A Class E ZVS amplifier with basic matching circuits

In high-efficiency Class E amplifiers matching circuits are commonly used to transform usually constant load resistance to nominal or off-nominal resistance of the amplifier to ensure its ZVS operation. In some applications such as: wireless power transfer systems, plasma generators, dc-dc power converters as well as in some transmitters Class E amplifiers operate with load resistance or impedance varied in a wide range. This requires the matching circuit to transform the whole range of load resistance into the range of nominal and off-nominal resistance of the amplifier. The paper presents theoretical results for Class E ZVS amplifier with basic parallel π 1a and π2a matching circuits loaded with variable resistance. Conditions for ZVS operation of the amplifier with transistor duty cycle D=0.5 and the matching circuits loaded with any load resistance are discussed. Analytical expressions setting the boundaries for ZVS operation of the Class E amplifier with the analyzed matching circuits are given as well. Examples of normalized characteristics of output voltage and output power vs. load resistance for the amplifier are also presented. A design example for the Class E amplifier with π1a matching circuit able to operate with any load resistance is described and verified by simulation with LTSpice.