OPEN LOOP CURRENT CONTROL BALLAST FOR LOW PRESSURE MERCURY GERMICIDAL UV LAMPS

摘要

An apparatus for starting and operating UV lamps, comprises an AC line powered circuit and a UV lamp. The circuit has a variable frequency AC source, providing AC current to the UV lamp and a ballasting inductor, connected in series with the UV lamp. The inductor and the lamp form a nonresonant coupling sub-circuit where a flow of current from the AC source through the UV lamp is limited by the ballasting inductor. The circuit does not develop dangerously high output voltages if the UV lamp is disconnected or burnt out, as would be the case with resonant output circuits, unless additional circuit protection was implemented. The impedance of the ballast inductor varies with the current frequency, enabling it to act as a current control element with changes in the output frequency. An open loop control circuit of the present invention maintains the lamp current at a relatively constant level without the complexity imposed by closed loop current control methods.