Transformer coupled switching transmitter for electronic article surveillance system
AssigneeSensormatic Electronics Corporation
InventorRichard L. Herring
Life of this patent
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Abstract
A transmitter circuit drives a transmit antenna for an electronic article surveillance system with an alternating drive signal. The transmitter circuit includes a DC power supply which converts an AC input power signal into a DC power supply potential, a switching circuit which forms an alternating signal from the DC power supply potential, and a transformer which couples the alternating signal to the antenna. The transformer provides isolation for the transmit antenna, as well as voltage step-down to a desired amplitude for the antenna driving signal. The DC potential supplied to the switching circuit may be regulated or unregulated.
Claims18
A transmitter circuit for driving an EAS system transmit antenna at a predetermined frequency, comprising:
- signal generating means for generating a signal that alternates at said predetermined frequency;
- and
- an isolation transformer for coupling to said antenna said signal generated by said signal generating means;
- said signal generating means including:
- DC power supply means for converting an AC input power signal into a DC power supply potential;
- means for deriving a positive DC level and negative DC level from said DC power supply potential;
- and
- means for alternately applying said positive DC level and said negative DC level to a primary winding of said transformer in accordance with a predetermined cycle to form said signal that alternates at said predetermined frequency.
A transmitter circuit for driving an EAS system transmit antenna at a predetermined frequency, comprising:
- signal generating means for generating a signal that alternates at said predetermined frequency;
- and
- a step-down transformer for stepping-down a voltage level of said signal generated by said signal generating means and applying the stepped-down signal to said antenna;
- said signal generating means including:
- DC power supply means for converting an AC input power signal into a DC power supply potential;
- means for deriving a positive DC level and negative DC level from said DC power supply potential;
- and
- means for alternately applying said positive DC level and said negative DC level to a primary winding of said transformer in accordance with a predetermined cycle to form said signal that alternates at said predetermined frequency.
A method of energizing a transmit antenna in an electronic article surveillance system, comprising the steps of:
- providing an isolation transformer having a primary winding and a secondary winding, said secondary winding being connected to said transmit antenna;
- and
- applying an alternating drive signal to said primary winding;
- said applying step including providing a switchable circuit connected to said primary winding and switching said switchable circuit between a first condition in which said switchable circuit applies a first DC drive signal to said primary winding and a second condition in which said switchable circuit applies to said primary winding a second DC drive signal that is opposite in polarity to said first DC drive signal.
A transmitter circuit for driving a transmit antenna in an electronic article surveillance system, the transmitter circuit comprising:
- DC power supply means for converting an AC input power signal into a DC power supply potential;
- a transformer including a primary winding and a secondary winding, said secondary winding being connected to said transmit antenna;
- switchable means for switchably interconnecting said DC power supply means and said primary winding of said transformer;
- and
- control means for switching said switchable means between a first condition in which said switchable means applies a first drive signal to said primary winding and a second condition in which said switchable means applies a second drive signal to said primary winding, said first and second drive signals being substantially equal in amplitude and opposite in polarity.
Dependencies are inferred from the claim text.