Discharge lamp lighting device, projector, and method for driving discharge lamp

1. A discharge lamp lighting device comprising:

a DC power supply unit that outputs a DC current;

an inverter that sequentially generates, from the DC current output from the DC power supply unit, a current pulse whose current direction alternately changes to supply the current pulse to a discharge lamp; and

a control unit that controls operations of the DC power supply unit and the inverter to adjust a waveform of the current pulse to be supplied to the discharge lamp,

wherein:

the control unit changes a pulse width of the current pulse every pulse such that consecutive pulses are applied for different lengths of time, and

the control unit randomly determines the pulse width of the current pulse within a predetermined fluctuation range such that a current-direction changing time period is not constant.

2. The discharge lamp lighting device according to claim 1 , wherein

the control unit changes a current value of the current pulse every pulse.

3. The discharge lamp lighting device according to claim 1 , wherein

the control unit generates a current pulse of a trapezoidal wave and changes a gradient of the trapezoidal wave every pulse.

4. The discharge lamp lighting device according to claim 3 , wherein the trapezoidal wave for each pulse slopes between a first current value and a second current value according to the corresponding gradient.

5. A projector comprising:

the discharge lamp lighting device according to claim 1 ;

a discharge lamp that is turned on by receiving the supply of a current pulse from the discharge lamp lighting device;

an image forming unit that modulates light emitted from the discharge lamp to form image light; and

a projection system that projects the image light formed by the image forming unit.

6. The discharge lamp lighting device according to claim 1 , wherein the control unit randomly determines a separate pulse width for each pulse.

7. A method for driving a discharge lamp, comprising:

sequentially generating a current pulse whose current direction alternately changes and whose pulse width is different every pulse such that consecutive pulses are applied for different lengths of time; and

supplying the current pulse to the discharge lamp to turn on the discharge lamp,

wherein the sequentially generating the current pulse includes randomly changing the pulse width of the current pulse within a predetermined fluctuation range such that a current-direction changing time period is not constant.

8. A discharge lamp lighting device comprising:

a DC power supply unit that outputs a DC current; and

an inverter that sequentially generates, from the DC current output from the DC power supply unit, a current pulse whose current direction alternately changes to supply the current pulse to a discharge lamp,

wherein:

a pulse width of the current pulse changes for every pulse such that consecutive pulses are applied for different lengths of time, and

the pulse width of the current pulse randomly changes within a predetermined fluctuation range such that a current-direction changing time period is not constant.

9. The discharge lamp lighting device according to claim 8 , wherein

a current value of the current pulse changes for every pulse.

10. The discharge lamp lighting device according to claim 8 , wherein

the current pulse is a trapezoidal wave and a gradient of the trapezoidal wave changes for every pulse.

11. A projector comprising:

the discharge lamp lighting device according to claim 8 ;

a discharge lamp that is turned on by receiving the supply of a current pulse from the discharge lamp lighting device;

an image forming unit that modulates light emitted from the discharge lamp to form image light; and

a projection system that projects the image light formed by the image forming unit.