Driving signal generating circuit of magnetic field generating coil

Abstract

The invention discloses a driving signal generating circuit of a magnetic field generating coil, which comprises a direct current applying and feedback circuit and a transformer alternating current coupling circuit, and is characterized in that the direct current applying and feedback circuit for generating a static magnetic field and the transformer alternating current coupling circuit for generating an alternating magnetic field are combined and designed; the alternating current component is innovatively superposed on the direct current component on the magnetic field generating coil in a transformer coupling mode, namely the static magnetic field and the alternating magnetic field are separately controlled when the static magnetic field and the alternating magnetic field are controlled, namely the direct current and the alternating current on the magnetic field generating coil are respectively controlled to realize alternating current and direct current separation; the effect of stably controlling alternating current and direct current is achieved, and a stable static magnetic field and an alternating magnetic field are generated. Experiments prove that two driving sources can be provided for the magnetic field generation coil, one driving source is a 50kHz and 50mA alternating current, the other driving source is a 20mA direct current, stable direct current driving with the fluctuation of the direct current applied to the magnetic field generation coil smaller than 5uA (the actual peak value is 1.3 uA) is achieved, and the influence of the alternating current on the direct current is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of coil electromagnetic field generation, and more specifically, relates to a drive signal generating circuit for a magnetic field generating coil, which is used for generating a drive signal for the coil to generate an AC / DC superimposed magnetic field. Background Art

[0002] The principle of coil generating magnetic field is based on the magnetic field phenomenon generated when current passes through a conductor, which is described by Ampere's law and Faraday's law of electromagnetic induction. Ampere's law states that when current passes through a conductor, a magnetic field is generated around it. For a straight wire, the strength of the magnetic field is proportional to the magnitude of the current and inversely proportional to the distance of the wire. For a coil (or solenoid), the strength of its magnetic field can be measured by Figure 1 The calculation is shown as follows:

[0003]

[0004] According to the above formula, in theory, applying a stable DC current or AC current to the coil can drive the corresponding stable magnetic field on the axis line. For example, a stable DC current or AC current can be generated by direct current feedback. For applications that generate static magnetic fields, DC current feedback control on the coil is relatively easy to implement. However, since the coil is an inductor, for applications that generate alternating magnetic fields, there will be a phase difference between the current and voltage when the AC current is applied to the coil, which is not conducive to the stability of DC feedback. For the driving requirements that require the simultaneous generation of a small-scale static magnetic field and an alternating magnetic field, that is, applying a stable DC component and a stable AC component to the coil at the same time, there is a certain degree of difficulty and application value. For example, in the operation of a nuclear magnetic resonance gyroscope, a stable static magnetic field needs to be applied as the main magnetic field to allow atoms to precess around it. Its measurement accuracy directly depends on the stability of the static magnetic field, but at the same time, its operation also requires an alternating magnetic field to be superimposed on the static magnetic field. For example, in the research and testing of certain magnetic materials in materials science, static magnetic fields are used to determine the magnetic properties of materials (such as saturation magnetization, hysteresis loop, etc.), while alternating magnetic fields are used to test the response of materials at different frequencies. How to reduce the stabilizing effect of AC current on DC current is a problem that needs to be solved. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a driving signal generating circuit for a magnetic field generating coil, which can provide two AC and DC currents to the coil to generate a stable static magnetic field and an AC magnetic field, and reduce the influence of the AC current on the DC current to achieve stable control of the DC current.

[0006] To achieve the above-mentioned object of the invention, the driving signal generating circuit of the magnetic field generating coil of the present invention is characterized by comprising:

[0007] The DC current application and feedback circuit is used to generate a stable DC current and apply it to the magnetic field generating coil L1 to generate a static magnetic field. It consists of a precision op amp U1, a transistor Q1, and a precision reference resistor R SET Composition, among which, V DC is the input DC reference voltage, DC reference voltage V DC Input to the positive input terminal of precision op amp U1. Due to the virtual short and virtual break characteristics of the op amp, the negative input terminal of precision op amp U1 is also a DC reference voltage V DC and through the precision reference resistor R SET to ground, which is the precision reference resistor R SET It provides a stable voltage reference. The base of transistor Q1 is connected to the output of precision amplifier U1, the collector of transistor Q1 is connected to the positive power supply Vcc, the emitter is connected to one end of magnetic field generating coil L1, and the other end of magnetic field generating coil L1 is connected to the negative input of precision amplifier U1. At this time, the voltage difference across the precision reference resistor is equal to the DC reference voltage V DC , flows through the precision reference resistor R SET The DC current I DC V DC / R SET , the magnetic field generating coil L1 works approximately in a constant current state;

[0008] The transformer AC coupling circuit is used to generate a stable AC current and apply it to the magnetic field generating coil L1 to generate an alternating magnetic field. It consists of a precision operational amplifier U2, a transformer group, and an isolation capacitor. Among them, V AC is the AC reference voltage, AC reference voltage V AC The input is to the positive input terminal of the precision operational amplifier U2, and the negative input terminal of the precision operational amplifier U2 is connected to its output terminal to form a voltage follower. The transformer group consists of two groups of parallel connected transformers, each group of which is composed of two transformers connected in series. The output terminal of the precision operational amplifier U2 is connected to one end of the primary coil of each group of two transformers connected in series, and is grounded after passing through the primary coils of the two transformers. One end of the two output ends after the secondary coils are connected in series is connected to one end of the magnetic field generating coil L1, that is, the emitter of the transistor Q1 and the connection end of the magnetic field generating coil L1 through an isolation capacitor, and the other end is directly connected to the other end of the magnetic field generating coil L1, that is, the precision reference resistor R SET Connecting terminal to magnetic field generating coil L1.

[0009] The object of the invention of the present invention is achieved in this way:

[0010] The driving signal generating circuit of the magnetic field generating coil of the present invention includes two parts: a DC current application and feedback circuit and a transformer AC coupling circuit. The DC current application and feedback circuit for generating a static magnetic field is combined with the transformer AC coupling circuit for generating an alternating magnetic field, and the AC component is superimposed on the DC component on the magnetic field generating coil in an innovative way through transformer coupling, that is, the static magnetic field and the alternating magnetic field are controlled separately when controlling the static magnetic field plus the alternating magnetic field, that is, the DC current and the AC current on the magnetic field generating coil are controlled separately to achieve AC and DC separation, so as to stably control the effect of AC and DC current, so as to generate a stable static magnetic field and AC magnetic field. Experiments have shown that the present invention can provide two driving sources for the magnetic field generating coil, one is an AC current of 50kHz and 50mA, and the other is a DC current of 20mA, so as to achieve a stable DC current drive with a DC current fluctuation of less than 5uA (the actual peak-to-peak value is 1.3uA) applied to the magnetic field generating coil, and reduce the influence of AC current on DC current.

[0011] The present invention has the following beneficial effects:

[0012] 1. Separately control the DC and AC on the magnetic field driving coil, and use a transformer to couple the AC to achieve the effect of isolating and suspending the AC part, thereby achieving stable control of the DC current.

[0013] 2. Use current feedback to control DC drive and use current feedback plus transistor structure to drive DC to obtain stable DC current.

[0014] 3. Transformer coupling is used to drive AC, and a two-series and two-parallel transformer group structure is used to share power. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a diagram of the formula for calculating the magnetic field of a coil or solenoid;

[0016] Figure 2 It is a schematic diagram of the principle of a specific implementation of the driving signal generating circuit of the magnetic field generating coil of the present invention; Figure 3 It is a flow chart. DETAILED DESCRIPTION

[0017] The specific implementation of the present invention is described below in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0018] Figure 2 It is a schematic diagram of the principle of a specific implementation of the drive signal generating circuit of the magnetic field generating coil of the present invention.

[0019] In this embodiment, if Figure 2 As shown, the driving signal generating circuit of the magnetic field generating coil of the present invention includes two parts: a DC current applying and feedback circuit 1 and a transformer AC coupling circuit 2.

[0020] like Figure 2 In the lower part, the DC current application and feedback circuit 1 is used to generate a stable DC current and apply it to the magnetic field generating coil L1 to generate a static magnetic field. It consists of a precision operational amplifier U1, a transistor Q1, and a precision reference resistor R SET Composition, among which, V DC is the input DC reference voltage, DC reference voltage V DC Input to the positive input terminal of precision op amp U1. Due to the virtual short and virtual break characteristics of the op amp, the negative input terminal of precision op amp U1 is also a DC reference voltage V DC and through the precision reference resistor R SET to ground, which is the precision reference resistor R SET It provides a stable voltage reference. The base of transistor Q1 is connected to the output of precision amplifier U1, the collector of transistor Q1 is connected to the positive power supply Vcc, the emitter is connected to one end of magnetic field generating coil L1, and the other end of magnetic field generating coil L1 is connected to the negative input of precision amplifier U1. At this time, the voltage difference across the precision reference resistor is equal to the DC reference voltage V DC , flows through the precision reference resistor R SET The DC current I DC V DC / R SET , the magnetic field generating coil L1 operates approximately in a constant current state.

[0021] The voltage at the base of transistor Q1, i.e. the output voltage of the magnetic field generating amplifier U1, is stabilized as the voltage reference V DC Add the voltage divided by the magnetic field generating coil L1 and the base-emitter voltage divided by the transistor Q1, which is about V DC +1V, transistor Q1 plays a role in expanding the current and enhancing the current driving capability. The DC current application and feedback circuit 1 realizes the application of stable DC current to the magnetic field generating coil L1. At the same time, in actual operation, in order to reduce the precision reference resistor R SET The resistance drift caused by heat generation can be solved by connecting multiple precision reference resistors in series to share the power, reduce the heat generation of a single resistor, and enhance the heat dissipation.

[0022] like Figure 2 In the upper part shown in the figure, the transformer AC coupling circuit 2 is used to generate a stable AC current and apply it to the magnetic field generating coil L1 to generate an alternating magnetic field. It is composed of a precision operational amplifier U2, a transformer group, and an isolation capacitor. Among them, V AC is the AC reference voltage, AC reference voltage VAC The input is to the positive input terminal of the precision operational amplifier U2, and the negative input terminal of the precision operational amplifier U2 is connected to its output terminal to form a voltage follower. The transformer group consists of two groups of parallel connected transformers, each group of which is composed of two transformers connected in series. The output terminal of the precision operational amplifier U2 is connected to one end of the primary coil of each group of two transformers connected in series, and is grounded after passing through the primary coils of the two transformers. One end of the two output ends after the secondary coils are connected in series is connected to one end of the magnetic field generating coil L1, that is, the emitter of the transistor Q1 and the connection end of the magnetic field generating coil L1 through an isolation capacitor, and the other end is directly connected to the other end of the magnetic field generating coil L1, that is, the precision reference resistor R SET Connecting terminal to magnetic field generating coil L1.

[0023] In the present invention, a voltage follower is constructed to enhance the driving capability, and the precision operational amplifier U2 inputs the AC reference voltage V AC , coupled to the magnetic field generating coil L1 through a transformer group of four transformers, two in parallel and two in series. The design of two in parallel and two in series allows the power to be distributed to each transformer, reducing the heating of the transformer and the signal loss in the transformer coupling. AC reference voltage V AC It is connected to the primary coil and then to the ground, and the secondary coil is connected to both ends of the magnetic field driving coil. The AC part is suspended to provide an AC voltage difference for the magnetic field generating coil L1, reducing its interference with the DC driving part of the magnetic field generating coil L1. At the same time, an external isolation capacitor is added to isolate the DC component. The combination of the isolation capacitor and the transformer ensures that the DC on the magnetic field generating coil L1 will not interfere with the AC voltage reference end to the greatest extent. At the same time, considering the influence of the tangent loss of the capacitor on the capacitance value, multiple capacitors can be connected in parallel to reduce the tangent loss.

[0024] The present invention mainly uses the above two circuit combinations, and innovatively adds DC and AC components to the magnetic field generating coil L1 through transformer coupling, that is, when controlling the static magnetic field plus the alternating magnetic field, the static magnetic field and the alternating magnetic field are controlled separately, that is, the DC and AC components on the magnetic field generating coil L1 are controlled separately to achieve AC and DC separation, which can stabilize the effect of DC control.

[0025] When the present invention is actually applied to design a driving signal generating circuit for a magnetic field generating coil, it is first necessary to calculate or actually measure the inductance and resistance parameters of the magnetic field generating coil based on the physical parameters of the magnetic field generating coil, and then calculate the current required to generate the magnetic field based on the size of the magnetic field to be generated and the shape and physical parameters of the magnetic field generating coil. The parameters of each circuit component are calculated and the circuit components are selected.

[0026] In this embodiment, the equivalent inductance of the magnetic field generating coil L1 to be driven is 25μH, and the equivalent resistance is 7.7Ω. It is hoped to generate a static magnetic field of 7μT and a 50kHz alternating magnetic field of 13μT~22μT. It is calculated that the DC current required by the magnetic field generating coil L1 is approximately 19.5mA, and the 50kHz AC current amplitude is approximately 36.1mA~61.1mA. Based on this, the drive signal generating circuit of the magnetic field generating coil of the present invention is designed.

[0027] The precision op amps U1 and U2 are both low bias voltage op amps LT1468-2, with a typical bias voltage of 30μV, a typical output current of ±22mA, a reference DC voltage of 4V, and a reference resistor R SET is 200Ω, at this time the DC current flowing through the magnetic field generating coil L1 is 4V / 200Ω=20mA, which is close to the output current limit of the op amp, so the transistor Q1 is used for current expansion, thus the following can be constructed: Figure 2 The DC current generation circuit in the lower part tests the sampling resistor R in the simulation. SET The peak-to-peak value of the current fluctuation is 1.3uA, which is within the required range.

[0028] The transformer group uses four transformers ADTT1-6+, whose working bandwidth is 0.015MHz~100MHz, meeting the use requirements of 50kHz. The resistance of its primary coil is 50Ω, the coil turns ratio is 1:1, and the maximum working power is 0.25W. It is planned to apply 50mA 50kHz AC current to the magnetic field generating coil L1. It is calculated that at this time, an AC voltage of about 1Vpp needs to be added to the magnetic field generating coil L1. If it is directly driven by a single coil, the power will exceed the maximum working power of the coil. Therefore, Figure 2 The transformer AC coupling circuit in the right half uses a two-series and two-parallel method to share the transformer power. The AC voltage reference is 3V. According to the simulation, the voltage applied to the magnetic field generating coil L1 is about one-third of the AC voltage reference. The current on the capacitor C1 is tested in the simulation. This current is the AC drive current of the magnetic field generating coil L1, and its amplitude is 50mA, which is within the required range.

[0029] Finally, the current on the magnetic field generating coil L1 is tested, and it can be observed that a 20mA direct current with a fluctuation peak value of 1.3uA and a 50mA 50kHz alternating current are superimposed on the magnetic field generating coil L1, realizing the driving of the static magnetic field and the alternating magnetic field. At this point, the core part of the circuit design of the present invention is completed.

[0030] Although the above describes the illustrative specific embodiments of the present invention to facilitate the understanding of the present invention by those skilled in the art, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

Claims

1. A driving signal generating circuit for a magnetic field generating coil, characterized in that: include: The DC current application and feedback circuit is used to generate a stable DC current and apply it to the magnetic field generating coil L1 to generate a static magnetic field. It consists of a precision op amp U1, a transistor Q1, and a precision reference resistor R SET Composition, among which, V DC is the input DC reference voltage, DC reference voltage V DC Input to the positive input terminal of precision op amp U1. Due to the virtual short and virtual break characteristics of the op amp, the negative input terminal of precision op amp U1 is also a DC reference voltage V DC and through the precision reference resistor R SET to ground, which is the precision reference resistor R SET It provides a stable voltage reference. The base of transistor Q1 is connected to the output of precision amplifier U1, the collector of transistor Q1 is connected to the positive power supply Vcc, the emitter is connected to one end of magnetic field generating coil L1, and the other end of magnetic field generating coil L1 is connected to the negative input of precision amplifier U1. At this time, the voltage difference across the precision reference resistor is equal to the DC reference voltage V DC , flows through the precision reference resistor R SET The DC current I DC V DC / R SET , the magnetic field generating coil L1 works approximately in a constant current state; The transformer AC coupling circuit is used to generate a stable AC current and apply it to the magnetic field generating coil L1 to generate an alternating magnetic field. It consists of a precision operational amplifier U2, a transformer group, and an isolation capacitor. Among them, V AC is the AC reference voltage, AC reference voltage V AC The input is to the positive input terminal of the precision operational amplifier U2, and the negative input terminal of the precision operational amplifier U2 is connected to its output terminal to form a voltage follower. The transformer group consists of two groups of parallel connected transformers, each group of which is composed of two transformers connected in series. The output terminal of the precision operational amplifier U2 is connected to one end of the primary coil of each group of two transformers connected in series, and is grounded after passing through the primary coils of the two transformers. One end of the two output ends after the secondary coils are connected in series is connected to one end of the magnetic field generating coil L1, that is, the emitter of the transistor Q1 and the connection end of the magnetic field generating coil L1 through an isolation capacitor, and the other end is directly connected to the other end of the magnetic field generating coil L1, that is, the precision reference resistor R SET Connecting terminal to magnetic field generating coil L1.

2. The driving signal generating circuit of the magnetic field generating coil according to claim 1, characterized in that: Precision reference resistor R SET Connect multiple precision reference resistors in series.

3. The driving signal generating circuit of the magnetic field generating coil according to claim 1, characterized in that: The isolation capacitor is a plurality of capacitors connected in parallel.

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