| 摘要 |
When a switch SW 1 is turned on by an HSYNC signal, a comparison circuit compares an output of a photodiode LD with a reference signal. The comparison result is stored in a capacitor C 1 . A main scan correction signal, which is supplied from a printer CPU, is formed to decrease a light amount at a central part in a main scan direction on a photoconductor drum 5 and to increase a light amount at both sides in the main scan direction. After the main scan correction signal is added to the voltage in the capacitor C 1 , a gain necessary for an APC control is provided by a gain circuit. The gain is converted to a laser drive current I 1 by a transistor Tr 1 . The laser drive current I 1 is chopped and modulated with a data signal by a transistor Tr 2 . Thus, the photodiode LD emits light with a high laser output at both sides in the main scan direction on the photoconductor drum and with a low laser output at the central part.
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