Patent ID: 8174208

Claim:
Driver for driving a gas discharge lamp having electrodes, each electrode having a tip, each respective tip subject to tip growth and tip destruction as a result of current supplied by the driver; the driver comprising: a controllable current source; and a controller for controlling the current source; wherein the controller ( 4 ) is configured to: (i) control the current source such as to generate a commutating lamp current with a predefined current frequency (f) and a duty cycle (Δ) and (ii) operate in a modulated duty cycle mode in which the duty cycle has a first value (Δ 1 ) during a first phase (P 1 ) alternated with a second value (Δ 2 ) equal to one minus the first value (Δ 2 =1−Δ 1 ) during a second phase (P 2 ), wherein the second phase (P 2 ) and first phase (P 1 ) have mutually equal duration, and wherein switching between the second phase (P 2 ) and first phase (P 1 ) and vice versa occurs at a predefined duty cycle switching frequency (fΔ); wherein in operation the controller varies current parameters in such a way that tip growth and tip destruction are alternated.