Constant autonomy despite coupling coefficient variations for a very low power contact-less application based on a parallel-resonant DC-DC converter

Contact-less applications main characteristic is the physical separation between the power source and the load. Energy is transferred by means of a transformer which coupling is low due to the separation between the windings: primary winding is in the side of the power source and secondary winding in the side of the load. In many of these applications the separation between the windings can be variable, and therefore coupling coefficient is also variable. In this paper a single-switch single-tuned parallel resonant converter is proposed to improve efficiency of the contact-less power supply. Also different techniques have been analysed through measurements on a real prototype to verify which one provides constant input power (and constant autonomy) to the power supply despite the possible coupling coefficient variations