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6. FUSING CONTROL
Above is a schematic of the fusing lamp control circuit. The circuit has both
ac and dc components, which are coupled through a photocoupler.
- Fusing Lamp ON/OFF -
To turn on the fusing lamp, the CPU supplies a
signal turns on a photocoupler
voltage to the lamp. The CPU decides whether to apply a continuous LOW
or a continuous HIGH (lamp off) at CN114-6 based on the input from the
thermistor at CN101-1. The voltage at CN101-1 increases as the tempera-
ture of the hot roller increases.
- Overheat Protection 1-
IC105 and Q111 form an overheat protection circuit. When the fusing unit is
operating within the normal range, pin 1 of IC105 stays LOW. Therefore,
stays on, allowing PC401 to operate.
Q111
If the hot roller's temperature reaches 230 degrees, the resistance of the ther-
mistor becomes approximately 1 kilo-ohm. At that point pin 1 of IC105 be-
comes HIGH, turning off Q111 and preventing PC401 from operating.
LOW
which turns on the triac controlling the ac
j
1 Nov, ;87
at CN114-6.
The LOW
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