A shunt-excited inductive power link

An alternative derivation of the separation-insensitive property of series-excited self-oscillating inductive power transfer circuits is presented. This analysis is based on network theory and does not include the explicit determination of frequency as a step in the derivation. The separation-insensitivity principle is extended to shunt-excited links which exhibit a theoretical voltage transfer function of unity while the coupling factor exceeds the reciprocal of the secondary quality factor. This requires the inclusion of a series resistor in the primary resonator's capacitive arm. Series RC elements are replaced by parallel forms in both the primary and secondary; this provides a more convenient output impedance level without the need for another transformer. A demonstration circuit is described and tested. It is found that separation-insensitivity occurs while the coupling factor exceeds the reciprocal of the loaded secondary quality factor. Somewhat inferior response is obtained from a simpler circuit having no added resistances in the primary.