This paper describes a design of power supply to control electric power widely with keeping the high power factor.
Magnetrons have been used extensively for household microwave ovens and industry microwave heredity heating devices, and they are operated by 3,000[V] ∼ 5,000[V] DC high voltage.
Power supply for driving magnetron is consisted of SMPS(switch mode power supply), HPFC(high power factor correction) circuit, microprocessor and interface, and HB(half bridge) DC-DC converter.
HPFC is composed of Boost converter, zero current detector, output voltage and current comparator and it is controlled by PWM(pulse width modulation) for the optimum condition in which output voltage and current are consistent with reference values by PFC using MC34262.
Conventional inverters for driving magnetron are 60[Hz] HVT inverter, transformer resonant ZVS(zero voltage switching) inverter, series resonant HB inverter etc., These control electrical power quantity by ON-OFF time under the condition of constant electrical power. In this paper, it is controlled by variable frequency for HB DC-DC converter system.
HB DC-DC converter is composed of a step-up transformer, a heater coil and a full wave rectifier to supply DC magnetron anode voltage for the second step-up transformer.
The proposed system with 300[W] power consumption is builted and it is confirmed that it can attain the 99.2[%] power factor and control input power of the magnetron up to 33.3[%] linearly by adjusting pulse duty ratio of the inverter through the experiment.