Heater Control Circuit; Configuration - Toshiba e-STUDIO200L Service Manual

13.4 Heater Control Circuit

13.4.1

Configuration

In this equipment, the surface temperature of the fuser roller is controlled by turning ON/OFF 2 heater
lamps (center and side) which have different heat-generating positions with the command from the
engine-CPU on the LGC board. The surface temperature of the fuser roller is detected by 3 thermistors
(center, side and edge) and then the information of the temperature is transmitted to the engine-CPU
and each control circuit. Based on the detected temperature, the engine-CPU transmits the control sig-
nal of the heater lamp to the control circuit (TRC: Triac) of each heater lamp on the switching regulator
via the temperature control circuit. The power supply to each fuser roller is thus controlled by driving
TRC. The temperature control circuit detects the overheating of the fuser roller. In case that the surface
temperature of the fuser roller has exceeded the specified temperature, the temperature control circuit
transmits an overheat detection signal to the engine CPU and turns the heater lamp OFF.
If the temperature control circuit does not function for some reason and the fuser roller is abnormally
overheated as the result, a forcible power-OFF circuit transmits a reset signal to the power switch to
turn the power OFF forcibly. In addition, if these control circuits do not function with thermistor abnor-
mality or other reasons and the fuser roller is abnormally overheated as the result, 2 thermostats (front
and center ones in the fuser unit) shut off the power supply to the heater lamps to protect the equip-
ment.
Fuser unit
Fuser front Fuser center
thermostat thermostat
Front
Fuser roller
Center heater lamp
Side heater lamp
Center Side
thermistor thermistor
Engine-
CPU
Forcible power-off
circuit
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Rear
Edge
thermistor
Overheat detection signal
+5VSW
Center heater lamp
control signal
Temperature
Side heater lamp
control circuit
control signal
Reset signal
Fig. 13-3
13 - 5
05/07
Switching regulator
Center heater lamp
control circuit
( TRC1 )
Side heater lamp
control circuit
( TRC2 )
Cover
opening/closing
interlock switch
LGC board
e-STUDIO200L/202L/203L/230/232/233/280/282/283
L
Noise
N
filter
Main
switch
AC line
DC line
FUSER UNIT
13