Comparative Study of High-Voltage Isolated Filament Power Supply for Driving a High-Power Magnetron

This article describes a filament power supply (FPS) for driving a high-power magnetron and presents a comparison of three applicable switching control techniques: switching frequency regulation, duty ratio regulation, and phase-shifted pulsewidth modulation (PWM). The FPS was designed based on a simple full-bridge converter. Considering that the reference potential of the filament has a high-voltage potential of several tens of kilovolts, a double-insulated transformer is applied. In addition, a simpler indirect sensing circuit is designed, and the linearity of the indirect voltage and current sensing of each switching control technique are compared. Given that runback control must be applied when driving the magnetron, it is designed to operate under a wide range of loads from a light load to the rated conditions. To guarantee the versatility of the FPS, its output specifications are selected as a maximum power of 289 W, a maximum output voltage of 17 Vrms, and a maximum output current of 17 Arms. A prototype FPS capable of tens of kilovolts of insulation and using an indirect sensing technique is manufactured and tested, and its design and operation are verified experimentally.