Canon FAX-L1000 - Manual (Page 193)

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FAX-L1000 Chapter 3: Technical Reference
b) Automatic power control of laser diode
The laser driver IC conducts the automatic power control (APC) of the laser diode so that
the laser diode emits a beam of constant intensity.
When the FORCED LASER ON signal (nLON) becomes “L,” or the VIDEO DATA
ENABLE signal (nENBL) and nVDO signal become “L,” the laser diode emits light
according to the standard voltage of laser driver PCB. The photo diode in the laser diode
detects the beam intensity and feeds back the corresponding current value to the control
amplification circuit. It is then compared with the current value set by the power adjustment
circuit, and the intensity of the current to the laser diode is controlled.
c) Horizontal synchronization control
The CPU generates an unblanking signal inside the IC501 based on the BD INPUT signal
(nBDI) sent from the BD PCB of the laser/scanner unit.
IC501 sets the FORCED LASER ON signal (nLON) to “L” during unblanking period. The
laser driver turns the laser diode ON when the nLON signal is “L.”
The laser beam turned on by the nLON signal is reflected at the small fixed BD mirror
located in the light path where the laser beam scanning starts, and is input to the BD PCB in
the laser/scanner unit.
The BD PCB detects the laser beam, generates a BD INPUT signal (nBDI), and sends it to
the CPU. The CPU generates the HORIZONTAL SYNC signal (nBD) according to the
nBDI signal and sends it to the SCNT board.