A high-isolation filament power supply device based on current hall sampling

Abstract

The application discloses a high-isolation filament power supply device based on current Hall sampling, which comprises a monitoring background, a front-stage module and a rear-stage module. The front-stage module is sequentially provided with an input filter, a step-down transformer, a rectifier bus circuit and an LLC two-switch half-bridge resonant inverter circuit; the rear-stage module is provided with a high-frequency isolation transformer with a high-voltage insulation structure, a high-frequency bridge rectification filter circuit, a current Hall sensor and a voltage Hall sensor. An output conductor passes through a detection hole of the current Hall sensor, and a current sampling signal is fed back to a frequency modulation controller after being regulated; the frequency modulation controller adjusts the inverter working frequency according to a current given value, so as to form 0-10A output current closed-loop control; current, voltage states and fault signals are converted by pressure-frequency conversion and transmitted by an optical fiber link, so that the isolation safety, constant current precision and anti-interference capability of high-suspended potential filament power supply are improved.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a high-isolation filament power supply device based on current Hall sampling. Background Technology

[0002] Filament power supplies are primarily used to provide heating energy to the filaments of klystrons, traveling wave tubes, and other vacuum electronic devices, enabling the filaments to generate stable thermionic emission, thereby ensuring the normal establishment and maintenance of the vacuum electronic devices' operating state. These filaments typically require a low-voltage, high-current DC power supply, and the filament temperature is directly related to the supply current. Simultaneously, the klystron filament and cathode are usually at a high potential of tens of kilovolts during operation. Although the filament power supply outputs low voltage and high current, the entire output circuit may be at a relatively high floating potential relative to the device's ground terminal. Therefore, the filament power supply needs to balance constant current accuracy and high-voltage isolation safety. Traditional filament power supplies generally use a power frequency transformer combined with a low-voltage rectification and regulation architecture, which has drawbacks such as insufficient isolation withstand voltage, low output current sampling accuracy, slow dynamic response, and limited protection functions. In high-voltage special load conditions such as klystrons, traditional filament power supplies struggle to achieve high-precision closed-loop control of the output current. They lack comprehensive monitoring and protection for input voltage, output electrical parameters, operating temperature, and drive status, making them prone to overvoltage, overcurrent, overtemperature, and drive failure, leading to filament damage and system shutdown. Furthermore, traditional power supplies often use wired signal transmission, which is highly susceptible to signal distortion, command misinterpretation, and delayed fault reporting in complex, strong electromagnetic environments, failing to meet the intelligent application requirements for remote parameter adjustment and precise fault location.

[0003] Existing filament power supplies typically consist of an input filter, a power frequency step-down transformer, a rectifier and filter circuit, a power regulation circuit, and a sampling control circuit. AC mains power is stepped down, isolated, and rectified before supplying power to the filament. The sampling control circuit usually uses a series sampling resistor to obtain the voltage signal corresponding to the output current, then compares this signal with a preset reference and adjusts the power devices. For high floating potential outputs, optocouplers, isolation amplifiers, or transformer coupling circuits are also needed to transmit the sampling and control signals. Therefore, existing technologies suffer from weak isolation performance, insufficient sampling accuracy, imperfect protection mechanisms, and poor electromagnetic interference resistance, making it difficult to meet the long-term stable power supply requirements of high-end klystron filaments.

[0004] However, in the high-potential, strong electromagnetic interference environment where the klystron is located, existing filament power supplies struggle to simultaneously guarantee high-voltage isolation safety and output current closed-loop control accuracy. The creepage distances and clearances of traditional insulation structures are often designed according to general low-voltage power supply specifications, making them susceptible to the coupling effects of high-voltage electric fields and parasitic capacitance. High-current sampling resistors generate additional losses and temperature rises, and their resistance values ​​change with temperature, leading to sampling errors. Furthermore, they cannot create inherent electrical isolation between the power circuit and the low-voltage control circuit. When the sampled signal is transmitted through long wired lines or through nonlinear isolation devices, amplitude deviations, waveform distortions, or response delays can easily occur. With filament resistance varying with temperature and input voltage fluctuating, these errors can further cause the actual output current to deviate from the set value, even resulting in start-up overshoot or continuous fluctuations. Therefore, how to improve the sampling accuracy and closed-loop regulation stability of the filament output current while meeting the high-voltage floating output isolation requirements is a technical problem that existing filament power supplies need to solve. Summary of the Invention

[0005] The purpose of this invention is to provide a high-isolation filament power supply device based on current Hall sampling, which overcomes the shortcomings of existing filament power supplies such as insufficient sampling accuracy, weak high-voltage isolation performance, imperfect protection mechanism, poor adaptability to electromagnetic environment, and insufficient remote controllability. It achieves high-precision closed-loop voltage regulation of output current, complete electrical isolation between high and low voltage, multi-dimensional fault protection under all operating conditions, and anti-interference remote fiber optic control, effectively improving the operating stability, control accuracy, and safety protection level of the filament power supply.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A high-isolation filament power supply device based on current Hall sampling includes a front-end module and a back-end module. The front-end module includes an input filter, a step-down transformer, a rectifier bus circuit, and a resonant inverter circuit connected in sequence, as well as a control circuit connected to the control terminal of the resonant inverter circuit. The back-end module includes a high-frequency isolation transformer, a high-frequency rectifier filter circuit, and a current Hall sensor. The primary winding of the high-frequency isolation transformer is connected to the output terminal of the resonant inverter circuit, and the secondary winding of the high-frequency isolation transformer is connected to the input terminal of the high-frequency rectifier filter circuit. A high-voltage insulation structure is provided between the primary and secondary windings. The output terminal of the high-frequency rectifier filter circuit is used to connect to the filament load. The current Hall sensor has a detection hole through which the output conductor of the high-frequency rectifier filter circuit passes. The sampling output terminal of the current Hall sensor is connected to the control circuit. The control circuit receives the output current setpoint signal and the current sampling signal output by the current Hall sensor, and adjusts the operating frequency of the resonant inverter circuit according to the deviation between the output current setpoint signal and the current sampling signal.

[0007] In one embodiment, the step-down transformer has a primary winding connected to AC mains power, a main power secondary winding, and multiple independent auxiliary secondary windings. The main power secondary winding is connected to the rectifier bus circuit and is used to output the main circuit AC voltage to the rectifier bus circuit. The multiple auxiliary secondary windings are connected to an auxiliary power supply board, which includes an auxiliary rectifier circuit, a positive voltage regulator circuit, a negative voltage regulator circuit, and a fan power supply regulator circuit, which are respectively connected to the multiple auxiliary secondary windings to form a positive auxiliary voltage, a negative auxiliary voltage, and a fan power supply voltage.

[0008] In one embodiment, the rectifier bus circuit includes a bridge rectifier connected to the main power secondary winding, a bus energy storage capacitor connected to the output terminal of the bridge rectifier, a current-limiting resistor connected in series between the bridge rectifier and the bus energy storage capacitor, and a relay contact connected in parallel with the current-limiting resistor; the control circuit includes a bus voltage sampling circuit and a soft-start control circuit, the soft-start control circuit being used to drive the relay contact to close after the bus energy storage capacitor has reached a set charging condition, so as to bypass the current-limiting resistor.

[0009] In one embodiment, the resonant inverter circuit is a half-bridge resonant inverter circuit, including a first power MOSFET and a second power MOSFET connected in series between the positive and negative terminals of the DC bus, and a resonant capacitor and a resonant inductor located between the midpoint of the half-bridge and the primary winding of the high-frequency isolation transformer; the control circuit includes a frequency modulation controller and a drive circuit, the frequency modulation controller outputs two complementary drive signals, the two complementary drive signals are respectively connected to the gates of the first power MOSFET and the second power MOSFET through the drive circuit, and a dead time is provided between the two complementary drive signals to prevent the first power MOSFET and the second power MOSFET from conducting simultaneously.

[0010] In one embodiment, the high-frequency isolation transformer includes a ferrite core, a primary winding and a secondary winding wound on the ferrite core. The primary winding is made of copper foil, and the secondary winding is made of high-voltage insulated wire. A multi-layer composite insulation layer and an insulation gap that meets the high-voltage creepage distance are provided between the primary winding and the secondary winding. The primary and secondary insulation withstand voltage of the high-frequency isolation transformer is not less than 40kV.

[0011] In one embodiment, the high-frequency rectifier filter circuit includes a bridge rectifier circuit composed of four high-frequency rectifier devices, an output filter capacitor connected between the output terminals of the bridge rectifier circuit, and an output filter inductor connected in series with the positive output terminal of the bridge rectifier circuit; the current Hall sensor is a closed-loop current Hall sensor, the positive output conductor of the high-frequency rectifier filter circuit passes through the detection hole of the current Hall sensor, and the sampling output terminal of the current Hall sensor is connected to a sampling resistor that converts the secondary current signal into a voltage signal; a voltage Hall sensor is also connected in parallel between the two output terminals of the high-frequency rectifier filter circuit.

[0012] In one embodiment, the control circuit includes a current signal conditioning circuit, a voltage signal conditioning circuit, and a voltage-to-frequency conversion circuit. The sampling output terminal of the current Hall sensor is connected to the current feedback terminal of the frequency modulation controller, the output current protection circuit, and the voltage-to-frequency conversion circuit via the current signal conditioning circuit. The sampling output terminal of the voltage Hall sensor is connected to the output overvoltage protection circuit and the voltage-to-frequency conversion circuit via the voltage signal conditioning circuit. The voltage-to-frequency conversion circuit is connected to an optical fiber transmitter to convert the output current sampling signal and the output voltage sampling signal into frequency signals and then transmit them outward via optical fiber.

[0013] In one embodiment, the control circuit further includes a remote setpoint circuit, a local setpoint circuit, and a setpoint signal selection circuit; the remote setpoint circuit includes an optical fiber receiver, a frequency-to-voltage conversion circuit, and a signal conditioning circuit connected in sequence; the local setpoint circuit includes an adjustable resistor and a reference voltage circuit connected to the adjustable resistor; the setpoint signal selection circuit is connected to the remote setpoint circuit, the local setpoint circuit, and the frequency modulation controller, respectively, and is used to select either the remote output current setpoint signal or the local output current setpoint signal as the current control reference of the frequency modulation controller.

[0014] In one embodiment, the control circuit further includes an input overvoltage and undervoltage detection circuit, a drive anomaly detection circuit, an output current overlimit detection circuit, an output overcurrent detection circuit, an output overvoltage detection circuit, an overtemperature detection circuit, a fault summary circuit, and a fault latching circuit. Multiple input terminals of the fault summary circuit are connected to the fault output terminals of each detection circuit, and the output terminal of the fault summary circuit is connected to the set terminal of the fault latching circuit. The blocking output terminal of the fault latching circuit is connected to the enable terminal of the frequency modulation controller and the drive circuit. The reset terminal of the fault latching circuit is connected to a local reset switch and a fiber optic remote reset circuit.

[0015] In one embodiment, the front-end module and the back-end module are respectively housed in independent housings. The housing of the back-end module includes an external insulating plate and a metal chassis disposed inside the external insulating plate. The back-end module is internally provided with a first epoxy insulating partition and a second epoxy insulating partition. The first epoxy insulating partition separates the primary side region of the high-frequency isolation transformer from the secondary output region, and the second epoxy insulating partition separates the secondary output region from the sampling signal lead-out region. The current Hall sensor and the voltage Hall sensor are respectively housed in a nylon insulating shell. The nylon insulating shell is filled with epoxy potting compound, and the sampling signal line led out from the nylon insulating shell is externally sleeved with a high-voltage heat shrink tubing or an epoxy insulating tube.

[0016] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: In this invention, by sequentially arranging input conversion, resonant inverter, high-frequency isolation converter, and high-frequency rectification and filtering in the main power transmission path, the AC input power can be converted into frequency-adjustable high-frequency AC power after filtering, step-down, and rectification. The high-frequency isolation transformer then completes voltage conversion and electrical isolation between high and low voltage circuits, adapting to the high floating potential operating environment of the klystron filament output circuit. The high-voltage insulation design between the primary and secondary sides of the high-frequency isolation transformer, combined with the partitioning of the front-end and rear-end modules, reduces crosstalk and coupling effects of the high-potential output circuit on the low-voltage control circuit. The output conductor passes through the detection hole of the current Hall sensor, allowing the output current to be converted into a corresponding sampling signal without directly contacting the low-voltage sampling circuit, reducing the additional losses, temperature rise, and resistance drift caused by traditional high-power sampling resistors. The control circuit adjusts the operating frequency of the resonant inverter circuit based on the deviation between the output current given signal and the current sampling signal, thus forming a closed-loop regulation of the output current. This ensures that the filament current remains stable despite input voltage fluctuations, filament resistance changes with temperature, and load variations, improving the consistency of filament heating temperature and electron emission state.

[0017] This invention also combines local and fiber optic remote input methods, allowing for selection of the appropriate output current setting mode based on the operating environment. The output current and voltage sampling signals, after conditioning and voltage-to-frequency conversion, can be transmitted via fiber optic cable, avoiding common-mode interference, pulse interference, and ground potential differences introduced by long metal signal lines in strong electromagnetic environments, thus improving the anti-interference capability of remote parameter transmission. The input soft-start circuit limits the surge current generated during the charging of the bus energy storage capacitor, while the output current soft-start control suppresses abnormal current output during startup and fault recovery. Detection circuits for input overvoltage and undervoltage, output overvoltage, output overcurrent, current over-limit, over-temperature, and drive abnormalities monitor the corresponding operating states. In case of abnormalities, fault summarization and latching circuits block the resonant inverter drive to prevent further fault escalation. After fault resolution, reset can be completed locally or remotely via fiber optic cable. Combined with heat dissipation measures for temperature and load status control, this helps reduce the operating temperature rise of power devices and rectifier devices, thereby improving the safety and reliability of the filament power supply under high potential, strong interference, and long-term continuous operation conditions. Attached Figure Description

[0018] Figure 1 This is an electrical design block diagram of the device of the present invention; Figure 2 This is a power circuit design diagram of the front-end module of the present invention; Figure 3 This is the auxiliary power design diagram of the front-end module of the present invention; Figure 4 This is a design diagram of the input soft start and input voltage detection of the front-end module of the present invention; Figure 5 The design diagram for the output current of the front-end module of this invention is provided. Figure 6 This is a design diagram of the MC33067 frequency modulation control for the front-end module of this invention; Figure 7 This is a design diagram of the output current sampling of the front-end module of the present invention; Figure 8 This is a design diagram of the output voltage sampling of the front-end module of this invention; Figure 9 This is a soft-start design diagram for the output current of the front-end module. Figure 10 Design drawing for the start / stop of the front-stage cooling fan invented for this front-stage module; Figures 11-17 This is a protection design diagram for the front-end module of the present invention; Figure 18 This is a fault reset design diagram for the front-end module of the present invention; Figure 19 This is the electrical schematic diagram of the subsequent module of the present invention; Figure 20 This is a schematic block diagram showing the structural layout of the filament power supply device of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] It should be noted that the terms "setup" and "connection" should be interpreted broadly. For example, they can refer to direct setup or connection, or indirect setup or connection through centered components or centered structures.

[0021] Furthermore, in embodiments of this invention, terms such as "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer" are used to indicate orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, or in a conventional placement or usage state. These terms are merely for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the structures, features, devices, or elements referred to must have a specific orientation or positional relationship, nor that they must be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0022] The various specific technical features and embodiments described in the detailed embodiments can be combined in any suitable manner without contradiction. For example, different implementation methods can be formed by combining different specific technical features / embodiments. In order to avoid unnecessary repetition, the various possible combinations of the various specific technical features / embodiments in this invention will not be described separately.

[0023] It should be noted that the "40kV high isolation" in this embodiment refers to the insulation withstand voltage between the primary and secondary sides of the high-frequency isolation transformer and between the front and rear modules, and does not refer to the 40kV output voltage at the filament end; the output voltage at the filament end is a low-voltage, high-current DC current adapted to the klystron filament, and its output circuit can be at a high floating potential along with the cathode. Figure 2 The main power switching unit shown is a two-switch half-bridge structure. Figure 19 The four rectifier devices shown form a bridge rectifier structure.

[0024] The principles of the present invention will be further explained below with reference to the accompanying drawings. Please refer to the accompanying drawings. Figures 1-20This invention discloses a high-isolation regulated filament power supply device based on Hall current sampling. The device adopts a modular split architecture for the front and rear stages and relies on Hall isolation sampling, LLC resonant high-frequency inverter, 40kV high-voltage isolation structure, fiber optic isolation communication, and multi-level fault protection to achieve high-precision, high-safety, and high-reliability regulated constant current power supply for filaments.

[0025] The monitoring backend establishes an isolated communication link with the front-end module via fiber optic cable. When the equipment is running normally, it sends a high-frequency current command signal to precisely adjust the power output and current. After the equipment fails and locks up, it can remotely send a reset signal to release the fault lock and restore the equipment to normal operation. At the same time, it can receive, store, and display various fault signals in real time, realizing remote monitoring, precise parameter control, and fault tracing.

[0026] When the equipment is working, the mains power first passes through an EMI filter to remove electromagnetic interference and is then fed into a step-down transformer. The step-down transformer converts the mains power into AC 110V and sends it to the power board. The power board rectifies the AC voltage to obtain the DC bus voltage, which is then converted into high-frequency AC power by an LLC two-switch half-bridge resonant inverter circuit and sent to the high-frequency transformer in the subsequent module. The high-frequency isolation transformer achieves a primary-secondary isolation withstand voltage of not less than 40kV and completes the voltage conversion. After bridge rectification and filtering by the high-frequency rectifier output board, a stable low-voltage, high-current DC power is output to supply the filament load, with a continuously adjustable output current range of 0-10A.

[0027] Front-end module design like Figure 1 As shown: The front-end module consists of an EMI filter, a step-down transformer, a power board, an auxiliary power board, a control board, and a front-end cooling fan.

[0028] Filter design: Equipped with a military-grade EMI filter, model ZYH-EF-5A, it suppresses low-frequency disturbances from the power grid and high-frequency harmonics generated by the switching power supply, while attenuating line-to-line differential-mode interference and line-to-ground common-mode interference, improving the overall electromagnetic compatibility performance. The filament power supply is used in high-voltage klystron applications, where the electromagnetic environment is complex. The military-grade filter features high reliability, low leakage current, and strong anti-interference characteristics, preventing LLC inverter harmonics from entering the power grid in reverse and blocking power grid fluctuations from affecting power supply control accuracy.

[0029] Step-down transformer design: The front-stage power frequency step-down transformer is the core power input conversion unit of the entire machine. It steps down the AC220V mains power into multiple independent AC power supplies, providing isolated power to the main power conversion board and the auxiliary power supply board, achieving electrical isolation and power distribution between strong and weak currents. The transformer's multi-independent winding design achieves complete electrical isolation between the main power and auxiliary power supplies, avoiding high-frequency disturbances in the main power circuit and load switching interference to the weak current control circuit, significantly improving the overall machine's anti-interference capability and system reliability.

[0030] Power matching calculation The maximum output parameters of the LLC main power stage of this device are: load resistance RL = 1.5Ω, maximum output current Iomax = 11A (maximum overcurrent point).

[0031] Formula for calculating maximum output power:

[0032] The main power input is taken from the 110V winding of the transformer, with a conversion efficiency of η=0.95. The required power at the front end is: ; To account for losses in the subsequent stages, this article will explain the design of the cooling fan for the subsequent stages. Formula for calculating the rated input current of a 110V winding:

[0033] Total rated power of the three 12V auxiliary windings:

[0034] Transformer output power: ;

[0035] Total input power of the transformer: ;

[0036] The 110V winding is designed with a margin, and the rated current is designed to be 2A.

[0037] The design power of the 110V winding is:

[0038] The total design power of the transformer is calculated based on a main output winding design power of 220W, a total power of 33W for the three auxiliary windings, and other losses of 17.7W excluding the power frequency transformer in the preceding stage. This represents the total heat output of the front stage. The difference between the two values ​​is 17.7W, representing the power frequency transformer loss.

[0039]

[0040] The rated total output power is 300W in the engineering design.

[0041] Transformer Parameter Specification Table

[0042] project Parameters and Specifications Input rated voltage AC220V 50Hz Input voltage range AC 176V~264V Main output winding AC110V / 2A Auxiliary output winding 3 independent AC12V / 1A channels Rated total output power 300W Overall machine full load efficiency ≥90% Work mode Long-term continuous full-load operation Cooling method Natural air cooling

[0043] Power board design: like Figure 2 As shown, the power board includes an input EMI circuit, a power-on soft-start circuit, a bus energy storage circuit, an LLC resonant inverter circuit, and a drive circuit. The rectified and filtered AC 110V AC power forms a DC bus voltage, providing DC input to the LLC inverter circuit. This device uses an MC33067 fixed pulse width modulation (PWM) control architecture. By controlling the operating frequency of the drive circuit, the gain of the resonant circuit is dynamically adjusted, ultimately achieving high-precision constant current output in conjunction with the subsequent high-frequency rectifier circuit.

[0044] By utilizing the leakage inductance of the primary side of a high-frequency isolation transformer to form a resonant inductor, external magnetic components and additional losses can be reduced. Through the coordination of the resonant inductor, resonant capacitor, magnetizing inductor, drive pulse width, and dead time, the power MOSFET can achieve soft-switching conditions within the selected effective operating range, while reducing switching losses and device temperature rise, making it suitable for long-term continuous full-load operation of the device.

[0045] DC bus parameter calculation

[0046] The peak DC bus voltage after full-wave rectification of the 110V AC power frequency voltage is: This voltage is the core basis for selecting the withstand voltage of half-bridge power MOSFETs and verifying circuit stress.

[0047] LLC Resonant Core Parameter Design

[0048] This invention employs an LLC resonant topology without an external resonant inductor, and constructs a resonant circuit based on the inherent leakage inductance of the primary side of a high-frequency high-voltage transformer. This results in fewer components, higher circuit consistency, and lower parasitic losses.

[0049] The design values ​​for the resonant inductor are: Lr = 10μH (leakage inductance of the primary side of the high-frequency transformer); the design values ​​for the resonant capacitor are: Cr = 200nF.

[0050] Formula for calculating resonant natural frequency:

[0051] The preset frequency range of the controller in this device is 1kHz to 80kHz. The low-frequency end is used for start-up, disabling, or adjustment of the boundary. The actual stable operating frequency under load is determined based on the resonant gain curve, the flux density of the high-frequency isolation transformer, and the switching waveform of the power MOSFET. By limiting the minimum effective load frequency, matching the drive pulse width, and the dead time, the resonant current obtains suitable soft-switching conditions during commutation, thereby reducing high-frequency switching losses and device temperature rise.

[0052] Resonant current pulse width: ≤5µs, used to verify the timing of the two-switch half-bridge drive.

[0053] Transformer magnetizing inductance design specifications: ratio of magnetizing inductance to resonant inductance K is selected as 10; based on Lr=10µH, the excitation inductance design range is: Lm=10×Lr, and the design value is 100µH.

[0054] The excitation inductance is reasonably selected, which can balance the gain adjustment range of the resonant circuit and the excitation circulating current loss, and take into account both the light load adjustment capability and the full load efficiency.

[0055] Resonant characteristic impedance: , The effective current of the resonant circuit under full load conditions Used for power device conduction loss verification and heat dissipation design.

[0056] Power device selection The two-switch half-bridge inverter uses IRFP460PBF-VB high-voltage MOSFETs with a drain-source voltage (Vdss) of 500V, a continuous drain current (Id) of 40A, and an on-resistance (RDS(on)) of 80mΩ@10V, paired with a DB40 standard heatsink. The MOSFETs have ample voltage and current tolerances, are suitable for 155.6V DC bus stress and 5.0A full-load resonant current, and offer controllable temperature rise and high reliability under long-term full-load conditions.

[0057] Auxiliary power supply board design: like Figure 3 As shown: The auxiliary power supply board is powered by three independent 12V AC auxiliary windings, completely independent of the main power circuit, achieving electrical isolation between the low-voltage control power supply and the high-voltage power supply. The auxiliary power supply board provides multiple clean DC power outputs: dual ±15V power outputs, using voltage regulators 7815 and 7915 with heat sinks, continuously powering the control board, power board driver chips, and sampling circuit; and a separate +12V power output, using voltage regulator 7812 with heat sink, powering the cooling fan and soft-start circuit.

[0058] The independent auxiliary power architecture ensures that the power supply of the low-voltage control system remains stable and unfluctuated during dynamic adjustment of main power, load changes, and fault switching of the whole machine, completely avoiding control disorder and drive malfunction caused by main power disturbance, and greatly improving the stability and anti-interference capability of the whole machine.

[0059] Control board design: The control board includes an input soft-start circuit and an input voltage detection circuit, an output current setting circuit, a control circuit, an output current soft-start circuit, a front-end module cooling fan start / stop circuit, a sampling circuit, a protection circuit, and a fault reset circuit.

[0060] During the power-on phase, the input soft-start circuit performs power-on buffering, effectively suppressing inrush current. The input voltage detection circuit monitors the input voltage status in real time, cooperating with the entire unit to complete power-on self-test, ensuring the initial power-on state of the equipment is safe, compliant, stable, and reliable. During normal operation, the sampling circuit collects core operating parameters such as input voltage, overall operating temperature, output voltage, and output current in real time with high precision, and synchronously feeds back the conditioned standard sampling signal to the control and protection circuits. The control circuit uses the MC33067 frequency modulation chip as its core, and dynamically adjusts the LLC half-bridge inverter operating frequency based on the output current command issued by the upper monitoring background. Relying on the system's linear frequency modulation constant current characteristics, it achieves high-precision, continuously adjustable closed-loop constant current control of the output current from 0 to 10A. At the same time, the output current soft-start circuit can effectively suppress output current fluctuations during power-on, start-up, shutdown, and fault recovery processes. The front-end module cooling fan start-up / shutdown circuit intelligently starts and stops the cooling equipment based on the real-time operating temperature of the power MOSFET and the overall output current status, achieving on-demand cooling while considering the equipment's heat dissipation reliability and low-power operation requirements. The fault protection circuit continuously monitors the overall operating parameters and power unit drive status. When any fault condition is detected, such as input over / under voltage, output overvoltage, output overcurrent, current over-limit, overall over-temperature, or drive abnormality, it can instantly block the inverter drive signal, cut off the main power circuit, and latch the fault status. Simultaneously, it uploads the precise fault code to the monitoring backend via fiber optic cable, achieving rapid fault protection, accurate fault location, and data traceability. After the potential fault is completely eliminated, the fault reset circuit can clear the system fault latch flag, reset the protection logic, and restore drive enable, allowing the equipment to return to normal startup and operation.

[0061] The specific operational mechanisms of each sub-circuit are as follows: Input soft start circuit like Figure 4 As shown, during the initial power-up phase, the current-limiting resistor suppresses the instantaneous surge current of the bus capacitor at the AC110V input rectifier, preventing damage to the front-end rectifier devices, power MOSFETs, and high-frequency transformer from the large current surge at power-up. By establishing the bus voltage in a stepped manner, the entire unit achieves a smooth power-up, eliminating startup spikes, improving power-up reliability and extending device lifespan. After achieving steady-state power-up, the unit automatically exits the soft-start state and enters normal operating mode.

[0062] Input voltage detection circuit like Figure 4As shown: This circuit acquires the DC bus voltage signal output from the front-end rectifier module in real time. Through high-precision voltage division sampling, multi-stage signal filtering, waveform conditioning, and level conversion, it converts the original high-voltage analog signal into a standard voltage signal compatible with the main controller. The circuit has built-in fixed threshold judgment logic, which can accurately monitor abnormal input voltage faults: the input overvoltage protection threshold is set to 120% of the rated input voltage, and the input undervoltage protection threshold is set to 80% of the rated input voltage. It monitors the bus voltage operating range in real time, and once the voltage exceeds the compliant threshold range, it immediately outputs an abnormal signal to the protection circuit, realizing accurate judgment and reliable protection against input overvoltage and undervoltage faults.

[0063] Output current setting circuit like Figure 5 As shown: The system receives high-frequency optical signals from the upper-level monitoring backend, converts them into a level signal or a locally provided level signal via an LM231, and performs signal isolation, filtering, amplitude calibration, and limiting to generate a high-precision, interference-free standard current reference value. This reference value serves as the target benchmark for closed-loop control of the overall output current, precisely corresponding to a continuously adjustable output range of 0–10A, enabling stepless and precise setting of the output current and meeting the equipment's requirements for refined frequency modulation and constant current control.

[0064] control circuit like Figure 6 As shown: The core of the closed-loop control system is based on the MC33067 frequency modulation control chip, combined with the output current setting circuit and the output current sampling circuit. It receives current sampling feedback signals in real time, compares them with the output current setting reference value, and dynamically adjusts the operating frequency of the LLC half-bridge inverter. Utilizing the linear control characteristic that "the higher the frequency, the greater the output current," it achieves high-precision closed-loop constant current control of the output current. Simultaneously, it unifies and coordinates the entire machine's logic, including soft-start timing, fan start / stop, fault diagnosis, and signal uploading, ensuring the dynamic response and steady-state accuracy of the entire machine.

[0065] Maximum frequency design Pins 1 and 2 of the MC33067 chip are pins for the internal main oscillation RC network. Precise RC timing parameters limit the system's maximum frequency modulation, corresponding to the device's full-power and full-current output conditions. The maximum frequency configuration parameters for this device are: timing resistor R176 with a value of 17.8kΩ and timing capacitor C106 with a value of 1nF. This parameter combination limits the system's upper limit operating frequency. It accurately matches the preset frequency range of 1 to 80 kHz for the whole machine, ensuring that the output current can be stably driven to the full 10A rated value under high frequency extreme conditions, without gain dead or output distortion problems.

[0066] Minimum frequency design Based on the 3-pin RC parameter configuration of the MC33067 chip, the minimum oscillation frequency of the system is limited to adapt to low-voltage, low-current start-up and shutdown conditions of the equipment. The minimum frequency of this device is set to 1kHz, and the timing resistor R170 is set to a value of [value missing]. This parameter combination limits the lower limit of the system's operating frequency to 1kHz, ensuring that the equipment can start smoothly at low frequencies and achieve 0A shockless start-stop, perfectly covering the small current fine-tuning range of 0.2 to 10A, and guaranteeing the linearity and stability of small current output.

[0067] Drive pulse width design Using pins 1 / 2 and 14 / 15 of the CD4098, pulse width control is performed on the drive output from the MC33067 to precisely limit the effective width of the inverter drive pulse, ensuring stable energy transfer in the LLC resonant circuit. The pulse width configuration parameters of this power supply drive strictly match the standard values ​​in the chip datasheet: the timing resistors R171 / R177 for the upper / lower transistor drive are 7.32kΩ, and the timing capacitors C112 / C114 are 1nF. This precise matching of the standard parameters in the chip datasheet fixes the effective drive pulse width. The inherent discharge pulse width of 4.1μs is matched to the LLC resonant circuit to ensure reliable freewheeling of the resonant current; the actual soft-switching operating range is verified by switching waveform testing.

[0068] Two-switch half-bridge drive dead-time design Pin 16 of the MC33067 chip is the dead-time control RC network pin, used to precisely set the dead time of the inverter drive signal and prevent shoot-through crosstalk between the upper and lower transistors. The drive pulse width configuration parameters strictly match the standard values ​​in the chip datasheet: timing resistor R173 is 15kΩ and timing capacitor C107 is 100pF. This dead time effectively avoids bridge arm shoot-through crosstalk, meets the safe operation requirements of power devices, and is completely covered by the inherent resonant discharge pulse width, ensuring sufficient freewheeling of the resonant current across the entire frequency adjustment range. This is beneficial for forming soft-switching characteristics under measured resonant commutation conditions, reducing high-frequency switching losses of the entire unit, and ensuring safe, stable, and efficient operation of the inverter circuit throughout the entire process.

[0069] Sampling circuit The sampling circuit includes an output current sampling circuit and an output voltage sampling circuit.

[0070] Output current sampling circuit (such as) Figure 7 (As shown) The output current sampling employs a high-precision Hall effect sensor LT58-S7, paired with a 1kΩ sampling resistor to achieve precise matching of the main circuit current signal. The raw analog signal acquired by the Hall sensor is shaped, amplified, and level-matched by the back-end operational amplifier circuit, then split into two independent output signals: the first serves as a closed-loop control sampling feedback signal, sent to the current regulation loop of the MC33067 main control chip, providing a real-time current reference for the overall constant current closed-loop control; the second is connected to the output current fault protection circuit, serving as the basis for judging output overcurrent and current exceeding limits, achieving rapid current limiting and shutdown protection. Simultaneously, the conditioned current sampling signal undergoes analog-to-frequency conversion via a voltage-to-frequency converter circuit, and a high-frequency pulse signal is uploaded in real-time to the remote monitoring backend via high-frequency fiber optic cable, enabling remote real-time acquisition and monitoring of the output current. The sampling signal corresponds to a ratio of 1A:1kHz, with the frequency linearly corresponding to the current value, resulting in high acquisition accuracy and strong anti-interference capability.

[0071] Output voltage sampling circuit (such as) Figure 8 (As shown) The output voltage sampling circuit uses a dedicated DLS-0.01C voltage Hall sensor to achieve isolated and accurate acquisition of the output main circuit voltage signal. The acquired raw voltage signal, after amplification, filtering, and voltage regulation, is also divided into two independent output signals: one is connected to the overall protection circuit to determine the output overvoltage fault state and cooperate with the system to complete voltage anomaly blocking protection; the other is converted from the analog voltage signal to a high-frequency pulse signal via a voltage-to-frequency conversion circuit and uploaded to the monitoring backend in real time via a fiber optic link, realizing remote online monitoring and data traceability of the output voltage. The sampling signal ratio is 2V:1kHz, enabling linear high-precision acquisition of the entire output voltage range.

[0072] Output current soft start circuit like Figure 9 As shown: This circuit is independent of the input soft-start circuit and is designed specifically for output-side low-current start control. Its core function is to prevent low-current start control of the output, which can effectively suppress loop zero-drift current during power-on, standby and fault recovery phases, and completely solve the problems of no-load zero-drift and abnormal micro-current output.

[0073] Front-end module cooling fan start / stop circuit like Figure 10 As shown: Real-time acquisition of the operating temperature of the front-end power MOSFETs and the overall output load current parameters of the unit. Based on the 40°C temperature threshold of the devices and the 2A load current, the system intelligently controls the start and stop of the cooling fan. Under low-temperature and light-load conditions, the fan shuts off to reduce overall operating noise and unnecessary power consumption. Under high-temperature, full-load, and extreme overcurrent conditions, the system automatically activates forced air cooling to dissipate heat from core heat-generating units such as the power MOSFETs, step-down transformers, and rectifier devices, preventing excessive temperature rise of power devices and ensuring the stable operation of the entire unit under long-term full load and extreme conditions.

[0074] Protection circuit The protection circuit is the core unit for overall machine safety protection, integrating input fault detection, drive fault detection, output current over-limit fault detection, output overcurrent fault detection, output overvoltage fault detection, front-end module over-temperature fault detection, and a total fault lockout circuit, forming a multi-dimensional, hierarchical, and fully closed-loop fault protection system. This circuit continuously monitors various operating parameters of the entire machine and the working status of the power drive unit, accurately identifying and distinguishing between transient interference and real faults. It features protection against false tripping, fault reporting without false alarms, fast response speed, and reliable latching. Once a valid fault condition is determined, it immediately executes ultra-fast protection logic, instantly blocking the LLC inverter drive signal, cutting off the main power output, and latching the fault state, completely preventing fault propagation and effectively protecting power devices and downstream load equipment. The specific fault detection and total latching protection mechanisms are as follows: Input fault detection (e.g.) Figure 11 (As shown)

[0075] This circuit monitors the DC bus voltage after rectification by the front-end module in real time and uses fixed threshold judgment logic to identify input abnormalities. When the input bus voltage fluctuation exceeds the upper limit of the rated voltage (120% overvoltage threshold) or falls below the lower limit of the rated voltage (80% undervoltage threshold), the circuit immediately outputs an input fault signal IN-ERRO and sends it to the back-end fault latch, triggering the overall fault protection mechanism, blocking power output, and avoiding risks such as inverter runaway and excessive stress on components caused by abnormal input voltage.

[0076] Driver fault detection (e.g.) Figure 12 (As shown) Used to monitor abnormal operating conditions of LLC inverter drive logic, it provides specific protection against shoot-through risk in the half-bridge arm. When an abnormal shoot-through state is detected where both inverter drive signals output by the MC33067 chip are simultaneously high, a drive fault signal QT-ERRO is immediately output and sent to the fault latch, quickly triggering protection blocking. This completely avoids shoot-through short-circuit faults caused by the simultaneous conduction of the upper and lower bridge arm MOSFETs, ensuring the safe operation of the inverter circuit.

[0077] Output current over-limit fault detection (e.g.) Figure 13 (As shown) This system is used to achieve refined output current limiting protection, preventing small current deviations and long-term overload operation. The system compares the output current setpoint with the actual sampled value in real time. When the actual output current exceeds 1.1 times the over-limit threshold of the real-time setpoint, the circuit outputs an over-limit fault signal OI-ERRO and sends it to the latch, triggering graded protection, suppressing output current overshoot, and ensuring the accuracy of constant current control and the long-term safety of the load.

[0078] Output overcurrent fault detection (e.g.) Figure 14 (As shown) As a hard overcurrent fallback protection on the output side, a fixed limit current threshold is set. When the actual current in the output circuit exceeds the hardware limit setting of 11A, the circuit immediately outputs an overcurrent fault signal OC-ERRO and sends it to the latch to perform rapid shutdown protection, forcibly cutting off the main power output, preventing high current surges from burning out power devices and loads, and meeting the overall machine's extreme fault protection requirements.

[0079] Output overvoltage fault detection (e.g.) Figure 15 (As shown) Used for monitoring and protecting against abnormal output voltage in the downstream stage, preventing overvoltage from damaging the load equipment. When the actual output voltage exceeds the hardware-set protection threshold of 16.5V, the circuit outputs an overvoltage fault signal OV-ERRO and sends it to the latch, triggering the voltage abnormality protection, quickly blocking the inverter drive, suppressing the output voltage rise, and achieving over-limit safety protection for the output voltage.

[0080] Overall over-temperature fault detection (e.g.) Figure 16 (As shown) The circuit collects the operating temperature of the core heat-generating components of the power MOSFETs in the front-end module in real time to achieve high-temperature overheat protection. When the real-time temperature of the power MOSFETs exceeds the hardware-set threshold of 80°C, the circuit outputs an over-temperature fault signal OT-ERRO and sends it to the latch, triggering the overheat protection and forcibly shutting down the power output. This prevents the power devices from aging at high temperatures and burning out due to thermal runaway, ensuring the stability of the entire machine under high-temperature conditions.

[0081] Total fault lockout protection (such as Figure 17 (As shown) The overall fault latching circuit is the core of the overall fault summary latch, summarizing all subdivided fault signals. When any of the following fault types—input fault, drive fault, output current over-limit fault, output overcurrent fault, output overvoltage fault, or overall over-temperature fault—is triggered, the corresponding fault signal is sent to the overall fault latching unit, which outputs a unified blocking signal. This simultaneously blocks the LLC inverter drive signal and the MC33067 chip enable signal, achieving complete shutdown protection for the entire machine and permanently latching the fault state until it is released by local or remote reset. This ensures that the fault state is traceable and lockable, prevents repeated fault triggering, and significantly improves the reliability and safety of the overall machine operation.

[0082] Fault reset circuit like Figure 18As shown: After the equipment fails the fault latch protection, it provides a dual recovery mechanism of manual reset and remote reset. After the fault is cleared, the fault reset circuit clears the system latch fault flag, resets the main control protection logic, and restores the driver enable, allowing the equipment to return to a normal start-up and working state. At the same time, the reset process has anti-bounce and delay fault-tolerant logic to avoid system abnormalities caused by accidental resets or frequent resets, ensuring that the equipment fault recovery process is safe and controllable.

[0083] Pre-amplifier cooling fan design: The pre-amplifier cooling fan provides forced air cooling for the low-voltage power area, auxiliary power supply, and mains frequency conversion unit of the entire unit. The components cooled include: LLC inverter MOSFETs (IRFP460PBF-VB, with DB40 heatsink), resonant inductors, 7815, 7915, and 7812 voltage regulator chips, the pre-amplifier step-down mains frequency transformer, and core components of the control board. By accurately calculating the full-load heat generation of each component, the fan airflow is matched and selected to ensure long-term stable operation at low temperatures for all pre-amplifier components.

[0084] The full-load heat generation of each component in the preamplifier stage is calculated based on a maximum output current of 10A for the filament power supply and a load of 1.5Ω, as follows: Losses of the front-stage step-down power frequency transformer Total input power of power frequency transformer at full load Conversion efficiency ≥90%, The total loss formula is as follows:

[0085] Including copper and iron losses, it is the largest heat source in the front stage, and forced air cooling can significantly reduce steady-state temperature rise.

[0086] Loss calculation of LLC inverter MOSFET (IRFP460PBF-VB) This device operates at an LLC frequency of 80kHz, with a primary-side resonant RMS current Ir = 5.0A. It employs a two-switch half-bridge soft-switching design, prioritizing conduction losses while allowing for a margin of safety in switching losses. The half-bridge uses two MOSFETs: IRFP460PBF-VB, with a drain-source voltage (Vdss) of 500V, continuous drain current (Id) of 40A, and on-resistance Rds(on) of 0.08Ω.

[0087] Formula for single-tube conduction loss:

[0088] Total conduction loss of 2 MOSFETs:

[0089] The device is equipped with a DB40 standard heatsink, which can completely cover the temperature rise caused by the loss under forced air cooling conditions.

[0090] Resonant inductor (integrated transformer leakage inductance) loss This solution does not have an external resonant inductor. It achieves the resonant function by relying on the 10μH leakage inductance of the primary side of the high-frequency transformer. The loss has been included in the total loss of the high-frequency transformer, so the front-end does not need to be recalculated. Only auxiliary convection heat dissipation is required.

[0091] High-frequency high-voltage transformer loss accounting This device uses an EE55 high-frequency transformer operating at full load and a frequency of 80kHz. The core is made of PC44 manganese-zinc ferrite material. The total transformer loss includes high-frequency copper losses in the windings and iron losses in the core. The iron loss is calculated using the Steinmetz formula, taking into account the EE55 core volume, the 80kHz operating frequency, and the maximum magnetic flux density of 0.32T. Considering the skin effect and proximity effect at 80kHz, the total AC copper loss of the primary and secondary windings is calculated. .

[0092] Total loss under full load:

[0093] Three-way voltage regulator loss calculation After rectification, the AC 12V output is approximately DC 17V. It outputs two channels of regulated 15V and one channel of regulated 12V. The voltage difference of a single channel of regulated 15V is ΔU1=2V, and the voltage difference of a single channel of regulated 12V is ΔU2=5V. The estimated maximum average operating current of regulated 12V is Ireg2=0.2A, and the estimated maximum average operating current of regulated 12V is Ireg1=0.5A, which meets the power supply requirements of control, drive, and fan.

[0094] Total loss across three paths:

[0095] Control board component loss Estimated overall loss under full load for low-voltage components such as the main control chip, sampling operational amplifier, and driver optocoupler. .

[0096] Remaining device losses For remaining components such as filters, main circuit capacitors, EMI circuits, filter inductors, and resonant capacitors, the estimated total loss under full load is as follows.

[0097] Summary of total heat output of the pre-stage

[0098] Pre-fan air volume selection calculation

[0099] This design uses the general formula for calculating air volume in industrial forced air cooling, with an ambient temperature of 25℃ and a maximum allowable temperature rise of ΔT = 20℃ for the components, ensuring long-term full-load heat dissipation redundancy.

[0100] In the formula: specific heat capacity of air c = 1005 J / (kg·℃), air density ρ = 1.29 kg / m³, and P is the total regional heating power Pt.

[0101] Substitute the total heat output of the pre-amplifier into the theoretically required air volume, and convert the air volume unit:

[0102]

[0103] To adapt to harsh operating conditions such as enclosed equipment environments, dust accumulation, and high-temperature derating, a safety margin of 2 times the project volume is reserved, and the final selected air volume is:

[0104] Fan selection: 12V / 80mA DC fan, dimensions 50*50*10mm, airflow 13.8CFM; or 12V / 87mA fan, dimensions 40x40x10mm, airflow 9.9CFM. This fully meets the heat dissipation requirements and provides ample cooling margin. This airflow can cover harsh operating conditions such as heat accumulation in enclosed chassis, high summer temperatures, and dust buildup. Long-term full-load temperature rise is controllable, with no risk of overheating, aging, or power degradation, perfectly matching the front-end heat dissipation design requirements of this system. After power-on, the system activates when the LLC inverter MOSFET heatsink temperature reaches 40°C, providing directional forced convection cooling for the LLC inverter MOSFET heatsink, 7812 voltage regulator chip, power frequency step-down transformer, and control board, ensuring long-term continuous and stable full-load operation of the front-end power unit.

[0105] Post-module design

[0106] like Figure 1 As shown: The downstream module includes a high-frequency isolation transformer, a current Hall sensor, a voltage Hall sensor, a high-frequency rectifier output board, and a downstream cooling fan.

[0107] High-frequency high-voltage transformer design

[0108] Core specifications: EE55 vertical PC44 manganese-zinc ferrite core, with low high-frequency loss and high saturation flux density, suitable for long-term high-frequency operation from 1kHz to 80kHz; the primary side is wound with copper foil to suppress high-frequency skin effect loss, with 25 turns Np; the secondary side uses 40kV high-voltage flexible conductor, with high insulation level, good high-frequency characteristics, and strong anti-aging ability, with 10 turns Ns; the primary-secondary transformation ratio n = Np / Ns = 2.5.

[0109] The primary leakage inductance of the high-frequency isolation transformer is directly used as the LLC resonant inductor. Figure 2In the hardware combination shown, the equivalent leakage inductance of the primary side can be designed to be 50μH through the winding structure and matched with the equivalent resonant capacitor. In the above 1kHz to 80kHz frequency modulation embodiment, it is preferred to adjust the equivalent resonant inductance Lr to 10μH and the equivalent resonant capacitor Cr to 200nF. The following calculations are based on Lr=10μH and Cr=200nF. The maximum operating magnetic flux density Bmax of the high-frequency isolation transformer is ≤0.32T. The primary and secondary sides adopt a multi-layer composite insulation structure, and the overall insulation withstand voltage reaches 40kV.

[0110] Calculate the margin based on the maximum limiting condition:

[0111] The EE55 transformer has a rated design power of ≥300W, fully covering 11A overcurrent impact, high temperature aging, and voltage fluctuation.

[0112] High-frequency rectifier output board design The high-frequency rectifier output board receives the high-frequency, low-voltage AC voltage output from the secondary side of the high-frequency isolation transformer. Through bridge high-frequency rectification and multi-stage filtering, it converts the high-frequency alternating voltage into a low-ripple, high-stability DC constant current output. This device uses four MBR60200PT high-frequency rectifier devices to form the four arms of the bridge rectifier circuit. During any conduction phase, two diagonally opposite rectifier devices carry the current, reducing device stress and conduction temperature rise, and improving the reliability of the output circuit. The output board effectively suppresses high-frequency switching ripple and load disturbances, ensuring long-term high-precision stability of the filament output current, and is suitable for the stringent power supply requirements of klysonic tube filaments.

[0113] Hall effect current design Output current sampling Hall

[0114] The LT58-S7 Hall effect current sensor, connected in series in the output DC loop, achieves electrically isolated current sampling. The LT58-S7 is a closed-loop Hall effect current sensor. The primary winding of the sensor passes through the power bus, and a matching sampling resistor is externally connected to the output side. The sensor acquires the DC current output from the load, linearly converting the primary current into a secondary current signal. The sampling resistor converts the current signal into a voltage signal and sends it to the current signal conditioning circuit of the control board, enabling real-time monitoring of the output current. The Hall effect provides strong and weak current isolation, avoiding the impact of high-voltage interference from the power loop on the control sampling accuracy.

[0115] Output voltage sampling Hall

[0116] A DLS-0.01C Hall effect voltage sensor is configured on the output DC bus to achieve isolated voltage sampling. The DLS-0.01C is a DC Hall effect voltage sensor, with its input connected in parallel across the output power terminals. Under full-load maximum output current of 10A, the Hall effect output samples the voltage, which is then fed into the voltage signal conditioning circuit of the control board to acquire the output bus voltage in real time. The Hall effect voltage achieves electrical isolation between the high-voltage power circuit and the low-voltage control circuit, improving the system's anti-interference capability and safety.

[0117] This device has multiple protection mechanisms, including input overvoltage / undervoltage, output overvoltage, output overcurrent, current over-limit, overall over-temperature, and drive abnormality. After a fault is triggered, the half-bridge inverter drive signal is immediately blocked, the main power output is cut off, the fault information is latched, and the information is uploaded to the backend via optical fiber to achieve rapid protection and fault location, ensuring the safety of high-voltage equipment and downstream filament loads.

[0118] Power stage cooling fan design: The power-up cooling fan is a dedicated cooling unit for the high-voltage conversion area of ​​the entire unit. Its core cooling components include the high-frequency high-voltage transformer and the high-frequency rectifier diode (MBR60200PT). The rectifier components are paired with either a DB40 standard heatsink or a custom high-efficiency heatsink. The power-up stage is the area of ​​concentrated high-frequency and high-voltage heat generation in the entire unit. The high-frequency transformer has high-frequency iron and copper losses, and the rectifier diode has high-frequency conduction and reverse recovery losses, making them the main heat sources of the entire unit. Therefore, it is necessary to accurately calculate the full-load heat generation of all components and match the appropriate fan airflow to ensure the high-voltage conversion unit operates at low temperatures, stably, and safely over the long term.

[0119] Loss calculation of the high-frequency rectifier diode (MBR60200PT) in the power stage The device has a full-load output current Io=10A and adopts a full-bridge high-frequency rectification architecture. The MBR60200PTB is an ultra-fast recovery high-voltage rectifier tube with a forward voltage drop Vf=0.75V and an operating frequency of 80kHz. The minimal reverse recovery loss is ignored, and only the dominant forward conduction loss is calculated.

[0120] Formula for forward conduction loss of a single tube within a single cycle:

[0121] At any given moment in steady state, two diagonal diodes can conduct simultaneously. Each of the two diodes conducting at the same time generates approximately 3.75W of conduction loss. The total continuous conduction loss under full load is:

[0122] When paired with a DB40 cooler or a custom cooler, temperature rise is controllable under forced air cooling conditions, with no hot spot buildup.

[0123] Losses of subsequent auxiliary components

[0124] Estimated overall losses of auxiliary components such as high-voltage filter capacitors, voltage equalizing resistors, and PCB traces in the later stage:

[0125] Summary of total heat generation of the power stage

[0126] The aforementioned 8.5W represents the additional heat dissipation load of the high-frequency rectifier output board and its auxiliary components; the 4.2W loss of the high-frequency isolation transformer has been listed separately in the aforementioned transformer loss calculation. If calculated as a whole for the downstream stage cavity, the total heat generation of the downstream stage is approximately 12.7W. The selected downstream fan, with a capacity of at least 5 CFM, provides sufficient margin for both calculation methods.

[0127] Selection and calculation of air volume for power generation fans This design uses the same industrial forced air cooling airflow calculation formula as the preamplifier, with an ambient temperature of 25℃ and a maximum allowable temperature rise of ΔT = 20℃ for the components, ensuring long-term full-load heat dissipation redundancy.

[0128] In the formula: specific heat capacity of air c = 1005 J / (kg·℃), air density ρ = 1.29 kg / m³, and P is the total regional heating power Pt.

[0129] Substitute the heat output of the rectifier output board into the theoretically required airflow calculation, and convert the airflow unit:

[0130]

[0131] To adapt to harsh operating conditions such as enclosed equipment environments, dust accumulation, and high-temperature derating, a safety margin of 2 times the project volume is reserved, and the final selected air volume is: If the equipment has good ventilation, the downstream cooling fan can be omitted, and natural cooling can be used instead.

[0132] Fan Selection: A small, high-speed axial flow fan (DC cooling fan: 12V, dimensions: 40mm×40mm×10mm, airflow ≥5CFM) is selected for the downstream stage, which fully meets the heat dissipation requirements of the high-voltage area. For high-insulation components such as the high-frequency transformer and high-voltage rectifier diodes, a 2.0 times safety margin is designed to effectively suppress high-frequency heat accumulation, delay high-voltage insulation aging, and ensure long-term stability of high-voltage isolation performance and output accuracy, perfectly adapting to the high-voltage high-frequency heat dissipation conditions of this device. Upon power-up, the device starts synchronously, providing directional air cooling for the high-frequency high-voltage transformer, the MBR60200PT high-frequency rectifier device heatsink, and the downstream high-voltage auxiliary components.

[0133] Structural design: As attached Figure 20As shown, this filament power supply device is divided into two independent units: a front-end module and a back-end module. Power transmission and signal interaction between the front-end module and the back-end module are achieved through electrical terminals and fiber optic interfaces. The split-type partitioned layout achieves physical isolation between strong and weak currents and high and low voltage areas, suppresses electromagnetic coupling interference, and meets the insulation and creepage distance safety specifications under 40kV high voltage conditions.

[0134] Front-end module The overall height of the preamplifier module is set at 60mm. Internally, it integrates an EMI filter, a power frequency step-down transformer, an LLC two-switch half-bridge power board, an auxiliary power board, and a control board. A 50*50*10mm or 40x40x10mm cooling fan provides forced air cooling for the LLC inverter MOSFET 7812 voltage regulator chip, the power frequency step-down transformer, and the control board. External interfaces of the preamplifier module include an AC220V input terminal and an independent protective earth (PE) terminal. Power output uses a 2-pin terminal to supply high-frequency AC power to the primary side of the high-frequency transformer in the subsequent module. A fiber optic flange is included to achieve opto-isolated transmission of control signals, blocking common-mode interference between high and low voltage circuits.

[0135] Post-module

[0136] The downstream module uses insulating board material ( Figure 20 The module features a composite structure of a green display and a metal chassis. The bottom of the rear-stage module has a 15mm thick epoxy insulation board, while the side walls and top have 5mm thick epoxy insulation boards. Ventilation holes are required on the top and side walls of the module. The internal metal chassis is 40mm high, and the overall height of the rear-stage module is 80mm. Two 5mm thick epoxy insulation boards are installed inside the rear-stage module to physically separate the high-voltage and low-voltage chambers: the first insulation board allows the high-voltage lead cable from the secondary side of the high-frequency transformer to pass through, with creepage distances and clearances designed according to the 40kV insulation level, separating the low-voltage primary chamber from the high-voltage output chamber to prevent high-voltage creepage and breakdown along the conductor surface; the second insulation board allows the low-voltage signal line for current Hall effect sampling to pass through the high-voltage and low-voltage zones, isolating the low-voltage sampling circuit from the high-voltage main circuit and preventing high-voltage interference into the low-voltage control circuit, which could damage the weak current equipment.

[0137] The downstream module houses a high-frequency high-voltage transformer, a high-frequency rectifier output board, and a downstream cooling fan. The downstream cooling fan provides forced air cooling to the high-frequency high-voltage transformer and the MBR60200PT high-frequency rectifier device heat sink, promptly removing the heat loss generated in the high-voltage conversion area, delaying the thermal aging of the high-voltage insulation medium, and ensuring stable insulation performance under long-term high-voltage operating conditions.

[0138] To ensure that the current and voltage sampling Hall sensors inside the downstream modules meet the 40kV withstand voltage insulation requirements, the sampling devices employ a multi-layered composite insulation protection scheme: The current and voltage sampling Hall sensors are equipped with dedicated nylon shells with pre-drilled central wiring holes, and the sampling Hall sensors are housed inside these shells; the sampling signal lines leading out from the Hall sensors are externally fitted with high-voltage heat-shrink tubing or epoxy-insulated conduits; after assembly, the interior of the nylon shell cavity is completely potted with epoxy resin. Simultaneously, the high-frequency, high-voltage power circuit uses 40kV-grade high-voltage conductors for wiring. This structural design forms a multi-layered insulation barrier, effectively isolating the high-voltage electric field, suppressing creepage and arcing along the signal lines, preventing high voltage from entering the upstream low-voltage control circuit, ensuring stable sampling signal acquisition, and meeting the overall 40kV high-voltage insulation safety requirements.

[0139] External electrical terminal configuration of the back-end module: Input pin 2: Connect to the high-frequency AC power output from the preamplifier module and connect to the primary winding of the high-frequency transformer; Metal chassis input 2-pin terminal: connects to the secondary winding of the high-frequency transformer; The main circuit output 2-pin terminal of the metal chassis is the low voltage and high current DC power output port of this filament power supply. This port can be at a high floating potential relative to ground and is used to supply power to the external klystron filament load. The metal chassis has 4 auxiliary terminals: two of which transmit output voltage sampling signals, and the other two provide power to the downstream cooling fan.

[0140] The structural drawings in the accompanying drawings of this invention are simplified schematic schemes, and can be optimized and adjusted according to different operating conditions during actual engineering implementation. By changing the specifications of components such as the step-down transformer, high-frequency transformer, LLC circuit, and half-bridge inverter unit, this device can achieve higher electrical isolation voltage levels, multi-level output power expansion, and adaptation to different output voltage / current specifications.

[0141] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-isolation filament power supply device based on current Hall sampling, comprising a front-end module and a back-end module, characterized in that: The front-end module includes an input filter, a step-down transformer, a rectifier bus circuit, and a resonant inverter circuit connected in sequence, as well as a control circuit connected to the control terminal of the resonant inverter circuit. The back-end module includes a high-frequency isolation transformer, a high-frequency rectifier filter circuit, and a current Hall sensor. The primary winding of the high-frequency isolation transformer is connected to the output terminal of the resonant inverter circuit, and the secondary winding of the high-frequency isolation transformer is connected to the input terminal of the high-frequency rectifier filter circuit. A high-voltage insulation structure is provided between the primary winding and the secondary winding. The output terminal of the high-frequency rectifier filter circuit is used to connect to a filament load. The current Hall sensor has a detection hole through which the output conductor of the high-frequency rectifier filter circuit passes. The sampling output terminal of the current Hall sensor is connected to the control circuit.

2. The high-isolation filament power supply device based on current Hall sampling according to claim 1, characterized in that: The step-down transformer has a primary winding connected to AC mains power, a main power secondary winding, and multiple independent auxiliary secondary windings; the main power secondary winding is connected to the rectifier bus circuit; the multiple auxiliary secondary windings are connected to an auxiliary power supply board, which includes an auxiliary rectifier circuit, a positive voltage regulator circuit, a negative voltage regulator circuit, and a fan power supply regulator circuit, which are respectively connected to the multiple auxiliary secondary windings to form a positive auxiliary voltage, a negative auxiliary voltage, and a fan power supply voltage.

3. The high-isolation filament power supply device based on current Hall sampling according to claim 2, characterized in that: The rectifier bus circuit includes a bridge rectifier connected to the main power secondary winding, a bus energy storage capacitor connected to the output terminal of the bridge rectifier, a current-limiting resistor connected in series between the bridge rectifier and the bus energy storage capacitor, and a relay contact connected in parallel with the current-limiting resistor; the control circuit includes a bus voltage sampling circuit and a soft-start control circuit.

4. The high-isolation filament power supply device based on current Hall sampling according to claim 1, characterized in that: The resonant inverter circuit is a half-bridge resonant inverter circuit, including a first power MOSFET and a second power MOSFET connected in series between the positive and negative terminals of the DC bus, and a resonant capacitor and a resonant inductor located between the midpoint of the half-bridge and the primary winding of the high-frequency isolation transformer; the control circuit includes a frequency modulation controller and a drive circuit, the frequency modulation controller outputs two complementary drive signals, the two complementary drive signals are respectively connected to the gates of the first power MOSFET and the second power MOSFET through the drive circuit, and a dead time is provided between the two complementary drive signals to prevent the first power MOSFET and the second power MOSFET from conducting simultaneously.

5. The high-isolation filament power supply device based on current Hall sampling according to claim 4, characterized in that: The high-frequency isolation transformer includes a ferrite core, a primary winding and a secondary winding wound on the ferrite core. The primary winding is made of copper foil, and the secondary winding is made of high-voltage insulated wire. A multi-layer composite insulation layer and an insulation gap that meets the high-voltage creepage distance are provided between the primary winding and the secondary winding. The primary and secondary insulation withstand voltage of the high-frequency isolation transformer is not less than 40kV.

6. The high-isolation filament power supply device based on current Hall sampling according to claim 4, characterized in that: The high-frequency rectifier and filter circuit includes a bridge rectifier circuit composed of four high-frequency rectifier devices, an output filter capacitor connected between the output terminals of the bridge rectifier circuit, and an output filter inductor connected in series with the positive output terminal of the bridge rectifier circuit. The current Hall sensor is a closed-loop current Hall sensor. The positive output conductor of the high-frequency rectifier and filter circuit passes through the detection hole of the current Hall sensor. The sampling output terminal of the current Hall sensor is connected to a sampling resistor that converts the secondary current signal into a voltage signal. A voltage Hall sensor is also connected in parallel between the two output terminals of the high-frequency rectifier and filter circuit.

7. The high-isolation filament power supply device based on current Hall sampling according to claim 6, characterized in that: The control circuit includes a current signal conditioning circuit, a voltage signal conditioning circuit, and a voltage-to-frequency conversion circuit. The sampling output terminal of the current Hall sensor is connected to the current feedback terminal of the frequency modulation controller, the output current protection circuit, and the voltage-to-frequency conversion circuit via the current signal conditioning circuit. The sampling output terminal of the voltage Hall sensor is connected to the output overvoltage protection circuit and the voltage-to-frequency conversion circuit via the voltage signal conditioning circuit. The voltage-to-frequency conversion circuit is connected to an optical fiber transmitter to convert the output current sampling signal and the output voltage sampling signal into frequency signals and then transmit them outward via optical fiber.

8. The high-isolation filament power supply device based on current Hall sampling according to claim 7, characterized in that: The control circuit further includes a remote setpoint circuit, a local setpoint circuit, and a setpoint signal selection circuit; the remote setpoint circuit includes an optical fiber receiver, a frequency-to-voltage conversion circuit, and a signal conditioning circuit connected in sequence; the local setpoint circuit includes an adjustable resistor and a reference voltage circuit connected to the adjustable resistor; the setpoint signal selection circuit is connected to the remote setpoint circuit, the local setpoint circuit, and the frequency modulation controller respectively.

9. The high-isolation filament power supply device based on current Hall sampling according to claim 7, characterized in that: The control circuit also includes an input overvoltage and undervoltage detection circuit, a drive abnormality detection circuit, an output current overlimit detection circuit, an output overcurrent detection circuit, an output overvoltage detection circuit, an overtemperature detection circuit, a fault summary circuit, and a fault latching circuit. The multiple input terminals of the fault summarization circuit are respectively connected to the fault output terminals of each detection circuit. The output terminal of the fault summarization circuit is connected to the set terminal of the fault latch circuit. The blocking output terminal of the fault latch circuit is respectively connected to the enable terminal of the frequency modulation controller and the drive circuit. The reset terminal of the fault latch circuit is respectively connected to a local reset switch and an optical fiber remote reset circuit.

10. The high-isolation filament power supply device based on current Hall sampling according to claim 9, characterized in that: The front-end module and the back-end module are respectively housed in independent housings. The housing of the back-end module includes an external insulating plate and a metal chassis disposed inside the external insulating plate. The back-end module is internally provided with a first epoxy insulating partition and a second epoxy insulating partition. The first epoxy insulating partition separates the primary side region of the high-frequency isolation transformer from the secondary output region, and the second epoxy insulating partition separates the secondary output region from the sampling signal lead-out region. The current Hall sensor and the voltage Hall sensor are respectively housed in a nylon insulating shell. The nylon insulating shell is filled with epoxy potting compound, and the sampling signal line led out from the nylon insulating shell is externally sleeved with a high-voltage heat shrink tubing or an epoxy insulating tube.

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