Laser Control Circuit - Canon LBP-1210 Service Manual

CHAPTER 2
B. Laser Control circuit
1. Outline
Engine controller PCB
+3.3V
/BDI 71
+5V
IC201
CPU
/CNT1 67
/CNT0 66
/BDO:HC 72
Interface controller
PCB
This circuit turns ON and OFF the laser diode (LD) at a constant intensity in response to the
VIDEO (/VDO, VDO) signals sent from the interface controller.
The /VDO, VDO signals sent from the interface controller are submitted to the logic circuit
in the laser driver IC. Meanwhile, the laser control signals (CNT0, CNT1) are sent from the CPU
(IC201) to perform the laser diode forced emission control, the image masking control, and laser
diode automatic power control (APC).
When the CNT0 signal is set "H" and the CNT1 signal is "L", the laser driver circuit turns ON
and OFF the laser diode according to the /VDO, VDO signals.
2. Automatic power control (APC)
The APC makes the laser diode (LD) emit at a constant intensity. This control is performed on
the laser driver IC according to the LASER CONTROL (CNT0, CNT1) signals sent from the engine
controller, prior to image formation (initial APC) and between lines (between-line APC).
When the CNT0 is "L" and CNT1 is "H", the sample hold circuit in the laser driver IC enters
2 - 30
Intermediate PCB
J201-15 J907-8
-16 /BDI -7
-13 -10
-18 CNT1 -5
-17 CNT0 -6
-12 /BD -11
J2-8 J902-5
-11 -2
-10 -3
Figure 2-4-2
Laser driver PCB
J901-3 J801-8
BD sensor
-4 /BDI -7
-1 -10
PD
(photodiode)
-6 CNT1 -5
-5 CNT0 -6
Logic
circuit
-9 VDO -2
-8 /VDO -3
Laser driver IC
LD
(laser diode)
Comparator
Sample
hold
circuit
C803
Drive
circuit