Discharge lamp lighting device and projection type image display apparatus having the same
A computing circuit computes a target value of a current to be supplied to a discharge lamp and generates a pulse control signal for superpose a pulse current. Furthermore, the computing circuit controls a current control circuit so that a pulse current is superposed on a lamp current at a predetermined cycle and power supplied to the discharge lamp is kept constant. For that purpose, the computing circuit lowers a DC current level of the lamp current when a pulse current is superposed on the lamp current, and exercises control so that an integrated amount of power at a predetermined cycle is equalized to a predetermined integrated amount of power.
1. A discharge lamp lighting device for supplying power to a discharge lamp, the discharge lamp lighting device comprising:
a computing circuit which outputs a signal for a target value of a current supplied to the discharge lamp and a pulse control signal to superpose a pulse current on the supplied current; and
a current control circuit which receives the signal for a target value and the pulse control signal and controls the current supplied to the discharge lamp, and which includes:
an error amplifier which compares a detected value of the current being supplied to the discharge lamp with the target value of the current; and
a level select switch which lowers an input level of the detected value of the current inputted to the error amplifier based on the pulse control signal, during a period of superposition of the pulse current.
2. The discharge lamp lighting device according to claim 1 ,
wherein the current control circuit lowers the input level of the detected value of the current by an amount of the pulse current to be superposed.
3. The discharge lamp lighting device according to claim 1 ,
wherein the level select switch is formed with a plurality of pairs of resistors and switches connected in parallel to the detected value input end of the error amplifier.
4. The discharge lamp lighting device according to claim 3 ,
wherein the level select switch selects ON/OFF of each of the plurality of switches according to the pulse control signal.
5. The discharge lamp lighting device according to claim 1 ,
wherein the level select switch is an amplifier for amplifying a level of the detected value of the current inputted to the error amplifier.
6. The discharge lamp lighting device according to claim 5 ,
wherein the level select switch selects a gain of the amplifier based on the pulse control signal.
7. The discharge lamp lighting device according to claim 1 ,
wherein the current control circuit controls an amount of power integrated during the period of superposition of the pulse current.
8. The discharge lamp lighting device according to claim 7 ,
wherein the current control circuit equalizes the amount of power integrated during the period of superposition of the pulse current to that during a period of non-superposition of the pulse current in a period having the same time length as that of the period of superposition.
9. A discharge lamp lighting device for lighting a discharge lamp by supplying power thereto, the discharge lamp lighting device comprising:
a current control circuit which controls power supplied to the discharge lamp; and
a computing circuit which superposes a pulse current on a lamp current for the discharge lamp at a predetermined cycle and controls the power at a constant value based on information concerning a voltage and a current of the power supplied to the discharge lamp;
wherein the computing circuit exercises control to lower a DC current level of the lamp current when the pulse current is superposed on the lamp current, thereby bringing the integrated amount of power in the predetermined cycle to a specified value.
10. The discharge lamp lighting device according to claim 9 ,
wherein the computing circuit equalizes the integrated amount of power when the pulse current is superposed at the predetermined cycle to that when the pulse current is not superposed.
11. The discharge lamp lighting device according to claim 9 ,
wherein, when a voltage applied to the discharge lamp is constant at the predetermined cycle, the computing circuit superposes the pulse current on the lamp current and lowers a DC current level of the lamp current, thereby controlling the integrated amount of current.
12. The discharge lamp lighting device according to claim 9 ,
wherein the integrated amount of the current when the pulse current is superposed is an additional value of a product of a DC current level of the lamp current and the predetermined cycle and a product of an amplitude of the pulse current and a time width of the pulse current.
13. An image display apparatus comprising:
a discharge lamp lighting device in turn comprising:
a computing circuit which outputs a signal for a target value of a current supplied to the discharge lamp and a pulse control signal to superpose a pulse current on the supplied current; and
a current control circuit which receives the signal for a target value and the pulse control signal and controls the current supplied to the discharge lamp, and which includes:
an error amplifier which compares a detected value of the current being supplied to the discharge lamp with the target value of the current; and
a level select switch which lowers an input level of the detected value of the current inputted to the error amplifier based on the pulse control signal, during a period of superposition of the pulse current;
an image display element which modulates light emitted from the discharge lamp lighting device to form an optical image corresponding to an image signal;
a drive circuit for driving the image display element based on the image signal; and
an optical system that projects light passing through the image display element to a screen.
14. The image display apparatus according to claim 13 ,
wherein the current control circuit lowers an input level of the detected value of the current by an amount of the pulse current to be superposed.
15. The image display apparatus according to claim 13 ,
the level select switch is formed with a plurality of pairs of resistors and switches connected in parallel to the detected value input end of the error amplifier.
16. The image display apparatus according to claim 15 ,
wherein the level select switch selects ON/OFF of each of the plurality of switches based on the pulse control signal.
17. The image display apparatus according to claim 13 ,
wherein the level select switch is an amplifier for amplifying a level of the detected value of the current inputted to the error amplifier.
18. The image display apparatus according to claim 17 ,
wherein the level select switch selects a gain of the amplifier based on the pulse control signal.
19. The image display apparatus according to claim 13 ,
wherein the current control circuit controls an amount of power integrated during the period of superposition of the pulse current.
20. The image display device according to claim 19 ,
wherein the current control circuit equalizes the amount of power integrated during the period of superposition of the pulse current to that during a period of non-superposition of the pulse current in a period having the same time length as that of the period of superposition.