November 2003 © TOSHIBA TEC 8 - 7 e-STUDIO350/450 LASER OPTICAL UNIT
8
Fig. 8-302 shows a block diagram of the semiconductive laser control circuit. The semiconductive laser
performs monitor efficiency regulation (a process to control monitor current for the light amount), 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 circuit. This monitor
output voltage is compared with the laser power voltage set for the control circuit for every scanning.
Laser driver circuit increases the forward current if the laser power is insufficient, 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 moni-
toring 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 current
reaches or becomes larger than the threshold cur-
rent and outputs the monitor current which is pro-
portionate to the optical output. The threshold cur-
rent 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 la-
ser is decreased as the temperature of the laser
rises, APC control needs to be performed to main-
tain 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
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