10 May 1996LASER EXPOSURE
5.4 AUTO POWER CONTROL (APC)
Detailed
Descriptions
A166D618.wmf
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, the output light intensity is
monitored through a photodiode (PD) enclosed in the laser diode. The
photodiode passes an electrical current that is proportional to the light
intensity. The output is not affected by temperature, so it faithfully reflects the
changes in the LD output, without adding anything itself.
Just after the main switch is turned on, the current drive IC on the LD drive
board excites the laser diode at full power (power level 32) and stores the
output of the photodiode as a reference. The IC monitors the current passing
through the photodiode. Then it increases or decreases the current to the
laser diode as necessary, comparing it with the reference level. Such auto
power control is done during printing while the laser diode is active.
The laser power level is adjusted on the production line. Do not touch the
variable resistors on the LD unit in the field.
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ACEC
