Fuser control
The fuser-control circuit controls the fuser components. The two fuser heaters provide the high
temperatures that permanently bond the toner to the media. The fuser thermistor monitors the fuser
temperatures. The thermal switch detects abnormally high fuser temperatures and interrupts the
supply of voltage to the fuser if the temperature is determined to be too high.
Figure 5-3 Fuser components
The fusing-heater safety circuit is located on the power supply and constantly monitors the fusing
temperature. The fusing heater adjusts the temperature of the fuser as required by the stage in the
printing process.
■ Start-up temperature control: The thermistor on the fuser heater has two different modes
depending on the temperature of the fuser when a print job is sent. If the fuser temperature is
below 85ºC (185ºF), the fuser continues to heat until it reaches a temperature of 100ºC (212ºF),
and then the main motor actuates. If the fuser temperature is 85ºC (185ºF) or higher at the
beginning of a print job, the main motor is actuated immediately.
■ Print temperature control: The fuser temperature is maintained at a target temperature
throughout a print job. This target temperature varies depending on the type of media and the
number of pages in the print job.
■ Between-pages temperature control: When printing on smaller-sized media, the fuser
temperature is decreased between the pages to prevent an abrupt rise in temperature because
of the larger gap between pages.
■ Print-speed adjustment to control temperature: For certain types of media and when printing
several pages continuously, the interval between pages is increased to allow the fuser to
maintain the temperature that is required for good fusing. If the fuser cools too much, the toner is
not correctly fused to the media.
88 5 Theory of operation
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