A fast switching bi-directional constant current source circuit and method for driving magnetic fields

Abstract

The application relates to a fast-switching bidirectional constant-current source circuit and method of driving a magnetic field. When the constant-current source passage is opened, a power amplifier outputs constant current, the current flows through a magnetic field coil and a sampling resistor. The voltage between the sampling resistor is collected, input to one end of a PI control module through a voltage follower, and the other end of the PI control module is connected to an output current size control signal. The difference between the two signals is calculated by using a PI algorithm, and the voltage control signal of the power amplifier is output, so as to control the output current of the constant-current source. The application can realize a fast-switching bidirectional constant-current source, provide a high-precision constant-current source for a gradient magnetic field, a bias magnetic field and a compensation magnetic field coil, solve the problem of long turn-off time of a resistor and a diode discharge loop, and improve the switching speed of the magnetic field.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fast switching bidirectional constant current source circuit, and particularly relates to a fast switching bidirectional constant current source circuit and method for driving a magnetic field. BACKGROUND

[0002] In the atomic cooling stage, the atoms are cooled by a magneto-optical trap system (MOT), and the cold atoms are captured in combination with a gradient magnetic field. The gradient magnetic field is realized by loading a current of a certain intensity in the anti-Helmholtz coil. In the free falling process of the cold atom group, an atomic state selection process is required, and a magnetic field in the vertical direction needs to be provided to provide a quantization axis, i.e., a bias magnetic field. The bias magnetic field is realized by loading a current of a certain intensity in the Helmholtz coil. In order to eliminate the influence of the geomagnetic field, a set of three-dimensional magnetic field coils need to be arranged around the magneto-optical trap to compensate for the geomagnetic field, so that the residual magnetic field in the center of the magneto-optical trap is zero. The geomagnetic field compensation is composed of three pairs of two orthogonal Helmholtz coils, which are symmetrically installed in the upper, lower, east, west and north directions of the magneto-optical trap system, and the geomagnetic field in the three directions is offset by loading a current of a certain intensity.

[0003] The fast switching bidirectional constant current source circuit is responsible for generating the constant current source circuit required by the gradient magnetic field, the bias magnetic field and the compensation magnetic field coil, and simultaneously switching control is performed in response to the digital trigger control signal of the data acquisition card. Since the current passing through the coil is generally in the order of amperes, when the coil current source is cut off, the internal current of the coil generally decays at an exponential speed due to the inductance, and will not be immediately turned off. The traditional magnetic field constant current source circuit design scheme adopts a resistance and diode discharge loop to improve the magnetic field turn-off speed, and the turn-off time reaches 30-40 ms under a working current of 1A. The residual magnetism of the gradient magnetic field during the non-turn-off process may interfere with the quantization axis of the subsequent atomic state selection process, and affect the state selection performance. Therefore, it is necessary to design a magnetic field constant current source circuit capable of fast turn-off. In addition, the stability of the magnetic field, especially the bias magnetic field, directly affects the atomic state selection process, and further affects the phase shift of the interference fringe, which becomes an important source of system error. Therefore, a high relative accuracy of the output current of the magnetic field constant current source circuit is required. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a fast switching bidirectional constant current source circuit and method for driving a magnetic field, to realize fast switching bidirectional constant current source, to provide high-precision constant current source for the gradient magnetic field, the bias magnetic field and the compensation magnetic field coil, and to solve the problem of long turn-off time of the resistance and diode discharge loop, and to improve the switching speed of the magnetic field.

[0005] The technical problem of the present application is solved by adopting the following technical scheme:

[0006] The application discloses a quick switch bidirectional constant current source circuit for driving a magnetic field, which comprises an output current size control module, a PI control module, a power amplification module, a switch control module, a sampling module and a display control module, wherein the switch control module comprises switch control 1 and switch control 2, the output current size control module adjusts an external input current size control signal and the switch control 1 through a control signal adjustment link, the output current size control module outputs a signal to the PI control module, meanwhile, the sampling module collects a voltage value between two ends of a sampling resistor and inputs the voltage value to the PI control module; the PI control module performs PI calculation and processing on two groups of signals input by the output current size control module and the sampling module, and then outputs the signals to the power amplification module for power amplification, and the amplified signals are used as a driving source to drive a magnetic field coil; meanwhile, the switch control 2 controls the on-off of a current in the magnetic field coil; the sampling module inputs the voltage value between the two ends of the sampling resistor to the display control module and the PI control module respectively, the display control module digitizes and processes the sampling voltage value, and converts the voltage value into a current value for display.

[0007] Moreover, the output current size control module outputs a signal, when the switch control 1 signal is high, the output is integrated as the value of the external input current size control signal; when the switch control 1 signal is low, the output is integrated as 0V.

[0008] Moreover, the PI control module comprises an operational amplifier, a resistor R34, a resistor R33 and a capacitor C40, wherein one end of the resistor R34 is connected to a negative input end of the operational amplifier and one end of the resistor R33, the other end of the resistor R33 is connected to one end of the capacitor C40, and the other end of the capacitor C40 is connected to an output end of the operational amplifier.

[0009] Moreover, the switch control 1 and the external input current size control signal are integrated as an output current size control signal; the switch control 2 controls the on-off of the current in the magnetic field coil, and eliminates the influence of residual current of the magnetic field coil when the constant current source is turned off.

[0010] Moreover, the sampling module comprises two voltage followers, the output end of one voltage follower is connected to the PI control module, and the output end of the other voltage follower is connected to the display control module.

[0011] Moreover, the display control module comprises an A / D conversion module, a display control chip, a liquid crystal display and an upper computer, wherein the input end of the A / D conversion module is connected to the output end of the other voltage follower, the output end of the A / D conversion module is connected to the display control chip, the display control chip is connected to the liquid crystal display for display of the current value, and the display control chip is responsible for serial communication with the upper computer, sending of data and receiving of control instructions.

[0012] The application further discloses a driving method of the quick switch bidirectional constant current source circuit for driving a magnetic field.

[0013] Step 1, when the constant current source path is opened, the power amplifier module outputs constant current, the current flows through the magnetic field coil and the sampling resistor;

[0014] Step 2, the voltage across the sampling resistor is collected, and after the voltage follower, it is input to one end of the PI control module, and the other end of the PI control module inputs the output current size control signal through the control signal adjustment link;

[0015] Step 3, the PI control module calculates the difference between the two signals by using the PI algorithm, and outputs the voltage to control the voltage output of the power amplifier module, thereby controlling the output current of the constant current source.

[0016] Moreover, the specific implementation method for calculating the difference between the two signals in step 3 is:

[0017]

[0018] Wherein, u1 is the voltage across the sampling resistor, u2 is the output current size control signal through the control signal adjustment link, u o is the output voltage of the PI control module, t is time, R33 is the input end resistor of the PI controller, R34 and C40 are the RC circuit connected between the negative input end and the output end of the PI control module.

[0019] The advantages and positive effects of the present application are:

[0020] 1. In the present application, when the constant current source path is opened, the power amplifier outputs constant current, the current flows through the magnetic field coil and the sampling resistor. The voltage across the sampling resistor is collected, and after the voltage follower, it is input to one end of the PI control module, and the other end of the PI control module inputs the output current size control signal, the difference between the two signals is calculated by using the PI algorithm, the output voltage controls the voltage output of the power amplifier, thereby controlling the output current of the constant current source. The present application can realize fast switching bidirectional constant current source, provide high-precision constant current source for gradient magnetic field, bias magnetic field and compensation magnetic field coil, and solve the problem of long shutdown time of the resistance and diode discharge loop, and improve the switching speed of the magnetic field.

[0021] 2, The application divides the coil current off into two steps by adding PI control link in the coil off process. When the switch control signal is "low", the coil current is rapidly reduced by PI control in the constant current source circuit, thereby greatly improving the discharge slow problem caused by the inductance of the coil; the conventional magnetic field coil FET switch control part is reserved, the FET is controlled to be turned off when the coil current is close to "0" by PI control, the complete current off is realized, the discharge time of the magnetic field coil at the off moment is greatly reduced, the magnetic field coil and the constant current source are physically isolated, and the current in the magnetic field coil is completely eliminated. Finally, the coil current is quickly and completely turned off.

[0022] 3, The application adopts a voltage reference chip with a temperature coefficient less than 1ppm / ℃ and a digital potentiometer with a temperature coefficient less than 5ppm / ℃ to jointly constitute an output current size control circuit, the precision of which is more than four times that of an analog potentiometer in a traditional scheme; a small-power resistance with a temperature coefficient of 5ppm / ℃ is used in series and parallel to realize the function of a high-power sampling resistance, and the performance of the small-power sampling resistance is more than one order of magnitude higher than that of a single high-power sampling resistance in a traditional scheme. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a structural composition block diagram of the application.

[0024] Figure 2 is a PI control algorithm principle diagram of the application.

[0025] Figure 3 is an output current size control module principle diagram of the application.

[0026] Figure 4 is a display control module principle diagram of the application.

[0027] Figure 5 is a power amplification module, switch control 2 and sampling module principle diagram of the application. DETAILED DESCRIPTION

[0028] The application will be further described in detail below with reference to the accompanying drawings.

[0029] A kind of drive magnetic field's fast switch bidirectional constant current source circuit, such as Figure 1As shown, the output current size control module, the PI control module, the power amplification module, the switch control module, the sampling module and the display control module, wherein the switch control module includes switch control 1 and switch control 2, the output current size control module adjusts the external input current size control signal and the switch control 1 through the control signal adjustment link, the output current size control module outputs the signal to the PI control module, at the same time, the sampling module collects the voltage value of the sampling resistor and inputs it to the PI control module; the PI control module performs PI calculation and processing on the two groups of signals input by the output current size control module and the sampling module, and outputs them to the power amplification module for power amplification, and the amplified signal is used as a driving source to drive the magnetic field coil; at the same time, the switch control 2 controls the on-off of the current in the magnetic field coil; the sampling module inputs the voltage value of the sampling resistor to the display control module and the PI control module respectively, and the display control module digitizes and processes the sampling voltage value and converts it into a current value for display.

[0030] As shown in Figure 2 The PI control module includes an operational amplifier, a resistor R34, a resistor R33 and a capacitor C40, wherein one end of the resistor R34 is connected to the negative input end of the operational amplifier and one end of the resistor R33, the other end of the resistor R33 is connected to one end of the capacitor C40, and the other end of the capacitor C40 is connected to the output end of the operational amplifier.

[0031] As shown in Figure 3 The output current adjustment 1 of the output current size control module is analog adjustment, the adjustment voltage is input to the internal AD conversion module of the display control chip through the voltage follower, the display control chip converts the voltage into output current adjustment 2, that is, the control instruction of the digital potentiometer, which is converted into the control voltage of the digital adjustment output current value, and the voltage is integrated with the switch control 1 through the signal adjustment link, and the integrated output current size control signal is output. When the switch control 1 signal is high, the output is integrated as the external input current size control signal value; when the switch control 1 signal is low, the output is integrated as 0V.

[0032] At the same time, the voltage reference chip with a temperature coefficient less than 1ppm / ℃ and the digital potentiometer with a temperature coefficient less than 5ppm / ℃ are used together to form the output current size control circuit, which improves the precision of the analog potentiometer in the traditional scheme by more than four times; the small power resistor with a temperature coefficient of 5ppm / ℃ is used in series and parallel to realize the function of the large power sampling resistor, which improves the performance of the single large power sampling resistor in the traditional scheme by more than one order of magnitude.

[0033] The display and control module includes: an A / D conversion module, a display and control chip, an LCD screen, and a host computer. The input of the A / D conversion module is connected to the output of another voltage follower. The output of the A / D conversion module is connected to the display and control chip. The display and control chip is connected to the LCD screen for displaying the current value. The display and control chip is responsible for serial communication with the host computer, sending data and receiving control commands. Figure 4 As shown, the A / D conversion module converts the voltage value across the sampling resistor into a digital signal and sends it to the display control chip, where it converts it into a current value and displays it on the LCD screen. The display control chip is responsible for serial communication with the host computer, sending the current data to the host computer and receiving control commands from the host computer. The display control chip collects the rising and falling edges of switch control 1, synchronously outputs the rising edge to switch control 2, delays the falling edge, and then outputs it to switch control 2. This control method not only ensures the discharge time of the magnetic field coil at the moment of turn-off, but also physically isolates the magnetic field coil from the constant current source, completely eliminating the leakage current inside the magnetic field coil.

[0034] The display control chip uses an ARM chip, designed based on the ARM Cortex-M4 core. The ARM Cortex-M4 processor provides a high-performance, low-cost platform that meets the requirements of small storage needs, simplified pin count, and low power consumption. Simultaneously, it offers excellent computing performance and superior system interrupt response capabilities. The ARM chip's CPU main frequency can reach 80MHz, and it includes a 12-bit A / D conversion module, 10 sets of physical GPIO modules (functionally multiplexed), a PWM module, and multiple data communication interfaces such as SPI synchronous serial communication interface, asynchronous serial communication interface, and CAN port, fully meeting the requirements of this invention for GPIO pins, asynchronous serial communication, and the A / D conversion module.

[0035] like Figure 5 As shown, the power amplifier module of this invention amplifies the output signal of the PI control module and connects the output to the load magnetic field coil. The switch control 2 is connected to the magnetic field coil and, under the control of the switch control signal output by the display and control chip, turns the magnetic field coil and the constant current source on or off, thus eliminating the influence of leakage current in the magnetic field coil when the constant current source is turned off. In the sampling module, one end of the sampling resistor is connected to the switch control 2 and the other end is grounded. The sampling module collects the voltage value across the sampling resistor, isolates it using a voltage follower, and outputs it to the AD conversion stages of the PI control module and the display and control module, respectively.

[0036] A driving method for a fast-switching bidirectional constant current source circuit that drives a magnetic field includes the following steps:

[0037] Step 1: When the constant current source path is turned on, the power amplifier module outputs a constant current, which flows through the magnetic field coil and the sampling resistor.

[0038] Step 2, the voltage across the sampling resistor is collected, after a voltage follower, input to one end of the PI control module, the other end of the PI control module input through the output current size control signal of the control signal adjustment link;

[0039] Step 3, the PI control module calculates the difference between the two signals by PI algorithm, and outputs the voltage control power amplifier module to control the output current of the constant current source.

[0040] The specific implementation method for calculating the difference between the two signals is:

[0041]

[0042] The Laplace inverse transform is performed to obtain:

[0043]

[0044] Wherein, u1 is the voltage across the sampling resistor, u2 is the output current size control signal through the control signal adjustment link, u o is the output voltage of the PI control module, t is time, since u2 is a given output current size control signal, which can be regarded as a constant value, the output voltage u o is only PI algorithm related to the voltage difference between u1 and u2, and the parameters

[0045] It should be emphasized that the embodiments described in the present application are illustrative rather than limiting, and therefore the present application includes and is not limited to the embodiments described in the specific embodiments, any other embodiments derived from the technical solutions of the present application by those skilled in the art also belong to the scope of protection of the present application.

Claims

1. A fast switching bi-directional constant current source circuit driven by a magnetic field, characterized by: The output current size control module, the PI control module, the power amplification module, the switch control module, the sampling module and the display control module are included, wherein the switch control module includes switch control 1 and switch control 2, the output current size control module adjusts the current size control signal inputted from outside and the switch control 1 through a control signal adjustment link, the output current size control module outputs a signal to the PI control module, meanwhile, the sampling module collects the voltage value between the two ends of a sampling resistor and inputs the voltage value to the PI control module; the PI control module performs PI calculation and processing on two groups of signals inputted from the output current size control module and the sampling module, and then outputs the signals to the power amplification module for power amplification, and the amplified signal is used as a driving source to drive a magnetic field coil; meanwhile, the switch control 2 controls the on-off of the current in the magnetic field coil; the sampling module inputs the voltage value between the two ends of the sampling resistor to the display control module and the PI control module respectively, and the display control module digitizes and processes the sampling voltage value and converts the voltage value into a current value for display.

2. A fast switching bi-directional constant current source circuit for driving a magnetic field according to claim 1, characterized in that: The output current size control module outputs a signal, when the switch control 1 signal is high, the output is integrated as the current size control signal value inputted from outside; when the switch control 1 signal is low, the output is integrated as 0V.

3. A fast switching bi-directional constant current source circuit for driving a magnetic field according to claim 1, wherein: The PI control module includes an operational amplifier, a resistor R34, a resistor R33 and a capacitor C40, wherein one end of the resistor R34 is connected to the negative input end of the operational amplifier and one end of the resistor R33, the other end of the resistor R33 is connected to one end of the capacitor C40, and the other end of the capacitor C40 is connected to the output end of the operational amplifier.

4. A fast switching bi-directional constant current source circuit for driving a magnetic field according to claim 1, wherein: The sampling module includes two voltage followers, the output end of one voltage follower is connected to the PI control module, and the output end of the other voltage follower is connected to the display control module.

5. A fast switching bi-directional constant current source circuit for driving a magnetic field according to claim 1, wherein: The display control module includes an A / D conversion module, a display control chip, a liquid crystal display and an upper computer, wherein the input end of the A / D conversion module is connected to the output end of the other voltage follower, the output end of the A / D conversion module is connected to the display control chip, the display control chip is connected to the liquid crystal display for display of the current value, and the display control chip is responsible for serial communication with the upper computer, sending data and receiving control instructions.

6. A driving method of a fast switching bidirectional constant current source circuit of a driving magnetic field as claimed in any one of claims 1 to 5, characterized by: The method includes the following steps: Step 1, when the constant current source path is turned on, the power amplification module outputs a constant current, and the current flows through the magnetic field coil and the sampling resistor; Step 2, the voltage between the two ends of the sampling resistor is collected, inputted to one end of the PI control module after a voltage follower, and the other end of the PI control module inputs the output current size control signal through a control signal adjustment link; Step 3, the PI control module calculates the difference value of the two signals by using the PI algorithm, and outputs a voltage to control the voltage output of the power amplification module, thereby controlling the output current of the constant current source.

7. The driving method of the fast switching bidirectional constant current source circuit for driving magnetic field according to claim 6, characterized in that: The specific implementation method for calculating the difference value of the two signals in step 3 is: Wherein, u1 is the voltage across the sampling resistor, u2 is the output current size control signal through the control signal adjustment link, u o is the output voltage of the PI control module, t is the time, R33 is the negative input resistor of the PI controller, R34 and C40 are the RC circuit connected between the negative input and output of the PI control module.

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