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e-STUDIO350/352/353/450/452/453
LASER OPTICAL UNIT
8
8 - 7
© 2003 - 2008 TOSHIBA TEC CORPORATION All rights reserved
Fig. 8-302 shows a block diagram of the semiconductive laser control circuit. The semiconductive la-
serperformsmonitorefciencyregulation(aprocesstocontrolmonitorcurrentforthelightamount),
and laser itself is adjusted to initial output emission of approx. 2.11 mW (approx. 421 µW on the drum
surface). The regulated voltage of the monitor output is fed back to the laser power comparison cir-
cuit. This monitor output voltage is compared with the laser power voltage set for the control circuit for
everyscanning.Laserdrivercircuitincreasestheforwardcurrentifthelaserpowerisinsufcient,and
decreases the current when the power is excessive to maintain a constant optical output.
8.3 Laser Diode
The laser used in this equipment is a AlGaAs type semiconductive laser. It is generated in the single-
horizontal mode, and its wavelength is approx. 785 nm. This semiconductive laser outputs 5mW with
standard DC power supply. Laser intensity is controlled by using the output from the PIN diode for
monitoring light output in the semiconductive laser.
Fig. 8-302
Fig. 8-301
Threshold current
Forward current
Monitor current
Current
(
mA
)
Optical Output
(
mW
)
Low temp.
High temp.Regulation
The relation between the current and optical output
of the semiconductive laser is as shown at right.
Light emission is started when the forward cur-
rent reaches or becomes larger than the threshold
current and outputs the monitor current which is
proportionate to the optical output. The threshold
current and monitor current differs depending on
each semiconductive laser. So optical output has
to be adjusted to maintain a constant value
.
Since the optical output of the semiconductive
laser is decreased as the temperature of the la-
ser rises, APC control needs to be performed to
maintain a constant optical output.
Monitor output
Monitor effi-
ciency regula-
tion circuit
Laser power
comparison
circuit
Laser driver
circuit
Semiconductive laser
Constant
optical output
Power source