PURPOSE: To accurately control lamp current using simple constitution by providing a means for setting a desired lamp current according to lamp voltage and a means for providing to a control circuit an output for reducing the difference between detected and desired values.
CONSTITUTION: A discharge lamp lighting circuit 1 provides an AC (rectangular) waveform and a pulse waveform at constant voltage to turn on a lamp La. When the lamp La is turned on, the lamp voltage decreases to near a short- circuit level, and then a set value for the desired lamp current is outputted to provide the constant current required to instantly turn on the lamp. A differential current detection means 5 detects the difference between that output value and an actual lamp current through comparison, and a control circuit 6 controls the lamp current according to the output of the means 5 so that the lamp current approximates the desired value. When the lamp La starts to light, instant lighting is performed, and a desired lamp current setting means 4 outputs a desired lamp current according to the lamp voltage in order to built up luminous flux on a predetermined curve.
SHIOMI TSUTOMU
NIIHORI HIROSHI
KITADOU MASAHARU
ITO HISAHARU
MATSUMOTO TATSUHIKO
