Sharp AR-121E Service Manual page 118

(4) Heater lamp control circuit
(1) Outline
The heater lamp control circuit detects the heat roller surface
temperature and converts in into a voltage level, which is in-
putted 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 simulation to turn
on/off the heater lamp according to the level, maintaining the
heat roller surface temperature at a constant level.
Thermistor
Heat
roller
HL
IC112
THOPEN
Selector
RY1
AC
12-14
5V
Driver
1
IC114
Q104
DTA143XKA
2
HL-
R112
120J1/4W
CPU
IC110
PR
ANo
+24V
PR-
AL-1000/1010
HLOUT(5-A4)
Driver
IC103
PR-
Thermostat
Heater lamp
HLOUT
TRC1
PC2