Patent Application
20080088251
First and second inverter input terminals 202,204 are adapted to receive a source of substantially direct current (DC) voltage, VRAIL, as provided by a front-end circuit 100. Front-end circuit typically includes a rectifier circuit in combination with some form of power factor correction circuitry (e.g., a boost converter, a valley-fill circuit, etc.). Inverter output terminals 206,208 are intended to be connected to an output circuit 300 via which ignition voltage and steady-state operating power is delivered to lamp 30. First inverter output terminal 206 is coupled to first inverter input terminal 202.
First and second inverter switches 220,240 are realized by suitable power switching devices, such as NPN type bipolar junction transistors (as depicted in
First base-drive circuit 230,342 is coupled to first inverter switch 220, and includes a series combination of a first base-drive winding 342 and a first base-drive resistor 230; the series combination of first base-drive winding 342 and first base-drive resistor 230 is coupled between base terminal 222 of first inverter switch 220 and second inverter output terminal 208. Second base-drive circuit 250,344 is coupled to second inverter switch 240, and includes a series combination of a second base-drive winding 344 and a second base-drive resistor 250; the series combination of second base-drive winding 344 and second base-drive resistor 250 is coupled between base terminal 242 of second inverter switch 240 and circuit ground 60.
Inverter startup circuit 286,288,290 is operably coupled to first inverter output terminal 206, second base-drive circuit 250,344, and base terminal 242 of second inverter switch 240. During operation, inverter startup circuit 286,288,290 provides a starting voltage for initially activating second inverter switch 240, thereby initiating self-oscillating operation of inverter 200′. Significantly, inverter startup circuit 286,288,290 provides for startup of inverter 200′ without requiring a voltage breakdown device, such as a diac. Consequently, inverter startup circuit 286,288,290 has significantly lower material cost, and provides ballast 20 with potentially higher reliability, than the prior art approach illustrated in
As described in
During operation of ballast 20, shortly after AC power is initially applied to input connections 102,104, the output voltage, VRAIL, of front-end circuit 100 assumes a value (e.g., 390 volts) that is approximately equal to the peak magnitude of the voltage provided by AC voltage source 40 (e.g., 277 volts rms at 60 hertz, corresponding to a peak magnitude of about 390 volts). Within inverter startup circuit 286,288,290, a substantially DC current flows through the circuit path including resistors 286,288 and capacitor 290, thereby charging up capacitor 290. When the voltage across capacitor 290 reaches a sufficient level, second inverter transistor 240 turns on, thereby allowing inverter 200′ to begin the process of self-oscillation. Subsequently, inverter transistors 220,240 are turned on and off by voltage signals provided by base-drive windings 342,344 which are magnetically coupled to a primary winding 340 within output circuit 300.
Referring again to
As illustrated in
Front-end circuit 100 includes a pair of input connections 102,104 and a pair of output connections 106,108. Input connections 102,104 are adapted to receive a source of alternating current (AC) voltage 40 (e.g., 277 volts at 60 hertz). Output connections 106,108 are coupled to first and second input terminals 202,204 of inverter 200′. During operation, front-end circuit 100 receives AC voltage source 40 and provides a substantially DC voltage, VRAIL, between output connections 106,108.
Resonant output circuit 300 preferably includes first, second, third, and fourth output connections 302,304,306,308, a series combination of a resonant inductor 310 and a primary winding 340 of a base-drive transformer, a resonant capacitor 320, and a direct current (DC) blocking capacitor 330. Output connections 302,304,306,308 are intended to be coupled to gas discharge lamp 30. The series combination of resonant inductor 310 and primary winding 340 of the base-drive transformer (wherein primary winding 340 is magnetically coupled to first and second base-drive windings 342,344, which constitute secondary windings of the base-drive transformer) is coupled between second inverter output terminal 208 and fourth output connection 308. Resonant capacitor 320 is coupled between second and third output connections 304,306. DC blocking capacitor 320 is coupled between first inverter output terminal 206 and first output connection 302.
Although the present invention has been described with reference to certain preferred embodiments, numerous modifications and variations can be made by those skilled in the art without departing from the novel spirit and scope of this invention.
