| 摘要 |
PROBLEM TO BE SOLVED: To provide an image forming device which regulates automatically the quantity of light of a laser light source with high accuracy by using capacitors which are made to conduct a charge and a discharge by a monitor current of a light quantity monitor element. SOLUTION: In an APC circuit 20, a control circuit 25 turns on switches SW1 and SW2 selectively in a sampling mode and one of the capacitors C1 and C2 is charged by a constant current source 26 for charge through the intermediary of a switch circuit 28. In a hold mode, the control circuit 25 turns off the switches SW1 and SW2 and an error amplifier 29 amplified an input voltage V3 from the capacitors C1 and C2 by an error in relation to a reference voltage Vref3 so as to increase or decrease a collector current of a transistor Tr1. Thereby the quantity of light of LD 3 is held at a constant value. The automatic light quantity regulation is conducted by changing over the capacities of the capacitors C1 and C2 by switching them over on the basis of the potentials thereof. Accordingly, the automatic light quantity regulation is conducted appropriately and the quality of an image is improved. |
