Modeling and Analysis of Class EF and Class E/F Inverters With Series-Tuned Resonant Networks

Class EF and Class E/F inverters are hybrid inverters that combine the improved switch voltage and current waveforms of Class F and Class F-1 inverters with the efficient switching of Class E inverters. As a result, their efficiency, output power and power output capability can be higher in some cases than the Class E inverter. Little is known about these inverters and no attempt has been made to provide an in depth analysis on their performance. The design equations that have been previously derived are limited and are only applicable under certain assumptions. This paper is the first to provide a comprehensive set of analytical analysis of Class EF and Class E/F inverters. The Class EF2 inverter is then studied in further detail and three special operation cases are defined that allow it to either operate at maximum power-output capability, maximum switching frequency, or maximum output power. Final design equations are provided to allow for rapid design and development. Experimental results are provided to confirm the accuracy of the performed analysis based on a 23-W Class EF2 inverter at 6.78-MHz and 8.60-MHz switching frequencies. The results also show that the Class EF2 inverter achieved an efficiency of 91% compared to a 88% efficiency when operated as a Class E inverter.