The DCNT board sends the video signal (VDO, /VDO) for image formation and the laser control signal (CNT0, CNT1) for switching the laser operation mode to

the logic circuit in the laser driver IC.

The laser driver IC performs laser control based on the combination of CNT0 and CNT1 signals.

The following chart shows the combination of the laser control signals (CNT0, CNT1).

5.3 Controlling the Intensity of Laser Light

5.3.1 Auto Photoelectric Current Control (APC)

This is the control to emit the definite level of laser diode.

There are initial APC during initial rotation (note 1) and line space APC during printing (note 2), which are performed in the same procedure. The following is its

procedure.

1) When the laser control signal (CNT0, CNT1) turned into LD APC mode, the laser driver emits LD forcedly.

2) After being detected with the photodiode (PD), the LD emission level as current is converted to the one as voltage and compared with the reference voltage (the

voltage equivalent to the target laser level).

3) The laser driver controls the laser current until it reaches the voltage of LD target level.

4) When the laser control signal turns into LD forced OFF mode, LD is forcedly off and the laser driver converts the adjusted laser level to the voltage of the con-

denser and keeps it.

Note 1. Initial APC

APC during initial rotation. Laser level is adjusted by APC.

Note 2. Line space APC

APC during printing. Adjustment of laser level for one line is performed before writing one line.

5-2

SCNT board

DCNT board

IC902

CPU

/BD

J901-6