F. Drum Heater Circuit1. OutlineThe inside of the photosensitive drum is equipped with a drum heater (60 W), andthe heater is controlled so that the surface of the drum remains a specific temperature.The drum heater is supplied with AC power through a power switch (SW1), doorswitch (SW2), and drum heater switch and by way of an AC driver.When the drum heater switch is ON and, in addition, the door switch (SW2) is ON,AC power is supplied regardless of the state (ON/OFF) of the power switch. When thedrum heater switch (SW3) is OFF, on the other hand, AC power is supplied to the drumheater only if the power switch is OFF.The drum heater drive circuit turns off when the drum heater drive signal (DHRD)generated by the DC controller PCB goes ‘0’, thereby supplying the drum heater withhalf-wave AC power.If the drum heater drive signal (DHRD) generated by the DC controller PCB is ‘1’, onthe other hand, full-wave AC power is supplied to the drum heater.The relationship between the state of the copier and the state (ON/OFF) of the drumheater circuit of the AC driver is as follows:Table 4-106The temperature of the drum is monitored at all times by a thermistor (TH) built intothe drum heater.If the surface temperature of the drum falls below a specific value, the output of thecomparison circuit goes ‘1’, turning on the trigger circuit; as a result, the triac turns on toturn on the drum heater.If the surface temperature of the drum is higher than a specific value, on the otherhand, the output of the comparison circuit goes ‘0’, turning off the drum heater.Drum surface temperature: 42°CThermal fuse rated temperature: 76°CCOPYRIGHT © 1997 CANON INC. CANON NP6350/NP6251 REV. 0 JULY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)CHAPTER 4 IMAGE FORMATION SYSTEM4-22State of copierPower plug connected andpower switch OFFDuring copyingDuring standbyDrum heater drive circuitOFF(half-wave AC power)ON(full-wave AC power)
