Output power-efficiency trade-off in DC-RF MOS-FET power inverter operating at 10 to 30 MHz

As the operating frequency increases beyond 10 MHz the power loss caused by the drain-source capacitance of each MOSFET remarkably increases unless a tank circuit containing the drain-source capacitance is built. DC-RF MOSFET power inverters of the single-ended voltage-tuned type are discussed in this context. Expressions for the drain efficiency, output power, and power gain are given in terms of the on-resistance, number of MOSFETs connected in parallel, frequency, turn-on phase angle, the wiring inductance, and the load impedance. The calculated values agree well with measured data. The tradeoff between the output power and drain efficiency is experimentally and theoretically confirmed, and is used to find the optimum design conditions in constructing a DC-RF MOSFET power inverter. The turn-on phase angle and load impedance must be optimized because they affect the power loss. Higher drain efficiency can be obtained for higher load impedance; however, the load impedance is usually specified as low value to increase the output power up to 600 W. It is shown that the drain efficiency was approximately about 64% at 28 MHz at best if the drain voltage is sinusoidal