Ricoh FT 4015 Service Manual page 69

20 December 1996 IMAGE FUSING
11.4.2 On/Off Control
When the main switch is turned on, the main board starts to output a trigger
pulse, which has the same timing as the zero cross signal, to the ac drive/dc
power supply board. This trigger pulse allows maximum ac power to be
applied to the fusing lamp. When the operating temperature is reached, the
CPU stops outputting the trigger pulse (the trigger stays HIGH) and the fusing
lamp turns off.
11.4.3 Phase Control Mode
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The main board sends the fusing lamp trigger pulse (LOW active) to the ac
drive/dc power supply board, which provides ac power to the fusing lamp at
the falling edge of each trigger pulse. The trigger pulse goes HIGH when the
main board receives the zero cross signal.
The amount of time that power is applied to the fusing lamp depends on the
temperature of the hot roller.
The trigger pulse (LOW part) is wider [C1] and power is supplied for longer
[D1] when the hot roller temperature is lower. It is narrower [C2] and power is
supplied for a shorter time [D2] when the hot roller is near the operating
temperature.
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