Patent ID: 7468586

Claim:
A ballast for powering at least one gas discharge lamp, the ballast comprising: an AC-to-DC converter having an input for receiving an AC supply voltage and an output for providing a DC rail voltage; an inverter coupled to the AC-to-DC converter, the inverter having a normal operating frequency, the inverter comprising: (i) first and second inverter transistors; (ii) a first base drive circuit coupled to the first inverter transistor; (iii) a second base drive circuit coupled to the second inverter transistor; (iv) an inverter ground; and (v) an inverter startup circuit coupled to the AC-to-DC converter, the second inverter transistor, and the inverter ground; an output circuit coupled to the inverter, the output circuit comprising: at least a first output connection ( 302 ) and a return output connection ( 310 ), wherein the first output connection ( 302 ) and the return output connection ( 310 ) are adapted for coupling to a first gas discharge lamp ( 72 ); a sensing transformer ( 360 ) coupled to the first output connection ( 302 ) and the return output connection ( 310 ); and a tuning capacitor ( 370 ) coupled in parallel with the sensing transformer ( 370 ); and an arc protection circuit coupled to the inverter and to the output circuit, the arc protection circuit comprising: a plurality of connections, including first and second connections ( 402 , 404 ) coupled to the tuning capacitor ( 370 ) of the output circuit ( 300 ), a third connection ( 406 ) coupled to the second inverter transistor and the second base drive circuit, a fourth connection ( 408 ) coupled to the inverter startup circuit, fifth and sixth connections ( 410 , 412 ) coupled to the AC-to-DC converter, and a seventh connection ( 414 ) coupled to the inverter ground; a microcontroller ( 440 ) having an input ( 442 ), an output ( 444 ), a DC supply input ( 446 ), and a ground input ( 448 ), wherein the DC supply input ( 446 ) is coupled to the seventh connection ( 414 ) and the ground input ( 448 ) is coupled to a reference node ( 416 ); a detection circuit ( 422 , 424 , 426 , 428 , 430 , 438 ) coupled between the first and second connections ( 402 , 404 ) and the input ( 442 ) of the microcontroller ( 440 ); a first shunting circuit ( 418 , 450 ) coupled to the third connection ( 406 ), the output ( 444 ) of the microcontroller, and the reference node ( 416 ); a second shunting circuit ( 460 , 468 ) coupled to the fourth connection ( 408 ), the output ( 444 ) of the microcontroller, and the reference node ( 416 ); and a DC voltage supply circuit ( 470 , 476 , 478 , 480 , 490 ) coupled to the fifth and sixth connections ( 410 , 412 ), the DC supply input ( 446 ) of the microcontroller, the seventh connection ( 414 ), and the reference node ( 416 ).