Patent ID: 7380150

Claim:
A power management circuit for a transponder system comprising: a power supply from an inductively couples circuit; a power supply from a battery, a voltage sensing circuitry for sensing a voltage of each said power supplies, a switching arrangement for selectively connecting one of said power supplies with at least one user, and control circuitry controlling said switching arrangement in response to an output of said voltage sensing circuitry wherein the voltage sensing circuitry includes threshold circuits that provide outputs for each power supply indicative of whether or not a respective power supply has a voltage considered sufficient for operation of said user, wherein the voltage sensing circuitry uses one of said power supplies to detect the voltage of another one of said power supplies and vice versa, and further comprising a battery charge circuit that is supplied by the power supply from the inductively coupled circuit when and if the voltage of said power supply exceeds a predetermined threshold wherein the predetermined threshold is selected to ensure proper basic functionality of circuitry within said transponder system.