power consumption and generally low precision in applications of 2.5A and above, which is restricted by the precision of power devices and control methods. Based on the constant current drive control technology of voltage-regulated series voltage negative feedback, the constant current source drive capacity can reach 3A, the output voltage range can reach 50V, and the overall conversion efficiency at the ampere level is greater than 80%. At the same time, the output precision reaches 1% FSR, the power consumption is extremely low, and the constant current source output dynamic range is wide.

[0018] (2) The current dynamic range of the present invention can reach 3A, and can be used in high-precision driving occasions, especially in applications requiring a large current range and high precision, such as motor drive and servo system drive, and has a very broad market application prospect.

[0019] (3) The present invention adopts a precision resistor direct feedback method to avoid the influence of operational amplifier gain error and offset voltage, and avoids the problem of reduced constant current control accuracy caused by sampling feedback loop shunt.

[0020] (4) The present invention introduces a phase compensation feedback network to increase the phase margin of the constant current source and improve the control stability of the inductive load of the constant current source.

[0021] (5) The present invention reduces the impact of noise crosstalk between the power circuit and the signal circuit by wiring the power ground and the signal ground separately and sharing the ground nearby. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a block diagram of the overall system composition of a high-precision voltage-regulated constant current source system suitable for a strong inductive load according to the first embodiment of the present invention;

[0023] Figure 2 A circuit diagram of a constant current source circuit for a high-precision voltage-regulated constant current source system suitable for a strong inductive load according to the first embodiment of the present invention;

[0024] Figure 3 The overall circuit diagram of the high-precision voltage-regulated constant-current source system suitable for strong inductive loads according to the first embodiment of the present invention;

[0025] Figure 4This is an output current stability diagram of a high-precision voltage-regulated constant current source system suitable for a strong inductive load according to the first embodiment of the present invention;

[0026] Figure 5 This is an output current step response waveform diagram of a high-precision voltage-regulated constant current source system suitable for a strong inductive load according to the first embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to more clearly illustrate the embodiments of the present invention, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are only embodiments of the present invention, and for those of ordinary skill in the art, other accompanying drawings and other implementation methods can be obtained based on these drawings without creative work.

[0028] Embodiment 1:

[0029] like Figure 1-5 As shown, the high-precision voltage-regulated constant current source system suitable for strong inductive loads of this embodiment is based on the voltage and current double closed-loop voltage regulation circuit and the adjustment tube and resistor parallel connection technology, which can make the constant current source drive capacity reach 3A, the output voltage is up to 50V, and the output accuracy is 1%. At the same time, the PCB board area is only 128mm*80mm, and the ampere level efficiency exceeds 80%. In addition, by changing the frequency characteristics through the parallel compensation capacitor C, the problem of self-excited oscillation of strong inductive loads is solved, and the phase margin of the constant current source system is improved, thereby improving the stability of the system.

[0030] It includes: a linear power supply, an MCU, an electrical isolation module, an AD / DA module, a switching power supply, a constant current source circuit, a compensation capacitor C, and a feedback voltage divider resistor. The MCU is connected to the DA module, the DA module is connected to the constant current source circuit, the constant current source circuit is connected to the AD module, the compensation capacitor C is respectively connected to the switching power supply, the constant current source circuit, and the feedback voltage divider resistor, the switching power supply is connected to the feedback voltage divider resistor, the switching power supply is connected to the constant current source circuit, the linear power supply is connected to the MCU, the AD / DA module, and the constant current source circuit; wherein, the constant current source circuit has a high-precision sampling resistor, and the high-precision sampling resistor is connected to the AD module. Specifically: the MCU communicates with the DA module to perform analog-to-digital conversion and generate a reference voltage signal. The voltage signal is converted into a current signal through the constant current source circuit. The current signal is converted into a measured voltage signal through the high-precision sampling resistor in the constant current source circuit and sent to the AD module for analog-to-digital conversion. The MCU communicates with the AD module to display its value. The AD / DA module includes an ADC chip and a DAC chip. The compensation capacitor C is used as an inductive load frequency compensation to compensate for the loop phase of the entire system. The switching power supply compensates for the loop phase of the entire system through the feedback voltage divider resistor R FB1 , R FB2The constant current source circuit adjusts the source voltage of the tube to maintain a constant value, so that the power consumption of the constant current source is kept at a low value. The linear power supply supplies power to the MCU, electrical isolation module, AD / DA module and the operational amplifier in the constant current source circuit. The switching power supply is fed back through the voltage divider resistor R FB1 , R FB2 Maintain the constant current source circuit to adjust the source voltage of the tube to be constant. FB1 and R FB2 The voltage of the source of the voltage-dividing feedback adjustment tube is set to R in order to reduce the current flowing through the resistor and prevent the load from rotating. FB1 =20kΩ, R FB2 =10kΩ. According to U FB =0.8V, and the minimum output current value is 80uA. The constant current source system is connected in series with an external load through a feedback voltage divider resistor. The external load is an inductive load, and the inductive load includes one or more of an excitation coil, a linear motor, and a voice coil motor.

[0031] The constant current source circuit includes resistor R1, filter capacitor C1, compensation capacitor C, resistor R1, filter capacitor C1 to form a strong inductive load frequency network compensation. The load impedance modulus after compensation is less than the DC impedance when the frequency is greater than 1kHz, and the system has strong resistance to high-frequency noise. The phase will be ahead of about 150 at low frequencies. ° The larger the compensation capacitor C is, the smaller the fluctuation of its relative impedance value is, so the compensation capacitor C value is selected to be 470uF. And a low ripple DC-DC circuit is selected to reduce the capacitor shunt situation.

[0032] When the input signal is referenced, the MCU communicates with the DAC (the range is 0 to 65535) to perform digital-to-analog conversion to obtain the reference voltage signal, and then the constant current source circuit performs voltage-to-current conversion (V ref =I out R sense ). MCU realizes the function of timing serial port receiving and sending, receiving the PC program-controlled current data and sending the sampled current data. In the program, it exchanges data with the ADC chip and the DAC chip, and the OLED displays the actual program-controlled output current and the preset value.

[0033] The constant current source circuit sampling load floating series voltage negative feedback structure has few components and simple structure, and it is also easy to set the feedback point. A precision operational amplifier outputs the compared voltage signal to the adjustment tube, which is converted into a current signal through the current amplification capability of the adjustment tube. The current signal flows through the sampling precision resistor to generate an actual voltage signal and is fed back to the input end of the op amp.

[0034] like Figure 3As shown in the figure, it is the principle diagram of the constant current drive system of this embodiment, which includes a power supply circuit composed of LM7815, LM7915, and LM7805; a constant current source circuit composed of the LM5117 core chip, in which the MOSFET is the switch tube CSD19536KCS, and the current feedback uses a constant current source circuit with I 2 The ADS1114 chip of C performs differential sampling of the voltage across the sampling resistor, and then feeds back to the control chip LM5117 for constant current regulation. At the same time, the voltage of the entire circuit is controlled through two feedback voltage-dividing resistors connected in series with the load. The design idea of ​​this embodiment is described as follows in conjunction with this figure:

[0035] Initially, the W1 sliding rheostat is used to calibrate and reduce the offset voltage. At the same time, the integral links R17 and C29 are added to improve the adjustment accuracy. The sliding rheostat W1 and the integral modulation constitute a calibration and offset voltage reduction module. The design idea of ​​the traditional constant current source system is to directly use the power amplifier for error feedback adjustment, resulting in low adjustment control accuracy.

[0036] The design and implementation idea of ​​the high-precision sampling resistor is to sample the load current through the high-precision, low-temperature drift sampling resistors R21 and R22, and isolate the signals at both ends of the sampling resistor through the high impedance of the AD input end to avoid reducing the constant current output accuracy due to the shunt of the acquisition line. In addition, in the PCB design, the sampling point should be taken at the root of the sampling resistors R21 and R22 to reduce the accuracy loss caused by the PCB routing impedance.

[0037] The design idea of ​​the compensation capacitor C is to compensate for the loop phase shift caused by the inductive load, eliminate the output oscillation problem caused by insufficient loop phase margin, and enable the constant current drive system to better drive the inductive load.

[0038] It should be noted that if Figure 2 As shown in the figure, it is the circuit diagram of the constant current source circuit of this embodiment, where R sense for Figure 3 The sampling resistors R21 and R22 are high-precision sampling resistors.

[0039] To ensure the performance of the constant current drive system, the parameter matching relationship of each module preferably meets the following requirements:

[0040] The constant current drive output and control ground lines should be designed separately, and the common ground point should be at the root of the power supply to avoid output crosstalk affecting the output current accuracy.

[0041] The performance of the constant current drive system was tested through the developed constant current drive system prototype, and the stability output measurement results of the high-precision constant current were carried out for nearly 2 minutes. The horizontal axis is time, and the unit is time / 50s, which means that 1 unit is 50s. The vertical axis is the output current of the constant current drive system, and the unit is ampere. It can be seen from the curve that the total maximum deviation of the output after power-on is 5mA, and the accuracy is 0.2%FSR.

[0042] In summary, after the driving capability of the traditional constant current source reaches the ampere level, its constant current accuracy can only reach 1%, realizing the constant current control requirements of wide dynamic range and high precision. At the same time, in order to better adapt to the driving of inductive loads, a phase compensation feedback network is introduced to increase the phase margin of the constant current source, and improve the control stability of the inductive load of the constant current source, so that the constant current drive system described in this embodiment can drive the inductive motor load well. By wiring each power ground and signal ground separately, sharing the ground nearby, and designing multiple ground lines separately, the crosstalk problem between the constant current drive output signals is avoided, and the accuracy of the constant current drive system is further improved.

[0043] This embodiment adopts a double closed-loop control strategy based on series voltage negative feedback amplification technology and step-down circuit voltage and current, which greatly improves the dynamic range of the constant current source. This embodiment introduces a phase compensation feedback network to increase the phase margin of the constant current source and improve the control stability of the inductive load of the constant current source. By wiring the power ground and signal ground separately and sharing the ground nearby, the crosstalk problem between the output and the analog signal is avoided.

[0044] The present invention is suitable for high-precision driving occasions, especially application occasions requiring a large current range and high precision, such as motor driving and servo system driving, and has a very broad market application prospect.

[0045] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A high-precision voltage-regulated constant current source system suitable for strong inductive loads, characterized in that: It includes an MCU, an AD / DA module, a switching power supply, a constant current source circuit, a compensation capacitor C, and a feedback voltage-dividing resistor; the MCU is connected to the DA module to generate a reference voltage signal; the DA module is connected to the constant current source circuit to convert the reference voltage signal into a current signal through the constant current source circuit; the constant current source circuit has a high-precision sampling resistor, the high-precision sampling resistor is connected to the AD module, and is used to convert the current signal into a measurement voltage signal through the high-precision sampling resistor and then send it to the AD module for analog-to-digital conversion; the compensation capacitor C is respectively connected to the switching power supply, the constant current source circuit, and the feedback voltage-dividing resistor to compensate for the phase of the loop composed of the switching power supply, the constant current source circuit, and the feedback voltage-dividing resistor; the switching power supply is connected to the feedback voltage-dividing resistor, the switching power supply is connected to the constant current source circuit, and the switching power supply maintains the constant current source circuit adjustment tube source voltage constant through the feedback voltage-dividing resistor; The feedback voltage-dividing resistor includes a resistor RFB1 and a resistor RFB2; The constant current source circuit comprises a resistor R1 and a filter capacitor C1. The resistor R1, the filter capacitor C1 and the compensation capacitor C cooperate to perform frequency network compensation for a strong inductive load.

2. A high-precision voltage-regulated constant current source system suitable for strong inductive loads as claimed in claim 1, characterized in that: The AD / DA module includes an ADC chip and a DAC chip.

3. A high-precision voltage-regulated constant current source system suitable for strong inductive loads as claimed in claim 2, characterized in that: The constant current source system also includes a PC. The MCU communicates with the PC to perform timed serial port transmission and reception, receives PC program-controlled current data and sends sampled current data, and interacts with the ADC chip and the DAC chip for data.

4. A high-precision voltage-regulated constant current source system suitable for strong inductive loads as claimed in claim 1, characterized in that: The constant current source system is connected in series with an external load via a feedback voltage-dividing resistor, and the external load is an inductive load.

5. A high-precision voltage-regulated constant current source system suitable for strong inductive loads as claimed in claim 1, characterized in that: The constant current source system further comprises a calibration module for reducing offset voltage, wherein the calibration module for reducing offset voltage comprises a sliding resistor W1 and an integral modulation, wherein the integral modulation comprises an integral link composed of a resistor R17 and a capacitor C29.

6. A high-precision voltage-regulated constant current source system suitable for strong inductive loads as claimed in claim 1, characterized in that: The high-precision sampling resistor is a high-precision low-temperature drift resistor, and the root of the high-precision sampling resistor is a sampling point.

7. A high-precision voltage-regulated constant current source system suitable for strong inductive loads as claimed in claim 1, characterized in that: The constant current source system also includes a linear power supply and an electrical isolation module. The linear power supply is used to provide electrical energy for the MCU, the electrical isolation module, the AD / DA module, and the operational amplifier in the constant current source circuit.

8. A high-precision voltage-regulated constant current source system suitable for strong inductive loads as claimed in claim 1, characterized in that: The ground wires of each module of the constant current source system are designed to be separated, and the common ground is at the root of the power supply.

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