Active current control circuit

Abstract

The present invention relates to the field of field emission devices, and more specifically, to an active current control circuit comprising: a field emission X-ray source module, a drain protection resistor, a first-stage MOS transistor circuit, and a second-stage MOS transistor circuit; the field emission X-ray source in the field emission X-ray source module is connected in series with a MOS transistor in the first-stage MOS transistor circuit via a drain protection resistor; the second-stage MOS transistor circuit includes two MOS transistors connected in parallel, and the two MOS transistors in the second-stage MOS transistor circuit are connected in series with the MOS transistor in the first-stage MOS transistor circuit. The active current control circuit in an embodiment of the present invention is capable of regulating and stabilizing the cathode emission current of the field emission X-ray source. It is suitable for cathode current control of cold cathode field emission X-ray sources, exhibiting real-time performance and high stability. It achieves cathode current stabilization and balance in the cold cathode field emission X-ray source by controlling cascaded MOSFETs using a low-voltage signal.

Description

Technical Field

[0001] The present invention relates to the field of field emission devices, and in particular to an active current control circuit. Background Art

[0002] In computed tomography (CT), traditional X-ray emission sources utilize a hot cathode, typically a tungsten wire. The cathode is heated to an extremely high temperature, allowing electrons in the cathode to gain sufficient energy to escape from the cathode surface, generating an electron beam. A high-voltage electric field is then applied to accelerate the electron beam generated by thermal emission. The high-speed electron beam then strikes a metal target at the anode, generating X-rays via bremsstrahlung. Traditional hot cathodes with metal wires have high operating temperatures, requiring a long time to heat to the required temperature, consuming large amounts of power, and are susceptible to damage during the heating and cooling processes, resulting in a short lifespan and difficulty in integration. CT imaging systems built with these light sources also experience motion artifacts due to the rotating imaging of the light source. In contrast, carbon nanotube-based cold cathode X-ray sources generate electron beams through field emission. This involves lowering the potential barrier height and narrowing the width of the cathode surface under the influence of an applied electric field. Electrons at the cathode escape into the vacuum via the tunneling effect, achieving high-speed, high-density electron emission. These sources offer the advantages of operating at room temperature, compact size, high temporal resolution, and programmable emission. Furthermore, they can be fabricated into multi-focal X-ray array sources, enabling static X-ray CT imaging. Existing cold cathode field emission X-ray sources all face a serious problem: the current stability of the cathode-emission electron beam is particularly poor, making it difficult to balance the X-ray dose. Existing field emission current control methods use a feedback control circuit to adjust the gate voltage based on the detected anode current, thereby controlling the cathode emission current and reducing X-ray source current fluctuations.

[0003] However, existing technologies use feedback control circuits to regulate current, sampling the anode current and adjusting the control grid voltage based on the results of computational analysis of the sampled data. This process, including current sampling, data calculation, and control, takes time. While this can stabilize the current to a certain extent, the feedback control has lags and still causes some fluctuations. In practical applications, X-ray sources require short pulses, which significantly impacts the feedback control time. Summary of the Invention

[0004] An embodiment of the present invention provides an active current control circuit to at least solve the technical problem in existing circuits that the operating current may change due to the Joule heating effect.

[0005] According to an embodiment of the present invention, an active current control circuit is provided, comprising: a field emission X-ray source module, a drain protection resistor, a first-stage MOS transistor circuit, and a second-stage MOS transistor circuit; the field emission X-ray source in the field emission X-ray source module is connected in series with a MOS transistor in the first-stage MOS transistor circuit via the drain protection resistor; the second-stage MOS transistor circuit includes two MOS transistors connected in parallel; the two MOS transistors in the second-stage MOS transistor circuit are connected in parallel and then connected in series with the MOS transistor in the first-stage MOS transistor circuit.

[0006] Furthermore, the MOS tube in the first-stage MOS tube circuit adopts a high-voltage MOS tube.

[0007] Furthermore, the pulse working state of the field emission X-ray source module is controlled by the MOS transistor in the first-stage MOS transistor circuit, and is controlled by applying a pulse signal to the gate of the MOS transistor in the first-stage MOS transistor circuit.

[0008] Furthermore, when the gate applied pulse signal is at a low level, the MOS tube in the first-stage MOS tube circuit operates in a cut-off state, and it will bear the high voltage from the cathode of the field emission X-ray source. When the gate applied pulse signal is at a high level, the high level causes the MOS tube in the first-stage MOS tube circuit to be in a fully open saturation region.

[0009] Furthermore, in the second-stage MOS tube circuit, the drains of the two parallel MOS tubes are connected to each other and the sources are connected to each other; the drains of the two parallel MOS tubes are connected to the source of the MOS tube in the first-stage MOS tube circuit.

[0010] Furthermore, the sources of the two MOS transistors in the second-stage MOS transistor circuit are grounded.

[0011] Furthermore, the cathode current of the field emission X-ray source is equal to the sum of the operating currents of the two MOS tubes connected in parallel in the second-stage MOS tube circuit.

[0012] Furthermore, the MOS tube in the first-stage MOS tube circuit and the two MOS tube gates in the second-stage MOS tube circuit are respectively connected to the MOS tube gate pulse drive power supply, the MOS tube gate DC drive power supply, and the MOS tube gate DC drive power supply through the MOS tube gate protection resistor.

[0013] Furthermore, a pulse signal is applied to the gate of the MOS tube in the first-stage MOS tube circuit, and parasitic inductance is generated on the lead, which forms an LC oscillation circuit with the parasitic capacitance generated by the gate.

[0014] Furthermore, the field emission X-ray source cathode in the field emission X-ray source module is connected in series with the drain of the MOS tube in the first-stage MOS tube circuit via a drain protection resistor.

[0015] The active current control circuit in this embodiment of the present invention can regulate and stabilize the cathode emission current of a field emission X-ray source. Suitable for cathode current control in cold cathode field emission X-ray sources, it offers real-time performance and high stability. It achieves cathode current stabilization and balance in cold cathode field emission X-ray sources by controlling cascaded MOSFETs using low-voltage signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0017] Figure 1 Schematic diagram of the active current control circuit of the present invention;

[0018] The figures are marked as follows: 1. Field emission X-ray source module; 2. First-stage MOS tube circuit; 3. Second-stage MOS tube circuit; 4. Field emission X-ray source anode; 5. Focusing electrode; 6. Field emission gate; 7. Field emission X-ray source cathode; 8. Anode power supply; 9. Focusing electrode power supply; 10. Field emission gate power supply; 11. Drain protection resistor; 12, 16, 17. MOS tube; 13, 18, 23. MOS tube gate protection resistor; 14. MOS tube gate pulse drive power supply; 15. MOS tube series expansion circuit; 19, 22. MOS tube gate DC drive power supply; 20. MOS tube gate drive series control circuit; 21. MOS tube parallel expansion circuit. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0020] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0021] In actual operation, under continuous operation, the channel width of the MOS tube will change with the applied high voltage, and the operating current will also change accordingly. If the continuous operating current is large, the operating current will change due to the Joule heating effect. To solve the above problems, the present invention proposes an active current control circuit and designs a circuit with multiple MOS tubes in cascade, which can achieve the regulation and stabilization of the cathode emission current of the field emission X-ray source. It is suitable for the cathode current control of the cold cathode field emission X-ray source, has the characteristics of real-time performance and high stability, and achieves the stabilization and balance of the cathode current of the cold cathode field emission X-ray source by controlling the cascaded MOSFET with a low-voltage signal. The present invention uses cascaded metal oxide semiconductor field effect transistors (MOSFET, MOS tube for short) as the current control circuit. For a given gate voltage, the current across the MOS tube DS is fixed and does not change with changes in the voltage applied to the two ends.

[0022] The basic contents of the technical solution of the present invention include:

[0023] (1) Select MOS tubes and design active current control circuits to stabilize and balance cathode current;

[0024] (2) Use MOS tubes in parallel to shunt the current;

[0025] (3) Use high-voltage MOS tubes in series to divide the voltage;

[0026] (4) Using a cascade circuit with multiple MOS tubes connected in series and parallel to adjust the operating current;

[0027] (5) The parallel MOS tube uses a small DC voltage to control the gate, and the series high-voltage MOS tube uses a low-voltage pulse signal to control the gate;

[0028] (6) The high-voltage end is the drain of the first-stage high-voltage MOS tube connected to the cathode of the field emission X-ray source through a protective resistor, and the low-voltage end is the source of the parallel MOS tube grounded;

[0029] (7) Connect each MOS tube driver in series so that all MOS tubes in each stage can be turned on at the same time.

[0030] The detailed technical solutions of the present invention are as follows:

[0031] The overall schematic diagram of the active current control circuit is as follows: Figure 1 As shown, the field emission X-ray source cathode 7 in the field emission X-ray source module 1 is connected to the drain of the MOS transistor 12 in the first-stage MOS transistor circuit 2 via a drain protection resistor 11. The drain protection resistor 11 prevents damage to the field emission X-ray source cathode 7 due to excessive current in the circuit when the MOS transistor 12 breaks down. The MOS transistor 12 at this stage is a high-voltage MOS transistor. The pulsed operating state of the field emission X-ray source module 1 is also controlled by the MOS transistor 12 at this stage. The on and off of the MOS transistor 12 is controlled by applying a pulse signal to the gate of the MOS transistor 12. When the gate signal is at a low level, that is, the MOS transistor 12 is in the off state, the MOS transistor 12 will bear the high voltage from the field emission X-ray source cathode 7. If the voltage exceeds the withstand voltage range of the MOS transistor 12, further MOS transistors can be connected in series to divide the voltage. The high level of the gate signal of the MOS transistor 12 at this stage generally puts the MOS transistor in a fully open saturation region.

[0032] The second-stage MOS transistors 16 and 17 in the second-stage MOS transistor circuit 3 are connected in parallel, that is, their drains are connected to each other, and their sources are connected to each other. The drains of the parallel MOS transistors 16 and 17 are connected to the source of the first-stage MOS transistor 12. The withstand voltage requirement of the MOS transistors 16 and 17 in this stage is not limited. Due to the voltage divider effect of the first-stage MOS transistor 12, the voltage across the drain and source of the MOS transistors 16 and 17 in this stage is relatively small, and therefore the withstand voltage requirement is not high. Since the field emission X-ray source cathode 7 and the two-stage MOS transistors are connected in series, the current of the field emission X-ray source cathode 7 is equal to the sum of the operating currents of the MOS transistors 16 and 17 of this stage. The main function of the MOS transistors 16 and 17 of this stage is to control the magnitude of the current emitted by the field emission X-ray source cathode 7. When the current is large, the MOS transistors will produce Joule heating effect, causing the MOS transistor channel width to change, and the stable operating current will also be affected and changed accordingly. Therefore, the MOS transistors 16 and 17 are connected in parallel to shunt the current in the circuit, thereby reducing the impact of the current heating effect on the operating state of the MOS transistors, so that the operating current of the MOS transistors is stabilized and balanced. For larger currents, MOS transistors can be connected in parallel to shunt the current until the MOS transistors maintain a stable operating state. The sources of the MOS transistors 16 and 17 of this stage are directly grounded.

[0033] In this embodiment, the gate of each stage of the MOS transistor is connected to the MOS transistor gate pulse drive power supply 14, the MOS transistor gate DC drive power supply 22, and the MOS transistor gate DC drive power supply 19 through the MOS transistor gate protection resistors 13, 18, and 23. The resistors can limit the gate current to prevent the gate from being broken down when the MOS transistor is turned on. For the first-stage MOS transistor 12, since a pulse signal is applied to the gate, parasitic inductance is generated on the lead, which forms an LC oscillation circuit with the parasitic capacitance generated by the gate. The series resistors can suppress the oscillation and protect the circuit.

[0034] In this embodiment, the number of first-stage MOS transistors connected in series can be determined based on the actual high voltage value applied and the withstand voltage of the selected MOS transistors. The number of parallel MOS transistors to be connected can be determined based on the actual operating current. The driving power supply of each stage of MOS transistors needs to be controlled by connecting them in series to ensure that they enter the operating state at the same time.

[0035] The key points and points to be protected of the present invention are at least:

[0036] The key point of the present invention is to utilize the characteristic that when a MOS tube has a given gate voltage and the voltage is greater than the turn-on voltage of the MOS tube, the current passing through the drain and source of the MOS tube is constant and does not change with the voltage applied to both ends. According to the actual high voltage required to load the field emission X-ray source and the emission current required by the cathode, multiple MOS tubes are connected in series or parallel. The two stages of MOS tubes in series respectively play the role of high voltage division and current shunting, which can not only realize the pulse control of field emission, but also enable the MOS tube to operate in a relatively ideal state, and achieve better current control and stability effects.

[0037] Compared with the prior art, the advantages of the present invention are at least:

[0038] (1) The existing current control method is to perform feedback adjustment control based on the real-time detection of the field emission X-ray emission current. The adjustment time is restricted by the steps of sampling, calculation feedback, etc., which makes the feedback adjustment have hysteresis. The method adopted by the present invention is to directly control the cathode current in real time through an active control circuit, which has a better effect on the stability control of the current.

[0039] (2) The existing feedback control circuit design of field emission X-rays is relatively complex, including multiple modules such as sampling, storage, calculation, and control, and has poor scalability. The method adopted in the present invention has a simple circuit structure and can meet different needs in practical applications through simple design changes.

[0040] The present invention has been designed to be equipped with a cascaded MOS tube current control circuit connected to a carbon nanotube cathode for high-voltage testing, and the experimental test results are feasible. The present invention can also be applied to similar scenarios where stable circuit current is required in field emission.

[0041] The serial numbers of the above embodiments of the present invention are for description only and do not represent the advantages or disadvantages of the embodiments.

[0042] In the above embodiments of the present invention, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0043] In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. Among them, the system embodiments described above are only exemplary. For example, the division of units can be a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of units or modules, which can be electrical or other forms.

[0044] Units described as separate components may or may not be physically separate, and components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple units. Some or all of the units may be selected to achieve the purpose of the present embodiment according to actual needs.

[0045] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0046] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server or network device, etc.) to execute all or part of the steps of the methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), mobile hard disk, magnetic disk or optical disk, etc. Various media that can store program codes.

[0047] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An active current control circuit, characterized in that: include: A field emission X-ray source module, a drain protection resistor, a first-stage MOS transistor circuit, and a second-stage MOS transistor circuit; the field emission X-ray source in the field emission X-ray source module is connected in series with the MOS transistor in the first-stage MOS transistor circuit via the drain protection resistor; the second-stage MOS transistor circuit includes two MOS transistors connected in parallel; the two MOS transistors in the second-stage MOS transistor circuit are connected in parallel and then connected in series with the MOS transistor in the first-stage MOS transistor circuit; The field emission X-ray source cathode in the field emission X-ray source module is connected in series with the drain of the MOS tube in the first-stage MOS tube circuit via the drain protection resistor; The pulse working state of the field emission X-ray source module is controlled by the MOS transistor in the first-stage MOS transistor circuit by applying a pulse signal to the gate of the MOS transistor in the first-stage MOS transistor circuit; When the gate applied pulse signal is at a low level, the MOS transistor in the first-stage MOS transistor circuit operates in a cut-off state and bears the high voltage from the cathode of the field emission X-ray source. When the gate applied pulse signal is at a high level, the high level causes the MOS transistor in the first-stage MOS transistor circuit to be in a fully turned-on saturation region. In the second-stage MOS transistor circuit, the drains of the two parallel MOS transistors are connected to each other, and the sources are connected to each other; the drains of the two parallel MOS transistors are connected to the source of the MOS transistor in the first-stage MOS transistor circuit; The source terminals of the two MOS transistors in the second-stage MOS transistor circuit are grounded; The MOS tube in the first-stage MOS tube circuit and the two MOS tube gates in the second-stage MOS tube circuit are respectively connected to the MOS tube gate pulse drive power supply, the MOS tube gate DC drive power supply, and the MOS tube gate DC drive power supply through the MOS tube gate protection resistor.

2. The active current control circuit according to claim 1, characterized in that: The MOS tube in the first-stage MOS tube circuit is a high-voltage MOS tube.

3. The active current control circuit according to claim 1, wherein: The cathode current of the field emission X-ray source is equal to the sum of the operating currents of the two MOS tubes connected in parallel in the second-stage MOS tube circuit.

4. The active current control circuit according to claim 1, characterized in that: A pulse signal is applied to the gate of the MOS tube in the first-stage MOS tube circuit, and parasitic inductance is generated on the lead, which forms an LC oscillation circuit with the parasitic capacitance generated by the gate.

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