Fluorescent lamp circuit
AssigneeU-Lite, Inc.
InventorsRobert P. Fuller, Larry A. Nordstrom
Life of this patent
Estimating the term…
Abstract
A d.c.-a.c. inverter circuit allows a standard type fluorescent lamp to be operated from a low-voltage source of d.c. power with a high degree of efficiency attributable in part to use of lamp current as base drive current for a power transistor controlling the energization of a transformer primary winding having two mutually connected secondary windings which apply voltages across the lamp through the power transistor. Additional efficiency is achieved by use of a second transistor under time delay control for supplying preheat current to the lamp and turn-on current to the power transistor only during the starting phase of lamp operation.
Claims15
A fluorescent lamp circuit comprising:
- a pair of input terminals for connection across a low voltage d.c. power source;
- a fluorescent lamp having a pair of electrodes at opposite ends of a gas-filled envelope;
- a transformer having a ferromagnetic core on which a primary winding, a first secondary winding and a second secondary winding are wound, said secondary windings being connected in series with one another in voltage aiding relationship;
- a bipolar transistor which, when conductive, connects said primary winding across said pair of input terminals;
- first biasing means which, in response to the connecting of said pair of input terminals across said power source, supplies forward driving current through the base of said transistor to cause said transistor to become partially conductive so that current from said power source begins to flow through said primary winding;
- means connecting one side of the serially-connected secondary windings to one end electrode of said fluorescent lamp and the other side through the base of said transistor via the path of said forward driving current thereof to the other end electrode;
- a diode connected across said forward driving current path of said transistor in anti-polarity relationship therewith;
- and
- a resistor connected from a common connection point of said serially-connected secondary windings to a common connection point of said diode, said forward driving current path of said transistor and one of said pair of input terminals;
- said resistor, diode, secondary windings and the impedance of said fluorescent lamp providing biasing conditions for said transistor which cause the conductivity of said transistor to undergo successive time cycles upon said pair of input terminals being connected across said power source, one half period of each time cycle being characterized by a rise and fall of transistor conductivity from zero to full and back to zero, and the other half period by a continuing zero conductivity, each cycle being initiated by said first biasing means at least during the first few seconds of operation, whereby voltages of one polarity are induced across said secondary windings by said primary winding to drive current of one direction through said fluorescent lamp via the base of said transistor as said transistor experiences its conductive half cycle, and voltages of opposite polarity to said one polarity develop across said secondary windings to drive current of the opposite direction through said fluorescent lamp via said diode as said transistor experiences its non-conductive half cycle, the flow of lamp current via the base of said transistor effecting an automatic adjustment of the transistor base drive to regulate said lamp current.
In a d.c. - a.c. inverter circuit comprising a pair of d.c. input terminals for connection across a d.c. power source, a pair of a.c. output terminals for connection across a load, a transformer having a ferromagnetic core on which a primary winding, a first secondary winding and a second secondary winding are wound, and a bipolar transistor having its collector-emitter path connected in series with said primary winding across said d.c. input terminals and having its base-emitter path connected in parallel anti-polarity relationship with a diode, the improvement wherein:
- said inverter circuit is arranged so that alternate half cycles of current flowing through a load connected to said a.c. output terminals is also caused to flow through said base-emitter path for automatically adjusting the forward base drive current of said transistor to compensate for changes in load current, there being provided for this purpose a connection of said first secondary winding, said second secondary winding and the parallel connection of said base-emitter path and diode in series with one another across said a.c. output terminals, said secondary windings being disposed in relation to said primary winding so that mutually aiding voltages are inductively developed in said secondary windings by voltage changes occurring in said primary winding.
Dependencies are inferred from the claim text.