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An article surveillance system includes a power line activated inductive magnetic field generator having an on duty cycle portion considerably less than 50%. A transformerless AC power line to DC converter and switching circuitry are connected to a series resonant circuit including a coil for derivi

An article surveillance system includes a power line activated inductive magnetic field generator having an on duty cycle portion considerably less than 50%. A transformerless AC power line to DC converter and switching circuitry are connected to a series resonant circuit including a coil for deriving the AC inductive magnetic field. During on duty cycle portions, the switches are activated and connected to the series resonant circuit and the power supply to cause resonant current to flow in the series circuit at an activation frequency for the switches, causing the coil to generate the magnetic field at the activation frequency.

대표청구항 ▼

A power-line-activated inductive magnetic field generator having an on-duty cycle portion considerably less than 50% for deriving an AC magnetic field having a predetermined frequency comprising: a transformerless AC-power-line-to-DC converter, a series resonant circuit including coil means, and swi

A power-line-activated inductive magnetic field generator having an on-duty cycle portion considerably less than 50% for deriving an AC magnetic field having a predetermined frequency comprising: a transformerless AC-power-line-to-DC converter, a series resonant circuit including coil means, and switch means activated during the on-duty cycle portions and deactivated during off-duty cycle portions, the switch means being activated at a selected frequency during the on-duty cycle portions and being connected to the resonant circuit as well as to the converter to cause resonant current to flow in the series circuit at the predetermined frequency during each on-duty cycle portion to thereby cause the coil means to derive the AC inductive magnetic field.