Specifications

3.8 EXPOSURE LAMP CONTROL CIRCUIT
The main board sends lamp trigger pulses to the ac drive board from
CN122-10. PC401 activates TRC401, which provides ac power to the
exposure lamp, at the trailing edge of each trigger pulse.
The voltage applied to the exposure lamp is also provided to the feedback
circuit. The feedback circuit steps down (TR401), rectifies (DB401), and
smoothes (zener diodes and capacitors) the lamp voltage. The CPU monitors
the lowest point of the smoothed wave (feedback signal), which is directly
proportional to the actual lamp voltage.
The CPU changes the timing of the trigger pulses in response to the
feedback voltage. If the lamp voltage is too low, the CPU sends the trigger
pulses earlier so that more ac power is applied to the exposure lamp. This
feedback control is performed instantly; so, the lamp voltage is always stable
even under fluctuating ac power conditions.
The voltage applied to the exposure lamp can be changed with SP mode #48
(Light Intensity Adjustment). The ADS voltage adjustment (SP mode #56)
must be done whenever the light intensity adjustment is done.
Main Board (PCB1) AC Drive Board (PCB2)
Zero
Cross
Feed back signal
TP111
(EXPO)
CN122-7
CN122-6
CN122-13
CN122-10
CN401-8
CN401-7
CN401-2
CN401-5
0V
+24V
VR401
R403
R401
R404
ZD
403
ZD
404
R406
DB401
24V
0V
Trigger Pulse
PC401
CN421
240V
220V
220V Only
Thermo-
SW (TS)
Exposure
Lamp
(L1)
T402
CN419-1
CN419-2
T407
AC115V
AC220V
AC240V
R411
CR401
L401
L402
C411
TRC401
R413
C401
R404
D401
ZD
401
ZD
402
B
C
D
A
CPU
E
CN108-1
TR401
AC power
Zero cross
Trigger pulse
Lamp power
Feedback
signal
Feedback
A
B
C
D
E
1 December 1990
2-21