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

A discharge lamp driver comprising:

• a discharge lamp drive unit configured to supply drive current to a discharge lamp having a first electrode and a second electrode;
• a control unit configured to control the discharge lamp drive unit;
• and
• a voltage detection part configured to detect an inter-electrode voltage of the discharge lamp,
• wherein, when the inter-electrode voltage is smaller than a first predetermined value, the control unit is configured to control the discharge lamp drive unit to provide
• a mixed period in which a first period in which alternating current is supplied and a second period in which direct current is supplied are alternately repeated and
• a third period alternately including a first direct-current period in which a direct current is supplied and a second direct-current period in which a direct current having opposite polarity to polarity of the direct current supplied in the first direct-current period is supplied, the third period in which a length of the first direct-current period is larger than a length of the second direct-current period,
• wherein the length of the second direct-current period is smaller than 0.5 ms,
• wherein a total of the lengths of the first direct-current periods in the third period is larger than a length of the second period, and
• wherein when the inter-electrode voltage is smaller than the first predetermined value, the control unit is configured to increase the length of the third period in a stepwise manner.