Solid state class DE RF power source

Class DE represents a new family of inverters, based on a Class D LCR series resonant inverter. Class DE differs in that the method of operation utilises the devices output capacitance to obtain zero voltage, zero current switching transitions. Hence switching losses (and switching EMI) can be very low, permitting operation to a high frequency. This paper presents the problems, solutions, results and feasibility of a Class DE inverter as an RF power source for frequencies up to 5 MHz and a power of 1 kW. At this frequency, the theoretical design requirements put some tight restrictions on dead time, phase and output capacitance. This presents some formidable problems in practically implementing the inverter. The most significant problems are: the gate drive circuitry including layout, isolation of the high side gate drive, nanosecond control of dead time, synchronization of high and low side gate drive pulses, phase control of the driving voltage and general layout of the power devices. Some novel solutions to the above problems are described. The simulation and experimental results are presented and the practical power and frequency limits of a Class DE inverter are discussed. The information presented should be useful in applications such as MHz DC-DC power converters, RF power sources for industrial heating and AM transmitters