American Telephone and Telegraph Company; At&t Information Systems

Mark A Eberhart

Burt Joseph Bossi

A power transfer circuit includes first and second windings (L1, L2) sharing a common magnetic core (101). Each winding has associated with it a parallel capacitor to thus form a pair of 'tank' circuits. The first winding (L1) is connected at one end to a voltage supply and, at the other end, to ground through an FET switch (100,200). The switch (100,200) is turned on and off at a predetermined frequency and at a 50% duty cycle. The second winding (L2) and associated capacitor (C2) achieves parallel resonance at the predetermined frequency. Similarly the combined first and second windings (L1,L2) and associated capacitors (C1,C2) achieve parallel resonance at said predetermined frequency. The second winding (L2) need not be electrically connected to the first winding (L1) which transfers energy to it through the magnetic core (101). The transfer circuit efficiently couples power across a dielectric interface to a pickup coil (L3). One particularly good application of the power transfer circuit is in connection with a contactless Smart Card.

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Shelbyville, IN, United States of America

Mark A Eberhart