Method and ballast for starting a discharge lamp

A ballast for operating a discharge lamp having a maximum power rating and a normal power rating, said ballast comprising:

• a power converter capable of applying a varying power to discharge lamp;
• a power commander which generates a particular run-up curve of the power with reference to time and which is connected to said power converter to vary the power along said run-up curve in a direction of decreasing from said maximum power rating to said normal power rating;
• said run-up curve being derived from a reference curve which gives a power level decreasing with time from a maximum value to said normal power rating, said maximum value being obtained substantially immediately upon energization of said ballast, and said maximum value exceeding said maximum power rating;
• said reference curve having an inflection point near said maximum power rating so as to define a first reference curve above said inflection point and a second reference curve below said inflection point;
• said first reference curve having a first average slope for a first reference time period from a point of said maximum value to said inflection point, and said second reference curve having a second average slope for a second reference time period which starts from the inflection point and lasts for the same time interval as said first reference time period, said second average slope being greater than said first average slope;
• said run-up curve being a continuous composite curve of a straight line of said maximum power rating defined by a portion below said reference curve and the remainder of said reference curve defined between said maximum power rating and said normal power rating.

A ballast for operating a discharge lamp having a maximum power rating and a normal power rating, said ballast comprising:

• a power converter capable of applying a varying power to discharge lamp;
• a power commander which generates a particular run-up curve of the power with reference to time and which is connected to said power converter to vary the power along said run-up curve in a direction of decreasing from said maximum power rating to said normal power rating;
• said run-up curve being derived from a reference curve which gives a power level decreasing with time from a maximum value to said normal power rating, said maximum value being obtained substantially immediately upon energization of said ballast, and said maximum value exceeding said maximum power rating;
• said reference curve having an inflection point near said maximum power rating so as to define a first reference curve above said inflection point and a second reference curve below said inflection point;
• said first reference curve having a first average slope for a first reference time period from a point of said maximum value to said inflection point, and said second reference curve having a second average slope for a second reference time period which starts from the inflection point and lasts for the same time interval as said first reference time period, said second average slope being greater than said first average slope;
• said run-up curve being a continuous composite curve of a straight line of said maximum power rating defined by a portion below said reference curve and the remainder of said reference curve defined between said maximum power rating and said normal power rating;
• said power commander includes a function generator having a capacitor, and first and second power sources of different voltage levels for charging said capacitor at a different rate, said second power source having a higher supplying voltage than said first power source,
• said reference curve being a reversal of a curve of charging the capacitor so that said inflection point is defined at a point of switching said first power source to said second power source for charging said capacitor, and
• said function generator further including a discharge path for discharging said capacitor when said discharge lamp is turned off.