Controlling The Intensity Of Laser Light; Apc Control; Pwm Control - Canon iR C6800 Series Service Manual

Chapter 6

6.3.2 Controlling the Intensity of Laser Light

6.3.2.1 APC Control

The machine uses APC control to make sure that the intensity of laser light remains at a specific level by controlling
the output of the laser diode of the laser driver.
For the control, the machine causes the DC controller to send the laser control signal (CNT0=1, CNT1=0) to the laser
drive IC on the laser driver PCB. As a result, the laser drive IC is set to APC mode, thus forcing the laser diode (LD)
to emit light. While the control is under, way, the laser driver IC uses the photo diode (PD) to monitor the laser diode
(LD), adjusting the output of the laser diode until a specific level of intensity is reached.
5V
Laser driver
PD
LD
F-6-8
1) Laser driver IC1
DC CON: DC controller

6.3.2.2 PWM Control

The machine uses PWM control to determine how long the laser unit must remain on to suit the image data coming
from to the main controller PCB.
The length of time (see Memo) is determined by the DC controller PCB (16 step activation patterns for each pixel).
Memo:
The relationship between the length of laser activation and the density of the image is as follows. The machine
exposes the light areas (non image areas) and leaves the dark areas (image areas) as they are; further, the darker the
image, the shorter the laser activation and, conversely, the lighter the image, the longer the laser activation.
100%
Shorter
F-6-9
6-8
J1901
[1]
Length of activation (t)
Longer
J1102
CNT0
DC-CON
CNT1
0002-9878
0002-9880