A high voltage microwave power filament voltage regulation circuit

Abstract

This application discloses a voltage adjustment circuit for a high-voltage microwave power supply filament. This voltage adjustment circuit is located on the high-voltage side of the microwave power transformer and includes: an auxiliary power supply circuit, whose input terminal is directly connected to the cathode filament winding on the high-voltage side, used to obtain AC power from the cathode filament winding and rectify and filter it to generate DC operating power; a switching circuit, whose power supply terminal is connected to the DC operating power output from the auxiliary power supply circuit; an inductive component connected to both ends of the power supply inductor in the cathode filament winding, with its first and second terminals respectively connected to the two paths of the switching circuit, and its third terminal connected to the second terminal of the power supply inductor; and a control circuit powered by the DC operating power supply, used to output a control signal to the switching circuit after the magnetron has started. By adjusting the overall inductance on the high-voltage side, the voltage of the power supply filament can be adjusted, thus delaying the aging of the power supply filament without modifying the transformer structure.

Description

Technical Field

[0001] This application relates to the field of high-voltage microwave technology, and in particular to a voltage adjustment circuit for a high-voltage microwave power supply filament. Background Technology

[0002] In high-end microwave sources (such as industrial microwave power supplies driving thorium tungsten carbide cathode magnetrons), the same transformer (half-bridge or full-bridge circuit structure driving the transformer) is typically used to generate the anode high voltage and the cathode filament (power supply filament) voltage. PWM or PFM technology is used to regulate the power supply's output voltage. Because the same transformer structure is used, only different secondary windings are used to generate the corresponding anode high voltage and cathode filament voltage. Both secondary windings are wound on the same magnetic core, so the voltages have a strong correlation. That is, the anode high voltage and the cathode filament voltage are corresponding, and since the anode high voltage is fixed, the cathode filament voltage is also fixed. Because the cathode filament (thorium tungsten carbide cathode) heats to approximately 1500℃-1600℃ when the microwave magnetron is operating, filament aging is accelerated, severely affecting its lifespan. Summary of the Invention

[0003] The voltage adjustment circuit for the high-voltage microwave power supply filament provided in this application can delay the aging of the power supply filament.

[0004] In a first aspect, this application provides a voltage adjustment circuit for a high-voltage microwave power supply filament. This voltage adjustment circuit is located on the high-voltage side of the microwave power transformer and includes: an auxiliary power supply circuit whose input terminal is directly connected to the cathode filament winding on the high-voltage side, for obtaining AC power from the cathode filament winding and rectifying and filtering it to generate a DC operating power supply; a switching circuit whose power supply terminal is connected to the DC operating power supply output by the auxiliary power supply circuit, whose control terminal receives a control signal, and whose two terminals are connected to the inductive component, for responding to the control signal to change the equivalent inductance value of the inductive component; and a control circuit powered by the DC operating power supply. Used to output the control signal after the magnetron is started; an inductive component connected in series with the power supply inductor in the cathode filament winding; the inductive component includes at least one inductor, and the first end of the inductive component is connected to the first path terminal of the switching circuit and the first end of the power supply inductor, the second end of the inductive component is connected to the second path terminal of the switching circuit, and the third end of the inductive component is connected to the second end of the power supply inductor; the switching circuit short-circuits or connects at least a portion of the inductance of the inductive component to the circuit by turning on or off its first path terminal and second path terminal, so as to change the total inductance value formed by the power supply inductor and the inductive component connected in series.

[0005] In some embodiments, the switching circuit includes at least one of a relay, a MOSFET, an IGBT, a thyristor, or a solid-state relay.

[0006] In some embodiments, the switching circuit is a relay, and further includes a freewheeling diode connected in parallel with the relay coil.

[0007] In some embodiments, the control circuit includes a microcontroller (MCU) that determines whether the magnetron has completed startup by monitoring the anode current and / or anode high voltage of the microwave power transformer.

[0008] In some embodiments, the voltage regulation circuit is encapsulated in an insulating housing, the interior of which is filled with insulating adhesive.

[0009] In a second aspect, this application provides a high-voltage microwave device, which includes: a microwave power transformer and a voltage adjustment circuit; the voltage adjustment circuit is as provided in the first aspect.

[0010] In some embodiments, the voltage regulation circuit is encapsulated in an insulating housing, the interior of which is filled with insulating adhesive.

[0011] The beneficial effect of this application is that it differs from the prior art. This voltage regulation circuit is applied to the high-voltage side of a microwave power transformer. The voltage regulation circuit includes: a control circuit; a switching circuit, the control terminal of which is connected to the control circuit; an inductive component, which includes at least one inductor, a first terminal of which is connected to a first path terminal of the switching circuit and a first terminal of the power supply inductor in the cathode filament winding on the high-voltage side, a second terminal of which is connected to a second path terminal of the switching circuit, and a third terminal of which is connected to a second terminal of the power supply inductor. The control circuit is configured to send a control signal to the control terminal of the switching circuit to cause the first... By connecting or disconnecting the primary and secondary terminals, the overall inductance on the high-voltage side is adjusted, thereby adjusting the voltage of the power filament. After the magnetron starts up, adjusting the overall inductance on the high-voltage side reduces the heating voltage of the power filament, allowing for continued power supply while maintaining the filament temperature without excessive heating. This slows down filament aging and extends its lifespan. Furthermore, compared to conventional methods that adjust the PWM duty cycle or change the transformer turns ratio on the low-voltage side, this application achieves dynamic adjustment of the filament voltage without modifying the original structure and winding turns of the microwave power transformer. Simultaneously, by drawing power from the cathode filament winding to supply power to the high-voltage side circuit, the use of a separate isolation transformer or complex optocoupler isolation signal transmission circuit is avoided, significantly reducing cost and insulation design complexity. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a schematic diagram of the structure of an embodiment of the high-voltage side of a microwave power transformer provided in this application; Figure 2 This is a schematic diagram of an embodiment of the voltage adjustment circuit provided in this application; Figure 3 yes Figure 2 A schematic diagram of the structure of one embodiment of the control circuit; Figure 4 This is a schematic diagram of an embodiment of the high-voltage microwave device provided in this application. Detailed Implementation

[0013] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It is understood that the specific embodiments described herein are only for explaining this application and not for limiting it. Furthermore, it should be noted that, for ease of description, only the parts related to this application are shown in the accompanying drawings, not all structures. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0014] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0015] When considering adjusting the high-voltage side filament voltage, those skilled in the art typically employ methods such as adjusting the PWM duty cycle or changing the transformer turns ratio on the low-voltage side. These methods either have poor adjustment accuracy or require redesigning the transformer. This application creatively proposes dynamically adjusting the inductance of the filament circuit directly on the high-voltage side. The biggest obstacle to achieving this is not the inductor switching itself, but rather how to provide a stable and safe low-voltage power supply to the switching circuit located at the high-voltage potential. Common solutions use isolation transformers or optocouplers, but this increases cost and complexity. This application further proposes a minimalist auxiliary power supply circuit (D18, D19, EC1) that draws power from the cathode filament winding itself. It cleverly utilizes the AC voltage of the filament winding, through full-wave rectification and filtering, to provide a 'bootstrapping' power supply to the high-voltage side switching and control circuits. This combination of circuit structures is not a simple superposition of inductor switching and power supply, but a systematic innovation specifically designed for the unique operating environment of high-voltage microwave power supplies.

[0016] In high-end microwave sources (such as industrial microwave power supplies that drive thorium tungsten carbide cathode magnetrons), the same transformer (a half-bridge or full-bridge circuit structure driving the transformer) is typically used to generate both the anode high voltage and the cathode filament (power supply filament) voltage. Figure 1 The circuit structure shown is related to the technology. PWM or PFM technology is used to regulate the power supply's output voltage. Because the same transformer structure is used, only different secondary windings are used to generate the corresponding anode high voltage and cathode filament voltage. Both secondary windings are wound on the same magnetic core, so the voltages have a strong correlation; that is, the anode high voltage and cathode filament voltage are corresponding. Since the anode high voltage is fixed, the cathode filament voltage is also fixed. Because the cathode filament (thorium tungsten carbide cathode) heats to approximately 1500℃-1600℃ when the microwave magnetron is working, filament aging is accelerated, severely affecting its lifespan.

[0017] Furthermore, the following is a brief description of the magnetron startup and operation process: A magnetron is a cleverly designed device that can efficiently convert electrical energy into high-power microwaves without requiring complex semiconductor amplifier circuits. A magnetron mainly consists of three core components: a cathode, an anode, and a magnet.

[0018] Cathode: Located in the center, it is heated when energized and is responsible for emitting electrons.

[0019] Anode: Surrounding the cathode, it is usually a copper block with multiple resonant cavities. The resonant cavity is the "container" for microwave oscillation.

[0020] Magnet: It generates a strong magnetic field parallel to the axis, penetrating the space between the cathode and anode.

[0021] The startup process is like turning a group of disordered electrons into an organized "spoke" array.

[0022] Electrons start: First, the cathode is heated by the filament, and a large number of electrons "boil" due to the heat and escape from the cathode surface, forming an electron cloud surrounding the cathode.

[0023] Electric field acceleration: When a very high DC voltage is applied between the cathode and anode (anode positive, cathode negative), the strong electric field pulls electrons radially from the cathode toward the anode.

[0024] Magnetic field deflection: Without a magnetic field, electrons would fly in a straight line to the anode, forming a simple current. However, because of the presence of a strong axial magnetic field, everything changes. According to the Lorentz force law in physics, a moving electron in a magnetic field experiences a lateral force. This force causes the electron, which was originally flying in a straight line, to no longer rush towards the anode, but instead rotate around the cathode along a curve. Operating mechanism: Energy conversion from "rotation" to "oscillation". Once electrons begin to rotate around the cathode, a more crucial stage begins.

[0025] The formation of "electron spokes": The rotating electron cloud is not uniform. When electrons pass through the gaps in the anode resonant cavity, they generate a weak high-frequency electromagnetic field within the cavity. This high-frequency field, in turn, "combs" the electron cloud, pushing, pulling, and gathering the electrons, ultimately forming a rotating group of electrons like spokes. This is the famous "electron spokes".

[0026] Maintaining oscillation (energy exchange): This is the most crucial step in the magnetron process. When the "electron spokes" sweep across the anode surface at a specific speed, electrons that happen to be in the decelerating electric field region transfer some of their kinetic energy to the high-frequency field, thus maintaining and enhancing the microwave oscillations in the resonant cavity. This process can be imagined as pushing a swing at the right time, making it swing higher and higher.

[0027] Energy output: Once the microwave oscillations in the resonant cavity accumulate to a certain level, the microwave energy can be guided out through structures such as antennas or coupling loops for external use.

[0028] In summary, the magnetron cleverly utilizes orthogonal electric and magnetic fields to continuously and efficiently pump the kinetic energy of electrons into a microwave electromagnetic field, thereby generating high-power oscillations. Once activated, the entire system achieves a self-sufficient dynamic equilibrium.

[0029] Based on the above, a phenomenon was discovered: after the magnetron is started, the cathode filament does not need continuous high-power heating. Sometimes, even when the heating is disconnected, microwaves can still be output, but after a long time, they will stop emitting waves. This revealed a problem: if the heating voltage of the filament can be reduced to continue replenishing energy, but only the temperature of the filament needs to be maintained, it is not possible to heat it too high, because the filament aging will be accelerated, which will seriously affect its lifespan.

[0030] The following explanation will be based on both physical principles and engineering practice: Even after the heating is disconnected after startup, the microwaves can still output microwaves for a period of time. This is due to the switching between two electron emission mechanisms: Start-up phase: Relies on thermionic emission. When the magnetron first starts working, the cathode is cold and contains no electrons. A large current must be supplied to the filament to heat the cathode to 1000-1600℃ (depending on the material), allowing the electrons to gain enough energy to "boil" out. This heating power is necessary in this stage to enable the cathode to emit electrons.

[0031] Operational Phase: Relies on secondary electron emission. Once the oscillation is established, high-speed electrons begin bombarding the cathode surface. This bombardment produces a physical phenomenon: secondary electron emission. A single high-speed electron colliding with the cathode may eject several electrons. When the magnetron enters a stable oscillation state, the number of secondary electrons generated by the electron bombardment is sufficient to maintain the electron cloud density within the tube.

[0032] Based on this, the cathode is "heated" by electrons themselves and "collides" to produce enough electrons, enabling it to work even when the heating is disconnected.

[0033] Although electron bombardment generates secondary electrons and heat, if the heat generated is insufficient to compensate for the radiative and conductive heat loss from the cathode surface to the environment, the cathode temperature will slowly decrease. When the cathode temperature drops below a certain threshold, the thermionic emission capability weakens significantly. Once thermionic emission is insufficient, the number of electrons bombarding the cathode decreases, leading to a decline in secondary electron production and creating a vicious cycle. When the electron cloud density falls below the minimum density required to maintain oscillation, microwave output will stop. Simply put: the cathode slowly cools down until it can no longer emit electrons.

[0034] This application proposes reducing the heating voltage of the filament while continuing to supply energy, only maintaining the temperature. From an engineering perspective, this technique requires consideration of the following points: The optimal operating temperature setting should not be set too high, as it would be at startup (that would severely accelerate filament evaporation and shorten lifespan). Nor should it be set too low, otherwise it will reach the aforementioned "collapse" critical point.

[0035] Ideally, a balance point should be found where the filament temperature just compensates for heat loss, ensuring that the cathode still has sufficient electron emission capability even when electron bombardment is insufficient (such as when microwave power is reduced).

[0036] Power and heating linkage control: If the magnetron output power is very high (meaning intense electron bombardment), the filament heating can be significantly reduced or even completely cut off (by self-sustaining).

[0037] If the output power is very low (light load) and the electron bombardment is weak, it is necessary to increase the filament's sustaining heating power to prevent the cathode from cooling down.

[0038] High-end switching power supplies monitor output power or current in real time and dynamically adjust filament voltage.

[0039] The essence of filament aging: The main causes of filament aging are evaporation at high temperatures (thinning of the tungsten filament) and the consumption of the cathode coating. If the temperature can be precisely controlled during continuous wave operation, keeping the cathode just above the "emission threshold," the lifespan of the magnetron can indeed be significantly extended. This is a crucial technique in industrial microwave sources that require continuous operation for tens of thousands of hours (such as plasma excitation and microwave drying).

[0040] See Figure 2 and Figure 3 Description: This voltage regulation circuit is applied to the high-voltage side of a microwave power transformer. The voltage regulation circuit includes: a control circuit, a switching circuit, and an inductive component.

[0041] The control terminal RLB of the switching circuit is connected to the control circuit.

[0042] An inductive component is connected in series with the power supply inductor L102. The inductive component includes at least one inductor. A first terminal of the inductive component is connected to the first terminal 5 of the switching circuit and the first terminal VA of the power supply inductor. A second terminal of the inductive component is connected to the second terminal 3 of the switching circuit, and a third terminal of the inductive component is connected to the second terminal VD of the power supply inductor. The switching circuit short-circuits or connects at least a portion of the inductance of the inductive component to the circuit by turning its first and second terminals on or off, thereby changing the total series inductance. For example, the inductive component includes... Figure 2The inductors L103, L104, L105, and L106 are described above. For example, the inductive component is connected to both ends of the power supply inductor in the cathode filament winding. It should be noted that the connection method between the inductive component and the power supply inductor L102 is described using a multi-terminal network as an example. In actual implementation, if the inductive component contains only one tapped inductor (i.e., the middle tap of an inductor is used as the second terminal, and the two ends are used as the first and third terminals respectively), or contains a series-parallel network composed of multiple inductors, it can be regarded as an implementation of a multi-terminal network. Those skilled in the art will understand that the connection method of a two-terminal network (i.e., the second terminal of the inductive component is directly connected to the second terminal of the power supply inductor) can be regarded as a degradation of the multi-terminal network and also falls within the protection scope of this application. This application uses a multi-terminal network as the main description object to clearly demonstrate the principle of inductance switching, rather than to limit the scope of protection.

[0043] The control circuit is configured to send a control signal to the control terminal of the switching circuit to make the first path terminal 5 and the second path terminal 3 of the switching circuit conduct or disconnect, thereby adjusting the overall inductance on the high-voltage side and thus adjusting the voltage of the power filament. In other words, by making the first path terminal 5 and the second path terminal 3 of the switching circuit conduct or disconnect, the total inductance value of the filament circuit can be adjusted, which is equivalent to adjusting the stored energy of the inductor (the overall inductance on the high-voltage side), and thus correspondingly changing the voltage of the cathode filament.

[0044] In some embodiments, the specific structure of the control circuit can be found in [reference needed]. Figure 3 .

[0045] In some embodiments, the switching circuit may include a relay, MOSFET, IGBT, SCR, or solid-state relay. It should be noted that when using a MOSFET or IGBT as the switching circuit, since the source (or emitter) potential may fluctuate with the connection point of the inductive component, the DC operating power output from the auxiliary power supply circuit should be connected to the control electrode of the switching transistor through a drive transformer, bootstrap drive circuit, or isolation drive optocoupler to ensure reliable drive.

[0046] It should be noted that when using MOSFETs or IGBTs as the switching circuit, the source (or emitter) potential may fluctuate with the connection point of the inductive component (i.e., operating in a floating ground state), meaning the DC power supply output from the auxiliary power supply circuit cannot directly drive the control electrode of the switching transistor. Therefore, this application provides the following optional driving schemes: Option 1: Use a driving transformer. Its primary side receives the control signal output by the control circuit, and its secondary side is connected to the control electrode and source (or emitter) of the switching transistor. The transformer magnetic coupling is used to achieve isolated driving. Option 2: Use a bootstrap drive circuit to charge the floating power supply during the turn-off period of the switching transistor through a bootstrap diode and a bootstrap capacitor, so as to provide sufficient gate (or base) drive voltage during the turn-on period. Option 3: Use an isolated driver optocoupler, with its input end connected to the control circuit and its output end connected to the control electrode and source (or emitter) of the switching transistor to achieve electrically isolated drive transmission.

[0047] In a preferred embodiment of this application, the switching circuit uses a relay, which has natural electrical isolation characteristics between its coil and contacts, and the driving circuit is simple (only one switching transistor is needed to control the coil's on / off state), without the need for additional high-voltage isolation driving processing, thus making it the most preferred implementation.

[0048] In a preferred embodiment of this application, the switching circuit uses a relay, whose coil driving is simple and has inherent isolation characteristics, requiring no additional driving processing. In some embodiments, the switching circuit is a relay and also includes a freewheeling diode connected in parallel with the relay coil.

[0049] To further improve circuit reliability and switching life, a transient overvoltage suppression circuit can be connected in parallel across the inductive component. When the switching circuit short-circuits part of the inductance of the inductive component, a transient back electromotive force will be generated between the circuit's terminals because the inductor current cannot change abruptly. By setting an RC series absorption circuit, a varistor, or a TVS diode, this transient overvoltage can be limited to a safe range, preventing arcing of the switch contacts or breakdown of semiconductor devices.

[0050] In some embodiments, the switching circuit includes: a coil RL2, a first contact 3, a second contact 5, and a third contact 4. A first end of the coil RL2 is connected to a control circuit, and a second end of the coil RL2 is connected to the operating power supply terminal VCC. The first contact 3 is connected to a second end of an inductive component. The second contact 5 is connected to a first end of the inductive component. The third contact 4 is an unconnected contact. The coil RL2 is configured to, according to a control signal, to either connect or disconnect the first and second contacts.

[0051] In some embodiments, the switching circuit further includes a diode assembly. The anode of the diode assembly is connected to the first terminal of the coil RL2, and the cathode of the diode assembly is connected to the operating power supply terminal VCC. Figure 2 As shown, the diode assembly includes diode D11 and diode D12. The anodes of diodes D11 and D12 are connected to the first terminal of coil RL2, and the cathodes of diodes D11 and D12 are connected to the operating power supply terminal VCC. Diodes D11 and D12 can be used as freewheeling diodes.

[0052] In some embodiments, the control circuit includes a drive unit and a control unit. A first terminal of the drive unit is connected to the control terminal RLB of the switching circuit, and a second terminal of the drive unit is connected to the third terminal of the cathode filament winding. A first pin of the control unit is connected to the control terminal of the drive unit, and the control unit is configured to control the connection or disconnection between the first and second terminals of the drive unit, thereby connecting or disconnecting the first and second pass terminals of the switching circuit.

[0053] In some embodiments, the control circuit includes a microcontroller (MCU) that determines whether the magnetron has completed startup by monitoring the anode current and / or anode high voltage of the microwave power transformer.

[0054] As a specific and feasible example of a judgment, the MCU is configured as follows: The anode current sampling signal is obtained by connecting a sampling resistor in series between the secondary center tap of the microwave power transformer and the reference ground (V2), and the anode high voltage sampling signal is obtained by a high voltage resistor divider. The magnetron is considered to have completed startup when both of the following conditions are met simultaneously: (1) The anode high voltage is established to more than 95% of the rated value; (2) The fluctuation range of the anode current within 10 consecutive seconds shall not exceed ±5%; If only the timer method is used, the startup can be determined to be complete after a delay of 60 seconds after the anode current first reaches the preset threshold.

[0055] The specific values ​​of the above thresholds can be adaptively adjusted by those skilled in the art based on the magnetron model, operating frequency, and load characteristics. This application is not limited to the above examples.

[0056] A microcontroller (MCU) can be used as a control unit.

[0057] The control circuit (MCU) is located on the high-voltage side, with its reference ground potential at the third terminal (V2) of the cathode filament winding. To determine the completion of magnetron startup, the MCU acquires the sampling signals of the anode current and / or anode high voltage in the following ways: Anode current sampling is achieved through a sampling resistor connected in series between the center tap of the secondary winding of the microwave power transformer and the reference ground (V2). The voltage across the sampling resistor is attenuated by a resistor divider network before being input to the MCU's ADC sampling pin. Anode high voltage sampling is achieved through a high-voltage resistor divider. The high-voltage end of the divider is connected to the anode output, and the low-voltage output is limited and protected before being input to another ADC sampling pin of the MCU. Since both the anode high voltage and anode current use V2 as the reference ground, no additional isolation circuit is required for direct sampling. To protect the microcontroller's ADC sampling pin from abnormal overvoltage surges, a limiting protection circuit is also provided at the sampling signal input. Specifically, each sampling signal is connected to the microcontroller's ADC pin through a series resistor. Simultaneously, a pair of reverse-connected series Zener diodes (such as 3.3V Zener diodes) or a low-capacitance TVS diode are connected in parallel between the ADC pin and the reference ground (V2) to clamp the input voltage within the microcontroller's safe operating range. Furthermore, the attenuation ratio of the sampling resistor voltage divider network should be designed based on the rated value of the anode high voltage (such as 3.0-5.5kV) and the microcontroller's ADC reference voltage (such as 3.3V or 5V) to ensure that the peak value of the sampling signal does not exceed 90% of the ADC reference voltage during normal operation.

[0058] As a specific example, the MCU determines that the magnetron has completed startup when it detects that the anode high voltage has built up to more than 95% of the rated value and the anode current fluctuates by no more than ±5% within 10 consecutive seconds. Alternatively, the MCU can also use a combination of timers and electrical parameters: after the anode current first reaches a preset threshold, a delay of 60 seconds is used to determine startup completion. Those skilled in the art can set corresponding judgment parameters according to the specific magnetron model and operating conditions.

[0059] In some embodiments, such as Figure 3 As shown, the driving unit includes: a switching transistor Q8, a first resistor R63, and a second resistor R62. The first terminal of the switching transistor Q8 is connected to the control terminal RLB of the switching circuit, and the second terminal of the switching transistor Q8 is connected to the third terminal V2 of the cathode filament winding and the control terminal of the switching transistor Q8. The first resistor R63 is connected between the first terminal of the switching transistor Q8 and the control terminal. The second resistor R62 is connected between the control terminal of the switching transistor Q8 and the control unit U2, for example, the second resistor R62 is connected between the control terminal of the switching transistor Q8 and the first pin 3 of the control unit U2.

[0060] In some embodiments, the second pin 2 and the third pin 6 of the control unit U2 are connected to the working power supply terminal VCC through the third resistor R57; the fourth pin 4 and the fifth pin 8 of the control unit U2 are connected to the working power supply terminal VCC; the sixth pin 1 of the control unit U2 is connected to the second end of the drive unit; the seventh pin 5 of the control unit U2 is connected to the third end V2 of the cathode filament winding through the first capacitor C55; and the third pin 6 of the control unit U2 is connected to the third end V2 of the cathode filament winding through the second capacitor EC2.

[0061] In some embodiments, such as Figure 2 As shown, the voltage adjustment circuit also includes an auxiliary power supply circuit. The first terminal of the auxiliary power supply circuit is connected to the first terminal VA of the cathode filament winding; the second terminal is connected to the second terminal VB of the cathode filament winding; the third terminal is connected to the control circuit and the switching circuit; and the fourth terminal is connected to the third terminal V2 of the cathode filament winding. The auxiliary power supply circuit can obtain auxiliary power from the cathode filament winding to power the control circuit and the switching circuit. The third terminal of the auxiliary power supply circuit can also serve as the operating power supply terminal.

[0062] For example, the auxiliary power supply circuit has its input terminal directly connected to the cathode filament winding on the high-voltage side, used to obtain AC power from the cathode filament winding and rectify and filter it to generate DC power. The control circuit is powered by the DC power supply and is used to output the control signal after the magnetron has started.

[0063] In some embodiments, the auxiliary power supply circuit includes: a first diode D18, a second diode D19, and a third capacitor EC1. The anode of the first diode D18 is connected to the first end of the cathode filament winding, and the cathode of the first diode D18 is connected to the control circuit and the switching circuit. The anode of the second diode D19 is connected to the second end of the cathode filament winding, and the cathode of the second diode D19 is connected to the control circuit and the switching circuit. The first end of the third capacitor EC1 is connected to the cathodes of the first diode D18 and the second diode D19, and the second end of the third capacitor EC1 is connected to the third end V2 of the cathode filament winding.

[0064] In some embodiments, the switching circuit has its power supply terminal connected to the DC operating power supply output by the auxiliary power supply circuit, its control terminal receiving a control signal, and its two path terminals connected to the inductive component, for responding to the control signal to change the equivalent inductance value of the inductive component.

[0065] In one application scenario, the cathode filament voltage is adjusted by changing the total inductance of the cathode filament circuit. Specifically, the total inductance is formed by connecting the power supply inductor L102 in series with inductive components (a series-parallel network consisting of L103, L104, L105, L106, etc.). By controlling the state of the switching switch RL2, some inductors in the inductive components can be short-circuited or connected to the circuit, thereby changing the total inductance. This application focuses on adding the switching switch RL2 (the switch type includes electronic switches such as relays, solid-state relays, MOSFETs, IGBTs, and thyristors) and the switch's driving circuit. When the magnetron is first started, L102 is an inductor, and the output cathode filament voltage is relatively high, resulting in a rapid heating process for the cathode filament. When the microwave reaches a stable state (approximately 1 minute and 30 seconds), the MCU (control circuit) monitors the anode current, anode high voltage, transformer power, etc. When it is necessary to reduce the filament voltage, the MCU sends a command to activate the switch driving circuit, changing the total inductance of the filament circuit by switching the state of RL2, thereby adjusting the filament voltage. In some embodiments, the control circuit monitors the anode current, anode high voltage, transformer power, etc., and when it is necessary to reduce the filament voltage, the control circuit sends a control signal to the control terminal of the switching circuit to make the first path terminal 5 and the second path terminal 3 of the switching circuit conduct or disconnect, adjusting the overall inductance on the high-voltage side, and thus adjusting the voltage of the power supply filament. That is, the heating voltage of the filament is reduced, while energy is continued to be supplied, only maintaining the temperature.

[0066] For example, replacing the L102 inductor with L103 and L104 connected in series makes it easier to change the inductance of L102. When the switch is turned on, it will short-circuit or open-circuit, which will bring about a change in the inductance.

[0067] Adjusting the inductance of L102 is equivalent to adjusting the energy stored in the inductor, which in turn changes the voltage of the cathode filament.

[0068] Furthermore, since the cathode filament voltage is superimposed on the anode high voltage, which reaches 3.0-5.5KV, a switching switch and corresponding drive circuit need to be designed for this high voltage. Insulation and auxiliary power supply present significant engineering challenges. Therefore, this application uses a switching switch (the switch type includes relays, solid-state relays, MOSFETs, IGBTs, thyristors, diodes, and other electronic switches) to adjust the energy storage inductance at the cathode filament, thereby adjusting the cathode filament voltage. The energy storage inductance at the cathode filament is adjusted using one or more inductors connected in series and parallel (one inductor is tapped). It also includes a circuit that directly uses the cathode filament winding for rectification and filtering to provide auxiliary power to the switching switch. Figure 2 D18, D19, and EC1 are for rectification and filtering, and the auxiliary power supply is superimposed on the anode high voltage.

[0069] The voltage regulation circuit can include time control, microwave stability monitoring, control of the cathode filament voltage versus anode current curve, anode current monitoring, etc., or it can be directly controlled by sending commands from the MCU.

[0070] Figure 3 U2 is the driver circuit control IC (control circuit), and Q8 is the driver enhancement transistor.

[0071] This part of the switching, inductor, and drive circuit is housed in a highly insulating plastic casing and treated with insulating glue to solve the insulation problem.

[0072] Those skilled in the art would readily conceive of adjusting the voltage by changing the inductance. However, directly operating the filament circuit at a high anode voltage of 3.0-5.5 kV presents two interconnected engineering challenges: First, how to provide a stable and reliable low-voltage power supply for the switching and control circuits located at the high voltage potential? Using isolation transformers or independent power supplies would increase size and cost, and the isolation withstand voltage design would be complex. Second, how to avoid complex isolation signal transmission circuitry? This application specifically addresses the aforementioned obstacles. Its innovation lies not in the "switching inductors" themselves, but in proposing a compact and low-cost combination scheme: Self-bootstrapping power supply: This innovative design utilizes the existing cathode filament windings as the input source for the auxiliary power supply (D18, D19, EC1), directly powering the high-voltage side circuit. This solves the power supply problem without requiring an additional isolation transformer, making it a clever design that achieves two goals at once.

[0073] Self-driven control: The control circuit is also powered by the bootstrap power supply and directly controls the switching circuit through a simple drive circuit (such as Q8). The entire control loop operates in a closed loop on the high-voltage side without the need to cross the high- and low-voltage isolation zone for signal transmission, which greatly simplifies the circuit and insulation design.

[0074] The complete technical path described above—"drawing power from the high-voltage side filament winding -> supplying power to the high-voltage side switch / control circuit -> driving the switch to switch the inductor"—is not a simple superposition of various known methods, but a systematic innovation addressing the specific challenge of "dynamic adjustment of the high-voltage microwave power supply filament voltage." Without this combination, those skilled in the art would face complex problems of isolated power supply and signal transmission, thus hindering their ability to implement dynamic inductor switching on the high-voltage side.

[0075] In some embodiments, a high-insulation relay (such as an insulation relay of 5KV or above) can be used as a switching switch, thus eliminating the need to draw power directly from the cathode filament winding for auxiliary power supply. However, inductance switching, switching, inter-station control, microwave stability monitoring, cathode filament voltage versus anode current curve control, and anode current monitoring are all still necessary.

[0076] See Figure 4 , Figure 4 This is a schematic diagram of an embodiment of the high-voltage microwave device provided in this application. The high-voltage microwave device 100 includes a microwave power transformer 10 and a voltage adjustment circuit 20. The voltage adjustment circuit 20 is as provided in any embodiment of this application. In some embodiments, the voltage adjustment circuit is encapsulated in an insulating housing. The voltage adjustment circuit is encapsulated in a highly insulating plastic housing and treated with insulating glue, thereby perfectly solving the insulation problem.

[0077] This voltage regulation circuit is applied to the high-voltage side of a microwave power transformer. The circuit includes: a control circuit; a switching circuit, the control terminal of which is connected to the control circuit; and an inductive component, which includes at least one inductor. The first end of the inductive component is connected to the first path terminal of the switching circuit and the first end of the power supply inductor in the cathode filament winding on the high-voltage side. The second end of the inductive component is connected to the second path terminal of the switching circuit, and the third end is connected to the second end of the power supply inductor. The control circuit is configured to send a control signal to the control terminal of the switching circuit to connect or disconnect the first and second path terminals of the switching circuit, adjusting the overall inductance on the high-voltage side, thereby adjusting the voltage of the power filament. After the magnetron starts up, adjusting the overall inductance on the high-voltage side reduces the heating voltage of the power filament, allowing for continued power replenishment while maintaining the filament temperature without excessive heating, thus delaying filament aging and extending its lifespan. From a physical mechanism perspective, the aging rate of thorium tungsten carbide cathode filaments is mainly affected by the filament operating temperature. According to the Richardson-Dushman formula and the Arrhenius relation between metal evaporation rate and temperature, the evaporation rate can decrease by more than an order of magnitude for every 100°C decrease in filament temperature. In the scheme of this application, after the magnetron starts up, the filament heating voltage can be reduced from the rated value during the start-up phase to the maintenance value (e.g., from about 6.3V to about 4.5V, depending on the magnetron model), and the corresponding filament operating temperature can be reduced from about 1550°C-1600°C to about 1300°C-1400°C. At this temperature reduction, the filament life is theoretically estimated to be extended by 2 to 5 times. The actual lifespan extension is affected by factors such as the magnetron duty cycle, heat dissipation conditions, and start-stop frequency, but the beneficial effect of reducing the maintenance heating power on delaying filament aging is definite and significant. For example, reducing the heating voltage of the power supply filament maintains the filament temperature above or equal to the temperature threshold. When the cathode temperature drops below the temperature threshold, the thermionic emission capability is significantly weakened. If thermionic emission is insufficient, the number of electrons bombarding the cathode will decrease, leading to a decline in secondary electron yield and creating a vicious cycle. Therefore, it is necessary to reduce the heating voltage of the power supply filament to maintain the filament temperature above or equal to the temperature threshold.

[0078] In the several embodiments provided in this application, it should be understood that the disclosed methods and devices can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed.

[0079] If the integrated units in the other embodiments described above are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, 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. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) or processor to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0080] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A voltage adjustment circuit for a high-voltage microwave power supply filament, characterized in that, The voltage adjustment circuit is located on the high-voltage side of the microwave power transformer and includes: An auxiliary power supply circuit is provided, the input of which is directly connected to the cathode filament winding on the high-voltage side. It is used to obtain AC power from the cathode filament winding and to rectify and filter it to generate DC power. An inductive component is connected in series with the power supply inductor in the cathode filament winding; the inductive component has at least three connection terminals, with its first terminal connected to the first terminal of the power supply inductor and its third terminal connected to the second terminal of the power supply inductor. A switching circuit, the power supply terminal of which is connected to the DC working power supply output by the auxiliary power supply circuit, and the two path terminals of which are respectively connected to the first terminal and the second terminal of the inductive component, is used to turn on or off in response to a control signal, so as to short-circuit or connect at least a portion of the inductance of the inductive component to the circuit, thereby changing the total inductance value formed by the power supply inductor and the inductive component in series. A control circuit, powered by the DC power supply, is used to output the control signal to the switching circuit after the magnetron is started.

2. The circuit according to claim 1, characterized in that, The auxiliary power supply circuit includes at least one diode and a capacitor, forming a half-wave rectifier filter circuit or a full-wave rectifier filter circuit; the auxiliary power supply circuit also includes a Zener diode connected in parallel to the output terminal of the rectifier filter circuit.

3. The circuit according to claim 1, characterized in that, The switching circuit includes at least one of a relay, MOSFET, IGBT, thyristor, or solid-state relay; when the switching circuit is a relay, it also includes a freewheeling diode connected in parallel with the relay coil.

4. The circuit according to claim 1, characterized in that, The inductive component includes multiple inductors, which are connected in series, in parallel, or in a hybrid series-parallel connection; or, the inductive component is an inductor with at least one center tap.

5. The circuit according to claim 1, characterized in that, The control circuit includes a microcontroller, which determines whether the magnetron has been started by monitoring the anode current and / or anode high voltage of the microwave power transformer. The monitoring signal is coupled to the sampling input terminal of the microcontroller through a resistor divider network and a limiting circuit. The microcontroller is also used to activate the switching circuit by outputting the control signal when the output power of the magnetron decreases, so as to increase the total inductance value and thereby increase the voltage of the power filament.

6. The circuit according to claim 5, characterized in that, The microcontroller obtains the anode current sampling signal through a sampling resistor connected in series between the secondary center tap of the microwave power transformer and the reference ground, and obtains the anode high voltage sampling signal through a high voltage resistor divider. The input terminals of the sampling signals are all equipped with amplitude limiting protection circuits.

7. The circuit according to claim 1, characterized in that, The voltage adjustment circuit is encapsulated in an insulating housing, the interior of which is filled with insulating adhesive; the withstand voltage rating of the insulating housing is not less than 8kV, and the dielectric strength of the insulating adhesive is not less than 12kV / mm.

8. The circuit according to claim 1, characterized in that, The inductive component is further connected in parallel with a transient overvoltage suppression circuit, which includes at least one of an RC series circuit, a varistor, or a TVS diode.

9. The circuit according to claim 1, characterized in that, The control circuit includes a timer, which outputs the control signal after a preset time threshold has elapsed since the magnetron starts up.

10. A high-voltage microwave device, characterized in that, It includes a microwave power transformer and a voltage regulation circuit as described in any one of claims 1 to 9.

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