Magnetron Driving Circuit With Thermal Current Limiting
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Solution Overview
Problem
The filament in a magnetron overheats due to excessive temperature rise, leading to material evaporation and a shortened service life, especially when the filament voltage remains at 3.3V or decreases, causing a decrease in output power.
Innovation Solution
A driving circuit for magnetron that includes a rectification circuit, transformer, and a component with a variable resistance value to limit current flow, using thermal relays and/or thermistors to regulate temperature and prevent overheating, ensuring stable operation and extending the magnetron's lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the filament voltage is maintained at 3.3V or reduced to ensure proper electron emission, then the magnetron can operate, but the filament temperature rises excessively causing material evaporation and shortened service life
Solution Approach 1:
The patent introduces a preheating circuit that applies a higher voltage (6.6V or higher) to the filament during a preheating period before normal operation. This preliminary action ensures the filament reaches optimal temperature for electron emission before the main operating voltage is applied, preventing excessive temperature rise during continuous operation and extending filament service life while maintaining reliable magnetron operation
Solution Approach 2:
The patent implements periodic switching between preheating mode and normal operation mode. The control circuit periodically applies high voltage to the filament for preheating, then switches to normal operating voltage. This periodic action allows the filament to maintain proper temperature for electron emission without continuous excessive heating, resolving the contradiction between operational reliability and temperature control
2Productivity
If the filament is continuously energized to maintain electron emission, then the magnetron can operate, but excessive heat generation intensifies material evaporation and reduces filament lifespan
Solution Approach 1:
The preheating circuit provides a preliminary high-voltage pulse to the filament before normal operation begins. This preliminary action ensures the filament is properly heated for electron emission, after which the voltage is reduced to normal operating levels. This approach maintains electron emission capability while avoiding continuous excessive heating that would reduce filament lifespan
Solution Approach 2:
The patent changes the voltage parameter applied to the filament over time - using a higher voltage (6.6V or higher) during the preheating phase, then switching to a lower normal operating voltage (3.3V or reduced voltage). This parameter change allows the filament to achieve necessary temperature for electron emission initially, then maintains operation at lower temperature to extend service life
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The circuit reduces filament heat generation and evaporation, allowing the magnetron to operate normally by utilizing secondary back bombardment of electrons, thereby improving the magnetron's service life and ensuring stable operation.
Implementation Method 1
a component having a variable resistance value, and the component is located in a circuit path between the first secondary coil, the anode of the magnetron, and the cathode of the magnetron, and configured to limit the current flowing through the magnetron, and the resistance value of the component is positively correlated with the temperature of the component
Implementation Method 2
the rectification circuit is configured to convert an alternating current into a direct current to supply power to the magnetron
Implementation Method 3
the transformer is configured to provide the AC for the rectification circuit
Implementation Method 4
the component will generate heat due to its own obstruction to current
Data Source
AI summary
A driving circuit for a magnetron, and a heating device, the driving circuit includes a rectification circuit, configured to convert an alternating current into a direct current so as to supply power to the magnetron. The driving circuit includes a transformer, a primary coil of the transformer being configured to be connected to an alternating current power supply terminal or an inverter circuit, a second secondary coil of the transformer being connected to the rectification circuit, and the transformer being configured to provide an alternating current for the rectification circuit; and a component having a variable resistance value, the component is in a circuit path formed by the first secondary coil, the anode of the magnetron, and the cathode of the magnetron and configured to limit a current flowing through the magnetron. A resistance value of the component is positively correlated with the temperature of the component.