Ricoh SP 200 Specifications download pdf (Page 40)

3.4 AUTO POWER CONTROL (APC)

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 machine is turned on, IC2 on the laser drive board excites the

laser diode at full power and the output of the photodiode is stored as a

reference in IC2. IC2 monitors the current passing through the photodiode

(PD). Then it increases or decreases the current to the laser diode as

necessary, comparing it with the reference level (LVL2). Such auto power

control is done during printing while the laser diode is active.

The laser diode level is adjusted on the production line. Do not touch the

variable resistors on the LD unit in the field.

IC 1 IC 2IC 3

LD5V

LVL1

ERR

LDOFF

LD1

DATA

LDOFF

LDERR

DATA

LEVEL

LD Drive Board

LVL2

A193D521.wmf

1 August 1996 LASER EXPOSURE

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Ricoh SP 200 Specifications Page 40