Method of regulating lamp current through a fluorescent lamp by pulse energizing a driving supply

A method of regulating an operating current conducted through a plasma between cathodes of a fluorescent lamp while the lamp is continuously lighted by energy supplied from an AC electrical source, the source delivering AC source current at a predetermined source frequency in half-cycles having a periodic half-cycle interval established by the source frequency, said regulating method comprising the steps of:

• connecting a resonant circuit including at least one electrical energy storage element in series in a current path through the plasma and the cathodes and the source;
• conducting half-cycles of primary source current to the resonant circuit during each entire periodic half-cycle interval;
• storing a normal amount of energy in the resonant circuit during each periodic half cycle interval as a result of conducting the primary source current to the resonant circuit;
• deriving the operating current from the energy stored in the resonant circuit;
• conducting the operating current through the plasma during lamp illumination intervals which occur at the same predetermined frequency as the half-cycles of the primary source current;
• during a predetermined conductive time interval of a duration less than the entire periodic half-cycle interval of each half-cycle of primary source current, conducting a charging current in addition to the primary current from the source to the resonant circuit, the charging current storing additional energy in the resonant circuit in a predetermined amount greater than that normal amount of energy stored in the resonant circuit by the primary source current;
• releasing the additional stored energy along with the normal stored energy as operating current during a lamp illumination interval occurring after the half cycle in which the charging current was conducted and the additional energy was stored to regulate the operating current delivered to the plasma;
• and
• performing said steps during each half-cycle and lamp illumination interval while the lamp is lighted.