Light source device, projector, and driving method of discharge lamp

A projector comprising:

• a discharge lamp having a first electrode and a second electrode that emits light by discharge between the first and the second electrodes;
• a driver that supplies alternating current to the first and the second electrodes so as to maintain the discharge, and changes a duty ratio of the alternating current in accordance with a predetermined pattern, the predetermined pattern including a plurality of section periods for which the duty ratio maintains mutually different values for a predetermined period;
• a light modulating device illuminated by illumination light from the discharge lamp;
• and
• a projection optical system that projects image formed by the light modulating device,
• wherein
• one cycle of the alternating current includes a positive polarity period and a negative polarity period for which a current value is positive and negative respectively,
• the driver varies the current value during a longer polarity period among the positive and the negative polarity periods, a time ratio of the longer polarity period to the one cycle of the alternate current being at least 50%, and
• the driver varies the current value during the longer polarity period so that the current value is at a maximum at an end of the longer polarity period.

A drive method of a discharge lamp having a first electrode and a second electrode comprising:

• supplying alternating current to the first and the second electrodes so as to maintain discharge between the first and the second electrodes for emission of light, one cycle of the alternating current including a positive polarity period and a negative polarity period for which a current value is positive and negative respectively;
• and
• changing a duty ratio of the alternating current in accordance with a predetermined pattern, the predetermined pattern including a plurality of section periods for which the duty ratio maintains mutually different values for a predetermined period;
• and
• varying the current value during a longer polarity period among the positive and the negative polarity periods so that the current value is at a maximum at an end of the longer polarity period, a time ratio of the longer polarity period to the one cycle of the alternate current being at least 50%.