Fluorescent lamp brightness contorl process by ballast frequency adjustment

A fluorescent ballast and control circuit comprising:

• a drive signal generator responsive to a drive frequency control signal for providing a ballast drive signal having a drive signal frequency proportional to the drive frequency control signal,
• a fluorescent ballast circuit responsive to the ballast drive signal and having an output voltage coupled to drive a fluorescent lamp load, the fluorescent ballast circuit being characterized to provide a change in the output voltage applied to the lamp load in response to a change in the ballast drive signal frequency,
• means for monitoring the brightness of the lamp load and for developing a brightness signal characterizing the brightness of the lamp load,
• a signal conditioner responsive to the brightness signal and to a reference signal for providing and adjusting the drive frequency control signal to keep the brightness signal substantially constant.

A fluorescent ballast and control circuit comprising:

• a drive signal generator responsive to a drive frequency control signal for providing a first and a second ballast drive signal, each respective ballast drive signal being phase shifted to insure that they do not overlap in time, each respective drive signal having a substantially equal number of volt-seconds and a frequency proportional to the drive frequency control signal,
• a fluorescent ballast circuit responsive to the ballast drive signal and having an output voltage coupled to drive a fluorescent lamp load, the fluorescent ballast circuit being characterized to provide a change in the output voltage applied to the lamp load in response to a change in the ballast drive signal frequency and having,
• a transformer having a primary winding and a secondary winding, a totem pole drive circuit being coupled to drive a first end of the primary winding in series with a resonant inductor, a second end of the primary winding being coupled to ground,
• the secondary winding being coupled in parallel with a resonant capacitor and the lamp load,
• means for monitoring the brightness of the lamp load and for developing a brightness signal characterizing the brightness of the lamp load,
• a signal conditioner responsive to the brightness signal and to a reference signal for providing and adjusting the drive frequency control signal to keep the brightness signal substantially constant.