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US 3,938,000 AGranted
Lamp driver for telephone panel indicator lamps
AssigneeGTE Automatic Electric Laboratories Incorporated
InventorCarlos S. Higashide
Life of this patent
Estimating the term…
Abstract
An electrical circuit for limiting surge currents through incandescent indicator or display lamps is disclosed. It is essentially a constant current device having a current controlling transistor in the load circuit to limit the initial surge current to a first value after, which the lamp itself limits the current. Provision is made for testing of the lamp and circuit by maintenance personnel.
Claims3
A lamp driver for switching electrical current from a power source to an incandescent lamp whose resistance is low during the first moments of application of power thereto;
- said lamp having one terminal connected to a first terminal of said power source, said lamp driver including a transistor having a base, a collector, and an emitter, a biasing diode having an anode and a cathode, said collector electrically connected to said incandescent lamp and said emitter electrically connected to a second terminal of said power source via said biasing diode in the anode to cathode direction, a zener diode in series with a first resistor having its anode connected to said second terminal and said resistor to said first terminal of said power source, said base electrically connected to a control input terminal operative to cause said transistor to begin conduction, and to said second terminal of said power source via a second resistor for maintaining said transistor in a nonconducting state and an isolating diode having its cathode connected to the junction of said zener diode and first resistor for maintaining a predetermined bias on said base during the conduction of said transistor.
Dependencies are inferred from the claim text.