Xerox Phaser 3300 Servce Manual page 74

Theory of Operation
2-32
Fuser AC Power Control
AC power to the Fuser is controlled with a Triac, a semiconductor switch. The
ON/OFF control is operated when the gate of the Triac is turned on/off by
Phototriac (insulating part).
When the 'HEATER ON' signal is turned on at engine, the LED of PC501
(Photo Triac) flashes. From the flashing light, the Triac (light receiving part)
takes the voltage, and the voltage is supplied to the gate of Triac and flows
into the Triac. As a result, the AC current flows in the lamp to create heat.
When the signal is off, the PC501 is off, the voltage is cut off at the gate of
Triac. The Triac is turned off, interrupting power to the lamp.
Triac (Q501) feature: 24 A-LV model/16 A-HV model, 600 V SWTCHING
Phototriac Coupler (PC501)
Turn On If Current: 15 mA ~ 50 mA (Design: 16 mA)
High Repetive Peak Off State Voltage: Min 600 V
Phaser 3300MFP Service Manual