Contactless battery charger for composite humidity and temperature wireless sensors

This paper presents the analysis and design of a DC-DC series resonant power converter used as a contactless battery charger (5V_DC -1A) for a mobile electronic device. The system is enclosed in a sealed spherical shell containing temperature and humidity wireless sensors and related electronic circuitry for real time composting process monitoring. Some particular characteristics of the device and its physical dimensions impose a maximum distance between the primary and the secondary transformer windings of 20mm. For transformer type core and windings configuration selection criteria, an experimental characterization of loosely coupled power transformers was evaluated. Both simulation and experimental results, obtained in a 150kHz laboratory prototype, were used as evidence of the developed theoretical models and analysis.