Toshiba DP120F, Service Manual

Page: 343 / 706

DP120F/DP125F Circuit Description 7-34 March 2000 © TOSHIBA TEC
The fuser control circuit consists of the PTC GA (IC45), A/D converter (IC54), and other periph-
eral devices. It calculates fixity according to the temperature information detected by the ther-
mistor to control the heater tube built in the fuser.
The A/D converter the ATH1 signal to a digital signal and outputs the ADCDO signal to the PTC
GA.
The PTC GA compares the predetermined value (control temperature, abnormal temperature)
stored in the internal registers with the ADCDO signal (measured value). If the measured value
is lower than the predetermined value, it then causes the HTON signal to be LOW to AC power
supply from the LVPS to the heater tube for increasing the fixing temperature. If the measured
value is higher than the predetermined value, it causes the HTON signal to be HIGH to cut off
the AC power supply to the heater tube for lowering the fixing temperature. If an abnormally
high or low temperature is found when the measured value is compared with the predetermined
value, the PTC GA causes the HTON signal to be HIGH to turn off the heater tube.
(For the heater drive circuit, refer to "7. 4 Heater Drive Circuit" in this chapter.)
If an abnormal condition occurs in the hardware and a large power attempts to flow into the
heater tube due to a sudden rise in the temperature, and so on, the fuse will blow to protect the
heater tube.
After a fixed time elapses while the machine is in a standby state with the printer power save
function setting ON, the PTC GA causes the HTON signal to go HIGH to cut off the power
supply to the heater tube, thereby controlling the power consumption.
3.4 Fuser Control Circuit
Fig. 7-3-4
07-03-04
Signal Name Type Active Description Destination
ATH1 I - Thermistor Measured Temperature Thermistor
Information
ADCDO O - A/D Converter Digital Output Signal PTC GA
HTON O H Heater Tube on Signal Heater tube