Auto Power Control (Apc) - Ricoh G035 Service Manual

LASER EXPOSURE

2.2.3 AUTO POWER CONTROL (APC)

BICU
IC2 and IC3 on the LDDR drive the laser diodes. 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, IC2 and IC3 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 (REF1 and REF2).
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 LDDR in the field.
G035
Front Cover Safety switch and
Upper Right Cover Switch
+5V
+5VLD
Error
LEVEL1
VIDEO
GAVD
(IC 7)
LDOFF
LDDR
VIDEO
IC 2
REF1
VIDEO
LEVEL2
IC 3
REF2
Error
2-12
Error
LD
PD
LD1
PB
LD
+5VLD
LD
PD
LD2
PB
LD
G035D502.WMF
SM