Self-dimming electronic ballast

A self-dimming electronic ballast for powering a gas discharge lamp from an AC line voltage, said ballast comprising:

• a converter for converting said AC line voltage into direct current at a high voltage;
• an inverter coupled to said converter and including
• a pair of series connected, alternately conducting transistors, said transistors switching at a predetermined frequency;
• a series resonant, parallel loaded output for coupling said transistors to said lamp;
• a control circuit for producing a control signal inversely proportional to said line voltage;
• a driver circuit coupled to said transistors, said driver circuit responsive to said control signal for increasing the frequency at which said transistors switch in response to a decrease in said AC line voltage, whereby the current through said lamp decreases when said line voltage decreases.

A method for dimming a flourescent lamp powered by an electronic ballast coupled to an AC input voltage, said method comprising the steps of:

• providing a ballast having a variable frequency inverter and a series resonant, parallel loaded output;
• decreasing said input voltage;
• and
• increasing the frequency of said inverter in response to a decrease in said input voltage.