Laser Control Circuit - Canon LBP-800 Service Manual

B. Laser Control Circuit
1. Outline
Engine controller PCB
IC201
+3.3V
+5V
CPU
VDO
J201-7
/VDO
J201-8
The CPU controls the following four modes: standby, APC emitting, masking and unmasking.
They are controlled by the LASER CONTROL signals (CNT0, CNT1) sent to the laser driver
(IC801) on the laser driver PCB.
When both CNT0 and CNT1 signals are "L", the laser driver enters the standby mode to reset
the laser driver PCB.
When CNT0 and CNT1 signals are "L" and "H" respectively, the laser driver enters the APC
emitting mode to make the laser diode emit the laser beam. The laser driver also performs the
Auto Power Control, stated in the following section.
When both CNT0 and CNT1 signals are "H", the laser driver enters the masking mode.
Regardless the VIDEO signals (VDO, /VDO), the laser driver prohibits the laser diode from emit-
ting the laser beam.
When CNT0 and CNT1 signals are "H" and "L" respectively, the laser driver enters the
unmasking mode to turn the laser ON/OFF according to the VDO, /VDO signals from the inter-
face controller.
/BDI
J208F-11 J801F-2
J208F-12 J801F-1
J208F-5 J801F-8
J208F-6 J801F-7
CNT0
J208F-9 J801F-3
CNT1
J208F-9 J801F-4
J208F-7 J801F-6
J208F-8 J801F-5
Figure 2-3-2
Laser driver PCB
IC801
Comparator
Sample
hold
circuit
Logic
circuit
C803
Drive
circuit
CHAPTER 2
BD sensor
(photodiode)
PD
LD
(laser diode)
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