A Differential Relaxation Oscillator for Inductive Power Transfer

We present a novel differential relaxation oscillator for inductive power transfer. The proposed oscillator offers an automatic adaption of the self-oscillation period to a change in the power link impedance, which ensures a high efficient operation for variable loads and coupling factors. A detailed circuit model of the self-oscillation system is provided with analytical design equations. We find a large self-oscillation range for variable coupling factors and loads. The theoretical results are confirmed by circuit simulation and measurements carried out on a low-power demonstrator system. We demonstrate non-resonant and robust self-adaption of the relaxation oscillator supplying an inductive power link with coupling factors ranging from k=0.6-0.9.