B. Laser Control Circuit - Canon LBP-3260 Service Manual

B. Laser Control Circuit

1. Outline
DC controller PCB
IC201
CPU
P14/
J201-C6 /PRNT
66
AN14
P05/
INTPS
IC202
49
NLON
48
NENBL
G.A.
56
NBDI
-C2 /VDO
-C1 VDO
This circuit switches ON and OFF the laser diode (LD) with a constant intensity in response to
the video signals (/VDO, VDO) sent from the video controller PCB.
The /VDO and VDO signals are converted into the low voltage differential signals to suppress
radiation noise from the video controller PCB and sent to the DC controller PCB, and then sent
to the receiver in the laser driver circuit. The receiver demodulates the low voltage differential
signals and transmits it as a VIDEO OUT signal (/VDOUT) to the logic circuit in the laser driver
IC.
If the VIDEO ENABLE signal (/LENBL) from the microprocessor (CPU: IC201) is "L", the laser
driver circuit turns the laser diode ON and OFF according to the /VDOUT signal.
The CPU monitors the LASER FAILURE DETECTION signal (DRVES) sent from the laser dri-
ver PCB to check whether the laser diode is generating laser normally or not.
The CPU emits laser forcibly when the /BDI signal is not input for 0.7 continuous seconds
from the BD PCB while the scanner motor runs at the specified speed, and notifies the video
controller of the BD failure when the DRVES signal is 3.805V or less and the laser failure when
J202
J1001
DRVES
-2
80 -10
+5V
J202-4 J1001-8
/LON
-10 -2
/LENBL
-11 -1
-3
-9 /VDO
-5
-7 VDO
-5/-8
-4/-7
J206
/BDI J6-2
-3
Figure 2-3-2
Laser driver PCB
PD
(Photo diode)
VCC
Logic IC
/VDOUT
Receiver
Power
adjustment
circuit
GND
BD PCB
CHAPTER 2
LD
(Laser diode)
Drive IC
Analog
adder
circuit
Laser driver IC
2 - 27