Discharge lamp driver, light source apparatus, projector, and discharge lamp driving method

A discharge lamp driver comprising:

• a discharge lamp driving unit configured to supply drive current to a discharge lamp including a first electrode and a second electrode;
• and
• a control unit configured to control the discharge lamp driving unit,
• wherein the drive current has a modulation drive period in which a first period and a second period are alternately repeated, the first period in which AC current having a frequency higher than 1 kHz is supplied to the discharge lamp, the second period in which DC current is supplied to the discharge lamp,
• wherein a polarity of the DC current supplied to the discharge lamp in the second period is inverted whenever the second period is provided, and
• wherein in the modulation drive period, the control unit
• periodically changes length of a first DC period and length of a second DC period, the first DC period included in a plurality of the second periods and in which DC current of a first polarity is supplied to the discharge lamp, the second DC period included in the plurality of the second periods and in which DC current of a second polarity is supplied to the discharge lamp, and
• increases one of the length of the first DC period and the length of the second DC period while decrease another of the length of the first DC period and the length of the second DC period.