Fundamental and third harmonic operation of SIT inverter and its application to RF thermal plasma generation

The purpose of this paper is to study the 3rd harmonic operation of a voltage source inverter power supply. A static induction transistor (SIT) inverter power supply is used in this experiment. This power supply can generate 14 kW in steady state operation and its upper limit frequency of the gate driver is 1.7 MHz. The advantage of the 3rd harmonic operation is that the RF power at higher frequency range beyond the switching limit can be generated. It should be also noted that the driver circuit needs no special modification for this operation. The conversion efficiency and maximum output power are investigated as a function of output frequency. The conversion efficiency with harmonic operation is a little lower than the conversion efficiency with fundamental operation. At the frequency of <3 MHz, the conversion efficiency is higher than that of conventional linear amplifiers when using this SIT inverter power supply.