High pressure lamp with lamp flicker suppression and lamp voltage control

A ballast for operating a gas discharge lamp comprising:

• a converter to generate a dc current;
• a current pulse generator to generate one or more current pulses, said one or more current pulses comprising a mean amplitude I2 and a time duration of Tp;
• a sum generator for combining the dc current and the one or more current pulses into an intermediate current waveform;
• and
• an inverter for converting the intermediate current waveform to an alternating lamp current combined with one or more current pulses, said alternating lamp current comprising a mean amplitude I1 and alternating half cycles, each half cycle occurring during a time T and said one or more current pulses comprising a mean amplitude I2 and the time duration of Tp, wherein the one or more current pulses commence in the later half of an alternating lamp current half cycle, and wherein the one or more current pulses are combined with the alternating lamp current to generate one or more current pulses in the later half of the alternating lamp current half cycle, the one or more current pulses commencing after a time delay Td from the end of a half cycle of the alternating lamp current.

A ballast for operating a gas discharge lamp comprising:

• a converter to generate a dc current:
• a current pulse generator to generate one or more current pulses, said one or more current pulses comprising a mean amplitude I2 and a time duration of Tp;
• a sum generator for combining the dc current and the one or more current pulses into an intermediate current waveform;
• and
• an inverter for converting the intermediate current waveform to an alternating lamp current combined with one or more current pulses, said alternating lamp current comprising a mean amplitude I1 and alternating half cycles, each half cycle occurring during a time T and said one or more current pulses comprising a mean amplitude I2 and the time duration of Tp, wherein the one or more current pulses commence in the later half of an alternating lamp current half cycle after a time delay Td, wherein the time delay Td is one of (i) greater than zero and less than or equal to 20.0 ms or (ii) greater than zero and less than or equal to 1.0 ms.

A ballast for operating a gas discharge lamp comprising:

• a converter to generate a dc current;
• a first inverter for converting the dc current to an alternating lamp current, said alternating lamp current comprising a mean amplitude I1 and alternating half cycles, each half cycle occurring during a time T;
• a current pulse generator to generate one or more current pulses of the same polarity, said one or more current pulses comprising a mean amplitude I2 and a time duration of Tp;
• a second inverter for converting the one or more current pulses to one or more current pulses of alternate polarity;
• and
• a sum generator for combining the alternating lamp current and the one or more bipolar current pulses, wherein the one or more bipolar current pulses are generated in the later half of an alternating lamp current half cycle, and wherein a leading edge of the one or more current pulses commences after a time delay Td from a trailing edge of the half cycle of the alternating lamp current.

A ballast for operating a gas discharge lamp comprising:

• a converter to generate a dc current;
• an inverter for converting the dc current to an alternating lamp current, said alternating lamp current comprising a mean amplitude I1 and alternating half cycles, each half cycle occurring during a time T;
• a current pulse generator to generate one or more bi-polar current pulses, said one or more current pulses comprising a mean amplitude I2 and a time duration of Tp;
• and
• a sum generator for combining the alternating lamp current and the one or more current pulses, wherein the one or more current pulses are generated in the later half of an alternating lamp current half cycle, and wherein a leading edge of the one or more current pulses commences after a time delay Td from a trailing edge of the half cycle of the alternating lamp current.

A method of operating a lamp to control the arc gap of the lamp, comprising:

• supplying a current to the lamp, the current comprising the combination of an alternating lamp current and one or more current pulses, said alternating lamp current comprising a mean amplitude I1 and alternating half cycles, each half cycle occurring during a time period T, and said one or more current pulses comprising a mean amplitude I2 and a time duration Tp, and wherein a leading edge of the one or more current pulses commences after a time delay Td from a trailing edge of the half cycle of the alternating lamp current;
• providing a default current ratio Ri, where Ri=I2/I1;
• providing a default duration ratio Rt, where Rt=Tp/T;
• controlling the current to maintain constant power to the lamp as a function of said default current ratio Ri and said default duration ratio Rt;
• supplying the current to the lamp;
• and
• monitoring the lamp voltage V, lamp current I, and change of lamp operating voltage over a change in time dV/dt.