Power regulator for a contactless credit card system

摘要

A power transfer arrangment provides regulated power transfer from a station to a contactless portable data card without the need for regulation circuitry on the card itself. The station includes a primary coil for magnetically coupling power to a secondary coil, located on the card, when the data card is brought into close association with the station. The arrangment includes a microprocessor, a power amplifier including the primary coil, a variable voltage source and apparatus for measuring current flow in the primary coil. When the portable data card is not in close association with the station, the microprocessor causes the variable voltage source to provide a sequence of stepped voltages. Quiescent current flow is measured at each step and stored in memory. When the portable data card is brought into close association with the station, the microprocessor causes the variable voltage source to provide a sequence of stepped voltages. Active current flow is measured at each step and stored in memory. Power delivered to the data card is calculated as the difference between active and quiescent currents-multiplied by the magnitude of the variable voltage source. The sequence of active current measurements continues until the calculated value of power delivered to the data card exceeds a predetermined threshold power, at which time the data card is receiving a precise, predetermined amount of power.