Auto Power Control (Apc) - Gestetner A294 Service Manual

2.4.3 AUTO POWER CONTROL (APC)

Image Data
L V D S
Clock
BGAVD
D/A
Converter
There are four LD drivers (IC408, IC409, IC422 and IC423) on the LDB (Laser
diode Drive Board). The LD drivers control the laser diodes on the 4-channel laser
diode array. Even if a constant electric current is applied to the laser diode, the
intensity of the output light changes with the temperature. The intensity of the
output decreases as the temperature increases.
In order to keep the output level constant, IC410 and IC411 monitor the current
passing through the photodiode (PD). Then they increase or decrease the current
to the laser diode as necessary, comparing it with the reference levels (V
apply APC separately to each laser diode using only one photo diode, the monitor
current is sent in turn to each laser diode.
This auto power control is done just after the machine is turned on and during
printing while the laser diode is active.
The reference levels are adjusted on the production line. Do not touch the variable
resistors on the LDB in the field.
SM
CÓPIA NÃO CONTROLADA
O U T O U T
IC406
O U T O U T
IC407
O U T O U T
IC421
O U T O U T
IC420
+
–
2-35
CÓPIA NÃO CONTROLADA
L D B
L D D
W R _ P U L S E
S E N S E _ I N
O U T
V
R E F
W R I T E _ L E V E L
IC408
W R _ P U L S E
S E N S E _ I N
O U T
V
R E F
W R I T E _ L E V E L
IC409
W R _ P U L S E
O U T
V
R E F
S E N S E _ I N
W R I T E _ L E V E L
IC422
W R _ P U L S E
O U T
V
R E F
+
W R I T E _ L E V E L
–
S E N S E _ I N
IC423
LASER EXPOSURE
LDA
IC410
Analog SW
IC411
Analog SW
PD Charge
A294D999.WMF
). To
REF
A294/A295