Patent ID: 7312783

Claim:
A light emitting element drive device comprising: a light emitting unit including at least one light emitting element operable to emit light with a luminance in accordance with a flow of current; a constant voltage source to supply the output voltage to the light emitting element of the light emitting unit; a switch means operable to turn ON/OFF the output of the constant voltage source at a predetermined timing and to adjust light emission luminance of the light emitting element according to a ratio of ON/OFF states; a current detecting means for detecting the value of a current flowing in the light emitting element; a sample and hold means for holding the value of the output of the current detecting means when the switch means is ON; and a controlling means for adjusting the output voltage of the constant voltage source so that the output value of the sample and hold means becomes a predetermined value, in which the controlling means includes: a constant current use reference voltage source, a constant current control use error amplifier for comparing the output of the sample and hold means and the constant current use reference voltage from the constant current use reference voltage source, a constant voltage use reference voltage source for changing the constant voltage use reference voltage in accordance with the output of the constant current control use error amplifier and outputting the same, and a constant voltage control use error amplifier for comparing the output voltage of the constant voltage source and the constant voltage use reference voltage from the constant voltage use reference voltage source, in which the output of the constant voltage source is controlled so as to become a value determined by the constant voltage use reference voltage in accordance with a result of comparison of the constant voltage control use error amplifier.