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(4) Heater lamp control circuit
1
Outline
The heater lamp control circuit detects the heat roller surface
temperature by the thermistor and converts it into the voltage level
(analog level) to output to the CPU analog input pin.
The CPU converts the analog voltage into a digital signal level and
compares it with the set value of the test command and turns on/off
the heater lamp to maintain the heat roller surface temperature at a
constant level.
When a paper jam occurs in the AR-5132, the control circuit operates
for max. 3 minutes to shorten the jam recovery time (8sec).
R269
R268
56KJ
1KF
D211
R267
10KF
The thermistor resistance becomes greater when the heat roller surface temperature is lower, and becomes smaller when the surface temperature
is higher. Therefore the thermistor pin voltage also becomes higher when the heat roller surface temperature is lower, and it becomes lower when
the surface temperature is higher. The thermistor pin voltage in inputted to the CPU analog port. The CPU controls ON/OFF of the heater lamp by
the input voltage level.
[High temperature protect circuit in case of hung up of
the CPU]
The IC204 3pin (reference voltage) of +5V is divided by R265 and
R264, and the thermistor pin voltage is inputted to the IC204 2pin.
When, therefore, the 2pin voltage becomes lower than the 3pin volt-
age (the heat roller surface temperature about 230°C), the output
1pin becomes HIGH to turn on Q207, pulling the HL signal to the
GND level and the heater lamp lighting signal is not generated.
VREF
R268
R269
D211
1KF
56KJ
MA704A
1
3
R267
10KF
R270
1KJ
Vref
R265
6.8KF
4
IC204A
3
+
1
FT H
2
-
LM358PS
8
R264
3.3KF
TH1
TH
AN1
HL
I/O
PR
CPU
AC
+12V1
R265
6.8KF
8
3
+
1
FTH
2
-
IC204A
R264
LM358PS
3.3KF
4
TH1
TH2
IC115
PR
1
I1
O1
2
I2
O2
3
I3
O3
4
I4
O4
HL
5
I5
O5
6
I6
O6
7
I7
O7
8
GND
SK
ULN2003
+12V
Heat roller
+
+24V
-PR
[When the heat roller surface temperature is lower than
the set level]
a. Since the thermistor pin voltage is higher than the set level, the
output signal (HL) form the CPU becomes HIGH.
b. This HL signal becomes the HL signal through IC115 and TR
Q206 and is inputted to the solid state relay (SSR).
When, therefore, the HL signal is HIGH, the internal triac is turned
on.
c. When the internal triac is turned on, a pulse is applied to the gate
of the external triac. A current flows from the power through the
heater lamp to the triac to turn on the heater lamp.
(4-5A)
9 – 14
IC104
1
16
PR
16
15
14
13
12
HL
11
+12V
10
9
+24V
R104
2.2K
Q207
470J
10K
Q206
DTA123YK
C602
R603
CR601
GATE
T1
T2
TD601
R604
Thermostat
170˚C
Heater
lump
HL
SSR601
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