Patent ID: 6861812

Claim:
A ballast for a discharge lamp comprising: a DC—DC converter adapted to receive an input DC voltage from a DC voltage source, said DC—DC converter including a switching element which is driven to repetitively switch said input DC voltage at a suitable switching frequency and for a suitable on-period so as to regulate a DC output being applied to drive the discharge lamp; a controller which monitors the DC output to make a feedback control of varying the duty of said switching element based upon the monitored DC output in order to regulate the DC output such that the DC—DC converter provides a high pre-starting voltage enabling the lamp to start as well as a low operating voltage for keeping the operation of the lamp; wherein said ballast includes: an input DC voltage monitor which monitors an input DC voltage supplied from said DC voltage source, and said controller including a start-accelerating means which varies at least one of the switching frequency and the on-period of said switching element based upon the monitored input DC voltage in a direction of accelerating the increase of the output DC voltage towards said pre-starting voltage, said start-accelerating means lowering the switching frequency of said switching element as the input DC voltage decreases.