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C. Controlling the Scanning Lamp
1. Outline
Figure 4-104 shows the circuit that controls the scanning lamp; the circuit has the
following functions:
• turns on and off the scanning lamp.
• controls scanning lamp pre-heating operation.
• controls scanning lamp intensity.
• controls the scanning lamp heater.
The copier’s scanning lamp is a fluorescent lamp.
In general, a fluorescent lamp is low in intensity immediately after power-on,
gradually increasing in intensity as time passes, without control; in particular, it takes a
long time before the intensity stabilizes in a low temperature environment.
If the ambient temperature drops below 15°C, the copier may enter and remain in
wait state before a specific intensity can be obtained. To prevent this from occurring, a
fluorescent lamp is provided for installation in low temperature environments.
To ensure that the lamp exposes an original at a stable intensity, a fluorescent lamp
adjusting sensor is used to monitor the intensity of the lamp during copying operation,
thereby controlling it to a specific value.
In addition, half pre-heating is executed between power-on and a press on the Copy
Start key so as to ensure that the lamp reaches its optimum intensity within a short
period of time after a press on the Copy Start key; thereafter, full pre-heating is
performed. (See Figure 4-105.)
Figure 4-104
COPYRIGHT
©
1997 CANON INC. CANON NP6218 REV. 0 MAY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)
CHAPTER 4 IMAGE FORMATION SYSTEM
4-4
(FL1)
J205
T401
Scanning lamp
Composite power
supply PCB
Fluorescent
lamp pre-
heating circuit
FLPRHT*
32KHzCLC
T101
T103
DC controller PCB
Micro-
processor
(Q301)
SW2
Fluorescent lamp
heater switch
5V
Fluorescent lamp
heater
Fluorescent lamp
thermistor
J701-1
(H2)
(TH3)
J202-1
-2
Fluores
cent lamp
intensity
sensor
-3
Main switch
Q108
FLTHON
FL ON
MPWM
FLS
Fluorescent
lamp drive
circuit
FLHTOFF*
FLTH
Micro-
processor
(Q512)
J211-3
J302-9
J211-9
FLTH
J317-1
-2
-4
VR301
Reversal
amplifier
circuit
Fluorescent lamp
heater
control circuit
Main transformer
(T101) drive circuit