Design of class-E ZVS inverter with loosely-coupled transformer at fixed coupling coefficient

Abstract

The design of Class-E zero-voltage switching (ZVS) inverter with a loosely-coupled transformer is introduced in this paper. In the presented approach, the magnetizing and leakage inductances of the transformer are absorbed into the main circuit. The synthesis of the transformer-version of Class-E ZVS inverter into its equivalent π2a topology is presented. The π2a topology improves the range of the optimum load resistance required to achieve ZVS. An example of the Class-E inverter with dc supply voltage 10 V, output power 10 W, switching frequency 100 kHz and at a coupling coefficient of 0.77 is considered. The inverter is designed to achieve both zero-voltage switching (ZVS) and zero derivative switching (ZDS) conditions. The analytical expressions are validated through simulation results for an optimum coupling coefficient of 0.77. In view of potential misalignment between the primary and secondary coils, simulation results are provided for coupling coefficients, which are lower and higher than the optimum value. It is shown that both ZVS and ZDS can be achieved at a coupling coefficient lower than the optimum value and is not possible to achieve ZVS at a coupling coefficient higher than the optimum value. Overall efficiency of 94.3% is achieved at a coupling coefficient of 0.77, 93.4% at 0.85, and 92.12% at 0.7. The presented approach can be used for transformers with reactive load impedances also.