| 摘要 |
PURPOSE: To uniformly maintain light intensity during warming up of a gas discharge lamp by providing a comparator which is a calibration circuit that automatically adjusts gain of a light return circuit, during warming up of a lamp. CONSTITUTION: A light intensity detector element 26 detects a part of light 10A from a lamp 10. Current signals from the element 26 is converted into voltage signals by an operational amplifier 28, and then supplied to D-A converter 30. At the same time, based on digital input 30B from an order-reverse counter 32, the converter 30 generates light return signal F2 '. Next, signal F2 ' is converted 34 into a voltage composing light return signal. The order-reverse counter 32 adjusts gain of the converter 30. During operation of the lamp 10 responding to non-light return signal F1 , the counter 32 counts by a clock signal 32A from a logical control unit 18. The counting direction depends on the output of a comparator 38. While the counter 32 is counting, a switch 16 prevents the light return signal F2 from being received as upper input of the comparator 14. |
