IC703
–
+
1
2
–
+
4
3
CONSTANT
VOLTAGE
CIRCUIT
VIN
F/F
ERROR AMP.
VOUT
OSC-
ILLATOR
PWM COMP.
O
VREF
OADJ
R
S
CONSTANT
VOLTAGE
CIRCUIT
OVERCURRENT
DETECTION
CIRCUIT
OVERHEAT
PROTECTIVE
CIRCUIT
COM
Fig. 23
9. Heater circuit
Though heater output is powered from AC line, the circuit is config-
ured to allow one side of AC to be turned on and off by TR701.
When heater ON/OFF terminal is turned to LOW, the current will flow
to the photo diode of PC702 to trigger the photo triac on the primary
side and also turn on TR701.
This will activate the heater output. On the contrary, when the heater
ON/OFF terminal is turned to HIGH, any current will not
flow to the photo diode of PC702 to turn off TR701.
This will deactivate the heater output.
If TR701 is broken in the short mode, any current will not flow to the
photo diode side of PC703 to turn off the photo transistor on the
secondary side, and Q703 will not be turned off.
Q703 is connected to the gate cathode of SR701, and SR701 is
usually turned off. However, when Q703 is turned off and the heater
ON/OFF control terminal is further turned to HIGH, SR701 will be
brought into the conductive state to cutoff the power supply to the
heater circuit on the primary side.
VM
(+24V)
R717
C713
HEATER N
R733
TR701
HEATER L
R716
PC702
C712
R725
F701
S701
AC-L
AC-N
HEATER
ON/OFF
PC703
Q703
C728
R730
R731
R732
C729
D711
SR701
F706
R728
R729
PC702
PC703
RL701
Fig. 24
FO-4500H
5 – 27
Summary of Contents for FO-4500
Page 16: ...M E M O FO 4500H 1 14 ...
Page 129: ...Control PWB parts layout Top side 6 11 FO 4500H ...
Page 130: ...Control PWB parts layout Bottom side 6 12 FO 4500H ...
Page 133: ...TEL LIU PWB parts layout 6 15 FO 4500H ...
Page 134: ...6 16 FO 4500H ...
Page 136: ...Power supply PWB parts layout 6 18 FO 4500H ...
Page 141: ...M E M O 6 23 FO 4500H ...
Page 149: ...Scanner unit Fig 6 Optical adjustment tool Fig 7 Fig 8 FO 4500H 8 6 ...