| 摘要 |
PURPOSE:To give a resistance against the stain due to dust or the like and to prevent the deterioration of sensitivity by providing an optical axis adjusting circuit causing an optical adjusting drive current less than a sensitivity check drive current to be conducted to a light emitting element so as to apply the optical axis adjustment with a sufficient margin. CONSTITUTION:Only the input control signal of an input terminal 11 goes to an H level and an input signal at input terminals 21, 31 goes to a L level at the normal drive to turn on a transistor (TR) 14 only. The signal of H level is given to only the input terminal 31 at the optical axis adjustment to turn on a TR 34 only and to turn off TRs 14, 24 causing the light emitting diode 1 to be driven. The signal of H level is given to the input terminal 21 only at the sensitivity check to turn on the TR 24 only and to turn off the other TRs 14, 34. Thus, the optical axis is adjusted sufficiently tightly and since a large drive current is used for the sensitivity check, then even when the photodetection level is reduced due to more or less dust, the defective sensitivity is not caused.
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