Xerox Phaser 3117 Service Manual page 126

Explanation about the condition of Normal Operation
If the fuser (P3.7) port becomes high, the Q6 is activated. A heat lamp starts operating by the activity.
As the temperature of the heat lamp is increased, the resistance value of the thermister is decreased.
Therefore, the electric potential of the circled A becomes low.
On/Off operation of the Q6 is only controlled by the fuser (P3.7) port because 5(+) of the
U11(Comparator) is always higher than 6 (-) within the normal control temperature rage.
Functions of the Malfunction Protection:
If the fuser port (P3.7) is turned on regardless of controlling due to system malfunction, the tempera-
ture of the heat roller goes abnormally high. At this time, the resistance value of the thermister becomes
low.
When the resistance value of the thermister becomes low, the electric potential of the circled A gets low,
and when the temperature goes over the certain temperature, the comparator (U11) gets a low output.
As a result, even though the fuser port is abnormally activated, it is disable to be over the regular tem-
perature. For maintaining a regular temperature, a protect circuit consists in it (This protection is set up
to start operating at the rage between 205°~210°)
12.1.2 PWM Controller
Function Description
PWM TIMER consists of each sub block which has various functions. The sub block is divided based on
this block diagram. The entire diagram of the PWMTIMER is organized as below.
PWM TIMER OPERATION is figured out if calculating PHCLK by the value selected by the register setting
and the divider. PHCLK is created by count block at the PWM TIMER
x
Circuit Description
Service Manual
12-3