Electric Circuit Description; Fuser Unit Control Circuit - Toshiba e-STUDIO2500c Service Manual

15.5 Electric Circuit Description

15.5.1

Fuser unit control circuit

[ 1 ] Configuration
In this equipment, 2 heater lamps (center and side) which have different heat-generating positions are
installed in the heat roller to heat up the fuser belt. Also, one heater lamp (pressure roller lamp) is
installed in the pressure roller. The fusing temperature is controlled by turning ON/OFF these heater
lamps with the command from the ASIC on the LGC board.
The surface temperature of the fuser belt is detected by a thermistor (fuser belt front thermistor) and 2
thermopiles (fuser belt center and rear thermopiles: non-contact type sensors), and the surface temper-
ature of the pressure roller is detected by 2 thermistors (pressure roller center and rear thermistors).
And then the information of these temperatures is output to the ASIC through an A/D converter.
Based on the detected temperature, the ASIC transmits the control signal of the heater lamp to the
drive circuit (TRC: Triac) of each heater lamp on the switching regulator via the heater lamp control cir-
cuit. The power supply to each heater lamp is thus controlled by driving TRC.
The forcible power-OFF circuit detects the overheating of the fuser belt and pressure roller by each
thermistor/thermopile other than the pressure roller rear thermistor. In case that the surface tempera-
ture of the fuser belt or the pressure roller has exceeded the specified temperature, the forcible power-
OFF circuit transmits an overheat detection signal to the ASIC and the heater lamp control circuit and
transmits a reset signal to the power switch to turn the power OFF forcibly.
In addition, if these control circuits do not function due to thermistor abnormality or for other reasons
and the fuser belt or the pressure roller is abnormally overheated as the result, 3 thermostats (fuser belt
center and rear thermostats, pressure roller thermostat) shut off the power supply to the heater lamps
to protect the equipment.
Fuser unit
Center heater lamp
Side heater lamp
Fuser belt
front thermistor
Pressure roller lamp
Pressure roller
center thermistor
LGC board
converter
Forcible power-off circuit
e-STUDIO2500c/3500c/3510c FUSER UNIT / PAPER EXIT SECTION
Fuser belt center Fuser belt rear
thermostat thermostat
Heat roller
Fuser belt Fuser belt
center rear
thermopile thermopile
Pressure roller thermostat
Pressure roller
Pressure roller
rear thermistor
IC72
IC41
A/D
ASIC
Overheat detection signal
Switching regulator
Center heater lamp
driving circuit
( TRC1 )
Side heater lamp
driving circuit
( TRC2 )
Pressure roller lamp
driving circuit
( TRC3 )
+5VSW
Center heater lamp
control signal
Side heater lamp
control signal
Heater lamp
control circuit
Pressure roller lamp
control signal
Reset signal
Fig. 15-2
15 - 6
L
N
Noise
filter
Cover interlock Main switch
switch
AC line
DC line
May 2006 © TOSHIBA TEC