Light beam detection circuit, light beam scan unit and image forming apparatus to detect light beam that changes light-amount thereof

Abstract

In order to detect a passage timing of a light beam and to suppress cost, a light beam detection circuit () includes a detection signal generation section () configured to receive a light beam for scanning of a scanning target (A) with one optical sensor (), and generate a detection signal corresponding to an amount of received light; a reference signal output section () configured to output a reference signal that is in proportion to a light-amount control signal of a light-emission element (LD) that emits the light beam; and a synchronizing signal generation section () configured to compare a detection signal generated by the detection signal generation section () with a reference signal output from the reference signal output section () to generate a synchronizing signal to determine a position to start scanning of the scanning target (A) with the light beam.